Interfaces static fluid

The profiles of pendant and sessile bubbles and drops are commonly used in determinations of surface and interfacial tensions and of contact angles. Such methods are possible because the interfaces of static fluid particles must be at equilibrium with respect to hydrostatic pressure gradients and increments in normal stress due to surface tension at a curved interface (see Chapter 1). It is simple to show that at any point on the surface... 

Noyes, and Whitney and Nernst were the first to introduce and develop the concept of unstirred layer (quoted in [23]). According to the theoretical views of Nernst, there is a layer of static fluid present at a solid-liquid interface. The concentration of a given substance in this layer is not equal to that in the bulk solution and diffusion is the primary mode of transport within the unstirred layer. The thickness of the unstirred layer, though undetermined, is critically dependent on the rate of stirring in the bulk phase. 

Far from a wellbore, the velocity of reservoir fluids is about one linear foot per day. Near a wellbore, the velocity can increase one-hundred fold. A static or quasi-static test such as the sessile drop (contact angle) test may not represent the dynamic behavior of the fluids in the field. The dynamic Wilhelmy device gives results which are comparable in interface velocity to the field displacement rate. The interface in the Wilhelmy test described here moved at a steady rate of 0.127 mm/sec or 36 ft/day. The wetting cycle for a hybrid-wetting crude oil system was not affected by moving at a rate less than 1 ft/day. 

The transfer of chemical molecules from oil to water is most often a surface area phenomenon caused by kinetic activity of the molecules. At the interface between the liquids (either static or moving), oil molecules (i.e., benzene, hexane, etc.) have a tendency to disperse from a high concentration (100% oil) to a low concentration (100% water) according to the functions of solubihty, molecular size, molecular shape, ionic properties, and several other related factors. The rate of dispersion across this interface boundary is controlled largely by temperature and contact surface area. If the two fluids are static (i.e., no flow), an equilibrium concentration will develop between them and further dispersion across the interface will not occur. This situation is fairly common in the unsaturated zone. 

Whilst certain of these methods involve measurements only at the liquid-vapour or liquid-liquid interfaces involved in the static methods we must usually consider besides the interfacial energy of the two fluids, that between each of them and a solid... 

The basic setup to determine static interfacial tension based on either the Wilhelmy plate method or the du Noiiy ring method (see Alternate Protocol 2) is shown in Figure D3.6.1. It consists of a force (or pressure) transducer mounted in the top of the tensiometer. A small platinum (Wilhelmy) plate or (du Noiiy) ring can be hooked into the force transducer. The sample container, which in most cases is a simple glass beaker, is located on a pedestal beneath the plate/ring setup. The height of the pedestal can be manually or automatically increased or decreased so that the location of the interface of the fluid sample relative to the ring or plate can be adjusted. The tensiometer should preferably rest on vibration dampers so that external vibrations do not affect the sensitive force transducer. The force transducer and motor are connected to an input/output control box that can be used to transmit the recorded interfacial tension data to an external input device such as a monitor, printer, or computer. The steps outlined below describe measurement at a liquid/gas interface. For a liquid/liquid interface, see the modifications outlined in Alternate Protocol 1. Other variations of the standard Wilhelmy plate method exist (e.g., the inclined plate method), which can also be used to determine static interfacial tension values (see Table D3.6.1). 

The polymer is sheared and then rotated by 90° by the dividing wall, the interfaces between the fluids increase. The interfaces are then re-oriented by 90° once the material enters a new section. The stretching-re-orientation sequence is repeated until the number of striations is so high that a seemingly homogeneous mixture is achieved. Figure 3.26 shows a sequence of cuts down a Kenics static mixer2. It can be seen that the number of striations... 

The channel structure of the mixer is a simple cross, i.e. four channels which all merge at one junction [71]. A cross was preferred over a T-channel mixer since two interfaces instead of only one are initially created when the fluids are contacted. The top channel feeds one fluid, while the other fluid is injected via the left and right channels. The last, bottom channel functions as mixing and outlet zone. Squares, much smaller than the channel width, are positioned at the walls of this mixing channel and function as static mixing elements. The squares are positioned on alternate sides of the channels and at a distance corresponding to multiple square widths. 

The flow cell translates time into distance and the combination of the three and varying the flow rates gave a range of observations from 0 to 30 s. SHG measurements of the static aqueous/dodecane interface were made at each port before and after the flow experiment to calibrate the observations from each port For a laminar (non-turbulent) flow, the two flow rates should be in the inverse ratio of the fluid viscosities this ratio for dodecane on water is 0.65 at 25°C, very close to the observed flow rate ratio of 0.67. The bulk flow rates for each liquid were measured by collecting the volume of liquid flowing in a known time. Since the cell operates under non-turbulent conditions, the velocity of each layer at the interface must be the same, but the average velocities of the two layers are different. Ideally a model of the flow conditions inside the cell would be used to accurately determine the velocity of the interface. Since this was not... 

Gas flow processes through microporous materials are important to many industrial applications involving membrane gas separations. Permeability measurements through mesoporous media have been published exhibiting a maximum at some relative pressure, a fact that has been attributed to the occurrence of capillary condensation and the menisci formed at the gas-liquid interface [1,2]. Although, similar results, implying a transition in the adsorbed phase, have been reported for microporous media [3] and several theoretical studies [4-6] have been carried out, a comprehensive explanation of the static and dynamic behavior of fluids in micropores is yet to be given, especially when supercritical conditions are considered. Supercritical fluids attract, nowadays, both industrial and scientific interest, due to their unique thermodynamic properties at the vicinity of the critical point. For example supercritical CO2 is widely used in industry as an extraction solvent as well as for chemical... 

Problem 2-21. Fluid Statics. When a cylindrical tank of liquid is rotated at constant angular velocity free surface attains a steady shape. If the undisturbed (nonrotating) height of the liquid is h, determine the shape of the interface. Be sure to state any and all assumptions. What is the role of interfacial tension When can it be neglected ... 

This book deals mainly with dynamic properties of amphiphiles at liquid/air and liquid/liquid interfaces rather than at solid/liquid interfaces. However static and dynamic contact angles are discussed in Appendix 3B as these phenomena are determined by the kinetics of adsorption of surfactants also at the fluid interface. Some specific aspects of lateral transport phenomena studied by many authors are briefly review in Appendix 3D. 

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