Numerical Simulation Of Flow And Heat Transfer Characteristics In Fluidized Bed Particle Receiver

As a kind of clean renewable energy,solar energy has the potential to replace the fossil fuels.Solar thermal technologies emerge as the times require.In recent years,concentrating solar power systems have been developing rapidly which provide a sustainable energy conversion system.The receiver is a key part of the concentrating solar power system and determines the thermal efficiency of the entire system.Indeed the research mainly focuses on how to improve the flow characteristics of the heat transfer medium by improving the structure in order to reach very high temperature and thermoelectric conversion efficiency.In this paper,the numerical study investigates the particle flow characteristics in fluidized bed particle receiver,using a commercial CFD package to study the flow and heat transfer characteristics of dilute and dense particles in this receiver.Based on Euler-Lagrangian model,the gas-solid two-phase flow model in the solar fluidized bed particle receiver is established.Discrete Phase Model(DPM)and Dense Discrete Phase Model(DDPM)are employed respectively to describe the dilute and dense particles in the receiver,using Discrete Element Model(DEM)to close the dense particle collisions.The impact of radiation source is considered by the Solar Load model and Discrete ordinate(DO).Based on the DPM method,the dilute particles flow and heat transfer in the inner circulating fluidized bed receiver was simulated.The particles flow and heat transfer characteristics,the temperature distribution and different gas mass flow rate were analyzed in detail.It is found that when the gas mass flow rate is increased,the recirculation characteristics of the particles and gas in the receiver are enhanced,and the receiver thermal performance is also enhanced.In addition,the thermal conductivity of gas-particle working fluid and absorption coefficient of the particle agglomerates increase as the particle volume fraction increases.Based on the DDPM-DEM model,the numerical simulation of the dense particle motion and heat transfer process in the double-cavity internal circulating fluidized bed receiver is carried out.The flow,collision and heat transfer of the particles are taking into account in the model.In this receiver,the dense particles internal flow characteristics and the impacts on the temperature distribution are studied in detail.It is found that the heat transfer between particles and gas is enhanced and the temperature distribution in the receiver is more uniform in this cavity which mainly due to the dense particles internal circulation.In addition,the particle temperature and the gas temperature are greatly improved,reaching 1400 K and 1200 K respectively.