Numerical investigation of reversed flow solar air heater roughened with circular and triangular shaped tubes

The roughness geometry has been introduced to improve the rate of heat transfer in a solar air heater duct. In the current work, circular and triangular shape geometries are used as roughness elements in the rectangular channel to enhance the thermal performance of reversed flow solar air heater (RFSAH). The important parameters selected for the research are Reynolds number (Re) varies from 5000 to 18000 (5 values), pitch ratio (P/e) varies from 4 to 12 (5 values), and height ratio (e/D) from 0.0392 to 0.1571 (4 values). A 2D CFD model was developed using ANSYS (Fluent 2022R1), and simulation was performed using k-ε (RNG) turbulence model and validated with one set of experimental results for smooth duct and previous research. The findings revealed that the highest value of heat transfer was augmented about 2.18 times and 2.35 times for circular and triangular roughness geometry respectively, as compared to the smooth channel at a Reynolds number of 12000. The thermohydraulic performance factor (TPF) is 1.58 and 1.7 at pitch ratios of 6 and 5 for circular and triangular roughness geometry respectively, at Re of 12000.