Software engineer needs help from Electrical Engineers!!

Discussion in 'Homework Help' started by bilalk, Oct 30, 2010.

  1. bilalk

    Thread Starter New Member

    Oct 12, 2010
    I need to find the value of T i.e. Temperature:

    log10 Psat = A – (B/T) – C log10T + DT + (E (F-T))/FT – log10 (F-T)


    - P = Pressure

    - Sat = Saturation

    - T = Temperature

    - A,B,C and D are Constants

    PLZZZ HELP.......Thanks.
  2. someonesdad

    Senior Member

    Jul 7, 2009
    You can't solve for T in terms of the other variables, as this is a non-algebraic equation. It would be like trying to solve sin(x) + 3*x = 4 for x algebraically.

    However, if you know the numerical values of the constants and other parameters, then it should be straightforward to solve for the roots numerically. The first task is to plot the function so you can get an idea of its behavior; this is easy with tools like python and matplotlib. Once you know about where the root you want is, you can solve for it with numerous techniques. Bisection and Newton-Raphson are always taught in elementary calculus courses, so consult any basic calculus book for those. Here's a technique that works well. Also consult any numerical techniques book, such as "Numerical Recipes in C", which can be found on the web. You can download the routines associated with the book "Numerical Methods in Engineering with Python" here; I like the routine for Ridders' method, which seems to work well.
    bilalk likes this.
  3. Georacer


    Nov 25, 2009
    Laplace transformation won't be of much help here. It doesn't handle logarithms very well.
    bilalk likes this.
  4. DonQ

    Active Member

    May 6, 2009
    My advice... Simplify.

    This equation may be great for getting 15 digits of accuracy in some simulation, but there are many places where it is completely undefined in the real world (T=0 or T=F or D=0 for a few).

    Chances are that you are only really interested in a relatively small range of temperature, across a relatively small range of several of the other variables. Find out what you can eliminate, find out what you can estimate, find a polynomial that fits across the range you are actually interested in, and then solve for that.

    You may only be able to get several digits of accuracy this way, but you probably don't really need to be counting atoms.
    bilalk likes this.
  5. bilalk

    Thread Starter New Member

    Oct 12, 2010
    Thnx for the help. Can't there be some matlab file that can help me with this ..........?
  6. bilalk

    Thread Starter New Member

    Oct 12, 2010
    I need to find the value of T i.e. Temperature, i mean to derive an equation for T from the below equation; as its a non algebric equation so numerical analysis can also do the purpose:

    log10 Psat = A – (B/T) – C log10T + DT + (E (F-T))/FT – log10 (F-T)


    Psat = Saturation Pressure

    T = Temperature

    A=29.357, B=.00219 ,C=7.86 and D=305.86 , E=305.86 , F=686.1 are Constants and values are known to me.

    Can there be a matlab file for this. .I am new to matlab.
    > PLZZZ HELP.......Thanks.
  7. bertus


    Apr 5, 2008

    I merged the threads as they are related.