Capillary Action

Capillary action
Phenomena
physics of capillary action
Numerical Example

1. CAPILLARY ACTION  Types of capillary action Equation for capillary rise  Numerical pproblems invloved  

3. Definition of capillarity     The process in which soil moisture moves in any direction through the fine (capillary) pores of the soil, under surface-tension forces with individual soil particles.   is the intermolecular attraction between liquid and solid materials. It occurs when liquid rises in narrow tubes, or is drawn into small openings such as those between grains of a rock, or even when a dry paper towel absorbs a liquid by drawing it into the narrow openings between the fibers.

4. EXAMPLES    thin layer chromatography   fountain pen   nibs   hydrology In physiology Wicking

5. Phenomena and physics of capillary action  The appparatus use to describe this is capillary tube . When the lower end of a vertical glass tube is placed in a liquid, such as water, a concave  meniscus  forms.  Adhesion  occurs between the fluid and the solid inner wall pulling the liquid column up until there is a sufficient mass of liquid for  gravitational forces  to overcome these intermolecular forces. The contact length (around the edge) between the top of the liquid column and the tube is proportional to the radius of the tube, while the weight of the liquid column is proportional to the square of the tube's radius. So, a narrow tube will draw a liquid column higher than a wider tube will, given that the inner water molecules cohere sufficiently to the outer ones.  

6. Types of capillary action  Capillary rise  Capillary fall

7. CAPILLARY RISE  and contact angle   .If the adhesive force between the liquid and solid is greater than the cohesive force within the liquid, the liquid is said to wet the surface and the surface of the liquid near the edge of the container will curve upward Contact angle : The angle between tangent to the liquid surface and the surface is called contact angle .

8. CAPILLARY FALL  In cases where the cohesive force is greater than adhesion, the liquid is said to be nonwetting and the liquid surface will curve downward near the edge of the container. As  mercury have higher cohesive forces compared to adhesive forces. -so the molecules of mercury are attracted towards its own molecules and will not stick with capillary wall. -level of mercury will fall because of higher attractive forces of surface molecules with inside molecules of mercury. -This is the reason why meniscus in this case is convex.

10. Capillary rise equation    

11. NUMERICAL PPROBLEM  Calculate the radius of a capillary tube if water rises to a height of 12.5 cm within it, assuming the angle of contact between the water and glass to be 0 o . SOLUTION: Using the formula: h = 2T/ rρg Radius of tube (r) = 2T/ hρg = [2 x 72.7 x 10-3]/0.125x 1000 x 9.8 = 1.2x10 -4  m = 0.12 mm

12.   SIMILAR NUMERICAL PPROBLEM  Two capillary tubes with the diameters of 0.1 mm and 0.3 mm are immersed by one end in a vessel of water at 20° C. How will the difference between the height of water in each capillary tube change, if we heat the water up to 70° C? Given that the surface tension of water is 0.0728 J/m2 calculate the capillary  rise in a glass tube that is 1 mm in radius. Given that the surface tension of ethanol is 0.032 J/m2 calculate the capy g illary rise in a glass tube that is 0.1 mm in radius. Assume that density of ethanol is 0.71 g/cm3.