Skip to main content
E
ecihan1-Visitor
1-Visitor
January 18, 2017
Solved

Help setting up a heat transfer equation

  • January 18, 2017
  • 12 replies
  • 7685 views

Hi,

Please see attached Mathcad Prime 3.1 worksheet and advise if I am setting up the definitions and equation up properly.  The correct answer should be around 307, but I'm pretty sure I need to set up the equation a different way.

Should I be setting the equation equal to Ts?

Thank you

Best answer by MJG

It appears you typed the constraint equation outside of the solve block and then moved it into the solve block.  When you do that, Prime fails to recognize that the equation is part of the solve block.  Instead, Prime treats it as two unrelated math areas that happen to overlap each other.

To correct this:

- Move the solve block away from your constraint equation (guess value & "find" equation should move with solve block).

- Cut the constraint equation.

- Paste it into the solve block.

Prime then calculates a value of 307.845.

12 replies

M
MJG1-VisitorAnswer
1-Visitor
January 18, 2017

It appears you typed the constraint equation outside of the solve block and then moved it into the solve block.  When you do that, Prime fails to recognize that the equation is part of the solve block.  Instead, Prime treats it as two unrelated math areas that happen to overlap each other.

To correct this:

- Move the solve block away from your constraint equation (guess value & "find" equation should move with solve block).

- Cut the constraint equation.

- Paste it into the solve block.

Prime then calculates a value of 307.845.

    E
    ecihan1-VisitorAuthor
    1-Visitor
    January 19, 2017

    This works.

    Thank you very much.

    V
    ValeryOchkov24-Ruby IV
    24-Ruby IV
    January 19, 2017

    1. It will be good to use units of temperature, length etc in your calculation!

    2. Better use root not Given/Fimd

    V
    ValeryOchkov24-Ruby IV
    24-Ruby IV
    January 19, 2017

    E
    ecihan1-VisitorAuthor
    1-Visitor
    January 19, 2017

    Are you sure the units for thermal conductivity are correct?

    This is what I have:

    Capture.PNG

    -
    -MFra-21-Topaz II
    21-Topaz II
    January 19, 2017

    HT solver.jpg

    V
    ValeryOchkov24-Ruby IV
    24-Ruby IV
    January 19, 2017

    F.M. написал(а):

    HT solver.jpg

    V
    ValeryOchkov24-Ruby IV
    24-Ruby IV
    January 20, 2017

    SB.png

    E
    ecihan1-VisitorAuthor
    1-Visitor
    January 19, 2017

    Attached is my updated worksheet where I have used both the root and given/find applications.  I noticed that the variable, L=0.003 m, not 0.0003 m, therefore the answer of Ts changes (extra zero, sorry!).

    The given/find solver gives Ts= 306.627 Kelvin.

    The root solver gives Ts= 308.852 Kelvin.

    The application of this problem is to find the surface temperature of the human skin (Ts), due to the internal temperature (Ti=308 Kelvin).  Therefore, the heat loss due to conduction of the skin, convection to the outside air (air temperature is 297 Kelvin), and emissivity of thermal radiation, Ti has to be greater than Ts.  I have go to with the answer of Ts= 306.627 Kelvin.

    Thank you for all the help.

    V
    ValeryOchkov24-Ruby IV
    24-Ruby IV
    January 20, 2017

    Erman Cihan написал(а):

    The given/find solver gives Ts= 306.627 Kelvin.

    The root solver gives Ts= 308.852 Kelvin.

    Sorry - it was my error

    HT.png

      Terms & ConditionsAccessibility statement