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Heat Transfer Model (heat + transfer_model)
Selected AbstractsThermal modeling and simulation of an integrated solid oxide fuel cell and charcoal gasification systemENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 3 2009C. Ozgur Colpan Abstract In this study we propose a novel integrated charcoal gasification and solid oxide fuel cell (SOFC) system, which is intended to produce electricity and heat simultaneously. This system mainly consists of an updraft gasifier using air and steam as the gasification agents, a planar and direct internal reforming SOFC and a low temperature gas cleanup system. The performance of this system is assessed through numerical modeling using a pre-developed and validated heat transfer model of the SOFC and thermodynamic models for the rest of the components. These models are used to simulate the performance of the cell and system for a case study. In addition, a parametric study is conducted to assess the effect of Reynolds number at the fuel channel inlet of the SOFC on the cell performance, e.g., fuel utilization and power density, and the system performance, e.g., electrical efficiency, exergetic efficiency, and power to heat ratio. The number of stacks is also calculated for different Reynolds numbers to discuss the economical feasibility of the integrated system. The results show that the electrical efficiency, exergetic efficiency and power to heat ratio of this system are 33.31%, 45.72%, and 1.004, respectively, for the base case. The parametric study points out that taking the Reynolds number low yields higher electrical and exergetic efficiencies for the system, but it also increases the cost of the system. © 2009 American Institute of Chemical Engineers Environ Prog, 2009 [source] Modelling thermal degradation of composite materialsFIRE AND MATERIALS, Issue 2 2007Javier Trelles Abstract A one,dimensional, transient thermal degradation heat transfer model for the response of composite materials when exposed to fire is presented. The model can handle layers of different materials. Material properties are functions of temperature. The reaction can be specified using Arrhenius-type parameters or by inputting a density,temperature relationship determined by any experimental technique such as thermogravimetric analysis. The model is validated against the experimental data presented in Boyer's 1984 dissertation. Overall, the model provides excellent agreement with the experimental data. It is shown that very little difference is found between results arrived at by Arrhenius kinetics and results obtained by specifying the easier to measure density,temperature relationship. From this it is concluded that this technique is a viable alternative to Arrhenius-type models. Copyright © 2006 John Wiley & Sons, Ltd. [source] Thermal properties of gypsum plasterboard at high temperaturesFIRE AND MATERIALS, Issue 1 2002Geoff Thomas Light timber frame wall and floor assemblies typically use gypsum-based boards as a lining to provide fire resistance. In order to model the thermal behaviour of such assemblies, the thermo-physical properties of gypsum plasterboard must be determined. The relevant literature and the chemistry of the two consecutive endothermic dehydration reactions that gypsum undergoes when heated are reviewed. The values determined for the thermo-physical properties are modified to create smooth enthalpy and thermal conductivity curves suitable for input into a finite element heat transfer model. These values are calibrated within a reasonable range and then validated using furnace and fire test data. The type of plasterboard used in these tests is an engineered product similar to the North American type C board. The temperature at which the second dehydration reaction occurs is altered to be consistent with later research with little apparent affect on the comparison with test results. Values for specific heat, mass loss rates and thermal conductivity for gypsum plasterboard that are suitable for use in finite element heat transfer modelling of light timber frame wall and floor assemblies are recommended. Copyright © 2002 John Wiley & Sons, Ltd. [source] Hydrologic and geochemical controls on soluble benzene migration in sedimentary basinsGEOFLUIDS (ELECTRONIC), Issue 2 2005Y. ZHANG Abstract The effects of groundwater flow and biodegradation on the long-distance migration of petroleum-derived benzene in oil-bearing sedimentary basins are evaluated. Using an idealized basin representation, a coupled groundwater flow and heat transfer model computes the hydraulic head, stream function, and temperature in the basin. A coupled mass transport model simulates water washing of benzene from an oil reservoir and its miscible, advective/dispersive transport by groundwater. Benzene mass transfer at the oil,water contact is computed assuming equilibrium partitioning. A first-order rate constant is used to represent aqueous benzene biodegradation. A sensitivity study is used to evaluate the effect of the variation in aquifer/geochemical parameters and oil reservoir location on benzene transport. Our results indicate that in a basin with active hydrodynamics, miscible benzene transport is dominated by advection. Diffusion may dominate within the cap rock when its permeability is less than 10,19 m2. Miscible benzene transport can form surface anomalies, sometimes adjacent to oil fields. Biodegradation controls the distance of transport down-gradient from a reservoir. We conclude that benzene detected in exploration wells may indicate an oil reservoir that lies hydraulically up-gradient. Geochemical sampling of hydrocarbons from springs and exploration wells can be useful only when the oil reservoir is located within about 20 km. Benzene soil gas anomalies may form due to regional hydrodynamics rather than separate phase migration. Diffusion alone cannot explain the elevated benzene concentration observed in carrier beds several km away from oil fields. [source] Evaluation of soluble benzene migration in the Uinta BasinGEOFLUIDS (ELECTRONIC), Issue 2 2005Y. ZHANG Abstract Field sampling and mathematical modeling are used to study the long-distance transport and attenuation of petroleum-derived benzene in the Uinta Basin, Utah. Benzene concentration was measured from oil and oil field formation waters of the Altamont-Bluebell and Pariette Bench oil fields in the basin. It was also measured from springs located in the regional groundwater discharge areas, hydraulically down-gradient from the oil fields sampled. The average benzene concentration in oils and co-produced waters is 1946 and 4.9 ppm at the Altamont-Bluebell field and 1533 and 0.6 ppm at the Pariette Bench field, respectively. Benzene concentration is below the detection limit in all springs sampled. Mathematical models are constructed along a north,south trending transect across the basin through both fields. The models represent groundwater flow, heat transfer and advective/dispersive benzene transport in the basin, as well as benzene diffusion within the oil reservoirs. The coupled groundwater flow and heat transfer model is calibrated using available thermal and hydrologic data. We were able to reproduce the observed excess fluid pressure within the lower Green River Formation and the observed convective temperature anomalies across the northern basin. Using the computed best-fit flow and temperature, the coupled transport model simulates water washing of benzene from the oil reservoirs. Without the effect of benzene attenuation, dissolved benzene reaches the regional groundwater discharge areas in measurable concentration (>0.01 ppm); with attenuation, benzene concentration diminishes to below the detection limit within 1,4 km from the reservoirs. Attenuation also controls the amount of water washing over time. In general, models that represent benzene attenuation in the basin produce results more consistent with field observations. [source] Thermal and mechanical numerical modelling of electric discharge machining processINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2008Nizar Ben Salah Abstract In electric discharge machining (EDM), the heat gradients caused by the electric discharge create a non-uniform local thermal expansion on the level of the surface layers of machined materials from where genesis of thermal stresses takes place. These thermal stresses, if exceeding yield stress, can remain and become residual after the cooling of the part. The modelling of these phenomena, during the heating by the electric discharge and the cooling by the dielectric liquid, requires a heat transfer model, the material behaviour identification, a thermo-mechanical model for the thermal and the residual stress models. This paper presents numerical results concerning the temperature distribution, the thermal and residual stresses of a stable steel material (AISI316L) machined by EDM. Comparison of numerical results with experimental data and numerical results from the literature shows good agreement and is hence quite satisfactory. Copyright © 2008 John Wiley & Sons, Ltd. [source] A simplified method for modelling the effect of blinds on window thermal performanceINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 7 2006D. Naylor Abstract An approximate method is presented for predicting the effect of a louvered blind on the centre-glass thermal performance of a fenestration. The method combines a one-dimensional heat transfer model with data from a numerical simulation of the window and blind. Sample results for a blind mounted on the indoor surface of a window show the effect of blind slat angle on heat transmission. Both summer and winter conditions are considered. The results show that a louvered blind can improve the U -value of a standard double-glazed window by up to 37%. Also, the radiation heat exchange with the room can be dramatically reduced (by up to 60%), which will improve the level of occupant comfort. However, there was found to be a trade-off between U -value and occupant comfort; placing the blind closer to the window improves the U -value, but increases the radiation heat exchange with the room. The predictions from the present simplified method compare well with results from a full two-dimensional computational fluid dynamics solution of the conjugate blind/window interaction. Copyright © 2005 John Wiley & Sons, Ltd. [source] Inter-particle contact heat transfer model: an extension to soils at elevated temperaturesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2005W. H. Leong Abstract A simple ,inter-particle contact heat transfer' model for predicting effective thermal conductivity of soils at moderate temperatures (0,30°C) has been extended up to 90°C. The extended model accounts for latent heat transport by water vapour diffusion in soil air above the permanent wilting point; below that point, the soil thermal conductivity is approximated by linear interpolation without latent heat effect. By and large the best results are obtained when the latent heat is used only in the ,self consistent approximation' model with an overall root mean square error of 35% for all soils under consideration or 26% when excluding volcanic soils. This option can also be applied to moderate temperatures at which the enhanced heat transfer is negligibly small. Copyright © 2005 John Wiley & Sons, Ltd. [source] Simulation of heat transfer during rotational moldingADVANCES IN POLYMER TECHNOLOGY, Issue 4 2003A. Greco Abstract In rotational molding, polymer powders are subjected to heating, melting, cooling, and subsequent solidification in biaxially rotating molds. Heat transfer phenomena during rotational molding are significantly affected by the presence of endothermic and exothermic transitions. In this paper instead of using the traditional moving interface method, a new approach is presented which is applicable to semicrystalline materials like linear low-density polyethylene. Melting is described by a statistical model and crystallization by a kinetic model. The model parameters are determined from differential scanning calorimetry measurements. The one-dimensional unsteady heat conduction equation is solved by a finite difference method. The numerical predictions are in good agreement with experimental data. The overall heat transfer model can be used for process optimization purposes. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 271,279, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10055 [source] Heat transfer during microwave combination heating: Computational modeling and MRI experimentsAICHE JOURNAL, Issue 9 2010Vineet Rakesh Abstract Combination of heating modes such as microwaves, convection, and radiant heating can be used to realistically achieve the quality and safety needed for cooking processes and, at the same time, make the processes faster. Physics-based computational modeling used in conjunction with MRI experimentation can be used to obtain critical understanding of combination heating. The objectives were to: (1) formulate a fully coupled electromagnetics - heat transfer model, (2) use magnetic resonance imaging (MRI) experiments to determine the 3D spatial and temporal variation of temperatures and validate the numerical model, (3) use the insight gained from the model and experiments to understand the combination heating process and to optimize it. The different factors that affect heating patterns during combination heating such as the type of heating modes used, placement of sample, and microwave cycling were considered. Objective functions were defined and minimized for design and optimization. The use of such techniques can lead to greater control and automation of combination heating process benefitting the food process and product developers immensely. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Particle-scale simulation of the flow and heat transfer behaviors in fluidized bed with immersed tubeAICHE JOURNAL, Issue 12 2009Yongzhi Zhao Abstract A kind of new modified computational fluid dynamics-discrete element method (CFD-DEM) method was founded by combining CFD based on unstructured mesh and DEM. The turbulent dense gas,solid two phase flow and the heat transfer in the equipment with complex geometry can be simulated by the programs based on the new method when the k-, turbulence model and the multiway coupling heat transfer model among particles, walls and gas were employed. The new CFD-DEM coupling method that combining k-, turbulence model and heat transfer model, was employed to simulate the flow and the heat transfer behaviors in the fluidized bed with an immersed tube. The microscale mechanism of heat transfer in the fluidized bed was explored by the simulation results and the critical factors that influence the heat transfer between the tube and the bed were discussed. The profiles of average solids fraction and heat transfer coefficient between gas-tube and particle-tube around the tube were obtained and the influences of fluidization parameters such as gas velocity and particle diameter on the transfer coefficient were explored by simulations. The computational results agree well with the experiment, which shows that the new CFD-DEM method is feasible and accurate for the simulation of complex gas,solid flow with heat transfer. And this will improve the farther simulation study of the gas,solid two phase flow with chemical reactions in the fluidized bed. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Ablative heat transfer in a shrinking packed-bed of ZnO undergoing solar thermal dissociationAICHE JOURNAL, Issue 7 2009L. O. Schunk Abstract A transient heat transfer model is formulated for a shrinking packed-bed of reacting ZnO particles exposed to concentrated solar irradiation. The model combines conduction, convection, and radiation heat transfer with simultaneous sintering and reaction kinetics. Validation is accomplished in terms of temperatures and dissociation rates experimentally measured using a solar-driven thermogravimeter with ZnO packed-bed samples subjected to solar flux concentration ratios in the range 1225,2133 suns and surface temperatures in the range 1834,2109 K. Operating conditions are typical of an ablation regime controlled by the rate of radiative heat transfer to the first layers of ZnO undergoing endothermic dissociation. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Effects of tool-embedded dielectric sensors on heat transfer phenomena during composite curePOLYMER COMPOSITES, Issue 2 2007A.A. Skordos The present study examines the effects that placement of tool-mounted dielectric sensors in the composite cure assembly has on the local thermal and degree-of-cure fields. A nonlinear heat transfer model, incorporating appropriate thermoset cure and thermal property submodels, is used to simulate the cure of carbon and glass composites of various thicknesses. The model is validated against experimental data obtained during the cure of composite samples in a resin-transfer molding tool. The results of the simulations show that embedding a sensor can have a significant effect on the thermal field, because of the thermal conductivity mismatch between the metal tool and the sensor substrate material. In the heating-up stage of the cure profile, sensors embedded in the heated tool side intensify thermal gradients, which causes a corresponding lag in the progress of the reaction in the area adjacent to the sensor. Exothermic effects are also intensified by the sensor presence, especially in the case of thick composite curing. These results suggest that control strategies based on the utilization of embedded sensors should take these effects into account. POLYM. COMPOS., 28:139,152, 2007. © 2007 Society of Plastics Engineers. [source] Ohmic heating of dairy fluids,effects of local electric field on temperature distributionASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Heng Jin Tham Abstract This paper presents the heat transfer model of a continuous flow ohmic heating process. The model fluid used was a mixture of reconstituted skimmed milk and whey protein concentrate solution. Two-dimensional numerical simulations of an annular ohmic heater were performed using a general purpose partial differential equation solver, FlexPDE. The momentum, energy, and electrical equations were solved for a laminar flow regime. Two models were used to determine the volumetric heating rate, one taking into account the local electric field by solving the Laplace equation while another model assumes an average voltage gradient applied between the two electrodes. Results show that while the wall temperature distribution is different for the two cases, the bulk fluid temperature and the average outlet temperature are the same. The predicted temperatures generally agree well with the measured temperatures. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Inter-particle contact heat transfer model: an extension to soils at elevated temperaturesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2005W. H. Leong Abstract A simple ,inter-particle contact heat transfer' model for predicting effective thermal conductivity of soils at moderate temperatures (0,30°C) has been extended up to 90°C. The extended model accounts for latent heat transport by water vapour diffusion in soil air above the permanent wilting point; below that point, the soil thermal conductivity is approximated by linear interpolation without latent heat effect. By and large the best results are obtained when the latent heat is used only in the ,self consistent approximation' model with an overall root mean square error of 35% for all soils under consideration or 26% when excluding volcanic soils. This option can also be applied to moderate temperatures at which the enhanced heat transfer is negligibly small. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||