Thermal performance augmentation in a solar air heater with twisted multiple V-baffles

A 3D numerical investigation of thermal performance augmentation of a twisted multiple V-baffles in a solar air heater is presented. Two important functions of the twisted multiple V-baffles are to generate multiple impinging flows upon the wall to improve the convective heat transfer (compared with a smooth channel) and reduce the pressure drop (compared with a typical multiple V-baffles). These outcomes enhance thermal performance. The results of heat transfer (in terms of a Nusselt number ratio), pressure drop (in terms of a friction factor ratio) and thermal performance (in terms of a thermal enhancement factor) of a twisted multiple V-baffles were compared with both a smooth channel and a typical multiple V-baffles. Eighty-one cases including those with a pitch ratio of PR = 0.4-2.0; blockage ratio, BR = 0.10-0.20; angle of attack, alpha = 30o - 60o and a fixed number of twisted loops, n = 2, were investigated in turbulent flow. The results revealed that the twisted multiple V-baffles created multiple impinging jets at the heated wall and help accelerate heat transfer between the wall and the fluid. Compared to a typical multiple V-baffles, the friction factor showed a large decrease while the Nusselt number was slightly lower leading to better thermal performance. Over the study range, PR = 0.4, BR = 0.20, and alpha = 60o appeared to yield the highest thermal enhancement factor, 2.81 at Re = 3000.