Transient cool-down of a porous medium in pulsating flow

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.…”

“…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. Pressurization of the solar thermal power system for use with 13 current synthetic oils above 400°C is cost-prohibitive.…”

“…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. This helps greatly reduce the 12 amount of the relatively more expensive molten salt that is required in a two-tank 13 storage system.…”

“…[13] investigated the year-round performance of a double-pass solar air heater with a 10 packed bed and reported an improvement in thermal performance, in terms of outlet 11 temperature and thermohydraulic efficiency, relative to a system without a packed bed. 12 Mawire et al [14] developed a simplified one-dimensional single-phase model for an 13 oil-pebble TES system to examine the thermal performance of three different pebble 14 materials; a high ratio of the total exergy to the total energy stored was suggested as a 15 good measure of thermal performance of the pebble material.…”

“…The thermal behavior, 9 including temperature profiles and cycle efficiency, are specifically investigated. 10 Based on the numerical results obtained, guidelines are provided for designing TES 11 thermoclines with various power capacities. exchanger.…”