_Article_  
Numerical Evaluation of the Transient Performance of Rock-Pile Seasonal Thermal Energy Storage Systems Coupled with Exhaust Heat Recovery +  
Footnote †: journal: Applied Physics Letters [PERSON]  
[PERSON] 1,2(c), [PERSON] 3, [PERSON] 3,*, [PERSON] 2, [PERSON] 1 and [PERSON] 1,*(c)  
systems: chemical heat storage (based on thermochemical reactions); latent heat storage (which employs phase change materials); and sensible heat storage (simply based on temperature increase/decrease of the storage media) [2], the latter is currently the cheapest and easiest one to implement [5]. It has been stated that a sensible heat storage costs up to 15 CAD/kWh, while a latent heat storage needs relatively higher costs, up to 150 CAD/kWh, depending on many factors such as the size, the material, and the applied technology [18]. For that reason, it is the most promising one for immediate use in large/industrial scales [19]. That happens as it generally implements inexpensive resources as fragmented rock and air [20], and it often dispenses the need of intermediate heat exchangers [16]. It has been shown previously that rock-bed storage systems frequently are more cost-effective than similar water-based systems for heating [11]. Still, other advantages of such systems can be highlighted. They are more environmentally friendly than their counterparts, as they use naturally occurring storage media, they can usually withstand very high temperatures, and they also have a high heat transfer coefficient between phases when in use, but low conductivity of heat when air flow is not present [12]. Despite being used mostly for solar applications, due to its flexibility, packed rock-bed TES can be employed in a wide range of energy-intensive industries. A good example is the development of the application for mine sites, where there is an opportunity to use fragmented rock packed in beds as a sensible energy storage. In these storages, air is used as the heat transfer fluid (HTF) and fragmented rocks are used as the storage media, which has been shown as a favorable approach for TES systems [21; 22; 23; 24; 25]. In order to fully understand the performance of TES systems, several parameters ought to be analyzed, which are hard to attain by analytical equations. Hence, computational simulations are usually a good method to investigate and enhance such systems, by improving the many factors affecting its operation. For that reason, several works in literature have taken the task to develop such computational models. 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]. [PERSON] 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, [PERSON] et al. investigated the possibility of using them to represent the stratification phenomena seen in experimental tests [27]. [PERSON] et al. elaborated a one-dimensional numerical model, followed by comparison validation against experimental data from small-scale testing [28]. Looking to investigate the effect of construction parameters on heat storages for industrial processes, [PERSON] et al. developed a quasi-one-dimensional transient model to study two-phase heat transfer on packed beds [16]. [PERSON] developed a one-dimensional model for airflow within a porous rock bed medium, and used it to study the effect of different charging and discharging flow direction schedules [29]. [PERSON] et al. studied a large-sized packed bed (created with bricks) circulating air as an HTF with experiments and a 1D energy model, and confirmed the viability of its fluid flow and heat transfer for solar applications [30]. Finally, [PERSON] et al.