Humidity when T is not constant in space

[Bankoletti]

Hi all!

How is humidity related to temperature in a system where temperature is constant in time but not in space?

As an example: If we have humid air trapped between two parallel walls with T1 and T2 respectively, how does humidity behave along the line from one to the other wall? Is absolute or relative (if any) humidity constant? Let's assume zero-G environment (= no gravity induced convection).

 

[Chestermiller]

Absolute humidity is constant, relative humidity is not.

 

[Bankoletti]

Absolute humidity is constant, relative humidity is not.

Hi, Chestermiller, thanks for looking into this! Do you have anything to back this up? Intuitively I'd agree with you (that the same amount of water remains in each unit of volume), but is this assumption really true as a fact or does water perhaps tend to distribute in such a way that relative humidity is equal (in other words that each volume unit is saturated to the same level)?

 

[Chestermiller]

Hi, Chestermiller, thanks for looking into this! Do you have anything to back this up? Intuitively I'd agree with you (that the same amount of water remains in each unit of volume), but is this assumption really true as a fact or does water perhaps tend to distribute in such a way that relative humidity is equal (in other words that each volume unit is saturated to the same level)?

If the concentration (partial pressure) varied, diffusion would act to homogenize the water vapor. Relative humidity is just a parameter that we define, and the system of air and water does not know that we have defined such an entity.