Outside humidity treatment is a main contributor to aircraft ECS (environmental control system) power requirements. To reduce this power, it is important to know exactly how to not exceed outlet humidity at the pack outlet. Liquid water at Low Pressure ducting participates to cabin cooling but, if this quantity is too high, a fog can be seen.

The purpose of the “Humidity Optimization Tool” project was to develop a tool able to predict generation and growth of water fogs in the ECS, in order to avoid them. The project was separated into three sub-topics:

1. Determination by tests of a visibility fog criteria based on physical properties (air speed, liquid water content, blowing temperature, droplet size, etc.);
2. Development of a 0D tool to predict the size of the water droplets (liquid or ice) downstream a: (i) Heat exchanger, (ii) Pack outlet turbine and (iii) Mixmanifold;
3. Validation of this tool.

The proper implementation of this research required two-phase flow expertise in two different fields: (i) numerical modelling and (ii) measurement techniques.