Comparative Study On Three CPC Of Low Concentration Ratio

Compound parabolic concentrator (CPC) is an ideal low-intermediate temperature solare collector. The theraml source at temperature80-250℃has a wide range of applications. As a solar concentrator of low concentration ratio, CPC has several advantages.The CPC can concentrate both direct irradiation and part of diffuse irradiation, besides it can obtain high temperature without tracking devices and has a simple structure and low cost. Currently CPC has been used for solar cooling, heating, water disinfection, and it play an important role in industrial process and low temperature heat power generation in the future.In this work, three CPC collecters with concentration ration of1.50,2.0and3.0combined U-shaped copper pipe vacuum tube are designed. The optical properties are simulated by software of Lighttools. The optical efficiency of direct irradiation at different projected incidence angles and diffuse irradiation of the three CPC are simulated and analyzed.Based on the principle of heat balance, a steady one-dimensional heat transfer physical model of CPC collecter is established by analyzing heat transfer process of U-shaped copper pipe vacuum tube. The1.5X CPC,2.0X CPC and3.0X CPC collector system with same aperture area are bulit and the steady collector efficiency of three CPC are experimental tested in sunny days at different inlet temperatures compared with numerical results. The experiment results show that CPC has a good thermal efficiency, the by fitting the experimental results we obtained each heat loss coefficient and intercept efficiency (CPC experimental optical efficiency) of the curves of thermal efficiency of three CPCs. The results show the heat loss coefficient can be reduced effectively by increasing concentration ratio of CPC. And under the same manufacturing methods, the surfaces of CPC is more consistent at a lower concentration ratio, the surfaces of higher concentration ratio CPC has a larger error since it is hard to manufacture.The influence of proportion of diffuse iradiation on low concentration ratio CPC reception performance is studied, according to the Energyplus meteorological data, irradiation energy of ideal CPC with CR of1.5,2,3,4and6receive on typical day and the whole year in six cities are compared. And the thermal performance of1.5X CPC,2.0X CPC and3.0X CPC collector system are experimental testing under different weather conditions at the inlet temperature of70℃. The result shows the proportion of diffuse iradiation has significant effect on colletion thermal performance of low concentration ratio CPC. The lower CR CPC collector has a higher efficiency of solar irradiation at a day of higher proportion of diffuse iradiation,and a higher as CR CPC collector achieve a better solar energy utilization only in sunny days when the proportion of diffuse iradiation is extremely low.