Volume 10 (2014): Issue 4 (December 2014)

The present paper was concerned with the experimental study of the time evolution of a single laminar vortex ring generated at the interface between water and isopropyl alcohol. The experiment was performed by the submerged injection of isopropyl alcohol in a water tank of 100×100×150 mm. A constant rate of Q₀ = 2 ml/min was maintained using a PHD Ultra 4400 Syringe Pump with a needle having the inner diameter D₀ = 0.4 mm. The dynamics of the vortex formation was recorded with a Photron Fastcam SA1 camera at 1000 fps equipped with an Edmund Optics objective VZM1000i. The numerical simulations were performed on a 2D geometry using the ANSYS-FLUENT code with the Volume of Fluid multiphase model and the viscous-laminar solver. The numerical flow patterns were found to be in good agreement with the experimental visualizations

The analysis and management of Hydrology time series is used for the development of models that allow predictions on future evolutions. After identifying the trends and the seasonal components, a residual analysis can be done to correlate them and make a prediction based on a statistical model. Programming language R contains multiple packages for time series analysis: ‘hydroTSM’ package is adapted to the time series used in Hydrology, package ‘TSA’ is used for general interpolation and statistical analysis, while the ‘forecast’ package includes exponential smoothing, all having outstanding capabilities in the graphical representation of time series. The purpose of this paper is to present some applications in which we use time series of precipitation and temperature from Fagaras in the time period 1966-1982. The data was analyzed and modeled by using the R language.

An important parameter in the hydraulic design of refrigeration and air-conditioning systems is the two-phase flow pressure drop. In this paper, the authors compare the numerical results obtained by using seven two-phase pressure-drop models with the experimental results found in the scientific literature, for the condensation of R600a and R717 (Ammonia = NH3) in horizontal tubes. Different mass flow rates and different conditions have been considered in order to see which correlation is applicable under specific operation conditions.

Accurate assessment of air-flow in ventilated spaces is of major importance for achieving healthy and comfortable indoor environment conditions. The CFD (Computational Fluid Dynamics) technique is nowadays one of the most used approaches in order to improve the indoor air quality in ventilated environments. Nevertheless, CFD has still two main challenges: turbulence modeling and experimental validation. As a result, the objective of this study is to evaluate the performance of different turbulence models potentially appropriate for the prediction of indoor airflow. Accordingly, results obtained with 6 turbulence models (standard k-ε model, RNG k-ε model, realizable k-ε model, LRN SST k-ω model, transition SST k-ω model and low Reynolds Stress-ω model) are thoroughly validated based on detailed experimental data. The configuration taken into account in this work corresponds to isothermal and anisothermal airflows produced by mixing ventilation systems in small enclosures at low room air changes per hour. In general, the transition SST k-ω model shows the better overall behavior in comparison with measurement values. Consequently, the application of this turbulence model is appropriate for air flows in ventilated spaces, being an interesting option to more sophisticated LES (Large Eddy Simulation) models as it requires less computational resources.