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<p>Although solar air heaters (SAHs) are simple to install and inexpensive, requiring no advanced technology to operate, their thermal efficiency is relatively low. However, many scientists are still working to improve their thermal performance (TP) through various techniques, given their diverse applications in both residential and industrial settings. One such method involves using a roughened airflow channel with different shapes and geometries. This creates higher turbulence in the fluid flow, thereby improving heat transfer rates (HTRs) (a positive effect), while increasing friction factor (a negative effect). Therefore, the biggest challenge is how to improve HTRs while simultaneously reducing friction factor. The aim and novelty of this work focus on the developments and updates in the overall TP of SAHs achieved when using a roughened airflow duct during only the last decade of the twenty-first century, unlike many other researchers. This allows researchers in this field to build upon the latest updates and start where others have left off. This work is also notable for including in detail a wide range of roughness configurations and focusing heavily on comparing different roughening methods and their impact on improving Nusselt number (Nu) as well as on the friction factor (<i>f</i>). Based on the findings of this review, the study recommends to operate the SAH with perforated rectangular fins as roughing elements, as it obtained the largest thermohydraulic performance parameter (THPP) of all the systems reviewed, of 5.1. When comparing the SAHs based on Nu improvement, the study recommends to use SAHs equipped with punched baffles of delta-shaped winglets, as it achieved a Nu improvement (HTRs) of 47.7 times compared to smooth duct, the highest Nu improvement ever the author knows. Regarding the improvement in the friction factor, the study recommends using the frustum jet impingement roughness integrated into the SAH, as it achieved the highest friction factor improvement of 13.9 times compared to smooth duct. Based on all of the above, it can be concluded that it is advisable to operate the SAHs that combine perforated rectangular fins, punched baffles of delta-shaped winglets, and frustum jet impingement because they achieve the better overall TP.</p>

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Current progress in rough solar air heaters

  • 期刊论文

  • 发表日期：

    2025年12月22日

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  • E. El-Bialy

摘要

Although solar air heaters (SAHs) are simple to install and inexpensive, requiring no advanced technology to operate, their thermal efficiency is relatively low. However, many scientists are still working to improve their thermal performance (TP) through various techniques, given their diverse applications in both residential and industrial settings. One such method involves using a roughened airflow channel with different shapes and geometries. This creates higher turbulence in the fluid flow, thereby improving heat transfer rates (HTRs) (a positive effect), while increasing friction factor (a negative effect). Therefore, the biggest challenge is how to improve HTRs while simultaneously reducing friction factor. The aim and novelty of this work focus on the developments and updates in the overall TP of SAHs achieved when using a roughened airflow duct during only the last decade of the twenty-first century, unlike many other researchers. This allows researchers in this field to build upon the latest updates and start where others have left off. This work is also notable for including in detail a wide range of roughness configurations and focusing heavily on comparing different roughening methods and their impact on improving Nusselt number (Nu) as well as on the friction factor (f). Based on the findings of this review, the study recommends to operate the SAH with perforated rectangular fins as roughing elements, as it obtained the largest thermohydraulic performance parameter (THPP) of all the systems reviewed, of 5.1. When comparing the SAHs based on Nu improvement, the study recommends to use SAHs equipped with punched baffles of delta-shaped winglets, as it achieved a Nu improvement (HTRs) of 47.7 times compared to smooth duct, the highest Nu improvement ever the author knows. Regarding the improvement in the friction factor, the study recommends using the frustum jet impingement roughness integrated into the SAH, as it achieved the highest friction factor improvement of 13.9 times compared to smooth duct. Based on all of the above, it can be concluded that it is advisable to operate the SAHs that combine perforated rectangular fins, punched baffles of delta-shaped winglets, and frustum jet impingement because they achieve the better overall TP.