Transition flows single phase

Another possible scenario in the pipeline transport of acid gas is a transition from single-phase to two-phase flow or vice versa. For such a situation, it is veiy difficult to perform a calculation. These calculations, which involve a combination of fluid flow and phase equilibrium, should be performed using available software. 

Here, g is the gravity acceleration and dc is the column diameter. All other parameters are the same as defined earlier. The transition from single-phase pore flow to two-phase pore flow can be obtained from the relation... 

The basis for single-phase and some two-phase friction loss (pressure drop) for fluid flow follows the Darcy and Fanning concepts. The exact transition from laminar or dscous flow to the turbulent condition is variously identified as between a Reynolds number of 2000 and 4000. 

Weekman and Myers (W3) measured wall-to-bed heat-transfer coefficients for downward cocurrent flow of air and water in the column used in the experiments referred to in Section V,A,4. The transition from homogeneous to pulsing flow corresponds to an increase of several hundred percent of the radial heat-transfer rate. The heat-transfer coefficients are much higher than those observed for single-phase liquid flow. Correlations were developed on the basis of a radial-transport model, and the penetration theory could be applied for the pulsing-flow pattern. 

In Chap. 3 the problems of single-phase flow are considered. Detailed data on flows of incompressible fluid and gas in smooth and rough micro-channels are presented. The chapter focuses on the transition from laminar to turbulent flow, and the thermal effects that cause oscillatory regimes. 

The phenomenon of critical flow is well known for the case of single-phase compressible flow through nozzles or orifices. When the differential pressure over the restriction is increased beyond a certain critical value, the mass flow rate ceases to increase. At that point it has reached its maximum possible value, called the critical flow rate, and the flow is characterized by the attainment of the critical state of the fluid at the throat of the restriction. This state is readily calculable for an isen-tropic expansion from gas dynamics. Since a two-phase gas-liquid mixture is a compressible fluid, a similar phenomenon may be expected to occur for such flows. In fact, two-phase critical flows have been observed, but they are more complicated than single-phase flows because of the liquid flashing as the pressure decreases along the flow path. The phase change may cause the flow pattern transition, and departure from phase equilibrium can be anticipated when the expansion is rapid. Interest in critical two-phase flow arises from the importance of predicting dis-... 

In the current state of the art, almost all multiphase CFD models available in commercial codes use some type of turbulence model based on extending models originally developed for single-phase flows. Such CFD models are thus meant to describe fully turbulent flows (as opposed to laminar or transitional flows). Nevertheless, many of these models have not been validated... 

M. S. Bhatti andR. K. Shah. "Thrbulent and Transition Flow Convective Heat Transfer in Ducts. Tn Handbook of Single-Phase Convective Heat Transfer, ed. S, Kaka9, R. K. Shah, and W. Aung, New York Wiley Interscience, 1987. 

As long as the wall temperature stays below that required for the formation of vapour bubbles, heat will be transferred by single-phase, forced flow. If the wall is adequately superheated, vapour bubbles can form even though the core liquid is still subcooled. This is a region of subcooled boiling. In this area, the wall temperature is virtually constant and lies a few Kelvin above the saturation temperature. The transition to nucleate boiling, is, by definition, at the point where the liquid reaches the saturation temperature at its centre, and with that the thermodynamic quality is r h = 0. In reality, as Fig. 4.53 indicates, the liquid at the core is still subcooled due to the radial temperature profile, whilst at the same time vapour bubbles form at the wall, so that the mean enthalpy is the same as that of the saturated liquid. As explained in the previous section, the... 

J. Lyngaae-Jorgensen, "Phase Transitions in Two Phase Polymer Blends During Single Shear Flow", Proceedings 8th Scandinavian Rubber Conf., Copenhagen, June 10-12, 1985. p. 525-562. 

J. G. Withers, Tube-Side Heat Transfer and Pressure Drop for Tubes Having Helical Internal Ridging With Turbulent/Transitional Flow of Single-Phase Fluid. Pt. 1. Single-Helix Ridging, Heat Transfer Eng. (2/1) 48-58,1980. 

Acoustic/ultrasonic techniques that have been developed into flow-monitoring instruments are Doppler, cross-correlation, and transit-time methods. An ultrasonic Doppler flowmeter has been applied to single-phase turbulent flows and mixed-phase (solid/liquid or gas/liquid) flows. The crosscorrelation technique is mainly for mixed-phase flows, whereas the transit-time method has been applied to single-phase flows, either liquid or gas, in large pipes. 

For the better understanding of blend morphologies, the fundamental mechanisms of morphology development are discussed, viz. the liquid-solid phase transition (crystallization), the liquid-liquid phase separation e.g., spinodal decomposition under non-isoquench depth), as well as the complex mechanism of the morphology generation that results from the competition between these two transitions. The effects of chemical reactions and flow fields on morphology development have also been discussed. Finally, several evidences of a local structure in single-phase polymer-polymer mixtures are presented. 

For the emergency relief design case of single phase venting all necessary design rules are published in technical regulations [91,92,93,94]. In tire case of incompressible fluids the necessary vent area is determined with the help of the following equation, which includes the assiunption of one-dimensional, isentropic flow without phase transition ... 

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