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Brems, A., Caceres, G., Dewil, R., Baeyens, J., & Pitie, E. (2013). Heat transfer to the riser-wall of a circulating fluidised bed (CFB). Energy, 50, 493–500.
Abstract: The circulating fluidized bed is of increasing importance for gas-solid and gas-catalytic reactions, for drying, and recently its use in solar energy capture and storage has been advocated. In all applications, the supply or withdrawal of heat is a major issue, and the heat transfer coefficient from the gas-solid suspension to the heat transfer surface needs to be determined as design parameter. The present paper investigates the heat transfer coefficient for different operating gas velocity and solids circulation flux, whilst covering the different hydrodynamic solid flow regimes of dilute, core-annulus or dense mode. Measured values of the wall-to-bed heat transfer coefficients are compared with empirical predictions of both Molodstof and Muzyka, and Golriz and Grace. The application of a packet renewal mechanism at the wall is also investigated, and introducing the predicted solid contact time at the wall provides a very fair estimate of the heat transfer coefficient. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.
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Caceres, G., Anrique, N., Girard, A., Degreve, J., Baeyens, J., & Zhang, H. L. (2013). Performance of molten salt solar power towers in Chile. J. Renew. Sustain. Energy, 5(5), 15 pp.
Abstract: Chile is facing important challenges to develop its energy sector. Estimations demonstrate that in its electricity consumption Chile will grow at an annual rate of 4.6% until 2030, despite ongoing efficiency improvements. To satisfy this demand in a sustainable way, the national energy policy promotes the integration of novel and clean power generation into the national power mix, with special emphasis on concentrated solar power (CSP). The present paper assesses the development of solar-based electricity generation in Chile by CSP, achieved by a Solar Power Tower plant (SPT) using molten salt as heat carrier and store. Such SPTs can be installed at different locations in Chile, and connected to the main national grid. Results show that each SPT plant can generate around 76 GWh(el) of net electricity, when considering solar irradiation as the sole energy source and at a 16% overall efficiency of the SPT process. For operation in a continuous mode, a hybrid configuration with integrated gas backup system increases the generating potential of each SPT to 135 GWh(el). A preliminary Levelized Energy Cost (LEC) calculation provides LEC values between 0.15 and 0.18 $/kWh, as function of the overall process efficiency and estimated investment cost. Chile's solar irradiation favors the implementation of SPT plants. (C) 2013 AIP Publishing LLC.
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Fernandes, D., Pitie, F., Caceres, G., & Baeyens, J. (2012). Thermal energy storage: “How previous findings determine current research priorities”. Energy, 39(1), 246–257.
Abstract: Thermal energy storage is an expanding field within the subject of renewable energy technologies. After a listing of the different possibilities available for energy storage, this paper provides a comparison of various materials for High Temperature Thermal Energy Storage (HTTS). Several attributes and needs of each solution are listed. One in particular is using the latent heat as one of the most efficient ways to store thermal energy. The mixture of phase change material (PCM) embedded in a metal foam is optimising the thermal properties of the material for latent heat energy storage. The results of previous studies show that mechanical and thermal properties of foam were extensively studied separately. This paper highlights the potential for an advanced study of thermo-mechanical properties of metal foams embedded with PCM. (c) 2012 Elsevier Ltd. All rights reserved.
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Parrado, C., Caceres, G., Bize, F., Bubnovich, V., Baeyens, J., Degreve, J., et al. (2015). Thermo-mechanical analysis of copper-encapsulated NaNO3-KNO3. Chem. Eng. Res. Des., 93, 224–231.
Abstract: The present paper presents a numerical study to investigate and assess the heat transfer behavior of a copper and salt composite. A mixture of nitrates, KNO3-NaNO3, within a deformable spherical shell coating of copper will be used as an encapsulated phase change material, E-PCM. In the context of a thermo-mechanical analysis of this E-PCM, a simulation is proposed to determine its storage capacity and properties The melting, or solidification of the encapsulated PCM particles do not provoke cracking of the deformable shell. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
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Zhang, H. L., Baeyens, J., Caceres, G., Degreve, J., & Lv, Y. Q. (2016). Thermal energy storage: Recent developments and practical aspects. Prog. Energy Combust. Sci., 53, 1–40.
Abstract: Thermal energy storage (TES) transfers heat to storage media during the charging period, and releases it at a later stage during the discharging step. It can be usefully applied in solar plants, or in industrial processes, such as metallurgical transformations. Sensible, latent and thermo-chemical media store heat in materials which change temperature, phase or chemical composition, respectively. Sensible heat storage is well-documented. Latent heat storage, using phase change materials (PCMs), mainly using liquid solid transition to store latent heat, allows a more compact, efficient and therefore economical system to operate. Thermo-chemical heat storage (TCS) is still at an early stage of laboratory and pilot research despite its attractive application for long term energy storage. The present review will assess previous research, while also adding novel treatments of the subject. TES systems are of growing importance within the energy awareness: TES can reduce the LCOE (levelized cost of electricity) of renewable energy processes, with the temperature of the storage medium being the most important parameter. Sensible heat storage is well-documented in literature and applied at large scale, hence limited in the content of the present review paper. Latent heat storage using PCMs is dealt with, specifically towards high temperature applications, where inorganic substances offer a high potential. Finally, the use of energy storage through reversible chemical reactions (thermo-chemical Storage, TCS) is assessed. Since PCM and TCS storage media need to be contained in a capsule (sphere, tube, sandwich plates) of appropriate materials, potential containment materials are examined. A heat transfer fluid (HTF) is required to convey the heat from capture, to storage and ultimate re-use. Particle suspensions offer a valid alternative to common HTF, and a preliminary assessment confirms the advantages of the upflow bubbling fluidized bed and demonstrates that particulate suspensions enable major savings in investment and operating costs. Novel treatments of the TES subject in the review involve the required encapsulation of the latent and chemical storage media, the novel development of powder circulation loops as heat transfer media, the conductivity enhancement of PCMs, the use of lithium salts, among others. (C) 2015 Elsevier Ltd. All rights reserved.
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Zhang, H. L., Baeyens, J., Degreve, J., & Caceres, G. (2013). Concentrated solar power plants: Review and design methodology. Renew. Sust. Energ. Rev., 22, 466–481.
Abstract: Concentrated solar power plants (CSPs) are gaining increasing interest, mostly as parabolic trough collectors (PTC) or solar tower collectors (STC). Notwithstanding CSP benefits, the daily and monthly variation of the solar irradiation flux is a main drawback. Despite the approximate match between hours of the day where solar radiation and energy demand peak, CSPs experience short term variations on cloudy days and cannot provide energy during night hours unless incorporating thermal energy storage (TES) and/or backup systems (BS) to operate continuously. To determine the optimum design and operation of the CSP throughout the year, whilst defining the required TES and/or BS, an accurate estimation of the daily solar irradiation is needed. Local solar irradiation data are mostly only available as monthly averages, and a predictive conversion into hourly data and direct irradiation is needed to provide a more accurate input into the CSP design. The paper (i) briefly reviews CSP technologies and STC advantages; (ii) presents a methodology to predict hourly beam (direct) irradiation from available monthly averages, based upon combined previous literature findings and available meteorological data; (iii) illustrates predictions for different selected STC locations; and finally (iv) describes the use of the predictions in simulating the required plant configuration of an optimum STC. The methodology and results demonstrate the potential of CSPs in general, whilst also defining the design background of STC plants. (C) 2013 Elsevier Ltd. All rights reserved.
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Zhang, H. L., Baeyens, J., Degreve, J., Caceres, G., Segal, R., & Pitie, F. (2014). Latent heat storage with tubular-encapsulated phase change materials (PCMs). Energy, 76, 66–72.
Abstract: Heat capture and storage is important in both solar energy projects and in the recovery of waste heat from industrial processes. Whereas heat capture will mostly rely on the use of a heat carrier, the high efficiency heat storage needs to combine sensible and latent heat storage with phase change materials (PCMs) to provide a high energy density storage. The present paper briefly reviews energy developments and storage techniques, with special emphasis on thermal energy storage and the use of PCM. It thereafter illustrates first results obtained when encapsulating NaNO3/KNO3-PCM in an AISI 321 tube, as example of a storage application using a multi-tubular exchanger filled with PCM. To increase the effective thermal conductivity of the PCM, 2 inserts i.e. metallic foam and metallic sponge are also tested. Experimental discharging (cooling) rates are interpreted by both solving the unsteady-state conduction equation, and by using Comsol Multiphysics. Predictions and experimental temperature evolutions are in fair agreement, and the effect of the inserts is clearly reflected by the increased effective thermal conductivity of the insert-PCM composite. Application of Comsol to predict the mechanical behavior of the system, when melting and associated expansion increase the internal pressure, demonstrates that the pressure build-up is far below the Young's modulus of the AISI 321 encapsulation and that this shell will not crack (C) 2014 Elsevier Ltd. All rights reserved.
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