Experimental investigation on heat transfer characteristics of rifled tubes with different flows

Abstract

Heat transfer augmentation methods could be utilized to enhance the thermal characteristics of heat transfer apparatus. Recently, numerous heat transfer augmentation methods are emerging and is used for improving heat transfer in heat exchangers such as evaporators, boilers, condensers, and other heat exchangers which is used in various enterprise applications. Rifled tube has shown tremendous enhancement in thermal energy and heat flow applications. In the present research, experimental investigations were made to evaluate the different parameters influencing the effectiveness of heat transfer and other characteristics of the internal rifled tube with internal helix angle 30o and 58o in a typical double pipe heat exchanger and those were compared with smooth tubes. The experimentations illustrate that the heat transfer rate of 58o helix angle rifled tube is greater than 30o helix angle rifled tube which is better than smooth tube. Moreover, it is confirmed that for the increase in volume flow rates of both cold and hot fluids the heat transfer performance also increases. Also, it is evident that due to swirl flow in rifled tubes with higher helix angle, the Nusselt number is higher than that of smooth tubes. Many researchers proved that nanofluids have a higher heat transfer coefficient due to its thermal conductivity hence water is being replaced by nanofluids. Experimental investigations were performed with TiO2-water based nanofluids of 0.2% and 0.3% concentrations using internally ribbed tubes of 58o helix angle alone since it is found to be more effective than other test sections. The observations indicate that as the Reynolds number increases, there is a significant increase in heat transfer coefficient that causes higher rates of convective heat transfer, due to high velocity and increase in mass flux. Also experimental results revealed that there is a significant enhancement in heat transfer rate for rifled tube with 58o helix angle and the Nusselt number increases by 16.9% than smooth tube and for 30o helix angle the Nusselt number increases by 7% than that of the smooth tube. Furthermore, because of the influence of nanofluid and its high thermal conductivity, there is a considerable amount of improvement in overall heat transfer coefficien newline