The role of enhancement techniques on heat and mass transfer characteristics of shell and tube spray evaporator: a detailed review

Falling film heat transfer of horizontal shell-side evaporators remains of interest to scientists due to the complexity of these phenomena for practical applications. However, characteristics of heat and mass transfers of spray evaporators are still subject to further enhancement. This study is to review the enhancement techniques and falling film flow especially the effect of nanoparticles suspended with refrigerants in order to confirm their role. The study covers the influence of surface geometry (bundles and external of tubes), normal single tube, low fins, and enhanced geometrical tubes; effect of additives; and the applications and problems related to refrigerant-based nanofluids. Heat transfer area with energy related cost and the significant efforts on empirical correlations for heat transfer coefficient are discussed. It is found that the interaction of the heat and mass transfer process on falling film flow and contradictions of thermal physical properties of nanofluids should all be taken into careful consideration. In addition, existing research on both heat and mass transfer regarding nanofluids are found to be inadequate, and still requires extensive experimental and theoretical work on their salient parameters. Finally, this study highlights the factors affecting efficiency, compactness, and cost of the spray evaporator and the potential of enhancement techniques.