High thermal performance of the solar air heater designs triggered by improved jet stability

Abstract

In this experimental work, the thermal and thermohydraulic performance of two novel designs of solar air heater employing confined submerged circular air jet arrays is investigated. Design-I consists of a wavy transparent acrylic sheet for air jet impingement from the top side of the absorber plate, while Design-II consists of a wavy metallic impinging plate for air jet impingement from the bottom side of the absorber plate. Both solar air heaters are designed to induce stable air jets for the range of mass flow rates ranging from 0.01 kg/s to 0.04 kg/s. Obtained results presented the superiority of Design-I in terms of heat transfer augmentation to air and compactness in size compared to Design-II. The thermal and thermohydraulic efficiency of Design-I corresponding to the mass flow rate of 0.04 kg/s is obtained as 89.72% and 89.16%, which is found to be 24.33% and 24.52% high compared to Design-II, respectively. In addition, the recommended value of the mass flow rate is obtained as 0.03 kg/s on the basis of thermohydraulic efficiency and operating cost, that presents an operating cost of 0.109 INR/kWh for Design-I. This work is extended for the numerical investigation to reveal the associated physics of fluid and heat transfer in solar air heater designs. In numerical investigation, 3D structured O-grid mesh is generated and RNG k-ε turbulence model is employed using the commercial CFD tool.