Driving differential pressures

Figure 13. Change in (a) driving differential pressure (end-to-end) with time, and evaluation of fracture aperture, as a proxy for (b) permeability change. Overlain on (b) are evaluations of permeability change constrained only on initial permeability magnitude and mass removal rate dM/dt. [Modifiedfrom Polak et ai, 2004].

Spectrum of postulated rod ejection accidents - Locating the CRDMs internally to the reactor vessel eliminates by design the rod ejection accident since there is no significant driving differential pressure over the driveline. 

Automatic filters are made with either viscous-coated or dry filter media. However, the cleaning or disposal of the loaded medium is essentially continuous and automatic. In most such devices the air passes horizontally through a movable filter curtain. As the filter loads with dust, the curtain is continuously or intermittently advanced to expose clean media to the air flow and to clean or dispose of the loaded medium. Movement of the curtain can be provided by a hand crank or a motor drive. Movement of a motor-driven curtain can be actuated automatically by a differential-pressure switch connected across the filter. 

Refrigeration, like dilution, reduces the vapor pressure of the material being stored, reducing the driving force (pressure differential) for a leak to the outside environment. If possible, the hazardous material should be cooled to or below its atmospheric pressure boiling point. At this temperature, the rate of flow of a liquid leak will depend only on liquid head or pressure, with no contribution from vapor pressure. The flow through any hole in the vapor space will be small and will be limited to breathing and diffusion. 

The driving force for the separation is differential pressure. CO2 tends to diffuse quickly through membranes and thus can be removed from the bulk gas stream. The low pressure side of the membrane that is rich in CO2 is normally operated at 10 to 20% of the feed pressure. 

The recirculation ratio for a unit is the lb rate of liquid leaving the outlet compared to the lb rate of vapor leaving. The liquid recirculation flow rate entering the unit is set by the differential pressure driving the system. 

Normally, the reactor temperature and the stripper level controllers regulate he movement of the regenerated and spent catalyst slide valves, le algorithm of these controllers can drive the valves either fully Of [ or fully closed if the controller set-point is unobtainable. It is ext nely important that a positive and stable pressure differential be mail ined across both the regenerated and spent catalyst slide valves. r safety, a low differential pressure controller overrides the tempera re/level controllers should these valves open too much. The shutdov is usually set at 2 psi (14 Kp). 

Gas separation performances (H2/n-butane, n-hexane/2-2 dimethylbutane) have been measured using a sweep gas (countercurrent mode) in order to increase the permeation driving force (no differential pressure was used) permeate and retentate compositions (see Figure 2) were analysed using on line gas chromatography. 

Virtually all normalization programs will calculate the normalized permeate flow, normalized salt rejection and/or passage, and differential pressure (some programs normalize it, some do not). Some programs also include net driving pressure as an output as well as the following outputs ... 

For the injection, a modified Ruska pump was used. The body of the pump was manufactured by the Ruska Instrument Company of Houston, Texas. It is equipped with an electronically controlled drive train developed at New Mexico State University. It can be controlled to run in either a constant rate, a constant pressure or a constant differential pressure mode. 

By addition of the driving force pressure, or pressure differential across the packed bed, additional liquid is forced through the capillaries below the equilibrium saturation point, thus reducing the residual moisture. 

In this expression, the differential or instantaneous rate of filtration per unit area dVIAdO) is given as the ratio of a driving force, pressure p, to the product of viscosity p, and the sum of cake resistance a(W/A) and filter medium resistance R. The mass of dry cake W is related to the volume of filtrate V by a simple material balance, thus ... 

The flowsheet shown in Figure 10.15 does not show the plumbing required to run a realistic pressure-driven dynamic simulation. The key feature is that the pressure in the stripper must be greater than that in the main column so that vapor can flow from the top of the stripper back to the main column. Therefore in the simulation, a pump and a control valve are placed in the liquid sidestream. A control valve is also placed in the stripper overhead vapor line. All this plumbing is shown in Figure 10.16. In a real physical setup, it is usually possible to use elevation differences to provide the necessary differential pressure driving force to get the liquid to flow from the main column into the stripper at a higher pressure and avoid the use of a pump. 

The polymer solutions with concentrations between 0.2 and 1.0 weight percent were injected by a dosing pump equipped with a variable speed drive. The polymer used was polyacrylamide SEPARAN AP45 (M = 4-5 xlO ). The pressure differences between pressure taps were measured with Philips differential pressure transducers (Model PD2), the outputs of which were connected to a computer (Hewlett Packard 1000) to enable direct analysis of the experimental data. 

Run DY-15 shown in Figure 4, In this experiment, the flow rate decreased to zero just before breakthrough of the driving fluid (at about T = 0.6 PV in a nominal waterflood). Substantial differences in the upstream pressure of the flow apparatus (400 psi at T = 1.2 PV) and the differential pressure across the core (75 psi at T = 1.2 PV) indicate that most of the emulsification and entrapment occurred in the entrance region of the sandpack. This mechanism was repeatedly observed in high pH, non-saline floods of moderate acid number (> 2.0) oils. 

The actual basis for separation can be the differential solubility in the membrane material or the membrane hole size. When separating gases hollow membrane fibres are popular, as the small diameter of the fibres allows than to withstand the substantial driving pressures involved. Separation of the components in liquid systems usually relies on some form of spirally wound membrane sheet and spacer. Once again, substantial differential pressures are involved across the membrane surface and this conventionally requires the use of some form of spacer to prevent closure of the channels. Not only do these spacers (e.g. coarse woven fabric)... 

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