Throttling devices

These components are used to reduce the pressure of flowing streams. The pressure reduction can be accomplished by simply placing a restriction in the flow line, such as a partially opened valve or a porous plug. Since these devices occupy a relatively small volume, the residence time of the passing fluid is small. Hence, there is little ener loss by the transfer of heat. Consequently, we can neglect heat transfer. Since there is also no shaft work, the energy balance reduces to a very simple equation, as the next example illustrates. 

Water at 350°C flows into a porous plug from a 10-MPa line. It exits at 1 bar. What is the exit temperature  

A steady-state energy balance with one stream in and one stream out is appropriate for this system. We will assume that the bulk kinetic energy of the stream is negligible and that the porous plug is sufficiently small as not to allow a significant rate of heat transfer. Rewriting Equation (2.50) on a mass basis, we get  

the energy balance reduces this system to an isenthalpic processd  

Looking up the value for the inlet stream from Appendix B.4, we find  

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A throttling device can also be placed in the suction piping to protect against overpressure or to limit the horsepower demand to the maximum available from the driver. 

Conventional methods of flow control used inefficient throttling devices such as valves, dampers, and vanes. These devices, although they have a low initial cost, introduce unacceptable running costs due to their inefficiency. Several speed control technologies can be used to improve motor system operation. 

The H-S plot is called a Mollier diagram and is particularly useful in analyzing throttling devices, steam turbines, and other fluid flow devices. A Mollier diagram for steam is presented in Figure 2-37 (standard engineering units) and in Figure 2-38 in SI units. 

Thrombolytic agents, 5 172t, 175-179 Thrombomodulin, 4 84, 88 Thrombosis, 4 83, 84 risk factors for, 4 90t Thromboxane, 4 103-104 Thromboxane A2, 4 85 Throttling devices, in refrigeration systems, 21 538... 

Assume a process each for the eight devices (1) turbines as adiabatic with 80% efficiency, (2) splitters as nonisopar-ametric devices, and (3) condensers as isobaric processes. Notice that throttling devices are automatically constant enthalpy processes. 

There are two variations of the basic set-up of the Joule-Thomson experiment which both yield practical information. In the isothermal Joule-Thomson experiment the temperature is held constant with a downstream heater, and the resultant heat input for the pressure decrease permits an experimental evaluation of (8H/8P)T, the isothermal Joule-Thomson coefficient. In the other variation there is no throttling device used, and the pressure is held constant. For the steady-state flow of gas the temperature change is measured for measurable inputs of heat. This experiment, of course, yields (8H/8T)P, or CP. Thus, the variations of this constant-flow experiment can yield all three of the important terms in Equation (7.46). 

Flow processes accompanied bysss processes. They include flow thxn and through throttling devices sh.tt... 

Flow processes accompanied by sharp reductions in pressure are called expansi processes. They include flow through nozzles, through turbines or expande and through throttling devices such as orifices and valves. 

The control valve is a variable orifice device in which the size of the orifice is adjusted to control a process variable. Consequently, the manufacturer, type, or even the size of a control valve has no effect on the energy dissipated in the control of a selected stream once the process pressure, line size, and pumps have been selected. This energy-independence of the control valve assures that continuous throttling of the flow stream is required to control a process variable. In those cases where a valve is used for shut-off or override control (not a continuous throttling device), energy savings can be realized by selecting a valve with a minimum pressure loss in the full-open position. 

In the case of bituminous coals pyrolysis and gasification in PCFB, the plant consists of pyrolysis reactor, gasifier, two cyclones, combustion chamber, air compressor, and throttling device (or gas turbine). 

CHOKE TUBE - Throttling device used to maintain correct pressure difference between high-side and low-side in refrigerating mechanism. Capillary tubes are sometimes called choke tubes. 

After the condensing process, a throttling device such as a valve, orihce plate, or capillary tube is used to expand the liquid refrigerant in order to reduce the pressure of the refrigerant liquid level to a boiling temperature below that of the heat source. After the expansion process, the refrigerant enters the evaporator in a two-phase state. 

Diener R, Schmidt J (2004) Sizing of throttling device for gas/liquid two-phase flow part 1 safety valves. Process Saf Prog 23(4) 335... 

While the superficial liquid velocity is a function of riser and downcomer gas holdup, it also influences these holdups. Hence, for a given airlift reactor geometiy, the superficial liquid velocity is a function of gas holdup. The superficial liquid velocity can only be changed in this reactor through geometry modifications (which will also affect gas holdup values) or through the use of a throttling device (Popovic and Robinson, 1988). 

The Joule-Thomson expansion occurs at constant enthalpy through a valve or throttling device... 

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