Thermal performance analysis of a quadruple-pass solar air collector assisted pilot-scale greenhouse dryer

•Four air channel modification has been tested.•Comparison of triple-pass and quadruple-pass solar air collectors.•Greenhouse dryer performance has been upgraded to achieve high thermal performance.•Comparison of integrated mode and single mode.•Maximum instantaneous collector efficiency was obtained as 90.30%. Solar air collectors can be utilized in different applications like process air preheaters, dryers, and fresh air providing in buildings. In addition to solar air collectors, greenhouse dryers can be utilized as direct type solar dryers. In the present study, a quadruple-pass solar air collector (QPSAC) which accompanied with a pilot-scale greenhouse dryer (GD) has been analyzed experimentally and numerically. In the first section of the study, some kinds of upgrading have been done to choose the effective design of dryer and solar collector. In the second section, manufacturing of successful designs has been performed and performance of them have been analyzed experimentally. Red pepper and kiwi have been dried in the fabricated drying system as products. The performance tests have been done at 0.008 and 0.010 kg/s flow rates. The achieved mean thermal efficiency for QPSAC is in the range of 71.63–80.66%. The highest instantaneous temperature difference in QPSAC was obtained as 28.10 °C at 0.008 kg/s air flow rate. Also, SMER obtained in the range of 0.21–0.36 kg/kWh. Experimental results indicated that integrating QPSAC with GD decreased drying time considerably. Moreover, maximum deviation between CFD and experimental findings is 10%.