Velocity error coefficient

Flow nozzles are commonly used in the measurement of steam and other high velocity fluids where erosion can occur. Nozzle flow coefficients are insensitive to small contour changes and reasonable accuracy can be maintained for long periods under difficult measurement conditions that would create unacceptable errors using an orifice installation. 

If the lower values in the brackets are applied, an additional 0.5 uncertainty (error on 5% risk level) has to be added arithmetically to the flow coefficient confidence limits. The use of flow straighteners is recommended in cases when a nonstandard type of upstream fitting disturbs the flow velocity profile. 

To evaluate the required condenser area, point values of the group UAT as a function of qc must be determined by a trial and error solution of equation 9.181. Integration of a plot of qc against 1/17AT will then give the required condenser area. This method takes into account point variations in temperature difference, overall coefficient and mass velocities and consequently produces a reasonably accurate value for the surface area required. 

The QUICK scheme has a truncation error of order h. However, similarly as in the case of the central differencing scheme, at high flow velocities some of the coupling coefficients of Eq. (37) become negative. 

If a particle is moving in a fluid which is in laminar flow, the drag coefficient is approximately equal to that in a still fluid, provided that the local relative velocity at the particular location of the particle is used in the calculation of the drag force. When the velocity gradient is sufficiently large to give a significant variation of velocity across the diameter of the particle, however, the estimated force may be somewhat in error. 

Checking to see that the units of all terms in all equations are consistent is perhaps another trivial and obvious step, but one that is often forgotten. It is essential to be particularly careful of the time units of parameters in dynamic models. Any units can be used (seconds, minutes, hours, etc.), but they cannot be mixed. We will use minutes in most of our examples, but it should be remembered that many parameters are commonly on other time bases and need to be converted appropriately, e.g., overall heat transfer coefficients in Btu/h °F ft or velocity in m/s. Dynamic simulation results are frequently in error because the engineer has forgotten a factor of 60 somewhere in the equations. 

Each echo has traveled a distance twice the cell length d further than the previous echo and so the velocity can be calculated by measuring the time delay t between successive echoes c = 2d/t. The cell length is determined accurately by calibration with a material of known ultrasonic velocity, e.g. distilled water 2d = cw.tw (where the subscripts refer to water). The attenuation coefficient is determined by measuring the amplitudes of successive echoes A = A0e-2cxd, and comparing them to the values determined for a calibration material. A number of sources of errors have to be taken into account if accurate measurements are to be made, e.g., diffraction and reflection (see below). 

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. 

Table 4.3 CNV97100 transport parameter estimated in whole small intestine, duodenum and ileum. Fits were performed simultaneously using Eqs. (26)-(29). No inhibitor was present. S.E. - standard error, CV % - coefficient of variation. Vmjotai maximal velocity in whole small intestine, VmQ maximal velocity in duodenum, Vmj maximal velocity in jejunum, Vmj maximal velocity in ileum. Vmo, Vmj, and Vmjotaj are secondary parameters computed from (CV % is the same).

Cas-Liquid Mass Transfer Gas-liquid mass transfer normally is correlated by means of the mass-transfer coefficient K a versus power level at various superficial gas velocities. The superficial gas velocity is the volume of gas at the average temperature and pressure at the midpoint in the taiik divided by the area of the vessel. In order to obtain the partial-pressure driving force, an assumption must be made of the partial pressure in equihbrium with the concentration of gas in the liquid. Many times this must be assumed, but if Fig. 18-26 is obtained in the pilot plant and the same assumption principle is used in evaluating the mixer in the full-scale tank, the error from the assumption is limited. 

On the other hand, Settari et al. (50) used a finite-element analysis in examining the consec[uences of both velocity-dependent and constant dispersion coefficients during a two-dimensional displacement. They found that fingers in the concentration distribution developed when the permeability was homogeneous, so long as the dispersion coefficients were sufficiently small. This was apparently the first successful use of truncation and round-off errors to play the roles of physical perturbations in initiating instabilities. Russell (51) later had a similar experience. 

The influence of temperature is especially significant for aqueous systems. Thus, US velocity in water varies by approximately 3 m/s per °C at 20°C therefore, an error of 0.1 °C in temperature will result in an error of 0.3 m/s in velocity. It should be noted that the temperature coefficient of the US velocity in pure water at temperatures up to 74°C is positive, unlike most other liquids. 

Preston coefficients may be readily measured for a polish process. The simplest method for measuring is to measure the polish rate and divide by the pressure and velocity. However, this method is sensitive to error in the polish rate measurement. A better measure of is obtained by measuring the polish rate over a range of velocities and pressures. If the polish rate behavior follows Preston s equation, i.e., if it is linear and intersects the origin, may then be obtained by differentiating Equation (4.1) with respect to either pressure or velocity. is then given by ... 

Figure 4. Sedimentation Velocity Analysis of ZDD. A, Primary data collected at 1 mg/ml (10 scans). B, Apparent sedimentation coefficient distribution function, g(s ) versus s. The error bars represent the standard error of the mean. The solid line is the fit to equation 4. Apparent s, D, and Ms,D values were calculated as described.

Remember that expresses the resistance of droplets of the 2th fraction to the air flow, Ai accounts for their concentration n , and j3 for the speed of their vertical gravitational fall according to (3.36) and (3.88). The velocity profiles have basically the same shape in the case of heavy droplets that fall down with acceleration and governed so by coefficients (3.81). There is no big error if these variable coefficients would be substituted by their means. 

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