Lab #
BAEN/CHEN-422-622!
page 1
UNIT OPERATION IN FOOD PROCESSING
Department of Biological and Agricultural Engineering
Texas A&M University
Heat Exchanger Demonstration Lab
Double Pipe HE
Tubular HE
Shell & Tube HE
Lab 4
BAEN/CHEN-422-622!
page 2
UNIT OPERATION IN FOOD PROCESSING
Department of Biological and Agricultural Engineering
Texas A&M University
Heat Exchanger Demonstration Lab
Summary
The process of heat exchange between two fluids that are at different temperatures and separated by a solid wall occurs in many engineering applications. The device used to implement
this exchange is termed a heat exchanger, and specific applications may be found in space
heating and air-conditioning, power production, waste heat recovery, and food & chemical
processing.
4.1 Background
Heat exchangers are typically classified according to flow arrangement and type of construction. The simplest heat exchanger is one for which the hot and cold fluids move in the same or
opposite directions in a concentric tube (or double-pipe construction). In the parallel flow arrangement the hot and cold fluids enter at the same end, flow in the same direction, and leave
at the same end. In the counterflow arrangement the fluids enter at opposite ends, flow in opposite directions, and leave at opposite ends. There are other configurations, like cross-flow,
shell-and-tube, finned and unfinned, among others. In this lab we are going to demonstrate the
working principles of a concentric tube heat exchanger.
The knowledge of the principles of heat transfer within the heat exchanger are needed in order
to design and/or evaluate the performance of a heat exchanger.
In a concentric tube heat exchanger:
Heat power emitted [W] = Qh ρh Cph (Thin-Thout)
Heat power absorbed [W] = Qc ρc Cpc (Tcin-Tcout)
(Properties must be evaluated separately for the cold and hot side using the average temperature)
Heat power lost = heat power emitted - heat power absorbed
Efficiency η = [(heat absorbed )/(heat power emitted)]x100
Log mean temperature difference [oC] = ΔTm=(ΔT1-ΔT2)/[ln(ΔT1/ΔT2)]
Overall heat transfer coefficient [W/m2oC] = U = q/(AΔTm) =
= (heat power absorbed)/(heat transmission area ΔTm)
In a concentric tube heat exchanger, the equations for calculating the performance characteristics (heat power emitted, heat power absorbed, heat power lost, efficiency, logarithmic mean
temperature difference, and overall heat transfer coefficient) are contained in Chapter 3.
Lab 4
BAEN/CHEN-422-622!
page 3
UNIT OPERATION IN FOOD PROCESSING
Department of Biological and Agricultural Engineering
Texas A&M University
Temperature efficiencies of the heat exchanger are:
a) for the cold medium
ηc = [(Tcout-Tcin)/(Thin-Tcin)]x100
b) for the hot medium
ηh = [(Thin-Thout)/(Thin-Tcin)]x100
c) mean temperature efficiency
ηmean = (ηc + ηh)/2
Temperature efficiency is an actual indicator of the actual heat transfer taking place in the heat
exchanger as a percentage of the maximum possible heat transfer that would take place if infinite surface area were available.
4.2 Objectives:
1.) Compare the working principles of a concentric tube heat exchanger operating under parallel and counter flow conditions.
2.) Demonstrate the effect of hot water temperature variation, and flow rate variation on the
performance characteristics of a concentric tube heat exchanger.
4.3 Apparatus:
Concentric tube heat exchanger with two flowmeters, and thermometers in the inlet and outer
side of the hot and cold fluid ( L = 1.6 m and A = 0.069 m2).
BAEN/CHEN-474!
page 4
UNIT OPERATION IN FOOD PROCESSING
Department of Biological and Agricultural Engineering
Texas A&M University
Lab 4
Experiment A : Parallel and Counterflow
Group 1
The Lab heat exchanger
Set equipment under parallel flow
conditions according to the front
panel of heat exchanger, and once
conditions have stabilized, take the
temperature readings for the inlet
and outlet thermometers of both the
cold and hot fluid.
Repeat the experiment using
counter flow set-up on heat exchanger.
Initial variables to be used:
Controlled hot water T
60 C
Hot water flow rate Qh
2000 cm3/min
Cold water flow rate Qc
1000 cm3/min
Experiment B : Changing the hot water flow rate
Group 2
The Lab heat exchanger
Set equipment under counter flow
conditions according to the front
panel of heat exchanger maintaining the hot water inlet temperature
at 60°C, and while changing the hot
water flow rate, take the temperature readings for the inlet and outlet
thermometers of both the cold and
hot fluid once conditions have stabilized.
Initial values to be used:
Controlled hot water T
60 C
Hot water flow rate Qh
2000 cm3/min
Cold water flow rate Qc
1000 cm3/min
BAEN/CHEN-474!
page 5
UNIT OPERATION IN FOOD PROCESSING
Department of Biological and Agricultural Engineering
Texas A&M University
Lab 4
Experiment C : Changing the hot water temperature
Group 3
Set equipment under counter flow
conditions according to the front
panel of heat exchanger maintaining the hot water flow rate at 2000
cm3/min and cold water at 1000
cm3/min, and while changing the
hot water temperature, take the
temperature readings for the inlet
and outlet thermometers of both the
cold and hot fluid once conditions
have stabilized.
The Lab heat exchanger
BAEN/CHEN-474!
page 6
UNIT OPERATION IN FOOD PROCESSING
Department of Biological and Agricultural Engineering
Texas A&M University
Lab 4
Results for change in direction
Readings
T h-in [C]
T h-mid [C]
T h-out [C]
T c-in [C]
T c-mid [C]
T c-out [C]
Power
emitted
[W]
Power
absorbed
[W]
Power lost
Efficiency
ΔTm
U
[W]
[%]
[C]
[W/m2K]
parallel flow
counterflow
Calculation
Flow direction
parallel flow
counterflow
Results for change in flow rate
Qh [cm3/min]
T h-in [C]
T h-out [C]
T c-in [C]
T c-out [C]
1000
2000
3000
4000
Calculations
Qh [cm3/min]
1000
2000
3000
4000
Power
emitted
[W]
Power
absorbed
[W]
Power lost
[W]
Efficiency
[%]
ΔTm
U
[C]
[W/m2K]
BAEN/CHEN-474!
page 7
UNIT OPERATION IN FOOD PROCESSING
Department of Biological and Agricultural Engineering
Texas A&M University
Lab 4
Results for change in temperature
Control set [C]
T h-in [C]
T h-out [C]
T c-in [C]
T c-out [C]
45
50
55
60
Calculations
Control set
[C]
Power
emitted
[W]
Power
absorbed
[W]
Power lost
[W]
Efficiency
[%]
ΔTm
U
[C]
[W/m2K]
45
50
55
60
Utilize appropriate conversion factors to ensure consistency of units when making calculations.
4.5 Results and Discussion
1.) Make all the calculations in the tables.
2.) Discuss the effect of fluid direction in the efficiency, and overall heat transfer coefficient of
the heat exchanger.
3.) Discuss the effect of temperature change, and flow rate variation in the efficiency, and
overall heat transfer coefficient of the heat exchanger.