Lecture 2

Lecture 2 - ater ater esources Resources ngineering...

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Unformatted text preview: ater ater esources Resources ngineering Engineering ecture 2- Lecture 2 otes by T Wagener & P Reed Notes by T. Wagener & P. Reed Penn State University 1 Principles of Flow in Hydrosystems 2 ater Properties – ass or Weight Water Properties Mass or Weight Mass density or density ρ (rho), is the mass per unit volume [kg/m 3 or Ns 2 /m 4 ]. (Mass density of water at 4 ° C is 1000kg/m 3 ). Density is often assumed constant, so that water is assumed incompressible in hydrology and hydraulics. Incompressibility does not always mean constant density because salt in water changes the ensity of water without changing its volume density of water without changing its volume. Specific weight γ (gamma) is the gravitational force (weight) per unit volume of water. (Specific weight of water at 4°C is 9810 N/m 3 or 62.4 /ft 3 lb/ft ). The relationship between density and specific weight is: g γ ρ = 3 This is an important characteristic for example when we are dealing with water with different levels of salt content or different temperatures [e.g. Estuaries, density currents, …]. Why is it Important? Example: Ocean Thermohaline Circulation 4 Evaporation makes water more saline and denser Freezing makes water more saline and denser Cold water is denser than warm water ater Properties - ressure Water Properties Pressure Pressure , p , is the force F acting over an area A lim A F d F P dA dA Δ → Δ = = Pressure at a point is equal in all directions. The pressure at depth y (assuming no pressure on the water surface) is y P y γ 5 ater Properties - ressure Water Properties Pressure 6 ater Properties - ressure Water Properties Pressure What is the horizontal pressure (in N per m 2 ) acting at the bottom of...
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Lecture 2 - ater ater esources Resources ngineering...

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