CuO 나노유체의 적용에 따른 평판형과 U-tube형 태양열 집열기의 성능비교에 대한 실험적 연구

Abstract

ABSTRACT

Experimental study on the efficiency comparison of flat-plate and U-tube solar collector using CuO nanofluid

Un-cheon Ju Advisor : Prof. Cho, Hong-hyun Mechanical&Metallurgical Education Chosun University

In this study, thermal efficiency of a flat-plate solar collector and a U-tube solar collector using a CuO nanofluid and water as a working fluid was investigated according to CuO nanoparticle size and concentration. Experiment was carried out under the mass flow rates of 0.033 kg/s and 0.047 kg/s respectively. Additionally, CuO nanoparticles with the size of 40 nm and 80 nm were used and concentration of nanofluid was changed by 0.1vol%, 0.3vol%, 0.5vol%, and 0.7vol%, respectively. The thermal conductivity increased non-linearly as the CuO nanofluid concentration increased. In addition, it was confirmed that the increase of thermal conductivity ratio gradually decreased when concentration of CuO nanofluid increased. Experimental results showed that the efficiency of solar collector showed the maximum when a mass flow rate of working fluid was 0.047 kg/s, CuO nanoparticle size was 40 nm, and CuO nanofluid concentration was 0.5vol%. In this case, the heat gain and heat loss coefficient of a flat-plate collector was 0.735 and 22.8, respectively. In addition, Heat gain and heat loss coefficient of U-tube solar collector was 0.695 and 16.66, respectively. When the efficiency of flat-plate and U-tube solar collector using CuO nanofluid was improved by 11.32% and 7.82%, respectively, compared to that using water. In order to increase the efficiency of the solar collector, the size of nanoparticle and concentration of nanofluid should be appropriately controlled and the mass flow rate in the system should be designed optimally. The smaller the size of nanoparticle in the nanofluid, the more active the Brownian motion, resulting in the better the absorption of solar energy. The high volume concentration of CuO nanofluid has good thermal conductivity, but the viscosity increases and the heat transfer performance decreases. On the other hand, the optimal concentration of CuO nanofluid is very important because it can not absorb whole of solar energy if the concentration of CuO nanofluid is low. Thus, the size and concentration of nanofluid are very important factors on the performance of solar collector. From the experimental result, the use of CuO nanofluid is superior to absorption of solar energy than the use water. Therefore, when the CuO nanofluid is used with optimal conditions, it is sure to improve the efficiency of solar collector.