Study On Heat Transfer Characterizations Of Multiple Micro-Jet Cylindrical Fin Based On Concentrating Solar Cell Cooling

Today,it is still an age of over reliance on fossil fuels such as coal,oil and natural gas,and the large amount of greenhouse gas emissions has brought about a series of environmental problems.As a result,every country in the world is doing its best to reduce greenhouse gas emissions and contribute to global environmental protection.Solar energy asrenewable energy sources,its development and using technology receive much attention,the effective utilization of solar energy for sustainable development has the vital significance.Concentrating Photovoltaic（CPV）power generation technology has been widely used in recent years because it promoted photoelectric conversion efficiency of solar cells,and relatively low cost.However,with the temperature increase of the cell,the photovoltaic conversion efficiency of the cell is decreased and its lifetime is shortened.Therefore,how to effectively reduce the temperature of solar cells is a key issue that researchers must address.In response to these problems,a new type heat sink combining a multiple micro-jet with cylindrical fin was developed,and experimental studies and numerical simulations were carried out to analyse the flow and heat transfer characteristics of the cooling medium inside the heat sink.Firstly,an experimental test platform for a new multiple micro-jet cylindrical fin heat sink cooling system has been built to investigate the internal heat transfer performance and flow state of the heat sink.Air is used as the cooling medium,the effects of every variable such as the input heat flow density q,the jet impact height/diameter ratio H/d and the jet Reynolds number Re_a on the internal flow and heat transfer characteristics of the heat sink are investigated,respectively.The experimental results show that the input heat flow density q,the jet Reynolds number Re_a and the jet impact height/diameter ratio H/d have a significant effect on the heat transfer performance of the cylindrical fin heat sink.Under a fixed jet impact height/diameter ratio H/d condition,the average temperature of the cooled surface decreases as the jet Reynolds number Re_a of increases,while the average heat transfer coefficient and the average Nussle number of the cooled surface are positively correlated with the jet Reynolds number Re_a.When the inlet cooling mass flow rate is constant,the increase of heat flow density q causes the average temperature of the cooled surface to increase.when the inlet cooling mass flow rate and heat flow density q are constant,in the range of 4≤H/d≤8,the average temperature of the cooled surface increases with increasing H/d,while the average heat transfer coefficient and the average Nussle number Nu of the cooled surface decrease with increasing H/d.Secondly,the three-dimensional physical and mathematical models of the flow and heat transfer of a new multiple micro-jet cylindrical fin heat sink were developed and its performances were investigated by numerical method.In the CFD numerical simulations,the effects of the heat sink structure,jet Reynolds number Re_a,jet impact height/dimension ratio H/d and heat flow density q on the heat transfer and flow characteristics of the heat sink were investigated by controlled variables method,respectively.The simulation results show that the overall temperature of a heat sink with a cylindrical fin structure is lower than the heat sink without fin,and that the former has a more uniform temperature distribution.The obtained flow field shows a return channel distributed around the jet orifice,which is conducive to the discharge of the return fluid into the environment,avoiding the formation of transverse flow and reducing the heat transfer effect.The cylindrical fins hinder the development of transverse flow,and destroy its boundary layer,and extend the heat transfer area of cooled surface,and improve the heat transfer performance of the heat sink.While the pressure drop of the heat sink increases with the increase of the jet Reynolds number Re_a,and the jet impact height/diameter ratio H/d and the cylindrical fin on the pressure drop are both negligible.Both the thermal resistance R_ab and the thermal effectivenessηof the heat sink decrease as the jet Reynolds number Re_a of the jet increases.Finally,experimental studies and numerical simulations showed that when the jet Reynolds number Re_a was1596～2874,the jet impact height/diameter ratio H/d was 4～8and heat flow density q was 6109W/m~2～34949W/m~2,the measured pressure drop of the cylindrical fin heat sink was in the range of 1354.64～3521.85Pa,the average convective heat transfer coefficient was 493.77～1036.12W/（m~2·K）,the thermal resistance is about1.05K/W～2.25K/W,and the thermal effectivenessηof the heat sink is between1.23～33.44,and the deviation between experimental and numerical simulation results is between 0～10.5%.