Evaluations on effect of volume fraction of injected air on exergo-economic performance of a shell and tube heat exchanger

Increasing heat transfer rate in heat exchangers is one of the topics interested by researchers which leads to economic savings. Various methods have been proposed in this field which are categorized into two main groups of active and passive techniques. Despite numerous investigations were conducted in this regards, very rare investigations have probed these methods from the economic viewpoints. Present study was carried out to investigate the effect of volume fraction (VF) of air bubbles on exergo-economic performance of horizontal shell and helically coiled tube exchanger (HSHTE). The air bubbles were injected into shell side via especial method. Holes with certain properties were fabricated on a plastic pipe with diameter of 3 mm for injecting air bubbles. Both counter flow and parallel flow were considered in this investigation. Present study showed that air injection has significant effect on thermal efficiency, exergy destruction and economic performance of the HSHTE. It was found that increment of VF increases number of thermal units, first law efficiently and exergy destruction increase by 4.5, 2.4 and 12.5 times, respectably. Furthermore, best values of Net profit per unit transferred heat load (դp) was about 9.3 × 10−5 ($/J) which presented up to 13% better financial performance in comparison with parallel flow.