A Numerical Study on the Application of Nanofluids in Refrigeration Systems

The use of nanofluids as secondary coolants in vapor compression refrigeration systems was numerically studied. A simulation model for a liquid-to-water heat pump, with reciprocating compressor and double-tube condenser and evaporator was studied. The multi-zone method was employed in the modeling of the heat exchangers. The waterbased nanofluid was supposed to flow through the inner circular section of the evaporator, while the refrigerant was left to the annular passage. A computational program was developed to solve the resulting non-linear system of algebraic equations. Different nanoparticles (Cu, Al2O3, CuO and TiO2) were studied for different volume fraction and particle diameters. Simulation results have shown that, for a given refrigerating capacity, evaporator area and refrigerant-side pressure drop are reduced when: (i) the volume fraction of nanoparticles increase; (ii) the diameter of nanoparticles decrease. Also, nanofluid-side pressure drop and, consequently, pumping power, increase with nanoparticle volume fraction and decrease with nanoparticle size. Results from a typical case-study indicated an evaporator area reduction, with the use of nanofluids as secondary coolant, if compared to the conventional basefluid (H2O).