Single phase vs two phase system for heat removal

[BasakAbhishek]

Hello,
I have to design a heat exchanger with variable load such that the outlet temperature of the shell side (gas at high pressure) is maintained at constant temperature. I have two options:
[Option1] Use single phase water on the tube side and control the shell side outlet temperature by adjusting the pump speed and by a bypass control valve in parallel to the heat exchanger.
[Option2] Use two phase water on the tube side (i.e. with boiling) with the pump maintained at a constant rpm, the varying load resulting in varying dryness fraction in the tube side exit, thus keeping the primary shell side exit at constant temperature.

My question is what is the pros and cons of the either system, in terms of:
(1) Complexity of the system
(2) Chemistry control (will be using DM water, is this an issue with potential scale formation in two phase flow)
(3) Stability issues (noncondensable gases, chf, oscillation flow stability, etc)

Any ideas?
Abhishek

 

[LittleInch]

How fast does the inlet gas temperature change?

What is the required outlet temp?

A water bath heater might work?

Can see how option 2 would work tbh. Anything two phase is going to get complicated.

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[EdStainless]

Are you heating or cooling the gas?
I presume heating.
Option 1 is easier to implement and control.
The biggest issue will be the time constants for response.
You will need to adjust your water temperature/flow very gradually as the heat transfer to the gas will be the limiting factor (I believe).
There is an alternate to Option 2.
Use continuously circulated hot water and adjust its temperature by using direct steam injection.
This would keep your flow all single phase but let you use steam for heating and it would use all of the energy in the steam.
In either case the size of the system will be important if you want stability.

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