Pressure head types

Linearizing the output of the transmitter. Functions such as square root extraction of the differential pressure for a head-type flowmeter can be done within the instrument instead of within the control system. 

Turbomachines can be compared with each other by dimensional analysis. This analysis produces various types of geometrically similar parameters. Dimensional analysis is a procedure where variables representing a physical situation are reduced into groups, which are dimensionless. These dimensionless groups can then be used to compare performance of various types of machines with each other. Dimensional analysis as used in turbomachines can be employed to (1) compare data from various types of machines—it is a useful technique in the development of blade passages and blade profiles, (2) select various types of units based on maximum efficiency and pressure head required, and (3) predict a prototype s performance from tests conducted on a smaller scale model or at lower speeds. 

Type S is a floating head type. As the tubes heat up, they expand. As they expand, the floating head moves back and forth, but the pressure seal is not at the sliding joint. The pressure seal is at the fixed shell Joint in the outer head, which contains the pressure. The floating head floats free inside the pressure vessel as the tubes move. Types P and W are floating heads where the movement of the head effects the seal between either the shell-side or tube-side fluid and atmosphere. 

Volume 1 explains that pumps ean be classified as either positive-displacement or kinetie. The same is true for compressors. In a positive displacement compressor the gas is transported from low pressure to high pressure in a device that reduces its volume and thus inereases its pressure. The most common type of positive displacement eompressors are reeiprocating and rotary (serew or vane) just as was the ease for pumps. Kinetic compressors impart a veloeity head to the gas, which is then converted to a pressure head in accordance with Bernoulli s Law as the gas is slowed down to the velocity in the discharge line. Just as was the case with pumps, centrifugal compressors are the only form of kinetic compressor commonly used. 

The capacity of this type of pump depends on the pressure head against which the pump must act (see Figure 3-49). 

A shell and tube heat exchanger, heat transfer area 50 m1 2 3, floating head type, carbon steel shell, stainless steel tubes, operating pressure 25 bar. 

The apparatus developed for yb measurements of BLM deserves brief comment since it can be used not only to examine the effects of various substances on BLM but is readily adaptable for studying other types of interfacial films and related adsorption phenomena at either air-water or oil-water interfaces (and bifaces). Unlike both the Wil-helmy plate and film balance methods, the present technique measures 7i directly. From the description of the apparatus and procedure that the present method relies on the ability to measure the very small pressure difference across an interface (or biface). For certain BLM s, the pressure heads measured are only fractions of a millimeter of water. Therefore, the method described here has been possible only as a result of developing pressure transducers of high sensitivity. 

Another operational limit in the CFB system involves gas suppliers. Three types of gas suppliers, i.e., a reciprocating compressor, a blower with throttle valve, and a compressor, are commonly used in the CFB system. For blower operation, as the gas flow rate decreases, the pressure head of the blower increases. For compressor operation, the pressure head of the compressor can be maintained constant with variable gas flow rates. The interactive behavior between a CFB system and a blower can be illustrated in Fig. 10.9, where dashed curves refer to the blower characteristics and solid curves refer to the riser pressure drop. At point A, the pressure drop across the riser matches the pressure head provided by a blower thus, a stable operation can be established. Since the pressure drop across the riser in fast fluidization increases with a decrease in the gas flow rate at a given solids circulation rate, a reduction in the gas flow rate causes the pressure drop to move upward on the curve in the figure to point B with an increase in the pressure drop of Spr. In the case shown in Fig. 10.9(a), with the same reduction in the gas flow rate, i.e., SQ, the increase in the pressure drop, Spr, from point A to point B is greater than that which can be provided by... 

Three basic types of flow meters are useful for liquid cryo-gens. These are the pressure drop or head type, the turbine type, and the momentum type. 

Head-type flowmeters include orifice plates, venturi tubes, weirs, flumes, and many others. They change the velocity or direction of the flow, creating a measurable differential pressure, or "pressure head," in the fluid. Head metering is one of the most ancient of flow detection techniques. There is evidence that the Egyptians used weirs for measurement of irrigation water flows in the days of the Pharaohs and that the Romans used orifices to meter water to households in Caesar s time. In the 18th century, Bernoulli established the basic relationship between the pressure head and velocity head, and Venturi published on the flow tube bearing his name. 

The variable-area flowmeter is a head-type flow sensor, but it does not measure the pressure drop across a fixed orifice instead, the pressure drop is held relatively constant, and the orifice area is varied to match the flow (Figure 3.98). In gravity-type variable-area flowmeters, increase in flow lifts the float, piston, or vane, and it is the weight of these flow elements that has... 

Figure 10.4 shows rnl as calculated by Eq. (10.4), varying the pressure head (Ah) and the type of soil (a value). The real diameter of a Rhizon sampler and optimal... 

Figure 10.4 Radius of influence of a Rhizon sampler as a function of the pressure head and the soil type.

Here Ah is the pressure head, p the density of the solution, and g the acceleration of gravity. Strictly speaking. Ah in this type of viscometer varies during the measurement. It is not correct merely to take the average Ah at the beginning and ending of the measurement since the flow is faster at first than near the end. The average Ah can however be calculated by the Meissner equation... 

Equation (51) can equally well be applied to a U-tube type viscometer, in which a capillary is connected to essentially a manometer (see, for example, Maron and Belner, 1955). The only modification is that the pressure head, Ah, is calculated from the difference in the decreasing meniscu of the capillary arm and that arising in the manometer arm. 

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