Experimental investigation of heat transfer performance of a manifold microchannel heat sink for cooling of concentrated solar cells

The ever increasing need for more efficient utilization of solar energy at higher concentration levels in today´s power technology; create a need for effective cooling methods to improve the dissipation heat flux level from concentrated solar cells. The present research is targeted at cooling small area, high concentration solar cells which are desired because of their higher electrical efficiency at higher concentration of solar flux. A novel manifold microchannel heat sink with high heat transfer coefficient was fabricated and tested. Manifold and microchannel are etched in two separate silicon substrates and eutectically bonded together to form a sealed heat sink. Compared to conventional microchannels, manifold microchannel provides less pressure drop due to short microchannels length, while allowing the redevelopment of thermal boundary layer in each channel to obtain high heat transfer coefficients. The microchannels can be directly microfabricated and integrated on the backside of the silicon solar cell and with a manifold fabricated in another silicon substrate; it can form a sealed heat sink. This type of designs not only minimizes the pressure drop, but also maximizes the heat transfer with eliminating the thermal interface resistance between the heated area and the heat sink. The experimental results suggest that the present heat sink can provide high heat transfer coefficients with only moderate pressure drops. Experimental results showed that a heat transfer coefficient of 65480 W/m²K can be achieved at a flow rate of 1.1 gr/s and heat flux of 75 W/cm² using water as the working fluid. Since for all cases the flow is in thermal entry region, Nusselt number is not constant and it is shown that Nusselt number is correlated with Reynolds number to the power of 0.62.