Thermal performance enhancement in a solar air heater fitted with flapped V-baffles: Numerical study

Considering solar energy equipment, a solar air heater is an engineering equipment that is widely used today. To get the most benefit from energy use, thermal performance enhancement of the equipment is very important. The paper focuses on enhancing thermal performance using passive technique, generally by using vortex generators (VG). The energy costs can be effectively managed by VG as well as improving thermal performance if the VG was optimally designed. The effect of flapped V-baffles (FVB) on thermal performance enhancement in a solar air heater in the turbulent flow regime was numerically investigated. The finite volume method using the SIMPLE algorithm was used to resolve the problem. The goal was to enhance the thermal performance (in terms of the thermal enhancement factor, TEF) by increasing the heat transfer together with reducing the pressure loss, compared with a conventional V-baffles (CVB). FVB with blockage ratios (BR) range of 0.1-0.3 and flapped angles ((3) range of 5 degrees-30 degrees were investigated. The constant parameters included the attack angle of (alpha) at 30 degrees, hole number (n) at 3, hole diameter ratio (dR) at 0.5 and pitch ratio (PR) at 1.0. V-baffles having holes without the flap (HVB) were also compared for all BR values. The results revealed that the FVB created the combination between the main vortex flow and an impinging jet flow (secondary flow). The impinging jet flow was generated by the holes having flaps and helped to decrease the dead zone at the heated wall behind the baffles, leading to an increase in the convective heat transfer. Moreover, the pressure loss was reduced due to the holes. Thus, the TEF can be improved when compared with the CVB. The rise of (3 for the FVB led to decreasing on Nu/Nu0, f/f0 and TEF while the increasing of BR gave the opposite. The fluid flow vies the holes without the flaps directly disrupted the main vortex flow led to decreasing the strengthened flow, both the Nu/Nu0 and TEF decreased. The FVB provided the Nu/Nu0, f/f0 and TEF by around 3.56-5.89 (higher than the CVB and HVB by around 1.45-21.59 % and 0.23-17.37 %, respectively), 5.14-48.16 (lower than the CVB by around 0.64-40.41 %) and 1.57-2.57 (higher than the CVB and HVB by around 3.52-28.43 % and 0.05-6.26 %, respectively). The FVB at (3 = 5 degrees, PR = 1.0 and BR = 0.1 gave the highest Nu/Nu0 and TEF at about 4.07 and 2.57 at Re = 4000, respectively.