Stagnation tube

The pitot-static tube includes an annular tube surrounding the stagnation tube, with holes in the sides through which the static pressure is measured. For this configuration, errors introduced by... 

The simplest pitot tube (invented by H. Pitot) is sketched in Fig. 5.6. This is sometimes called an impact tube or stagnation tube. It consists of a bent, transparent tube with one vertical leg projecting out of the flow and another leg pointing directly upstream in the flow. 

Pitot Tubes. The fundamental design of a pitot tube is shown in Eigure 9a. The opening into the flow stream measures the total or stagnation pressure of the stream whereas a wall tap senses static pressure. The velocity at the tip opening, lA can be obtained by the Bernoulli equation ... 

This states that the sum of the velocity pressure 0.5pv plus the static pressure / the total pressure, is constant along a streamline. In the case of standard air density (1.2 kg m ), 0.5pv becomes 0.6v. When a Pitot-static tube is immersed into the flow, as in Fig. 12.19, the velocity at the stagnation point at the tube nose is f = 0 and the local static pressure equals the total pressure p,. The flow static pressure p, is measured a short distance downstream from the surface of the tube. The flow velocity is obtained by applying Eq. (12.27) ... 

PIV velocity measurements made it possible to evaluate the flame temperature field [23], following the method demonstrated in Ref. [25]. The calculated thermal structure of lean limit methane flame is shown in Figure 3.1.7. The differences between the structures of lean limit methane and propane flames are fundamental. The most striking phenomenon seen from Figure 3.1.7 is the low temperature in the stagnation zone (the calculated temperatures near the tube axis seem unrealistically low, probably due to very low gas velocities in the stagnation core). 

In region III near the tube center, viscous stresses scale by the tube radius and for small capillary numbers do not significantly distort the bubble shape from a spherical segment. Thus, even though surfactant collects near the front stagnation point (and depletes near the rear stagnation point), the bubble ends are treated as spherical caps at the equilibrium tension, aQ. Region... 

The pitot tube is a device for measuring v(r), the local velocity at a given position in the conduit, as illustrated in Fig. 10-1. The measured velocity is then used in Eq. (10-2) to determine the flow rate. It consists of a differential pressure measuring device (e.g., a manometer, transducer, or DP cell) that measures the pressure difference between two tubes. One tube is attached to a hollow probe that can be positioned at any radial location in the conduit, and the other is attached to the wall of the conduit in the same axial plane as the end of the probe. The local velocity of the streamline that impinges on the end of the probe is v(r). The fluid element that impacts the open end of the probe must come to rest at that point, because there is no flow through the probe or the DP cell this is known as the stagnation point. The Bernoulli equation can be applied to the fluid streamline that impacts the probe tip ... 

The measured pressure difference AP is the difference between the stagnation pressure in the velocity probe at the point where it connects to the DP cell and the static pressure at the corresponding point in the tube connected to the wall. Since there is no flow in the vertical direction, the difference in pressure between any two vertical elevations is strictly... 

An estimate of the temperature of the clusters in the reactor tube can be obtained from the velocity of the atomic species in the beam. This velocity, assuming insignificant slippage, is related to the "stagnation" temperature by( 18)... 

Equation (4.4), which connects the known variables, unbumed gas pressure, temperature, and density, is not an independent equation. In the coordinate system chosen, //, is (lie velocity fed into the wave and u2 is the velocity coming out of the wave. In the laboratory coordinate system, the velocity ahead of the wave is zero, the wave velocity is uh and (u — u2) is the velocity of the burned gases with respect to the tube. The unknowns in the system are U, u2, P2, T2, and p2. The chemical energy release is q, and the stagnation adiabatic combustion temperature is T, for n-> = 0. The symbols follow the normal convention. 

In Fig. 15.4, the measured turbulent flame speeds, normalized with mixture-specific laminar flame velocities obtained recently by Vagelopoulos et al. [14], are compared with experimental and theoretical results obtained in earlier studies. Also shown in the figure are the measurements made by Abdel-Gayed et al. [3] for methane-air mixtures with = 0.9 and = 1 a correlation of measured turbulent flame speeds with intensity obtained by Cheng and Shepherd [1] for rod-stabilized v-flames, tube-stabilized conical flames, and stagnation-flow stabilized flames, Ut/Ul = l + i.2 u /U ) a correlation of measured turbulent flame... 

The EPA Method 2 probe uses a standard S-type Pitot tube to determine the velocity pressure by measuring gas flow as a unidirectional vector. This method is typically 10-20% higher than the calculated flue gas rate from the FCC heat balance. The newly develop EPA Method 2F probe is a five-holed prism tip with a thermocouple. A centrally located tap measures the stagnation pressure, while two lateral taps measure the static pressure. The yaw angle is determined by rotating the probe until the difference between the two lateral holes is zero. This method closely matches the... 

The incident shock wave moves down the tube, heating and accelerating the test gas. In RST mode, the shock hits an end plate and reflects back to the test gas, further heating the gas and initiating stagnation conditions. Subsequently, a rarefaction wave travels down the tube and quenches all further reactions. 

Fig. 1. Photograph of flow field and flame front shape from the work by Uberoi (1959). Flame is propagating downward in a vertical tube small particles added to the gaseous mixture indicate streamlines before and behind flame front. One can see stagnation zone close to tube wall.

The integral Eq. (59) together with the surface shape Eq. (56) would determine the flame propagation velocity along the tube axis as a function of the normal flame velocity and the density ratio a. The width of the stagnation zone could be derived by integration... 

The performed numerical calculations for the case of cylindrical symmetry yielded the same qualitative dependence of the flame surface shape, the propagation velocity, and thickness of the stagnation zone, as iu the case of the plane channel. The quantitative results for the cylindrical tube are somewhat different, e.g., the dimensionless propagation velocity along the tube axis at a real a proves to be 50 percent higher than in the case of plane symmetry. 

The formula for the pitot tube follows directly from the stagnation-pressure relation. The difference between the stagnation- and the static-pressure heads is seen to be h, which is the dynamic-pressure head. Hence for a pitot tube pointed directly upstream and in a flow without appreciable turbulence, the equation is... 

Fig. 8.2c. Mass transfer at an impinging jet electrode. I, central core potential region II, established flow region III, stagnation region ( wall-tube region) IV, wall-jet region (from Ref. 13 with permission).

Figure 31 presents a schematic of the stagnation jet reactor. The reactor is a slim cylindrical vessel with diameter D and length 2h. In each half of the reactor, there is a propeller fitted inside a draft tube. The only function of the impeller is the generation of a jet with a large axial momentum. The rotational motion of the jet should be as small as possible. 

---