Thermodynamics - evaporator condenser

[James MEng]

Hello - fundamental thermo question which is puzzling me...

It concerns a multiple effect evaporator with condenser. Hot vapour is water, cooling medium is water.

My question stems from the following:
When the flow of cooling water to the condenser is increased, the pressure in the condenser (and thus the pressure profile of the entire evaporator) is reduced.

Here's how I understand it...

• Heat transfer area of condenser remains constant
• Overall heat transfer coefficient is increased slightly; given that the Reynolds number on cold side is increased
• Cooling water temperature out is reduced (assuming heat load is constant and inlet temperature is the same)

How does this in turn lead to a reduction in evaporator pressure, please explain in basic terms (what's actually physically happening rather than just formulae! :thumbs:).

Thanks in advance for any replies

Edit: Also the mass flow rate of condensate will be the same for a given flow "in" of water and steam. Some thermodynamic activity is occurring here I just cannot work out what!

 

[Chestermiller]

I'm wondering where it said that the outlet pressure from the condenser would be decreased. This doesn't seem reasonable to me.