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AcknowledgementsSpecial thanks to Prof. R. Sittig ad his team from Institute of Electrophysics of Technical University of Braunschweig for permanent support mn the measurements.Keywords cx thrmal design >>, cx efficiency)> Abstract The paper presents the microchannel cooling structure. This very efficient heat sink is dedicated for power electronic applications characterised by high heat flux densities combined with high overall power levels.The conducted measurements show that to meet both thenmal and mechanical demands; the structure can achieve thermal resistance of 0. 1K/W. overtake the heat flux of the order of 100 250W/cm2 [3] become the most popular solution in the field of power electronics applications. The most intricate such a solution, characterised by the extremely large LOB 2005 -Pn.Jcii 0.1 Supcl-r )olm Suu1aLes for lBowecr 1loLCiis LISIK Zhigi¢niw DEl Own5 -L)i--;c11i ISBSN :9(U1548tf-5 I,.I LOB 2005 -1)ecsdcii 0.4 Supcl-r )olm S$u,>e for lBowecr tEloamic LISIK Zhigi¢niw DEl Own5 -L)i--;c11i ISBSN :9(U1548tf-5 i,.4

The present paper focuses on the high-pressure metal-organic vapor phase epitaxy (MOVPE) upside-down vertical reactor (where the inlet of cold gases is below a hot susceptor). This study aims to investigate thermo-kinetic phenomena taking place during the GaN (gallium nitride) growth process using trimethylgallium and ammonia at a pressure of above 2 bar. High pressure accelerates the growth process, but it results in poor thickness and quality in the obtained layers; hence, understanding the factors influencing non-uniformity is crucial. The present investigations have been conducted with the aid of ANSYS Fluent finite volume method commercial software. The obtained results confirm the possibility of increasing the growth rate by more than six times through increasing the pressure from 0.5 bar to 2.5 bar. The analysis shows which zones vortexes form in. Special attention should be paid to the transitional flow within the growth zone as well as the viewport. Furthermore, the normal reactor design cannot be used under the considered conditions, even for the lower pressure value of 0.5 bar, due to high turbulences.