Globally optimal synthesis of heat exchanger networks. Part III: Non‐isothermal mixing in minimal and non‐minimal networks
Chenglin Chang, Zuwei Liao, André L.H. Costa, Miguel J. Bagajewicz
Abstract
Abstract In this work, the enumeration algorithms presented in Parts I and II for the globally optimal synthesis of minimal and non‐minimal heat exchanger networks are extended to consider non‐isothermal mixing. New mathematical models, including non‐isothermal mixing constraints, are proposed to target the bounds of energy consumption and the binding exchanger minimum approximation temperature. These models are solved using the algorithms, which involve solving systems of equations instead of mathematical programming. Three global optimization strategies are proposed to optimize each enumerated structure, involving the use of a global solver directly, or the use of a Golden Search based on energy consumption and a flowrate optimization model considering non‐isothermal mixing. The flowrate optimization model is reformulated as a convex problem, which is solved by using nonlinear programming or a mathematical programming‐free methodology, that is, solving Karush–Kuhn–Tucker equations. A new Global Optimum Search Algorithm is developed and examples are tested comparing different optimization strategies.