OCR Text |
Show The combustion reaction in the porous matrix is the heat source, yielding the heat of reaction to the embedded heat-exchanger tube surfaces (heat sink). The equilibrium of the combustion reaction is, therefore, dependent upon the balance of heat released by the combustion reaction and the heat extracted by the heat sink. Thus, the combustion temperature and flame location, as well as combustion stability in this device, are sinkcontrolled according to the sink's ability to absorb and to conduct the heat. As a result, the combustion characteristics such as intensity, efficiency, and emissions all interact strongly with the heat-transfer process within the porous matrix. On the other hand, rate and distribution of heat transfer from the combustion products and the porous matrix to the heat sink is dependent upon the combustion regimes, such as the location and intensity of the combustion reaction. This suggests that the major research and development effort should be focused on the interaction of combustion and heat transfer to explore the mechanism of the combined convective/radiative heat-transfer enhancement. Seven major problems should be addressed: • Combustion stability and turndown ratio • Combustion intensity and efficiency • Heat-transfer rate to tubes in rows • Thermal efficiency of the unit • Wall temperature of heat-exchanger tubes • Combustion emissions • Pressure drop. The major parameters that have important effects on the interaction of combustion and heat transfer can be defined as follows: • Structure of porous matrix - including materials, porosity, and characteristic size of pores • Structure of heat sink - including tube diameter, tube spacing, number of rows of tubes, and arrangement of the tubes • Operation regime - including the firing rate, the ratio of air/fuel mixture, and the surface temperature of the tubes. 7 INSTITUTE o F GAS TEe H N 0 LOG Y |