| With the growing demand in green energy, developing efficient solar collectors is urgent. Although compound parabolic collectors (CPC) have perfect thermal features within 80～250℃, it is lack of mature technology because of insufficient research investment. Focusing on key technical parameters of CPC, receiving half angle, layout of tube, and optimizing heating temperature were mainly studied in this paper.The research work mainly includes the following four aspects:1. CPC degsin:the solar radiation calculation is modeled and the radition intensity for four typical day of Nanjing was calculated. Three receiving half angle of 10°,20°,30° circle tubular CPC using vacuum tube of inner pipe radius R with four kinds:single R, single 2R, double level R+R and hyperboloid were degsined.2. Simulation of optical collectors:TRACEPRO software based on MCRT method was used for the optical properties of CPC. Optical model of CPC solar collector with different half Angle, different layout scheme was established and simulated. Calculation of CPC absorber radiation strength, total optical efficiency and energy density on the surface of the absorber was analyzed.3. Simulation and analysis of collecting efficiency:CPC one-dimensional steady-state heat transfer model and instantaneous thermal efficiency model were established. Using ethylene glycol as working fluid, collecting efficiency of different half angle, different inlet temperature, mass flow rate,different environment temperature,wind speed of CPCwere simulated using FLUENT software.4. Economic analysis:Using F-diagram thermal performance and economy analysis model, the whole life cycle cost savings and paypack period of different temperature of different collector types were analysised.The main conclusions are as following:1. Corresponding to three receiving half angle of 10°,20°,30°, increasing the radius of absorber, horizontal layout of two absorber and hyperboloid design can increase the actual maximum receiving half angle, but concentrating ratio and heating temperature relatively decreased. And it is concluded that with receiving half angle greater than 30°, hyperboloid design scheme is more advantage.2. With the increase of fluid inlet mass flow, collecting efficiency increase first and then levele off. Mass flow rate increased from 0.01 kg/s to 0.2 kg/s, collecting efficiency for 10°,20°,30° CPC increased by 4.76%,4.92%,4.94% respectively, import and export pressure difference increased from (2.23Pa,4.15Pa,65.13Pa) to (54.82Pa,105.72Pa,157.82Pa),respectively; For different inlet temperature, three collectors efficiency was different.When inlet temperature is 40℃, collecting efficiency for 10°,20°,30℃PC was 54.54%,57.15%,58.26%, comparied to 46.52%,43.02%,37.64% at 150℃; The environment temperature and wind speed has minimal impact to 10° CPC.3. Comparison of different thermal fluid:when inlet temperature is between 40～120℃, thermal efficiency of ethylene glycol is 5.67% higher than oil.4. Criterion of collecting temperature:through the economic analysis, considering the optical efficiency, collectiing efficiency, it is concluded that when collecting temperature is less than 80℃, receiving half angle of CPC collector greater than 30°, vacuum tube or flat collector were recommended; with collecting temperature in rang of 80～120℃, receiving half angle in 20°～30° was recommended; with collecting temperature in rang of 130～150℃, receiving half angle in 10°～20° was recommended; When collecting temperature is greater than 150℃, receiving half angle less than 10°as recommended.The innovation of this paper is to put forward choosing optimal receiving half angle of CPC corresponding to different temperature, and when receiving half angle greater than 30°, hyperboloid design scheme has more advantages.The results of this paper will have significance to the design and application of CPC. |
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