Hindawi Publishing Corporation Journal of Renewable Energy Volume 2013, Article ID 151578, 13 pages http://dx.doi.org/10.1155/2013/151578 Research Article Thermal Performance of Solar Air Heater Having Absorber Plate with V-Down Discrete Rib Roughness for Space-Heating Applications Rajendra Karwa and V. Srivastava Department of Mechanical Engineering, Faculty of Engineering & Architecture, Jai Narain Vyas University, Jodhpur 342 011, Rajasthan, India Correspondence should be addressed to Rajendra Karwa; karwa_r@yahoo.com Received 15 August 2012; Revised 29 October 2012; Accepted 30 October 2012 Academic Editor: Zuhal Oktay Copyright © 2013 R. Karwa and V. Srivastava. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e paper presents results of thermal performance analysis of a solar air heater with v-down discrete rib roughness on the air �ow side of the absorber plate, which supplies heated air for space heating applications. e air heater operates in a closed loop mode with inlet air at a �xed temperature of 295 K from the conditional space. e ambient temperature varied from 278 K to 288 K corresponding to the winter season of Western Rajasthan, India. e results of the analysis are presented in the form of performance plots, which can be utili�ed by a designer for calculating desired air �ow 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. e 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 �owing through the collector duct is one of the key parameters. Arti�cial roughness on heat transferring surface of asym- metrically heated high aspect ratio rectangular ducts, mod- eled as solar air heater ducts, has been shown to signi�cantly enhance the heat transfer coefficient with minimum pressure loss penalty because the roughness creates turbulence near the heat transferring surface only [1–7]. us such roughness can be used on the air �ow 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(b) depicts the basic roughness geometries com- piled 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. Arti�cial roughness on a heat transferring surface creates local wall turbulence due to a complex �ow 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]. e enhancement in the case of the transverse ribs (at   ) occurs only due to the �ow, separated at the ribs, reattaching between the ribs while it has been attributed both to the reattachment effect and the secondary �ow of the air induced by the rib inclination in the case of inclined and v-pattern ribs [7, 9] as depicted in Figure 2. e secondary �ow (movement of heated air in contact with the plate surface) is along the plate surface to the side wall in the case of the inclined ribs. is exposes the heated plate to a relatively lower temperature air of the axial or primary �ow over the ribs. In the case of v-down ribs, there are two contradictory effects: the secondary �ow is towards the central axis where it interacts with the axial �ow