# Energy-Based Thermo-Hydraulic Performance of Roughened Absorber in Solar Air Heater Duct
## 6 Conclusions  
An analytical study was performed to estimate the exergy efficiency of an SAH absorber surface with conical protrusion ribs. The exergy efficiency of the roughened absorber surface was compared to the exergy efficiency of the smooth solar air heater, operating with comparable conditions, to determine the enhancement factor. The parameters of the conical protrusion ribs were tuned for optimal exergy efficiency based on the findings. The study's key findings are listed below:  
1. The roughness of the conical protrusion ribs has a substantial impact on the exergy efficiency of the SAH duct. At \(e/D=0.044\) and \(p/e=10\), the maximum exergy efficiency was found to be 0.0202.  
2. Exergy efficiency is a function of solar insolation as well. When the solar insolation is increased from 600 to 1000 W/m\({}^{2}\), the maximum exergy efficiency increases from 0.0122 to 0.0185.  
3. Exergy efficiency is a strong function of the Reynolds number; higher Reynolds numbers always result in a lower value of exergy efficiency, regardless of the rib parameters, due to high friction factors and pumping power, while, for low Reynolds numbers, the exact values of rib parameters determine the exergy efficiency.  
4. There is a set of ideal conical protrusion rib parameters that match certain operating conditions, resulting in the highest exergy efficiency. The optimum rib height is determined to be 0.020, 0.0289, 0.036 and 0.044 when the temperature increase parameter is in the respective ranges of 0.0076-0.0087 K\(\cdot\)m\({}^{2}\)/W, 0.0087-0.0104 K\(\cdot\)m\({}^{2}\)/W, 0.0104-0.0111 K\(\cdot\)m\({}^{2}\)/W and above 0.0111 K\(\cdot\)m\({}^{2}\)/W. Similarly, the rib pitches of 12 and 10 are determined to be optimum solutions when the temperature increase parameter is in the respective range of 0.0076-0.0092 K\(\cdot\)m\({}^{2}\)/W and above 0.0092 K\(\cdot\)m\({}^{2}\)/W.  
5. The temperature increase parameter affects the optimum rib height and rib pitch, and the range of temperature increase parameter for optimum ribs parameters changes significantly with solar insolation.  
6. When the temperature increase parameter is \(T/I>0.0141\) K\(\cdot\)m\({}^{2}\)/W, a unique optimum combination of rib height of \(e/D=0.044\) and rib pitch of \(p/e=10\) is found to be independent from the value of solar insolation.  
The analysis of the solar air heater thermo-hydraulic performance was used to find the optimum parameters of the conical rib protrusion ribs for the highest exergy efficiency under  
Figure 14: Optimized rib pitch.  
certain operating circumstances. The exergy efficiency characteristics will aid the designer in determining the conical protrusion rib specifications under various operating situations.  
Conceptualization, T.A.; methodology, T.A. and M.I.H.S.; software, H.A.; validation, T.A., M.I.H.S. and H.A.; formal analysis, P.B.; investigation, T.A., H.A. and K.S.; resources, T.A. and M.I.H.S.; data curation, H.A. and M.A.A.; writing--original draft preparation, T.A.; writing--review and editing, M.I.H.S., H.A. and K.S.; visualization, T.A. and M.A.A.; supervision, T.A.; project administration, T.A. and H.A.; funding acquisition, P.B. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Data Availability Statement: Data available on request.  
The authors declare no conflict of interest.