Development of an energy-efficient indirect type dryer using a triangular duct solar air heater with the synergistic effect of pin-fins and discrete V-ribs: A 3-D CFD study

A high-performance triangular duct solar air heater (TSAH) incorporating discrete V-ribs and pin-fins is numerically analysed to enhance thermo-hydraulic and drying performance for indirect-type solar dryers (ITSD). Three-dimensional CFD simulations are performed for 5000 ≤ Re ≤ 15,000, exploring the effects of pitch ratio (P/e = 5-15), gap width (g/e = 0.2-0.8), and solid/porous pin-fins. Introducing a gap at the V-rib apex increases local turbulence and secondary flow interactions, yielding a Nusselt number enhancement of 3.36 and a friction factor increase of 2.98 for g/e = 0.4 at Re = 5000, resulting in a THPP of 2.35. Integrating porous pin-fins further enhances vortex mixing and thermal interaction, achieving a maximum THPP of 2.68, which surpasses the existing rib geometries. When applied to mushroom drying in an ITSD, the enhanced TSAH delivers higher outlet air temperatures and stronger secondary flow intensity, leading to a 66% reduction in drying time and a 54% increase in effective diffusivity compared to a smooth-plate SAH. The results demonstrate that combining discrete V-ribs with porous pin-fins offers a synergistic improvement in heat transfer, pressure drop balance, and drying kinetics, enabling energy-efficient drying applications.