Influence Of Cooling Conditions On The Heat Transfer Performance Of Pulsating Heat Pipe And Its Application In Solar Energy Collecting

As a high-efficiency heat transfer element,pulsating heat pipe has great application potential in the fields of electronic cooling,space,nuclear energy,solar energy and other fields.In different application fields,the heating and cooling conditions are different,and the working temperature range is different.Based on this,the effect of cooling water flow and temperature on the heat transfer performance of the plate pulsating heat pipe is studied.At the same time,the pulsating heat pipe was applied to solar heat collection,and the operating characteristics and heat absorption process of the concentrating pulsating heat pipe solar collector under low and medium temperature cooling conditions were studied.The main research contents and conclusions are as follows:(1)By building an experimental system of heat transfer performance of pulsating heat pipes,the effect of different cooling water flow rates on the heat transfer performance of pulsating heat pipes is studied.As the cooling water flow increases,the heat transfer resistance of pulsating heat pipes increases.When the heating power is low,the heat transfer resistance of the pulsating heat pipe decreases with increasing cooling water temperature;when the heating power is high,the heat transfer resistance of the pulsating heat pipe changes little with the cooling water temperature.The filling rate of 50% and 80% has little effect on the heat transfer performance of the pulsating heat transfer tube.The thermal resistance changes with the cooling water temperature at the two filling rates are consistent.(2)The heat transfer resistance of the pulsating heat pipe at the temperature of the medium-temperature cooling water is lower than that of the pulsating heat pipe at the temperature of the low-temperature cooling water.When the cooling water temperature is lower,the heat transfer resistance of the HFE-7300 pulsating heat pipe with a lower boiling point is lower.At higher heating power or higher cooling water temperature,HFE-7500 with higher boiling point should be used.At this time,the working medium in the pulsating heat pipe is not easy to be dried and the heat transfer effect is better.(3)To explore the absorption principle of nanofluids,and use a spectrophotometer to measure the transmittance of carbon nanotube fluids and pure water and HFE-7100.The research results show that the higher the concentration of carbon nanotubes,the lower the transmittance,and the transmittance of 0.0375wt% carbon nanotube fluid to light is zero.In the infrared region,the optical properties of water dominate,while in the ultraviolet and visible regions,the absorption coefficient is more sensitive to changes in the volume fraction of nanoparticles.Finally,a solution of hydroxylated multi-walled carbon nanotubes and refrigerant HFE-7500 was prepared by a two-step method,but the fluid stability was poor and large-scale agglomeration was prone to occur.(4)The experimental research on the operating performance and heat absorption process of the concentrating pulsating heat pipe solar collector.The operating characteristics and light-to-heat conversion efficiency of concentrating pulsating heat pipe solar collectors are studied.When the concentration of 0.0015wt% carbon nanotube fluid is higher than that of pure water and 0.0375wt% and 0.00375wt% carbon nanotube fluid as the working fluid,the temperature of the evaporation section of the pulsating heat pipe solar collector is higher.The minimum light-to-heat conversion efficiency of water and HFE-7100 is only 24%.The light-to-heat conversion efficiency of the carbon nanotube aqueous dispersion reaches about 50%,and the difference in light-to-heat conversion efficiency of the nanofluids of different concentrations is small.However,when the concentration of carbon nanotubes is high,the viscosity of the solution is higher,which increases the resistance of the working fluid of the pulsating heat pipe and is not conducive to the transfer of heat.The concentration of 0.0015wt% carbon nanotube fluid is suitable for the heat collection of the pulsating heat pipe solar collector Working fluid.