Research On Heat Transfer Characteristics Of Loop Heat Pipe Based On Concentrator Solar Cell Cooling

In recent years,the photoelectric performance of concentrator solar cells in a solar power generation system has been improved dramatically.However,only a fraction of incoming sunlight striking the concentrator solar cell is converted into electrical energy.The remainder of the absorbed energy will be converted into thermal energy in the cell and may cause the cell temperature to rise,which may lead to the reduction of the photoelectric conversion efficiency and shortened the service life of concentrator solar cell with high light intensity and large current.Accordingly,it is necessary to develop an efficient thermal management system for the concentrator solar cell to ensure the cell working with safety and stability.Based on traditional cooling technologies(air cooling,liquid cooling)and new cooling technologies(micro-channel cooling,jet impingement cooling,etc.),this paper proposes a heat dissipation scheme for biporous capillary wick loop heat pipe system heat dissipation scheme.Its advantages of high heat coefficient,anti-gravity,long heat transmission distance,and variable operating angle can effectively solve the heat dissipation problem of concentrator solar cell.According to the heat dissipation characteristics of the concentrator solar cell,this paper mainly studies the preparation of biporous capillary wick and the heat transfer characteristics of the loop heat pipe.First,the biporous capillary wick was prepared by the combination of the powder metallurgy sintering method and the addition of the poreforming agent.The phase composition,microstructure,and properties of capillary wick were systematically studied by corresponding physical test and characterization methods such as X-ray diffraction spectroscopy(XRD),scanning electron microscope(SEM)and pore size analyzer.Furthermore,the loop heat pipe system was designed and manufactured,and this research proceeds with the experimental comparison and scrutiny of the operating characteristics of the loop heat pipe with the single capillary wick and the biporous capillary wick.The main research results are as follows:(1)After the pore-forming agent Ca Cl2 is fully dissolved,the capillary wick sample presents a double-pore structure.The porosity,permeability,and pumping amount of the capillary wick rise with the increase of the pore-forming agent content and decrease with the increase of the sintering temperature.The porosity of the capillary wick decreases with the extension of the holding time.The capillary pumping performance is affected by the interaction of porosity and permeability,and high porosity and permeability will lead a better performance of the capillary pumping.Chernyshev & Maydanik Model can be used to estimate the effective thermal conductivity of biporous capillary wick.In this paper,the biporous capillary wick was prepared at sintering temperature which is 700?? 900? for 2 hours and with more than 20% of pore-forming agent content meeting the application requirements of LHP capillary wick,with the porosity of 62.37% ? 69.13% and permeability of 3.78×10-11? 6.2×10-11 m2.(2)The start-up operation state of the biporous capillary wick LHP system is similar to that of the single capillary wick LHP system.When the heater temperature reaches the highest temperature that the solar cell can be allowed,the heating flux of LHP with biporous capillary wick is 75000W/m2,while that of LHP with a single capillary wick is only 50000W/m2.The coolant temperature,operating inclination,and filling rate have apparent effects on the performances of the loop heat pipe.Compared with LHP with single capillary wick,the LHP with biporous capillary wick system has a more steady operational state,a more reliable capacity of heat-mass exchange and circulation,and can adjust the thermal response more quickly to maintain the internal balance of the system.Under the same circumstances,the heat transfer coefficients of the loop heat pipe evaporator rise with the increase of power until it stabilizes.The thermal resistance and heat leakage temperature of LHP with biporous capillary wick is lower than that of LHP with single capillary wick,and the heat transfer performance of LHP with biporous capillary wick is excellent.In the application of heat dissipation of concentrator solar cells,the biporous capillary wick loop heat pipe has a better application prospect.The heat transfer performance of LHP with biporous capillary wick can be further improved by optimizing the capillary structure in the subsequent studies.