Constructal Theory: Tree-Shaped Flows and Energy Systems for Aircraft

Attention is drawn to constructal theory and design, which relies on global maximization of performance in the pursuitofe owsystem architecture. Exergy analysisestablishesthetheoreticalperformancelimit.Thermodynamic optimization (orentropygenerationminimization )bringsthedesignascloselyaspermissibletothetheoreticallimit. The design is destined to remain imperfect because of constraints (e nite sizes, times, and costs ). Improvements are registered by spreading the imperfection, for example, e ow resistances, through the system. Resistances compete againsteach otherand must be optimized together. Optimal spreading meansgeometricform. System architecture is generated by the constructal principle: constrained global optimization and constraints in a morphing e ow medium. In e ows that connect a volume (or area) with one point, the resulting structure is a tree of low-resistance links, and high-resistance interstices. These structures are robust, diverse, and everywhere. A key example is the extraction of maximum exergy from a hot-gas stream that is cooled and discharged into the ambient. The optimal cone guration consists ofa heat transfer surface with a temperaturethat decays exponentially in the e owdirection. Additional examples show that the complete structure of a heat exchanger for an environmental control system can be derived based on this method.