Protection of an Aerowindow, One Scheme to Enhance the Cavity Efficiency of a Solid Particle Solar Receiver

2009 ◽  
Author(s):  
Taide Tan ◽  
Yitung Chen
Keyword(s):  
Heat Transfer ◽  
Solid Particle ◽  
Conceptual Design ◽  
Particle Distribution ◽  
Convection Heat Transfer ◽  
Open Aperture ◽  
Convection Heat ◽  
Air Jet ◽  
Exit Temperature ◽  
Solar Receiver

The existing open aperture of a Solid Particle Solar Receiver (SPSR) lowers the cavity efficiency by convection heat transfer. Aerowindows have the potential of increasing the efficiency of an SPSR. Aerodynamic windows consist of a transparent gas stream, which is injected from an air jet, across the receiver aperture to isolate its interior from the surrounding atmosphere. In the present paper, the influences of an aerowindow are investigated numerically on the cavity efficiency, particle exit temperature, and particle distribution of an SPSR. Different injection velocities, injection temperatures and injection directions of an air jet have been studied in order to form an efficient aerowindow. The numerical results provide a reference idea to enhance the performance in the conceptual design of an SPSR.

A Modeling Analysis of Non-Melting Solid Fuel Particle Heating

2003 ◽  
Author(s):  
Ali A. Rostami ◽  
Susan E. Wrenn ◽  
Mohammad R. Hajaligol
Keyword(s):  
Heat Transfer ◽  
Weight Loss ◽  
Solid Particle ◽  
Convection Heat Transfer ◽  
Total Weight ◽  
Fuel Particle ◽  
Total Weight Loss ◽  
Convection Heat ◽  
Particle Heating ◽  
Internal Convection

The heating of fuel particles is generally the first step in the process of gasification or combustion of solid fuels such as coal and biomass. The particle heating that is achieved via combined convection and radiation effects requires a rigorous analysis of heat transfer within as well as outside of the particle, which makes the lumped capacity approximation unsuitable. A more adequate representation of the heating-up process requires the inclusion of the internal convection within the solid particle, the blowing effects on the particle surface, the spatial and temporal variations of the solid thermal conductivity as well as the heat of pyrolysis reactions. The internal convection tends to equalize the temperature distribution within the solid, while the blowing effect contributes to the boundary layer thickening and eventually to a reduction in the convection heat transfer to the particle. To include the above-mentioned effects, a kinetic model for the total weight loss of the solid material was coupled with the heating model. A simple first-order reaction model for the total weight loss was utilized in this study. For materials with high moisture contents, the heat of pyrolysis reactions is an important factor in the heating rate and non-uniform heating of the solid particle. Thermal equilibrium between the solid and evolved gases was assumed within the particle and the equations for the conservation of mass and energy were solved numerically. Results show that surface blowing which is due to the devolatilization of the particle tends to reduce the convection heat transfer from the hot gases to the particle. Internal convection contributes to thermal uniformity in the particle. Heat of pyrolysis reactions plays an important role in the heating profile of the particle. It delays the temperature rise of the particle until most of the volatile materials is released.

Performance of Solid Particle Receivers With or Without the Protection of an Aerowindow

2008 ◽  
Author(s):  
Taide Tan ◽  
Yitung Chen ◽  
Zhuoqi Chen
Keyword(s):  
Solar Radiation ◽  
Solid Particle ◽  
Convection Heat Transfer ◽  
Radiation Energy ◽  
Solid Particles ◽  
Wind Effect ◽  
Air Jet ◽  
Optimal Injection ◽  
Solar Receiver ◽  
Prototype Design

A solid particle solar receiver (SPSR) is a direct absorption central receiver that uses solid particles enclosed in a cavity to absorb concentrated solar radiation. However, the existing open aperture lowers the overall efficiency by convection heat transfer. Aerowindows have the potential of increasing the efficiency of an SPSR by reducing convective losses from an open receiver aperture and eliminate reflection, convection and reradiation losses from a comparable glass window. Aerodynamic windows consist of a transparent gas stream, which is injected from an air jet, across the receiver aperture to isolate its interior from the surrounding atmosphere. Even though, the wind conditions may still have important effect on the performance of SPSRs. In the present paper, the wind effect on the performance of an SPSR is investigated numerically. The mass, momentum and energy exchange between the solid particle and air flow are simulated by the two-way coupling Euler-Lagrange method in the realizable k-ε turbulence 3D model. The independence of the calculating domain is studied in order to select a proper domain for the numerical simulation. Solar ray tracing method is employed in calculating the solar radiation energy. The numerical investigation of the performance of the SPSR is focusing on optimizing the prototype design and finding out the best working condition for the SPSR. In order to investigate the influences of the wind speed and wind blowing direction on the performance of the receiver, different wind conditions of and different air jet injection conditions are simulated numerically. The cavity thermal efficiencies are calculated and the optimal injection conditions are analyzed for different wind conditions.

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