Core flow

The most widely used approach to channel flow calculations assumes a steady qua si-one-dimensional flow in the channel core, modified to account for boundary layers on the channel walls. Electrode wall and sidewall boundary layers may be treated differently, and the core flow may contain nonuniformities. 

The pressure vessel is 79 ft high with an upper diameter of 23 ft and lower diameter of 20 ft. This height is key to establishing natural circulation core flow by providing a chimney in the space between the top of the core and the steam separator assembly. This large top diameter increases the water inventory above the core (no accumulators needed), and the smaller lower diameter reduces the volume of water needed to be replaced to provide core cooling. 

Annular flow (A) existed at high gas superficial velocities and at the entire range of liquid superficial velocities. In annular flow, liquid film formed at the side wall with part of the liquid remaining in the three corners of the channel, while the continuous gas core flowed concurrently with the liquid phase. 

For all flow conditions tested in that study, a bubbly flow pattern with bubbles much smaller than the channel diameter (100 pm) was never observed. While liquid-only flows (or liquid slugs) containing small spherical bubbles were not observed, small droplets were observed inside gas core flows. Furthermore, no stratified flow occurred in the micro-channel as reported in previous studies of two-phase flow patterns in channels with a diameter close to 1 mm (Damianides and Westwater 1988 Fukano and Kariyasaki 1993 Triplett et al. 1999a Zhao and Bi 2001a). 

Pressure oscillations with RMS value up to 10 kPa in two models of lean-burn gas turbine combustors, with heat release around 100 kW, have been actively controlled by the oscillation of fuel flow. The flames were stabilized behind an annular ring and a step in one arrangement, and downstream of an expansion and aided by swirl in the other. Control was sensitive to the location of addition of oscillated fuel. Oscillations in the annular flow were attenuated by 12 dB for an overall equivalence ratio of 0.7 by the oscillation of fuel in the core flow and comprising 10% of the total fuel flow, but negligibly for equivalence ratios greater than 0.75. Oscillation of less than 4% of the total fuel in the annulus flow led to attenuation by 6 dB for all values of equivalence ratio considered. In the swirling flow, control was more effective with oscillations imposed on the flow of fuel in a central axial jet than in the main flow, and oscillations were ameliorated by 10 dB for equivalence ratio up to 0.75, above which the flame moved downstream so that the effectiveness of the actuator declined. The amelioration of pressure oscillations resulted in an increase in NOj, emissions by between 5% and 15%. 

The BWR reqnires substantially lower primary coolant flow through the core than pressurized water reactors. The core flow of a BWR is the sum of the feedwater flow and the recirculation flow, which is typical... 

Nuclear Boiler Assembly. This assembly consists of the equipment and instrumentation necessary to produce, contain, and control the steam required by the turbine-generator. The principal components of the nuclear boiler are (1) reactor vessel and internals—reactor pressure vessel, jet pumps for reactor water circulation, steam separators and dryers, and core support structure (2) reactor water recirculation system—pumps, valves, and piping used in providing and controlling core flow (3) main steam lines—main steam safety and relief valves, piping, and pipe supports from reactor pressure vessel up to and including the isolation valves outside of the primary containment barrier (4) control rod drive system—control rods, control rod drive mechanisms and hydraulic system for insertion and withdrawal of the control rods and (5) nuclear fuel and in-core instrumentation,... 

A characteristic of micro channel reactors is their narrow residence-time distribution. This is important, for example, to obtain clean products. This property is not imaginable without the influence of dispersion. Just considering the laminar flow would deliver an extremely wide residence-time distribution. The near wall flow is close to stagnation because a fluid element at the wall of the channel is, by definition, fixed to the wall for an endlessly long time, in contrast to the fast core flow. The phenomenon that prevents such a behavior is the known dispersion effect and is demonstrated in Figure 3.88. 

Van de Velden et al. (2008) used PEPT to study the movement and population density of particles in the CFB-riser. The PEPT results were used to obtain (i) the vertical particle movement and population density in a cross-sectional area of the riser (ii) the transport gas velocity required to operate in a fully established circulation mode (iii) the overall particle movement mode (core flow versus core/annulus flow) and (iv) the particle slip velocity. Figure 7 shows an example of PEPT data for the two principal flow regimes. 

Absolute H-atom measurements also were made using the Na/Li method (1(3) in sulfur free flames. An aerosol of an equimolar solution of NaCl and LiCl was added to the central core flow through the nebulizer. Relative intensity measurements were made of the Na 589.0 nm and Li 670.8 nm emission from which the H-atom concentrations were calculated. The H-atom measurements could only be made in the sulfur free flames. Reaction of Na or Li with sulfur species would render the technique inoperative. 

Such flow can be treated adequately using the boundary layer assumptions but the freestream velocity gradients exist purely because of the boundary layer growth and the boundary layer and inviscid core flows must be simultaneously considered. There are, nevertheless, many important practical problems in which such interactions can be ignored. 

The core flow conductivity is primarily determined by the temperature, pressure, and alkali (potassium) seed level output by the combustor, with generator inlet temperature being the single most Important parameter governing the level of alkali seed ionization and, therefore, free electron production. 

Two sets, i.e., four experiments, of core flow studies are compared. Sets No. 1 and No. 2 were tertiary miscible and immiscible CO2 floods without mobility control. The same core from each set, after plain CO2 injection, was restored to waterflood residual oil saturation and flooded with 0.05% AEGS 25-12 surfactant in brine. There was almost no difference between the oil saturation distributions in the cores between experiments, with the average Sorw values of 37 1 saturation percent in both sets of experiments. CO2 was injected continuously in all experiments at a nominal rate of 1 ft/day. No attempt was made to preform a foam, or to inject alternate slugs of surfactant solution and CO2. 

Figure 5. Normalized surfactant concentration from a core flow adsorption test.

The CT images identified several mechanisms that help to explain how mobility-control surfactant causes CO2 to be stable against both gravity and viscous forces during tertiary miscible core flow experiments. 

Fig. 2 Multi - electrode core flow cell configuration.

IONS OR DISPERSIONS OF HEAVY CRUDE OIL in water or brine have been used in several parts of the world for pipeline transportation of both waxy and heavy asphaltic-type crude oils. The hydrodynamically stabilized dispersion transportation concept is described by the Shell Oil Corporation core flow technology (i). The use of surfactants and water to form oil-in-water emulsions with crude oils is the subject of a long series of patents and was proposed for use in transporting Prudhoe Bay crude oil (2). Furthermore, surfactants may be injected into a well bore to effect emulsification in the pump or tubing for the production of heavy crude oils as oil-in-water emulsions (3, 4). 

The magnitude of the last term is determined by its coefficient. This is yielded by setting for cp, a mean value (cpa + cpb)/2 = 1.42514kJ/kgK and putting a< — ao = 1, that means that we assume the mass fraction of water vapour to be low a< = 0 in the core flow, and large ao = 1 at the wall, because this is where the water vapour condenses. With a/D = 1 the magnitude of the coefficient is 0.593. As all the other expressions are of order 1 the mass transfer term cannot be neglected. This would only be possible if (ao — ao was very small and of the order 10 A... 

The coordinate transformation makes all the velocities coincide. The boundary layer approaches the core flow asymptotically and in principle stretches into infinity. The deviation of the velocity wx from that of the core flow is, however, negligibly small at a finite distance from the wall. Therefore the boundary layer thickness can be defined as the distance from the wall at which wx/wx is slightly different from one. As an example, if we choose the value of 0.99 for Wj/uico, the numerical calculation yields that this value will be reached at the point r]+ m 4.910. 

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