heat pumps, nanofluids, simulation
A simulation model was developed for the performance prediction of a vapor compression heat pump using nanoscale colloidal solutions (nanofluids) as condenser coolants. The model was intended for a liquid-to-liquid heat pump, with reciprocating compressor, thermostatic expansion valve and counter-flow double-tube condenser and evaporator. The compressor is characterized (input data) by its swept volume, shaft speed and isentropic and volumetric efficiencies curves, and the expansion device, by the evaporator superheat. The condenser is divided into three zones, desuperheating, condensing and subcooling. Likewise, the evaporator is divided into the boiling and superheating zones. The heat exchangers are characterized (input data) by their geometry (inner and outer tube diameters and length). Operational input data also include condenser subcooling and heat transfer fluids (condenser and evaporator) mass flow rates and inlet thermodynamic states. A computational program was developed to solve the resulting non-linear system of algebraic equations. Solution of the system provides the cycle overall thermal performance, as well as condensing and evaporating pressures and the thermodynamic states of refrigerant and heat transfer fluids at all points of the cycle. Preliminary results were obtained for the simulation of a 19 kW nominal capacity water-to-water/(H2O-Cu nanofluid) heat pump. A 5.4% increase in the heating coefficient of performance, for a typical operating condition, was predicted for a nanoparticle volume fraction of 2%.