Pressure compressible fluids

Finally, safety systems related to the manipulation of high pressure compressible fluids are necessary all along the process loop. Strict parameter control, safety control and periodic valve actuation requires an automation system the operator controls the process through a computer. 

A static bottom hole pressure survey (SBHP) is useful for determining the reservoir pressure near the well, undisturbed by the effects of production. This often cannot be achieved by simply correcting a surface pressure measurement, because the tubing contents may be unknown, or the tubing contains a compressible fluid whose density varies with pressure (which itself has an unknown profile). 

Erequenfly, the term compressed fluid, a more general expression than supercritical fluid, is used. A compressed fluid can be either a supercritical fluid, a near-critical fluid, an expanded Hquid, or a highly compressed gas, depending on temperature, pressure, and composition. 

The mechanisms that control dmg deUvery from pumps may be classified as vapor-pressure, electromechanical, or elastomeric. The vapor-pressure controlled implantable system depends on the principle that at a given temperature, a Hquid ia equiUbrium with its vapor phase produces a constant pressure that is iadependent of the enclosing volume. The two-chamber system contains iafusate ia a flexible beUows-type reservoir and the Hquid power source ia a separate chamber (142). The vapor pressure compresses the dmg reservoir causiag dmg release at a constant rate. Dmg maybe added to the reservoir percutaneously via a septum, compressing the fluid vapor iato the Hquid state. 

A key limitation of sizing Eq. (8-109) is the limitation to incompressible flmds. For gases and vapors, density is dependent on pressure. For convenience, compressible fluids are often assumed to follow the ideal-gas-law model. Deviations from ideal behavior are corrected for, to first order, with nommity values of compressibihty factor Z. (See Sec. 2, Thvsical and Chemical Data, for definitions and data for common fluids.) For compressible fluids... 

Pressure Safety Valve (PSV) A safety valve is a spring loaded valve actuated by static pressure upstream of the valve and characterized by rapid opening or pop action. A safety valve is normally used with compressible fluids. 

For compressible fluids one must be careful that when sonic or choking velocity is reached, further decreases in downstream pressure do not produce additional flow. This occurs at an upstream to downstream absolute pressure ratio of about 2 1. Critical flow due to sonic velocity has practically no application to liquids. The speed of sound in liquids is very liigh. See Sonic Velocity later in this chapter. 

The Lapple charts for compressible fluid flow are a good example for this operation. Assumptions of the gas obeying the ideal gas law, a horizontal pipe, and constant friction factor over the pipe length were used. Compressible flow analysis is normally used where pressure drop produces a change in density of more than 10%. 

The length of the column is also defined by the Poiseuille equation that describes the flow of a fluid through an open tube in terms of the tube radius, the pressure applied across the tube (column), the viscosity of the fluid and the linear velocity of the fluid. Thus, for a compressible fluid. 

The following analysis enables one to calculate the diameter of a pipeline transporting any compressible fluid. The required inputs are volumetric flow rate, the specific gravity of the gas relative to air, flow conditions, compressibility factor Z where Z is defined by nZRT = PV, the pressure at the point of origin and the destination, the pipe length, and pipe constants such as effective roughness. The working equations have been obtained from the literature. Since the friction factor... 

Compressible fluid flow occurs between the two extremes of isothermal and adiabatic conditions. For adiabatic flow the temperature decreases (normally) for decreases in pressure, and the condition is represented by p V (k) = constant. Adiabatic flow is often assumed in short and well-insulated pipe, supporting the assumption that no heat is transferred to or from the pipe contents, except for the small heat generated by fricdon during flow. Isothermal pVa = constant temperature, and is the mechanism usually (not always) assumed for most process piping design. This is in reality close to actual conditions for many process and utility service applications. 

Friction Pressure Drop For Compressible Fluid Flow... 

Simplified Flow Formula For Compressible Fluids Pressure Drop, Rate of Flow and Pipe Sizes ... 

All flowing gases and vapors (compressible fluids) including steam (w hich is a vapor) are limited or approach a maximum in mass flow velocity or rate, i.e., Ibs/sec or Ibs/hr through a pipe depending upon the specific upstream or starting pressure. This maximum rate of flow cannot be exceeded regardless of how much the dow nstream pressure is further reduced [3]. To determine the actual velocity in a pipe, calculate by... 

This maximum velocity of a compressible fluid in a pipe is limited by the velocity of propagation of a pressure wave that travels at the speed of sound in the fluid [3]. This speed of sound is specific for each individual gas or vapor or liquid and is a function of the ratio of specific heats of the fluid. The pressure reduces and the velocity increases as the fluid flows downstream through the pipe, wdth the maximum velocity occurring at the downstream end of the pipe. WTien, or if, the pressure drop is great enough, the discharge or exit or outlet velocity will reach the velocity of sound for that fluid. 

If the outlet or discharge pressure is lowered further, the pressure upstream at the origin will not detect it because the pressure w ave can only travel at sonic velocity. Therefore, the change in pressure dow nstream w ill not be detected upstream. The excess pre.ssure drop obtained by lowering the outlet pressure after the maximum discharge has been reached takes place beyond the end of the pipe [3]. This pressure is lost in shock waves and turbulence of the jetting fluid. See References 12, 13, 24, and 15 for further expansion of shock waves and detonadon waves through compressible fluids. 

For example, for a line discharging a compressible fluid to atmosphere, the AP is the inlet gauge pressure or the difference between the absolute inlet pressure and atmospheric pressure absolute. When AP/Pi falls outside the limits of the K curves on the charts, sonic velocity occurs at the point of discharge or at some restriction within the pipe, and the limiting value for Y and AP must be determined from the tables on Figure 2-38A, and used in the velocity equation, Vj, above [3]. 

For compressible fluids flowng through nozzles and orifices use Figures 2-17 and 2-18, using hL or AP as differential static head or pressure differential across taps located one diameter upstream at 0.5 diameters dow nstream from the inlet face of orifice plate or nozzle, when values of C are taken from Figures 2-17 and 2-18 [3]. For any fluid ... 

Popping Pressure the pressure at which the internal pressure in a vessel rises to a value that causes the inlet valve seat to begin to open and to continue in the opening direction to begin to relieve the internal overpressure greater than the set pressure of the device. For compressible fluid service. 

Simmer the audible or visible escape of fluid between the seat/disk of a pressure-relieving valve at an inlet static pressure below the popping pressure, but at no measurable capacity of flow. For compressible fluid service. 

When fluids are in motion, the pressure losses may be determined through the principle of conservation of energy. For slightly compressible fluids this leads to... 

Under extreme pressure, a fluid may be compressed up to 7 per cent of its original volume. Highly compressible fluids produce sluggish system operation. This does not present a serious problem in small, low-speed operations, but it must be considered in the operating instructions. 

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