Pressure-velocity limiting

After the equilibrium condition is maintained for approximately 30 min, the load is increased. At some advanced load increment, the friction torque and/or temperature will not stabilize. The PV product at which it last stabilized is designated the limiting pressure-velocity for that material at that specific velocity. Although results are not transferable to other sample configurations, the test provides information useful for comparing thermoplastic composite systems. ... 

TABLE 3-25. LIMITING PRESSURE VELOCITY PROPERTIES OF ACETAL... 

TABLE 3-42. LIMITING PRESSURE VELOCITY OF THERMOCOMP NYLON 6,6/6, and 6/10... 

As normally designed, vapor flow through a typical high-lift safety reliefs valve is characterized by limiting sonic velocity and critical flow pressure conditions at the orifice (nozzle throat), and for a given orifice size and gas composition, mass flow is directly proportional to the absolute upstream pressure. 

Since the pressure drop is quite high, there is a possibility of approaching sonic velocity in the line. This will result in a potential noise problem. Hence, it is a good practice to limit the velocity to 60 percent of the sonic velocity or a 0.6 Mach number. 

In the relationships proposed by Brode (1959) and in Figure 6.33, velocity has no upper limit, although Figure 6.33 is approximately bounded by scaled pressures of 0.05 and 0.2 (scaled energies of approximately 0.1 and 0.7). Baum (1984) states, however, that there is an upper limit to velocity, as follows The maximum velocity... 

A very small pressure difference is obtained for low rates of flow of gases, and the lower limit of velocity that can be measured is usually set by the minimum difference in pressure that can be measured. This limitation is serious, and various methods have been adopted for increasing the reading of the instrument although they involve the need for calibration. Correct alignment of the instrument with respect to the direction of flow is important this is attained when the differential reading is a maximum. 

To generate a sufficient pressure drop for good gas distribution, a high velocity through the grid openings may be required. It is best to limit this velocity to less than 60 m/s to minimize attrition of the bed material. The maximum hole velocity allowable may be even lower for very soft materials that attrite easily. The pressure drop and the gas velocity through the hole in the gas distributor are related by the equation... 

Microfiltration is a unit operation for the separation of small particles. The separation limits are between 0.02 and 10 (jum particle dimensions. Microfiltration can be carried out in a dead-end mode and a cross-flow mode. In downstream processing, the cross-flow filtration is carried out continuously or discontinuously. The most important parameters that determine the productivity of cross-flow microfiltration are transmembrane pressure, velocity, particle size and surface, viscosity of the liquid and additives such as surfactants, and changing the surface and surface tension. 

The results in the table may be summarised in the statement that from low pressures up to a certain limiting pressure the velocities are proportional to the oxygen pressure and are also a function of the rate of supply of vapour from the surface of the phosphorus. In fact, if in... 

Valves <80 to 108 Avoid sonic velocities, limit pressure drop, and mass flow, replace with special low noise valves, vibration isolation and lagging. 

This means that in the elastic region, pressure and density are linearly related. Beyond the elastic region, the wave velocity increases with pressure or density and Pip is not linearly proportional. Wave velocity continues to increase with stress or pressure throughout the region of interest. Therefore, up to the elastic limit, the sound velocity in a material is constant. Beyond the elastic limit, the velocity increases with increasing pressure. Let us look at a major implication of this fact. Consider the pressure wave shown in Figure 14.3. 

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