Influence of air humidity on the cooling process of electronic systems
The subject of the research proposal was a pilot study on the influence of air humidity on the cooling process of electronic circuits.
- Previously available publications focused on the theoretical description of the influence of humidity on thermophysical parameters of air (viscosity, specific heat, thermal conductivity, Nusselt number, etc.) and did not include experimental studies. Therefore, in the framework of the project carried out, it was considered crucial to carry out experimental studies and confirm or exclude the influence of humidity on the efficiency of the cooling process of electronic systems.
- The first step was to purchase a thermal test chamber from the company's own funds. The Binder ED115 chamber was chosen because of the gravity circulation shell heating system used and the high stability of the chamber conditions. Due to the limitations of the permissible humidity in the chamber, it was decided at this stage that it was necessary to carry out the key research for the scientific operation in the climate chamber. Due to the air movements forced by the mixing fan inside the climatic chamber, it was necessary to design and construct an internal measurement chamber that would shield the electronic system under test and at the same time enable measurements to be carried out under stable temperature and humidity conditions. It was also necessary to equip the measuring chamber with an opening that would allow air to be mixed throughout the system and, once conditions had stabilised, to be cut off from the air circulation in the climate chamber. After a number of trials with different solutions, the measuring chamber was finally built consisting of a frame made of Bosch Rexroth profiles, to which aluminium sheet metal walls were bolted. Following the recommendations of the JEDEC JESD-51 standards and the size of the climatic chamber planned for use, the measuring chamber was in the form of a cube with a side of 34 cm. A thermal transmission window, adjustable rosette vent and cable grommets were placed in the individual walls. Modular cable grommets from Icotek were used. The advantage of the measurement chamber constructed in this way was that it could be reconfigured at will during experiments. Once the final version of the measurement chamber was completed, it was tested in a thermal test chamber to confirm its mechanical stability at elevated temperatures and to determine how to optimise cable routing. A set of Sensirion SHT-85 miniature temperature and humidity sensors were used to control the conditions inside the climate chamber and the measuring chamber, their choice being dictated by their small size and operating temperature range. In the next stage, a circuit was built to regulate and stabilise the junction temperature of the working transistor (60/90/120/150 0C). Once the system temperature was stabilised, the power dissipated in the transistor circuit provided a measure of its cooling efficiency.
- An ESPEC SH-661 climate chamber provided by the Department of Infrared and Thermal Imaging Technology of the IOE WAT was used for the tests. The measuring transistor together with a heat sink was placed in the measuring chamber and the latter in the climate chamber. The power dissipated in the transistor was read using an AXIOMET AX-178 microvoltmeter connected to the controller and was recorded directly on the computer. Measurements were carried out for successive combinations of temperature and relative humidity resulting from the range of control of the chamber parameters. Several series of measurements were made: stabilisation of conditions-measurement-restoration of initial conditions-measurement-etc. Finally, the measuring transistor was placed on a channel heat sink with a Sanyo Denki 9GT fan and the tests performed earlier for natural convection conditions were repeated. However, reproducible measurement results were not obtained. The reason was that the measurement chamber was too small, leading to strong turbulence. Based on the results obtained, there was no significant effect of air humidity on the cooling efficiency of the systems, for natural convection. This phenomenon can therefore be neglected in the modelling and design of systems.
- It is planned to continue this research. However, it will be necessary to gain access to a much larger climate chamber or to build our own, e.g. based on the design of a freezing chamber.
Project leader: dr inż. Marcin Kałuża
Years: 2018 – 2019
Project funded by the National Science Centre under the MINIATURA competition.
Publication:
Kopeć, Michał & Olbrycht, Robert & Gamorski, Piotr & Kałuża, Marcin. (2018). The Influence of Air Humidity on Convective Cooling Conditions of Electronic Devices. IEEE Transactions on Industrial Electronics. PP. 1-1. 10.1109/TIE.2018.2823661.