Which pressure difference describes capillary pressure?

Which pressure difference describes capillary pressure?

• A. Capillary Pressure
• B. Hydrostatic Pressure
• C. Differential Pressure
• D. Bubble Point Pressure

Answer: (A)

Capillary pressure is the pressure difference between the two immiscible fluids that meet at a curved interface inside a capillary or pore throat. This difference arises because of interfacial tension and the curvature of the meniscus formed between the fluids. In a simple capillary tube, the relationship is Pc = 2γ cosθ / r, where γ is the interfacial tension, θ is the contact angle, and r is the capillary radius. This means smaller pores require larger pressure differences to move one fluid into the space occupied by the other, which is why capillary effects strongly influence fluid distribution in porous media. The other terms describe different concepts: hydrostatic pressure is the pressure due to the weight of a fluid column (rho g h) and is not about the interface between two fluids; differential pressure is a general term for any pressure difference and doesn’t specify capillary interfaces; bubble point pressure is the pressure at which a gas starts to come out of a liquid, not the pressure difference across a fluid–fluid interface in a capillary.

Capillary pressure is the pressure difference between the two immiscible fluids that meet at a curved interface inside a capillary or pore throat. This difference arises because of interfacial tension and the curvature of the meniscus formed between the fluids. In a simple capillary tube, the relationship is Pc = 2γ cosθ / r, where γ is the interfacial tension, θ is the contact angle, and r is the capillary radius. This means smaller pores require larger pressure differences to move one fluid into the space occupied by the other, which is why capillary effects strongly influence fluid distribution in porous media.

The other terms describe different concepts: hydrostatic pressure is the pressure due to the weight of a fluid column (rho g h) and is not about the interface between two fluids; differential pressure is a general term for any pressure difference and doesn’t specify capillary interfaces; bubble point pressure is the pressure at which a gas starts to come out of a liquid, not the pressure difference across a fluid–fluid interface in a capillary.