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Humid Air : Specific heat capacity

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1. Introduction
2. Humid air specific heat capacity calculation

3. Dry air specific heat capacity

4. Dry air isentropic ratio

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1. Introduction

The absolute humidity is calculated from the specific heat of dry air and the specific heat of water ponderated by the absolute humidity.

2. Humid air specific heat capacity calculation

How to calculate the specific heat capacity of humid air ?

With :
ω = Absolute humidity of air (-)
Cp' = specific heat of humid air (J/K/kg_dry_air)

3. Dry air specific heat capacity

What is the specific heat of air at usual temperature and pressure ?

The specific heat capacity of air at 300K is Cp = 1.005 kJ/kg/K. The specific heat capacity of air is varying with the temperature as reported in the table below :

Temperature in K	Cp in kJ/kg/K	Cv in kJ/kg/K
250	1.003	0.716
300	1.005	0.718
350	1.008	0.721
400	1.013	0.726
450	1.020	0.733
500	1.029	0.742

4. Dry air isentropic coefficient k

For air, at ambient temperature k = Cp/Cv = 1.4

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