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Sample Calculations
T lm = (T 1 t2) (T 2 t1)ln [(T 1-t2)/(T 2-t1)]
= (42.2 48.8) (27.0-47.2)ln [(42.2 48.8)/ (27.0 47.2)]
= -12.16
h = () ( h)= (1000 kg/m 3)(10 L/min)(1 m 3/ 1000 L)(1 min/ 60
s)= 0.17 kg/s
Q = (m h) (C ph ) (T h)= (0.17 kg/s)(4.18 kJ/ kg K)(-15.2 + 273
K)
= 183.19 kW
Cmin = (c) (C pc)= (1000 kg/m 3)(10 L/min)(1 m 3/1000 L)(1 min/
60s)(4.18 kJ/kg K)= 0.7106 kW/K
Thin avg = 42.2 + 36.4 + 34.5 + 33.4 + 32.95
Tcin avg = 47.2 + 49.5 + 45.3 + 44.8 + 44.7
5
Qmax = C min (Thin - T cin)= (0.7106 kW/K)[(35.9 45.6) + 273 K]=
187.1 kW
Qavg = 183.19 + 173.46 + 189.30 + 190.37 + 190.805
= Q avg Qmax
= 185.424187.100
= 0.99Where;T lm = The mean temperature differenceh = Mass flow
rate
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Q = Heat generatedQavg = Average heat generatedQmax = Maximum
heat generatedThin avg = Average temperature of hot water inTcin
avg = Average temperature of cold water in = Efficiency
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Abstract
The objective of this experiment is to study the function and
the working of shell and tube heatexchanger. In the experiment, the
comparison between co-current flow and counter-current flowwas
conducted. Calculations on the heat transfer and heat loss were
carried out for energy
balance study. The logarithmic mean temperature difference (also
known as log meantemperature difference or LMTD) and heat transfer
coefficient was also calculated for thisexperiment. From the data
collected, it is found out that configuration of Shell and Tube
heatexchanger in counter current flow has a higher effectiveness
than the co-current flow withefficiency of 99%. The maximum amount
of heat transfer that can be obtained is higher withcountercurrent
than co-current (parallel) exchange or flow is because
countercurrent maintains aslowly declining difference or
gradient.
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Conclusion
This experiment shows that the shell and tube heat exchanger
follows the basic law ofthermodynamics. Heat transfer always occurs
from a region of high temperature to anotherregion of lower
temperature. Heat transfer changes the internal energy of both
systems involvedaccording to the First Law of Thermodynamics. The
Second Law of Thermodynamics definesthe concept of thermodynamic
entropy, by measurable heat transfer. In parallel (co-current)
flowconfiguration, the exit temperature of the hot fluid is always
higher than the exit temperature ofthe cold fluid. In
counter-current flow configuration, the exit temperature of the hot
fluid is alsohigher than the exit temperature of the cold fluid.
However, in counter current flowconfiguration, the exit temperature
of the cold fluid is higher than the exit temperature of thecold
fluid in co-current configuration. Hence, it is clear that for heat
exchanger, counter currentflow configuration has a higher
effectiveness than the co-current flow configuration. Theexperiment
shows that when the flow rate of one of the stream increases, the
rate of heat transfer
will also increases. The amount of heat loss form the hot water
is not equal to the heat gain bythe cold water due to the heat loss
to the surrounding. From the calculations done, the LMTD(log mean
temperature difference) for co-current flow is higher than the
counter-current flow.However, the overall heat transfer coefficient
for counter-current flow is higher than the co-current flow with
efficiency of 99%. As a conclusion, counter current flow
configuration of heatexchanger is more preferred for practical
application.
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Recommendations
1. For the water flowing into the boiler, the feed water used
has to be using treated water.The reason for this is because if the
experiment was using tap water, impurities wouldaccumulate in the
boiler and will affect the flow and conduction of heat energy.
2. The boiler should be insulated to prevent any loss of heat to
the surrounding which wouldaffect the hot water in temperature and
waste energy to heat up the water.
3. All the temperature and flow rate readings are taken
simultaneously as CW inlettemperature is increasing gradually and
CW outlet temperature varies together with theHW inlet/outlet
temperature.
4. To increase the accuracy of the data obtained, the experiment
should be repeated severaltimes and take the average from the
data.
