NEWTON:Heat Capacity Air and Humidity
 
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Name: Sarah
Status: student
Grade: 9-12
Country: Canada
Country: India
Date: Spummer 2014


Question:
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.


Replies:
Hi Sarah,

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 23C, a dew point of 9C and 760 mmHg 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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