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Show Residence time Tr is represented by L/U, and chemical reaction time Tc by M/Pr, where, M denotes mass unit to undergo reaction. Damkohlernumber is then described as: When flow only. D - ~r _ prL PL a- ~c - MU ex:: U pressure level in a reactor is changed keeping the mass rate constant,Damkohler number will be propotional to p2 3.2 Mathematical Modeling Analysis For a large Damkohler number, the reaction process will be controlled by mixing, thus deminishing the importance of the chemical reaction rate to determine flow pattern. The result of flame simulation using mathematical model best illustrates this trend as shown in Figure 6, where the length of external recirculation zone, LelLo, is plotted as a function of relative Damkoler number, Da/Dao. It is apparent that the flow pattern remains unchanged for a largeDamkohler number, while it is greatly influenced by the chemical reaction rate for a low Damkohler number. One may argue that this result is mere representation of the reaction modeling used in the simulation code, which alternatively selects either a chemically or a mixingcontrolled reaction rate. The importance of this practice is, however, to clarify the range of Damkohler number for which pressure effect is essential. As indicated by the experimental results in Section 2.2 the flow patterns for Type D burner remained unchanged regardless of the pressure level. This supports the present analysis. However, as for Type C burner,pressure change can modify the flow field to a certain degree. The effect of pressure on flame pattern was also evident for the low Reynolds number group,Type A and Type B burners. Some inconvenience with the mathematical model was that the effect of pressure could not be identified for flows created by Type C burner in contrast to the experimental results. A detailed review of the calculation results revealed that for no part of the flow field is chemical reaction a determining process, implying no pressure effect can be present in the calculation. The discrepancy between the simulation and experiment is possibly due to selecting an excessively high chemical reaction rate which gives a high Damkohler number. The activation energy and frequency factor for the global reaction rate employed here 11 |