Heat transfer prediction of granular flow in moving bed heat exchanger: Characteristics of heat transfer enhancement and dynamic control

Abstract

To realize the heat transfer between granular flow and sCO2 cycle, moving bed heat exchangers have been widely applied in Concentrating Solar Power systems. This work developed a prediction model for heat transfer enhancements and dynamic control strategies in a shell-and-plate moving bed heat exchanger. For fast evaluation of heat transfer performances in granular flow, the continuum model was adopted with different thermal resistances. The wall effect of near-wall region was modified by contact thermal resistance, and the equivalent heat diffusion in bulk region was reflected by penetration thermal resistance. The results showed that, the decrement of penetration thermal resistance can improve heat transfer effectively. To weaken the penetration thermal resistance, the thinner thermal boundary layer and the higher effective thermal conductivity are urgently required. The staggered arrangement is a valid way to limit the development of thermal boundary layer. The bank of heat exchanger plates offset horizontally from the previous bank, and the re-evolution of temperature distributions is equal to the equivalent thermal mixing between different banks. Meanwhile, the effective thermal conductivity can be improved by particle self-diffusions perpendicular to the major flow direction. For the particle migrations, the local disturbances can be applied. The relatively decrement of penetration thermal resistance can achieve 45.7% at a disturbance intensity of 5 × 10−7 m2/s. The outlet temperature of sCO2 can be well controlled by the transient temperature–velocity feedback method with relaxation coefficients. The relatively decrement of temperature fluctuation is larger than 80% with a relaxation coefficient of 40.