Heat Transfer Coefficient of Air for Changing Humidity Levels

[bjb123]

I have an incubator that needs to operate in 10% - 95% relative humidity, non condensing. I am running all my tests in a lab with 40%-45% humidity. Is there a method for me to determine what the effects will be on the internal gradient and warm up times (if any) for this large range of humidity? I would like to avoid going to a chamber for this testing if I can prove that the system will still perform to specification in 10% and 95% humidity levels.

Other relevent information
System internal temperature: 32C to 38C
System external temperature: 15C to 28C

 

[TD2K]

First, I'll be happy to defer to our HVAC people here if I'm wrong.

Theoretically, I would expect the humidity levels to affect the heat transfer coefficient since the thermal conductivity of the mixture, heat capacity and density would all be affected.

However, even at 28C and 95% humidity, the water level in the air is less than 8% by volume and less by mass. Thus, its effect would be minor IMO. While the humidity is an important factor in people's perception of warm/cold, it's not as relevant for the heat transfer example you have here.

 

[Yeldud]

Perhaps i'm misinterpreting your concern, but when i see operating requirements of 10%-95% RH non condensing, this is a typical limitation seen on equipment, and is primarily a reference to the need to avoid condensation on the electrical components in the unit (for obvious reasons). Why they stop at 10% i'm not sure, possibly due to static electricity buildup, which can still be a problem at higher rh than 10%. RH below this does not frequntly occur in normal ambients, except when its very cold outdoors and the indoor environment has little or no internal moisture generation. This is why it is desirable to humidify the indoor environment in the winter, particularly in cold climates. So i think you can interpret this to mean, as long as your room conditions are within the RH envelope specified you can ignore the impact on the unit performance. IMHO

 

[lilling]

As long as there is no condensation, the impact of moisture is practically neglectable at temperature below 38 C.

 

[25362]

If the lab experiments release moisture, the humid atmosphere becomes a bit lighter, and if the lab is suitably vented, convection currents may develop. TD2K, Lilling and Yeldud: is there a possibility that heat exchange may change as a result ?