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Heat Transfer from Air to Dynamic Fluid in Pipe

  1. Jul 28, 2010 #1
    I need some help estimating the heat transfer of a system. If I have an exposed length of pipe with a dynamic fluid moving at a constant volumetric rate through a very hot room, what equation is most appropriate to calculate the exit temperature of the fluid?

    Given:
    Initial temperature of the fluid
    Temperature of the room
    Material properties of the pipe and fluid

    Thanks,
     
  2. jcsd
  3. Jul 31, 2010 #2
    Heat transfer calculations can get complicated, but if you need just a ball park estimate your problem can be made simple. The main resistance to heat transfer from your hot room to the pipe will be the interface between the air and the outside surface of the pipe. The thermal resistance of the pipe itself and the fluid interface to the pipe's interior is most likely to be small in comparison.

    Heat will be transfered to the pipe's outer surface by thermal radiation and natural convection (assuming no breezes in the room). Roughly this will occur at the rate of about (2 BTU per hour )* ft2 * delta F, where ft2 is the surface area of the pipe in square feet and delta F is the temperature difference between the pipe and the room.

    So, compute the heat added to the first foot of pipe, then compute the temperature rise of the fluid, temp rise = heat input/(cp * mass flow)

    where:
    heat input is BTU/hour
    cp is the thermal capacity of the fluid BTU/F/lb (for example, Cp of water = 1 btu/F/lb)
    mass flow is lb/hour


    Continue computing the heat rise for addition foot sections of pipe and adding them up until you've done the pipe's entire length (this is a numeric solution procedure to a differential equation).

    Good luck!

    Jay


     
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