# Heat Transfer for a Reboiler?

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1. Jul 30, 2015

### pxp004

For a general cooler or heater, the calculations for heat transfer are based on the tube side and shell side. So

1) For a reboiler would the vaporizer be the "shell" since that's where the heat transfer occurs?

2) How do you account for the phase change? I used Q = m*cP*dT to calculate duty. Since steam is condensing in the tubes, I was told to use Q = m*Hv instead, where "Hv" is the latent heat of steam and "m" is the flow (kg/s) I have from operating data. I looked up Hv at the given temperature and it was around 1900 kJ/kg. So I calculated the duty to be 200 kW.
I have cP and dT data for my process acid (which is being vaporized). So in order to check myself, I used Q = m*cP*dT for my process acid. I dont have operating data for flow on the process side, so I used the flow specified on the datasheet for the exchanger since they should reasonably be the same. The thing is, when I calculated the duty on the process side, I got 900 W. Thats no where near 200 kW.
So I dont understand where I'm going wrong. If someone can explain whats wrong with my method above and how to make calculations for a reboiler, that would be wonderful.

2. Aug 1, 2015

### Staff: Mentor

You need to provide more information. Is this a reboiler for a distillation column? If so, there is one stream entering the reboiler, and two streams exiting. Do you know the properties of any of these streams, like composition? Do you know how to calculate the enthalpy of any of these streams, given its composition, and the temperature and pressure of the reboiler? What is the identification (e.g., liquid from tray above) of the one stream entering and the two streams exiting?

Chet