Nanoparticles, Nanofluids, Nanorefrigerants, Heat transfer, Efficiency
The monetary savings from energy efficient systems & responsibility felt to contribute to save environment are encouraging researchers to use different technologies & advancements in science to make their equipments & systems more & more energy efficient. Refrigeration systems are no exceptions.Â The advances in nanotechnology have lead to emerging of new generation heat transfer fluids called nanofluids. Researchers are trying to use these nanofluids to improve energy efficiency of refrigeration systems. This paper presents a literature review of the research in this field. This paper briefs about basics, historical developments, nanoparticle production techniques, nanofluids & its preparation method and limitations of using nanofluids. The paper discusses about limitations of literature reviewed and also informs about future research required in this field. Â Reviewed literature is classified in two sections. First section evaluates basic properties of nanofluids like thermal conductivity, viscosity, heat transfer coefficient, friction factor and second section analyses the application of nanofluids in refrigeration system performance. Â From literature reviewed it can be said that, for application of nanofluids in refrigeration further research is needed in both fundamental science & in direct application. Heat transfer depends on thermal conductivity of nanofluid, and compressor energy efficiency depends upon viscosity & friction factor. Therefore, focus for fundamental research should be on determining these thermo-physical properties, mechanism of thermal transport & tribological behavior. Â An application related research is also equally important. It needs to be carried out simultaneously with basic research so that basic research can be more focused on obtaining desirable properties, and developing a new generation, highly efficient heat transfer fluid. An applied research must focus on stability of nanorefrigerants. Â The use of nanofluids appears promising, but has several challenges. Nanofluids stability and its production cost are major hurdles in using nanofluids. Â Since research about nanofluids is only in primitive stage large amount of research is possible in this field. This presents a big challenge to find suitable nanofluids of desirable properties for refrigeration application. Â While evaluating performance of refrigeration system, effect of nanofluid preparation method, effect of various types of nanoparticle materials, variation of sizes of nanoparticles, variation of concentration (volume fraction) of nanoparticles, variation of suspension concentration in refrigerant needs to be investigated.Â Available nanoparticle materials are limited, however there are too many combinations of base fluid (refrigerants & oils) with nanoparticles and too many variables (sizes, concentration) & alternatives to explore & research. Development of nanoparticle production technique will further enhance nanofluid research possibilities. Any new development of nanoparticle material shall also go through all production, research, & experimentation steps. Public concern about nanoparticles safety both in production and in use shall also be required to be considered. Possibility of using non-toxic or biodegradable nanoparticles can be explored. Low cost, high volume production of stable green nanofluids suitable for refrigeration application is one of the most challenging objectives. Â Though research with nanofluids is in primitive stage at this stage, it will not be a surprise if just like any other refrigerant; nanorefrigerants will be commercially available in future.