THE EFFECT OF CORRUGATION ON HEAT TRANSFER AND PRESSURE DROP IN A SOLAR AIR HEATER: A NUMERICAL INVESTIGATION

Abstract

Solar is a green source of energy. The foremost objective is the efficient heating of air by enhancing the thermal efficiency of solar air heaters. Even a small enhancement in the efficiency will increase its life, power output and reduce its operating cost. In the current study, a double-pass, trapezoidal cross-sectioned channel with four different arrangements of corrugations at the bottom and trailing walls of the outlet pass is numerically investigated at the Re number equal to 9400. Corrugations are of trapezoidal shape having the pitch-to-height ratio (<i>p/e</i>) equal to 4. Four different arrangements of trapezoidal corrugation at the bottom wall and the trailing wall of the outlet pass is investigated. When compared to a smooth trapezoidal channel, it turns out that an inline arrangement of corrugation enhances heat transfer by 33&#37; while increases the friction factor by up to 27&#37;. Also, compared to a staggered ribbed trapezoidal channel, inline corrugation patterns improve heat transfer by 7&#37; and reduce friction by up to 16&#37;. Corrugation is a better alternative to ribs. Inline and staggered arrangements give similar enhancement in the thermal performance factor. As the space for passive cooling ducts in solar air heaters is limited therefore concerns regarding fabrication and less mechanical strength arise. So an inline arrangement is selected as the optimum one. At the outlet pass, the thermal performance factor of 1.1 was achieved for the best configuration. The effect of increasing Reynolds number in the trapezoidal corrugated channel shows an increasing trend in Nu/Nu_o, pressure drop, and thermal performance factor.