Transverse Heat Transfer and Nusselt Number

A gas-phase microburner can be axially divided into three zones preheating zone, combustion zone and post-combustion zone. Given that radiative heat transfer is not as important and gas-phase conductivity is low, the burner walls are primarily responsible for heat recirculation, which is essential for heating up the inlet gases, via wall conduction, to their ignition temperature in the preheating zone. Thus, heat 

Axial profiles of the Nusselt number (symbols) and averaged gas and surface temperatures, and the Nusselt number fit (line) calculated from Table 10.1. A jump in the Nu profile occurs when the gas and wall temperatures cross (indicated with a thin vertical line). Redrawn from [23]. 

In the preheating zone of microbumers, CFD indicates that the asymptotic Nu value tends towards the constant temperature condition of the Graetz problem 

Alternatively, the dimensionless groups can be set constant in the pseudo-2D model using a crude average of the asymptotes of the two zones in the case of Nu. The last row in Table 10.1 shows such constant (i.e. not a function of axial distance) Nu and Sh (round) values. 

This work was funded through the Army Research Laboratory Composite Materials Research program at the University of Delaware Center for Composite Materials, the Army Research Office under contract DAAD19-01-0582 and the National Science Foundation CBET-0729714 program. Any findings, opinions and conclusions or recommendations expressed here are those of the authors and do not necessarily reflect the views of the Army Research Laboratory or the Army Research Office. 

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