| According to domestic and foreign literature,the research progress,key technologies and existing problems of flat-plate solar collectors are analyzed.On this basis,thermal efficiency of the carbon-plastic flat-plate collectors is studied through experiments and numerical simulation methods.This research has a certain guiding role in the use of solar energy.According to the heat transfer process and structural characteristics of the solar flat-plate collector,the heat balance equation of the collector is established.According to the existing research,the calculation process of the heat loss of the collector is simplified,and the heat loss coefficient is calculated by the empirical formula.In order to facilitate experimental research,the efficiency factor and thermal migration factor are introduced,and the temperature of the inlet fluid of the collector is used to replace the surface temperature of the heat-absorbing plate,which is difficult to measure,and a mathematical model of the efficiency of the solar flat-plate collector is established.Set up an outdoor steady-state efficiency test bench for the solar collector,and conduct thermal performance tests on the carbon-plastic flat-plate solar collector.Under different flow conditions,a full-day efficiency experiment was performed on the collector.The maximum useful power when the operating flow is 0.012kg/s,0.016kg/s,0.056kg/s,and 0.103kg/s are 383.56W,375.12W,437.65W,470.67W,the maximum instantaneous efficiency is 0.63,0.65,0.73,0.78,respectively.The analysis found that within a certain flow range,the instantaneous efficiency of the collector will increase with the increase of the flow,but this trend will gradually become smaller.When the flow rate increases to a certain extent,the continuous increase of its value will no longer have a significant impact on the efficiency of the collector.The experimental data of working condition 2 is selected for analysis,and the instantaneous efficiency curve of the carbon-plastic flat-plate collector based on the normalized temperature difference is obtained through the linear fitting of Origin software,the maximum efficiency value is0.70,and the total heat loss coefficient is 5.16 W/(m~2·K).Compared with traditional metal flat solar collectors and plastic flat solar collectors,the maximum efficiency of the carbon-plastic flat solar collector is 0.13 higher than that of the plastic flat solar collector,and 0.03 lower than that of the tube-sheet metal flat solar collector.The thermal performance lies between the two.Through Fluent simulation analysis of the collector model,under the conditions of a simulated flow rate of 0.016kg/s,a solar illuminance of 800W/m~2and an ambient temperature of 303K,the outlet temperatures at different inlet temperatures were obtained,then the discrete points of the instantaneous efficiency were calculated and the curve of the simulated instantaneous efficiency was fitted by the least square method.Compared with the experimental efficiency curve,the errors of the instantaneous efficiency intercept and the total heat loss coefficient are 1.4%and 5.8%,respectively.The numerical simulation results are compared with the experimental results,and the error is small,which verifies the reliability and accuracy of the numerical simulation,and shows that it is feasible to use the numerical simulation method to calculate the efficiency of the heat absorption unit.According to the numerical calculation results,the flow velocity distribution and temperature distribution cloud diagram of the carbon plastic flat-plate solar collector are obtained.The useful power and instantaneous efficiency of the 7 heat absorption units are calculated through the mass flow rate and the temperature difference between the inlet and the outlet of each heat absorption unit.The comparative analysis shows that the farther away from the inlet of the collector,the smaller the mass flow of the pipe,the greater the temperature difference between the inlet and outlet water,and the lower the useful power and heat collection efficiency of the corresponding heat absorption unit.The heat collection performance of the heat absorption unit in the middle of the heat collector can better reflect the overall heat collection state of the heat collector.Establish the expression of the efficiency factor and material content of the carbon-plastic flat plate collector.By drawing the nomogram,combined with the actual collector application size,the structure of the heat-absorbing plate is optimized,and the thickness and width of the optimized heat-absorbing plate are 0.46mm and 114mm respectively.This research provides guidance for the promotion and application of carbon-plastic flat-plate collectors. |
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