Coefficient of velocity

Coefficient of velocity The coefficient describing the actual velocity of a jet, compared to the theoretical value. 

Coefficient of velocity Cv. The velocity that would be attained at the vena contracta if friction did not exist may be termed the ideal velocity Vi. (This is frequently called theoretical velocity, but this is a misuse of the word theoretical. Any correct theory should allow for the fact that friction exists and affects the result. Otherwise, it is not correct theory but merely an incorrect hypotheses.) Owing to friction, the actual average velocity V is less than the ideal velocity, and the ratio V/Vl is called the coefficient of velocity. Thus, V = C VL. 

The coefficient of velocity may be determined by a velocity traverse of the jet with a fine pitot tube in order to obtain the mean velocity. This is subject to some slight error, as it is impossible to measure the velocity at the outer edge of the jet. The velocity may also be computed approximately from the coordinates of the trajectory. The ideal velocity is computed by the Bernoulli theorem. 

Non-activated adsorption. This is characterised by (a) zero or negative temperature coefficient of velocity, (b) initial rate independent of coverage, and (c) rate proportional to pressure. 

Treatment of W somnifera seeds with 100-ppm gibberellic acid resulted in improved percentage germination, speed of germination, emergence, coefficient of velocity of... 

The above equation neglects velocity of approach to the orifice. Typically, the coefficient of velocity, Cy, is assumed to be 0.8. 

The coefficient of discharge is a composite of several components that affect the flow. Two of these components are the coefficients of contraction and velocity. In this work no attempt was made to evaluate the components separately. According to Prandtl [ ] the coefficient of velocity differs considerably from unity for small orifices and low velocities w hen the ratio of the orifice diameter to the pipe diameter is small. For large openings and high velocities it is usually close to unity. 

If the number of molecules of A and B in unit volume be denoted by p and q, the product pq will represent the frequency of the encounters of these molecules. If each motion of the various molecules be equally favourable to the formation of new substances, the velocity. . . may be made equal to pq, the coefficient of velocity being supposed dependent on temperature. This view, already known from the theory of gaseous dissociation, may now be extended as follows so as to apply to all states of aggregation. ... 

An expression for the mean germination rate of a population was devised by Kotowski [11]. This expresses the so-called coefficient of velocity (0 (though not strictly a measure of velocity or speed but of rate) thus ... 

The coefficient of friction may also depend on the relative velocity of the two surfaces. This will, for example, affect the local temperature, the extent... 

In the absence of skidding, the coefficient of static friction applies at each instant, the portion of the tire that is in contact with the pavement has zero velocity. Rolling tire friction is more of the type discussed in Section XII-2E. If, however, skidding occurs, then since rubber is the softer material, the coefficient of friction as given by Eq. XII-5 is determined mainly by the properties of the rubber used and will be nearly the same for various types of pavement. Actual values of p, turn out to be about unity. 

Thus if Amontons law is obeyed, the initial velocity is determined entirely by the coefficient of friction and the length of the skid marks. The mass of the vehicle is not involved, neither is the size or width of the tire treads, nor how hard the brakes were applied, so long as the application is sufficient to maintain skidding. 

As might be expected, this simple picture does not hold perfectly. The coefficient of friction tends to increase with increasing velocity and also is smaller if the pavement is wet [14]. On a wet road, /x may be as small as 0.2, and, in fact, one of the principal reasons for patterning the tread and sides of the tire is to prevent the confinement of a water layer between the tire and the road surface. Similarly, the texture of the road surface is important to the wet friction behavior. Properly applied, however, measurements of skid length provide a conservative estimate of the speed of the vehicle when the brakes are first applied, and it has become a routine matter for data of this kind to be obtained at the scene of a serious accident. 

Fig. XIl-5. Coefficient of friction of steel sliding on hexafluoropropylene as a function of load (first traverse). Velocity 0.01 cm/sec 25°C. (From Ref. 31.)...

The application of a small external electric field A to a semiconductor results in a net average velocity component of the carriers (electrons or holes) called the drift velocity, v. The coefficient of proportionality between E and is known as the carrier mobility p. At higher fields, where the drift velocity becomes comparable to the thennal... 

Other orientational correlation coefficients can be calculated in the same way as tf correlation coefficients that we have discussed already. Thus, the reorientational coiTelatio coefficient of a single rigid molecule indicates the degree to which the orientation of molecule at a time t is related to its orientation at time 0. The angular velocity autocorrelatio function is the rotational equivalent of the velocity correlation function ... 

The friction coefficient determines the strength of the viscous drag felt by atoms as they move through the medium its magnitude is related to the diffusion coefficient, D, through the relation Y= kgT/mD. Because the value of y is related to the rate of decay of velocity correlations in the medium, its numerical value determines the relative importance of the systematic dynamic and stochastic elements of the Langevin equation. At low values of the friction coefficient, the dynamical aspects dominate and Newtonian mechanics is recovered as y —> 0. At high values of y, the random collisions dominate and the motion is diffusion-like. 

The dynamic viscosity, or coefficient of viscosity, 77 of a Newtonian fluid is defined as the force per unit area necessary to maintain a unit velocity gradient at right angles to the direction of flow between two parallel planes a unit distance apart. The SI unit is pascal-second or newton-second per meter squared [N s m ]. The c.g.s. unit of viscosity is the poise [P] 1 cP = 1 mN s m . The dynamic viscosity decreases with the temperature approximately according to the equation log rj = A + BIT. Values of A and B for a large number of liquids are given by Barrer, Trans. Faraday Soc. 39 48 (1943). 

In Sec. 2.2 we saw that the coefficient of viscosity is defined as the factor of proportionality between the shearing force per unit area = F /A and the velocity gradient dv/dy within a liquid [Eq. (2.2)] ... 

Velocity, m /min Wear factor Dynamic K X 10-", 1/Pa " coefficient of friction Test duration, h... 

Although it has been common practice to specify the pressure loss in ordinary valves in terms of either equivalent length of straight pipe of the same size or velocity head loss, it is becoming more common to specify flow rate and pressure drop characteristics in the same terms as has been the practice for valves designed specifically for control service, namely, in terms of the valve coefficient, C. The flow coefficient of a valve is defined as the volume of Hquid at a specified density that flows through the fully opened valve with a unit pressure drop, eg, = 1 when 3.79 L/min (1 gal /min) pass through the valve... 

The coefficient of restitution is defined as the ratio of the vertical components of the impact and rebound velocities resulting when a bad is dropped or thrown onto a playing surface. The velocities or related rebound heights may be measured photographically. Criteria such as bad inflation pressure, air temperature, and other detads must be specified. 

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