HTRI nuclear heat exchanger: As the temperature difference of the cold fluid increases, should the heat exchange area be reduced?
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For example, for a hot fluid medium A in the shell side: inlet at 85, outlet at 66; medium B is cooling water, with an inlet at 32 and an outlet at 42. If medium B is replaced, the inlet becomes 50 and the outlet becomes 65. According to Q=KS△t=WcCpc(t2-t1)=WhCph(T1-T2), the heat release rate of medium A remains constant, the temperature difference stays the same, and the mass flow rate of cooling water B remains unchanged. Does the heat exchange area increase?
To conclude first: in this case, when medium B is changed to 50 in and 65 out (assuming it is hot water), the required heat exchange area increases. Otherwise, the outlet temperature of the hot fluid medium cannot be reduced to the desired 65 degrees. Let’s analyze the reasons again: when medium B is cooling water, flow is from 32 to 42 in the tube side, with a temperature rise of 10 degrees. When medium B is replaced with hot water, the flow enters at 50 and exits at 65, with a temperature rise of 15 degrees. According to Q=KS△t=WcCpc(t2-t1)=WhCph(T1-T2), if the temperature of the hot fluid is to remain at 85 degrees on the inlet side and 66 degrees on the outlet side, then the heat released by the hot fluid, Q, remains unchanged ； Assuming that the specific heats of cold water and hot water are approximately equal, the required flow rate of hot water should be: cold water flow rate X (10/15). It is expected that the effect of the reduced flow rate in the tube side on heat transfer in the tube side will be greater than the effect of the increased absolute temperature and reduced viscosity. Therefore, both the K value and the △t value are reduced. Furthermore, from the relationship S = Q / (K △t), it can be seen that since the numerator Q remains constant while the value of the denominator product decreases, the required heat exchange area S increases.
Medium B changes from cooling water to hot water (from 32 inlet/42 outlet to 50 inlet/65 outlet). If the inlet flow rate remains unchanged, the heat exchange area was 70 M2 before; now it is 150 M2. Is this figure not absurd?
Medium B changes from cooling water to hot water (from 32 inlet/42 outlet to 50 inlet/65 outlet). If the inlet flow rate remains unchanged, the heat exchange area was 70 M2 before; now it is 150 M2. Is this figure not absurd?
The hot water flow rate needs to be reduced to approximately X(10/15) of the cooling water flow rate; otherwise, there will be an imbalance in the heat between the hot and cold materials. It is basically normal for the heat exchange area to be adjusted from 70 M2 to 150 M2, as the heat transfer temperature difference △t has decreased to slightly less than half of its original value.
As the heat transfer driving force (i.e., the relative heat transfer temperature difference) decreases, the area increases, and by a significant amount at that. Nearly doubled
Mm-hmm, Medium A needs to be cooled to 66°C, while Medium B needs to have its temperature increased from 50°C to 65°C. This is almost 66°C; the temperature difference is too small