Effect of Parametric Uncertainties, Variations, and Tolerances on Thermohydraulic Performance of Flat Plate Solar Air Heater

The paper presents results of an analysis carried out using a mathematical model to find the effect of the uncertainties, variations, and tolerances in design and ambient parameters on the thermohydraulic performance of flat plate solar air heater. Analysis shows that, for the range of flow rates considered, a duct height of 10？mm is preferred from the thermohydraulic consideration. The thermal efficiency changes by about 2.6% on variation in the wind heat transfer coefficient, ±5？K variation in sky temperature affects the efficiency by about ±1.3%, and solar insolation variation from 500 to 1000？Wm？2 affects the efficiency by about ？1.5 to 1.3% at the lowest flow rate of 0.01？kgs？1？m？2 of the absorber plate with black paint. In general, these effects reduce with increase in flow rate and are lower for collector with selective coating on the absorber plate surface. The tolerances in the duct height and absorber plate emissivity should be small while positive tolerance of 3° in the collector slope for winter operation and ±3° for year round operation, and a positive tolerance for the gap between the absorber plate and glass cover at nominal value of 40？mm are recommended. 1. Introduction Solar energy, a renewable energy source, is readily converted into heat using a solar collector. The simplest and the most common design of a solar collector used to heat air for space heating, drying applications, or similar industrial application is shown in Figure 1(a), wherein the air is propelled through the rectangular duct of the air heater behind a flat aluminium or steel absorber plate with the help of a blower or fan. One or two transparent covers are placed at a gap over the absorber plate to arrest the heat loss in the upward direction from the heated absorber plate. The collector is usually installed facing south to receive maximum solar radiation. The sun-facing side of the absorber plate is painted black for high solar radiation absorptance. Figure 1: (a) Schematic diagram of a solar air heater and (b) heat balance. Figure 1(b) depicts the energy flow in a solar air heater with single glass cover. A part of the solar radiation absorbed at the absorber plate surface is transferred to the air flowing through the air heater duct and is the useful heat gain. Remaining energy is lost to the surroundings and sky through the glass cover, back and edges of the air heater, and is termed as heat loss from the collector. The heat transfers from the heated absorber plate to the inner surface of the glass cover by free convection and radiation, through the cover by