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Hermetic reciprocating compressors are widely used in small-and medium-size refrigeration systems based on the vapor-compression cycle. One of the main parts of this type of compressor is the automatic valve system used to control the suction and discharge processes. As the suction and discharge losses represent a large amount of the total thermodynamic losses (47%), a small improvement in the suction and discharge processes can produce expressive increases in the thermodynamic efficiency of the compressor. In this work, a new numerical methodology is applied to solve the flow through reed-type valves. The numerical results were experimentally validated through the pressure distribution acting on the frontal disk of a radial diffuser, which is a geometry usually used to model this type of valve. The numerical results for the velocity and pressure fields were comprehensively explored during the opening and closing movement imposed to the reed. The good quality of these results show that the numerical methodology is very promising in terms of solving the flow in the actual dynamics of reed-type valves. ARTICLE HISTORY

Phase change computational simulations using a diffuse interface treatment for pressure were investigated in order to quantify the spurious currents and its consequences on the interface transport in the present paper. In addition, benchmarks were conducted with a sharp interface treatment for pressure. Namely, a Delta function method (Delta) was employed for the diffuse interface treatment and a ghost fluid method (GFM) for the sharp approach. An additional force term in the nondivergent form of the momentum equation is proposed for the first time in the literature, and its impact on interface motion during simulations of bubble growth by intense phase change has been quantified. In addition, the influence of recoil force on interface position was evaluated in simulations of water bubble condensation at near critical pressure. Finally, simulations of a complex industrial application were performed using the diffuse interface treatment, namely a case of film boiling with the development of Rayleigh-Taylor instability. Both interface treatments presented excellent results for the interface evolution in time. Even with the presence of some relevant spurious currents in the Delta method, the bubble evolution in time was accurately predicted. The sharp interface treatment potential was especially evident using a mass density flux of 1.0 kg/(m 2 s) or higher. Therefore, a diffuse interface treatment for pressure has been presented as an appropriate strategy for most phase change simulations since the presence of the spurious currents did not disturb the interface position, and its magnitude was low for even moderate phase change intensities. The inclusion of the source term due to the additional force in the non-divergent form of the momentum equation and the recoil force term was irrelevant in the cases tested. Lastly, the film boiling simulation using the diffuse interface treatment revealed the possibility of treating complex 3D cases for industrial applications with this method.

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With the usage of a robust and efficient method, validated with literature data, numerical experiments were developed to analyze isolated rising bubbles and quantify fluid dynamic forces acting on them. An integral method is presented and used for the calculus, allowing the observation of the evolution of the total fluid dynamic force and the momentum rate of change in different types of rising bubbles. Drag coefficients were calculated and compared with literature correlations. Results showed that the present method is qualified to be applied for numerical experiments of isolated rising bubbles.