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The equation is derived for capillary flow in a cylindrical tube in the absence of a gravitational field, but is sufficiently accurate in many cases when the capillary force is still significantly greater than the gravitational force. In his paper from 1921 Washburn applies Poiseuille's Law for fluid motion in a circular tube.
The capillary length will vary for different liquids and different conditions. Here is a picture of a water droplet on a lotus leaf. If the temperature is 20 o then = 2.71mm . The capillary length or capillary constant is a length scaling factor that relates gravity and surface tension.
Capillary action of water (polar) compared to mercury (non-polar), in each case with respect to a polar surface such as glass (≡Si–OH). Capillary action (sometimes called capillarity, capillary motion, capillary rise, capillary effect, or wicking) is the process of a liquid flowing in a narrow space without the assistance of external forces like gravity.
An interesting phenomena, capillary rise of water (as pictured to the right) provides a good example of how these properties come together to drive flow through a capillary tube and how these properties are measured in a system. There are two general equations that describe the force up and force down relationship of two fluids in equilibrium.
The capillary length is a length scaling factor that relates gravity, density, and surface tension, and is directly responsible for the shape a droplet for a specific fluid will take. The capillary length stems from the Laplace pressure, using the radius of the droplet. Using the capillary length we can define microdrops and macrodrops.
Flow through the pores in an oil reservoir has capillary number values in the order of 10 −6, whereas flow of oil through an oil well drill pipe has a capillary number in the order of unity. [ 4 ] The capillary number plays a role in the dynamics of capillary flow ; in particular, it governs the dynamic contact angle of a flowing droplet at ...
For a water-filled glass tube in air at standard conditions for temperature and pressure, γ = 0.0728 N/m at 20 °C, ρ = 1000 kg/m 3, and g = 9.81 m/s 2. Because water spreads on clean glass, the effective equilibrium contact angle is approximately zero. [4] For these values, the height of the water column is
As all blood vessels allow a degree of protein leak , true equilibrium across the membrane cannot occur and there is a continuous flow of water with small solutes. The molecular sieving properties of the capillary wall reside in a recently-discovered endocapillary layer rather than in the dimensions of pores through or between the endothelial ...