This paper presents the thermal modelling and performance predictions of high-temperature sensible heat storage (SHS) models of 50 MJ capacity designed for solar thermal power plant applications in the temperature range of 523-648 K. The SHS unit is a regenerator-type heat exchanger which stores/releases the heat on passing hot/cold heat transfer fluid (HTF) through the tubes embedded into it. A mathematical model of cylindrical configuration with embedded multi-tube is developed employing concrete and cast steel as the storage media. The number of embedded charging/discharging tubes in the storage model is optimized based on the charging time using the finite element method-based simulation tool, COMSOL Multiphysics. Numerically predicted results match well with the data reported in the literature. Thermal performance parameters of SHS bed such as charging/discharging time, energy stored/recovered, charging/discharging energy efficiency and overall efficiency have been evaluated. Axial variations of HTF temperature during charging/discharging cycle are analysed, and the parametric studies are carried out by varying the flow rate of HTF. For cast steel bed, the increase in HTF velocity resulted in the proportional reduction in charging/ discharging time, while these effects in concrete were less because of its low thermal conductivity.
List of symbolsC ps Specific heat of solid-state SHSM (J/kg K) C pf Specific heat of HTF (J/kg K) k s Thermal conductivity of solid-state SHSM (W/ m K) k f Thermal conductivity of HTF (W/m K) q s Density of solid-state SHSM (kg/m 3 ) q f Density of HTF (kg/m3) l Dynamic viscosity of HTF (Ns/m 2 ) c Kinematic viscosity of HTF (mm 2 /s) d Internal diameter of the charging tubes (m) D Diameter of SHS bed (m) L Length of SHS bed (m) n Number of charging tubes Q Heat storage capacity (J) t Charging time (s) T ch Volume average temperature of SHS bed at the end of charging (K) T ini Initial temperature of SHS bed (K) T inlet HTF inlet temperature (K) T outlet HTF outlet temperature (K) T atm Atmospheric temperature (K) DT Charging temperature range (K) ṽ Velocity of HTF (m/s) V r Volume of solid-state SHSM required (m 3 ) V a Actual volume of solid-state SHSM including factor of safety (m 3 ) mMass of solid-state SHSM (kg) g ch Charging energy efficiency g disch Discharging energy efficiency g overall Overall efficiency
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