| The process of solar energy utilization is affected by the characteristics of low solar heat flux,periodicity,intermittence and instability.Therefore,solar heat collection and storage has become one of the key technologies of solar photothermal utilization system.As the core component of solar thermal utilization system,solar collector tube is particularly important to improve its thermal efficiency.Therefore,a new type of solar collector tube is proposed in this paper,which takes the transverse corrugated tube as the heat exchange inner tube and the molten salt of binary nitrate（60%Na NO3-40%KNO3）)as the phase change material（PCM）.By using the research method of numerical simulation and experimental verification,the experimental research of indoor solar collector pipe system is carried out based on a program to control the simulation of solar radiation power;By means of numerical simulation,the effects of the thickness of PCM layer,the flow rate of heating air in the tube and the solar radiation intensity on the thermal characteristics of the solar collector tube with PCM and the solar collector tube with transverse inner tube structure coupled with PCM layer are studied.The main conclusions are as follows:The conventional solar collector tube with air velocity of 1m/s and solar radiation intensity set as a fixed value is compared with the solar collector tube with PCM layer under the same conditions.The experimental results show that after adding PCM layer,the influence of solar periodicity and instability on the collector tube is significantly reduced and the heat collection performance of the collector is improved.Comparing the simulation and experimental results of the collector tube with PCM,it is found that there is a maximum temperature difference between the average air temperature in the two tubes at 167min,which is 12.7°C.The Root Mean Square Error（RMSE）in the whole process is 0.1044,which shows that the simulation method is more accurate.The simulation results show that the average cooling rate of the air in the conventional collector tube is 15.5°C/min 15 minutes after the conventional collector tube stops heating.After adding PCM,the average cooling rate decreases to 1.49°C/min,and its total heat collection（including heat extraction and heat storage）is 227.5 k J higher than that of conventional heat collection tubes.In terms of heat collection efficiency,compared with conventional heat collection tubes,the heat collection efficiency increased by 9.4%after adding PCM.Through the comparative analysis of solar collector tubes with PCM layer thickness of 3,13,23 and 33 mm respectively,it is concluded that with the increase of PCM layer thickness,the heat collection capacity of collector tube system first increases,then decreases and then increases.When the PCM layer thickness is 33mm,the cooling rate is the lowest,only 0.41°C/min.Compared with the conventional heat collecting tube,the heat collection is increased by 30.1%.The conventional solar collector tube with air velocity of 0.5,1,2 and 3m/s in the tube and the solar collector tube with PCM layer are simulated and compared.The results show that the greater the initial velocity at the inlet of the air in the pipe,the higher the velocity increase at the outlet.After adding PCM,with the increase of air flow rate in the tube,the temperature difference relative to the heated air in the conventional collector tube decreases at the same flow rate;By comparing the conventional solar collector tube and the solar collector tube with PCM layer under different solar radiation intensity,it is found that with the increase of solar radiation intensity,the increase of total heat collection with PCM collector tube first increases and then decreases,and the maximum increase amplitude reaches 16%.Through the simulation research and comparison of the striated tube heat collectors with PCM layers with different groove pitches and groove depths,the results show that:The increase of the pitch and groove depth of the transversely corrugated tube will increase the average temperature of the air in the tube.The influence of groove depth on the maximum temperature is greater,and the relationship between groove depth and the maximum temperature is almost linear.However,with the increase of groove depth and pitch,the flow resistance in the transverse corrugated tube also increases,resulting in the increase of forced convection power consumption in the system.When the pitch is5mm and the groove depth is 2.12mm,the flow resistance of the pipeline is the smallest,between 0.35～0.381,the heat exchange effect is better,and the forced convection power consumption in the system is less,and its comprehensive heat exchange performance is the best. |
