Forced convection cooling in telecommunication cartridge

Abstract

In electronics cooling forced convection has displaced free convection. The aim of this research was to find out the most important parameters in forced convection and define guidelines for good thermal design.System pressure drop was studied both theoretically and measuring. A full installed cartridge was divided into single flow resistances which pressure drops were measured in the windtunnel. The results show where the total pressure drop consists of.The effect of air velocity on component and heat board temperatures was measured in the windtunnel. Heat dissipation was kept as a constant. It was found that component temperatures as a function of velocity differ according to the components junction to ambient thermal resistance. From the results it was calculated a cooling efficiency. At the approach velocity of 1m/s the cooling efficiency is 70-80 %.In forced convection it is very important to know fan performance. Fan as a part of a system was studied changing fans location in relation to a cartridge. At small distancies fans location in horizontal or in vertical direction did not affect significantly on component temperatures. On the suction side of the fans air flow was uniform and component temperatures lower than on the exhaust side of the fans.The effect of altitude on convective heat transfer and fan performance was studied both theoretically and measuring. The measurements were done in a hypobaric chamber at altitude levels of 0m, 1000m, 2000m, 3000m and 4000m. It was again found that component temperature rises differ according to the components junction to ambient thermal resistance. In general theoretically calculated values correlate very well with the measured values. At 3000m temperatures rose 18% in free convection when calculated value was 19% and in forced convection 21% when expected was 22% for laminar flow. Fans rotation speed increased ~2% per 1000m i.e. ~7% up to 3000m. /Kir10