Hanoi University of Mining and Geology, HUMG
Chemical Engineering Laboratory, ECH 155A
Advanced Program K2

Experiment 1: Determination of the exchanger effectiveness. NTU method
Instructor: Nguyễn Thị Linh Experiment’s day:29-7-2015
Student: Nguyễn Thị Lệ Thủy Deadline: 4-8-2015
ID: CTTT11210134
Group7: Nguyễn Thị Lệ Thủy
Nguyễn Thị Thu Trang
Trương Hải Thượng
Lê Vĩnh Thịnh



Introduction:
A heat exchanger is a device which allows heat transfer to happen between two fluids at different temperatures separated by a solid wall. The most simple is built with two concentric tubes, where fluids may either move in the same or in opposite direction. In parallel flow, hot and cold fluids may enter and leave at the same end while flowing in the same direction. In counter current flow fluids may enter and leave at opposite ends, flowing in opposite directions.
/
Parallel Counter current
Goal of the experiment: The main goal of this experiment is to determine the exchanger effectiveness experimentally as well as theoretically (by using the NTU method) and compare the two values. To estimate the hot and cold water outlet temperature, the students may compare with the measured values.
Theory
There are 3 types of heat exchanging: Conduction, convection and radiation
Conduction:
The conduction happens when heat transports through the thickness of the tube from the internal surface to the external surface. In dimensionless and stationary cases, heat transfer rate through a wall will be given by the following expression:
𝑞𝐾.𝐴
𝑇
2
𝑇
1
𝑥 (1)
Where: 𝑞 is the heat transfer rate (𝑤), 𝐾 is thermal conductivity of the wall
𝑤
𝑚.𝐾), 𝐴 is the perpendicular area to the direction of heat flow
𝑚
2), 𝑙 is the wall thickness (𝑚),
𝑇
2 is the temperature on the cold surface of the wall (𝐾),
𝑇
1 is the temperature on the hot surface of the wall (𝐾).
Convection:
The heat transfer mode between a surface and a fluid in motion which are at different temperature. The convection heat transfer rate of surface and a fluid is given by Newton`s law of cooling, which is expressed as:
𝑞=𝐴.ℎ
𝑇
𝑠
𝑇) (2)
Where 𝑞 is the convection heat transfer rate (𝑤), ℎ is the convection heat transfer coefficient
𝑤
𝑚
2.𝐾𝐴 is the heat transfer area
𝑚
2),
𝑇
𝑠 is the surface temperature (𝐾),
𝑇 is the Fluid temperature (𝐾).




Experimental Method
Check that the valves are opened and that we have countercurrent flow configuration.
Check that the heating tank is filled with water above th level switch.
Switch on pump and the resistor (equipment supply).
Set the tank temperature in 60oC (ST16).
Fix the hot water flow in 2 l/min approx (SC1) and adjust cold water flow to reach stationary operation conditions, keeping constant temperature set for the tank.
Write down the temperature anf flow measurements on the experiment sheet.
Set the valves appropriately in order to invert cold water flow direction to produce a parallel flow configuration.
Make sure that 60oC temperature are kept in the tank and that the same hot and cold water flows set in step 5 are also maintained.
Once the system is stabilized, write down the temperature measurements and flows values on the experiment sheet.
Once the measurements have been taken, calculate the experimental effectiveness, the theoretical effectiveness by the NTU method and the theoritical temperature at exchanger outlet.
Result









Counter current
Parralel

e
0.435685

0.402542


Qh(w)
Qc
1443.94
1789.388


1306.687
1442.608


∆Tlm
12.36119

10.73984


U.A(w.k)
116.812

121.667


NTU
0.849433

0.884557


CR
0.991391

0.991592


eNTU
0.460202

0.41587


Th,o (oC)
42.9

39.70961


Tc.o (oC)
43.4

38.72012



















Counter current:

Counter current
Parallel

ST16
60
60

ST1
53.4
52.9

ST2
42.9
43.4

ST3
42.2
29.3

ST4
38.9
35

ST5
38.2
37.8

ST6
34.6
39