Experiments on air bubbles injection into a vertical shell and coiled tube heat exchanger; exergy and NTU analysis

Highlights: • Air bubbles injection was employed to enhance the performance of a vertical shell and coiled tube heat exchanger. • Air bubbles were injected into the shell side of heat exchanger via a new method at different conditions. • NTU enhancement and Exergy loss due to air bubbles injection were studied. • Present type of air bubble injection significantly increased the amount NTU and performance of heat exchanger. - Abstract: In this paper, attempts are made to increase the number of thermal units (NTU) and performance in a vertical shell and coiled tube heat exchanger via air bubble injection into the shell side of heat exchanger. Besides, exergy loss due to air bubble injection is investigated. Indeed, air bubble injection and bubbles mobility (because of buoyancy force) can intensify the NTU and exergy loss by mixing the thermal boundary layer and increasing the turbulence level of the fluid flow. Air bubbles were injected inside the heat exchanger via a special method and at new different conditions in this paper. It was demonstrated that the amount of NTU and effectiveness can be significantly improved due to air bubbles injection