Efficiencies assessment of an indoor designed solar air heater characterized by V baffle blocks having staggered racetrack-shaped perforation geometry

Abstract

The outcome of an experimental study carried to maximize the thermal efficiency of a rectangular section solar air heater duct having V-baffle blocks with staggered racetrack-shaped openings are presented in this paper. The investigation encompasses the methodology to determine first the baffle blocks' optimum parameters yielding the thermohydraulic performance factor (η) value greater than unity and then finalizing the 'best optimum parameters' that maximize the duct's thermal (ηth) and effective (ηeff) efficiencies. The thermal and fluid flow characteristics are studied under a constant heat flux at the duct's top wall for turbulent airflow condition. The effect of relative roughness height (e ⁄H) ranging from 0.4 to 0.7, relative pitch (p ⁄e) ranging from 2 to 10 and Reynolds number (Re) ranging from 5000 to 15000 are investigated on 45° V-baffle blocks with apex pointing both in downstream and upstream directions. The result shows that the air jets issuing through racetrack openings intensify the turbulence in the wake of baffle blocks leading to a substantial rise in Nusselt number (Nu) and friction factor (f) relative to smooth duct. The V-down baffle blocks obtain the maximum enhancement of Nusselt number and friction factor over the smooth duct with range 1.358 to 4.559 and 4.03 to 39.07, respectively. The V-down baffle blocks' parameters, e/H of 0.5, p/e of 4 and Re of 13021, provides a maximum value of thermohydraulic performance factor as 1.435. V-up baffle block with e/H of 0.7, p/e of 6 at Re of 12,322 reports the highest thermal and effective efficiencies values as 96.6% and 91.8%, respectively.