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Need help with CBT practice problem #28


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hi all,

Due to copyright concerns and lack of legal knowledge, I cannot post the problem itself here.

I just do not understand why in the solution the enthalpy of the heating jacket is being used instead of the enthalpy at saturated steam pressure of 0 psia. The question is obviously asking for the feed rate to the evaporator, not the heating jacket. 

And I have a feeling this confusion is from my lack of understanding of an evaporator, and I am confusing myself with the feeds?

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  • 4 months later...

Let's simplify the problem:

1. Saturated Water @ P1 --> EVAPORATOR --> Saturated Steam @ P1           |           Q = m (water) x delta H (vaporization @ P1)

2. Saturated Steam @ P2 --> Heating Jacket of EVAPORATOR --> Saturated Water @ P2         |           Q = m (steam) x delta H (condensation @ P2)

The convective heat transfer between sat. steam (@ P2) and inlet water (@ P1) (Q=UA x delta T) must be equal to the heat of condensation of steam in the jacket AND heat of vaporization of water in the EVAPORATOR. Depending on what the question asks for, either steam or water, you may use the first or second equation. 

 

Edited by GasPro
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