Turbulent air flow

Randomness.—The word random is used frequently to describe erratic and apparently unpredictable variations of an observed quantity. The noise voltage measured at the terminals of a hot resistor, the amplitude of a radar signal that has been reflected from the surface of the sea, and the velocity measured at some point in a turbulent air flow are all examples of random or unpredictable phenomena. 

Cohen, L. S., andT. J. Hanratty, 1968, Effects of Waves at a Gas-Liquid Interface on a Turbulent Air Flow, J. Fluid Mech. 31 461. (3)... 

The design and necessary calculations for the labyrinth calorimeter with turbulent air flow but low heat losses, have been presented earlier (7). See Figure 1. The advantage over micromethods such as DSC is that effects of sheet density and caliper of fiber entities... 

A turbulent air flow should not be present at each area location. 

Ghosh, S Hunt, J.C.R., Phillips, J.C., and Miller, P.C.H. (1993) Dynamics of turbulent air-flow in droplet driven sprays, Applied Scientific Resarch 51, 257-262. 

Heat Transfer from a Plate to a High-Turbulence Air Flow" Heat Transfer-Soviet Research, 11, No. 5, 1979. 

For a 125 mm wafer, the air flow at the very edge is no longer laminar once the rotation rate exceeds about 3700 rpm. At 6000 rpm, the transition occurs at a radial position of 49 mm the outer 14 mm is in the transition or turbulent flow regime on a 125 mm wafer at this speed. In the turbulent region, the evaporation rate depends on radial position and varies with the spin speed to a power other than one-haIf. The result is expected to be a non-uniform resist thickness. While this effect is probably not important for the wafers in use today, it may become important in the future. The critical speed for a 200 mm wafer is only 1430 rpm. Above this value, at least part of the wafer will be in the turbulent air flow regime. 

Attempts to explore this complicated interaction and to model the response of the eddy viscosity and turbulent shear stresses to the time variation of pressure gradients in turbulent air flow over a solid wavy surface have been made by Thorsness et al. [85] and Abrams and Hanratty [89]. Large variations of the amplitude and phase angle of the surface shear stress with the dimensionless wave number were predicted (Figure 3). The analysis shows that the surface shear stress fluctuation is shifted upstream with respect to the wave elevation and the phase shift varies in the range of 0-80° in comparison to the constant phase shift predicted by Benjamin [84],... 

In general, the dry deposition velocity will be the combined effect of both resistances. However, at highly turbulent air flow conditions R =0 and the dry deposition velocity is dependent only on the surface processes. Alkaline surfaces, such as lead peroxide or triethanolamine, are ideal absorbers of SO2 for which = 0. In this case, the dry deposition velocity if dependent on the aerodynamic processes. Typical ranges for dry deposition velocities onto various materials imder outdoor and indoor conditions are given in Table 2.1. 

Mass transfer by molecular diffusion resides at the other end of the spectrum. It yields the lowest possible mass transfer rate and sets an upper limit on time requirements. The solvent spill considered in Practice Problem 4.4, for example, requires several days to complete evaporation by diffusion into stagnant air. The same data applied to turbulent air flow at the same temperature yield an estimate of several minutes, lower by three orders of magnitude. The factor of 1000 can thus be viewed as separating the two extremes of diffusive and turbulent mass transfer. 

Assessment of a multistage gravity separation in turbulent air flow... 

J. Tomas and T. Groger, Assessment of a Multistage Gravity Separation in Turbulent Air Flow, Proceedings of the Third Israeli Conference for Conveying and Handling of Particulate Solids, 2000, pp. 9.20-9.27... 

The volatilization from soil is more complicated because of the numerous additional mechanisms that are present in the soil, as shown in Figure 7.1. To be volatilized from soil, the herbicide may be lost directly from its solid form to its gaseous form, or it may be released from being adsorbed to soil particles into the soil solution, diffuse into the soil air, and move to the surface to be dispersed into the turbulent air flow above the soil. How close this turbulent region is to the surface depends on the condition of the soil surface. Cultivation practice and soil texture determine the number and size of the clods on the surface, and thus the relative smoothness will determine the evenness of the application of the herbicide and influence the air flow and microclimate at the air-soil interface. The air within the soil is virtually static above this, there is an area of laminar... 

Protection using low turbulence air flow permits germ-free air to move on parallel streamlines. The recommended velocity for vertical flow is 0.3 m/s, with 0.45 m/s recommended for horizontal flow. This is equivalent to an air flow rate of 1000-1500m / hr per m of room area - very much higher than typical air-conditioning systems. 

---