TABLE OF CONTENTS The best equipment design is the least expensive and safe design that meets the specification and performs the duty. Since all businesses are motivated by profit, economic evaluation plays an important role in process design. There are many ways to reach the same destination. The best way is the least expensive way in terms time, money, and safety.
It is the number of variables which are not fixed or specified in a design, and therefore, are free to be adjusted for optimum design.
F = M - N
where:
| M | = | number of variables, such as equipment type, pressure, temperature etc., |
| N | = | number of independent sources of information, such as heat and material balances. |
The degrees of freedom, F, has two components.
F = F 1 + F 2
where:
F 1 = environmental degrees of freedom : variables whose values are fixed by the environment of the process, such as cooling water supply temperature or the inlet and outlet temperatures of process side of a heat exchanger etc. This is a freedom lost by the optimizer. F 2= economic degrees of freedom : variables that the designer can adjust to maximize the profitability, such as the type of an exchanger or the cooling water flow rate etc.
| 1. | The following table lists the variables of a heat exchanger handling fluids with no change of phase:
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