Abstract
Air as a heat transfer fluid has been widely studied in concentrated solar-power generations, but the solar energy absorbed by air inside transparent and opaque tubes has not been comparatively investigated. The heat transfer was studied experimentally and numerically for a fluidized granular bed air receiver with a non-uniform energy flux and the fluidization occurs inside cylindrical metal and quartz glass tubes. The experiments were conducted in a solar simulator with 19 xenon short-arc lamps and showed that the thermal efficiencies in the quartz tube are higher than those in the metal tube. A numerical model was established to study the fluidized heat transport inside the quartz tube, which includes effective thermal conductivities for the conduction, the Syamlal–O’Brien drag model to describe the pressure drop, a modified P-1 model for the radiation, and a two-fluid model (TFM) for gas–solid two-phase flow. The local thermal non-equilibrium model is used to relate the air temperatures to particle temperatures. Comparisons with experimental data show that this model can be used to predict the heat transport inside the quartz glass tube. The maximum relative error was 7.7% when the current is 100 A and the air mass flow rate is 0.53 g/s.
Highlights
The receiver is a key component which drives the working temperature of the thermodynamic cycle, thereby it determines the global efficiency of solar thermal power generation
Particle receivers can work at high temperatures (>700 ◦ C) and keep good mechanical and chemical stability when the particle temperatures are higher than 1000 ◦ C
Because the receiver was directly exposed to the incident flux from the solar simulator, the granular and air temperatures increased
Summary
The receiver is a key component which drives the working temperature of the thermodynamic cycle, thereby it determines the global efficiency of solar thermal power generation. When the Neumann boundary condition is applied in the simulation of particle receivers, the radiative heat loss between walls and ambient environment is often neglected. A comparative study on the fluidized heat absorption inside the quartz tube and the opaque metal tube has not yet been carried out and it is unclear which has a higher thermal efficiency. Because the difference in fluidized particle heat absorption between a single quartz tube and an opaque metal tube has not been investigated, experiments were conducted to investigate their thermal performances at different air mass flow rates, packed particle masses, and energy fluxes. A numerical model was established and applied to simulate the heat absorption inside a quartz glass tube and the varied heat loss caused by the varied particle temperatures is considered.
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