Thermal characteristics of a flat plate solar collector: Influence of air mass flow rate and correlation analysis among process parameters

Abstract

Present research focuses on the analysis of temperature profile, heat transfer characteristics and thermal efficiency of a flat plate solar air collector (FPSAC) at different air mass flow rates. Further, the interrelationship among several variables was also investigated using multivariate analysis. Experiments were performed with FPSAC at non-load conditions in the outdoor environment at natural convection (NC) and forced convection (FC) conditions. Air with mass flow rate (ṁ) of 0.01, 0.015 and 0.02 kg/s exhibited 30.73%, 57.88% and 96.40% enhanced convective heat transfer coefficient (hc,p-a) than 0.006 kg/s. Moreover, increase of ṁ from 0.006 kg/s to 0.02 kg/s augmented the thermal efficiency (ηth) from 22.53 to 32.3%. With regard to 0.006 kg/s, air mass flow rate of 0.02 kg/s produced 8.6% and 4.3% reduced heat transfer coefficient from absorber plate to glass due to convection (hc,p-g) and radiation (hr,p-g). Pearson correlation analysis indicated a strong positive effect of solar intensity on the temperature of absorber plate, glass cover and outlet air of collector, but a weak correlation with collector inlet air temperature, useful heat gain, ηth, and hc,p-a. Further, a positive correlation of solar intensity with hc,p-g and hr,p-g was also noticed. Principal component analysis enabled the visualization of association among solar intensity, temperature of different components of collector, heat transfer coefficients, thermal efficiency and time of the day. The analysis indicated that useful heat gain, heat transfer coefficient of air and thermal efficiency of the collector were not highly influenced by solar intensity.