6Thermal energy storage improves the load stability and efficiency of solar thermal 7 power plants by reducing fluctuations and intermittency inherent to solar radiation. This paper 8 presents a numerical study on the transient response of packed bed latent heat thermal energy 9 storage system in removing fluctuations in the heat transfer fluid (HTF) temperature during the 10 charging and discharging period. The packed bed consisting of spherical shaped encapsulated 11 phase change materials (PCMs) is integrated in an organic Rankine cycle-based solar thermal 12 power plant for electricity generation. A comprehensive numerical model is developed using 13 flow equations for HTF and two-temperature non-equilibrium energy equation for heat 14 transfer, coupled with enthalpy method to account for phase change in PCM. Systematic 15 parametric studies are performed to understand the effect of mass flow rate, inlet charging 16 system, storage system dimension and encapsulation of the shell diameter on the dynamic 17 behaviour of the storage system. The overall effectiveness and transient temperature difference 18 in HTF temperature in a cycle are computed for different geometrical and operational 19parameters to evaluate the system performance. It is found that the ability of the latent heat 20 thermal energy storage system to store and release energy is significantly improved by 21 increasing mass flow rate and inlet charging temperature. The transient variation in the HTF 22 temperature can be effectively reduced by decreasing porosity. 23 Keywords: Phase change material, encapsulation, Organic Rankine Cycle (ORC)-based solar 24 thermal power plant, temperature fluctuations 25 ∆T Difference between maximum and minimum temperature of heat transfer fluid at outlet, °C t Time, s tc Charging time, s td Discharging time, s ∆t Time interval, s U Superficial velocity of heat transfer fluid (=̇), m/s U0 Interstitial velocity (= ), m/s u Velocity vector, m/s Greek symbols 27 Porosity Dynamic viscosity, kg/m.s Permeability, m 2 λ Relaxation factor Density, kg/m 3 Effectiveness Subscript 28 c Charging d Discharging l Liquid max Maximum min Minimum n n th time step o Overall s Solid Abbreviation 29 CSP Concentrating Solar Power HTF Heat Transfer Fluid LHTES Latent Heat Thermal Energy Storage ORC Organic Rankine Cycle PCM Phase change material SHS Sensible Heat Storage 4 TES Thermal Energy Storage UDF User Defined Function UDS User Defined Scalar 30 5 1. Introduction 31 Solar energy is one of the most abundant forms of renewable energy sources in many 32 parts of the world. However, meeting energy demand from this source is challenging due to its 33 intermittent and unpredictable nature over short time scales during the day time. The energy 34 production is driven by the efficiency of systems as well as by the economics of power 35 generation. Thermal energy storage technologies have the potential to make solar radiation a 36 reliable option for electricity generation by Organic Rankine Cycle (ORC)-based solar thermal 37...
This paper deals with phase change material (PCM), used in conjunction with thermal conductivity enhancer (TCE), as a means of thermal management of electronic systems. Eicosane is used as PCM, while aluminium pin or plate fins are used as TCE. The test section considered in all cases is a 42×42mm2 base with a TCE height of 25mm. An electrical heater at the heat sink base is used to simulate the heat generation in electronic chips. Various volumetric fractions of TCE in the conglomerate of PCM and TCE are considered. The case with 8% TCE volume fraction was found to have the best thermal performance. With this volume fraction of TCE, the effects of fin dimension and fin shape are also investigated. It is found that a large number of small cross-sectional area fins is preferable. A numerical model is also developed to enable an interpretation of experimental results.
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