Questions and Answers
What is interfacial tension?
The force per unit length required to create new surface between two fluids, expressed in units of dynes/cm.
What is adhesion tension defined as?
AT = σso − σsw
How does the contact angle affect wettability?
The smaller the contact angle, the greater the area wetted by water.
What influences the value of the contact angle?
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In a static system, pressures vary only with _____?
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What is the formula for water pressure in the capillary at height h?
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What does a positive adhesion tension indicate?
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What is the relationship between the pressure difference across the interface and the densities of the fluids?
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Study Notes
Capillary Pressure Overview
- Capillary pressure is influenced by interfacial tension, adhesion tension, wettability, and chemical properties of fluids and solids.
Interfacial Tension
- Interfacial tension (σ12) between two fluids signifies the force needed to create new surface area.
- Measured in dynes/cm, it reflects specific surface energy.
Adhesion Tension
- Occurs when two immiscible fluids contact a solid surface.
- The force balance equation is: σso = σsw + σwo cos θ, where θ is the contact angle.
- Adhesion tension (AT) is defined as: AT = σso − σsw.
Wettability and Contact Angle
- The wetting of a solid surface changes according to the contact angle (θ).
- Smaller contact angles result in larger wetted areas by water, thus enhancing wettability.
- Wettability is linked to the adhesion tension.
Influence of Chemical Properties
- Molecular interactions at solid-fluid and fluid-fluid interfaces affect interfacial tensions and thus contact angles.
- The chemical makeup of solids and fluids, particularly mineralogy and fluid types (oil and water), affect wettability.
Capillary Action Mechanics
- In a vertical capillary tube submerged in water, a preferentially water-wet glass draws water up to a height (h).
- The pressure at the free water level (h = 0) in the beaker is represented as pa.
- Water pressure in the capillary at height h is calculated as pw = pa − ρwgh, with ρw being water density and g the gravitational constant.
- Air pressure on the opposite side is pg = pa − ρggh, where ρg is the density of air.
- The pressure difference across the interface is given by: pg − pw = (ρw − ρg)gh.
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Description
This quiz covers the fundamental concepts of capillary pressure, focusing on interfacial tension and adhesion tension in fluids. It explores the forces at play when two immiscible fluids interact with solid surfaces. Dive into the specific measurements of surface energy involved in these processes.
