Estudo Geralhttps://estudogeral.sib.uc.ptThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 15 Dec 2019 00:30:43 GMT2019-12-15T00:30:43Z5041- A Lagrangian-Eulerian model of particle dispersion in a turbulent plane mixing layerhttp://hdl.handle.net/10316/8171Title: A Lagrangian-Eulerian model of particle dispersion in a turbulent plane mixing layer
Authors: Oliveira, L. A.; Costa, V. A. F.; Baliga, B. R.
Abstract: A Lagrangian-Eulerian model for the dispersion of solid particles in a two-dimensional, incompressible, turbulent flow is reported and validated. Prediction of the continuous phase is done by solving an Eulerian model using a control-volume finite element method (CVFEM). A Lagrangian model is also applied, using a Runge-Kutta method to obtain the particle trajectories. The effect of fluid turbulence upon particle dispersion is taken into consideration through a simple stochastic approach. Validation tests are performed by comparing predictions for both phases in a particle-laden, plane mixing layer airflow with corresponding measurements formerly reported by other authors. Even though some limitations are detected in the calculation of particle dispersion, on the whole the validation results are rather successful. Copyright © 2002 John Wiley & Sons, Ltd.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/10316/81712002-01-01T00:00:00Z
- Optimization of a thermal energy storage system provided with an adsorption module – A GenOpt application in a TRNSYS/MATLAB modelhttp://hdl.handle.net/10316/80264Title: Optimization of a thermal energy storage system provided with an adsorption module – A GenOpt application in a TRNSYS/MATLAB model
Authors: Fernandes, M.S.; Gaspar, A.R.; Costa, V.A.F.; Costa, J.J.; Brites, G.J.V.N.
Abstract: The optimization and assessment study of a thermal energy adsorption storage system is presented. The system integrates an adsorption heat storage module in a conventional hot water storage tank of a solar thermal system, operating with the silica-gel/water adsorption pair. The system was modeled using TRNSYS® and MATLAB®, and was previously assessed and improved through a set of parametric tests for each main component. In this work, the GenOpt® optimization software was used to obtain the optimal performance of the whole system. It is found that a slender and lengthy adsorber with a large number of thin fins, a thick and lengthy condenser, and an evaporator with a large number of lengthy tubes improve the system’s performance, by increasing the heat transfer areas and the adsorbent mass. The performance also improves by controlling the adsorber-condenser valve only through the system’s pressure and opening the evaporator-adsorber valve at the hot water setpoint temperature. The optimized system presents a 16% saving in annual backup energy consumption compared with a similar conventional storage system, thus validating the results of the previous segregated parametric study. This optimized system operates at the highest performance with the same configuration in different locations/climates, as only the inclination of the solar collector affects the results: larger inclinations improve the system’s performance, by favoring its operation in Winter. Results present this system as a promising solution to increase the energy storage capacity of solar thermal systems, and potentially of systems using other primary energy sources.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10316/802642018-01-01T00:00:00Z
- Modeling and simulation of wetted porous thermal barriers operating under high temperature or high heat fluxhttp://hdl.handle.net/10316/4177Title: Modeling and simulation of wetted porous thermal barriers operating under high temperature or high heat flux
Authors: Costa, V. A. F.; Mendonça, M. L.; Figueiredo, A. R.
Abstract: Porous media with high water content can be successfully used as thermal barriers to operate under high exposure temperatures and/or high heat fluxes. Modeling and simulation of such systems presents difficulties and challenges, which are pointed and worked out in this work. Liquid water and water vapor transfers are considered, including the capillary effects for the liquid phase, as well as the air transfer inside the porous medium. Heat transfer model includes conduction, radiation, enthalpy convection, sensible heating and phase change. A realistic model is considered at the exposed boundary in what concerns mass transfer: the outflow mass transfer is dictated by the water effusion and not by the convection transfer mechanism between the exposed surface and the environment. A set of numerical aspects is detailed, concerning both the numerical modeling and the solution of the discretization equations, which are crucial to obtain successful simulations. Some illustrative results are presented, showing the potential of the wetted porous media when used as thermal barriers, as well as the capabilities of the presented physical and numerical models to deal with such systems.
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10316/41772008-01-01T00:00:00Z
- Numerical model for the prediction of dilute, three-dimensional, turbulent fluid-particle flows, using a Lagrangian approach for particle tracking and a CVFEM for the carrier phasehttp://hdl.handle.net/10316/8166Title: Numerical model for the prediction of dilute, three-dimensional, turbulent fluid-particle flows, using a Lagrangian approach for particle tracking and a CVFEM for the carrier phase
Authors: Oliveira, L. A.; Costa, V. A. F.; Baliga, B. R.
Abstract: A numerical model for dilute, three-dimensional, turbulent, incompressible fluid-solid particle flows and its application to a demonstration problem are presented. An Eulerian description is used to model the flow of the fluid (carrier) phase, and the governing equations are solved using a control-volume finite element method (CVFEM). The motion of the solid (particulate) phase is simulated using a Lagrangian approach. An efficient algorithm is proposed for locating the particles in the finite element mesh. In the demonstration problem, which involves a particle-laden axisymmetric jet, a modified k-ε turbulence model is used to characterize the velocity and length scales of the turbulent flow of the fluid phase. The effect of turbulence on the particle trajectories is accounted for through a stochastic model. The effect of the particles on the fluid time-mean velocity and turbulence (two-way coupling) is also addressed. Comparisons between predictions and available experimental data for the demonstration problem are presented. Satisfactory agreement is obtained. Copyright © 2008 John Wiley & Sons, Ltd.
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10316/81662008-01-01T00:00:00Z