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Koya University

Faculty of Engineering Chemical Engineering Department

Laboratory of Heat Transfer Experiment Number Three

Heat Exchanger (Counter flow)

Instructor: Dr.Barham & Mrs.Farah

Name of Student: Aree Salah Tahir

Experiment Contacted on: 15/Dec/2014

Report Submitted on: 18/Dec /2014

Group:A

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List of content:

Aim………………………………………………………….3

Introduction...…………………………….……………..….4

Background Theory ……………………………………….5

Procedure …………………………………………………..6

Equipment and components used........................................7

Calculation.............................................................................8

Plots………………………………………………………9-10

Discussion ………………………………………………….11

References ………………………………………………….12

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Aim:

The objective of this experiment is to calculate the rate of the heat

transfer log mean temperature difference, and the overall heat transfer

coefficient in case of Counter flow.

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Introduction:

Up to this point we have learned how to analyze conduction and

convection heat transfer in various systems with different geometries.

This information, however, is not very useful unless it can be applied

to practical situations. For this reason we shall devote this experiment

to a prototypical application of heat transfer analysis known as a heat

exchanger.

A heat exchanger is a device that efficiently transfers heat from a

warmer fluid to a colder fluid. A device we are probably all familiar

with is the automobile radiator. Other applications for heat exchangers

are found in heating and air conditioning systems. Heat exchangers

are categorized in many ways, but the two most common practices

are, by the method of construction, and by the flow arrangements. The

analysis for designing an effective heat exchanger is very important;

after all who'd want to be caught on the side of a deserted desert road

with an overheated engine!

In this experiment we will study a concentric tube heat exchanger with

parallel and counter flow. For the analysis of this heat exchanger we

will need to find important quantities such as the heat transfer

coefficient, power emitted, absorbed, and lost, the log mean

temperature difference, and the overall efficiency to compare the two

types of flow. {1}

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Background Theory:

One of the most common, conductive-convective, heat exchanger types

is the concentric tube heat exchanger. These exchangers are built of

coaxial tubes placed the ones inside the others. When both the fluids

enter from the same side and flow through the same direction we have

the Counter flow, otherwise, if the fluids enter from opposite sides and

flow through the contrary direction we have the countercurrent flow.

Usually the countercurrent flow is more efficient from the heat

transfer point of view. This type of heat exchangers can also be built

with the internal tube made with longitudinal fins which could be

placed either in its internal surface or in its external one or both. This

configuration is useful mainly if one of the fluids is a gas or a liquid

with a very high viscosity and it's very difficult to have a good thermal

convection coefficient. The heat transfer from the hot fluid to the cold

fluid is given by the following equation:

Q = U * A * ∆TLMTD

Where: U: is the overall heat transfer coefficient.

A: is the internal exchange surface area between the two

fluids.

∆TLMTD is a log means temperature difference, and it's given

by:

∆TLMTD = ∆𝑇𝑚𝑎𝑥.−∆𝑇𝑚𝑖𝑛.

𝑙𝑛 ∆𝑇𝑚𝑎𝑥.

∆𝑇𝑚𝑖𝑛.

{2}

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Procedure:

1. Switch on master switch.

2. To Set hot water flow rate using cylinder and stopwatch

3. Switch on heater. Heating from an ambient temperature of 20 to

60°C requires approx. 20 min

4. Set Counter flow by open ball valve 1 and 4, and closed ball valve 2

and 3 in figure

5. Set a high cold-water flow rate with flow-control valve. Allow water

to run briefly.

6. Carefully open bleeder valve for cold-water flow.

7. Close again when water emerges.

8. It is appropriate to bleed the hot-water circuit when warm, as

bubbles form while ever the temperature is still high.

9. Switch on pump.

10. Use flow-control valve to set high hot-water flow rate. Allow

water to run briefly.

11. Carefully open bleeder valve for hot-water flow.

12. Close again when water emerges. Take care when system is hot:

Danger of scalding as water emerges. {3}

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Equipment and components used:

1- Vent valve

2- Temperature sensor

3- Ball valve

4- Pump

5- Heater with thermostat

6- Tank

7- Water connections

8- Flow rate sensor

9- Valve to adjust flow rate

10- Main switch and emergency pump and heater switches

11- Displays.

12- And we using cylinder and stopwatch to determine flaw rate of hot

water. {4}

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calculation:

Table of calculation:

NO M

cold

M

hote

∆T

logmean

զ ͦ u

1 0.0082 0.016 16.02 0.7 1.28

2 0.016 0.016 19.7 1.09 1.6

3 0.025 0.016 38.73 1.26 0.957

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Plots:

Plot (1)

Plot (2)

16.02; 0.0082

19.7; 0.016

38.73; 0.025

0

0.005

0.01

0.015

0.02

0.025

0.03

0 5 10 15 20 25 30 35 40 45

M c

old

∆T logmean

Plot between M cold & ∆T logmean

0.7; 0.0082

1.09; 0.016

1.26; 0.025

0

0.005

0.01

0.015

0.02

0.025

0.03

0 0.2 0.4 0.6 0.8 1 1.2 1.4

M c

old

զ ͦ

Plot between M cold & զ ͦ

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Plot (3)

1.28; 0.0082

1.6; 0.016

0.957; 0.025

y = -0.0141x + 0.0344

0

0.005

0.01

0.015

0.02

0.025

0.03

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

M c

old

u

Plot between M cold & u

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Discussion:

A- In plot (1 & 2) show that the Mcold is directly proportional increase

while (∆Tlogmean) and (զ ͦ) also increase

But in the plot (3) increase Mcold when (u) is also increase but in point 3

(0.957,0.025) there is a error.

B- We insulate the pipe in order not to transfer heat to out.

C-The Valve to adjust hot flow rate does not work so we will measurement by

ourselves.

D- counter flow heat exchanger is better then the parallel flow because

counter flow type is more effective because of the uniform temperature

difference between hot and cold fluids throughout the pass compared to

parallel flow configuration.

E- The ball valves are used to set the desired flow rates and adjust between

parallel and counter flow modes.

F- for a second we open the vent valve and close it for safety to allow air or

stem go out.

G- Types of heat exchangers:

1-Shell and tube heat exchanger

2-Plate heat exchanger

3-Adiabatic wheel heat exchanger

4-Plate fin heat exchanger

5-Fluid heat exchangers

6-Waste heat recovery units

7-Dynamic scraped surface heat exchanger

8-Phase-change heat exchangers

H- Heat exchangers are used in many industries, some of which include:

1-Waste water treatment 2-Refrigeration systems

3-Wine-brewery industry 4-Petroleum industry

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References:

1- http://www.engr.iupui.edu/~mrnalim/me314lab/lab10.htm

2- F.P Incropera and D.P DeWitt, "Fundamentals of Heat and Mass Transfer", 4th Edition, John Wiley and Sons, 2002.

3- Applied heat laboratory sheet by Koya University, college of

engineering, department of chemical engineering.

4- http://www.gunt.de/static/s3452_1.php