Port-Based Modeling of Transport Phenomena in 1-D Thermofluid Systems and Object-Oriented Implementation With the Modelica Language

In this article, we present the physical foundations and the development of a Modelica library with components for modeling 1-D thermofluid systems. Modelica was selected because it is an object-oriented modeling language that facilitates the incremental design of the library. Modelica also allows the modeling of acausal components, where the input/output relation is defined by the boundary conditions under which models are simulated. We model single-substance systems that are macroscopically homogeneous, isotropic, and uncharged, which we call “simple systems.” To model the behavior of these systems, we assume the postulate of classical irreversible thermodynamics. For the graphical representation of complex systems, we utilize a modified bond graph symbology to enhance the readability of the diagrams. We also implement the equations for viscosity and thermal conductivity to complete the IAPWS-95 model of water, enabling its use as a fluid in the piping systems presented in our examples.