oa Design and investigation of a single air collector

Air collectors (also called air heaters) may be considered as adiabatic radiative heat exchangers allowing the transformation of the solar radiant energy into heat that is transferred convectively from the absorber to the working fluid. There are basically two types of air collectors. The simple design flat absorber plate with the working fluid flowing over or/and under flowing it, and the absorber-matrix air collector with the working fluid flowing through it. Technical problems linked with usable materials are encountered when using matrix air heaters. This leads to high costs when trying to use performance matrix products such as wire screens. Flat plate collectors of conventional design usually feature a black painted metal plate representing the radiation absorber with the air flowing over or under the plate thereby receiving the heat by convection. High mass flow rates and small flow channel heights are necessary in order to achieve satisfactory heat transfer rate from the absorber to the air stream. Matrix collectors offer large heat transfer area to volume ratios and therefore higher heat transfer rates. Several researchers took up the concept of using porous materials as absorbers. The present investigation reports the development and testing of on an efficient singleglazed corrugated plate absorber air heater. It is developed to toke advantage of the design simplicity and relatively low cost of conventional air collectors. It mainly consists of a corrugated sheet of black-painted galvanized steel

This type of collector can be used for drying or heating applications. Design betterments applied to such single glazed air heater has led to an improvement of the thermal performance with higher heat transfer rates to the air. The use of the absorber in the middle of the collector led to an improvement of 22% compared to the bottom-placed absorber taken as a reference. More improvements may be achieved if the absorber is inclined by an angle of 30° allowing more heat to be recovered (an improvement of 20% to 30% is usually expected). Drilling the mid-placed absorber would lead to a better mixing of the air and may result in higher temperature rises.