Heat transfer analysis of double helical coiled tube heat exchanger using carbon nano tube nanofluids

Abstract

Industries have always been facing the challenge of enhancing the heat transfer efficiency of thermal devices. Changes in the design of construction and variations in fluid usage are attempted. The advent of nanotechnology has enabled the use of nanofluids as a cooling medium in heat exchangers. Also, heat exchangers are generally larger in size and involve high-pressure drop. It has been learnt from the literature that most of the past works involve shell and tube type heat exchangers and very few have researched tube-in-tube type design. But, helical heat exchangers recently utilised in the industries for several benefits. Hence to resolve the problems, an experimental setup arranged in the new design of Double Helical Coiled Tube Heat exchanger (DHCTHX) was designed and developed as per industrial standards. This tube-in-tube heat exchanger is compact in size and operated with multiwall carbon nanotube (MWCNT) water-based nanofluid for heat transfer enhancement. Nanofluids are used in thermal systems for reducing heat, i.e., as cooling applications. The stability of nanofluids is a significant problem while considering practical applications as a cooling medium. The nanofluid used in this investigation was prepared through a two-step method by dispersing MWCNT nanoparticles (50-90nm) in distilled water and for increasing the stability, 2% SDBS (Sodium Dodecyl Benzene Sulfonate ) was added. The nanofluid was characterized using SEM (Scanning Electron Microscopy), UV (Ultra Violet rays), ZETA (Zeta potential, or electro-kinetic potential of solid-liquid dispersions) and pH tests. The stability analysis was done by keeping the nanofluids under static condition for one month. The investigation for heat transfer enhancement was carried out by the MWCNT volume like 0.2%, 0.4%, then 0.6%, a variety of flow rates and also by varying the temperatures. newline