Béchir Chaouachi

Numerical Prediction of Flow Patterns in Bubble Pumps

In the present study, the ammonia-water mixing flow in a bubble pump is numerically simulated. The flow patterns of a two-phase flow in a bubble pump were studied under different conditions of heat flux and tube diameter. A one-dimensional two-fluid model was developed under constant heat flux. This model was used to predict the variations in void fraction and liquid and vapor velocities throughout the tube. Then, the void fraction profile and the curve of liquid velocity versus vapor velocity were used to predict the flow patterns along the tube length. It was found that at heat fluxes below 15 kW m ―2 , bubbly, slug, and churn flows are the dominating regimes, and the length of these flow regimes depends on the tube diameter. For heat fluxes higher than 15 kW m ―2 , the bubble pump operates under the churn and annular regimes, and the bubble pump performance is improved when the tube diameter increases.

Simulation of an autonomous solar vacuum membrane distillation for seawater desalination

AbstractSeveral papers deal with membrane distillation of seawater and mainly focus on the choice of membranes and comparison of this technique with other desalination techniques, but there are very few studies that quantitatively estimate the potential of this technology coupled with solar energy. The objective of this work is to develop a model describing the operation of a desalination membrane powered by solar energy. This model determines the performance of the unit over time and for any day of the year. This model is established from the balance equations of mass and heat on the different units (membrane, exchanger, condenser, and field of solar collectors). The model is used to evaluate the evolution of the distillate flow rate and temperature changes for different flows. The model also allows to estimate the productivity of the unit during the year. The simulation of the operation of the unit shows that the daily production of distilled water is between 63 and 188 kg/m2 for the days of 21 December...

MODELING OF BOILING TWO-PHASE FLOW IN THE BUBBLE PUMP OF DIFFUSION-ABSORPTION REFRIGERATION CYCLES

ABSTRACT 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.

Simulation of thermal and hydrodynamic behavior of a solar bubble pump

The CFD software presents an advanced numerical tool for the simulation of monophasic and diphasic flows in heated or boiling pipes. The bubble pump, which is the driving element of the diffusion absorption machines, shows an example of the heated tubes. This article is devoted to the study of the behavior of flows in a bubble pump of a solar diffusion absorption refrigeration machine, uniformly heated along its section of length 1m and diameter 10mm, using the CFD (Computational Fluid Dynamic) software, Fluent package. This work has been realized supposing that the regime is laminar and the flow is monophasic. Numerical simulation permits to study the effect of heating flux on the temperature and flow velocity distribution. Where water, is used as a working fluid along the tube of the bubble pump. This work shows that the variation of the heating flux has no effect on the fluid velocity in the tube. However, it has an effect on the distribution of the fluid temperature along the section.