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This work presents a numerical model developed to simulate steady-state refrigerant flow along a tube of a bubble pump at operating conditions of interest for diffusion-absorption refrigeration systems. The flow is considered one-dimensional, and non-metastable flow is neglected. The two-fluid model was employed to simulate the two-phase flow, considering the hydrodynamic nonequilibrium between the liquid and the vapor phases. Comparisons were made for void fraction versus vapor quality using the homogeneous model, the Rouhani and Axelsson drift model, and the Zivi annular model. The results show a great similarity among the values achieved in the present work and those calculated using the Rouhani and Axelsson and Zivi correlations. On the basis of the numerical simulations, a detailed description of the flow characteristics was obtained. The influence of the heat source on the flow characteristics was numerically examined. [ABSTRACT FROM AUTHOR]

This article deals with comparative study of low-pressure superheated steam drying (LPSSD) and vacuum drying using coal particles as model material. The focus is made on the inversion temperature, which means that the drying rate in the two drying processes becomes equal. This temperature is of great importance because it allows the choice of drying agent for given operating conditions. The effect of external and internal parameters on the drying kinetics and the inversion temperature were investigated. Several studies have shown discrepancies of inversion temperature values basing on the constant rate period (CRP) and the falling rate period (FRP). This work points out gaps in these temperature values using the two calculation methods. [ABSTRACT FROM AUTHOR]

The present study aimed at developing a theoretical model to simulate the drying process of a porous particle in low-pressure superheated steam drying (LPSSD). Spherical and porous particles of ceramic and coal are used as the model material in this work. Experimental data for ceramic and coal particles reported in the literature were used for the model validation. The effect of particle thermophysical properties and operating variables is tested. Results showed that a decrease in pressure and an increase in the fluid temperature during drying lead to an elevation of mass flux during the constant rate period (CRP) and the falling rate period (FRP) of the drying process. Moreover, this increase in mass flux is more significant for particles with the highest effective porosity. Thus, we conclude that decreasing pressure and increasing the drying fluid temperature reduce the mass flow. [ABSTRACT FROM AUTHOR]