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Concept of Pressure head and velocity head

  1. Jan 16, 2013 #1
    I am rather confused regarding the exact definitions of pressure head and velocity head. wikipedia defines pressure head as "a term used in fluid mechanics to represent the internal energy of a fluid due to the pressure exerted on its container. " But how can pressure head represent energy since it has dimension M°L[itex]^{1}[/itex]T°. Please clear my concept.
  2. jcsd
  3. Jan 17, 2013 #2
    This wikipedia definition is awful. Pressure is force per unit area, and the term "head" usually refers to how high a given pressure can raise a static column of liquid (typically water). I think of internal energy as a thermodynamic concept, and, although pressure affects the internal energy of a material, it is not its internal energy. Pressure has units of energy per unit volume, so some people think of it as an energy concept, but this conceptualization has never worked for me. Velocity head relates to the stagnation pressure of a liquid or gas. Basically, how high a column of water the stagnation pressure could support.
  4. Jan 18, 2013 #3
    Bernoulli's equation is an energy conservation equation, with relations of a specific point along a streamline:
    Velocity --> kinetic energy
    elevation --> potential energy
    pressure --> internal energy

    one way to look at it is from PV=nRT
    or P = nRT/V
    since internal energy U is a function of T ....

    P = F/A = (F d ) / (A d ) = W / V = energy / volume

    Most people when manipulating Bernoulli, think of the parts of the equation in the same way Chestemiller describes, at least I do.
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