Effect of Different Surface Coated Tubes on the Performance of Shell and Tube Heat Exchanger

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 9, Issue 9, September 2019)

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Effect of Different Surface Coated Tubes on the Performance of

Shell and Tube Heat Exchanger

Kailash U. Makhija

1

, Prof. T. A. Koli

2

, Dr. V. H. Patil

3

1_{Research Scholar,}2_{Head of Department,}3_{Principal, Mechanical Engineering, GF’s GCOE Jalgaon, India} Abstract: Heat Exchangers (HEs) are used in almost all

engineering and industrial applications. These are the mechanical devices which exchanges the heat from hot fluid to another cold fluid. The performance of Heat Exchangers depends on the temperature differences of the fluids, design of heat exchanger and materials used to achieve the heat transfer rate. The heat transfer rate can be improved by providing metal coating on the metal-fluid contact surfaces.

The paper presents an effect of different material coating of tubes on the testing and analysis of single Shell and Tube Heat Exchanger. For that event, coating materials selected as Zinc, Copper and Brass for testing and results are compared with uncoated tube in parameters of Log Mean Temperature Difference (LMTD) and Effectiveness.

Keywords: Metal Coating, Heat Exchangers, Heat Transfer Rate, LMTD, Effectiveness, etc.

I. BACKGROUND

The main difference in Heat Exchanger and mixing chamber is that heat exchanger do not allow the two fluids to mix. In car radiator, heat is exchanged between hot water and air. The hot water flowing through radiator tubes surrounded by plate fins and air flows over the fins.

Heat transfer in a HE involves convection phenomenon in each fluid-tube surfaves and conduction through the tube metal thickness separating the hot and cold fluids.

The rate of heat transfer between the hot and cold fluids at any location in a HE depends on the quantity of the temperature difference, thermal conductivity of tube material and heat transfer coefficient, at that location. In the analysis of HE, it is general to measure the Logarithmic Mean Temperature Difference LMTD, which is defined as natural log of mean temperature difference between the two fluids for the complete HE and effectiveness.

[image:1.612.358.525.227.356.2]

HEs are manufactured in a various types. Parallel Flow HE, transfers the heat from high temperature fluid inside the tube to low temperature fluid outside the tube. It is also called as shell and tube HE. Both fluids flows in same direction. Such type of HE requires more surface area. Figure 1 shows the parallel flow HE.

Figure 1 Parallel Flow HE

The another type of HE is Counter Flow HE, in this HE, the high temperature fluid and low temperature fluid flows in opposite direction. This type of HE are common in industries because of flow direction and effective rate of heat transfer. Figure 2 shows the counter flow HE.

Figure 2 Counter Flow HE

II. EXPERIMENTATION

A] Setup:

[image:1.612.352.532.424.572.2]

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The double pipe heat exchanger has been fabricated by using 25.4 mm diameter shell and 12.7 mm diameter tube made by Galvanized Iron. The other tubes are coated by Zinc, Copper and Brass material with thickness 1 micron. The geyser has been used here is 3 liter capacity having power consumption rate 3000 watt. Within 10 minutes, the

water starts heating up to 700C. The pump used have 0.5

[image:2.612.338.546.136.275.2]

HP, 2800 RPM. The centrifugal pump is used for the experimental work having the maximum head up to 25 feet. Four Thermocouples of K type (DS18B20) are mounted to indicate the temperature of hot water inlet, hot water outlet, cold water inlet and cold water outlet. Also, two flow sensors (YS201) are used to measure the flow rates of hot as well as cold water. All sensors have been placed on respective positions of heat exchanger and Arduino UNO had used to display the readings from sensors. The PVC pipe line has been used to circulate the cold water through system and insulated hot water line has been used for hot water. The arrangement of parallel flow and counter flow was done by operating various valves. The Table 1 and 2 shows the observations for Parallel and Counter Flow HE.

[image:2.612.66.272.383.545.2]

Figure 3 Experimental Setup

Figure 4 Water Flow Circuit Diagram of HE

B] Experimental Procedure

The trial of heat exchanger has been taken by changing the coated tubes and comparison made based on coated tubes and GI tube. For that event, following procedure was adopted in parallel flow as well as in counter flow:

1. Initially, make sure that all electrical connections

are proper.

2. Use first GI Tube for testing.

3. Make parallel flow arrangement.

4. Start the pump and geyser and allow water to pass

through system.

5. Check the display unit and observe the temperatures

read by thermocouples and flow rate of both fluids.

6. When the ideal conditions are reached (i.e. the hot

water temperature is 650C, and both flow rate are

0.04 Kg/s by bypass valve)

7. Note down the all observations shown by display

unit.

8. After taking the readings for parallel flow, switch

OFF the system.

9. Again make the counter flow arrangement.

10. Follow the procedure from step 4 to step 7 for

counter flow arrangement.

11. After complete observations using GI tube, change

the tube by Zinc Coated Tube using disassembly of heat exchanger.

12. Again follow the same procedure from step 1 to step

10 for observations.

13. Repeat steps for Copper tubes and Brass Tubes in

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Table 1

Observations (Parallel Flow)

Sr. No . T y p e o f T u b e Ho t Water I n let T em p . ( 0 C) Ho t Water Ou tlet T em p . ( 0 C) C o ld W ater I n let T em p . ( 0 C) C o ld W ater Ou tlet T em p . ( 0 C) Ho t Water Flo w R ate (Kg /s ) C o ld W ater Flo w R ate (Kg /s ) 1 Un co

ated ₆₅ ₅₃ ₃₀ ₄₁ _{0.04 0.04}

2

Z

n

C

o

ated ₆₅ ₅₁ ₃₀ ₄₂

0.04 0.04 3 C u C o

ated ₆₅ ₅₀ ₃₀ ₄₂

0.04 0.04 4 B r C o

ated ₆₅ ₅₀ ₃₀ ₄₀

0.04 0.04

Table 2

Observations (Counter Flow)

Sr. No . T y p e o f T u b e Ho t Water I n let T em p . ( 0 C) Ho t Water Ou tlet T em p . ( 0 C) C o ld W ater I n let T em p . ( 0 C) C o ld W ater Ou tlet T em p . ( 0 C) Ho t Water Flo w R ate (Kg /s ) C o ld W ater Flo w R ate (Kg /s ) 1 Un co ate

d 65 54 30 40 0.04 0.04

2

Z

n

C

o

ated ₆₅ ₅₆ ₃₀ ₄₀

0.04 0.04 3 C u C o

ated ₆₅ ₅₄ ₃₀ ₄₆

0.04 0.04 4 B r C o

ated ₆₅ ₅₅ ₃₀ ₄₃

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C] Sample Calculations

For Parallel Flow Uncoated Tube

Temperature of Hot Water Inlet (Thi) = 650C

Temperature of Hot Water Outlet (Tho) = 53

0 C

Temperature of Cold Water Inlet (Tci) = 300C

Temperature of Cold Water Outlet (Tco) = 410C

Theta1 = Thi - Tci = 65-30 = 35

Theta2 = Tho - Tco = 53-41 = 12

LMTD = 21.486

[image:4.612.65.272.421.717.2]

Similarly all the calculations are tabulated in Table 3.

Table 3 Experimental Results

S

r.

No

.

He

at

Ex

ch

an

g

er

Ty

p

e

LM

TD

(

0 C)

Eff

ec

ti

v

en

ess

(%

)

1 Parallel Flow

Uncoated Type 21.49 34.29

2 Parallel Flow Zn

Coated Type 19.14 40.00

3 Parallel Flow Cu

4 Parallel Flow Br

5 Counter Flow

Uncoated Type 24.50 28.57

6 Counter Flow Zn

7 Counter Flow Cu

8 Counter Flow Br

III. COMPRESSIBLE FLUID DYNAMICS (CFD)ANALYSIS

Heat transfer analysis has been performed in ANSYS Fluent 19.0 software. Initially, a geometry had modelled in geometry modeler. The dimensions taken for designing the heat exchanger are shell diameter is 25.4 mm and tube diameter is 12.7 mm. the overall length of heat exchanger is 800 mm. A fluid domain has been added in geometry by considering volume enclosed by shell and tube. The inlets and outlets are specified and boundary conditions are specified. After that meshing has been done. The default mesh size is selected and mesh sizing is performed with face meshing to obtain accurate results. The material properties are specified. After doing all necessary conditions, the solution has started and results are shown by temperature counters (Figure 5, 6) and volume rendering (Figure 7).

A] Steps for Ansys Fluent

1. Start Ansys Fluent in Workbench.

2. Create the geometry of heat exchanger using given

details. (Shell diameter =25.4 mm, Tube diameter =12.7 mm, Length = 800 mm)

3. Create the solid domain and fluid domain.

4. Name the inlet, outlet and wall as per both fluids.

5. Go to setup

6. Mesh the generated geometry. (Use default meshing

and mesh sizing with face meshing)

7. Define the materials and fluids. (GI for Shell, select

the material for tube as required for analysis, water as fluid)

8. Specify the boundary conditions. (Hot and cold

water inlets and outlets, temperature of both fluids inlet)

9. Solve the model with default setting parameters and

up to 50 iterations.

10. Observe the results by adding temperature counters

at inlet and outlet.

11. Observe the volume rendering along length of heat

exchanger for temperature variation.

12. Perform above steps for all types of heat

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International Journal of Emerging Technology and Advanced Engineering

[image:5.612.57.552.90.563.2]

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Figure 5 Temperature Counter for Inlet of Parallel Flow Uncoated

Heat Exchanger

[image:5.612.336.550.151.564.2]

Figure 6 Temperature Counter for Outlet of Parallel Flow Uncoated Heat Exchanger

Figure 7 Volume Rendering for Parallel Flow Uncoated Heat Exchanger

Table 4

CFD Results (Parallel and Counter Flow HE)

Sr. No.

Heat Exchanger Type

LMTD

(0C)

Effectivene ss (%)

1 Parallel Flow

Uncoated Type

23.65 27.14

2 Parallel Flow

Zn Coated Type

23.65 27.14

3 Parallel Flow

Cu Coated Type

23.65 27.14

4 Parallel Flow Br

Coated Type

23.65 27.14

5 Counter Flow

Uncoated Type

24.36 32.06

6 Counter Flow

Zn Coated Type

24.36 32.03

7 Counter Flow

Cu Coated Type

24.36 32.06

8 Counter Flow

Br Coated Type

24.36 32.03

IV. RESULTS AND DISCUSSION

Figure 8 Comparison of LMTD by Experimental and Ansys Method

10 15 20 25 30 35

LMTD (0_C)

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Figure 8 shows the comparison between the

experimental and Ansys values of LMTD. All the values are close to the agreement. The maximum value of LMTD observed is 25.50 for counter flow with zinc coated tube experimentally to that of all counter flow arrangements by Ansys which is 24.36. This proves that the experimental setup is quite better and results within agreements. There is slight variation in LMTD by using coatings. The thickness of coating is also one of the criteria for variation in LMTD. The Ansys method gives same results for parallel and counter flow with coatings. Since the coating thickness considered here is 1 micron is too smaller to enhance the heat transfer rate.

Figure 9 Comparison of Effectiveness by Experimental and Ansys

Method

Figure 9 shows the comparison between the experimental and Ansys values of effectiveness. All the values are close to the agreement. The maximum value of effectiveness observed is 45.71 for counter flow with copper coated tube experimentally to that of all counter flow arrangements by Ansys which is 32.06.

V. CONCLUSION

The present study includes the performance of heat exchanger by using different coatings. For that purpose four materials are selected galvanized iron, zinc, copper and brass. Coating thickness of 1 micron had done on tube at outer side of heat exchanger. The experimental and Ansys Fluent method was adopted for measuring the performance of heat exchanger.

It can be concluded from the study that the heat exchanger performance depends on various parameters including hot water and cold water temperatures, mass flow rates and properties. The variation in any of the parameter results in change of performance.

It is concluded that the experimental method is well suitable for obtaining the performance of such heat exchangers. The Ansys method gives the results but it is complex and time consuming. However, experimental work can be validated with Ansys work.

It is concluded that the coating changes the performance of heat exchanger. The maximum effectiveness obtained in copper coated counter flow heat exchanger and is 45.71%. Thus it is concluded that, it is better to use copper coating for heat exchange process. Because of coating it is also concluded that the surface area of coated surface is useful in heat exchange. It is also concluded that the costing thickness of 1 micron does not change the considerable performance of heat exchanger.

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