NRB: Single-Unit Example 1

Single Unit Material Balance Example

Once you have completed the Degrees of Freedom analysis, you literally have a roadmap for solving the system.

As in any simple algebraic problem (OK, it is a system of algebraic equations so maybe its not THAT simple!) you have matched the number of unknowns with the number of equations. You now simply use those equations to find those unknowns!

OUTCOME:

Do the calculations suggested in the degree-of-freedom analysis

TEST YOURSELF

Let's actually solve the example that we have already looked at...

SIMPLE-FLOWCHART

How many Unknowns are there?
How many different Species (material balances) are there?
How many Process Specifications are we given?
How many Physical Constraints are there?
The total number of Degrees of Freedom is





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Let's start with material balances....

Using a differential balance equation (since it is a continuous process), let's write down our material balance equations....

If we can solve them, let's do so now....

Next, let's write down our process specifications....

If we can solve them, do it now...

Finally, let's write down our physical constraints....

If we can solve them, do it now...

IMPORTANT

We may need to solve several (all) of these simultaneously or there may be a "preferred" order in which we should solve them!

TEST YOURSELF

Try one yourself...