Numerical study to optimize the heat transfer rate of
tube in tube type helical coil heat exchanger

Abstract

Technological advancement in fluid mechanics and heat transfer analysis has impact on the development of new type of heat exchanger for industrial and domestic purpose. In traditional heat exchangers the surface area is less as compared to volume so the use of swirl devices and extended surface or change in design of heat exchanger give birth to helical coil tube in tube type heat exchanger.helical coil tube in tube type of heat exchangers are used in automobile industry, chemical and food processing indus try, cryogenic applications and heat recovery system in nuclear power plant, for domestic purpose this type of heat exchanger is used for refrigerator and air conditioner appliances. Here in this study a brief analysis of helical coil tube in tube type heat exchanger with different boundary conditions are studied. The variation of effectiveness, LMTD, Nusselt number, friction factor, pumping power are studied with respect to Reynolds number are studied. The properties of inner fluid were find out through FLUENT package and influence of outer surface condition of heat exchanger was studied turbulent flow model with counter flow arrangement was selected for analysis purpose. Here the main coil diameter was varied as 64mm, 72mm, 80mm and the inner tube diameterwas fixed and various outer wall condition was imposed and the best result was chosen for this type of heat exchanger. Nusselt number increased as the Reynolds number goes on increases due to more turbulence created by flow arrangement, friction factor decreases with increase in Reynolds number due to dominate of surface roughness, pumping power increases with increase in Reynolds number as the pressure drop increases. Effectiveness is more in the case of insulated outer wall condition compared to other cases. With increase in coil diameter the Nusselt number increases, friction factor increases, pumping power increases, effective ness increses. Variation of outer wall condition has very less influence on the properties of inner fluid such as Nusselt number, friction factor and pumping power.