Solar air heaters are advantageous for space heating, industrial applications, and agricultural drying due to their cost-effectiveness and low maintenance. However, smooth absorber plates in solar air heaters have lower thermal efficiency compared to roughened plates due to limited convective heat transfer. Improving efficiency while minimizing heat loss is crucial. This study explores the effects of geometrical and operational parameters, including roughness, on the efficiency of a solar air heater with an inline-pattern teardrop dimple imprinted absorber plate. The research experimentally evaluates teardrop dimple imprinted solar air heater performance by varying pitch ratio (PT/PL) and airflow rate <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="42108_2025_336_Article_IEq1.gif" Format="GIF" Height="24" Rendition="HTML" Resolution="72" Type="Linedraw" Width="40" /> </InlineMediaObject> <EquationSource Format="TEX">$\left({\dot{M}}_{\text{a}}\right)$</EquationSource> <EquationSource Format="MATHML"><math> <mfenced close=")" open="("> <msub> <mover accent="true"> <mi>M</mi> <mo>˙</mo> </mover> <mtext>a</mtext> </msub> </mfenced> </math></EquationSource> </InlineEquation>. Five airflow rates (0.010, 0.020, 0.031, 0.042, and 0.053 kg/s) corresponding to Reynolds numbers of 1971.66 to 11,013.10, and three pitch ratios (0.88, 1, and 1.33) were tested. Key performance metrics: efficiencies, heat removal factors (Fo, FR), collector efficiency (F'), global thermal heat loss coefficient (ULos), Nusselt number <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="42108_2025_336_Article_IEq2.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="TEX">$\left(\overline{Nu }\right)$</EquationSource> <EquationSource Format="MATHML"><math> <mfenced close=")" open="("> <mover> <mrow> <mi mathvariant="italic">Nu</mi> </mrow> <mo>¯</mo> </mover> </mfenced> </math></EquationSource> </InlineEquation>, and friction factor <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="42108_2025_336_Article_IEq3.gif" Format="GIF" Height="22" Rendition="HTML" Resolution="72" Type="Linedraw" Width="28" /> </InlineMediaObject> <EquationSource Format="TEX">$\left(\overline{f }\right)$</EquationSource> <EquationSource Format="MATHML"><math> <mfenced close=")" open="("> <mover> <mi>f</mi> <mo>¯</mo> </mover> </mfenced> </math></EquationSource> </InlineEquation> were evaluated under various conditions. Results show that teardrop dimple imprinted solar air heater surpasses flat plate solar air heaters in efficiency, heat removal rate, and lower global thermal loss. Particularly, the Nusselt number for teardrop dimple imprinted solar air heater at a pitch ratio of 0.88 was 1.10–1.32 times and 1.30–1.58 times higher than at pitch ratios of 1 and 1.33, respectively, and 1.96–2.78 times greater than flat plate solar air heaters. These findings underscore teardrop dimple imprinted solar air heater’s potential for enhancing thermal performance in solar air heating applications.

Influence of geometry and operating parameters on thermohydraulic and thermal characteristics of the teardrop-imprinted solar air heater

期刊论文
发表日期：

2025年3月4日

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S. Panda,
R. Kumar

摘要

Solar air heaters are advantageous for space heating, industrial applications, and agricultural drying due to their cost-effectiveness and low maintenance. However, smooth absorber plates in solar air heaters have lower thermal efficiency compared to roughened plates due to limited convective heat transfer. Improving efficiency while minimizing heat loss is crucial. This study explores the effects of geometrical and operational parameters, including roughness, on the efficiency of a solar air heater with an inline-pattern teardrop dimple imprinted absorber plate. The research experimentally evaluates teardrop dimple imprinted solar air heater performance by varying pitch ratio (P_T/P_L) and airflow rate $\left({\dot{M}}_{\text{a}}\right)$ $({\dot{M}}_{a})$ . Five airflow rates (0.010, 0.020, 0.031, 0.042, and 0.053 kg/s) corresponding to Reynolds numbers of 1971.66 to 11,013.10, and three pitch ratios (0.88, 1, and 1.33) were tested. Key performance metrics: efficiencies, heat removal factors (F_o, F_R), collector efficiency (F'), global thermal heat loss coefficient (U_Los), Nusselt number $\left(\overline{Nu }\right)$ $(\bar{Nu})$ , and friction factor $\left(\overline{f }\right)$ $(\bar{f})$ were evaluated under various conditions. Results show that teardrop dimple imprinted solar air heater surpasses flat plate solar air heaters in efficiency, heat removal rate, and lower global thermal loss. Particularly, the Nusselt number for teardrop dimple imprinted solar air heater at a pitch ratio of 0.88 was 1.10–1.32 times and 1.30–1.58 times higher than at pitch ratios of 1 and 1.33, respectively, and 1.96–2.78 times greater than flat plate solar air heaters. These findings underscore teardrop dimple imprinted solar air heater’s potential for enhancing thermal performance in solar air heating applications.