EHD Gas-Liquid Two-Phase Flow

Abstract

Flow and heat transfer enhancement due to an electromagnetic field (EMF) and pulses (EMP) on single and two phase fluid flow in a heat exchanging system has increased in importance as a result of recent developments in high power transformers and transmission line cable cooling systems (Chang and Watson 1994). In the boiling water and pressurized water type nuclear power plants (BWR and PWR), the boiling phenomenon becomes important to estimate heat flow at the nuclear fuel bundle surface when the reactor or turbine is being tripped, since the heat transport system is under EMF or EMP, and quite often “lightning” strikes or other types of EMP are the cause of these trips. In a nuclear fusion reactor primary heat transport system, EMP and EMF effects would become a more common problem, since relatively large magnetic field and pulse currents must be used to confine or generate plasmas. However, the effects of the EMF or EMP on the quantities of engineering interest such as the critical heat flux, heat transfer rate and pressure drops are poorly understood at the present stage. The direction of the electric or magnetic field to the gas-liquid interface may be complex, in a two-phase flow and in some case EMF or EMP may also be generated as a result of fluid flow (see Fig. 20.1). Here we must note that the effect of leak EMF becomes significantly important as a result of recent development on the new materials such as less conductive ceramics and insulative polymers. Modelling of electrohydrodynamically induced flow has been studied for a simple geometry, such as pipe, annulus and parallel plates etc. by numerical simulation techniques. However, it is difficult to calculate more complex geometries, since the charged particle transport and Poisson’s equations are required to solve in additional to the conservation of mass, momentum and energy equations. On the other hand, the volume averaged conservation equations are normally used to simulate multi-phase flow phenomena due to the additional complexity between two-phase interfaces. In this case, the volume averaged conservation equations, F(z′, t) for each phase were introduced from the averaging of the three-dimensional conservation equations, f(x, y, z, t), and hence, the complex three dimensional flow piping system with many different flow components, such as pumps, heat exchangers etc., can be included in calculations. For EHD two-phase flow model, six conservation equations, three interfacial jump conditions and several constitutive equations are required. In this chapter, END equations for two phase pipe flow is outlined.