Flow measurements static head

In order to avoid the need to measure velocity head, the loop piping must be sized to have a velocity pressure less than 5% of the static pressure. Flow conditions at the required overload capacity should be checked for critical pressure drop to ensure that valves are adequately sized. For ease of control, the loop gas cooler is usually placed downstream of the discharge throttle valve. Care should be taken to check that choke flow will not occur in the cooler tubes. Another cause of concern is cooler heat capacity and/or cooling water approach temperature. A check of these items, especially with regard to expected ambient condi-... 

The net head or pressure measured in ft. or m that causes a liquid to flow through the suction side of a pump, enter the pump chamber, and reach the impeller. When the source of liquid is above the pump, NPSH equals the barometric pressure plus the static head, less the entrance head, frictional losses in the suction piping and vapor pressure of the liquid. When the source of liquid is below the pump, NPSH equals the barometric pressure less the static head, entrance head, frictional losses in the suction piping and vapor pressure of the liquid. NPSH is specific for each pump design and application and must be supplied by the manufacturer. 

In bubble columns the static head of the fluid is the dominant component of the pressure drop and consequendy it is important to determine the void fraction of the dispersion. All quanuties will be measured as posidve in the upward direction, this being the direction of flow of the dispersed phase. Assuming that the gas bubbles are of uniform size and are uniformly distributed over any cross section of the column, the gas and liquid velocities relative to the column are... 

Liquid Flow Measurement. The requirement of accurate liquid flow measurement can also elevate process equipment (see Figure 7-8). If liquid is near the boiling point, a static head is required in the front of the control valve to overcome pipe friction losses and avoid flashing in the line. Minimum equipment elevation, orifice range and minimum line size can be used if the orifice is as close to the equipment as possible and the piping has only one elbow up to the control valve. 

As the pressure drop goes below a value of 0.10 in. H2O/ft of packed depth, the modified Equation 1-4 may predict a pressure drop that is lower than the experimentally determined value. At a very low pressure drop, measurement tolerances, as well as static head due to the gas phase, may be significant. In addition, at low gas rates, the gas phase may not be in completely turbulent flow. 

The liquid flow into the line was determined by the continuous measurement of the decrease in static head of the liquid in the calibrated storage tank, and by measurement of the pressure drop across the remote on-off valve located near the storage tank. The flow from the end of the line was determined at the gas restrictor from differential pressure and fluid temperature measurements. Line flow measurements were checked at the receiver tank where the vented gas and liquid accumulation were measured. 

There have been various applications to cryogenics of these head-type meters in the form of orifice plates, Venturi, and flow nozzles (see Fig. 8.11). This type of meter is probably the oldest method of measuring flowing fluids. The distinctive feature of head meters is that a restriction is employed to cause a change in the static pressure of the flowing fluid. This pressure change is measured as the difference between the static head and the total head at one section of the channel. 

For a closed conduit under pressure it is necessary to measure the static pressure also. Static pressure is simply the difference between the pressure of the fluid flowing outside the pitot tube and the pressure inside the pitot tube this is also called the differential head h. The... 

HEAD DYNAMIC OR TOTAL - In flowing fluid, the sum of the static and velocity heads at the point of measurement. 

The noncavitating pressure distribution for the Venturi is shown in Fig. 3. The data are plotted in terms of a pressure coefficient Cp as a function of the axial distance from the minimum pressure point. Cp is conventionally defined as the difference between the local wall and free-stream static-pressure head ijix — ho) divided by the velocity head F /2g. Free-stream conditions are measured in the approach section about 1 in. upstream from the quarter roimd. The solid line (Fig. 3) represents a computed ideal flow solution. The dashed line represents experimental data obtained with nitrogen and water in the cavitation tunnel and from a scaled-up aerodynamic model studied in a large wind tunnel. The experimental results shown are all for a Reynolds number of about 600,000. The data for the various fluids are in good agreement, especially in the critical minimum-pressure region. The experimental pressure distribution shown here is assumed to apply at incipient cavitation, or more exactly, to the single-phase liquid condition just prior to the first visible cavitation. 

The pitot tube is the standard method for measuring air velocity in ductwork and can accommodate the presence of solvent vapours and high temperatures. However, dust laden air may cause false readings. In use the head of the pitot tube must face into tfie gas flow. The standard pitot tube consists of a pair of concentric tubes. The inner tube has an open end that faces into the gas stream and measures the total gas pressure. The outer tube, which is sealed to the inner tube at its leading end has a series of holes at right angles to the gas flow that measure the static pressure of the gas. The tubes are connected to the opposite ends of a manometer that measures the differential pressure which is proportional to the gas velocity. 

Flow-stream pressures. Static pressure is pressing measured perpendicularly to the direction of flow. This is the pressiu-e that one would sense when moving downstream with the fluid. Total pressure is pressiue in the direction of flow, where pressure as a function of direction is at a maximum. Total pressure would be sensed if the stream were brought to rest isentropically. Velocity pressure is the difference between static and total pressure measured at a specific region in the direction of flow. It is called velocity head when measured in height of fluid. Velocity pressure is equal to V2pV, where p is the fluid density and V is the fluid velocity. 

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