Improved solar-thermal heat exchanger for space heating with surface roughness: A numerical parametric investigation and its optimization

Abstract

The heat exists in solar radiation can be extracted and utilized in drying and heating applications. In the present study, an attempt is made to improve the performance of a solar-thermal heat exchanger consisting of a flat-plate collector by producing roughness on the heat-absorbing surface. A repeated pattern of staggered arc roughness is introduced along the streamlines and the roughness is characterized using height ratio, relative pitch, number of gaps, etc. The influence of the roughness characteristics is studied on the thermal performance by computational fluid dynamics. The developed model is validated with well-established relations before predicting the results for the proposed design. The effective mixing of the viscous sublayer and free stream results in a significant enhancement in the thermal performance and it is predicted that the proposed model improves heat transfer up to 5.57 times that obtained in the conventional one. The comparative heat transfer over continuous arc-shaped roughness is increased from 32.72% to 62.46% and 44.62%–62.46% with the variation of number of gap and, gap with ratio from 1 to 3, and 0.5 to 1.0, respectively However, the disturbance in the streamlined pattern in the flowfield resulted in a pressure loss/pumping power increment of 4.46 times in the system. The results are summarized in correlation for heat augmentation and pressure loss which estimate results with the accuracy of 12% and 10%, respectively.