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Feb 19, 2019
05:44 AM

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Feb 19, 2019
05:44 AM

Solving ODEs in mathcad prime 2.0

I need help solving these ODEs. File is attached and the ODEs to solve are at the bottom of the worksheet.

Thanks! Help is greatly appreciated.

3 REPLIES 3

Feb 19, 2019
06:39 AM

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Feb 19, 2019
06:39 AM

Prime can solve ODEs only numerically.

You have to use a solve block with odesolve and you have to provide initial conditions.

Furthermore you have to write d/dz P(z) and not just d/dz P(z).

Additionally you can't write v^2 (z) as this is interpreted as v^2 * (z). You have to write v(z)^2.

I spot functions v,x,z and rho, all dependent on z.

But what about the expression d/dz (c.p*T.f) ? Is there a fitfth function dependent on z (which one - c.p or T.f - neither is defined) and you have only four equations??

Also it may be problematic that you have a function x but x is also used as a variable (x=0013)

Feb 20, 2019
12:47 AM

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Feb 20, 2019
12:47 AM

x is a variable for molar fraction, it is not a function. And the variable x is itself dependant on z coordinate.

Equations are there for calculating cp(z) and Tf is to be found, it the temperature and tells the temperature along z axis.

Yes four equations, for v(z), x(z), Tf(z), and P(z).

The other variables such as h, cp, rho are also dependant on z coordinate but we have direct equations to calculate the values at any point z.

Feb 20, 2019
01:15 AM

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Feb 20, 2019
01:15 AM

@Asad wrote:

x is a variable for molar fraction, it is not a function. And the variable x is itself dependant on z coordinate.

And this means that x actually IS a function of z but you had used x as a single variable with the constant value 0.013

The other variables such as h, cp, rho are also dependant on z coordinate but we have direct equations to calculate the values at any point z.

And so you have to provide those functions! None of them are defined in your sheet as far as I can see!

And as already written you also have to provide initial conditions!