The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Filip Johnsson - One of the best experts on this subject based on the ideXlab platform.
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time series analysis of pressure fluctuations in gas solid Fluidized Beds a review
International Journal of Multiphase Flow, 2011Co-Authors: Ruud J Van Ommen, Srdjan Sasic, Filip Johnsson, John Van Der Schaaf, Stefan Gheorghiu, Marc Olivi CoppensAbstract:This work reviews methods for time-series analysis for characterization of the dynamics of gas-solid Fluidized Beds from in-bed pressure measurements for different fluidization regimes. The paper covers analysis in time domain, frequency domain, and in state space. It is a follow-up and an update of a similar review paper written a decade ago. We use the same pressure time-series as used by Johnsson et al. (2000). The paper updates the previous review and includes additional methods for time-series analysis, which have been proposed to investigate dynamics of gas-solid Fluidized Beds. Results and underlying assumptions of the methods are discussed. Analysis in the time domain is often the simplest approach. The standard deviation of pressure fluctuations is widely used to identify regimes in Fluidized Beds, but its disadvantage is that it is an indirect measure of the dynamics of the flow. The so-called average cycle time provides information about the relevant time scales of the system, making it an easy-to-calculate alternative to frequency analysis. Autoregressive methods can be used to show an analogy between a Fluidized bed and a single or a set of simple mechanical systems acting in parallel. The most common frequency domain method is the power spectrum. We show that - as an alternative to the often used non-parametric methods to estimate the power spectrum - parametric methods can be useful. To capture transient effects on a longer time scale (>1 s), either the transient power spectral density or wavelet analysis can be applied. For the state space analysis, the information given by the Kolmogorov entropy is equivalent to that of the average frequency, obtained in the frequency domain. However, an advantage of certain state space methods, such as attractor comparison, is that they are more sensitive to small changes than frequency domain methods; this feature can be used for, e.g., on-line monitoring. In general, we conclude that, over the past decade, progress has been made in understanding Fluidized-bed dynamics by extracting the relevant information from pressure fluctuation data, but the picture is still incomplete.
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characterization of fluid dynamics of Fluidized Beds by analysis of pressure fluctuations
Progress in Energy and Combustion Science, 2007Co-Authors: Srdjan Sasic, Bo G Leckner, Filip JohnssonAbstract:This paper reviews procedures for investigating the fluid-dynamic behavior of gas–solid Fluidized Beds using pressure signals as obtained from modeling or experiments. The procedures studied are applicable to all types of Fluidized-bed reactor. Models generating pressure data in such systems are presented with respect to complexity and amount of information provided. There is a discussion on how a calculated pressure can be compared to a measured signal in order to create a reliable representation of the fluid dynamics of the system. The type of information resulting from various ways of measuring the pressure in Fluidized Beds is discussed, as well as the use of absolute versus differential pressure probes. Time series analysis is reviewed; it can be applied to modeled and measured pressure signals in time, frequency, time–frequency and state space. Also, recommendations are provided on the use of the methods of analysis examined. The sources of pressure fluctuations, propagation features and the nature of pressure waves in Fluidized Beds are discussed. Finally, examples from the literature are presented, illustrating the outcome of the procedures discussed.
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digital image analysis of hydrodynamics two dimensional bubbling Fluidized Beds
Chemical Engineering Science, 2004Co-Authors: Laihong Shen, Filip Johnsson, Bo G LecknerAbstract:Abstract A new method of digital image analysis has been developed to study the hydrodynamics of two-dimensional bubbling Fluidized Beds with a digital video camera. The method comprises simultaneous of the size and velocity of gas bubbles, and the axial and radial distribution of bubble voidage. It provides a better estimation of the visible bubble flow than from local probe methods. Also a good estimation of the throughflow can be gotten, which is of great importance for combustor applications. Parallel to the approach of Darton et al. (Transactions of the Institution Chemical Engineering 55 (1977) 274) for three-dimensional Fluidized Beds, an equation for the bubble diameter of two-dimensional Beds is developed, D b =0.89[(U 0 −U mf ) (h+3.0 A 0 /t)] 2/3 g 1/3 , where h is the bed height above air distributor; t is the thickness of the two-dimensional bed. For Group B particle and a given gas velocity U 0 , if the bed height is sufficient, bubble diameter D b could be able to reach a maximum value at a certain height. The height is defined as the maximum bubble height h ∗ , beyond which bubbles do not grow further and become unstable and break up. The height h ∗ is a particle-size dependency, and can be expressed as h ∗ =A(1+3 exp (−U 0 /U mf ))D t , where A =0.45 and D t is the bed diameter. The bubble rising velocity U b can be described by U b =Φ gD b (Φ=0.80−1.0) within the height h ∗ . Also, the bubble velocity is kept constant beyond the height h ∗ . The bubble density δ b is not uniform over the bed cross-section. It increases with particle size, and increases quite slowly for high fluidization velocities. The gas throughflow decreases much slowly along with the bed height. Beyond the height h ∗ , the gas throughflow is almost kept constant. Also, the throughflow is a significant part of the total gas flow, especially for high fluidization velocity, and increases almost linearly with the fluidization velocity.
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non intrusive determination of bubble and slug length scales in Fluidized Beds by decomposition of the power spectral density of pressure time series
International Journal of Multiphase Flow, 2002Co-Authors: Filip Johnsson, Van Der John J Schaaf, J Jaap C Schouten, Van Den Cm BleekAbstract:Abstract In this paper we show that spectral analysis of non-intrusive time dependent pressure measurements in bubbling and circulating gas–solid Fluidized Beds permits to obtain the first estimates of bubble, gas slug, and solids cluster length scales from pressure fluctuation data. These length scales are calculated from the incoherent cross power spectra of pressure signals measured in the bubbling or circulating bed and in the plenum. Remarkable quantitative agreement with bubble diameter data is found, and equally remarkable agreement is obtained with independent estimates of gas slug lengths by others in circulating Fluidized Beds. These results demonstrate the possibility of greatly expanding the information that can be obtained non-intrusively from gas–solid Fluidized Beds.
John R Grace - One of the best experts on this subject based on the ideXlab platform.
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a perspective on electrostatics in gas solid Fluidized Beds challenges and future research needs
Powder Technology, 2018Co-Authors: Xiaotao Bi, Farzam Fotovat, John R GraceAbstract:Abstract This paper provides a perspective on the current knowledge and potential areas of future research related to electrostatics in Fluidized Beds. Aspects addressed include characterization techniques, charge generation and dissipation mechanisms, interplay between the electrostatics and hydrodynamics, charge control methods, applications of tribo-electrostatic fluidization systems, and computational simulations which account for electrostatic charges. This is a complex research field involving fluid mechanics, powders and electrical physics, with potential rewards in terms of safety, process monitoring and new applications.
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electrostatics in gas solid Fluidized Beds a review
Chemical Engineering Science, 2017Co-Authors: Farzam Fotovat, Xiaotao Bi, John R GraceAbstract:Abstract Gas-solid Fluidized Beds, by their nature, are associated with intense and frequent collisions of solid particles with each other and with the vessel wall, causing tribo-electrification. Accumulation of electrostatic charges in Fluidized bed reactors can result in severe problems such as agglomeration, wall fouling, nuisance and hazardous discharge, all reducing the process performance and raising significant safety concerns. Tribo-charging of particles in Fluidized Beds has also been exploited in a number of useful applications. In this review, the characterization methods of electrostatics and the mechanisms of charge generation and distribution in Fluidized Beds are presented, followed by an account of the interplay between the hydrodynamics and electrostatic phenomena. Furthermore, techniques of electrostatic charge control in Fluidized Beds are reviewed, and applications of tribo-electrostatic fluidization systems are summarized. Finally, computational fluid dynamics simulations of the electrostatic effects on the hydrodynamic characteristics of Fluidized Beds are outlined.
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Decoupling electrostatic signals from gas–solid bubbling Fluidized Beds
Powder Technology, 2016Co-Authors: Chuan He, Xiaotao Bi, John R GraceAbstract:Abstract Electrostatic signals registered by collision probes in gas–solid Fluidized Beds contain useful information. However, the signal has been poorly understood, with questions, such as what the signal means and how to extract useful information, being unanswered. In this study, different decoupling methods based on a simple charge transfer and induction model are proposed and applied to obtain both the particle charge density and the bubble rise velocity by decoupling electrostatic charge/current signals from a previously developed dual-material probe in both two- and three-dimensional freely bubbling Fluidized Beds. A signal processing procedure including a bubble selection algorithm is proposed and applied to screen electrostatic signals from the probe in bubbling Fluidized Beds. Decoupled results from two selected methods showed consistent trends and had the same order of magnitudes as those obtained from the analysis of video images and Faraday cup measurements. The effects of the bubble selection algorithm criteria on interpreted results are also investigated.
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on the superficial gas velocity in deep gas solids Fluidized Beds
Chemical Engineering Science, 2011Co-Authors: Tingwen Li, John R Grace, Lawrence J. Shadle, Chris GuentherAbstract:The superficial gas velocity is one of the key parameters used to determine the flow hydrodynamics in gas–solids Fluidized Beds. However, the superficial velocity varies with height in practice, and there is no consistent basis for its specification. Different approaches to determine the superficial gas velocity in a deep gas–solids system are shown to cause difficulties in developing models and in comparing predictions with experimental results. In addition, the reference conditions for superficial gas velocity are important in modeling of deep gas–solids systems where there is a considerable pressure drop.
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On the superficial gas velocity in deep gas–solids Fluidized Beds
Chemical Engineering Science, 2011Co-Authors: Tingwen Li, John R Grace, Lawrence J. Shadle, Chris GuentherAbstract:The superficial gas velocity is one of the key parameters used to determine the flow hydrodynamics in gas–solids Fluidized Beds. However, the superficial velocity varies with height in practice, and there is no consistent basis for its specification. Different approaches to determine the superficial gas velocity in a deep gas–solids system are shown to cause difficulties in developing models and in comparing predictions with experimental results. In addition, the reference conditions for superficial gas velocity are important in modeling of deep gas–solids systems where there is a considerable pressure drop.
Jam Hans Kuipers - One of the best experts on this subject based on the ideXlab platform.
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two fluid modeling of three dimensional cylindrical gas solid Fluidized Beds using the kinetic theory of granular flow
Chemical Engineering Science, 2013Co-Authors: Vikrant Vijay Verma, N Niels G Deen, J Johan T Padding, Jam Hans KuipersAbstract:A highly efficient numerical scheme has been incorporated to solve a traditional two-fluid model for dense gas–solid flow in large scale Fluidized Beds. Difficulties associated with the numerical solution and boundary condition enforcement especially in the azimuthally direction and at the axis of the cylindrical domain are discussed in detail. Higher order discretization schemes with deferred correction approach have been implemented for the convection terms. The p–e algorithm (Van der Hoef et al., 2006) has been implemented to deal with densely packed regions in the Fluidized bed. A modified SIMPLE algorithm is used to solve the pressure and volume fraction corrections, and a projection method is used to obtain solutions of the momentum equations. The resulting semi-implicit method allows for using larger time steps and produces accurate results in a stable and efficient manner. Numerical tests on bubbling Fluidized Beds are undertaken and compared with experimental data reported by Laverman et al., 2012. The simulation results are found to be in good agreement. In addition a comparative study has been performed quantifying the effects of grid size, flux limiters, frictional model and coefficient of restitution.
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spout Fluidized Beds recent advances in experimental and numerical studies
Chemical Engineering Science, 2013Co-Authors: Vinayak S Sutkar, N Niels G Deen, Jam Hans KuipersAbstract:Abstract In the past few decades, the applicability of spout Fluidized Beds has been augmented immensely. This is not only due to the fact that these systems combine characteristics of spouted and Fluidized Beds but also to their efficacy to handle chemical transformations involving simultaneous heat and mass transfer in combination with varying particles size. This is important in applications such as granulation, coating, drying, pyrolysis and combustion etc. The present work aims at critically analyzing the recent advances in experimental and numerical studies of spout Fluidized Beds. Initially, the discussion will concentrate on experimental studies emphasizing variation of minimum spouting and spout-fluidizing velocity, operating pressure, mixing and jet penetration length. Furthermore, flow regime maps will be discussed. Subsequently, the application of various numerical modeling strategies is highlighted. Also, recommendations are given for future work required in experimental and modeling studies.
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coarse grid simulation of bed expansion characteristics of industrial scale gas solid bubbling Fluidized Beds
Chemical Engineering Science, 2010Co-Authors: Junwu Wang, Van Der Ma Martin Hoef, Jam Hans KuipersAbstract:Two-fluid modeling of the hydrodynamics of industrial-scale gas-Fluidized Beds proves a long-standing challenge for both engineers and scientists. In this study, we suggest a simple method to modify currently available drag correlations to allow for the effect of unresolved sub-grid scale structures, by assuming that the particles inside each computational cell are presented in the form of a two-phase structure. This method would thus make it possible to simulate the hydrodynamics of industrial-scale bubbling Fluidized Beds of Geldart B and D particles with a coarse computational mesh. It is shown that with the proposed modification of the drag force correlation, the experimentally measured bed expansion characteristics of industrial-scale bubbling Fluidized Beds can be reasonably predicted at acceptable computational cost. Also the simulation result for the macroscopic solid circulation pattern is in qualitative agreement with the experimental data.
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numerical simulation of dense gas solid Fluidized Beds a multiscale modeling strategy
Annual Review of Fluid Mechanics, 2008Co-Authors: Van Der Ma Martin Hoef, N Niels G Deen, Van Martin Sint M Annaland, Jam Hans KuipersAbstract:Gas-solid Fluidized Beds are widely applied in many chemical processes involving physical and/or chemical transformations, and for this reason they are the subject of intense research in chemical engineering science. Over the years, researchers have developed a large number of numerical models of gas-Fluidized Beds that describe gas-solid flow at different levels of detail. In this review, we discriminate these models on the basis of whether a Lagrangian or a Eulerian approach is used for the gas and/or particulate flow and subsequently classify them into five main categories, three of which we discuss in more detail. Specifically, these are resolved discrete particle models (also called direct numerical simulations), unresolved discrete particle models (also called discrete element models), and two-fluid models. For each of the levels of description, we give the general equations of motion and indicate how they can be solved numerically by finite-difference techniques, followed by some illustrative examples of a Fluidized bed simulation. Finally, we address some of the challenges ahead in the multiscale modeling of gas-Fluidized Beds
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review of discrete particle modeling of Fluidized Beds
Chemical Engineering Science, 2007Co-Authors: N Niels G Deen, Van Martin Sint M Annaland, Van Der Ma Martin Hoef, Jam Hans KuipersAbstract:This paper reviews the use of discrete particle models (DPMs) for the study of the flow phenomena prevailing in Fluidized Beds. DPMs describe the gas-phase as a continuum, whereas each of the individual particles is treated as a discrete entity. The DPMs accounts for the gas–particle and particle–particle interactions. This model is part of a multi-level modeling approach and has proven to be very useful to generate closure information required in more coarse-grained models. In this paper, a basic DPM, based on both the hard- and soft-sphere approaches is described. The importance of the closures for particle–particle and gas–particle interaction is demonstrated with several illustrative examples. Finally, an outlook for the use of DPMs for the investigation of various chemical engineering problems in the area of fluidization is given.
N Niels G Deen - One of the best experts on this subject based on the ideXlab platform.
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effect of superficial gas velocity on the solid temperature distribution in gas Fluidized Beds with heat production
Industrial & Engineering Chemistry Research, 2017Co-Authors: Mohammad M Banaei, Jeroen Jegers, Martin Van Sint Annaland, J.a.m. Kuipers, N Niels G DeenAbstract:The hydrodynamics and heat transfer of cylindrical gas–solid Fluidized Beds for polyolefin production was investigated with the two-fluid model (TFM) based on the kinetic theory of granular flow (KTGF). It was found that the Fluidized bed becomes more isothermal with increasing superficial gas velocity. This is mainly due to the increase of solids circulation and improvement in gas solid contact. It was also found that the average Nusselt number weakly depends on the gas velocity. The TFM results were qualitatively compared with simulation results of computational fluid dynamics combined with the discrete element model (CFD-DEM). The TFM results were in very good agreement with the CFD-DEM outcomes, so the TFM can be a reliable source for further investigations of Fluidized Beds especially large lab-scale reactors
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two fluid modeling of three dimensional cylindrical gas solid Fluidized Beds using the kinetic theory of granular flow
Chemical Engineering Science, 2013Co-Authors: Vikrant Vijay Verma, N Niels G Deen, J Johan T Padding, Jam Hans KuipersAbstract:A highly efficient numerical scheme has been incorporated to solve a traditional two-fluid model for dense gas–solid flow in large scale Fluidized Beds. Difficulties associated with the numerical solution and boundary condition enforcement especially in the azimuthally direction and at the axis of the cylindrical domain are discussed in detail. Higher order discretization schemes with deferred correction approach have been implemented for the convection terms. The p–e algorithm (Van der Hoef et al., 2006) has been implemented to deal with densely packed regions in the Fluidized bed. A modified SIMPLE algorithm is used to solve the pressure and volume fraction corrections, and a projection method is used to obtain solutions of the momentum equations. The resulting semi-implicit method allows for using larger time steps and produces accurate results in a stable and efficient manner. Numerical tests on bubbling Fluidized Beds are undertaken and compared with experimental data reported by Laverman et al., 2012. The simulation results are found to be in good agreement. In addition a comparative study has been performed quantifying the effects of grid size, flux limiters, frictional model and coefficient of restitution.
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spout Fluidized Beds recent advances in experimental and numerical studies
Chemical Engineering Science, 2013Co-Authors: Vinayak S Sutkar, N Niels G Deen, Jam Hans KuipersAbstract:Abstract In the past few decades, the applicability of spout Fluidized Beds has been augmented immensely. This is not only due to the fact that these systems combine characteristics of spouted and Fluidized Beds but also to their efficacy to handle chemical transformations involving simultaneous heat and mass transfer in combination with varying particles size. This is important in applications such as granulation, coating, drying, pyrolysis and combustion etc. The present work aims at critically analyzing the recent advances in experimental and numerical studies of spout Fluidized Beds. Initially, the discussion will concentrate on experimental studies emphasizing variation of minimum spouting and spout-fluidizing velocity, operating pressure, mixing and jet penetration length. Furthermore, flow regime maps will be discussed. Subsequently, the application of various numerical modeling strategies is highlighted. Also, recommendations are given for future work required in experimental and modeling studies.
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numerical and experimental study on multiple spout Fluidized Beds
Chemical Engineering Science, 2011Co-Authors: Maureen S Van Buijtenen, N Niels G Deen, J.a.m. Kuipers, Willemjan Van Dijk, Thomas Leadbeater, David ParkerAbstract:In this paper we study the effect of multiple spouts on the bed dynamics in a pseudo-2D triple-spout Fluidized bed, employing the discrete particle model (DPM) and non-intrusive measurement techniques such as particle image velocimetry (PIV) and positron emission particle tracking (PEPT). A flow regime map was constructed, revealing new regimes that were not reported so far. The multiple-interacting-spouts regime (C) has been studied in detail for a double- and triple-spout Fluidized bed, where the corresponding fluidization regime for a single-spout Fluidized bed has been studied as a reference case. The experimental results obtained with PIV and PEPT agree very well for all the three cases, showing the good performance of these techniques. The DPM simulation results slightly deviate from the experiments which is attributed to particle–wall effects that are more dominant in pseudo-2D Beds than in 3D systems. The investigated multiple-interacting-spouts regime is a fully new flow regime that does not appear in single-spout Fluidized Beds. Two flow patterns have been observed, viz. particle circulation in between the spouts near the bottom of the bed, and an apparent single-spout fluidization motion at a higher location upwards in the bed. These findings show that the presence of multiple spouts in a spout Fluidized bed highly affect the flow behaviour, which cannot be distinguished by solely investigating single-spout Fluidized Beds.
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numerical simulation of dense gas solid Fluidized Beds a multiscale modeling strategy
Annual Review of Fluid Mechanics, 2008Co-Authors: Van Der Ma Martin Hoef, N Niels G Deen, Van Martin Sint M Annaland, Jam Hans KuipersAbstract:Gas-solid Fluidized Beds are widely applied in many chemical processes involving physical and/or chemical transformations, and for this reason they are the subject of intense research in chemical engineering science. Over the years, researchers have developed a large number of numerical models of gas-Fluidized Beds that describe gas-solid flow at different levels of detail. In this review, we discriminate these models on the basis of whether a Lagrangian or a Eulerian approach is used for the gas and/or particulate flow and subsequently classify them into five main categories, three of which we discuss in more detail. Specifically, these are resolved discrete particle models (also called direct numerical simulations), unresolved discrete particle models (also called discrete element models), and two-fluid models. For each of the levels of description, we give the general equations of motion and indicate how they can be solved numerically by finite-difference techniques, followed by some illustrative examples of a Fluidized bed simulation. Finally, we address some of the challenges ahead in the multiscale modeling of gas-Fluidized Beds
Cristina Sobrino - One of the best experts on this subject based on the ideXlab platform.
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A review of solar thermal energy storage in Beds of particles: Packed and Fluidized Beds
Solar Energy, 2018Co-Authors: José Antonio Almendros-ibáñez, M. Fernández-torrijos, M. Díaz-heras, J. F. Belmonte, Cristina SobrinoAbstract:This review summarizes different solar thermal energy storage techniques from a particle technology perspective, including sensible, latent and thermochemical techniques for low- and high-temperature applications that use particles as the storage medium in the thermal energy storage system. The focus is on applications, experimental results, modeling and future trends. This review describes two different particle technologies used to store thermal energy: packed and Fluidized Beds. The advantages and disadvantages of both technologies are reviewed throughout different studies found in the literature for various thermal energy storage systems. Packed Beds have the main advantage of thermal stratification, which increases the efficiency of solar collectors in low-temperature sensible energy storage systems and augments the exergy content in the bed. Moreover, they have been proven to be suitable as dual-media thermocline storage systems for CSP plants. In contrast, the high mixing rates of Fluidized Beds makes them suitable for the rapid distribution of concentrated solar energy in particle receiver CSP systems. In addition, their high heat and mass transfer rates, compared with those of packed Beds, make them the preferred particle technology for thermochemical energy storage applications. This review also notes that it is important to find new materials with an appropriate size and density that can be properly used in a Fluidized bed. Additionally, more specific research efforts are necessary to improve the understanding of the behavior of these materials during the fluidization process and over a high number of charging/discharging cycles.
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Modeling the Heat Transfer Coefficient Between a Surface and Fixed and Fluidized Beds With Phase Change Material
Journal of Heat Transfer-Transactions of the Asme, 2016Co-Authors: M. A. Izquierdo-barrientos, Cristina Sobrino, José Antonio Almendros-ibáñezAbstract:The objective of this work is to model the heat transfer coefficient between an immersed surface and fixed and bubbling Fluidized Beds of granular phase change material (PCM). The model consists of a two-region model with two different voidages in which steady and transient conduction problems are solved for the fixed and Fluidized bed cases, respectively. The model is validated with experimental data obtained under fixed and Fluidized conditions for sand, a common material used in fixed and Fluidized Beds for sensible heat storage, and for a granular PCM with a phase change temperature of approximately 50 degrees C. The superficial gas velocity is varied to quantify its influence on the convective heat transfer coefficient for both the materials. The model proposed for the PCM properly predicts the experimental results, except for high flow rates, which cause the contact times between the surface and particles to be very small and lead the model to overpredict the results.