ASA 127th Meeting M.I.T. 1994 June 6-10

3aED3. Computer graphic simulations of microscopic particle collisions for determining macroscopic thermodynamics along a path.

Devin P. Espindle

Murray S. Korman

Dept. of Phys., U.S. Naval Acad., Annapolis, MD 21402

The heat absorbed by an ideal monotomic gas during an isothermal expansion---when a piston slowly moves from volume point V[sub 1] to V[sub 2] in a cylinder---is a standard problem in thermodynamics. Students taking the SP226 Heat, Light and Sound course learn that the process involves (a) an understanding of the kinetic energy loss that a gas molecule makes with the slowly moving piston ``called the bunt,'' (b) the drop in internal energy of the gas as a collection, which leads to a slight drop in temperature of the gas, and (c) the transfer of heat from the reservoir to the gas until an equilibrium temperature is reached. This problem is modeled in two dimensions on a computer. The collisions involve N elastic scatterers that each have a cross section of radius r[sub 0]. The heat resevoir is modeled by molecules having a random distribution of velocities at the wall boundary which is in contact with the gas. The piston is modeled as a wall which moves at the speed V[sub wall]. Thermodynamic calculations involving work, heat and entropy are attempted for the model system. Adiabatic and free expansions are also simulated and compared with the well-known theoretical results. Work is extended to cover collisions involving intermolecular potentials.