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Heat Transfer/ Fluid Dynamics

  1. Nov 3, 2011 #1
    I need help, hope somebody can give me a hint

    Determine the appropiate orifice sizes for uniform exit temperatures of 140F from the four units in 70F ambient/ sea level pressure? Components (50W, 500W, 1000W and 300W)

    Thank you
     
  2. jcsd
  3. Nov 3, 2011 #2
    you are going to have to be a little more specific here. Internal flow, external flow, modes of heat transfer? you clearly must be confused, you need to learn how to ask the right questions
     
  4. Nov 3, 2011 #3
    Sorry,

    I do have a problem. It is a cabinet, it has 4 components. Each component has has an inlet an an exit orifice where the air passes through. I would like to determine the orifice size for uniform exit temperatures of 140F from the four components in 70F ambient at sea level pressure.
     
  5. Nov 3, 2011 #4
    Am I correct in saying that the air is heated inside the compartment? I will assume that I am. for started lets make a control volume. Say we make a control volume around one compartment. We know by conservation of mass that mdotin=mdotout, and that Q=mdot*cp*dt, where dt=To-Ti. So if we say that Q is the power given off by the heater inside the compartment (which is given in the problem) then we have everything we need to solve the problem.

    remember that mdot=(rho)(A)(V), you know rho given the 1 atm at 70
    you know Ti=70
    To=140
    Given Q
    Solve for mdot

    But you need to know a flow rate to know a velocity at which the air is entering the compartment so you can solve for area and then diameter.

    I may have miss understood your question but if you are given a flow rate or velocity then follow these steps.
     
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