Designing and prototyping a small scale steam driven jet pump

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I

NTERNSHIP

Designing and prototyping a small

scale steam driven jet pump

Author:

K.J.J. Bramer

Supervisors:

Utwente: Dr.Ir. H.W.M. Hoeijmakers Philips: Theo Stolk

A report submitted in fulfillment of the internship for Master of mechanical engineering Msc

in the

Engineering fluid dynamics

Mechanical engineering - University of Twente

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UNIVERSITY OF TWENTE

Abstract

Mechanical engineering Engineering fluid dynamics

Msc

Protoyping processof of a steam driven jet pump

by Koen BRAMER

Philips’ Technical Expert Group located in Drachten, The Netherlands, is the technical support for the whole Philips company. One of the top selling products is the Philips Garment steamer with separate boiler unit. While this apparatus consumes steam for ironing clothing, a boiler is present to deliver the needed steam. When the boiler is empty it needs an automatic refill of water in order to provide a constant and reliable steam production. Currently this refill of water is provided by an electric solenoid pump. Be-cause of customer experience an alternative is desired to replace the exist-ing solenoid pump. A good alternative might be a steam driven jet pump. However, large scale steam driven jet pumps steam driven jet pumps are already used in nuclear power plants, the working of this type of pump on the small scale is very poorly researched.

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List of Figures

2.1 Schematic overview of an SDJP. [Sentinel,2016]. . . 4

2.2 Infinitesimal flowtube. . . 5

2.3 Achievable pressure ratio against local Mach number. . . 7

2.4 Used functions and their quantities in XSteam.[Klinkert,2007] 13 3.1 Different nozzle flows with constant entry conditions . . . . 16

3.2 Radius versus the length of the steam nozzle. . . 18

3.3 Rendered view of the steam nozzle with festo joint. . . 20

3.4 Water nozzle design. . . 21

3.5 Water nozzle test. . . 22

3.6 water nozzle test. . . 23

3.7 schematic side view of the model that is used in the experi-ment . . . 24

3.8 Test set up with pressurized box. . . 25

3.9 Final design 1 ( MC length 18 mm) . . . 26

3.10 Final design 2 ( MC length 14 mm) . . . 26

3.11 Final design 3 . . . 27

3.12 Final design 4 . . . 27

3.13 Electric circuit of a ’Wheatstone bridge’ . . . 29

4.1 Set up of the nozzle experiment. . . 31

4.2 Pressure and velocity calculated with matlab against the lentgh of the nozzle[0−0.04m] . . . 32

4.3 Suction pressure at the exit of nozzle 1 (ABS) versus time with air as primary fluid. . . 33

4.4 Suction pressure at the exit of nozzle 2 (HTM 140) versus time with air as primary fluid. . . 33

4.5 Suction pressure at the exit of nozzle 1 (ABS) versus time with steam as primary fluid. . . 34

4.6 Suction pressure at the exit of nozzle 2 (HTM 140) versus time with steam as primary fluid. . . 34

4.7 Pressure at the exit of straight nozzle versus time with air as primary fluid. . . 35

4.8 Pressure at the exit of straight nozzle versus time with steam as primary fluid. . . 35

4.9 Experimental set up for design 1 . . . 36

4.10 Experimental set up for design 2 . . . 37

4.11 Experimental set up for design 2 with one feeding hose. . . 38

4.12 Pressure loss distribution due to skin friction. . . 39

4.13 Massflow . . . 40

4.14 Massflow . . . 41

4.15 Massflow complemented with last point . . . 42

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4.17 Outcoming flow. Flow area:2.4.10−6m2 . . . 43

4.18 Model with a mixing chamber length of 40 mm with a water nozzle area of3∗10−6_m2_. _{. . . .} ₄₄

4.19 Volume flow rate against exit diameter(red part). . . 44

4.20 Massflows of the four different models using two different primary fluids.. . . 47

4.21 Final-1 . . . 48

4.22 Final-2 . . . 48

4.23 Final-4 . . . 49

4.24 Final-1 . . . 49

5.1 Possible location for a premature shock wave to happen. . . 52

5.2 Speed of sound in a homogeneous two-phase mixture as a function of the volume fraction[α] . . . 54

A.1 Physical properties of the HTM 140 material. . . 55

A.2 Physical properties of the ABS material. . . 56

A.3 Physical properties of Plexiglas( PMMA.) . . . 57

B.1 Roughness measurement for the HTM 140. . . 59

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List of Tables

3.1 Start parameters . . . 17

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List of Abbreviations

SDJP SteamDrivenJetpump

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Chapter 1

Introducing the steam driven

jet pump(SDJP)

1.1 History and developments

The working principle of the steam driven jet pump was first patented in the United Kingdom in 1858. The main reason for supporting the devel-opment of the pump was the existing problem of feeding the boiler of a locomotive in a reliable way. Until then, the boiler was fed by inefficient pumps, that were mostly manually driven. Because of the harsh conditions in which the pumps had to function, a more efficient and reliable pump was desired. When Henri Giffard first came up with his idea of this new type of pump everyone was skeptical about it and it was widely doubted through-out the pumping industry. But when in practice the pump was working properly that image of the pump changed.

Next to feeding boilers of large ships and locomotives the SDJP is also used as a steam driven air jet ejector to remove non condensable gases from the condenser in modern steam power plants. Nuclear plants use the SDJP as a safety valve when the pressure in the cooling baths, due to temperature rising, exceeds the safety limit. Because it has no moving parts it is very attractive for this industry. In 1986 the SDJP was first applied in the nu-clear cooling industry at the Canada Deuterium Uranium reactors.[Aybar and Beithou,1999.] This shows the high usability of the SDJP.

The biggest advantage of a SDJP is the absence of moving parts in the pump. However the pump may be favorable compared to ’normal’ pumps, there is not much accessible information. Mostly companies work on the development of the SDJP, which means information about this develop-ment is kept confidentially. Especially information about the small scale SDJP is hard to come by. For that reason it will be investigated in this re-port.

1.2 Goal of this study

The main goal of this study is to make a functioning prototype of an SDJP on a small scale.

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enough to fit in the apparatus which it is designed for. It also must be a reliable pump which does not need technical know how to operate it when it is implemented in the Garment cleaner. Though it is not focused on in this report, the noise which is produced by the pump must be minimized.

1.3 Approach

Like stated above the steam driven jet pump was at first designed to feed large locomotive boilers. Although it has been researched thoroughly through-out the years and large scale SDJP’s are frequent deployed on big industrial plants , small scale SDJP’s are a unknown territory and little is known about the validity of the design parameters on this scale. Therefore A small scale prototype has to be built and the functioning of this pump has to be re-searched to gain understanding on the pitfalls designing on a small scale. In 2007, Luuk Klinkert already studied this subject for Philips during his Thesis and developed a Matlab model to validate and, partially calculate, the geometry of the pump based on several assumptions.[Klinkert,2007] Based on this model, a prototype is made and tested. The pump has to fulfill separate functions which together make the full functioning pump. During the process some functions will demand more attention due to the level of robustness of the design.

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Chapter 2

Descriptions, assumptions and

derivations

2.1 Description

Figure2.1shows a schematic overview of an SDJP.

Steam enters the pump at part 1, and flows through a ’De laval nozzle’. In this nozzle the velocity of the steam flow is changed from subsonic to su-personic, and the pressure is reduced in order to create a suction pressure at the end of the nozzle. This suction pressure has to be low enough in order to draw water into the flow from the water tank(flow 2).

In part 3 the flow enters the mixing chamber and the steam and water is mixed. Because of the low temperature of the feeding water, most of the steam will condense. At the beginning of the mixing chamber the two flows are still separate flows and their contact area is small. Also the velocity of the steam flow is higher than Mach 1, and the velocity of the water flow is really low(assumed 0). Because of this difference the major part of the momentum is exchanged in this part of the pump. It must be kept in mind that the transfer of mass and momentum also plays a big role in a rise of the pressure at the end of the pump.

Due to the shear force that is exerted between the two flows in the entrance of the mixing chamber, the contact area enlarges which results in a better exchange of mass and energy.

Now, more and more steam condenses on the water. Because the specific volume of the mixed flows is much lower than the sum of the specific vol-umes before the mixing, the pressure reduces. This reduction is due to the phase change of the condensing steam whereby a lower specific volume is obtained. however for a small part the pressure also increases because of the mixing of the supersonic steam flow with the subsonic water flow. But this pressure rise is negligible.[Klinkert,2007]

The main goal of the SDJP was to create a higher pressure at the exit of the pump to feed water to the boiler. So the pressure at point 5 should be higher than the pressure at point 1. The energy that is needed for this pressure rise at the exit of the pump is gained when latent heat is released during the phase change of the steam to water. This also causes a rise in temperature in the resulting water flow.

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leads to higher boiling temperatures.

After the mixing chamber nozzle, a shock wave should occur in order to let the last steam condense into water. This means that only water will leave the pump. This shock wave will also provide a pressure rise. Because the main goal was to leave the pump with a higher pressure, a diffuser is added to further increase the pressure to the desired value. The velocity will decrease but the total pressure will rise.

FIGURE2.1: Schematic overview of an SDJP. [Sentinel,2016]

2.2 Geometry

As can be seen in Figure2.1the most important parts of the pump are the nozzles. Though there is not much known about it, the water nozzle is re-ally important. The set up for this nozzle isn’t well defined.

The dimensions of all the different parts determine if the pump works prop-erly and finally can feed the boiler with water. The determining of the proper geometry and testing the functioning of these nozzles in reality will be the main focus of this report.

2.2.1 Area changes in Quasi one-dimensional isentropic flow.

To create an area velocity relation in a duct, Eulers equation of motion for odimensional steady flow is used. For now, external forces are ne-glected.

In Figure 2.2a infinitesimal part of a flow through an converging duct is represented. When only first order terms of the force balans are taken into account, the Euler relation becomes:

dp

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FIGURE2.2: Infinitesimal flowtube.

Also the massflow through the duct is known:

˙

m=ρAv (2.2)

The mass flow should be constant. This holds in differential form:

dA A +

dρ ρ +

dv

v = 0 (2.3)

The speed of sound,a, in a gas in when an isentropic flow is assumed is:

a2 = dp

dρ (2.4)

Now combine equation2.1with equation2.4we get :

c a2 +

dp

dρ = 0 (2.5)

Substituting equation 2.5 into the differential form of the constant mass flow(equation2.3) , the Hugoniot relation is found:

dA A =

dv v (M

2₋₁₎ _(2.6)

WhereM is defined as the Mach number. This is the average local speed in the flow divided by the local sound speed. Derivation from:[Jonker,2014]

M = v

a (2.7)

Dependent on the value of the Mach numberM,dAanddv have equal or opposite signs. At this point 4 differentsituationscan be described. Mcan be bigger or smaller than 1 when entering the duct. AlsodA_A Can be positive or negative along the flow.

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• Situation 2: M < 1and dA_A < 1. This means that the speedv has to increase. This is called a subsonic converging nozzle.

• Situation 3: M > 1and dA_A > 1. This means that the speedv has to increase. This is called a supersonic converging nozzle

• Situation 4: M > 1and dA_A < 1. This means that the speedv has to decrease. This is called a supersonic diffuser.

From equation2.3it can be seen that for an isentropic flow , the value of the velocity change is the opposite of the value of the pressure change.

2.2.2 Choked flow

Equation2.6shows that the only place to obtain sonic conditions is where the change in area,dA, is equal to zero. It is impossible to start with sub-sonic conditions and obtain a sub-sonic condition before the area change is zero. This means for a converging nozzle the sonic conditions are reached before the exit of the nozzle and for a converging diverging nozzle it means sonic conditions are reached before the throat. From this it can be concluded that the maximum Mach number at the smallest area, at most, can be equal to one( the sonic condition).

Hence, the maximum flow rate occurs when sonic conditions are present at the smallest area of the nozzle. This is called a choked flow. When the choked flow is realized the flow rate cannot be increased any further. [PRITCHARD,2011]

2.3 Assumptions and derivations

2.3.1 Steam nozzle

The function of the steam nozzle is to reduce the pressure at the end of the nozzle below a value of the ambient pressure. This low pressure is needed for drawing water out of the water tank into the pump. In the case of a Philips garment cleaner, the boiler pressure is around 5 bar ( 6 barg). The ambient pressure will be approximately 1 bar.THe water tank wil be at am-bient pressure. So the pressure at the end of the steam nozzle has to be below 1 bar in order to draw water into the pump.

To create a lower pressure, with the use of a incoming subsonic flow, at the end of the nozzle , the use of a converging nozzle is examined. For this the isentropic flow relations are used. For saturated steamγ = 1.135 is assumed. Furthermore the stagnation conditions at the beginning of the nozzle can be used.

The isentropic flow relations are: [PRITCHARD,2011]

T0

T = 1 + γ−1

2 M

2 _(2.8)

p0

p = (1 + γ−1

2 M

2₎γ−γ1 _(2.9)

ρ0

ρ = (1 + γ−1

2 M

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For the steam nozzle the most important parameter is the exit static pres-sure. This pressure must be below 1 bar in order to draw water out of the water tank, as said before. Figure2.3shows the relation between the Mach number and the pressure ratio of the converging nozzle.This is the rela-tion between the existing total pressure and the maximum obtainable static pressure. From the Hugionot relations it can be obtained that the maximum Mach number can at most equal to 1. WhenM = 1the area change is equal to zero. Resulting in a maximum pressure ratio of 0.5774 at the the throat( the area change is zero, so M must be equal to 1.) This means, With the given stagnation conditions, that a suction pressure at the end of the nozzle never can be achieved using only a converging nozzle. therefore, a ’De laval nozzle’ has to be used in order to achieve the desired pressure ratio. In

or-FIGURE 2.3: Achievable pressure ratio against local Mach number.

der to find a proper geometry for the different nozzles several assumptions and derivations have to be done. First the entering flow is examined.

Incoming flow velocity

In order to find a proper geometry for the different nozzles several assump-tions and derivaassump-tions have to be done. First the entering flow is examined.

The entering steam flow comes out of a boiler at a pressure of 5 bar. This pressure is kept constant with the use of a smart thermostat.

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Assuming adiabatic flow and no initial velocity the equation for the exit velocity of the boiler becomes:

v2_e

2 =hi−he (2.11)

using h=CpT

v_e2 = 2Cp(Ti−Te) (2.12)

Define:

Cp

Cv

=γ , Cp(1−

1

γ) =R (2.13)

Rewrite this equation and useR = R0

¯

M whereRis the specific gas constant,

R0the universal gas constant andM¯ is the molecular mass of the gas.

Cp =

γR

γ−1 (2.14)

Cp =

γR0 ¯

M(γ−1) (2.15)

Equation2.12now becomes:

v_e2 = 2 _¯γR0Ti

M(γ−1)[1−

Te

Tc

] (2.16)

Using the isentropic flow relations the final expression becomes:

ve= q

(2 γRTi (γ−1)[1−(

pe

pi )

γ−1

γ _]) _(2.17)

We should really keep in mind that the derivations so far have been done using the ideal gas laws. It is known that steam is not a ideal gas, but it will give a good insight in the order of magnitude of the maximum exit speed.[Anderson(Jr.),2003.]

Area-pressure relation

Next an Area pressure relation is needed in order to give insight in the de-sired geometry related to dede-sired the pressure ratio. In order to assure the working of the ’De laval nozzle’, using an incoming subsonic flow, a choked flow must be assumed at the throat. Otherwise the Mach number will be lower than 1 at the throat and the diffusing part of the nozzle will increase the pressure instead of lowering it to a desired value.

We introduce1as the area relation between the throat and exit area:

1 = Ae

At

(2.18)

Using equation2.12and rewritingCp yields:

Ti−Tt=

γ−1 2

v_t2

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Ti =Tt(1 +

γ−1 2

v2_t γRTt

) (2.20)

Furthermore the local speed of sound( for now: in the throat ) is defined as:

γRTt=a2 (2.21)

And at the throat of a choked ’De laval nozzle’M = 1, so:

v_t2

a2 = 1 (2.22)

Now equation2.20reads:

Ti =Tt(1 +

γ−1

2 ) (2.23)

Tt

Ti

= 2

γ+ 1 (2.24)

In the same way expressions can be found for the pressure and the density:

pt

pi = (Tt

Tc )

γ

γ−1 _{= (} 2

γ+ 1) γ

γ−1 _(2.25)

ρt

ρi

= ( 2

γ+ 1)

1

γ−1 _(2.26)

Because the mass flow is constant through the nozzle we can state:

˙

m=ρtAtvt=ρeAeve (2.27)

using1:

1 = vtρt

veρe

(2.28)

1 = ( 2 γ+1)

1

γ−1_ρ_i_v_t

p (2γRTi

(γ−1)[1−( pe pi)

γ−1

γ _])_ρ e

(2.29)

Replace the speed at the throatvt:

1 = ( 2 γ+1)

1

γ−1_ρ

i

√

γRTt

p (2γRTi

(γ−1)[1−( pe pi)

γ−1

γ _])_ρ e

(2.30)

Rewrite:

1 = ( 2 γ+1)

1

γ−1 pi RTi

p

(_γ₋2₁[1−(pe pi)

γ−1 γ _]) .1 ρe . s Tt Ti (2.31)

Rewriting further gives the desired result:

1 = ( 2 γ+1)

1

γ−1₍pi pe)

1

γ

p

(γ+1_γ₋₁[1−(pe pi)

γ−1

γ _])

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Now a relation is obtained for the Geometry as a function of the desired pressure ratio. When designing the steam nozzle it can’t be stated enough that the Mach number at the throat should be equal to one in order to work correct. Although saturated steam cannot be treated as callorically perfect gas, the way it behaves when flowing through the nozzles is similar. Con-densation can cause changes in the flow variables at the exit of the nozzle. However, the same Area pressure relations for obtaining the right geometry can be used[Anderson(Jr.),2003, Klinkert,2007.]

2.3.2 Mixing Chamber

After the steam flow exits the steam nozzle at supersonic speed, it enters the mixing chamber. In the mixing chamber the water from the water reservoir is mixed with the steam flow. Before the steam enters the mixing chamber, water is drawn into the pump from the reservoir through the water nozzle. Because this is a really important feature of the pump it has to be examined first.

Water nozzle

As stated above, the water nozzle is the part of the pump that provides the proper water flow into the pump. Because, a suction pressure is provided at the exit of the steam nozzle, it makes sense that the water nozzle needs to be placed close to the exit of the steam nozzle.

The geometry of the exit of the steam nozzle is circular and therefore it is convenient to chose a circular geometry for the water nozzle also. In this way the water nozzle is producing a steady and balanced acceleration and it distributes the water flow uniform into the mixing chamber[Vanini., 1995.]The water nozzle should be concentric with the steam nozzle but can be inside the steam nozzle or surrounding it.

With a central steam nozzle the steam only contacts the walls of the steam nozzle. However, with a central water nozzle the steam would not only contact the walls of the steam nozzle but also the walls of the central water nozzle. The increase of contact area will inevitably contribute in more wall friction and lower the efficiency of the pump.

Massflow for the water nozzle

To determine the proper massflow of water into the SDJP, the influence of the geometry of the water nozzle on this mass flow has to be examined. When all the flow variables are known, the massflow can be calculated. The flow velocity From the water reservoir through the nozzle into the mixing chamber is assumed smaller than M= 0.3. This means that, for this part of the water flow, incompressibility can be assumed. In equation2.33the area can be calculated by the radius of the water nozzle. The density of water at ambient pressure at room temperature can be found in XSteam.m (see section2.3.4.) Eventually the speed can be determined with Bernoullis law.

˙

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Geometry of the water nozzle

It is assumed that the exit of the water- and steam nozzle are close enough to each other that the pressure is equal at both nozzle exits [Klinkert,2007.] The assumption for the geometry from the water nozzle will be taken from the report of [Klinkert,2007.] Klinkert build this assumption on the work of: [Deberne et al.,1999.]

The mixing chamber

It is important that the exit flow variables of the chosen steam nozzle are entered as the incoming flow variables of the mixing chamber. The water tank is set at room temperature and at an ambient pressure of 1 bar. This means that the water tank is not pressurized.

In the mixing chamber, the steam with the water from the water tank is mixed. It is really important that enough water is fed into the mixing cham-ber in order for the steam to condense. Because of the phase change of the steam to water through condensing of the steam, the specific volume of the mixture will decrease enormously. This will result in a pressure drop. Ofcourse there is a supersonic flow that enters a convergent nozzle which results in a pressure rise, but the pressure drop due to the phase change will be dominant over this pressure rise. So the totalpressure in the mixing chamber will drop. The energy that is needed for the pump to get an higher exit pressure at the end of the pump is present in the form of latent heat that is released during the phase change of the steam. this means that the sub cooled water from the water tank will rise in temperature.

The entrance and exit diameter are known from the geometry of the steam and water nozzle. The only real unknown variable is the length of the mixing chamber. It is important that a large part of the steam condenses in the mixing chamber, for this the mixing chamber should be relatively long. However, the quantity of the skin friction in increases linearly with the length of mixing chamber. For this reason the mixing chamber should be as short as possible. Only these two influences are significant for the length of the mixing chamber.

Another important factor for the condensing of the steam is the amount of water that is drawn into the mixing chamber.

The exit diameter needs to provide that the local mach number stays a lit-tle higher than one at the end of the mixing chamber in order to prevent shock waves inside the mixing chamber. Then, when the minimum radius is reached the Mach number will change,or, a shock wave will occur. Fur-thermore, is the diameter of the mixing chamber linearly decreasing from entrance to exit diameter.

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2.3.3 Diffuser

After the flow leaves the mixing chamber supersonic. The flow needs to transfer to subsonic, and after that, enter the diffuser. Because the pressure at the end of the mixing chamber is very low and the exit pressure of the pump should be around 5 bar( total pressure), the shock wave should pro-vide an increase of the pressure.

The increase of the pressure over the shock wave, summed with the pres-sure increase that is obtained in the subsonic diffuser, should be high enough to give an exit pressure that is higher than the boiler pressure, which is equal to the pressure that enters the pump. This also determines the loca-tion of the shock wave[Klinkert,2007.] When the back pressure is lowered the shock wave moves more in the direction of the diffuser exit [Ander-son(Jr.), 2003.] The shock wave also condenses the last amount of steam that is still present at the end of the mixing chamber. This is important to guarantee a fully subsonic flow in the diffuser.

The shock wave that occurs is assumed very small. In this way the area of the shock wave is assumed constant. This is a very important assump-tion: The properties behind the shock wave now only depend on the prop-erties before the shock wave[Anderson(Jr.),2003.] It has to be kept in mind that this assumption is not totally right, though the location of the shock wave is very important for the functioning of the pump. If the shock wave occurs already in the mixing chamber, the pressure rise that is obtained, is just not sufficient. From the assumption we get the following relations for the shock wave. Situation a and b will be before and after the shock wave respectively[Anderson(Jr.),2003]:

ρaua =ρbub (2.34)

0.5u2_a+ha= 0.5u2b+hb (2.35)

ρau2a+pa=ρbu2b +pb (2.36)

hb can be found when the pressure and density at point b are known. It is said that the water after the shock wave is ’just’ evaporated and is thus saturated water. Also this assumption is done and used in the model by Klinkert,2007.

When the shock wave can be located accurately, the fluid after the shock will completely consist out of water. The diverging angle should not exceed 7◦in order to prevent detachment of the flow from the wall[Anderson(Jr.), 2003.]

Now bernoullis law( due to low velocities) can be used to calculate the exit conditions:

Aρbub =Aρcuc (2.37)

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The total exit pressure is[Klinkert,2007]:

ptotal−exit= 0.5ρbu2b +pc (2.39)

When this pressure is higher than the boiler pressure the pump works prop-erly.

2.3.4 XSteam.m in matlab

The proper functioning of the pump depends next to the geometry also on the properties of the fluids that flow through it. In this case the fluid is water (liquid or gas form). In order to determine the desired properties in an accurate and efficient way, the relations formulated by the IAFWS are used. These relations are mostly used to create diagrams and tables, but when using changing operating conditions the relations itself are more useful. Magnus Holmgren from www.x-eng.com implemented these relations in matlab as a function called XSteam.

XSteam uses standard units. The units and their symbols are stated in figure 2.4.

For example:Xsteam(0h_pt0,1,20)gives the enthalpy of water at 1 bar and 20 deg.Celsius.

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Chapter 3

Experiment

3.1 Introduction

In order for the SDJP to work properly, different functions have to be ful-filled. The most important parts of the SDJP to fulfill these functions are: the steam nozzle, water nozzle, the mixing chamber and thereafter the lo-cation of the shock wave just before with the diffuser. Because of all the uncertainties and the assumptions in the design process, a prototype has to be made in order to check the working of the pump in reality.

The geometries are, if needed, manufactured and tested individually in or-der to get a good insight in the working principle. Also different manu-facturing methods can be used in order to vary for example the surface roughness or certain tolerances. In this way the sensibility of those differ-ent factors can be examined and this gives again insight in the robustness of the design. The base for the design is the Matlab script of Luuk Klinkert [Klinkert,2007.]

Because of the type of process, the knowledge gained in the experiments from parts of the pump that were designed and tested first (See the Results of the experiments further in this report), is used in the design of the follow-ing parts. This means that the design parameters used for example in the mixing chamber, depend on the results of the steam nozzle experiments. It might be advisable to first consult the appurtenant Results chapter for ev-ery function that is tested experimentally (described in this section), before continuing to the next experiment in this chapter.

3.2 Steam nozzle

3.2.1 Approach

The first main function of the pump is to lower the pressure at the end of the steam nozzle. This function stands on its own and for this reason the steam nozzle can be tested separate from the other parts. The steam nozzle should guide the incoming steam and provide the needed suction pressure at the exit of the nozzle in order to draw water into the pump. The nozzle changes the velocity of the flow from subsonic to supersonic. The critical condition for this transition is that the Mach number in the throat is equal to 1, and that means choked flow should be present.

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check the validity of these assumptions under real working conditions. The most important target of the steam nozzle is to reduce the pressure at the exit of the nozzle below 1 bar. When a flow is going through a ’De laval nozzle’, entering with a subsonic flow, several situations are possible when the flow goes through the nozzle. The important parameters are the Mach number at the throat of the nozzle and the ambient pressure in which the exit of the nozzle flows into, see [Martinez,2016]. When a fluid is led

FIGURE3.1: Different nozzle flows with constant entry con-ditions

through such a nozzle, we may encounter the following flow regimes:

• Patha: The flow enters the nozzle subsonic and stays subsonic through-out the length of the nozzle.

• Pathb: The flow enters the nozzle subsonic and reaches just the sonic speed at the throat and then becomes subsonic again.

• Pathc: The flow enters the nozzle subsonic and reaches just the sonic speed at the throat. After the throat the flow becomes supersonic. Before the exit of the nozzle a normal shock will occur and after this shock the flow will be subsonic again. The flow may detach from the wall

• Pathd: This flow is equal to the flow of pathcbut the normal shock occurs just at the exit of the nozzle.

• Pathe: The flow enters the nozzle subsonic and reaches just the sonic speed at the throat. After the throat the flow becomes supersonic and it stays supersonic throughout the whole length of the nozzle. An oblique shock will appear at the exit of the nozzle so the pressure is equalized with the higher ambient pressure.This type of flow is called ’over-expanded’.

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TABLE3.1: Start parameters

Parameter Value

Boilerpressure [bar] 5 Boilertemperature [K] 424.99 Steam produce rate [g/min] 100 Exit radius[m] 5∗10−3

• Pathg: The flow enters the nozzle subsonic and reaches just the sonic speed at the throat. After the throat the flow becomes supersonic and it stays supersonic throughout the whole length of the nozzle. Expan-sions waves occur because the exit pressure is higher than the ambient pressure. This is often the case when nozzles work under vacuum so this is not likely to occur. This situation is called ’under-expanded.’

3.2.2 Design

For designing a working prototype the operating conditions for the pump have to be determined. For the basic parameters the Perfect CareSilence garment cleaner from Philips is used.This is a garment cleaner which makes use of a boiler to produce steam. The constant boiler pressure is 5 bar ( 6 bar ground). The maximum constant steam rate is 100 g/min. With XSteam.m(Matlab) the boiler temperature can also be determined. The im-portant parameters are displayed in table 3.1. The steam produce rate is stated in the case when there is constantly taken steam from the boiler. It must be taken into account that when there is drawn steam for a shorter time, the flow rate can be higher. This higher flow rate may be necessary when using an SDJP. For convenience the pump will first be designed for the given flow rate.

The mass flow rate coming into the nozzle is :

100

60∗1000 = 1.667∗10

−3kg

s (3.1)

The density of the steam coming out of the boiler is 2.668_mkg3(XSteam.m).

With the given radius, the incoming steam velocity into the nozzle is known.

ventrance = ˙

m ρ∗A =

1.667∗10−3

2.668∗(5∗10−4₎2_∗_π = 7.95

m

s (3.2)

Furthermore we keep the entrance radius of the nozzle the same as the exit radius of the boiler.

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FIGURE3.2: Radius versus the length of the steam nozzle.

3.2.3 Manufacturing process

In order to work properly the nozzle has to be made with very high pre-cision. The nozzle shape is calculated in Matlab and next drawn in Solid-Works. To get a feeling for the dimensions of the design, the model was printed on a low-end 3D printer. As expected the surface quality was really poor but it gave a good insight of how small the nozzle really is.

As said before, the surface roughness is really important in order for the nozzle to work properly. This means that the geometry has to be manufac-tured with high very high tolerances. When looking at a revolved geome-try that has to be made with very high precision, the use of a CNC turning machine pops up. However the smallest diameter of the nozzle is in the middle. This would mean that a really small chisel has to be used with a rel-atively large length in order to obtain a precision at the most critical point. So where the surface quality has to be the highest, in order to prevent pre-mature shock waves, the CNC turning machine will be the least accurate. Making the nozzle out of two separate parts would solve the problem of the accuracy because the chisel could reach the small diameter in a more stable way. However this would bring a discontinuity in the nozzle which itself would result in a certain ’surface roughness’.

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This means switching from geometries, which may be necessary in the first stage of the prototyping process, is very labor-intensive and therefore not favorable. Though this method must be kept in mind when the right geom-etry is found and a final high precision design of the pump has to be made. Because flexibility is really important in the prototyping process, the use of 3D printing technology can be a good option. The 3D printer can print almost every geometry. A drawing can be made in Solidworks and sent to the printer easily. When using the high-end printers that are available at Philips Drachten, a high surface quality can be reached, dependent on the material that is used. Because high temperature steam has to flow through the nozzle it is very important that the material can withstand those tem-peratures during the tests. After researching this manufacturing method, together with the rapid prototyping department it is decided to use the 3D printing process for manufacturing the geometries that need to be tested. There are materials available that can withstand high temperatures for a short amount of time and simultaneously have a high surface quality. For the steam nozzle there are two types of materials used: Nozzle 1 is made from the ABS series and nozzle 2 is made from HTM 140 material .See Ap-pendixAandBfor the material properties. As said before, when the final geometry of the pump is obtained, another method could be considered to manufacture the pump. For example sinker EDM.

3.2.4 Measurement set up

To fully understand the working principle of the steam nozzle and its ef-ficiency it is important to filter out as much uncertainties during the mea-surement as possible. One of the most important parameters for the steam nozzle is the incoming steam flow. In the calculations it is assumed that a fully developed stable steam flow is leaving the boiler and entering the steam nozzle.

For the measurement the use is made of a steam generating machine which can simulate the boiler conditions perfectly. The use of a steam generator provides a stable incoming steam flow for the steam nozzle. In this way

The main function of the steam nozzle is to lower the pressure at its end. To measure the pressure at the end of the nozzle a piezoresistive pressure sen-sor is used (see subsection3.7). A0.5mmhole is drilled near the exit of the nozzle and a Festo4mmtube joint is used to connect the pressure sensor. These Dimensions are chosen with the feasibility of the tools and machines that are available in the workplace and are set equal for every nozzle that is measured. See figure3.3.

3.3 Water nozzle

3.3.1 Approach

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FIGURE3.3: Rendered view of the steam nozzle with festo joint.

the working of the pump. Because of that reason it is experimentally re-searched how the water flows into the flow and what influence this has on the composition of the flow in the mixing chamber.

Most sources only provide information about the calculation of the flow variables, but a detailed formation of the alignment of the different parts of the pump is mostly absent. For building a prototype, this is very important. For that reason, this relative simple but important part of the pump, has to be examined individually.

3.3.2 Design

Because a small scale SDJP is prototyped, a central steam nozzle is chosen. The working principle is exactly the same for both situations, however for manufacturing and the mentioned efficiency reasons, a central steam nozzle with a surrounding concentric water nozzle is preferred. The water nozzle would simply become to small other ways.

For the dimensions of the water nozzle it is important to know the dimen-sions of the mixing chamber also. Simply because of the fact that they have to be connected.

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FIGURE3.4: Water nozzle design

To predict what will happen, during the experiment, inside the water noz-zle, the influence of the varying distance will be looked at. This varying distance will provide a varying area for the water to flow through.

The pressure difference between the exit of the steam nozzle and the wa-ter reservoir, that is at ambient pressure, is the driving force for the wawa-ter to flow into the pump. Using Bernoullis law for incompressible flow we can get the following equation for the water flow velocity out of the water nozzle. See equation3.3.

δpis the pressure difference obtained by the steam nozzle.

δp= 1

2 ∗ρwater∗v 2

water (3.3)

The average outgoing flow velocity from the water nozzle will then approx-imately be:

vwater = s

δp∗2

ρwater

(3.4)

With an assumed constant density of the water and a constant known speed, the mass flow only depends on the Area change obtsined by the varying distance of the nozzle. The mass flow again is:

˙

mw =ρwAwvw (3.5)

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The adjustable steam nozzle is again made from HTM 140 in the 3D printer, because of its performance and heat resistancy. The transparent part of the set up is made from PMMA. In this way the flow inside the water nozzle and the mixing chamber can be observed easily. It must be kept in mind that the surface roughness of the transparent material is much higher than desired in the full functioning pump. However it seams still desirable, be-cause of the transparancy of the material.

After the transparent part was manufactured and tested it became clear that the level of transparancy is very low due to the manufacturing pro-cess. Also is it really hard to make a smooth mixing chamber. With this nozzle design we don’t get proper results ( see section4.) That is why the the design is altered. See figure3.5and3.6.

FIGURE3.5: Water nozzle test.

In this way The gray part can also be manufactured on The 3D printer with the HTM140 material. In this way the surface quality is higher and will probably give more reliable results.

The measurement will be set up in the same way as the steam nozzle ex-periment. First of all the test will be performed with a air. This can be done quite well because the only important factor is the changing are of the wa-ter nozzle exit.

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FIGURE3.6: water nozzle test.

To determine the mass flow of the water, the duration of the measurement is measured. Simultaneously the weight of the water reservoir is recorded with a high precision weighing scale. In this way the mass flow rate can be determined easily.

When testing the different distances between the two concentric nozzles and therefore different flow rates it is expected that the distribution of the water flow will differ in every situation. To gain a good insight in this factor of the pump, a high definition camera is used to capture these out coming flows.

3.4 Mixing chamber

3.4.1 Approach

From the test with the water nozzle, which was also performed with a small mixing chamber, information was gained about influences of certain ge-ometries. See The results chapter. The length of the mixing chamber as wall as the through flow area of the water nozzle do have a major influence on the behavior inside the mixing chamber. The behavior in the mixing cham-ber is very hard to predict and therefore different geometry combinations of mixing chamber length and water nozzle area have to be investigated. It is desired that after this testing a relation is found between those varying geometries and the location of the shock wave.

3.4.2 Design

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indicates that, either more water needs to be sucked in, or the mixing cham-ber length must be enlarged.

When using the same mixing chamber length of 20 mm with a water nozzle area of1.7∗10−5m2, gave an continuous heated liquid water outflow from the mixing chamber. This means that the transition from supersonic to sub-sonic speed took place inside the mixing chamber.

In order to get insight in the location of the shock wave the following design is made. See figure3.7. Six Different models are made. There Will be tested

FIGURE3.7: schematic side view of the model that is used in the experiment

with mixing chamber lengths of 30-40-50 mm. Two different water nozzle areas are investigated. The largest area for the water nozzle that still gave a non fluid flow at the end of the mixing chamber in the previous experi-ment :3.6∗10−6m2and 20 percent larger. This results in two series of three nozzles that have to be tested. In each of the models the tube to detect the shock wave is made 20 mm. This gives enough length, because the shock wave is expected directly at the end of the mixing chamber. (dA= 0at the end of the mixing chamber. See also equation2.6)

At this point in the process it is important to gain insight in the location of the shock wave. Also: is the flow in the mixing chamber supersonic?!! Therefore the tests are done with the exit flow directing at ambient pressure as well as in an pressurize box. This is important because the location of the chock wave depends on the upstream as well on the downstream con-ditions. An example of the test set up with the pressurized box is shown below.

The testing nozzles are made again on the 3D printer from the ABS mate-rial. Despite the HTM 140 is preferred, the ABS material is used. This is done because the HTM140 material was out of stock for a long time and the available time to test the different designs is limited.

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FIGURE3.8: Test set up with pressurized box.

The box can be pressurized with compressed air. An safety valve that is set to 5 bar maintains the pressure in the box at 5 bar. Different values to this valve can be applied to investigate the influence of the back pressure if desired.

The set up for testing can be seen in figure3.8. Again festo joints will be used to connect the pressure taps to the pressure sensors. The static pres-sure is meapres-sured in the same way as before. See section3.7.

3.5 Diffuser

Due to the problems faced in the experiments done with the mixing cham-ber (section4.3.3), the experiments with the diffuser do not start with a clear vision from the previous parts of the pump i.e. the entering conditions of the diffuser are not known yet. This is caused by the unpredictable behavior of the mixing chamber and with that the location of the shock wave. The ’all supersonic’ assumption for the mixing chamber has to be questioned and might cause problems for the whole functioning of the pump.

3.5.1 Design

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model from the ’water nozzle tests’ is used as a guideline. and from the experience obtained till this point some alterations will be made and a dif-fuser will be added. There are four designs made to gain as much insight as possible in different geometry requirements. the angle of the diffuser will be7◦ in order to prevent unexpected behavior there. The most important goal of these experiments is to gain insight in the influence of certain quan-tities for geometries.

If the Matlab model is followed, the exit diameter of the mixing chamber, which is equal to the entrance diameter of the diffuser, must be 3 mm. With a set exit diameter and angle for the diffuser its length can also be deter-mined. The mixing chamber lengths used in the mixing chamber experi-ments proved to be way to long. For this reason the gained experience is used and the mixing chamber lengths are set to 18 and 14 mm respectively for the first two models. The inflow of the water nozzle is a very important part. From the mixing chamber experiments it became clear that the water has to be guided into the mixing chamber as good as possible. The water nozzle areas are kept at3.10−6m2 in al four designs.The first two ’final de-signs’ are shown below. Final design 1 will be used as a reference model and the other three models will be slightly altered and compared with it.

FIGURE3.9: Final design 1 ( MC length 18 mm)

FIGURE3.10: Final design 2 ( MC length 14 mm)

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As already stated in section 4.3.3, there is only time left for designing four nozzles. So two slightly altered designs can be made, next to the al-ready chosen two models, and tested in order to gain insight in the influ-ence of the quantity of some geometries. One model is made just as ’final design 1’, but in this case with an altered larger exit diameter( 3.5 mm) of the mixing chamber. This is done because of the dis-functioning of the mod-els in the mixing chamber tests until the exit diameter was changed to 3.5 mm. This results in an exit diameter for the diffuser of 7 mm.

This design is shown below:

The 4th design will be again the same as ’final design 1’but with a longer

FIGURE3.11: Final design 3

diffuser. This also results in a larger exit diameter(7.9mm). See the figure below.

FIGURE3.12: Final design 4

The models are 3D printed with HTM 140 again!

Measurement set up

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3.6 Steam versus air as a fluidum

A lot of the complexity of the performed experiments comes from the use of steam as the fluidum in the pump. When the steam passes through the nozzle and into the mixing chamber, it partially condenses and thus under-goes a phase change. This means that the flow variables constantly change throughout the length of the pump. The rate of the change of these vari-ables is hard to measure during an experiment and is mainly caused by the dryness of the steam. Because of the condensing steam the mass of the flu-idum also constantly changes over the length the complex behavior of the steam is needed to create the working of the pump as a whole, otherwise the total pressure could never rise according to Bernoulli.[Philip S. Schmidt Ofodike A. Ezekoye,2006]

When performing an experiment to find out if a particular function is achieved, for example: obtaining a suction pressure at the end of the first nozzle, it is important to exclude possible uncertainties and negative side effects caused by these uncertainties. To obtain some of the working principles of the pump steam is not per se needed. For simplicity reasons it is more con-venient to chose a fluidum that doesn’t bring those uncertainties into the experiment.

When replacing the steam for another fluidum, it is obvious to choose air as a substitute. Though it may not have the same properties as steam it will give a good insight in the working of some parts. May it be at a smaller efficiency. Air is easily to obtain and also very simple to compress. With special industrial valves the pressure and mass flow can be be regulated very easily but in an accurate way.

After the test is performed with air it can always be tested with steam af-terwards. With these simple, but accurate tests, a certain hypothesis can be tested.

3.7 Equipment

3.7.1 Steam generator

For generating a constant and reliable steam flow into the pump, a steam generator is used. The Cellkraft precision evaporator E-6000 can deliver a steam flow of maximum of100g/minat a pressure of maximum 5 bar. The temperature can also be set really accurate equal to the boiler temperature. In this way the generator can simulate the boiler conditions really accurate.

3.7.2 Pressure sensor

In order to measure the pressure simple and accurate a piezoresistive pres-sure sensor is used. The OMRON 2SMPP-03 can meapres-sure prespres-sures from

−0.5bar to +0.5bar. Because the ambient pressure and temperature kept reasonably constant, the sensor works really accurate. The sensors working principle is based upon a Wheatstone bridge. See figure3.13.

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altered the value ofV0 will change.

The voltage can be expressed in terms of the different known values R1 , R2 and R3 and the unknown value of the piezoresistive strain gauge: R4, used in the sensor . The diaphragm in the sensor will change the resis-tance of the strain gauge and in this way the pressure can be determined really accurate. The output voltage is linearly related to the pressure that is measured relative to the ambient pressure. It should be noticed that a very stable feeding current should be used in order to obtain the desired accu-racy. This value should e remained between 100 and 130µA. This current is profided with a Keithly 2400 SOURCEMETER.

V0=

_R₁_.R₃₋_R₂_.R₄

R1 +R2 +R3 +R4

.I (3.6)

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Chapter 4

Results

4.1 Steam nozzle

First of all experiments are done on different types of steam nozzles. vary-ing not only in geometry but also in surface quality. In the matlab model it could be noticed that the surface roughness has a great influence on the design. How higher the quality of the surface the better the performance of the nozzle. The surface roughness is measured and the results are given in AppendixB. It can be seen that the average surface roughness of the HTM 140 is much lower than that of the ABS series.

4.1.1 Set up

The set up for the experiment is shown in figure4.1. Because a choked flow is necessary, and thus expected, during the experiment, the nozzle needs to be retained in a solid support. The white tube that is clamped, is the actual nozzle with the festo joint attached to measure the pressure(see also figure3.3.) The black tube on the left is the insulated steam feeding tube. In case when the experiment is executed with air, the steam feeding tube is replaced with an air tube connected to a compressor.

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4.1.2 Matlab results

The expectation from Matlab calculations [Klinkert,2007] is that this geom-etry gives, with steam as a primary fluid, an exit pressure of about−0.5bar. This might be optimistic because the surface roughness has a really high influence to this value. In figure4.14the expected pressure and stream ve-locity are shown.

FIGURE4.2: Pressure and velocity calculated with matlab against the lentgh of the nozzle[0−0.04m]

4.1.3 Air

Geometry 1is manufactured on the 3D printer using two different plastic based materials. The two nozzles are first tested with air as a medium in-stead of steam. This test can give already a relevant insight in the perfor-mance and is also really easy to carry out. The measurement is switched on and after that, the 5 bar air flow is led into the nozzle. This is the switch from positive to negative pressure in the figures4.3and4.4.

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FIGURE 4.3: Suction pressure at the exit of nozzle 1 (ABS) versus time with air as primary fluid.

FIGURE4.4: Suction pressure at the exit of nozzle 2 (HTM 140) versus time with air as primary fluid.

4.1.4 Steam

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FIGURE4.5: Suction pressure at the exit of nozzle 1 (ABS) versus time with steam as primary fluid.

FIGURE4.6: Suction pressure at the exit of nozzle 2 (HTM 140) versus time with steam as primary fluid.

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FIGURE 4.7: Pressure at the exit of straight nozzle versus time with air as primary fluid.

FIGURE 4.8: Pressure at the exit of straight nozzle versus time with steam as primary fluid.

4.2 Water nozzle

From the experiment with the steam nozzle it became clear that the nozzle made from the HTM140 material performed almost as expected from the calculations. As mentioned before, this geometry and material are used in further experiments if a steam nozzle is needed.

In this experiment different through flow areas for the water were exam-ined. During the experiment it became clear that there are a lot of factors that influence and deteriorate the measurements of the mass flow signifi-cantly.

4.2.1 Switching design

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FIGURE4.9: Experimental set up for design 1

While testing this set up it became clear very fast that this design was not accurate enough to give reliable results. The values of the suction pres-sure as well as mass flow values were really diversified. Leakage of water steam and air where happening at the larger thread due to the large toler-ances that were obtained during the manufactering. These large tolertoler-ances also resulted in a very low transparancy of the waternozzle.

This gave enough reason why another more accurate design is chosen. This second design can be seen in figure3.5and the appurtenant experimental set up is displayed in figure4.10.

With this new design the leakage problems were solved and the gained values were already a lot more stable. However, a pulsating flow was ob-tained. The hose that connected the water nozzle with the watertank was vibrating heavily, while the suction pressure was constant. It seemed that two waterfeeding holes led to inconsistent water flow into the water noz-zle. To check this, the same, second, design was used, but one waterfeeding hose was shut off. See figure4.11. This design works properly and is used for obatining results from the experiment.

4.2.2 Final design

The second design with one feeding hose is used for obtaining the results of the experiment. First the massflow rate is measured.

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FIGURE4.10: Experimental set up for design 2

The suction pressure measured at the waterfeeding hose was, for Air and steam as a primary fluid,−0.22barand−0.33barrespectively. It remained constant through the whole experiment.

To get more feeling for the actual mass flow from the water tank into the nozzle,pressure drops due to resistances must be taken into account also. This is done by using the Darcy-weisenbach equation. This equation is used to determine the pressure drop that arises because the water flows through a tube.

Ploss=f∗

L

D∗0.5∗ρ∗v

2 _(4.1)

In this equation the only unfamiliar parameter is the friction factorf. This friction factor can be determined by using a moody chart. However the speed of the water in al cases is so low that laminair flow can be assumed. For laminair flow the friction factor is determined by:

f = 64

Reynolds (4.2)

4.2.3 Skin friction in the mixing chamber.

Another important resistance, resulting in a pressure loss is the skin fric-tion in the mixing chamber. This can also be determined with the darcy-weisenbach equation, though it needs som rewriting. It must also be kept in mind that the flow in this case is turbulent.

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FIGURE 4.11: Experimental set up for design 2 with one feeding hose.

in flow regimes with a Reynolds number above 3000. [Lunowa,2011.]

1

f = 1.8log{( /D

3.7 )

1.11₊6.9

Re} (4.3)

is the measured surface roughness shown in Appendix B The equation For this part of the pressure loss now becomes:

PlossM C =

Z Length

0

( xρv(x)

2

6.48∗D(x)∗log{(/D_3.7)1.11₊6.9 Re}2

)dx (4.4)

And finally:

PlossM C = Pn−1

i=1

(xi+1−xi) 2 ((

ρv(xi+1)2

6.48∗D(xi+1)∗log{(/D₃_.₇)1.11+_Re₍6_xi.9 +1}

2)+ (

ρv(xi)2

6.48∗D(xi)∗log{(/D₃_.₇)1.11+_Re6₍._xi9₎}2 ))

In this situation we divide the domain of x ( axial direction) in ’n’ steps. We define the following parameters to use during the calculation of the pressure loss: The diameter varies linearly over the length. D1 is the entry diameter and D2 is the exit diameter. The lineair formula for the diameter as a function ofxthen becomes:

D(x) =D1 +(D2−D1)

Length (4.5)

The local speed can also be determined:

v(x) = ventry∗D1 2

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We also assume that the density is increasing linearly during the travel through the mixing chamber. This is not reality but for now we only want to gain an insight in the pressure losses due to skin friction. With the steam wetness found in matlab this is can be expressed as[Klinkert,2007] :

ρ= 1

((ζ∗ρ−_water1 ) + ((1−ζ)∗ρ−_air1)) (4.7)

Usingζ as the steam wetness value.

In figure 4.12 an example is given for the derived pressure loss distribu-tion in the mixing chamber. This is a situadistribu-tion with aζ of about 0.9 at the beginning of the mixing chamber to 0.2 at the end of the mixing chamber( these values differ per situation but these are the values used for this plot.) Though, it is known that the density of the fluid mixture is not exactly changing linear throughout the mixing chamber, it will give a good inside in the the numbers that can be expected during the measurement. The total pressure loss is the summation of all the individual pressure losses. Now

FIGURE4.12: Pressure loss distribution due to skin friction.

the assumed pressure losses in the feeding tube as well as the pressure losses due to skin friction in the mixing chamber can be calculated. For air are the values ofζ estimated while for steam the values that are calcu-lated by Matlab are used.

Now the figures4.13and4.14are complemented with the measured mass-flow values and the theoretical achievable massmass-flow with pressure losses taken into account.

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FIGURE4.13: Massflow

by a bad estimation of the density of the fluid, resulting in a wrong calcu-lated skin friction pressure loss. In this case the measurement with air as primary fluid are not very helpful for further understanding of the func-tioning of this part. For this reason further research is done with steam as primary fluid.

When using steam as a primary fluid, the real behaviour of the water can be predicted quite well. The measured values are slightly lower than theoretically expected, but the trend is the same. See figure4.14. However, this seems only through for the smaller massflows. When the area is in-creased to its maximum value, for this set up, the deviation is enlarging. In figure4.15the maximum value for the water nozzle area that can be mea-sured with this set up is added to the previous graph.

In the first graph, the outcoming flow was still a mixture of water and steam. With a larger water nozzle area the droplets in the flow became big-ger and the flow got more and more unevenly distributed.

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FIGURE4.14: Massflow

out of the mixing chamber should not consist completely out of liquid wa-ter. When this happens the switch from supersonic flow to subsonic flow happens in the mixing chamber. which means that a shock wave happens inside the mixing chamber.

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FIGURE4.15: Massflow complemented with last point

4.3 Mixing chamber

At first all the six nozzles were tested with air as a primary fluid. This is done with the models like in figure3.7. No back pressure is applied at the exit of the models (only the ambient pressure).

4.3.1 Measuring

When measuring with the models in this set up,the behavior was not as expected. At the water suction inlet occurred a positive pressure in stead of a suction pressure. This happened with all six models. Even when the tests are performed with steam the same behavior occurs.The steam as a primary fluid should increase the efficiency of the steam nozzle. However this has no influence on this test.

Now the question rises why this behavior is observed. The models behave like they cant start up. A good possibility might be choking of the mixing chamber. Due to the mixing chamber length in combination with the exit diameter(Dout = 2.85mm). To investigate this possible cause of the prob-lem, one model is ’sacrificed’ and altered slightly to determine if the mixing chamber chokes.

In figure4.18can the model be seen. The part that will be altered to detect if choking happens, is colored red.

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FIGURE4.16: Outcoming flow. Flow area:1.1.10−6_m2

FIGURE4.17: Outcoming flow. Flow area:2.4.10−6_m2

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FIGURE 4.18: Model with a mixing chamber length of 40 mm with a water nozzle area of3∗10−6m2.

FIGURE 4.19: Volume flow rate against exit diameter(red part).

As can be seen in the graph, the volume flow rate is almost constant when the outflow diameter is altered. This means that no choked flow is present inside the mixing chamber and that the exit diameter of the mixing chamber is not the leading factor for the dis-functioning of the models. The choking, and thus the restriction of the mass flow, already happens in the steam nozzle. Just as expected from the design.

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So, choking might not be the cause of the dis-functioning of the model, but the exit diameter( red part) does influence the results. Still, no back pressure is applied in these experiments.

4.3.2 Retrospection

It is striking that all of the six models are not behaving is expected. While trying to analyze the problem and find out what is happening, we have to go back in our process and see what changes to the model might be the cause for the dis-functioning of the models.

A big difference with the ’water nozzle tests’( section 4.2) is the addition of the straight tube behind the mixing chamber. This tube, together with the pressure taps, was added in order to locate the shock wave that should be present somewhere at the end of the mixing chamber. Because the pur-pose of these tests is to find a robust combination of geometries that will lead to guaranteed supersonic flow in the Mixing chamber. This tube how-ever, might cause additional pressure loss which causes a different bound-ary condition at the exit of the model.

Another important factor might be the lengthening of the mixing cham-ber. In the ’water nozzle tests’ the mixing chamber length had a maximum value of 20 mm. Because the water particles where not distributed evenly in the flow at the end of the mixing chamber, it was expected that the mixing chamber was to short to obtain a nice evenly distributed flow. This assump-tion might be totally wrong. It is clear now that the flow distribuassump-tion in the mixing chamber is very hard to predict but very important for proper func-tioning of the pump.

The geometry of the water inflow section of the water nozzle into the mix-ing chamber is also different . This change is made because of the manu-facturing process. The 3D printer needs this tapered shape in order to get enough support during the printing process. However, this might not be the main cause of the problem, it might be contributing to the unexpected behavior.

The difference in the used printing material must also be kept in mind! The surface roughness is higher and the behavior of the material wit high temperatures is not known.

4.3.3 Analyzing and detecting the problem

To check if the additional tube at the end of the mixing chamber causes the absence of the (proper)suction pressure, the tube section is removed of all models. This should give a model that is more equal to the model that is used in the ’water nozzle tests’. Now the only difference is the mixing chamber length and the water inflow section. And for the series with the larger water nozzle area, this are is also larger.

Designing and prototyping a small scale steam driven jet pump

I