I have a chemical reactor producing a humidified stream of hydrogen gas and I need to cool it down to near ambient temperature using a heat exchanger, say 25 degrees Celsius.

Within the reactor I measure a gas temperature of 70 degrees Celsius and 100% relative humidity. In the lab I measure a gas flow rate of 10 liters per minute using a calibrated mass flow controller after the gas passes through a jacketed reflux condenser, a water trap, and a tube of silica desiccant. Between the mass flow controller and the silica gel I measure a temperature close to ambient and a relative humidity of 40%.

How would I size an off-the-shelf air cooled heat exchanger to create the same level of gas cooling as the reflux condenser? The silica gel is only there to protect the mass flow controller, I would be okay with 95% relative humidity hydrogen as long as the temperature is near ambient.

In my mind I think I could purchase any small, cheap air cooled heat exchanger off Amazon but I'd rather try to approach the problem analytically. I plan on having a water trap after the heat exchanger to catch the condensed water vapor.

  • $\begingroup$ Please edit this block of text - some formatting would probably let others read it. $\endgroup$
    – Solar Mike
    Sep 23, 2022 at 6:54

1 Answer 1


You could start with calculating required heat flux for cooling down your stream, then you can use online calculator, for example this. Keep in mind 2 things:

  • If you expect condensation as the stream cools down, this may impede function of the air cooler, so you may need to use a condenser instead.
  • Trying to go with the stream temperature near ambient might be difficult, if your cooling fluid is the ambient air.
  • $\begingroup$ Thanks for the tips! Could you elaborate on how to calculate the heat flux? A link to a tutorial would be fine if you know any simple ones. And what would be the difference between a heat and a condenser? $\endgroup$ Sep 27, 2022 at 5:33
  • $\begingroup$ @DallonPenney "Heat flux" is the process duty as one of the basic input parameters here. You can calculate it from cooled stream enthalpy difference between outlet and inlet multiplied by flowrate. $\endgroup$ Sep 27, 2022 at 15:06

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