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The current study examines the transition region of axisymmetric isothermal and buoyant jets of low Reynolds number, directed vertically upward into a stagnant, unstratified ambient. The region in which measurements were obtained allows examination of two types of transition occurring in the jet: from nozzle exit dominated to fully developed, and from momentum to buoyancy-dominated flow. Isothermal velocity data were acquired using a two-channel laser-Doppler anemometer for Reynolds numbers ranging from 850 to 7405. The buoyant cases studied had Froude numbers ranging from 12 to 6425 and Reynolds numbers from 525 to 6500. In each case data were taken from 5 to 44 nozzle diameters downstream. Curve fit approximations of the data were developed by assuming polynomial similarity profiles for the measured quantities. Each profile was individually curve fit because in the transition region under consideration the flow field is not necessarily similar. Profile constants were then curve fit to determine profile variation as a function of nozzle exit parameters and downstream location. These allow prediction of the downstream velocity flow field and turbulent flow field as a function of the Reynolds number, Froude number, and density ratio at the nozzle exit. Profile width and entrainment increased at low Reynolds number. Axial and radial velocity fluctuations were found to increase at low Reynolds number. The buoyant cases studied were found to have lower velocity fluctuations and significantly lower Reynolds stresses than isothermal cases of similar Reynolds number.

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Uncertainty analysis in the initial stages of any experimental work is essential in obtaining high-quality data. It insures that the proposed experiment has been thoroughly planned, and that the quantities to be calculated from the experimental measurements will be known with reasonable accuracy and precision. While an uncertainty analysis helps insure reliable results, there is another equally significant aspect in the experimental planning stage: minimization of experimental equipment expenses. A method is presented here in which these two essential experimental elements are combined and viewed as an optimization problem for systematic examination. The analysis allows a systematic search for the least expensive combination of experimental equipment that will give the desired accuracy of results. For the numerical solution the Sequential Gradient Restoration Algorithm (SGRA) is selected. A typical experimental fluid flow and heat transfer problem is given, demonstrating the analysis and numerical solution.

A laser-induced Rayleigh light scattering (RLS) system was used to measure transient gas temperatures in a simulated rapid chemical vapor deposition (RCVD) reactor. The test section geometry was an axisymmetric jet of carrier gas directed down, impinging on a heated wafer surface. RLS was used to measure instantaneous gas temperature at several locations above the wafer as it was heated from room temperature to 475 K. Gas flow rate and wafer temperature correspond to jet Reynolds number Rei=60, wafer maximum Grashof number GrH=4.4×106, and maximum mixed convection parameter GrH/Rei2=1200; all conditions typical of impinging jet reactors common in the numerical literature. Uncertainty of RLS transient temperature from a propagated error analysis was ±2–4 K. Peak gas temperature fluctuations were large (in the order of 25 to 75 °C). Both flow visualization and RLS measurements showed that the flow field was momentum dominated prior to heating initiation, but became unstable by GrH/Rei2=5. It then consisted of buoyancy-induced plumes and recirculations. Up to the peak wafer temperature, the flow field continued to be highly three-dimensional, unsteady, and dominated by buoyancy. RLS measurements are shown to provide information on carrier gas instantaneous temperature and flow field stability, both critical issues in RCVD processing. [S0022-1481(00)02401-4]