Thermal characteristics of packed bed storage system

Abstract

The thermal behaviour of a packed bed storage system charged with hot air is modelled using two partial differential equations representing the energy conservation in the air and solid phases constituting the bed. These two equations are coupled through the heat exchange process between the two phases.A fully implicit numerical scheme based on forward, upwind and central differencing for the time, first and second space derivatives, respectively, is used to solve the modelling equations. Marching technique is used for the air equation and a tri-diagonal matrix solver is employed to solve the solid equation. The solution yields the thermal structure of the bed, namely the air and solid temperature distribution inside the bed at any particular time, and the variation of total energy stored in the bed with time. The effect of bed length, solid diameter and void fraction on the thermal characteristics of the packed bed is studied. Further, the performance of the bed under variable inlet air temperature and mass flow rate is investigated. KEY WORDS Packed bed storageEnergy storage

Understanding, controlling and optimising the cooling of waste thermal treatment beds including STARx Hottpads

“…Recalling equation (6) , it is seen that the bulk density of a material is a function of its particle density as well as its porosity . Relatedly, it has been reported that the heat load in a packed bed (relative to a set temperature) is increased through use of materials with greater particle density ( Aly and El-Sharkawy, 1990 ; Elouali et al, 2019 ; Hrifech et al, 2020 ; Romaní et al., 2019 ) and/or reduced porosity ( Abdel-Salam et al, 1991 ; Ismail and Stuginsky, 1999 ). Altering either of these parameters in this manner would also lead to an increase in the bed bulk density ( equation (6) ).…”

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“…The temperature profiles is chosen to validate the model because it represents the dynamic response of the TES at multiple time steps, which embedding the complex heat transfer phenomena within the tank. It provides an illustration about the temperature gradient and thermal stratification within the tank [57], as well as the level of stored and discharged thermal energy [58].…”

Numerical Evaluation of the Transient Performance of Rock-Pile Seasonal Thermal Energy Storage Systems Coupled with Exhaust Heat Recovery

“…Thermal energy storage (TES) allows for energy to be stored in the form of heat in times of low or null demand, and used later whenever demand rises [2]. Such technologies aid in the reduction of both carbon footprints and energy costs from small (residential) to big (industrial) scales, being even deemed vital in some applications [4,5]. Such technologies are mostly used in solar energy applications, mainly concentrated solar power plants (CSP) [3,[6][7][8] and solar district heating [9][10][11][12][13], but waste-heat storage systems can also take great advantage of their use [14][15][16][17].…”

“…Some of these that can be highlighted focused on the heat and mass transfer phenomena occurring within packed beds used as thermal energy storage [26]. Abdel-Salam et al established a cylindrical coordinate-based 1D numerical model, through which it was revealed that the increase of bed length improves storage capacity while not affecting the rate of charge [4]. By implementing the finite difference method in models with distinct number of sections, Arias et al investigated the possibility of using them to represent the stratification phenomena seen in experimental tests [27].…”

“…Mertens et al [8] and Rodat et al [33] investigated, in detail, both numerically and experimentally, the performance of sand and rock beds, which allowed for the impact of several design and operating conditions, as temperature and HTF velocity, to be evaluated on thermal energy storage performance. Air mass flow has been shown to enhance interphase heat transfer rates, decreasing charging time [4], while some have suggested that air density would not directly affect said heat transfer [29]. It has also been stated that volumetric heat capacity would play a major role on overall system performance [28].…”