ABSTRACT
In evaporating and condensing systems, the assumption is often made that there exists thermodynamic equilibrium between the two phases. Thus, the phases are assumed to co-exist at their saturation temperature. Even though it is usually a good approximation to assume that local thermodynamic equilibrium applies at the vapor-liquid interfaces, temperature gradients within the respective phases can give rise to situations in which, on average, the flow departs grossly from equilibrium. Many of the phase change situations encountered in practice involve multi-component rather than single-component fluids. For example, in the process industry, reboilers and condensers associated with distillation processes always have to deal with mixtures of fluids, such as hydrocarbon mixtures. In a gas-liquid flow, since the interfaces are deformable, there are in principle an infinite number of ways in which the interfaces can be distributed within the flow. Though nearly all two-phase flows are fluctuating in nature, there exist several flow patterns where gross intermittency occurs.
