Estudo experimental e modelo de simulação para a determinação do inventário em sistemas de refrigeração carregados com os fluidos R-134a e HFO-1234yf

Abstract

The present work is a theoretical/experimental study on the inventory in refrigeration systems loaded with the fluids R-134a and HFO-1234yf. The first is a chlorine-free hydrofluorocarbon (HFC) with ozone depletion potential (ODP) equal to zero, but with a global warming potential (GWP) of 1430, which is considered a high value. The HFO-1234yf belongs to a new family of refrigerants, the hidrofluorolefins (HFO), with thermodynamic properties are similar to the R-134a. In the same way, it presents an ODP equal to zero, but a very low GWP equal to 4, considered a substitute of the R-134a for new applications and with the potential to replace it in the automotive air conditioners of the current cars. In this work, the bibliographical review addressed several issues involving one-phase and twophase flow within pipes, such as flow patterns, void fraction and correlations used in its determination, calculation of heat transfer coefficient and methods for estimating pressure loss. Experimental results were obtained using the fluids R-134a and HFO-1234yf, with mass velocity of 300 kg/s-m2 and 400 kg/s-m2, boiling temperatures of 25°C and 30°C and a large range of quality at the test section of the experimental apparatus. These results were analyzed and compared with the results obtained by a simulation model using eight different correlations for determination of the void fraction. The best results for mass prediction were obtained by the correlations of Hughmark (1962) and Zivi (1964), using the Gnielinski (1976) and Shah (2013) correlations for the determination of the heat transfer coefficients at the one-phase and two-phase regions of the condenser respectively. In this situation, the model has presented of approximately 78% accuracy for mass prediction.