Experimental operating range evaluation of flat-plate pulsating heat pipes for high-heat flux automotive power electronics cooling

Abstract

Flat-plate pulsating heat pipes are a promising future technology to passively increase the power density of power electronics in mobile applications by means of a more efficient thermal management. However, in the design phase, it is not known how different thermal boundary conditions are affecting the operation range of a pulsating heat pipe. To experimentally assess this dependency, the present work aims to evaluate the performance of a flat-plate pulsating heat pipe for electric mobility and different operating conditions. To this purpose, a flexible test section was designed allowing to raise different heating and cooling conditions. A novel array of multiple hotspots was employed which realistically represents a power semiconductor layout. This way, a local heat flux of up to 200W/cm2 was introduced to the pulsating heat pipe. In the condenser section, the coolant temperatures were varied between 10°C and 60°C, representing real conditions of a driving cycle. The investigated aluminum pulsating heat pipe consists of 22 rectangular channels and two different newest generation refrigerants R1233zdE and R1234yf were used as working fluids. Based on the new experimental evidence, our previously published thermal resistance model was adapted. A posteriori comparison with previous calculations confirms the validity of the numerical assumptions and shows a good agreement with the obtained results. For the first time, our investigation shows that pulsating heat pipes can robustly achieve heat flux densities above 100W/cm2 at conditions representative for automotive electronics applications. The real implementation potential was demonstrated, as an considerable 5 to 11 times higher effective thermal conductivity than solid aluminum was obtained depending on the integration concept.