ABSTRACT

The working medium is air in a solar air heater (SAH) and because of its low heat-transfer coefficient, SAH results in poor performance. By placing artificial-roughness over the heat-collector plate, the performance of a SAH can be improved significantly. The improvement in thermal and hydraulic performance by providing multiple-arc-rib roughnesses patterns with the gap is discussed and generalized correlations are developed for Nusselt number and friction factor based on results collected from the experimentation (under steady condition). In total seven parameters were considered to study heat transfer and friction characteristics, that is, Reynolds number, rib-pitch, rib-height, number of gaps, arc-attack angle, rib, and gap width. In comparison to smooth collector-plate type of solar air heater, the 5.76 and 6.05 times higher Nusselt number and friction factor obtained in the proposed roughened SAH. Besides this, the developed mathematical expression for Nusselt number and friction factor shows close-fit with the experimental data under the error band of only 10 and 12%, respectively.

摘要

太阳能空气加热器（SAH）中的工作介质是空气，由于其低传热系数，SAH导致性能不佳。通过在集热板上放置人工粗糙度，可以显着提高 SAH 的性能。讨论了通过提供带间隙的多弧肋粗糙度模式来改善热性能和水力性能，并根据从实验中收集的结果（在稳定条件下）开发了努塞尔数和摩擦系数的广义相关性。总共考虑了七个参数来研究传热和摩擦特性，即雷诺数、肋间距、肋高度、间隙数、弧攻角、肋和间隙宽度。与光滑集热板式太阳能空气加热器相比，5.76 和 6. 在提议的粗糙 SAH 中获得的努塞尔数和摩擦系数高 05 倍。除此之外，所开发的努塞尔数和摩擦系数的数学表达式分别在仅 10% 和 12% 的误差带下与实验数据非常吻合。