## 1 Introduction  
The particle heating receiver (PHR), which uses solid particles as thermal energy storage (TES) and heat transfer media (HTM), has recently attracted many researchers' attention for its use in concentrated solar power (CSP) systems. Many of the drawbacks of the common HTMs that are now in use, such as air, steam, molten salt, and synthetic oil,are avoided with the use of such receivers. Using air as an HTM requires excessively large receivers and heat exchangers [1]. Furthermore, the pressure drop through the receiver and heat exchanger piping is an additional issue; so, pumping becomes problematic and therefore increases the investment cost. Despite the high thermal capacity, low cost, and availability of water, and its capability to be used as a direct steam source to feed the power unit, its drawbacks are oxidization, freezing, and difficulty in storing steam at high pressure [2]. The advantages of oil are high operating temperatures, low specific volume, and low pressure [1]. The main issue with heavy oils is that typical hydrocarbons decompose at around 400 \({}^{\circ}\)C, which, in turn, limits their operating temperature and therefore restricts their application in low-efficiency CSP cycles. Other disadvantages of oils are deterioration over time, expense, and flammability. In current molten salt commercial solar tower power plants, the molten salt used is a 40/60% mixture of KNO\({}_{3}\)/NaNO\({}_{3}\)[3]. The operational temperature range, as stated previously, is between 290 \({}^{\circ}\)C and 565 \({}^{\circ}\)C. With the highest temperature of 565 \({}^{\circ}\)C, only a steam cycle can be used, and more efficient power cycles cannot be integrated since their operational temperature is higher than 565 \({}^{\circ}\)C. Other commonly considered molten salts include carbonate salts, which have a higher stability limit (>650 \({}^{\circ}\)C) and a higher melting point (<390 \({}^{\circ}\)C), but a relatively higher price. Fluoride salts have an even higher stability limit (>700 \({}^{\circ}\)C), but they are toxic, relatively expensive, and have a higher melting point (>450 \({}^{\circ}\)C) [4]. The U.S. Department of Energy (DOE) is supporting the development of a chloride salt, which has high heat capacity but a high melting point (>750 \({}^{\circ}\)C) [5; 6; 7]. However, increasing the operational temperature range for molten salts brings additional challenges. In particular, it increases the corrosiveness of the material. This limits the lifetime of the components and increases the levelized cost of electricity (LCOE) of the plant. Particulate materials are found to be a good alternative to molten salts both as the HTM and the TES in higher-temperature systems for multiple reasons, including their thermal conductivity not limiting their capacity to store heat [8]. Most importantly, silica sand and similar particulates have demonstrated exceptionally stability well beyond 1000 \({}^{\circ}\)C [9], which is far above the decomposition thresholds of commonplace nitrate salts [10; 11] and organic fluids [12]. In addition, in comparison to conventional HTMs, solid particulates (1) simplify energy storage without the need for separate tanks or heat exchangers; (2) when natural, are abundantly available at a low cost; (3) undergo no toxic decomposition and carry no environmental risk; and (4) do not require freeze protection. Recent endeavors, backed by the US DOE, have showcased the viability of natural particulates (sand) as both an HTM and TES in CSP systems, particularly through the direct heating of sand in PHR systems [13; 14]. However, the particulates' thermophysical properties, heat resistance, crack resistance, hazards, and cost should be taken into account since the particulates will be stored in a larger amount in TES to be used during off-sun times. Various researchers have suggested many potential solid particulates as an HTM/TES, like quartz, sand, cristobalite, bauxite, alumina, ceria, graphite, olivine, silicon carbide, calcined flint clay, etc. [15; 16].