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 Drafting for Capillary Pressure article 

Fix previous addition to article at the introduction:

This pressure difference arises due to curvature at the interface of the two fluids, which forms because the wetting phase typically diffuses across the capillary walls before the non-wetting phase. This curvature and ultimately, pressure difference, is a function of how easily the fluids wet the capillary walls, the fluid saturation properties, and the capillary pore properties.

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Capillary pressure is observed naturally, and utilized in various microfluidic and petrochemical applications.

History

In the early 19th century, capillary pressure was general defined by Young, Laplace and Plateau as Pc=(sigma)(1/r1+1/r2) where sigma is the interfacial tension and r1 and r2 are the radii of the interfacial curvatures.

Porous plate capillary pressure experiment

(Add citations, fix formulas)

Equations and measurements

Move Young-Laplace information here (general and vertical tubes with g/h)

The Young-Laplace equation can also be expressed as gh(rho1-rho2) for vertical, cylindrical capillaries, where g is the gravity, h is the height of the tube and rho is the density of the two fluids of interest.

Leverett J Function

In porous media (pre-existing, additions)

In nature

Needle ice

Human physiology

In microfluidics

Microfluidics (link to Wikipedia page) is the control of small volumes of fluid flow through porous material or narrow channels, primarily by manipulating capillary forces. (Add sentence about microfluidics in biotechnology specifically)

Capillary pressure is one of many geometry-related characteristics that can be altered in a microfluidic device to optimize a certain process. For instance, as the capillary pressure increases, a wettable surface in a channel will pull the liquid through the conduit. Likewise, fluid will resist wetting a non-wettable surface. By taking advantage of capillary pressure, we eliminate the need for an additional pump in the system.

The capillary pressure in a microchannel can be described as

Pc=-y[(cos(a_b)+cos(a_t))/d+((cosa_l)+cos(a_r))/w]

where gamma is the surface tension of the liquid, alpha_b,t,l,r, are the contact angles at the bottom, top, left and right sides of the channel, and d and w are the depth and width. The negative pressure represents the fluid being pulled into the microchannel.

(Insert impact of surface tension on capillary pressure and minimizing it with surfactants)

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The take-home pregnancy test is one of the most famous examples of a device that has utilized capillary forces to transport fluid.

In the petrochemical industry

With oil and gas applications, capillary pressure exists between oil, brine, and gas within the capillaries of rock.

See also

- Surface tension

- Bond number

- Capillary pressure hysteresis

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Ideas to add to article on Capillary Pressure

1. Capillary pressure in biomedical applications (i.e. microfluidics)

2. Capillary pressure in the environmental/energy sector (oil)

3. Capillary pressure in nature (biological and environmental)

4. Elaborate on porous media (maybe rearrange as a sub-section of the various applications/occurrences of capillary pressure)

Relevant Subjects

1. Microfluidics

2. Capillary number, capillary forces, capillary action

3. Membranes/porous media

Potential Sources

1. General

2. Biotechnology/related Discusses the effect(s) of several fluid plugs in a capillary on the capillary pressure drop with a focus on biotechnology

3. Capillary pressure as the driving force in paper-based diagnostic assays

4. Oil/energy/related Analysis of capillary pressure and capillary pressure curves, derived from rock model (applications in oil)

5. Dynamic capillary pressure in low permeability reservoirs

6. Naturally occurring Capillary pressure changes in the body as venous hypertension (high blood pressure)