Review of drop impact on heated walls

Slip and no-slip velocity boundary conditions at interface of porous, plain media

A study of spontaneous combustion characteristics of a turkish lignite: particle size, moisture of coal, humidity of air

A two-dimensional mathematical model for the combustion of straw in a cross-current, moving bed was developed as part of a tool for optimizing operating conditions and design parameters. To verify the model and to increase the understanding of straw bed combustion, laboratory fixed-bed experiments were performed in a 15 cm diameter and 137 cm long vertical reactor. Air was introduced through the bottom plate and the straw was ignited from the top with an electrical radiation source. The temperature was measured at eight positions within the bed and gas analysis was performed for O 2 , CO 2 , CO, C x H y , NO x , NH 3 and SO 2 . The inlet air flow rate and air preheat temperature were varied. The experimental data for ignition front temperatures and front propagation velocity compared reasonably well with the modelling results. A higher air inlet temperature resulted in lower maximum bed temperatures, which was successfully modelled. A limited parameter analysis study was performed. Measurement of NO from the bed showed that, within the air inlet flow rates investigated, the conversion of fuel nitrogen to NO decreased with increasing air flow rate during ignition front propagation, while the conversion increased during the char burnout phase.

Modelling and experiments of straw combustion in a grate furnace

A one-dimensional, unsteady mathematical model is presented of fixed-bed countercurrent wood gasifiers, which couples heat and mass transport with wood drying and devolatilization, char gasification, and combustion of both char and gas-phase species. The model is used to simulate the structure of the reaction fronts and the gasification behavior of a laboratory-scale plant as the reactor throughput and the air-to-wood (or char) weight ratio are varied. It is observed that a wide zone, acting essentially as a countercurrent heat exchanger, separates combustion/gasification from devolatilization/ drying. Moreover, the former zone presents interesting dynamic patterns driven by the highly variable solid/gas heat transfer rates. For a constant air-to-wood weight ratio, the gasification process is improved by increasing the reactor throughput as a result of higher temperatures, in spite of the simultaneous reduction in the amount of char generated from wood devolatilization. In fact, an increase in the air-to-wood (or char) ratio always lowers the efficiency of the gasification process. Finally, good agreement is obtained between predictions and experiments for the axial temperature profiles and the composition of the producer gas. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2306 –2319, 2004

/pdf/modeling-wood-gasification-in-a-countercurrent-fixed-bed-anpe23dbil.pdf

Modeling wood gasification in a countercurrent fixed‐bed reactor

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/31263/0000169.pdf?sequence=1

Adiabatic reverse combustion in a packed bed

Role of gas-phase reaction and gas-solid thermal nonequilibrium in reverse combustion

Analysis of levitation of saturated liquid droplets on permeable surfaces

The process of adiabatic reverse combustion when air is supplied through a packed bed of wood particles is examined in the oxygen-limited regime when both the gas phase reaction and the gas-solid surface reaction are significant. The local, volume-averaged conservation equations that allow for the thermal and chemical nonequilibrium between the gas and solid phases are used to describe propagation of the reaction front through the fuel bed. The role of the air pore velocity and the homogeneous reaction rate on the front speed, the adiabatic temperature, the degree of solid consumption, and the unburnt volatiles concentration in the post gas-phase oxidation regime, are explored. The volumetric solid phase pyrolysis is considered to be the mechanism producing the volatile fuel. First-order Arrhenius kinetics are used in the single-step reaction models. It is found that the gas-phase reaction becomes dominant over the heterogeneous reaction at high air pore velocities, thus reducing the degree of solid consumption. The adiabatic temperature and the propagation speed increase with the air pore velocity. This behavior is qualitatively in agreement with the general experimental observations (performed previously) of the transition from smoldering to flaming.

Role of gas-phase reaction in reverse combustion

http://scientiairanica.sharif.edu/article_3012_e67e539303ca77299c60ada41870ea59.pdf

M. Fatehi

Papers

Adiabatic reverse combustion in a packed bed

Role of gas-phase reaction and gas-solid thermal nonequilibrium in reverse combustion

Analysis of levitation of saturated liquid droplets on permeable surfaces

Role of gas-phase reaction in reverse combustion

Combustion in Porous Media