# Energy-Based Thermo-Hydraulic Performance of Roughened Absorber in Solar Air Heater Duct  
[PERSON]  
1 CSIR-Central Building Research Institute Roorkee, Roorkee 247667, India; [EMAIL_ADDRESS]  
[PERSON]  
3 Mechanical Engineering Department, King Saud University, Riyadh 11421, Saudi Arabia; [EMAIL_ADDRESS]  
[PERSON]  
3 Mechanical Engineering Department, King Saud University, Riyadh 11421, Saudi Arabia; [EMAIL_ADDRESS]  
[PERSON]  
4 Department of Industrial Engineering, College of Engineering, Prince Sattam Bin Abdulaziz University, Al-Khanqi 16273, Saudi Arabia; [EMAIL_ADDRESS]  
[PERSON]  
5 Faculty of Engineering, University of Rijeka, 51000 Rijeka, Croatia  
result, research is concentrating on the creation of techniques that are both energy efficient and economically viable. For instance, roughened absorber plates can be used to improve the heat exchange between absorber plate and air flow [5]. Wires can be attached in a variety of ways to achieve surface roughness on the absorber plate: ribs with transverse wires [6; 7], angle wire ribs [8], V-shaped wire ribs [9], multi V-shaped ribs [10], discrete V-shaped ribs [11], multi V-shaped ribs with gaps [12], L-shaped ribs [13], multi arc-shaped ribs with gaps [14] and S-shaped ribs with gaps [15]. Heat transfer enhancement by chamfered ribs with grooves [16; 17] and rectangular ribs with grooves [18; 19] has also been explored. By locally promoting turbulence in the air flow and disrupting the sub-laminar layer on the absorber surface by means of the roughness on the absorber plate, thermal performance can be improved. Heat transfer can be further increased by employing ribs with large height. Large-height ribs create more turbulence in the air flow, but also low circulation regions and hot zones in the vicinity of ribs. The hot zones are suppressed by employing the perforated ribs. Air jets issuing through these perforations strike on the hot zones and promote the flow turbulence. Perforated ribs also reduce the pressure drop significantly [20; 21]. The performance of solar air heaters with dimple ribs on the absorber was investigated by [PERSON] and [PERSON] [22]. The following parameters of dimple ribs were employed: a relative rib pitch between 0.018 and 0.037 and relative rib height between 8 and 12. The results revealed that dimple ribs lead to significant heat transfer enhancement without an excessive pressure drop penalty. In a similar manner, [PERSON] et al. [23; 24] investigated the performance of arc-shaped dimple ribs on the absorber using the experimental approach with the following rib parameters: a relative rib height between 0.021 and 0.036, relative rib pitch between 10 and 20 and arc angle between 45\({}^{\circ}\) and 75\({}^{\circ}\). The arc-shaped dimple ribs achieved considerable heat transfer enhancement as a result of flow separation, vortex generation and vortex shading in the flow. Another study [25] examined the effects of relative print dia of spherical dimple ribs, relative long way length and relative short way length of the absorber. It was determined that friction factors and Nusselt numbers are more than 2.2 and 3.2 times higher than in conventional smooth surfaces, respectively. Similarly, air mass flow rates were varied in the range between 0.009 and 0.0028 kg/s to analyze the effect on dimple ribs. The increase of air temperature in the air duct with dimple ribs was 4.6 \({}^{\circ}\)C compared to a conventional smooth duct with air mass flow of 0.009 kg/s [26]. Semi-spherical protrusion ribs have been exploited to study further the improvement of SAH performance. The effects of relative rib pitch and rib height, as well as the angle of attack, were studied in [27]. In the continuation of a similar work on protrusion ribs, the author of [28] designed a new conical protrusion rib and numerically investigated its performance in terms of friction factors and Nusselt numbers. The conical protrusion ribs were studied for relative rib pitches between 6 and 12 and relative rib heights between 0.020 and 0.044.