Fluid mass can go past point or through area over time {fluid flow}|.
pipe
Fluid velocity at different pipe radii differs. Highest velocity is in center. Velocity is zero at pipe walls.
conservation
Same fluid amount at one point must be at another point. Otherwise, fluid builds. Same fluid volume passes any point, during time. At pipe points, inflow equals outflow.
pressure
Around pipe loops, pressures add to zero.
rate
Flow rate increases with increase in molecule velocity, temperature, pressure, and/or mean free path. Flow rate decreases with increase in cross-sectional area, molecule mass, and/or molecule collision frequency.
Flow in pipes can have constant velocity at each radius, with no sideways motion {streamline flow}|.
Flow in pipes can have sideways motion or different velocities at same pipe radius {turbulent flow}|. Trapped gases in fluid can cause turbulence.
High-speed flow and/or pipe edges can pull fluid apart, making vacuum spaces {cavitation, fluid}|.
Fluids have flow rate through area {flux, fluid}|. Flux is energy, mass, momentum, or charge change D divided by cross-sectional area A times time t: D / (A * t).
pipe
In pipes, masses entering and leaving cross-sectional areas are equal. Otherwise, fluid builds, or vacuum happens. Mass m flowing through pipe equals fluid density d times fluid velocity v times cross-sectional area A: m = d*v*A. For liquid, fluid density is constant, and fluid velocity going in vi times cross-sectional area at entrance Ai equals fluid velocity going out vo times cross-sectional area at exit Ao: vi * Ai = vo * Ao. For gas, fluid density varies, and fluid density at entrance di times fluid velocity going in vi times cross-sectional area at entrance Ai equals fluid density at exit do times fluid velocity going out vo times cross-sectional area at exit Ao: di * vi * Ai = do * vo * Ao.
Flux equals constant times gradient {Fick's first law of diffusion} {Fick first law of diffusion}: dm / (A * dt) = dC / ds, where m is mass, A is cross-sectional area, t is time, C is concentration difference, and s is distance.
Pressure, temperature, concentration, or force change over time relates to quantity change over distance {Fick's second law of diffusion} {Fick second law of diffusion}: dP / dt = dm / ds, where P is pressure, t is time, m is mass, and s is distance.
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Date Modified: 2022.0225