Search results for "Heat Transfer"
showing 10 items of 442 documents
A mesh less approch based upon Radial basis function Hermite collocation method for predicting the cooling and the freezing times of foods
2005
This work presents a meshless numerical scheme for the solution of time dependent non linear heat transfer problems in terms of a radial basis function Hermite collocation approach. The proposed scheme is applied to foodstuff's samples during freezing process; evaluation of the time evolution of the temperature profile along the sample, as well as at the core, is carried out. The moving phase-change zone is identified in the domain and plotted at several timesteps. The robustness of the proposed scheme is tested by a comparison of the obtained numerical results with those found using a Finite Volume Method and with experimental results.
Turbulent heat transfer in spacer-filled channels: Experimental and computational study and selection of turbulence models
2019
Abstract Heat transfer in spacer-filled channels of the kind used in Membrane Distillation was studied in the Reynolds number range 100–2000, encompassing both steady laminar and early-turbulent flow conditions. Experimental data, including distributions of the local heat transfer coefficient h, were obtained by Liquid Crystal Thermography and Digital Image Processing. Alternative turbulence models, both of first order (k-e, RNG k-e, k-ω, BSL k-ω, SST k-ω) and of second order (LRR RS, SSG RS, ω RS, BSL RS), were tested for their ability to predict measured distributions and mean values of h. The best agreement with the experimental results was provided by first-order ω-based models able to …
CFD parametrical study of the spacer geometry for Membrane Distillation
Membrane Distillation (MD) is a thermal process that separates water from aqueous solutions containing non-volatile components such as salt. Water vapor from the hot feed channel permeates through a hydrophobic membrane thanks to a partial pressure gradient, and condenses in the cool channel. One of the main advantages of MD is the easy coupling with renewable resources, as the solar thermal energy. In the various MD configurations developed, net spacers are used in order to support the membrane, thus creating the channels; moreover, they can counteract the side effects of temperature polarization by promoting mixing. However, the presence of the spacer involves an increase of pressure drop…
Temperature distribution analysis in spacer filled channels for membrane distillation
2012
New considerations for modelling a MED-TVC plant under dynamic conditions
2019
Abstract The multiple-effect distillation (MED) technology is nowadays the most promising desalination process to be coupled with variable heat sources, thus leading to a more sustainable way to produce water. In order to prove the potential of this, it is of major interest to develop powerful modelling tools to predict the performance of this coupling. Only a few models have been presented so far. They show promising results but were based on some simplifying assumptions and non-physical constraints that could limit the analysis of the dynamic behaviour of a MED plant. This paper presents new considerations for the dynamic modelling of a MED plant associated with a thermal vapour compressi…
A Thermochromic Liquid Crystals Image Analysis technique to investigate temperature polarization in spacer-filled channels for Membrane Distillation
2013
The analysis of flow fields and temperature distributions is of paramount importance in the development and optimization of new spacer-filled channel geometries for Membrane Distillation modules. The literature reports only few studies on the experimental characterization of such channels and, to the authors’ knowledge, none of them presents local information concerning the temperature distribution on the membrane surface. In the present work, a non-intrusive experimental technique named TLC-IA-TP is presented: it is based on the use of Thermochromic Liquid Crystals (TLCs) and digital Image Analysis (IA) and it is applied here for the first time to the analysis of Temperature Polarization (…
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…
Mass transfer in channels in the presence of wall transpiration
Mass transfer to or from transpiring walls is studied. Examples from different fields of engineering, notably involving membrane processes, are illustrated, and analogies or differences with respect to heat transfer problems are discussed. With special reference to plane channel flow, suitable dimensionless parameters are introduced, and the dependence of the Sherwood number upon these parameters is computed by a number of approaches of different complexity, from two-dimensional CFD to simple algebraic correlations.
CFD prediction of flow, heat and mass transfer in woven spacer-filled channels for membrane processes
2021
Abstract Flow and heat or mass transfer in channels provided with woven spacers made up of mutually orthogonal filaments were studied by Computational Fluid Dynamics. The problem addressed was the combined effect of the parameters that characterize the process: pitch to height ratio P/H (2, 3 and 4), flow attack angle θ (0, 7, 15, 20, 30, 40 and 45°) and Reynolds number Re (from ~1 to ~4000). The Prandtl number was 4.33, representative of water at ~40°C, while the Schmidt number was 600, representative of NaCl solutions. Simulations were performed by the finite volume code Ansys CFX™ 18.1 using very fine grids of ~6 to ~14 million volumes. For Re > ~400, the SST turbulence model was used to…
CFD Investigation of Spacer-Filled Channels for Membrane Distillation
2019
The membrane distillation (MD) process for water desalination is affected by temperature polarization, which reduces the driving force and the efficiency of the process. To counteract this phenomenon, spacer-filled channels are used, which enhance mixing and heat transfer but also cause higher pressure drops. Therefore, in the design of MD modules, the choice of the spacer is crucial for process efficiency. In the present work, different overlapped spacers are investigated by computational fluid dynamics (CFD) and results are compared with experiments carried out with thermochromic liquid crystals (TLC). Results are reported for different flow attack angles and for Reynolds numbers (Re) ran…