# 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

## 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 ?

The specific heat capacity of humid air at ambient temperature can be calculated thanks to the following formula :

### Cp' = 1005 + 1884*ω

With :
ω = 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