Thermal Performance of a Counter-Flow Double-Pass Solar Air Heater With The Steady and Pulsating Flow

Abstract

 The tubular solar absorber is placed perpendicularly to the direction of airflow.  Pulsating flow increases the thermal performance by up to 15.2%  Thermal performance is directly proportional to the pulsating frequency.The present work studied the influence of pulsating flow as an active method on the thermal performance of a double-pass solar air heater with a tubular solar absorber. A ball valve has been used as a pulse generator mounted at the downstream flow of the solar air heater. The experiments were under indoor conditions with a constant heat flux of 1000 W/m 2 , and different air mass flow rates ranged from 0.01 to 0.03 kg/s. Moreover, the study covered three pulsation frequencies varied from 1 to 3 Hz. Based on the experimental outcomes, it can be observed that the heat transfer rate is enhanced by applying the pulsating flow, where it was found that the outlet temperature in the case of applying the pulsating flow rises by about 25.6 -27% as compared with the steady flow case. Moreover, pulsating flow offers a higher effective thermal performance by about 15.2 % at the maximum air mass flow rate compared with the steady flow. In addition, the findings pointed out that varying the pulsation frequency from 1 to 3 Hz produces an enhancement in heat transfer rate and in solar heater effective efficiency, where it was found that when changing the frequency from 1 to 3, the increment of effective efficiency ranged from 3.8 to 6.9 % depending on the air mass flow value.

Performance Enhancement of Solar Air Heater by Integrating Innovative Absorber Design and Automatic Control Flow Rate

“…In both instances, black paint with 2% nanomaterial incorporated in it is employed as a coating agent. Hussein et al 19) investigated the effect of pulsing flow as an active technique on the thermal efficiency of a double-pass SAH using a tubular solar absorber. Based on the results of the experiment, it was concluded that applying pulsing flow increases the rate of heat transfer.…”