Hydraulics: Fluid Properties

• Hydraulics studies the mechanical properties of fluids based on their specific characteristics, forces, and conditions.

Fluid Properties

• Mass signifies the amount of matter in a body, measured in kilograms (kg) in the International System of Units
• Unlike weight, which is a vector, mass is a scalar quantity
• Density is a vector quantity expressing the mass amount within a volume, symbolized as p.
• Average density is the ratio of an object's mass to its volume
• Specific weight, symbolized as γ, is the ratio between an object's weight and its volume
• Relative density and specific weight compare absolute values to a standard substance (water at 4°C and 1 atmosphere)
• Viscosity defines a fluid's resistance to tangential deformation, attributed to molecular cohesion forces, with all known fluids exhibiting this property
• Zero viscosity is an accepted approximation for certain applications, defining an ideal fluid as one lacking viscosity
• Viscosity manifests in moving liquids, expressed as the relationship between shear stress and velocity gradient, known as absolute or dynamic viscosity, typically represented by the Greek letter μ
• Fluids under shear stress deform, forming parallel layers, each with constant velocity

Newton's Law and Viscosity

• A fluid's resistance to deformation depends on its viscosity and the deformation's velocity
• Increased velocity results in greater resistance

Limit Layer

• A fluid in contact with a solid boundary shares the boundary's velocity
• This principle clarifies fluids' resistance to solids intending to pass through them

Vapor Pressure

• Vapor pressure is the pressure where the liquid and vapor phases achieve dynamic equilibrium at a specific temperature, with its value remaining independent of the amounts of liquid and vapor present as long as both phases exist
• This phenomenon extends to solids transitioning to the gaseous state (sublimation), also characterized by vapor pressure
• Liquid and gaseous phases in equilibrium are termed saturated liquid and vapor, with the property inversely related to intermolecular forces
• Inversely proportional relationship between pressure and energy needed for state change
• Equilibrium occurs when a liquid is introduced to a vacuum at constant temperature, evaporating rapidly until equilibrium is reached between both phases
• The dynamic equilibrium is reached faster when there is a greater contact surface
• The saturation pressure depends on factors, the most important is the nature of the liquid

Surface Tension

• Surface tension is the energy required to increase a liquid's surface area per unit area
• This resists liquid surface increases
• Tension results from intermolecular forces, leading to capillary action where surface elevates or depresses at solid contact
• Interior liquid molecules experience balanced attraction, while surface molecules face inward pull
• Surface tension measures forces needed to expand liquid area, influencing droplet formation where a sphere minimizes surface area for a volume
• Hydrogen bonds contribute to water's high surface tension

Hydrostatics

• Hydrostatics studies fluids in equilibrium, relying on Pascal's and Archimedes' principles

Pressure

• Pressure measures force projection perpendicularly per unit surface, represented by p, expressed in pascals (Pa) in the International System of Units
• Atmospheric pressure results from the weight per surface area on Earth
• A vacuum is defined as the total or partial extraction of the atmospheric air from a container
• Absolute pressure references absolute zero, while relative pressure references atmospheric pressure
• The sum of static pressure and dynamic pressure exerted defines total pressure.

Hydrostatic Equation

• The equation balancing liquid mass. The pressure difference in a liquid column equals its weight

Pascal's Principle

• Pascal's principle states that pressure on a confined, incompressible fluid is equally transmitted
• This is demonstrated with a sphere where pressure applied through an opening results in water exiting all orifices equally
• Pascal's principle application in hydraulic presses

Archimedes' Principle

• Archimedes' principle states that an object immersed in fluid experiences upward thrust equal to the weight of displaced fluid
• The buoyant force relies on liquid density and submerged volume, not pressure

Hydrodynamics

• Hydrodynamics studies liquid dynamics. Approximations include fluid as incompressible, negligible viscosity, and flow in a stable regime.
• Fluid flow transitions with uniform trajectories (laminar) or irregular ones (turbulent).Laminar flow occurs at low speeds, turbulent flow at high speeds or direction changes

Fluid Regime

• Viscosity dominates inertia at low speeds = laminar. Reversed at high speeds = turbulence

Flow Rate

• Flow rate is the liquid volume passing a section per time unit
• m(kilogrammes)/ second is the amount of mass per second

Continuity Equation

• Based on liquid incompressibility, it states fluid quantity passing two points without sources or sinks is constant

Bernoulli's Equation

• For ideal fluid, total energy from pressure, velocity, height remains constant

Torricelli's Theorem

• Torricelli's Theorem applies Bernoulli's equation to find liquid exit speed from depth. Expression equals object's speed if falling freely from the liquid surface

Output

• Output from a nozzle determined via a practical application of the theorem

Water Hammer

• Water hammer: overpressure and depression from sudden change in flow

Centrifugal Pumps

• Converts mechanical energy to hydraulic energy
• Increases fluid velocity via rotating blades
• Fluid flows through open passages (diffuser), converting velocity to pressure

Pump Curves

• Illustrates pump performance like flow rate, pressure, power, and efficiency

Aspiration

• Aspiration by a conduit rises liquid via atmospheric pressure
• Max theoretical height is 10.33 meters

Priming

• Priming essential step for centrifugal pumps

Cavitation

• Rapid bubbles from pressure under liquid's saturation pressure
• Damages pumps and can only be avoided by decreasing the altitude of aspiration

Coupling

• Pumps coupled in parallel increase flow, in series increase pressure

Hydraulic Installation

• Transfers extinguishing agent (water or foam) from supply to a fire
• Requires Q/V for fire, pressure equalizes for delivery

Load Loss

• Load loss relates to energy reduction in a moving fluid from drag
• Pressure results from resistance

Curve of Installation

• Curve: depicts continuous, local pressure loss over flow rate
• Pressure lowers as conduit gets longer
• As diameter reduces, flow increases

Performance

• Flow exists where pressure delivered is constant
• Operations should be slow, not sudden, to reduce possible danger
• When diameter increases, so does water pressure
• If less water pressure, then decreases the amount push.