Heat Capacity Air and Humidity
Date: Spummer 2014
This question is very complex. Several parameters have to be taken into account, depending upon what it is you want to know. Here are some of the parameters:
1. What is the temperature ?
2. What is the pressure?
3. What is the water content of the air in question?
4. Is the heat capacity measured at constant pressure, volume, or temperature?
This is a multivariable problem that does not converge onto a single solution.
Highly simplified, moist air.
Let us assume you are thinking about isobaric heat capacity measured in Joules per gram-Kelvin.
We find that dry air, 273K, at sea level is 1.0035 J/gmK.
For an altitude of 194 meters above sea level (an average for humans), an indoor temperature of 23°C, a dew point of 9°C and 760 mm–Hg sea level, we get 11.012 J/gmK.
For steam, we see 2.08 J/gmK.
The reason : Water has a huge heat capacity. Pervasive H bonding allows vibratory motions and bond length stretching to buffer changes in temperature.
Peter E. Hughes, Ph.D. Milford, NH
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Update: November 2011