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# Tricky solve block.. V14

## Tricky solve block.. V14

(OP)
I'm trying to solve some equations for a variable. I don't think there are too many unknowns, but is there a way to check? Any ideas on how to solve this?

The material is heat transfer and the file is attached.

Thanks for any help.

### RE: Tricky solve block.. V14

You have five equations but you are solving for just one variable. That can't work.

You are using seven different variables but you only assign a value to three of them. Again, that can't work. E, F, eps2 and NTU are undefined.

As you provide five equations I suppose you want to solve for five variables.

On the other other hadn, on second sight it may be much easier than that.The variables you provide w/o values are thought to be just shortcuts.
You can calculate them from the bottom up - F first, then up to NTU and at last a new eps1. Kind of iteration? To make this using a solve block you would have to turn all those variables into functions of eps1.

See attached file. But there sure is something wrong with those equations as regardless of the guess value eps1 calculates to zero, which obviously isn't correct.

### RE: Tricky solve block.. V14

Correction! (Unfortunately it doesn't seem to be possible to edit a post after sending it, so I have to add another one).
I forgot a closing parenthesis (or better I should have deleted the opening one) which was the reason for the solve block yielding zero.
No the result is -0.11. Not sure if a negative value is acceptable for effectiveness, though.
The guess value must not be 0 or 1 as those values throw a division by zero with the equations you provided.

### RE: Tricky solve block.. V14

(OP)
Thanks for your help rmix. The effectiveness should be positive but I have may have made an error putting in the equations.
I messed around with the symbolic solving functions of mathcad but was not able to replicate making the other equations functions of eps1. Was that manual or was there a trick to that?

### RE: Tricky solve block.. V14

#### Quote (SirRobin)

I messed around with the symbolic solving functions
Why? It doesn't look like you are in need of a symbolic solution. And I doubt that mathcad would be able to give you an usuable symbolic solution at all.
Whats wrong with a numeric solve block? As you have no additional constraints or a system of equations, I guess you could also try as an alternative the use of the root() function.

#### Quote (SirRobin)

was not able to replicate making the other equations functions of eps1. Was that manual or was there a trick to that?
Not sure what the question/prolem is!? Of course I had to setup the function definitions manually to make your file work - bring them in correct order (from bottom up), adding argument eps1 and changing the boolean to an assignment equal sign.

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