(302e) A Novel Method of Modeling Simple Thermodynamic System: a Case Study of a Tank Model

In chemical process engineering, engineers are dealing with all kinds of models with arbitary complexities. Nevertheless these models can be decomposed into a number of atomic systems according to different modeling requirements. One of the most important atomic systems is the simple thermodynamic system, which is, by definition, a system that is devoid of any internal adiabatic, rigid, and impermeable boundaries and is not acted upon by external force fields or inertial forces. The state of a simple thermodynamic system can be determined by some state variables. In this work, we present a new method of modeling the simple thermodynamic system.

A tank example which can be modeled as a simple thermodynamic system has been built and presented. In this tank model, balance equations of mass and energy are formulated at first. Apart from the conventional approach, which solves energy balance by transforming the energy representation in terms of extensive quantities to temperature explicit representation which is in terms of intensive quantity, we keep the energy balance equation in the form of extensive quantities. The internal energy is calculated from Helmholtz free energy which contains a factor of energy of ideal gas mixture and a factor of residual energy that deviates from the ideal state. By providing the information of equation of state (EOS) and heat capacity, this procedure can be performed routinely and one of the great advantages is the calculations of all the relevant intensive quantities can be performed directly by evaluating the partial derivatives of Helmholtz free energy.