Stagnation point temperature

When a thermometer is placed in a flowing gas stream, most of the thermometer s surface has gas flowing past it but a stagnation point occurs at its upstream side. Thus instead of measuring the temperature T, it measures a value that is slightly higher. This can be accommodated by introducing a correction factor known as the recovery factor r/. 

As indicated by Fig. 23 and Fig. 24, the source function can be highly asymmetrical. For the liquid droplet corresponding to Fig. 23, one would expect the internal temperature to be higher near the back and front of the sphere because of the spikes in the source function in those regions. As a result, the evaporation rate should be enhanced at the rear stagnation point and the front of the sphere. To calculate the evaporation rate when internal heating occurs, one must solve the full problem of conduction within the sphere coupled with convective heat and mass transport in the surrounding gas. 

Fig. 2 Reported growth rate of tin oxide, prepared from (Ctf3)4Sn + O2, as a function of temperature. Borman et al. [39] used a hot wall reactor with various diameters shown in the legend, [TMT] = 99-390 ppm. Ghostagore [32,33] used a horizontal cold wall reactor with [TMT] = 117-310 ppm. Chow et al. [54] used a stagnation-point flow reactor, and Vetrone et al. [55] a horizontal hot-wall reactor with a tilted substrate...

Air flows at a velocity of 2 m/s normal to the axis of a circular cylinder with a diameter of 2.5 cm. The surface of the cylinder is kept at a uniform surface temperature of 50°C and the temperature in the air stream ahead of the cylinder is 10°C. Assuming that the flow is two-dimensional. And the heat transfer rate in the vicinity of the stagnation point. 

Consider two-dimensional air flow normal to a plane surface. If the initial air temperature is 20°C, the surface temperature 80°C. and the air velocity in the free stream ahead of the plate is 1 m/s, plot the variation of heat transfer rate in the vicinity of the stagnation point. 

An airflow at 540°C and l atm impinges on the front side of a porous horizontal cylinder 7.5 cm in diameter at a velocity of 600 m/s. Air is injected through the porous material to maintain the surface temperature at 150°C. Calculate the heat-transfer rate at a distance of 0.75 cm from the stagnation point and with an injection parameter of 0.5. 

We consider the laminar two-dimensional motion of fluid past a hot semi-infinite plate, with the free stream velocity and temperature denoted by, Uoo and Too- We will focus our attention on the top of the plate, for which the temperature is T - that is greater than Too, while assuming the leading edge of the plate as the stagnation point. Governing equations are written in dimensional form (indicated by the quantities with asterisk), along with the Boussinesq approximation to represent the buoyancy effect,... 

Nonadiabaticity and Lewis numbers differing from unity modify the rate of heat release per unit area. Let us rule out distributed heat loss and consider nonadiabaticity associated with the temperature of the product stream at infinity,, differing from the adiabatic flame temperature, T j-. If the product stream is hotter (a superadiabatic condition), then by enhancing heat conduction (through reducing distances over which heat conduction occurs) and by bringing the reactive-diffusive zone closer to the product side of the stagnation point, an increase in k results in an increase in the flame temperature at the reactive-diffusive zone and thereby increases... 

Stream, is equivalent by symmetry to a one-stream problem in which one of the reactant streams is directed normally onto an infinite adiabatic flat plate at which the no-slip condition is replaced by a zero-stress condition a number of theoretical analyses of this problem have been published (for example, [101], [102], [103], [107], [112], [118]), and nonadiabatic problems also have been studied [112], [118]. The results of these analyses are qualitatively similar to those just discussed, but the multiple-valued dependence of upon k is now found to occur for J > 4 in the symmetric problem by removing the possibility of thermal adjustments occurring in the product stream, the introduction of symmetry strengthens the dependence of the flame temperature on the Lewis number and enables abrupt extinctions to be encountered for many real reactant mixtures that have Lej > 1. There are clear experimental confirmations of this qualitative prediction [114], [120]. As K is increased for reactants with Lcj > 1 to a sufficient extent, the two flames move closer together but experience abrupt extinction at a critical value of k before they reach the stagnation point for reactants with Lcj < 1, the two flames tend to merge at the plane of symmetry prior to abrupt extinction. 

Fig. 18. CO coverage (H) as a function of the Pt substrate temperature measured during CO oxidation at a pressure of 20 mbar. (D) indicate temperatures where equilibrium CO surface coverage was too low to be detected. CO2 production (A) simultaneously measured by mass spectrometry in the exhaust gas. The measurement were carried out under laminar flow conditions in a stagnation point flow onto the Pt catalyst surface. Solid lines are results of a numerical reactive flow simulation for a CO/02/Ar-stagnation point flow onto the Pt foil corresponding to the experimental flow conditions (CO 15 seem O2 30 seem Ar 105 seem).

The eigentemperature is identical to the temperature at the stagnation point in a flow at velocity ws on a body. It holds for this, that... 

We see that the Ts depends on the rate of heat release q and that the overall effect of convection is to reduce the surface temperature and make it nonuniform, with the surface temperature being highest at q = 1 (i.e., the downstream stagnation point of the sphere) and lower at the front, q = — 1. The asymmetry is due to the fact that the radial temperature gradient is slightly increased at the front relative to the back and thus requires a slightly lower surface temperature to sustain the heat flux q, compared with the surface temperature that is required at the back. 

The images of the single-brush flame were complemented by profiles of temperature, velocity, and calculated strain rates at the stagnation plane (not shown here), and the effects of forcing amplitude and frequency on the reduction in the mean extinction strain rate close to the axis were quantified while previous results [15] were extended to include the effects of bulk velocity and separation on extinction times. The amplitude of imposed oscillations was quoted in terms of the rms of the axial velocity fluctuations at the nominal stagnation point normalized by the bulk velocity [14],... 

In this expression, T, and T° are the recovery and total jet (nozzle) temperatures, respectively. The available results suggest that effectiveness depends on the nozzle geometry and axial nozzle-to-plate distance (Hid) and the radial displacement from the stagnation point (rid), but it is independent of the nozzle exit Reynolds number [86,87]. 

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