Shell and Tube heat exchanger

Observed from table 9 of the shell and tube heat exchanger, the greatest change in temperature of the hot fluid (T hot) of of 9.8K is when the hot fluid has a volumetric flow ( V hot) rate of 10g/s and the cold stream of 40g/s. At 30g/s V hot and 30 g/s V cold , T hot was 6.1 K and for 10 g/s cold and 40 g/s T hot was 3.6 K. From this experimental data it can be concluded the most effective way to cool hot fluid in a shell and tube heat exchanger is to have a slow moving cold stream and a fast moving hot stream. This can be explained as the fast moving cold fluid allows a high temperature gradient to be maintained between the hot and cold fluid maximising the absorption the heat from hot fluid into the cold fluid allowing the temperature gradient to be maintained.From the cold fluid from table 7 and 9 it can be observed the largest value of T cold is 13.9 k at 10 g/s V cold and 40 g/s V hot. At 30g/s cold and 30 g/s hot T cold is 6k and at 40g/s cold and 10g/s hot T cold is 1.9 K. From this data is can be deduced that at the slower the cold stream and the greater the hot stream the larger the change in temperature. It can be concluded that and cold are inversely proportional.

Plate heat exchanger

Table 5 shows that a plate heat exchanger works on a similar principle to a shell and tube heat exchanger. T hot is the highest when V cold is 40 g/s and V hot is 10g/s. When V hot and V cold are 30 g/s, T hot is 17.1 K and when V hot is 10g/s and V cold is 40g/s T hot is 7.5 g/s. Similar to the shell and tube heat exchanger the faster the cold fluid and slower the hot fluid the greater the value of T hot as more heat is absorbed by the cold stream. When comparing table 6 and 9 it is observed that T hot is greater in the plate heat exchanger in comparison to the shell and tube heat exchanger showing in the plate heat exchanger is more effective .From the same principle T cold is greatest at V cold of 10g/s and V hot of 40g/s where the cold fluid is moving slowly absorbing heat from the fast moving hot stream. The value of T cold is observed to be 27.1 K which double this value of the shell and tube heat exchanger showing it is a very effective heat exchanger. Concentric tube heat exchanger

Similarly to the plate and shell and tube heat exchanger, in concentric tube heat exchanger the slower the hot or cold fluid the greater the change in temperature shown. The largest value of T hot is 13.1 K when V cold is 40g/s and Vhot is 10 g/s. The greatest value of t cold is 14.7 K when V cold is 10g/s and V hot is 40 g/s. T hot and T cold values a bit higher than in the shell and tube heat exchanger however the plate heat exchanger still has the greatest values of T hot and T cold therefore the most effective.

Efficiency values are calculated from the power emitted from the hot stream ( ) and the power emitted from the cold stream should be increased and should be decreased in order to increase efficiency. From equation 6 and 7 it can be observed that is increased by increasing Vcold and T cold and can be decreased by decreasing V hot and T hot. The shell and tube heat exchanger had the lowest power consumption therefore can be seen to be the most economical

Efficiency

In the concentric tube heat exchanger the highest thermal efficiency of 102.52% is seen when Vcold is 30g/s and V hot is 30g/s. The second highest thermal efficiency of 100.5% is seen when V cold is 10g/s and V hot is 40 g/s and subsequently the lowest thermal efficiency is seen at 40g/s V cold and 10g/s V hot. From table 1 that efficiency of the concentric tube heat exchanger exceeded 100 % which is not theoretically possible. The reasons for this error could be that the heat exchanger was not insulted well leading to a transfer between the exchanger to the surroundings. Other reasons include water leakage seen from the connections of the heat exchanger.

For the plate heat exchanger in table 2 it can be deduced that the greatest thermal efficiency of 95.81% occurred when V cold and V hot are both 30g/s. The second highest thermal efficiency of 94.50 % occurs when V cold is 40g/s and V hot is 10g/s and the lowest thermal efficiency is when V cold is 10g/s and V hot is 40g/s. The highest efficiency of V cold and V hot at 30g/s can be explained as due to counter current flow the hot and cold stream flow at the same rate in opposite directions therefore temperature gradient is maintain leading to efficient heat exchanger. The shell and tube heat exchanger is shown to have the greatest thermal efficiency of 99.62 % when at Vcold and Vhot is 30g/s explained by the same reason above.

When comparing all three heat exchanger the concentric tube has the highest thermal efficiency at V cold and V hot is 30g/s even though the plate heat exchanger showed the greatest values of T hot and T cold it was shown to be the most inefficient heat exchanger.

In industry the highest efficiency, change in value of T hot and cost will be considered and decision would be made by engineering on the application of the heat exchanger. Theoretically the plate heat exchange is meant to be the most efficient however in this experiment it is the most inefficient therefore the accuracy of these results should be questions and the experiment should be repeated using different apparatus.

Conclusion

T hot is highest when V hot is 10g/s and V cold is 40g/s T cold is highest when V hot is 40g/s and V cold is 10 g/s and cold are inversely proportional.