Capillarity
Capillarity refers to the ability of a liquid to flow in narrow spaces without the assistance of external forces, such as gravity. This phenomenon is due to the cohesive and adhesive properties of the liquid, which allow it to climb or descend through small openings, such as tubes or porous materials. Capillarity plays a significant role in various engineering applications, including fluid dynamics and material science.
4 Key excerpts on "Capillarity"
eBook - ePubThe Science For Conservators Series
Volume 2: Cleaning
- Matthew Cushman(Author)
- 2005(Publication Date)
- Routledge(Publisher)
...This “blotting paper” effect is known as Capillarity and is important in conservation in many ways. For example, it is used in blotting up liquids such as water or molten wax. In cleaning it transports solvents to inaccessible dirt in fine crevices or pores and carries dirty solvent off surfaces to which poultices have been applied. It can also act destructively; if it carries water into cracks in objects it may help to cause corrosion or, if it freezes, the water will expand and cause stresses which break the object. Capillarity To explain Capillarity you have to think of the forces between the two different kinds of molecules – those in the liquid and those in the material of the tube or pore. There are attractive forces between all molecules; the important question is, which ones are the stronger – the cohesive forces between the molecules of liquid or the adhesive forces between the molecules in the liquid and those in the solid? The balance between these forces determines whether the liquids will be drawn up a fine tube and what the shape of the curved surface (called a meniscus) will be where the liquid touches a solid. There are two cases: Figure 3.1 a A concave and b a convex meniscus of a liquid. meniscus Where there is a strong attraction between the liquid and the solid, the liquid climbs up the solid’s surface as in (a). Where the balance lies the other way, and the cohesive forces are strong but the adhesive forces weak, the liquid pulls in towards itself as in (b). Strong Capillarity is to be expected with polar liquids which, although they cohere strongly, may offer a mechanism for strong intermolecular forces from solid to liquid. If the solid can offer hydrogen bonds to a polar liquid (for example water) there will be absorption. Such materials (for example, cotton, wood and proteinaceous materials) are hydrophilic which means water-loving. Greasy surfaces repel water and are termed hydrophobic or water-hating...
eBook - ePubHandbook of Molecular Gastronomy
Scientific Foundations, Educational Practices, and Culinary Applications
- Christophe Lavelle, Herve This, Alan L. Kelly, Roisin Burke, Christophe Lavelle, Herve This, Alan L. Kelly, Roisin Burke(Authors)
- 2021(Publication Date)
- CRC Press(Publisher)
...reached for dF = 0. And because: d V = 4 π r 2 d r At equilibrium, dF = 0, so that: P e x t − P i n t = − 2 γ r This is the Laplace equation (De Gennes et al., 2004). Using this relationship, one can now calculate the “capillary rise”, i.e., the tendency of liquids to move upward in thin (this should be characterized using the “capillary length”) tubes (Daoud and Williams, 1999). If we consider a tube of which the lower part is in a liquid, this liquid moves upward by a distance h, and a meniscus is formed. P being the atmospheric pressure, and r the radius of the tube, the distance h can be calculated (Figure 15.3). FIGURE 15.3 When the lower end of a tube is in a liquid, the liquid rises by Capillarity. The pressure inside the liquid, at the middle of the air–liquid interface M can be calculated using the Laplace law. If P air is the pressure (ambient) of the air, then: P M − P a i r = − 2 γ r Because of the weight of the liquid, we can also express the hydrostatic pressure: P M − P a i r = − 2 ρ g h Equating the two, we get: h = 2 γ ρ g r From this formula, we see the importance of not only the surface tension but also the. density and the radius. In culinary processes, when the density cannot be changed, one can improve Capillarity by increasing the surface tension or reducing the radius. The Example of “Shitao” Finally, let us observe that Capillarity occurs generally for both aqueous solutions and oils in most plant and animal tissues, because culinary systems are full of both hydrophobic and hydrophilic compounds, establishing contacts by a diversity of intermolecular forces (Figure 15.4). However, the penetration of liquids inside such tissues does not always occur, and the problem of giving a specific flavour to the inside of three-dimensional ingredients does not always have a solution. FIGURE 15.4 The energies of various intermolecular interactions. FIGURE 15.5 A “Shitao” system produced by the French chef Pierre Gagnaire, served in Hong Kong in 2005...
eBook - ePub- Steven Vogel(Author)
- 2012(Publication Date)
- University of Chicago Press(Publisher)
...6 Raising Water Houseplants, even though they grow only slowly in the low light of our homes, need watering fairly often. Plants demand prodigious quantities of liquid water, often hundreds of times as much as they could possibly use to make sugar from carbon dioxide in photosynthesis. Almost all that water comes from the soil and has to be raised to the leaves. Nothing in physical biology makes a better story than the tale of the ascent of water—mechanically counterintuitive, historically curious, structurally specialized, globally critical. The pumping system has no moving parts, costs the plant no metabolic energy, moves more water than all the circulatory systems of animals combined, does so against far higher resistance, and depends on a mechanism with no close analog in human technology. While a few details remain obscure, we’re quite confident that we understand the overall picture—remarkable for something that at first blush sounds pretty bizarre. First we have to dispose of a mechanism that I see mentioned here and there, mainly in books written by physicists. Capillarity is easy to demonstrate, but it simply doesn’t pass quantitative muster. The standard demonstration of Capillarity is a fixture of high school courses in physical science, one of those never-fail items on which we teachers rely. One simply inserts a thin glass (i.e. capillary) tube partway into a container of water, and water obligingly rises in the tube, as in figure 6.1. The narrower the bore of the tube, the higher the water rises. The only potential fly in the ointment is that water has to “wet” the inside of the tube. That is, water must be attracted to the glass surface—which it will be if the glass is clean and thus, as we say, hydrophilic. Grease the glass with some hydrocarbon-based ointment, and the water level in the tube sinks beneath that in the container—the surface has been made hydrophobic...
eBook - ePubIntegrated Reservoir Asset Management
Principles and Best Practices
- John Fanchi(Author)
- 2010(Publication Date)
- Gulf Professional Publishing(Publisher)
...The forces are given by and The density gradient Γ is the weight of the fluid per unit length per unit cross-sectional area. For example, the density gradient of water Γ w is approximately 0.433 psia/ft at standard conditions. If we assume an air-water system, the force down is where the cross-sectional area of the capillary tube is π r 2. Capillary pressure P c is defined as the force per unit area; thus Expressing capillary pressure in terms of force up per unit area gives (10.3.4) where r = pore radius (cm) σ = interfacial (or surface) tension (mN/m or dyne/cm) θ = contact angle (degrees) Equation (10.3.4) shows that an increase in pore radius will cause a reduction in capillary pressure, while a decrease in IFT will cause a decrease in capillary pressure. This effect is illustrated in Figure 10.3, which shows the behavior of two immiscible fluids, one a wetting phase and the other a non-wetting phase. Reducing capillary tube diameter increases capillary pressure and allows the wetting phase to move higher in the small-diameter capillary tube than it can in the larger-diameter capillary tubes. Figure 10.3 Capillary tubes and capillary pressure. Capillary pressure in reservoirs depends on the interfacial tension between two immiscible fluids, the contact angle between rock and fluid, and the pore radius of the rock. The contact angle is a function of wettability, and pore radius is a microscopic rock property. Equation (10.3.4) shows that P c decreases as pore radius increases. Rocks with large-pore radii usually have a larger permeability than rock with smaller-pore radii. Thus, high-permeability rocks have lower P c than lower-permeability rocks that contain the same fluids. Capillary forces explain why water is retained in oil and gas zones. In water-wet reservoirs, water coats rock surfaces and is preferentially held in smaller pores. Non-wetting hydrocarbon phases occupy the central parts of larger pores...
