Gas Flow in Pipes and Channels

Isothermal Gas Flow in Pipes and Channels Isothermal compressible flow is often encountered in long transport lines, where there is sufficient heat transfer to maintain constant temperature. Velocities and Mach numbers are usually small, yet compressibility 

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Isothermal Gas Flow in Pipes and Channels Isothermal compressible flow is often encountered in long transport lines, where there is sufficient heat transfer to maintain constant temperature. Velocities and Mach numbers are usually small, yet compressibihty effects are important when the total pressure drop is a large fraction of the absolute pressure. For an ideal gas with p = pM. JKT, integration of the differential form of the momentum or mechanical energy balance equations, assuming a constant fric tion factor/over a length L of a channel of constant cross section and hydraulic diameter D, yields,... 

Throttling and adiabatic expansion of gas in turbo-expanders occur as a result of gas flow in pipes and channels of variable cross-section. To determine the temperature, pressure, and degree of supersaturation of a mixture in these devices it is necessary to carry out appropriate gas-dynamic calculations. An approach to performing such calculations, based on ref. [5], is outlined below. 

For adiabatic, steady-state, and developed gas-liquid two-phase flow in a smooth pipe, assuming immiscible and incompressible phases, the essential variables are pu, pG, Pl, Pg, cr, dh, g, 9, Uls, and Uas, where subscripts L and G represent liquid and gas (or vapor), respectively, p is the density, p is the viscosity, cr is the surface tension, dh is the channel hydraulic diameter, 9 is the channel angle of inclination with respect to the gravity force, or the contact angle, g is the acceleration due to gravity, and Uls and Ugs are the liquid and gas superficial velocities, respectively. The independent dimensionless parameters can be chosen as Ap/pu (where Ap = Pl-Pg), and... 

Membrane gas-separation systems have found their first applications in the recovery of organics from process vents and effluent air [5]. More than a hundred systems have been installed in the past few years. The technique itself therefore has a solid commercial background. Membranes are assembled typically in spiral-wound modules, as shown in Fig. 7.3. Sheets of membrane interlayered with spacers are wound around a perforated central pipe. The gas mixture to be processed is fed into the annulus between the module housing and the pipe, which becomes a collector for the permeate. The spacers serve to create channels for the gas flow. The membranes separate the feed side from the permeate side. 

Fuvpi, %uvP2/ and Vuvp3 are the average liquid velocities for transducers 1, 2, and 3, respectively, from channel 0 to the channel where the gas-liquid interface is located. The constant 0.7 is obtained in the region 0single-phase turbulent flow the assumption made here is that the gas phase is located in the upper part of the pipe and the liquid velocity, not disturbed by the gas phase, develops in the lower part of the pipe as it does in single-phase turbulent flow. 

Molecular flow occurs under conditions where Kn > 0.5 - the mean free path of the particles exceeds the smallest dimension of the flow channel. Under such conditions, with thin-walled orifices, for example, gas particles will pass through almost without collision. With pipes and ducts, however, this is not the case. Particularly for low Kn values (1-10) of the particles that enter the duct, some may reach the exit whilst the remainder return to the entrance after a number of collisions with the duct walls. What is important about such collisions is that, on collision with a wall, the particles are regarded as being immobilised for a very short time before emerging in any direction with equal probability (according to the cosine law). This describes diffuse or random scattering where no particular direction is favoured. To describe this process, the concept of transmission probability (Pr) was introduced by Clausing. 

Annular flow The liquid phase flows along the pipe or channel walls, as a more or less continuous stream, with the gas phase acting as a core. The gas phase may carry droplets of liquid that may be generated by the breakup of waves on the surface of the liquid film. Some liquid drops may fall back into the liquid phase, so that there may be a continuous liquid interchange between the continuous liquid phase and the gas phase. Furthermore, the liquid may contain entrained gas bubbles. The pattern detail will depend very strongly on the flow conditions in the system. Hewitt and Hall Taylor describe a subpattern of annu-... 

The flow diagram of RVCS is shown in Fig 2 The system consists of a RPV recuperator(RVR), a RPV cooler(RVC), orifices and valves As illustrated in Fig 1 and Fig 2, a bypass flow is extracted from the blower outlet and flows downward through the tube side of the RVR, which is installed in the annular region outside the IHX, and is cooled down from 550t to 250 Then the cold bypass flow enters an annular channel outside the RVR and flows upward into the shell side of a little cooler (RVC) and is cooled form 250°c to 190 t , the 190 c cold gas enters the gap between the RPV and core vessel and is heated by the two vessel from 190 to 220x At last, the 220 X bypass gas flows upward through some vertical pipes and comes into the RVR shell side and returns to the blower inlet The main technical data of the RVCS is given in table 4... 

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