Experimental investigation of an evacuated tube solar air heater with baffles and perforated twisted tapes for air heating applications

The operational impact of integrating a Solar Evacuated-Tube Air Heater with a baffle and Perforated Twisted Tape (SETAHBPTT) on one side of the baffle in every evacuated tube (ET) for a pitch length of 57 mm, Hole (3 holes) Diameter of 2 mm on the twisted tape, and various air flow rates were studied. The novel airflow pattern of splitting the airflow within the ET and perforated twisted tape (PTT) inserts was placed to increase the outlet temperature at higher air flow rates and compensate for the pressure drop at the same time, and it was experimentally investigated to scale the impact of PTT insertion on the performance of SETAHBPTT. An analytical model is developed for the flow pattern in SETAHBPTT, and its results were validated with the experimental results, both results were in good agreement with minimum deviation. The temperature rise of the outlet is highest at 318.47 K for the least mass flow rate of 100 kg/h. The peak thermal efficiency is 59.7% for the mass flow rate of 500 kg/h. An optimum mass flow rate of air for the maximum effective thermal efficiency is 51.21% at 300 kg/h. For an airflow rate of 100 kg/h, the maximum exergy efficiency was 2.37%, and the exergy efficiency decreased with an increasing airflow rate. The Levelized Cost of Heating, which is the cost of producing heated air per kilo Watt hour, was 0.023 INR for the proposed system.