Search results for "25"
showing 10 items of 3263 documents
Multi Stage Flash Desalination with Direct Mixing Condensation
2011
Multi Stage Flash desalination technology has been a leading technology in the desalination market for the last four decades. However as a result of the continuous increase of costs for the special materials required for the tube bundles the share of MSF technology in the market is nowadays steadily shrinking. Aim of the present work is to present a novel configuration for the MSF process. In the proposed arrangement evaporation occurs in a multi stage vertical column filled with packing material to enhance the achievement of flashing equilibrium in each stage, while condensation occurs in a second column through direct mixing with a colder water stream. Thermal integration for the recovery…
Towards 1 kW power production in a reverse electrodialysis pilot plant with saline waters and concentrated brines
2017
Abstract Reverse electrodialysis (RED) is a promising technology to extract energy from salinity gradients, especially in the areas where concentrated brine and saline waters are available as feed streams. A first pilot-scale plant was recently built in Trapani (Italy), and tested with real brackish water and brine from saltworks. The present work focuses on the scale-up of the pilot plant, reaching more than 400 m 2 of total membrane area installed and representing the largest operating RED plant so far reported in the literature. With a nominal power capacity of 1 kW, the pilot plant reached almost 700 W of power capacity using artificial brine and brackish water, while a 50% decrease in …
Numerical prediction of flow fields in baffled stirred vessels: A comparison of alternative modelling approaches
1998
Abstract Numerical simulations of the flow field in baffled mixing tanks, based on three alternative methods, are presented and discussed. In the first method, the impeller is not explicitly simulated, and its effects are modelled by imposing suitable, empirically derived, boundary conditions to the external flow. In the second method, the whole vessel volume is divided into two concentric, partially overlapping, regions. In the inner region, containing the impeller, the flow field is simulated in the rotating reference frame of the latter, while in the outer region simulations are conducted in the reference frame of the laboratory. Information is iteratively exchanged between the two regio…
Dense solid–liquid off-bottom suspension dynamics: Simulation and experiment
2009
Dense solid–liquid off-bottom suspension inside a baffled mechanically stirred tank equipped with a standard Rushton turbine is investigated. Dynamic evolution of the suspension from start-up to steady-state conditions has been determined by both visual experiments and computational fluid dynamics (CFDs). A classical Eulerian–Eulerian multifluid model (MFM) along with the “homogeneous” k–ε turbulence model is adopted to simulate suspension dynamics. In these systems the drag inter-phase force affects both solids suspension and distribution. Therefore, different computational approaches are tested in order to compute this term. Simulation results are compared with images obtained from the re…
Analysis of the bubbling behaviour of 2-D gas solid fluidized beds part II: Comparison between experiments and numerical simulations via Digital Imag…
2009
In the field of gas–solid fluidization, bubbles, and all features regarding them, have a very great importance, as they significantly affect the process performance. Numerous experimental studies on bubbles, and their formation, evolution, and properties, have been performed in the past. These investigations appear particularly difficult, due to the nature of these systems, since the gas phase is distributed in both the bubble and the emulsion phase. Several experimental approaches have been developed to tackle this study. Among these, the Digital Image Analysis Technique purposely developed in Part I of the present work, based on the use of a video camera for monitoring the phenomenon coup…
CFD PREDICTION OF BUBBLES BEHAVIOUR IN 2-DIMENSIONAL GAS-SOLID FLUIDIZED BEDS
2008
In recent years the use of Computational Fluid Dynamics (CFD) is significantly increasing to simulate multi-phase flows. It is invariably emphasized that a necessary step towards the development of reliable fully predictive CFD models is an extensive experimental validation of the simulation results. This work in particular focuses on the CFD simulation of a lab-scale 2D fluidized bed and the relevant experiments, in order to validate the prediction capability of the used codes and models. It must be emphasized that both experimental and computational quantitative data have been obtained by means of an original Digital Image Analysis Technique, that allows coherent comparison of computation…
On some issues in the computational modelling of spacer-filled channels for membrane distillation
2017
Abstract This study addresses issues which arise in the computational and experimental modelling of flow and heat/mass transfer in membrane distillation and other processes adopting spacer-filled channels (either planar or spiral wound), but have not been sufficiently clarified in the literature so far. Most of the argumentations presented are based on original computational results obtained by the authors by finite volume simulations; some literature results are also considered. The questions addressed regard the choice of scales for the reduction of data and the definition of dimensionless numbers ( Re , f , Nu , Sh ); the definition of average heat or mass transfer coefficients; the comb…
Pressure drop at low reynolds numbers in woven-spacer-filled channels for membrane processes: CFD prediction and experimental validation
2017
The energy consumption due to pumping power is a crucial issue in membrane processes. Spacers provide mechanical stability and promote mixing, yet increasing pressure drop. Woven spacers and their behaviour at low Reynolds numbers are less studied in the literature. Nevertheless, they are typical of some membrane technologies, as reverse electrodialysis (RED). RED is a promising technology for electric power generation by the chemical potential difference of two salt solutions within a stack equipped by selective ion-exchange membranes. The mechanical energy required for pumping the feed solutions, can dramatically reduce the net power output. In this work computational fluid dynamics (CFD)…
Experimental and computational investigation of heat transfer in channels filled by woven spacers
2017
Abstract Models of woven-type spacer-filled channels were investigated by Computational Fluid Dynamics (CFD) and parallel experiments in order to characterize the performance of Membrane Distillation (MD) modules. The case of overlapped spacers was analysed in a companion paper. Experiments were based on a non-intrusive technique using Thermochromic Liquid Crystals (TLC) and digital image processing, and provided the distribution of the local convective heat transfer coefficient on a thermally active wall. CFD simulations ranged from steady-state conditions to unsteady and early turbulent flow, covering a Reynolds number interval of great practical interest in real MD applications. A specif…
Investigation of heat transfer in spacer-filled channels by experiments and direct numerical simulations
2016
Abstract The analysis of flow fields and heat or mass transfer phenomena is of great importance in the optimum design of spacer-filled channel geometries for a variety of membrane-based processes. In the present work, models of spacer-filled channels often adopted in Membrane Distillation are simultaneously investigated by experiments and Computational Fluid Dynamics (CFD). Experiments rely on a non-intrusive technique, based on the use of Thermochromic Liquid Crystals (TLC) and digital image processing, and provide the local distribution of the convective heat transfer coefficient on a thermally active wall. CFD relies on steady-state (laminar flow) simulations in the lower end of the Reyn…