Heat transfer enhancement of a solar air heater using capsule-shaped turbulators: a numerical analysis

The development of a laminar sublayer inside the channel of the solar collector results in a poor heat transfer coefficient. Adding artificial roughness to the absorber plate in the form of turbulators is an effective and promising method of increasing heat transmission by interrupting the laminar sublayer. In this study, a capsule-shaped turbulator is used to enhance the thermal performance of the solar air heater. With flow Re (Reynolds number) fluctuating from 3000 to 21,000, the flow and heat transfer-related parameters of an air heater fitted with turbulators were numerically examined. The orientation angle of the capsule turbulator corresponding to the flow direction is modified from 0° to 90° in steps of 15°. The outcomes indicated that the overall thermal performance of the solar collector was optimized for the orientation angle of 45° at all the Reynolds numbers chosen for the study. Beyond this angle, the turbulators block the flow, increasing the pumping power. The number of rows of turbulator, pitch and height ratios of the optimized turbulator design is varied in the range of 1-3, 0.025-0.25 and 0.004-0.008, respectively, to determine their optimum values for better performance. It is observed that the turbulator having two rows with a pitch ratio of 0.05 and height ratio of 0.006 produces a relatively higher overall thermal enhancement by about 15.76% when compared with the base model without turbulators. The same configuration yields about 52.64% improvement in the exergy efficiency with respect to the base model.