Question

In process A: Pure methanol liquid enters a heat exchanger at 25C and exits at 100C as a vapor. In process B: Pure methanol vapor enters a heat exchanger at 25C and exits at 100 C as a vapor. The heat required for process A is ______ the heat required for process B.

Greater than

Less than

Equal to

Answer 1

The heat required in Process A is greater than in Process B

This is because, in Process A, methanol is liquid. Thus, first it is heated to its boiling point, then we need to provide energy for vaporizing it ( Lambda - Energy to convert liquid to vapor) and then we need to further provide energy to heat the vapor.

In Process B, we just need to provide energy to vapor which is far less than that of Process A.

Latent heat is much higher than small sensible heat changes over small temperature differences.