Nanofluids are fluids containing nanometer-sized particles of metals, oxides, carbides, nitrides, or nanotubes. They exhibit enhanced thermal performance when used in a heat exchanger as heat transfer fluids. Alumina (Al2O3) is the most commonly used nanoparticle due to its enhanced thermal conductivity. The work presented here, deals with numerical simulations performed in a tube-in-tube heat exchanger to study and compare flow characteristics and thermal performance of a tube-in-tube heat exchanger using water and Al2O3/water nanofluid. A local element-by-element analysis utilizing e-NTU method is employed for simulating the heat exchanger. Profiles of hot and cooling fluid temperatures, pressure drop, heat transfer rate along the length of the heat exchanger are studied. Results show that heat exchanger with nanofluid gives improved heat transfer rate when compared with water. However, the pressure drop is more, which puts a limit on the operating conditions.
Vapour compression refrigeration is the most widely used method in domestic and commercial air conditioning and refrigeration systems. R22 (difluoromonochloromethane) is the most widely used HCFC (hydro chlorofluorocarbon) refrigerant in residential, commercial, industrial and transport cooling systems. Montreal protocol in 1987 banned the use of CFCs (chlorofluorocarbon) due to their adverse impact on the environment causing ozone depletion and global warming. HCFCs are also being phased out, though they are less destructive than CFCs. The present work explores compressor performance using alternate environment friendly working fluids so that R22 can be replaced in future. The refrigerants used for the studies are R134a (tetrafluoroethane), R290 (propane) and R600a (isobutane). Compressor performance is analysed by varying refrigerant mass flow rate, evaporator and condenser temperatures and studying their effect on compressor size, power and discharge temperature. A numerical simulation code has been developed in MATLAB using refrigerant properties taken from REFPROP.
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