摘要：In many industrial applications, the conventional heat transfer fluids are refrigerants, water, engine oil, ethylene glycol etc. Even though an improvement in energy efficiency is possible from the topological and configuration points of view, much more is needed from the perspective of the heat transfer fluid. Despite considerable research and developmental efforts on enhanced heat transfer surfaces, major improvements in cooling capabilities have been constrained because of the poor thermal conductivities of traditional heat transfer fluids used in today’s thermal management systems. In the development of any energy-efficient heat transfer fluids, the thermal conductivity enhancement in heat transfer plays a vital role. One such latest advancement in heat transfer fluids, is the use of nano-sized (1 - 100 nm) solid particles as an additive suspended in the base fluid which is a technique for heat transfer enhancement. Improving the thermal conductivity is the key idea in enhancing the heat transfer characteristics of conventional fluids and in turn the heat transfer coefficient. Hwang et al [1] reported that the nanofluids are claimed to be a non-agglomerated mono-dispersed particles in the base fluids, which proved to be enhancing the heat transfer more than 50% in real-time applications even when the volume ratio of the nano-particle to base fluid is less than 0.3%. It has been reported by Das et al [2] that nanofluids with less than 2% volume fraction are extremely stable and remain suspended in the liquid indefinitely. In many thermal industrial appliances, heat exchangers are used to exchange the heat between the hot and cold fluids; for example, solar water heater. A survey of the published literature indicates that only very limited work has been done till date in finding the heat transfer coefficient of a nanofluid with metal nanoparticles in variety of heat exchangers, while undergoing the cooling process. Cooling heat transfer experiments with nanofluids would find application in solar air conditioning, solar water heaters, building heating, industrial process heaters, and milk pasteurization etc. Therefore, it is important to study the heat transfer characteristics, such as, thermal conductivity, viscosity, heat transfer coefficient and pressure drop of any new working fluid before it is used in a system for any specific application
