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Sandip K. Saha - One of the best experts on this subject based on the ideXlab platform.

  • latent heat thermal storage with variable porosity metal matrix a numerical study
    Renewable Energy, 2018
    Co-Authors: Ashish Kumar, Sandip K. Saha
    Abstract:

    Abstract In this paper, a novel design of multitube shell and tube latent heat thermal energy storage system (LHTES) with variable porosity metal matrix in PCM is presented. The shell side of the LHTES contains a phase change material, whereas heat transfer fluid (HTF) flows through seven tubes with internal fins. Metal matrix, as a thermal conductivity enhancer (TCE), is used to augment heat transfer in PCM, however the temperature distribution in PCM is found to be non-uniform along the length of the storage system for constant porosity metal matrix in PCM, which affects the thermal performance of the LHTES. A numerical model is developed to investigate the fluid flow and heat transfer characteristics using the momentum equation and the two-temperature non-equilibrium energy equation coupled with the Enthalpy Method to account for phase change in PCM. The numerical model is first validated with the experimental results and further extended to identify the effects of geometrical parameters on the temperature distribution in PCM. A relationship between porosity and ratio of length to annular diameter of the storage system is developed for porosity varying from 0.95 to 0.85. It is found that the size of LHTES with variable metal matrix porosity can be reduced for the same effectiveness.

  • Numerical analysis of latent heat thermal energy storage using encapsulated phase change material for solar thermal power plant
    Renewable Energy, 2016
    Co-Authors: Kunal Bhagat, Sandip K. Saha
    Abstract:

    Thermal energy storage improves the load stability and efficiency of solar thermal power plants by reducing fluctuations and intermittency inherent to solar radiation. This paper presents a numerical study on the transient response of packed bed latent heat thermal energy storage system in removing fluctuations in the heat transfer fluid (HTF) temperature during the charging and discharging period. The packed bed consisting of spherical shaped encapsulated phase change materials (PCMs) is integrated in an organic Rankine cycle-based solar thermal power plant for electricity generation. A comprehensive numerical model is developed using flow equations for HTF and two-temperature non-equilibrium energy equation for heat transfer, coupled with Enthalpy Method to account for phase change in PCM. Systematic parametric studies are performed to understand the effect of mass flow rate, inlet charging system, storage system dimension and encapsulation of the shell diameter on the dynamic behaviour of the storage system. The overall effectiveness and transient temperature difference in HTF temperature in a cycle are computed for different geometrical and operational parameters to evaluate the system performance. It is found that the ability of the latent heat thermal energy storage system to store and release energy is significantly improved by increasing mass flow rate and inlet charging temperature. The transient variation in the HTF temperature can be effectively reduced by decreasing porosity.

J S Saini - One of the best experts on this subject based on the ideXlab platform.

  • an analysis of a packed bed latent heat thermal energy storage system using pcm capsules numerical investigation
    Renewable Energy, 2009
    Co-Authors: Felix A Regin, S C Solanki, J S Saini
    Abstract:

    This paper is aimed at analyzing the behavior of a packed bed latent heat thermal energy storage system. The packed bed is composed of spherical capsules filled with paraffin wax as PCM usable with a solar water heating system. The model developed in this study uses the fundamental equations similar to those of Schumann, except that the phase change phenomena of PCM inside the capsules are analyzed by using Enthalpy Method. The equations are numerically solved, and the results obtained are used for the thermal performance analysis of both charging and discharging processes. The effects of the inlet heat transfer fluid temperature (Stefan number), mass flow rate and phase change temperature range on the thermal performance of the capsules of various radii have been investigated. The results indicate that for the proper modeling of performance of the system the phase change temperature range of the PCM must be accurately known, and should be taken into account.

  • latent heat thermal energy storage using cylindrical capsule numerical and experimental investigations
    Renewable Energy, 2006
    Co-Authors: Felix A Regin, S C Solanki, J S Saini
    Abstract:

    This paper is aimed at analyzing the melting behavior of paraffin wax as a phase change material (PCM) encapsulated in a cylindrical capsule, used in a latent heat thermal energy storage system with a solar water heating collector. The heat for melting of PCM in the capsule is provided by hot water surrounding it. Since it is observed experimentally that the phase change occurs in a range of temperature, the present analysis considers this range instead of constant phase change temperature and the deviation between the results of these two is presented. The numerical analysis has been carried out by using Enthalpy Method and the results are verified with the experimental data. The experiments have been done by visualization technique without disturbing the actual process of melting. Three distinct stages of melting process have been identified as revealed by visualization studies. Results indicate that the melting process is chiefly governed by the magnitude of the Stefan number, Ste, phase change temperature range and the capsule radius. The analysis shows that the agreement between analytical and experimental results is significantly improved when the results are obtained considering phase change temperature range and the natural convection in the liquid phase instead of considering the process to be conduction dominated only.

Felix A Regin - One of the best experts on this subject based on the ideXlab platform.

  • an analysis of a packed bed latent heat thermal energy storage system using pcm capsules numerical investigation
    Renewable Energy, 2009
    Co-Authors: Felix A Regin, S C Solanki, J S Saini
    Abstract:

    This paper is aimed at analyzing the behavior of a packed bed latent heat thermal energy storage system. The packed bed is composed of spherical capsules filled with paraffin wax as PCM usable with a solar water heating system. The model developed in this study uses the fundamental equations similar to those of Schumann, except that the phase change phenomena of PCM inside the capsules are analyzed by using Enthalpy Method. The equations are numerically solved, and the results obtained are used for the thermal performance analysis of both charging and discharging processes. The effects of the inlet heat transfer fluid temperature (Stefan number), mass flow rate and phase change temperature range on the thermal performance of the capsules of various radii have been investigated. The results indicate that for the proper modeling of performance of the system the phase change temperature range of the PCM must be accurately known, and should be taken into account.

  • latent heat thermal energy storage using cylindrical capsule numerical and experimental investigations
    Renewable Energy, 2006
    Co-Authors: Felix A Regin, S C Solanki, J S Saini
    Abstract:

    This paper is aimed at analyzing the melting behavior of paraffin wax as a phase change material (PCM) encapsulated in a cylindrical capsule, used in a latent heat thermal energy storage system with a solar water heating collector. The heat for melting of PCM in the capsule is provided by hot water surrounding it. Since it is observed experimentally that the phase change occurs in a range of temperature, the present analysis considers this range instead of constant phase change temperature and the deviation between the results of these two is presented. The numerical analysis has been carried out by using Enthalpy Method and the results are verified with the experimental data. The experiments have been done by visualization technique without disturbing the actual process of melting. Three distinct stages of melting process have been identified as revealed by visualization studies. Results indicate that the melting process is chiefly governed by the magnitude of the Stefan number, Ste, phase change temperature range and the capsule radius. The analysis shows that the agreement between analytical and experimental results is significantly improved when the results are obtained considering phase change temperature range and the natural convection in the liquid phase instead of considering the process to be conduction dominated only.

Vaughan R Voller - One of the best experts on this subject based on the ideXlab platform.

  • a geomorphic Enthalpy Method description and application to the evolution of fluvial deltas under sea level cycles
    Computers & Geosciences, 2019
    Co-Authors: William Anderson, Jorge Lorenzotrueba, Vaughan R Voller
    Abstract:

    Abstract Fluvial deltas are composites of two primary sedimentary environments: a depositional fluvial region and an offshore region. The fluvial region is defined by two geomorphic moving boundaries: an alluvial-bedrock transition (ABT), which separates the sediment prism from the non-erodible bedrock basement, and the shoreline (SH), where the delta meets the ocean. The trajectories of these boundaries in time and space define the evolution of the shape of the sedimentary prism, and are often used as stratigraphic indicators, particularly in seismic studies, of changes in relative sea level and the identification of stratigraphic sequences. In order to better understand the relative role of sea-level variations, sediment supply, and basin geometry on the evolution of the ABT and SH, we develop a forward stratigraphic model that accounts for curvature changes of the fluvial surface and treats the SH and ABT as moving boundaries (i.e., internal boundaries that are not known a priori and their location must be calculated as part of the solution to the overall problem). This forward model extends a numerical technique from heat transfer (i.e., Enthalpy Method), previously applied to the evolution of sedimentary basins, to account for sea-level variations, including eustatic sea-level cycles. In general, model results demonstrate the importance of the dynamics of the fluvial surface on the system response under a large range of input parameter values. Specifically, model results suggest that time lags in the ABT response during sea-level cycles can result in geologically long-lived river incision in the upper and mid portions of the fluvial surface during sea-level rise. These results suggest that the relationship between the coastal onlap configuration of strata and relative changes in sea level is complex, and therefore not necessarily a good indicator of contemporaneous sea-level changes.

  • an Enthalpy Method for modeling dendritic growth in a binary alloy
    International Journal of Heat and Mass Transfer, 2008
    Co-Authors: Vaughan R Voller
    Abstract:

    An Enthalpy fixed grid Method is developed for modeling dendritic growth in an under-cooled binary alloy. The proposed numerical Method couples explicit finite difference solutions of equations expressing the conservation of Enthalpy and solute to an iterative procedure that enforces node by node consistency between Enthalpy, solute, liquid fraction, and interface under-cooling. Calculations made with the scheme, are consistent with previously reported work, agree well with limit analytical solutions, approach the correct steady-state tip operating conditions, show grid size independence, are relatively free of grid anisotropy, and can be obtained with a low CPU cost.

  • An Enthalpy Method for moving boundary problems on the earth's surface
    International Journal of Numerical Methods for Heat & Fluid Flow, 2006
    Co-Authors: Vaughan R Voller, John B. Swenson, Wonsuck Kim, Chris Paola
    Abstract:

    Purpose – To present a novel moving boundary problem related to the shoreline movement in a sedimentary basin and demonstrate that numerical techniques from heat transfer, in particular Enthalpy Methods, can be adapted to solve this problem.Design/Methodology/approach – The problem of interest involves tracking the movement (on a geological time scale) of the shoreline of a sedimentary ocean basin in response to sediment input, sediment transport (via diffusion), variable ocean base topography, and changing sea level. An analysis of this problem shows that it is a generalized Stefan melting problem; the distinctive feature, a latent heat term that can be a function of both space and time. In this light, the approach used in this work is to explore how previous analytical solutions and numerical tools developed for the classical Stefan melting problem (in particular fixed grid Enthalpy Methods) can be adapted to resolve the shoreline moving boundary problem.Findings – For a particular one‐dimensional case,...

  • ON THE Enthalpy Method
    International Journal of Numerical Methods for Heat & Fluid Flow, 1993
    Co-Authors: C. R. Swaminathan, Vaughan R Voller
    Abstract:

    Two common fixed grid Enthalpy Methods used in the numerical modelling of phase change problems are the apparent heat capacity and the source based Methods. In this paper, a general Enthalpy Method that includes as subsets both apparent heat capacity and source based Methods, is derived. Following this, an optimal Enthalpy scheme is identified. The superiority of the optimal scheme over the apparent heat capacity and the source based schemes is illustrated by solving sample phase change problems.

  • a general Enthalpy Method for modeling solidification processes
    Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 1992
    Co-Authors: C. R. Swaminathan, Vaughan R Voller
    Abstract:

    In the present work, a general implicit source-based Enthalpy Method is presented for the analysis of solidification systems. The proposed approach is both robust and efficient. The performance of the Method is illustrated by application to a number of problems taken from recent metallurgical literature.

Eberhard Gill - One of the best experts on this subject based on the ideXlab platform.

  • design and characterisation of a bi modal solar thermal propulsion and power system for small satellites
    Applied Thermal Engineering, 2021
    Co-Authors: Fiona Leverone, Angelo Cervone, Matteo Pini, Eberhard Gill
    Abstract:

    Abstract Small satellites with increased capabilities in terms of power and propulsion are being demanded for future missions. This paper addresses an alternative bi-modal solution which consists of a solar thermal propulsion system coupled with a micro-Organic Rankine Cycle system, to co-generate thrust and electrical power. Current literature on bi-modal systems is limited to static power conversion systems such as thermionic conversion processes. Therefore, this paper expands the research of bi-modal systems to dynamic power conversion systems and latent heat storage systems. The paper documents the design process, key design parameters, and feasibility of this system for a Geostationary Transfer Orbit to Lunar Orbit insertion mission. The results of a single-objective optimisation show the system is most suitable on-board small satellites with a gross mass above 300 kg. The propellant accounts for 50% of the total system mass. The final design uses Silicon as the latent heat energy storage system due to its high specific energy of more than 250 Wh/kg. Additionally, the Enthalpy Method is used to describe the dynamic behaviour of the phase change material and results show the insulation thermal conductivity has the largest effect, up to 17%, on the receiver’s maximum achievable steady-state temperature.