Lab Manual 2

KC21001 LABORATORY 4
LAB MANUAL 2
Group 1
1. Adam bin Abdul Rahman BK13110006

2. Corezza Adele Chin BK13160546
3. Nigel Pearce Paramanathan BK13110277
4. Rasrina bte Razin Wong BK13110367
Experiment HE3: Double Pipe Heat Exchanger
Date: 01/04/2015
Objectives
1. To investigate the effects of cold water flow rate on the heat-transfer efficiency (n),
real heat-transfer coefficient (kre) and theoretical heat-transfer coefficient (kth).
2. To investigate the best conditions of heat exchanger in the double tube heat exchanger:
compare between co-current and counter-current configurations, compare between
laminar and turbulent flows.
Theory and Explanation

Heat is normally transfer from high temperature region to a lower temperature region
until it reaches thermal equilibrium as stated in the second law of thermodynamics. Heat
exchangers are a device that exchange the heat between two fluids of different temperatures
that are separated by a solid wall. The temperature gradient, or the differences in temperature
facilitate this transfer of heat. Transfer of heat happens by three principle means: radiation,
conduction and convection. In the use of heat exchangers radiation does take place. However,
in comparison to conduction and convection, radiation does not play a major role. Conduction
occurs as the heat from the higher temperature fluid passes through the solid wall. To
maximize the heat transfer, the wall should be thin and made of a very conductive material.
The biggest contribution to heat transfer in a heat exchanger is made through convection.
The double-pipe heat exchanger is one of the simplest types of heat exchangers. It is
called a double-pipe exchanger because one fluid flows inside a pipe and the other fluid flows
between that pipe and another pipe that surrounds the first. This is a concentric tube
construction. Flow in a double-pipe heat exchanger can be co-current or counter-current.
There are two flow configurations: co-current is when the flow of the two streams is in the
same direction, counter current is when the flow of the streams is in opposite directions.
Co-current Operation
1
LAB MANUAL 2
In co-current operation, the hot and cold fluid streams flow in the same direction
across the heat transfer surface (the two fluid streams enter the heat exchanger at the same
end).
Figure 1: Mechanism of co-current flow arrangement in double tube heat exchanger
Counter-current Operation
In counter-current operation, the hot and cold fluid streams flow in opposites directions
across the heat transfer surface. The fluids travel roughly perpendicular to one another
through the exchanger. The counter current design is most efficient, in that it can transfer the
most heat from the heat (transfer) medium.
Figure 2: Mechanism of counter-current flow arrangement in double tube heat exchanger
The determination of the overall heat-transfer coefficient is necessary in order to

determine the heat transferred from the inner pipe to the outer pipe. This coefficient takes
into account all of the conductive and convective resistances (k and h, respectively) between
fluids separated by the inner pipe, and also takes into account thermal resistances caused by
fouling (rust, scaling, i.e.) on both sides of the inner pipe. The type of fluid flow is an important
factor in the determination of the heat transfer coefficient. Two major classifications of fluid
flow occur which greatly affect coefficient. If the fluid moves in parallel layers with molecular
momentum transfer between adjacent layers, one speaks of laminar flow; if mixing of the
fluid layers occurs because of bulk fluid motion we call it turbulent flow.
The only part of the overall heat-transfer coefficient that needs to be determined is
the convective heat-transfer coefficients. Correlations are used to relate the Reynolds number
2
LAB MANUAL 2
to the heat-transfer coefficient. The Reynolds number is a dimensionless ratio of the inertial

and viscous forces in flow. Re = .
For laminar flow, the rate of heat transfer is predominantly governed by thermal
conduction between the layers of the fluid. Heat transfer for turbulent flows, however, is
largely a result of gross fluid motion, that is, convective movement of the fluid; thermal
conductivity, in this case, plays a minor role in the transfer of heat.
For a plate exchanger: Nu = 0,383 Re 0.65

x Pr0.4
For a tube exchanger: Nu = 4 Pr1/3 (laminar flow)
Nu = 0.0225 Re 0.8 x Pr0.4 (turbulent flow)

Where, Nu = ; Pr = ; v = ; D is the diameter of the tube.

The observed viscosity in some dimensionless numbers is very temperature-sensitive.
Laminar flow : Re < 2100
Turbulent flow : Re > 2100

Hydraulic diameter: hydro =4
P
Where = section perpendicular to the flow, and P = wet perimeter
3.464 P2
De = d0
d0
Dc
Passage surface, aCT = (P d0 ) B
P
The power transmission of fluid:
f = fQfCpf(ts-te) cold water receive power
c = cQcCpc(Te-Ts) hot water transfer power
c f
=
2
f
Heat-transfer efficiency, n =
c
Heat-transfer coefficient:
3
LAB MANUAL 2
T1
ln
T 2
(a) Real heat-transfer coefficient, kre =
S T1 T 2
R1 R2
Where S = 2LRm, Rm = , T1 = Te ts and T2 = Ts te
2
(b) Theoretical heat-transfer coefficient,
1
kth =
R2
Rm ln
1 Rm R1 Rm

hc R1 R 2 hf
Where = 43 kcal/hmK
Experimental Procedure
1. Connect the cold water tube to prepare a co-current configuration system.

2. Supply pressure and make sure the four indicators to indicate the ambient temperature.
3. Supply pressure to the thermos regulator group to open the valve of the hot water flow
meter for a flow ranging between 20 to 40 L/h.
4. Regulate the inlet hot water temperature to Te=80oC.
5. Wait for the temperature of the hot water to stable by observe the indicators relating to
the hot water.
6. Adjust the hot water flow rate to 40 L/h.
7. Open the cold water valve and adjust to 10 L/h.
8. Wait for the four indicators for about 5 minutes to stabilize before record the values.
9. Increase the cold water flow rate to 20, 30, and 40 L/h.
10. Repeat step 1-9 for counter-current configuration.
11. Cut off the supply of thermos regulator, close the two hot and cold water valves, and
switch off the general supply of the unit.
4
LAB MANUAL 2
Result
(a) Co-current configuration
q (L/h) 40 40 40 40
d (L/h) 10 20 30 40
Hot water inlet
temperature, Te (oC)
Hot water exit
temperature, Ts (oC)
Cold water inlet
temperature, te (oC)
Cold water exit
temperature, ts (oC)
(b) Counter-current configuration

q (L/h) 40 40 40 40
d (L/h) 10 20 30 40
Hot water inlet
temperature, Te (oC)
Hot water exit
temperature, Ts (oC)
Cold water inlet
temperature, te (oC)
Cold water exit
temperature, ts (oC)
References
1. Holman, J. P. (2010). Heat Transfer 10th Edition. Singapore: McGraw-Hill.
2. Perry H. Robert & Green W. Don. (2008). Perrys Chemical Engineers Handbook 8th
Edition. Singapore: McGraw-Hill Publications.
3. Williams, J. (2002). Double-Pipe Heat Exchanger. Project No. 1H Laboratory Manual.

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KC21001 LABORATORY 4

1. Adam bin Abdul Rahman BK13110006

Experiment HE3: Double Pipe Heat Exchanger

Theory and Explanation

Figure 1: Mechanism of co-current flow arrangement in double tube heat exchanger

Figure 2: Mechanism of counter-current flow arrangement in double tube heat exchanger

The determination of the overall heat-transfer coefficient is necessary in order to

For a plate exchanger: Nu = 0,383 Re 0.65

The observed viscosity in some dimensionless numbers is very temperature-sensitive.

Laminar flow : Re < 2100

Turbulent flow : Re > 2100

Where = section perpendicular to the flow, and P = wet perimeter

f = fQfCpf(ts-te) cold water receive power

c = cQcCpc(Te-Ts) hot water transfer power

(b) Theoretical heat-transfer coefficient,

1. Connect the cold water tube to prepare a co-current configuration system.

(a) Co-current configuration

(b) Counter-current configuration

1. Holman, J. P. (2010). Heat Transfer 10th Edition. Singapore: McGraw-Hill.

3. Williams, J. (2002). Double-Pipe Heat Exchanger. Project No. 1H Laboratory Manual.

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