Energy and exergy evaluation of new design nabla shaped tubular solar air heater (∇ TSAH): Experimental investigation.

Solar air heating (SAH) is a low-cost method for air heating using solar energy. An energy and exergy performance is performed experimentally on new designed tubular SAH having tubular absorber of adjacent tubes forming flat pack. Each tube of the absorber contains three adjacent internal tubes forming nabla shape (∇). The nabla tubular SAH (∇TSAH) performance is studied compared to ordinary tubular SAH (OTSAH) having tubular absorber only for single pass (SP) and double pass (DP) flow conditions and different mass flow rates of air (MFRA). The study is investigated under upper Egypt hot climate conditions and 0.018–0.081 kg/s MFRA. The results demonstrate that ∇TSAH has higher outlet air temperature, energy gain, higher energy, exergy, and thermohydraulic efficiencies, and lower top losses than the OTSAH. The new design boosts the exit air temperature by about 13.5 and 5 °C for SP and DP, respectively compared to OTSAH. Moreover, it enhances the energy efficiency by about 28.1% and 71.5% and the exergy efficiency by about 56.2% and 76.8% compared to OTSAH and flat plate SAH (FSAH), respectively at 0.027 kg/s. The maximum ∇TSAH output net energy gain is achieved at 0.072 kg/s for SP and 0.036 kg/s for DP. [Display omitted] • Energy and exergy of new designed Nabla-shaped SAH are investigated experimentally. • Maximum outlet air temperature rise is 50.2 °C for ∇TSAH and 36.7 °C for OTSAH. • ∇TSAH performance is greater than that of OTSAH and the latter is greater than that of FSAH. • Average daily energy efficiency is 88.4% for ∇TSAH, 77.3% for OTSAH, and 72% for FSAH. • Average daily energy efficiency is 3.89% for ∇TSAH, 2.49% for OTSAH, and 2.2% for FSAH. [ABSTRACT FROM AUTHOR]