ABSTRACT

This research paper aims to investigate the effect of frustum shape roughness geometry on the thermal characteristic (Nusselt no. and friction factor) of solar air heaters (SAH). The study includes experimental and numerical investigation of a solar air heater equipped with frustum roughened absorber plate under varying operating conditions. Frustum shape roughness element produced more disturbances and greater mixing of primary and secondary flow that resulted in greater augmentation in thermal characteristics of SAH. The investigation was conducted in varying Reynolds number range of 2500 -12,500. Dimensionless parameter for Frustrum shaped roughness is varied as relative frustum height (e/D_h) 0.013–0.054, relative frustum pitch (p/e) 8–14, Relative frustum height to base diameter (e/d₁) 0.37–0.75 and relative frustum diametral ratio (d₁/d₂) 1–3. To save time and resources a three-dimensional numerical simulation was also performed. This simulation helped to visualize flow field behavior with the help of streamline, temperature, turbulence kinetic energy and pressure contours. Maximum performance for roughened system was obtained at optimum value of flow and geometric configuration within the range of investigated parameters. The geometric orientation of proposed roughness geometry produced tremendous rise in Nusselt number (Nu) with an acceptable rise in friction (f). Maximum enhancement in Nu for varying p/e, e/D_h, e/d₁, and d₁/d₂ was, 4.58, 5.21, 6.62 and 6.09 times and that of friction was 5.59, 4.69, 4.92 and 4.66 times respectively over conventional smooth SAH.

摘要

本研究论文旨在研究平截头体形状粗糙度几何形状对太阳能空气加热器（SAH）热特性（努塞尔数和摩擦系数）的影响。该研究包括对配备有截锥体粗糙吸热板的太阳能空气加热器在不同操作条件下的实验和数值研究。截锥体形状粗糙度元素产生更多的扰动以及初级流和次级流的更大混合，从而导致 SAH 的热特性更大程度地增强。该调查是在 2500 -12,500 的不同雷诺数范围内进行的。平截头体形状粗糙度的无量纲参数变化为相对平截头体高度 (e/D _h ) 0.013–0.054，相对平截头体节距 (p/e) 8–14，相对平截头体高度与基底直径 (e/d ₁₎) 0.37–0.75 和相对平截头体直径比 (d ₁ /d ₂ ) 1–3。为了节省时间和资源，还进行了三维数值模拟。该模拟借助流线、温度、湍流动能和压力等值线，帮助可视化流场行为。粗糙化系统的最大性能是在研究参数范围内的最佳流量和几何配置值下获得的。所提出的粗糙度几何形状的几何方向导致努塞尔数 (Nu) 大幅上升，摩擦力 (f) 上升可接受。对于不同的 p/e、e/D _h、e/d ₁和 d ₁ /d _{2 ，Nu 的最大增强}与传统光滑SAH相比，其摩擦力分别为4.58、5.21、6.62和6.09倍，摩擦力分别为5.59、4.69、4.92和4.66倍。