| Solar photovoltaic battery photoelectric conversion efficiency is usually only 8%-20%,most of the rest of the solar energy is converted into heat energy gathered on the photovoltaic cells,photovoltaic(pv)power output capacity of a battery will decrease with the rising of temperature,and photoelectric conversion efficiency decrease will result in more solar energy into heat energy gathered to form a negative cycle.According to this situation,the photovoltaic Thermal comprehensive utilization technology,referred to as PV/T technology(Photovoltaics/Thermal)can solve this problem well.In order to reduce the heat transfer process between the PV/T cycle and the heat pump system cycle and the design of direct expansion solar PV/T heat pump system can be more efficient conversion and utilization of solar energy resources.In this paper,PV evaporator,the core technology component of direct expansion PV/T system,is studied.Firstly,the working principle of the existing direct expansion solar PV/T heat pump system and the heat transfer model of PV evaporator are introduced.According to the disadvantages of the traditional tubeplate evaporator,an improved half-tube evaporator with inner groove is proposed.The commercial finite element analysis software Fluent is used to model and calculate the drainage basin in the traditional structural evaporator and the proposed improved structural evaporator.The distribution of parameters such as temperature,velocity,density and gas-phase volume fraction of refrigerant R22 in the tube is analyzed under the solar radiant heat flow of 1000W/m2 with the main pipe length of 1 meter.At the same time,the velocity decomposition cloud map method is used to analyze the flow area exchange situation at the elbow,and the results show that:Under the simulated flow of 12s,the volume gas content at the outlet of the working medium is 1.95%higher than that of the traditional structure,40.3%higher than that of the traditional structure,and the temperature is 1.52K higher than that of the traditional structure,0.55%higher than that of the previous year.In the center area of the elbow,the flow will move toward the outer circle of the elbow,while the working medium at the wall will move toward the inner circle of the elbow when squeezed.This phenomenon leads to local low temperature areas on the pipe wall and the side of the plate at the outlet of the elbow,resulting in uneven temperature distribution.The improvement of the structure can alleviate this situation.Then the solid part of the PV evaporator is simulated and calculated to get the temperature and stress distribution of the tubeplate structure.The results show that:The plate side temperature of the traditional structure decreases from the initial 30℃ to 22.06℃ after working for 12s,and the plate side temperature of the improved structure decreases to 18.12℃,which is 3.94℃ lower than that of the traditional structure and 17.88%lower than that of the traditional structure.The improved structure evaporator has a much higher capacity of removing heat from the plate side than the traditional structure.Because of the low temperature difference and small temperature amplitude of the PV evaporator,the strain has little influence.Finally,the plate side temperature of the two types of evaporators were substituted into the output characteristic equation of the solar photovoltaic cell to obtain the maximum output power of the photovoltaic cell and the variation of the photoelectric conversion efficiency with the evaporator plate temperature.The results show that:The maximum output power of the evaporator with the improved structure is increased by 3W compared with that of the traditional structure,with a year-on-year growth of 2.2%.The photoelectric conversion efficiency is increased by 0.2%,with a year-on-year growth of 2.08%.The improved evaporator with the improved structure can effectively improve the power output capacity of the photovoltaic cell. |
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