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The objective of the present work was to research the storage behavior of a fluidized bed filled with a granular phase change material (PCM) with a small particle diameter (d p = 0.54 mm). The performance of the fluidized bed was compared to that of well-known storage methods such as fluidized beds with sand and packed beds based of sand and PCM. For this purpose, heating experiments were conducted in a cylindrical bed with air as the working fluid.The influence of the bed height and flow rate on the storage and recovery efficiencies of the fluidized bed of PCM was analyzed. Additionally, the stability of the PCM during various charging-discharging cycles was studied.The results indicate that this PCM is an alternative material that can be used in fluidized bed systems to increase the efficiency of storing thermal * Corresponding author. NOTICE: this is the author's version of a work that was accepted for publication in Chemical Engineering Journal. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. The cycling test shows that the PCM is stable under bubbling conditions up to 15 cycles, which corresponds to approximately 75 hours of continuous operation. A definitive version was subsequently published in Chemical Engineering

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A new model is proposed for obtaining the velocity profile of the particle ejected from the bubble dome in a freely bubbling 2-D fluidized bed. Its basis is the supposition that the initial velocity of the ejected particles, with a direction perpendicular to the dome contour, depends on bubble velocity and bubble growth velocity. This model differs from those previously appearing in the literature in that it is valid not only for vertical-ascent circular bubbles.Experiments were carried out in a freely bubbling 2-D fluidized bed using a high-speed video camera to measure the velocity profile. Upon comparing these results with the proposed model, it was established that, excepting some isolated cases, the model properly predicts the magnitude and direction of the maximum particle ejection velocity and the velocity profile.Using the work of Shen et al. (2004. Digital image analysis of hydrodynamics two-dimensional bubbling fluidized beds. Chemical Engineering Science 59, 2607-2617), we obtain two general equations for the bubble velocity and the bubble growth velocity in a 2-D fluidized bed. These expressions, together with the proposed model, can be used to calculate the initial velocity of the ejected particles.

This work presents an experimental study to determine the capacity of a phase change material (PCM) in granular form to be used in fixed and bubbling fluidized beds for thermal energy storage. The experimental measurements are focused on determination of the heat transfer coefficient between a heated surface immersed in the bed and the granular PCM. The flow rate is varied to quantify its influence on the heat transfer coefficient. The PCM used is Rubitherm GR50 with a phase change temperature of approximately 50• C. The PCM is available in two different particle sizes, 0.54 mm and 1.64 mm, of which the finer is used in the fluidized bed and the coarser is used in the fixed bed. In addition, the results obtained for the PCM are compared with the heat transfer coefficients measured for sand, a material commonly used for thermal storage. * Corresponding author. NOTICE: this is the author's version of a work that was accepted for publication in Applied Thermal Engineering. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Applied Thermal Engineering 78 (2015) pp. 373-379. doi:10.1016/j.applthermaleng.2014.12.044 In comparing the heat transfer coefficients for fixed and fluidized beds, the heat transfer coefficients in the fluidized bed with PCM are nearly three times higher than those for the fixed bed at the same gas flow rate. This increase in the heat transfer is a result of two main factors: first, the continuous renewal of PCM particles from the heated surface when they are fluidized, and second, the large quantities of energy in latent form absorbed by the PCM. In the fixed bed there is no renovation of particles, consequently only a small percentage of particles are able to change its phase. Hence, there is no increase in the heat transfer coefficient due to this fact.