Steam Generator Physical Model

Abstract

Simulating the effect of clogging requires a detailed representation of the two-phase flow in the riser. This rules out simple models based on energy balance and global approximations such as log mean temperature difference or number of transfer unit. Computational multi-fluid dynamics is becoming increasingly powerful but for now it is still confined to simple geometries and requires long computation times. There is an intermediate approach which allows to take into account implicitly the properties of the two phase flow by locally averaging physical quantities both spatially and temporally. This is the interpenetrating-media paradigm which relies on the two following concepts:

• both phases are present everywhere with a certain probability, the presence fraction;

• the interfaces are not described explicitly in the model but are taken into account when averaging.

Direct application of these principles leads to a set of balance equations commonly known as the two-fluids or 6 equations model which are usually closed by empirical laws describing the interfacial exchanges. The model described in this chapter is derived from this general framework.