An experimental test rig is utilized to measure the effects of the flow configuration and particularly the rib geometry, on the thermal performances of solar air heaters. Since the heat transfer rate within the entry length is relatively high, the implementation of the ribs needs to be justified. Computational fluid dynamics simulations are also conducted to support the experiments and to provide detailed visualization of the flow field. The experimental data approves that the numerical simulation can estimate the heat transfer and pressure drop with reasonable accuracy. It appears from the results that achieving a particular spacing between the first ribs within the entry length, greater than the normal spacing in the fully developed region, yields a better performance. It is shown that in relatively short channels where the ratio of channel length to hydraulic diameter is small, the application of wider spacing in the entry length results in almost the same heat transfer rates, while it benefits from a much smaller pressure drop. In a presented case study, the application of irregular spacing improves the thermal performance of a flat plate solar collector by 11% compared to the collectors having ribs with regular spacing.

实验装置被用来测量流动结构，特别是肋的几何形状，对太阳能空气加热器的热性能的影响。由于进入长度内的传热率相对较高，因此需要证明肋的实施是合理的。还进行了计算流体动力学模拟，以支持实验并提供流场的详细可视化。实验数据证明，数值模拟可以合理地估计传热和压降。从结果看来，在进入长度内在第一肋之间实现特定的间隔大于在完全展开区域中的正常间隔，会产生更好的性能。结果表明，在通道长度与水力直径之比较小的相对较短的通道中，在入口长度中采用较宽的间距会导致几乎相同的传热速率，而这得益于较小的压降。在提出的案例研究中，与具有规则间距的肋条的集热器相比，不规则间距的应用将平板太阳能集热器的热性能提高了11％。