| OCR Text |
Show the bed itself. The working-fluid cooled tubes installed in the bed extract heat released in the combustion zone by the combined convective/radiative heat transfer. Mechanisms of the combined convective/radiative/conductive heat transfer within the surface combustor-heater can be described as follows: • Heat release from fuel/oxidant reaction takes place in gas phase. • The gaseous products of combustion heat up the solid particles via convection because gas radiation is negligible. • The heat load embedded in the porous matrix removes heat by convection between the gas flow and the load surfaces, as well as by radiation and conduction between the solid particles and the load surfaces; convection and radiation are equally important components of the overall heat-transfer process. • Ratio of heat transferred by convection and radiation depends upon the porous matrix structure, operating regime, and location of the heat-exchange surface. • The characteristics of fuel/oxidant mixture combustion are dependent upon heat removal from the gas phase to the solid particles and also to the load via convection, namely, combustion-heat transfer interaction. • Compared with conventional convective heat-transfer devices, heat transfer to the load in the surface combustor-heater is enhanced by the intense convection from the gas flow as well as the significant radiation from the solid particles. • Compared with conventional combustion devices, simultaneous heat removal from the combustion zone decreases the temperature of the combustion reaction, resulting in significant reduction of NOx emissions. Therefore, some of the significant advantages of the surface combustor-heater described above can be expected: • High combustion intensity, because the combustion zone within the porous matrix is more narrow than the flame occupation in gas space • High heat-transfer rate, because of intensive combined convective/radiative/conductive heat transfer to the tube surfaces • Low NOx emissions, because of low combustion temperature • Low CO and THC emissions, because of good mixing and extensive combustion in the gas phase of the porous matrix. Interaction of Combustion and Heat Transfer The major technical challenge of the surface combustor-heater is the interaction between combustion and heat transfer taking place Simultaneously within the porous matrix. 6 INS TITUTE o F GAS TEe H N 0 LOG Y |
