Exhaust velocity

Laser Doppler Velocimeters. Laser Doppler flow meters have been developed to measure Hquid or gas velocities in both open and closed conduits. Velocity is measured by detecting the frequency shift in the light scattered by natural or added contaminant particles in the flow. Operation is conceptually analogous to the Doppler ultrasonic meters. Laser Doppler meters can be appHed to very low flows and have the advantage of sensing at a distance, without mechanical contact or interaction. The technique has greatest appHcation in open-flow studies such as the deterrnination of engine exhaust velocities and ship wake characteristics. 

By viriue of its vertical construction, the turbo-type tray dryer has a stack effect, the resulting draft being frequently sufficient to operate the dryer with natural draft. Pressure at points within the dryer is maintained close to atmospheric, as low as 0.1, usually less than 0.5 mm of water. Most of the roof area is used as a breeching, lowering the exhaust velocity to settle dust back into the dryer. 

The effective stack height (equivalent to the effective height of the emission) is the sum of the actual stack height, the plume rise due to the exhaust velocity (momentum) of the issuing gases, and the buoyancy rise, which is a function of the temperature of the gases being emitted and the atmospheric conditions. 

This is usually not a problem with small exhausts. With large exhausts (opening area larger than 0.1 m-), parts of a worker or of tools could easily come between the source and the exhaust. This diminishes the efficiency and could also spread the contaminant in unwanted directions, even if the exhaust velocity is... 

Method A Calculating Contaminant and Exhaust Velocities at All Points in the Flow Field Local exhaust hoods are used to remove contaminants at the point of generation before they escape into the workplace air. The efficiency of any local exhaust system is greatly affected by the flow field generated by the exhaust opening. Therefore, accurate modeling of this flow field is essential for reliable predictions. However, solving the airflow field is a formidable task and often must be done numerically. 

FIGURE >0.70 The capture of tracer gas released at five times the diameter of the exhaust inlet when the radius of the exhaust hood is 0. tS m, the radius of the exhaust hood inlet is 0.037 m, and the width of the exhaust jet is 8.0 mm. fej Suction alone with average inlet velocity of 12.7 m s. (b) Combined suction and Injection with the average inlet and exhaust velocities of 12 8 rn s and 7.7 m s . respectively. (Figures are courtesy of the Health and Safety Executive, Research Division. Sheffield. UK.)... 

The final example is shown in Fig. 10.86. Several workers are breaking gates off of castings on the conveyor by hand. Much dust is generated by this operation and the dust rises due to buoyancy. To remove the dust, an exterior hood was placed beside the conveyor and a supply inlet was placed above the workers. The supply airflow is blown toward the breathing zone of the workers and the dust source. In this case, as the workers and the dust source are located within the supply airflow, the airflow functions to supply the workers with clean air and to transport the dust toward the exhaust inlet. The velocity of supply air is relatively low, 1.1 m s , and the exhaust velocity at the hood face is 2.75 m s . The dimensions of the system are indicated in the figure, and the depth of the device is 6.0 m (compare with Sections 10.3.3 and 10.4.6). 

F = (H+ cosor) (wVe/g) + (Pe-P0)Ae where oc = half of the divergence angle of the nozzle, w - weight rate of proplnt flow, g = acceleration of gravity, Ve = exit flow velocity, Pe = nozzle exit pressure, PQ = external atm pressure, and Ae = cross section at nozzle exit plane. An effective exhaust velocity is defined by... 

Assuming isentropic expansion of the combustion gases through the nozzle and Pe = Ptt, the exhaust velocity can be determined from the equation... 

V, Exhaust velocity W Wetted perimeter of port X0 Mole fraction of oxidizing species... 

Isp is also related to the characteristic exhaust velocity (C ), calculated from the P-t... 

The primary component of the hypersonic flame spraying process is an internal combustion device, which produces an "exhaust" similar to that found in a rocket. This exhaust is produced by the internal combustion of oxygen and fuel gases. A combustion flame temperature of approximately 5500°F. is created, with exhaust velocities of 4,500 feet per second. 

Sufficient atomic particle research has been accomplished to warrant discussion of possible methods of applying energy available from particle mass annihilation to rocket propulsion. Complete conversion of matter to energy would allow exhaust velocities near that of light to be obtained from a propulsion device. Antimatter, by definition is matter made up of antiparticles, such as antineutrons, negatrons (antiprotons), and positrons (anheledrons). An annihilation property is known to exist between particles with one particle termed the anhparticle of the other. 

The performance of propints is a unique function of the temp of the hot reaction products, their compn and their pressure. The pro-pint bums at constant pressure and forms a set of products which are in thermal and chemical equilibrium with each other. The multiplicity of the reaction products requires that the combustion chamber conditions be calcd from the solution of simultaneous equations of pressure and energy balances. This calcn is best performed by computer, although the manual scheme has been described well by Sutton (Ref 14) and Barr re et al (Ref 10). The chamber conditions determine the condition in the nozzle which in turn characterizes the rocket engine performance in terms of specific impulse and characteristic exhaust velocity... 

II. A. 4. Variation of effective exhaust velocity with exit... 

Being simply the quotient of the thrust and the total weight flow, the specific impulse is a performance parameter readily measured experimentally with good accuracy. This fact accounts for its popular acceptance. With regard to convenience there is no greater merit in the use of I P instead of c. As for the effective exhaust velocity, the specific impulse is evaluated for optimum conditions when theoretical comparisons are made between various propellant combinations. For pe = pa then ... 

II. A. 2.. .. the effective exhaust velocity as determined by the ratio of F to w can be taken to be the optimum value of ue even if the actual experimental nozzle is somewhat off design. Herein lies the practical significance of the concept of the effective exhaust velocity. 

C =Vj/CF=gIs/CF=gF/tf (1/Cp) where Vj = effective exhaust velocity Cp= thrust coefficient g=gravitational acceleration (general) Is= specific impulse F = thrust... 

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