Pressure hydraulic transport

The sensitivity of the pressure drop to the coefficient of solids-surface friction /j.f may well account for the wide scatter in the results shown earlier in Figure 5.10. Unfortunately this quantity has been measured by only very few investigators. It must be emphasised that in the design of any hydraulic transport system it is extremely important to have a knowledge of the coefficient of friction. 

There have been several studies involving the use of media consisting of fine dense particles suspended in water for transporting coarse particles. The fine suspension behaves as a homogeneous fluid of increased density, but its viscosity is not sufficiently altered to have a significant effect on the pressure drop during turbulent flow, the normal condition for hydraulic transport. The cost of the dense particles may, however, be appreciable and their complete separation from the coarse particles may be difficult. 

Khan, A. R PIRIE, R. L. and Richardson, J. F. Chem. Eng. Sci. 42 (1987) 767. Hydraulic transport of solids in horizontal pipelines — predictive methods for pressure gradient. 

Either a liquid or a gas can be used as the carrier fluid, depending on the size and properties of the particles, but there are important differences between hydraulic (liquid) and pneumatic (gas) transport. For example, in liquid (hydraulic) transport the fluid-particle and particle-particle interactions dominate over the particle-wall interactions, whereas in gas (pneumatic) transport the particle-particle and particle-wall interactions tend to dominate over the fluid-particle interactions. A typical practical approach, which gives reasonable results for a wide variety of flow conditions in both cases, is to determine the fluid only pressure drop and then apply a correction to account for the effect of the particles from the fluid-particle, particle-particle, and/or particle-wall interactions. A great number of publications have been devoted to this subject, and summaries of much of this work are given by Darby (1986), Govier and Aziz (1972), Klinzing et al. (1997), Molerus (1993), and Wasp et al. (1977). This approach will be addressed shortly. 

One major difference between pneumatic transport and hydraulic transport is that the gas-solid interaction for pneumatic transport is generally much smaller than the particle-particle and particle-wall interaction. There are two primary modes of pneumatic transport dense phase and dilute phase. In the former, the transport occurs below the saltation velocity (which is roughly equivalent to the minimum deposit velocity) in plug flow, dune flow, or sliding bed flow. Dilute phase transport occurs above the saltation velocity in suspended flow. The saltation velocity is not the same as the entrainment or pickup velocity, however, which is approximately 50% greater than the saltation velocity. The pressure gradient-velocity relationship is similar to the one for hydraulic transport, as shown in... 

Fig. 15-4, except that transport is possible in the dense phase in which the pressure gradient, though quite large, is still usually not as large as for hydraulic transport. The entire curve shifts up and to the right as the solids mass flux increases. A comparison of typical operating conditions for dilute and dense phase pneumatic transport is shown in Table 15-1. 

Notwithstanding any particular structural model, water transport in PEMs, in general, should be considered a superposition of diffusion in gradients of activity or concentration and hydraulic permeation in gradients of liquid or capillary pressure. Hydraulic permeation is the predominant mechanism xmder conditions for which water uptake is controlled by capillary condensation, whereas diffusion contributes significantly if water strongly interacts with the polymeric host. The molar flux of liquid water in the membrane, N, is thus given by... 

With the accumulation of spent micro fuel elements in the external reservoir 16, they are being discharged as follows. The external reservoir 16 is cut off from the coolant circuit. Then, the stop valve of the external reservoir 16 is opened, and the spent micro fuel elements are sucked off from reservoir 16 by the hydraulic transport and enter the atmospheric pressure container 17. 

Raj, R. S. 1972. Pressure loss in hydraulic transport of solids in inclined pipes. Paper presented at Hydrotransport 2, Coventry, England. 

Wood D. J. 1979. Pressure gradient requirements for re-establishment of slurry flow. In Sixth International Conference on Hydraulic Transport of Solids in Pipes, p. 217. Cranfield, UK BHRA Group. 

Sauermann, H. B. 1982. The Influence of particle diameter on the pressure gradients of gold slimes pumping In Proceedings of the 8th International Conference on the Hydraulic Transport of Solids in Pipes. Jahannesburg, South Africa, August 1982, Paper El, pp. 241 246. Cranfield, UK BRHA Group. 

Hydraulic transport can be achieved using a coal-water slurry, which can be efficiently pressurized by means of displacement pumps up to 70-100 bar with no inert gas detriment [1]. In addition to stability and viscosity, the main measure for slurry quality is the solids concentration. This determines the energy density and the amount of water, which hampers process efficiency. Figure 4.4 shows the influence of the slurry solids concentration on the cold gas efficiency for several solid fuels. Figures 4.4 is compiled using a GE gasifier model with radiant and... 

Physical factors include mechanical stresses and temperature. In normal tissues, convection is driven by the pressure difference between blood and lymph vessels. In muscles, convection can also occur due to tissue contraction/relaxation. In solid tumors, there are no functional lymphatics and the IFP is elevated uniformly in the center. Thus, interstitial convection is negligible. In addition to the fluid pressure, drug transport may depend on solid stresses that can be elevated in regions with rapidly proliferating tumor cells, "" causing collapse of tumor microvessels and an increase in vascular resistance to convection in the blood. Temperature change can directly affect the diffusion coefficient and the hydraulic conductivity since both parameters are inversely proportional to the viscosity of interstitial fluid that decreases with increasing temperature. The temperature in tissues is stable and close to 37°C under normal conditions... 

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,... 

Modules Eveiy module design used in other membrane operations has been tried in peivaporation. One unique requirement is for low hydraulic resistance on the permeate side, since permeate pressure is veiy low (O.I-I Pa). The rule for near-vacuum operation is the bigger the channel, the better the transport. Another unique need is for neat input. The heat of evaporation comes from the liquid, and intermediate heating is usually necessary. Of course economy is always a factor. Plate-and-frame construc tion was the first to be used in large installations, and it continues to be quite important. Some smaller plants use spiral-wound modules, and some membranes can be made as capiUaiy bundles. The capillaiy device with the feed on... 

Oedema refers to an accumulation of interstitial fluid to a point where it is palpable or visible. In general this point is reached with a fluid volume of 2-3 liters. Oedema formation is the result of a shift of fluid into the interstitial space due to primary disturbances in the hydraulic forces governing transcapillary fluid transport and of subsequent excessive fluid reabsorption by the kidneys. Deranged capillary hydraulic pressures initiate oedema formation in congestive heart failure, and liver cirrhosis whereas a deranged plasma oncotic pressure... 

The stability of shales is governed by a complicated relationship between transport processes in shales (e.g., hydraulic flow, osmosis, diffusion of ions, pressure) and chemical changes (e.g., ion exchange, alteration of water content, swelling pressure). 

NAPL will migrate from the liquid phase into the vapor phase until the vapor pressure is reached for that liquid. NAPL will move from the liquid phase into the water phase until the solubility is reached. Also, NAPL will move from the gas phase into any water that is not saturated with respect to that NAPL. Because hydraulic conductivities can be so low under highly unsaturated conditions, the gas phase may move much more rapidly than either of the liquid phases, and NAPLs can be transported to wetter zones where the NAPL can then move from the gas phase to a previously uncontaminated water phase. To understand and model these multiphase systems, the characteristic behavior and the diffusion coefficients for each phase must be known for each sediment or type of porous media, leading to an incredible amount of information, much of which is at present lacking. 

Hydraulic mobilization utilizes positive pressure or negative pressure (vacuum) as the force that transports the focused protein zones toward the detection point. During hydraulic mobilization, it is necessary to apply an electric field across the capillary in order to maintain focused protein zones.78 The main disadvantage of this type of mobilization is the parabolic shape of the hydrodynamic flow profile, which can decrease resolution. For this reason, only weak forces are used. 

From an instrument perspective, the simplest hydraulic approach to transport focused zones to the detector is by gravity mobilization.79 In this technique, focused proteins are transported toward the detection point using a difference in the levels of anolyte and catholyte contained in the reservoirs. The force generated by the liquid-height difference can be manipulated to be extremely small compared with pressure or vacuum. Flow velocity can also be modulated by changing the capillary dimensions or, in the case of large-bore capillaries, with internal diameters greater than 50 pm, by the addition of viscous polymers. 

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