Abstract Recent research has shown that flat plate double-pass solar air heaters (DPSAH) exhibit higher thermal performance compared to conventional flat plate single-pass solar air heaters (SPSAH). However, scientific literature on design and performance evaluation of a curved DPSAH is scarce. In this paper, we systematically investigated various designs of DPSAH and reported its performance characteristics using a validated numerical model. Higher outlet air temperature by about 5 °C was observed when the DPSAH absorber plate is located at the mid of the insulating wall and transparent glass cover. Furthermore, putting asymmetric semi-circular roughened surfaces shows better performance than symmetric circular shapes as the reattachment of vortices with the absorber plate is more frequent in the former case. Two new correlations were developed for Nusselt number ( N u ) and friction factor ( f ) as a function of Reynolds number ( R e ) and relative roughness height ( d H ) . The values of N u and f obtained from the developed correlations agree well with data from the model.

中文翻译：

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双通道弧形太阳能空气加热器的高效设计

摘要 最近的研究表明，与传统的平板单通道太阳能空气加热器（SPSAH）相比，平板双通道太阳能空气加热器（DPSAH）具有更高的热性能。然而，关于弯曲 DPSAH 的设计和性能评估的科学文献很少。在本文中，我们系统地研究了 DPSAH 的各种设计，并使用经过验证的数值模型报告了其性能特征。当 DPSAH 吸收板位于绝缘壁和透明玻璃盖的中间时，观察到更高的出口空气温度约 5°C。此外，放置非对称半圆形粗糙表面比对称圆形具有更好的性能，因为在前一种情况下涡流与吸收板的重新附着更为频繁。作为雷诺数 (R e) 和相对粗糙度高度 (d H) 的函数，为努塞尔数 (N u) 和摩擦系数 (f) 开发了两个新的相关性。从开发的相关性中获得的 N u 和 f 的值与来自模型的数据非常吻合。