09. March 2021

Mollier's h-x-diagram

The tool for determining air state changes

Air and the moisture it contains:

Humidity, moist or dry air, warm or cold air. Everyone can imagine something under these terms and can also tell something about it. We give you an overview of this topic, clear up any errors and use the very helpful tool "hx - diagram" for this.

At this point we would like to thank the Kaut company for providing us with the diagram.


What is the h,x diagram?

h stands for enthalpy - the energy content of a substance in 1 kJ / kg

x stands for water content - the absolute amount of water in g / kg of dry air

The h,x - diagram was developed in 1923 by Richard Mollier. It enables changes in the state of humid air due to heating, humidification, dehumidification or cooling to be clearly displayed. The status changes can be determined graphically directly from the diagram.

It is an important tool for the refrigeration and air conditioning industry. In addition, this diagram can also be very useful for your own 4 walls.


The structure

The X-axis represents the water content x.

The y-axis shows the air temperature in °C.

The partial pressure of the water vapor is given as the second x-axis.



Isenthalpens - Lines of equal specific enthalpy

The isenthalpes are lines of the same specific enthalpy. The lines run steeply downwards. The scaling is shown below the saturation line. The lines are parallel to each other.

The enthalpy h is given in 1kJ/kg.

In the diagram shown, the value range is from 0kJ/kg to 90kJ/kg


Lines of equal absolute humidity

The lines are vertical and parallel to each other. The value is read directly from the X-axis.

Absolute humidity x stated in 1g/kg.

In the diagram shown, the value range is from 0g/kg to 25g/kg


Lines of equal relative humidity

A curved line not parallel to each other.

They are limited with the dew line (1.0 - 100%).

The relative humidity indicates how large the amount of vapor present in the air is in relation to the saturation amount of vapor.

The relative humidity φ is given in 1%.

In the diagram shown, the range of values ​​is from 0% to 100°C.

lines of equal density

The lines of equal density run from left to right with a slight gradient.

The density [RHO] ϱ is specified in 1kg/m 3 .

In the diagram shown, the range of values ​​is from 1.09 kg/m 3  to 1.38 kg/m 3.


The isotherm - lines of equal temperatures

The lines of equal temperatures run parallel to the x-axis at 0°C.

With increasing temperatures, the lines rise slightly in the course. Below 0°C the lines fall off slightly.

The temperature T is given in 1°C.

In the diagram shown, the value range is from -20°C to +55°C.

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