A cooler for dense-array CPV receivers based on metal foam

Photovoltaic cells in concentrator photovoltaic systems are sensitive to overload their heat cooling systems due to exposure to a high incident radiation flux. This has unwanted repercussions which translate to a decline in both conversion efficiency and lifespan of the solar cell. The situation worsens when closely packed solar cell systems are used. Such systems demand active cooling with forced flow of the coolant so as to maintain the device within the acceptable operating temperatures for desired reliability.  Cooling heat exchanger systems such as fins in channels, micro-channels, pin fins and tortuous flow paths have been previously studied for possible application in concentrator photovoltaic systems but have been deemed insufficient. Consequently, researchers have sought other means of achieving the same goal. To this note, another extended-surface solution cooling mechanisms such as, the adoption of a cooling plate containing a metal foam have been suggested. This technique has been observed to be excellent but increased compression of the foam has been noted to amplify the pressure loss in flow through the foam, therefore creating a parasitic-type power demand for coolant pumping purposes. To this effect, there is need to lower this intensified power demand for water pumping purposes for a concentrator photovoltaic system.

Recently, Dr Yuri Flitsanov and Professor Abraham Kribus from the School of Mechanical Engineering at Tel Aviv University in Israel developed a cooler for dense-array concentrator photovoltaic receivers based on metal foam. For this purpose, the scholarly pair hoped to advance an empirical setup for forced flow heat transfer in a cooling plate heat exchanger filled with unmodified metal foam. Their work is published in the research journal, Solar Energy.

The research team began by evaluating of open-cell metal foams as heat transfer enhancers in a cold plate suitable for concentrating photovoltaic receivers. Next, they tested aluminum based foams in a compact heat exchanger with forced convection of water over a range of flow rates and heating rates. Eventually, they characterized the heat transfer rate and pressure drop as a function of water flow rate through the heat exchanger.

The authors observed that the performance of the foam based heat exchanger was positively competitive when compared to commercial cooling plate solutions. Furthermore, it was noted that performance improvement could be achieved without foam compression and that the desired performance goals could be accomplished with different combinations of materials, dimensions and coolant flow rates.

Yuri Flitsanov and Professor Abraham Kribus successfully presented an experimental study of forced flow heat transfer in a cooling plate heat exchanger filled with unmodified metal foam. It has been seen that the combination of heat transfer and pressure drop performance with the metal foam solution yields a more efficient system when compared to commercial coolers. Furthermore, the metal foam based cooler is a promising solution for dense array concentrator photovoltaic receiver, with competitive performance and potential for low cost fabrication. Altogether, the impact of the metal foam cooler from a case study shows that using the metal foam cooler can increase the electricity production by about 1.5%.