The paper presents results of thermal performance analysis of a solar air heater with v-down discrete rib roughness on the air flow side of the absorber plate, which supplies heated air for space heating applications. The air heater operates in a closed loop mode with inlet air at a fixed temperature of 295？K from the conditional space. The ambient temperature varied from 278？K to 288？K corresponding to the winter season of Western Rajasthan, India. The results of the analysis are presented in the form of performance plots, which can be utilized by a designer for calculating desired air flow rate at different ambient temperature and solar insolation values. 1. Introduction Flat plate solar air heaters have been employed for space heating, drying, and similar industrial applications requiring heated air at low to moderate temperatures. The thermal efficiency of a solar air heater (collector) is a function of many design and operating parameters. Convective heat transfer coefficient between the absorber plate and air flowing through the collector duct is one of the key parameters. Artificial roughness on heat transferring surface of asymmetrically heated high aspect ratio rectangular ducts, modeled as solar air heater ducts, has been shown to significantly enhance the heat transfer coefficient with minimum pressure loss penalty because the roughness creates turbulence near the heat transferring surface only [1–7]. Thus such roughness can be used on the air flow side of the absorber plate of the solar air heaters as shown in Figure 1(a) for the improvement of their thermal efficiency. Figure 1: (a) Schematic diagram and longitudinal section of a solar air heater with roughened absorber plate, (b) roughness for solar air heater ducts: (i)–(iv) plan view, (v)–(vii) longitudinal section [ 8]. Figure 1(b) depicts the basic roughness geometries compiled by Karwa et al. [8], which includes different rib arrangements, such as transverse, angled, continuous, and discrete, in v-pattern for ribs of different shapes (circular, square, chamfered, wedge, etc.), and expanded metal wire mesh. Artificial roughness on a heat transferring surface creates local wall turbulence due to a complex flow structure depending on the shape and arrangement of the ribs and hence the degree of the heat transfer enhancement in both the heat transfer coefficient and friction factor also varies with the roughness type. Heat transfer enhancement in the case of the inclined or the v-pattern ribs has been reported to be higher than the transverse ribs [9]. The enhancement in the case of the
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