Heat-Transfer Characteristics of Liquid Sodium in a Solar Receiver Tube with a Nonuniform Heat Flux

Abstract

This paper presents a numerical simulation on the heat transfer of liquid sodium in a solar receiver tube, as the liquid sodium is a promising heat-transfer candidate for the next generation solar-power-tower (SPT) system. A comparison between three mediums—solar salt, Hitec and liquid sodium—is presented under uniform and nonuniform heat-flux configurations. We studied the effects of mass flow rate (Qm), inlet temperature (Tin), and maximum heat flux (qomax), on the average heat-transfer coefficient (h) and the friction coefficient (f) of the three mediums. The results show that the h of liquid sodium is about 2.5 to 5 times than other two molten salts when Tin is varying from 550 to 800 K, Qm is 1.0 kg/s, and qomax is 0.1 MW/m2. For maximum heat fluxes from 0.1 to 0.3 MW/m2, the h of liquid sodium is always an order of magnitude larger than that of Hitec and Solar-Salt (S-S), while maintaining a small friction coefficient.

An optimisation study of a solar tower receiver: the influence of geometry and material, heat flux, and heat transfer fluid on thermal and mechanical performance

“…( 19), ( 20), (21), and ( 22) are used to evaluate the physical properties, for Hitec (7% NaNO 3 , 53% KNO 3 , 40% NaNO 2 ) it is obtained from Eqs. (23), ( 24), (25), and (26) [15,39,40,41]. Molten salt is stable as a heat transfer fluid up to temperatures of 595 C, and the temperature at which the decomposition of molten salt starts is between 600 to 700 C. It is challenging to operate a solar receiver with molten salt with a peak heat flux more than 0.8 MW/m 2 .…”

“…Messaoud et al [3], utilised helical fins to achieve a better heat transfer from the receiver to the heat transfer fluid, and a receiver with four helical fins was considered the best design. Liu et al [4] developed a numerical model which used four different inserts with non-uniform heat flux. Twisted tapes had the highest Nusselt number and the lowest difference in circumference temperature.…”

Nonuniform Heat Transfer Model and Performance of Molten Salt Cavity Receiver

“…In available design processes [17,34], the fluid temperature and surface temperature of the cavity receiver are normally assumed to be uniform. In a practical cavity receiver, the fluid temperature and surface temperature increases along the flow direction for heat absorption, so the temperature variation should be further considered.…”

“…Lu et al [16] further reported the enhanced heat transfer performance of a molten salt receiver with a spirally grooved tube. Liu et al [17] compared the heat-transfer characteristics of solar salt, Hitec and liquid sodium in a solar receiver tube with nonuniform heat flux.…”

“…Many researchers [17,34] have designed their cavity receiver by the thermal resistance model with uniform fluid and surface temperatures, but the uniform model ignores large wall and fluid temperature differences in the practical receiver. On the other hand, direct simulation of this cavity receiver needs too great a calculation cost because of many receiver tubes and the complex structure in receiver.…”