Humidity evolution (breathing effect) in enclosures with electronics

Packaging and enclosures used for protecting power electronics operating outdoors are designed to withstand the local climatic and environmental changes. Hermetic enclosures are expensive and therefore other solutions for protecting the electronics from a harsh environment are required. One of the dangerous parameters is high humidity of air. Moisture can inevitable reach the electronics either due to diffusion through the wall of an enclosure or small holes, which are designed for electrical or other connections. A driving force for humid air movement is the temperature difference between the operating electronics and the surrounding environment. This temperature, thus, gives rise to a natural convection, which we also refer to as breathing. Robust and intelligent enclosure designs must account for this breathing as it can significantly change the humidity distribution in the enclosure. In the current work we suggest a modelling procedure to investigate a breathing effect for an enclosure with opening (hole). The simulations are carried out by solving an energy equation coupled with the Navier-Stokes equation. The movement of moisture is considered through a convection-diffusion equation. The approach is verified by measuring the temperature and humidity profiles in a test setup (container) while also considering the moisture flux outside the container. The test setup is a vertical cylinder enabling to simplify the modeling to 2D case. The experimental measurements are compared to simulations and good agreement is obtained.