I’m genuinely seeking help with heat exchanger calculations; I have some questions.
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I need to perform a simple calculation of the heat exchange area for a shell-and-tube heat exchanger. However, I’m confused regarding some of the data that requires reference to tables in the formulas; I hope those who have experience with this can offer some guidance. Briefly put, our heat exchangers primarily condense water vapor that has undergone vacuum dehydration; this occurs under vacuum conditions. The degree of vacuum is generally around 0.095 MP. The inlet and outlet temperatures are typically 80°C for the steam and 36°C for the water. When calculating the heat exchange area, what is the constant-pressure specific heat capacity in this case? Should it be taken from the value at 58 degrees? Will the low pressure and phase change affect the lookup table data? How to check it? I am not familiar with the calculation of the heat transfer coefficient. . I’ve just started working with design, and everything is still a bit unclear to me. I hope those who are more experienced can give me some guidance; I’m truly seeking help. Thank you. The principles of chemical engineering cover condensation processes in which no phase change occurs. What if a phase change does take place, and this happens under vacuum conditions? Is there any difference? The phase change from gas to liquid should generally also be exothermic; I’m a bit confused and hope those with more experience can give me some guidance. Thank you.
First, calculate the heat transfer amount: the sensible heat of the steam + the phase change heat + the sensible heat of the water. Then, use zone analysis to calculate the heat transfer and pressure drop for each section, which will allow for the selection of an appropriate heat exchanger. Since the calculation of two-phase flow is relatively complex and the accuracy of the calculations is not very high, it is best to leave a larger margin.
Reply to 3# cubomb: Thank you for your advice regarding the sensible heat calculation you mentioned. Is it mass flow rate times specific heat at constant pressure times temperature difference? If so, at what temperature should the specific heat at constant pressure be looked up? If not, then how is it calculated? How is the phase change heat calculated? I truly seek advice humbly and am working hard to learn.
It is mainly calculated based on heat balance; taking phase-change heat transfer into account, it can also be calculated using the enthalpy difference directly