Seeking advice on heat transfer issues in heat exchangers
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May I ask about the reboiler at the bottom of the tower? Tube side: For the material in the bottom of the tower, flow is from bottom to top (cold fluid); phase change occurs. Shell side: For the hot solvent, flow is from top to bottom (hot fluid). Question 1: Assume the temperature of the hot fluid at the inlet is 80 degrees, and it drops to 70 degrees at the outlet. What should the export temperature be if the import temperature is 85 degrees? Is it 75, or lower than 75? Question 2: If the import temperature remains unchanged but the import flow rate increases, then should the export temperature be higher than 70 degrees? Question 3: I’m not sure whether the total Q value here is a constant or a variable – is the total heat transfer amount fixed, or does it increase as the flow rate of the hot fluid rises? Question 4: If the heat exchanger gets scaled, do those values change? P
1、It’s around 75 degrees, I guess； 2. Yes ； 3. It generally changes all the time, so it needs to be controlled ； 4. The heat transfer coefficient decreases, and accordingly the amount of heat transferred also decreases ；
Hehe. After calculating it manually once, the relationship between them became clear.
Question 1: The specific heat capacity changes with temperature; generally, it increases as the temperature rises. A temperature increase of 15 degrees has little effect on the specific heat capacity, so the outlet temperature should be around 75. Question 2: If the parameters on the cold side remain unchanged, according to the law of conservation of energy, that is generally the case. Question 3: Total Q represents the total heat load, which is the amount of heat released or absorbed by the material within the heat exchanger; any change in any of the parameters will affect this heat load. Question 4: In the case of scaling, the first thing to change is the heat transfer coefficient; if the scaling is severe, it can also cause changes in the flow rate. It is recommended that the original poster read a book on principles of chemical engineering; it is simple, clear, and systematic.