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DESIGN OF DOUBLE PIPE HEAT EXCHANGER
Mrs. Kirti B.Zare
1, Ms. Dipika Kanchan
2, Ms. Nupur Patel
31, 2, 3
Chemical Engineering, D.Y. Patil Institute of Engineering, Management and Research, Akurdi, Pune, (India)
ABSTRACT
Heat exchanger is one of the important devices in cooling and heating process in Factories, buildings, transports and others. The heat exchanger is found in large Construction to support cooling process such as fossil fuel power plant. In the present study, heat transfer from hot water to cold water by double pipe heat exchanger consists concentric tube is experimentally investigated. The horizontal double pipe heat exchanger is made from Galvanised iron tube with inner tube and outer tube. The inner tube is consists of 26mm internal &
34 mm outer diameter. The outer tube is consisting of 68 mm internal & 76 mm outer diameter.
A set of the experiments were carried out to investigate for counter flow & parallel flow to determine heat transfer coefficient in a double pipe heat exchanger.
Keywords: Coefficient of heat transfer, counter flow, Double pipe, Heat Exchanger parallel flow.
I. INTRODUCTION
Horizontal double pipe heat exchanger uses various inserts inside tube so as to enhance heat transfer and hence increase heat transfer coefficient [1, 2, 3].These types of heat exchangers found their applications in heat recovery processes, air conditioning and refrigeration systems, chemical reactors, and food and dairy processes [2].The double pipe heat exchanger would normally be used for many continuous systems having small to medium headuties. The heat exchanger is a device which transferred the heat from hot medium to cold medium without mixed both of medium since both mediums are separated with a solid wall generally. There are many types of heat exchanger that used based on the application. For example, double pipe heat exchanger is used in chemical process like condensing the vapour to the liquid. When to construct this type of heat exchanger, the size of material that want to uses must be considered since it affected the overall heat transfer coefficient. For this type of heat exchanger, the outlet temperature for both hot and cold fluids that produced is estimated by using the best design of this type of heat exchanger.
162 | P a g e Figure No: 1.1 Double pipe Heat Exchanger
The double pipe heat exchanger is used in industry such as condenser for chemical process and cooling fluid process. This double pipe heat exchanger is designed in a large size for large application in industry. For this research, the small heat exchanger of double pipe type is constructed which wants to make it practicality in daily life such in cooling the hot air from engine bay into intake manifold of car[7]. To make this small double pipe heat exchanger type become practicality, the best design for this small double pipe heat exchanger is choose.
The objectives of this research are as follows:
i. To study about heat transfer analysis in heat exchanger.
ii. To design the heat exchanger based on TEMA specification
The most popular are those of recuperative type. The fluids are physically separated by heat transfer surface and the heat is transferred from hot to cold agent [4].
1.1 Classification According To Transfer Processes
Heat exchangers are classified according to transfer processes into indirect- and direct contact types.
1.1.1Indirect-Contact Heat Exchangers
In an indirect-contact heat exchanger, the fluid streams remain separate and the heat transfers continuously through an impervious dividing wall or into and out of a wall in a transient manner. Thus, ideally, there is no direct contact between thermally interacting fluids. This type of heat exchanger also referred to as a surface heat exchanger, can be further classified into direct-transfer type, storage type, and fluidized-bed exchangers [12].
`fluids because each fluid flows in separate fluid passages. In general, there are no moving parts in most such heat exchangers. This type of exchanger is designated as a recuperative heat exchanger or simply as a recuperate. {Some examples of direct transfer type heat exchangers are tubular, plate-type, and extended surface exchangers. Note that the term recuperate is not commonly used in the process industry for shell 4and-tube and plate heat exchangers, although they are also considered as recuperates. Recuperates are further sub classified as prime surface exchangers and extended-surface exchangers. Prime surface exchangers do not employ fins or extended surfaces on any fluid side. Plain tubular exchangers, shell-and-tube exchangers with plain tubes, and plate exchangers are good examples of prime surface exchangers. Recuperates constitute a vast majority of all heat exchangers [13].
163 | P a g e 1.1.1.2 Storage Type Exchangers
In a storage type exchanger, both fluids flow alternatively through the same flow passages, and hence heat transfer is intermittent. The heat transfer surface (or flow passages) is generally cellular in structure and is referred to as a matrix or it is a permeable (porous) solid material, referred to as a packed bed. When hot gas flows over the heat transfer surface. The thermal energy from the hot gas is stored in the matrix wall, and thus the hot gas is being cooled during the matrix heating period. As cold gas flows through the same passages later (i.e., during the matrix cooling period), the matrix wall gives up thermal energy, which is absorbed by the cold fluid. Thus, heat is not transferred continuously through the wall as in a direct-transfer type exchanger (recuperate), but the corresponding thermal energy is alternately stored and released by the matrix wall [12]. This storage type heat exchanger is also referred to as a regenerative heat exchanger, or simply as a regenerator. The actual time that hot gas takes to flow through a cold regenerator matrix is called the hot period or hot blow, and the time that cold gas flows through the hot regenerator matrix is called the cold period or cold blow. For successful operation, it is not necessary to have hot- and cold-gas flow periods of equal duration. There is some unavoidable carryover of a small fraction of the fluid trapped in the passage to the other fluid stream just after switching of the fluids; this is referred to as carryover leakage. In addition, if the hot and cold fluids are at diff erent pressures, there will be leakage from the high-pressure fluid to the low-pressure fluid past the radial, peripheral, and axial seals, or across the valves [13]. This leakage is referred to as pressure leakage. Since these leaks are unavoidable, regenerators are used exclusively in gas-to-gas heat (and mass) transfer applications with sensible heat transfer; in some applications, regenerators may transfer moisture from humid air to dry air up to about 5%. For heat transfer analysis of regenerators, the "-NTU method of recuperates needs to be modified to take into account the thermal energy storage capacity of the matrix [12].
1.1.1.3 Fluidized-Bed Heat Exchangers
In a fluidized-bed heat exchanger, one side of a two-fluid exchanger is immersed in a bed of finely divided solid material, such as a tube bundle immersed in a bed of sand or coal particles[11]. If the upward fluid velocity on the bed side is low, the solid particles will remain fixed in position in the bed and the fluid will flow through the interstices of the bed. If the upward fluid velocity is high, the solid particles will be carried away with the fluid.
At a „„proper‟‟ value of the fluid velocity, the upward drag force is slightly higher than the weight of the bed particles. As a result, the solid particles will float with an increase in bed volume, and the bed behaves as a liquid. This characteristic of the bed is referred to as a fluidized condition. Under this condition, the fluid pressure drop through the bed remains almost constant, independent of the flow rate, and a strong mixing of the solid particles occurs [12]. This results in a uniform temperature for the total bed (gas and particles) with an apparent thermal conductivity of the solid particles as infinity. Very high heat transfer coefficients are achieved on the fluidized side compared to particle-free or dilute-phase particle gas flows. Chemical reaction is common on the fluidized side in many process applications, and combustion takes place in coal combustion fluidized beds. The common applications of the fluidized-bed heat exchanger are drying, mixing, adsorption, reactor engineering, coal combustion, and waste heat recovery [12].
1.2 Direct-Contact Heat Exchangers
In a direct-contact exchanger, two fluid streams come into direct contact, exchange heat, and are then separated.
Common applications of a direct-contact exchanger involve mass transfer in addition to heat transfer, such as in
164 | P a g e evaporative cooling and rectification; applications involving only sensible heat transfer are rare. The enthalpy of phase change in such an exchanger generally represents a significant portion of the total energy transfer. The phase change generally enhances the heat transfer rate. Compared to indirect contact recuperates and regenerators, in direct-contact heat exchangers:
(1) Very high heat transfer rates are achievable
(2) The exchanger construction is relatively inexpensive (3) The fouling problem is generally non-existent
The absence of a heat transfer surface (wall) between the two fluids. However, the applications are limited to those cases where a direct contact of two fluid streams is permissible [10].
1.2.1 Immiscible Fluid Exchangers
In this type, two immiscible fluid streams are brought into direct contact. These fluids may be single-phase fluids, or they may involve condensation or vaporization. Condensation of organic vapours and oil vapours with water or air are typical examples [13].
1.2.2. Gas–Liquid Exchangers
In this type, one fluid is a gas (more commonly, air) and the other a low-pressure liquid (more commonly, water) and are readily separable after the energy exchange. In either cooling of liquid (water) or humidification of gas (air) applications, liquid partially evaporates and the vapour is carried away with the gas. In these exchangers, more than 90% of the energy transfer is by virtue of mass transfer (due to the evaporation of the liquid), and convective heat transfer is a minor mechanism [11]. A „„wet‟‟ (water) cooling tower with forced- or natural-draft airflow is the most common application. Other applications are the air-conditioning spray chamber, spray drier, spray tower, and spray pond.
1.2.3 Liquid–Vapour Exchangers
In this type, typically steam is partially or fully condensed using cooling water, or water is heated with waste steam through direct contact in the exchanger. Noncondensables and residual steam and hot water are the outlet streams. Common examples are desuperheaters and open feed water heaters (also known as deaerators) in power plants [10].
II.REALTED WORK 2.1 Scopes of Research
The scopes of this research are as follows:
i. Study on heat transfer for heat exchanger specific to double pipe heat Exchanger types.
ii. Design the double pipe heat exchanger by using Solid- Works
iii. Temperature distribution in parallel flow & counter flow heat exachger.
iv. Analysis the heat exchanger specific to flow rate of hot and cold fluid.
vi overall heat transfer coefficient in parallel & counter flow.
vii. To obtain effectiveness in parallel ae well as counter flow.
2.2 Significance of Research
The significances of this research are as follows:
165 | P a g e i. To determine the best design for double pipe heat exchanger type.
ii. To fabricate the double pipe heat exchanger.
Heat exchanger is a special equipment type because when heat exchanger indirectly fired by a combustion process, it becomes furnace, boiler, heater, tube-still heater and engine. Vice versa, when heat exchanger make a change in phase in one of flowing fluid such as condensation of steam to water, it becomes a chiller, evaporator,sublimator, distillation-column reboiler, still, condenser or cooler-condenser. Heat exchanger may be designed for chemical reactions or energy-generation processes which become an integral part of reaction system such as a nuclear reactor, catalytic reactor or polymer [5].Normally, heat exchanger is used only for the transfer and useful elimination or recovery of heat without changed in phase. The fluids on either side of the barrier usually liquids but they can be gasses such as steam, air and hydrocarbon vapour or can be liquid metals such as sodium or mercury. In some application, heat exchanger fluids may use fused salts [6].
III. EXPERIMENTAL SET UP
The important parts of experimental set-up are blower, the test section containing horizontal concentric copper pipes, hot air tank and cold water tank, rotameter, monoblack pump, whose selection is already discussed in previous section.
All these instruments are selected as per the requirements depending upon their measuring range, accuracy and availability in the market. The test section is made up of copper tubes as it has higher thermal conductivity.
Specification:
1. Inner Tube Material: Galvanizing Iron Internal diameter of inner tube (di) = 26mm Outer diameter of inner tube (do) = 34 mm Length of inner tube (Li) = 1.2 m
Thickness of inner Tube (ti) = 4 mm 2. Outer Tube Material: Galvanizing Iron
Internal diameter of inner tube (di) = 68mm Outer diameter of inner tube (do) = 76 mm Length of inner tube (Lo) = 1.2 m
Thickness of inner Tube (to) = 4 mm 3. Specific Heat of Water = 4.186 Kw/kg0K
166 | P a g e Figure No: 3.1 Inlet & Outlet flow of Double pipe Heat Exchanger
To achieve a particular engineering objective, it is very important to apply certain principles so that the product development is done economically. This economic is important for the design and selection of good heat transfer equipment. The heat exchangers are manufactured in different types, however the simplest form of the heat exchanger consist of two concentric pipes of different diameters known as double pipe heat exchanger. In this type of heat exchanger, one fluid flows through the small pipe and another fluid flows through the space between both the pipes [7]. The flows of these two different fluids, one is at higher temperature called hot fluid and another is at lower temperature called cold fluid, can be in same or in opposite directions. If the flows are in same direction then the heat exchanger is called as parallel flow heat exchanger and if the flows are in opposite direction then the heat exchanger is called as counter flow heat exchanger.
Figure No: 3.2Double pipe heat exchangers with different flow and their respective temperature profile for Parallel flow
167 | P a g e Figure No: 3.3 Figure No: 3.2Double pipe heat exchangers with different flow and their respective
temperature profile for counter flow
Figure No: 3.4 Double pipe Heat Exchanger (Isometric view in solid works)
The further development is done in the heat exchangers to facilitate them in different applications as per requirement. These heat exchangers are different from the conventional heat exchangers such that they have large heat transfer surface area per unit volume and are known as compact heat exchanger [8]
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IV. RESULT
4.1 Parallel Flow:
Sr No.
Hot water Flow rate Qh (lpm)
cold water Flow rate Qc (lpm)
Hot water Inlet temp.
Thi (T1)
Hot water Outlet temp.
Thi (T2)
cold water inlet Tci (T3)
cold water outlet Tco (T4)
1. 1.1 4 51 49 29 30
2. 1.4 1 53 48 36 33
3. 1.5 0.9 55 47 38 31
Table No: 4.1 Parallel flow
Graph No: 4.1 Hot water profile for hot water flow rate vs. inlet temp. of hot water
Graph No: 4.2 Hot water profile for hot water flow rate vs. outlet temp. of hot water
169 | P a g e Graph No: 4.3 Cold water profile for cold water flow rate vs. inlet temp. of cold water
Graph No: 4.4 Cold water profile for cold water flow rate vs. outer temp. of cold water
4.2 counter flow:
Sr No.
Hot water Flow rate Qh (lpm)
cold water Flow rate Qc (lpm)
Hot water Inlet temp.
Thi (T1)
Hot water Outlet temp.
Thi (T2)
cold water inlet Tci (T3)
cold water outlet Tco (T4)
1 1.1 4 51 48 29 30
2 1.4 1 53
4936 33
170 | P a g e Graph No: 4. 5 Hot water profile for hot water flow rate vs. inlet temp. of hot water
Graph No: 4. 6 Hot water profile for hot water flow rate vs. outlet temp. of hot water
Graph No: 4. 7 Cold water profile for cold water flow rate vs. inlet temp. of cold water
171 | P a g e Graph No: 4. 8 Cold water profile for cold water flow rate vs. outlet temp. of cold water
V.CALCULATION
1. Heat Transfer from hot water (qn):
qn = mh. cph.(Thi- Tho)
2. Heat Transfer rate to cold water (qc):
qc = Mc Cpc (Tco-Tci)
3 . Average heat transfer rate (q) : q = qn – qc / 2
4.L.M.T.D :
∆Tm = ∆Ti - ∆To / ln ( ∆Ti/ ∆To)
5.Oveall Heat transfer Based on Internal Area of Tube Ui = q = Ui Ai (∆Tm)
Ai = π di L 6. Effectiveness :
n = Mh Cph ( Thi- Tho) / Mc Cpo ( Tco – Tci) Sr
No.
qn ( Kwatt ) Qc (Kwatt) Average q ( K watt ) LMTD (0K) U ( Inner Watt/m0K)
U ( Outer Watt/m0K)
Effectiveness (%) Parallel Flow
1 0.2787 0.153 0.215 3 731.21 559.1 54.89
Counter Flow
2 0.229 0.278 0.2535 3.34 774.3 592.1 82.37
Table No: 5.1 Parallel & Counter flow effectiveness
172 | P a g e Graph No: 5.1Profile of Parallel flow
Graph No: 5.2Profile of counter flow
Graph No: 5.3 Effectiveness profile for parallel flow &counter flow
173 | P a g e
V.CONCLUSION
Experimental investigations of heat transfer characteristics of double pipe heat exchanger fitted with inserted concentric tubes for parallel & counter flow. The review indicates that Heat Exchangers are the heat transfer devices which are used in different applications. The heat exchangers can be used to recover the resources like water as it is converted into the steam which is condensed by using the condenser. Heat exchangers also useful for the economical running of industries and to control the pollution as in case of economizer and air pre-heater.
A good agreement is obtained between the experimental results of counter & parallel flow in that counter flow is more efficient for same flow rate.
REFERENCES
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Acknowledgments
This research was supported by Dr. D. Y. Patil Institute of Engineering, Management &Research, Akurdi, and Pune.We are thankful to our Principal Dr. Mrs .A. V. Patil. for provided expertise that greatly assisted the research.
We have to express our appreciation to the Mr.Bhushan Zare for sharing their pearls of wisdom with us during the course of this research.
