Enhancement of Cooling Effectiveness by Porous Materials in Coolant Passage

Cyclic operation of molten-salt thermal energy storage in thermoclines for solar power plants

“…Only the discharge of a thermocline system was 17 considered in these works [18][19][20][21]; the temperature distribution and cycle efficiency 18 under cyclic operation as a function of the operating conditions was not considered, 19 and is the focus of the present study. This cyclic operation of a molten-salt 20 thermocline for solar thermal electricity generation is distinct from previous studies of 21 pulsating/oscillating flow conditions [10][11][12]; a molten-salt input/output flow at 9 constant temperature levels is essential in the charge/discharge of a thermocline, as is 1 a narrow heat exchange zone [18] (also termed thermocline zone) in the storage tank. 2 There is a clear need for a theoretical model which predicts the cycle efficiency.…”

“…Therminol VP-1 has a low freezing point of 12C, and is 7 stable up to 400C, which is higher in comparison to Caloria, the HTF used previously. 8 However, use of Therminol VP-1 as the heat storage medium above 400C in 9 practical applications is difficult due to its high vapor pressure (> 1 MPa). In order 10 to improve the Rankine cycle efficiency to a level higher than 40%, the desired 11 storage medium must withstand temperatures above 450C [2] while featuring low 12 vapor pressures.…”

“…5 A molten-salt TES thermocline uses only a single tank as the storage container 6 and can thus potentially reduce costs significantly relative to a two-tank TES such as 7 that used in the Solar Two demonstration plant [3,4]. In the thermocline, hot and 8 cold regions of molten salt rely on buoyancy forces to maintain stable thermal 9 stratification in a single tank. A low-cost filler material compatible with molten salts, 10 such as quartzite rock [5], is used to occupy most of the volume of the thermocline 11 and acts as the primary thermal storage material.…”

“…The heat exchange and energy storage in packed-bed porous media 21 are important in many applications, and have attracted extensive research interest. 22 Koh et al [8,9] introduced the use of porous media for cooling high temperature al. [12] studied the transient thermal effects in a porous medium subject to oscillatory 6 flow of hot and cold fluid.…”

“…20 While heat transfer in packed-bed porous media has been widely studied, only 21 limited investigations of the thermal performance of molten-salt thermocline TES 22 8 have been reported despite its significance to solar thermal electricity generation. 1 Pacheco et al [1] described the development of a molten-salt thermocline system and 2 compared it to a two-tank system; they suggested the molten-salt thermocline system In a recent study, the discharge efficiency of thermal energy storage in 9 thermocline tanks under an adiabatic wall condition was investigated for different 10 melt flowrates, filler particle diameters and tank heights [18]. The influence of the 11 interstitial heat transfer rate and the filler thermal conductivity were discussed in [19].…”