Heat Transfer of the Critical Air Flow in a Nozzle : 3rd Report, Study on Heat Transfer of the Critical Air Flow in a Convergent Nozzle

Abstract

The authors have published the numerical and experimental studies of heat transfer in parallel nozzles with two-dimensional critical flows in their previous 1st and 2nd reports. In this report, the studies are extended to the case of convergent nozzles. The compressible laminar flows are considered for convergent nozzles at the critical state, and heat transfer characteristics are calculated numerically. According to the results, the critical flow rate increases with a decrease of convergent ratio, and the variation of local Nusselt numbers along the flow direction becomes small by the effects of accelerated boundary layers. Furthermore, the experimental values of mean Nusselt numbers of the critical flow "Numc" agree well with the numerical results calculated on the basis of a laminar flow in the long-size convergent nozzles. From the comparison between the experimental and the analytical results, the range of nozzle characteristics numbers where laminar flows occupy the whole length of the nozzle is determined. Beyond this range described above, a turbulence arises and a turbulent flow is predominant in the critical nozzle, therefore, an experimental expression of mean Nusselt number is presented.