Experimental evaluation of the performance of newly designed tubular SAH with infinity (∞) shaped inner tubes

Abstract

A new design of tubular solar air heater (SAH) is examined experimentally in this work. The SAH absorber consists of one row of adjacent equal tubes forming flat pack. Each tube contains two adjacent inner tubes, the diameter of each of which equals the radius of the outer tube. The two inner tubes form the shape of infinity (∞), therefore, the new design is expressed as infinity shaped tubular SAH (∞TSAH). The performance of the ∞TSAH is examined against ordinary tubular SAH (OTSAH)) having tubular absorber consists of one row of only adjacent equal tubes. The comparison is performed at different mass flow rates of the air (MFRs) and under single pass flow (SPF) and double pass flow (DPF) of the air. The findings show clearly that the output air temperature, energy efficiency and thermohydraulic efficiency, of ∞TSAH are better than that of OTSAH. The maximum output air temperature rise is about 47.1 °C and 37.1 °C for ∞TSAH and OTSAH, respectively at MFR of 0.017 kg/s and DPF condition. In addition, the ∞TSAH achieves maximum energy efficiency of 84.5% at MFR of 0.079 kg/s and DPF condition with percentage increment of 8.4% relative to OTSAH which achieves energy efficiency of 77.3% at the same condition. Moreover, the ∞TSAH achieves maximum thermohydraulic efficiency of 79% at MFR of 0.052 kg/s and DPF condition, while OTSAH achieves a value of 72.6% at MFR of 0.079 kg/s and DPF condition.