Fluids

Abstract

This monograph is primarily devoted to cryogenic solids but, inevitably, the question is asked “… What is the difference in heat capacity, thermal expansion, or bulk modulus between gas, liquid and solid?…” Gases are dilute assemblies of atoms (or molecules), so that their properties depend on the kinetic energy of translation and for molecules also on energies of rotation and other “internal energies”; at normal pressures mutual interaction is usually a small perturbation. By contrast, liquids and solids are both about 1000 times more dense, and interactions play a dominant rôle. Liquids and dense gases are more difficult to model than crystals, because they lack the long range order which allows us to apply the concept of periodicity to the vibrating atoms and the electron gas (Chs. 2 and 6); also the hindered translational and rotational motions are not approximated by harmonic vibrations. Thus the three phases require separate discussion.