Nanoscale thermal systems in subcritical region
Doctor of Philosophy thesis
The behavior of a nanoscale fluid system in the subcritical region is investigated using molecular simulation. The fluid used is argon and the intermolecular forces are represented by the Lennard-Jones potential. The simulations show that the phase change in a nanoscale system becomes continuous as opposed to the constant temperature and constant pressure phase change for a macroscale system. Then nonlinear curve fitting was performed using two cubic equations to obtain a representation of the simulation data. The continuous phase change behavior predicted by the molecular simulation is verified by using an approximate analytical analysis. A cubical system is defined for five different configurations based on the minimization of the interfacial surface area. These systems are then analyzed to define their thermodynamic behavior by using a technique to minimize the Helmholtz free energy. It is also shown how this continuous phase change alters the behavior of nanoscale thermal systems in subcritical thermodynamic cycles. A nanoscale vapor heat engine shows a lower efficiency than the macroscale vapor heat engine and the coefficient of performance for a nanoscale refrigeration cycle is higher than that for a macroscale refrigeration cycle.