Changing gas pressure supplied to a heat exchanger

[akcullin]

We have a gas heat exchanger datasheet for an exchanger sized by a third party, and I am wanting to do a sensitivity analysis of sorts to see what happens to the duty of the heat exchanger if pressure of the gas (heated by glycol) is changed.

To clarify, the inlet mass flow rate would be identical, as well as the inlet temperature and desired outlet temperature. Therefore, the desired duty is identical to what is on my datasheet. However, if I were to say increase the pressure from 500 to 700 psig, would I maintain the same outlet temperature? Would I have to change the flow rate of my heating medium?

With an increase pressure, there is a density increases, which then leads to a velocity decrease of the gas. This intuitively makes me think that the gas has more time in the exchanger for heat transfer so it should exit warmer and that overall duty should be greater. The equation I have for the convective heat transfer coefficient depends only on mass flow rate, however, and not velocity, which doesn't make intuitive sense to me.

Thanks in advance for helping me to wrap my heat around this. I'm new to heat exchanger design and I'm finding them to be quite complex and depend on many different variables.

[shahla]

Dear Acullin
As u know by decreasing the velocity u decrease the Reynold's number which results to lower exchanger duty .
It is not matter of time because heat duty of exchanger is described by cal/hr or whatsoever .

[shahla]

Dear Acullin
As u know by decreasing the velocity u decrease the Reynold's number which results to lower exchanger duty .
It is not matter of time because heat duty of exchanger is described by cal/hr or whatsoever .

[akcullin]

Dear Acullin
As u know by decreasing the velocity u decrease the Reynold's number which results to lower exchanger duty .
It is not matter of time because heat duty of exchanger is described by cal/hr or whatsoever .

Reynolds number is also dependent on density, however, and the density increase is proportional to the velocity decrease from what I can tell (since mass flow rate is held constant and velocity, density, and mass flow rate are related by the formula mass flow rate = density x velocity x cross-sectional area. Area stays constant so an increase in density must cause an proportionally equal decrease in velocity).

Therefore, the only variable that could change the Reynolds number in this case is viscosity - which, from my understanding, will change with the pressure change.