Projeto e construção de uma bomba de calor a CO2 operando em ciclo transcrítico e modelagem dinâmica do conjunto evaporador solar-válvula de expansão

Abstract

Recently, the interest for natural fluids has increased by industry and scientific community as a way of replacing the traditional CFCs and HCFCs. Then, the CO2 presents itself as one of the most promising alternatives especially in heat pumps for residential water heating. In this work, it was developed a theoretical and experimental investigation of the dynamic behavior of the CO2 heat pump's solar evaporator and expansion valve, operating in transcritical mode, used to heat water for residential use. The CO2 presents peculiar thermodynamic properties that directly influence the dynamic behavior of systems that use it primarily as refrigerant in relation to parameters such as convective coefficient and pressure loss. Heat pumps, operating with solar evaporators, have higher COP than traditional pumps, and parameters, such as, solar radiation, ambient temperature, collector area and fluid refrigerant affect the thermal efficiency of these systems. Mathematical models for the solar evaporator and expansion valve were developed using the equations of conservation of mass, momentum, energy and correlations drawn from the literature developed exclusively for CO2. The results obtained from the models of the solar evaporator and expansion valve were compared with the experimental results in a prototype built with data got from literature. Measurements of temperature and pressure allowed the determination of temperature profile that were then compared to the values obtained by using the model. The comparative study concluded that the developed model presents as a useful tool for analyzing the dynamic behavior of the heat pump.