Calculation of heat exchanger area for the same fluid
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This post was last edited by leinuo55 on 2018-3-14 at 10:39. I have a question: there is a catalytic combustion project, with a gas flow rate of 1000 m/h and an inlet gas temperature of 30°C. It is assumed that the gas temperature rises to 500°C after passing through the combustion furnace. The cold air exchanges heat with the exhaust gas after combustion before entering the combustion furnace, and it is required that the cold air be heated to 300°C. Ignoring heat losses, and due to mass conservation before and after the combustion furnace – that is, the masses of the cold and hot fluids are equal – the specific heats of air at low and high temperatures are approximately the same. Using the heat balance equation Q=cmΔt, it can be shown that the temperature rise of the cold fluid is equal to the temperature drop of the hot fluid. In this case, does the logarithmic temperature difference have any meaning? What value should be used for Δtm when calculating the area of the heat exchanger? The process is shown in the diagram
Since the qualitative temperatures are different, the specific heat capacities are also different; the temperature changes must be different as well
After combustion, your feed and output materials will definitely be different; use ASPEN to calculate how much the specific heat capacity has changed, so as to determine the temperature rise of the incoming and outgoing materials. After all, combustion involves a chemical reaction, so the material becomes different from its original form~~
The logarithmic mean temperature difference certainly makes sense. The logarithmic mean temperature difference is used to calculate heat transfer, not to calculate heat quantity.