Optimization Design Of CPC And Its Influence On The Operation Characteristics Of Pulsating Heat Pipe Solar Collector

Compound Parabolic Concentrator(CPC)is a non-imaging concentrator that approximates an ideal concentrator.It is designed based on the principle of edge-ray principle and has a light trapping effect on the incident light in the range of the receiving angle,and can concentrate the radiation in the receiving angle range on the absorber.It has a high light collection efficiency and can collect various wavelengths and some scattered light.Without tracking devices,it only needs seasonal adjustment and has great potential for application in the mid-to-low temperature solar energy field.As a high-efficiency heat transfer device,the pulsating heat pipe has great potential for application in cooling of aviation equipment,cooling of electronic components,utilization of residual heat,and solar energy.Combining CPC and pulsating heat pipe,a CPC pulsating heat pipe solar collector was proposed.On the one hand,the concentrating effect of CPC increases the heat flux in the heat-absorbing section(evaporation section)of the pulsating heat pipe and enhances the heat transfer capability of the pulsating heat pipe.On the other hand,the smaller diameter of the pulsating heat pipe enables the CPC to be realized at a smaller scale.3-5x spotlight for easy integration with buildings.A theoretical and experimental study was conducted on the effect of the concentrating properties of CPC and the effect of the concentration characteristics of CPC on the operating characteristics of the new type of collector.(1)Through Monte Carlo Ray Tracing Method(MCRT),the concentrating characteristics of round-tube CPC were studied by self-programming,and the effects of truncation ratio,incident angle of light,and multiple of condenser on the characteristics of light collection were analyzed.The concentrating effect causes two heat flux peaks on the circular tube heat absorber.As the angle of incident light increases,the peak heat flux moves to the upper part of the heat absorber.When the incident ray angle is smaller than the receiving half angle,the average heat flux density increases almost linearly with the increase of the concentration ratio.When the received half angle is exceeded,the average heat flux density drops sharply.The average heat flux increases slowly with the truncation ratio,and the overall change is small.(2)The effects of the rotation of the focusing surface,translation,truncation of the CPC starting point and the offset of the absorber position on the condenser characteristics of the absorber were analyzed.The results of the study show that the rotation,translation,and cut-off of the CPC start point have little effect on the heat flow density of the absorber.When the absorber is assembled with the CPC,try to avoid the offset and left and right offset of the absorber.If the incident light has a high incidence probability of receiving the half-angle angle,consider moving the absorber up properly.(3)The absorber was optimized and an elliptical tube heat exchanger was used to replace the round tube heat absorber.After the replacement,the optical efficiency increases,and the peak value of the heat flux decreases.When the incident angle of the light exceeds the receiving half-angle,the optical efficiency is still higher than that of the round tube,and the solar radiation energy can also be absorbed at a large incident angle.(4)A numerical model was established for the heat collection unit in the optimized collector,and the effect of different tilt angles and solar radiation intensity on the thermal performance of the collector was compared and simulated using FLUENT.The results show that the heat collector's heat collection performance increases with the increase of solar radiation intensity;when the tilt angles are different,the heat collector's heat collection performance has little change and basically no effect;the heat collection efficiency of the elliptical heat absorber All of them are better than the circular pipe heat absorber;after the start point of CPC is truncated,the heat collection efficiency is reduced very little.In practical engineering applications,the start point of CPC can be truncated,and the requirement for reducing the machining accuracy is easy to manufacture and install.(5)An experimental study was conducted on the thermal performance of the pulsating heat pipe solar collector of CPC.It was found that the inlet water temperature of the working medium and the collector had a great influence on the heat collection performance of the pulsating heat pipe solar collector,while the pulsating heat pipe solar energy was measured under different tilt angles.The thermal performance of the collector does not change much.The thermal efficiency of the collector using R134 a is better than that of R123.The water temperature at the inlet of the collector increases,and the collector efficiency of the collector decreases.