System-Induced Instabilities in Forced Convection Flows With Subcooled Boiling

Abstract

A combined analytical and experimental program was carried out to investigate the problem of hydrodynamic stability of forced-convection flows with boiling. The study was restricted to the flow of water in small channels (<".250 I.D.), high length-to-diameter ratios (25-200), moderate temperature and pressure (Ti~700F; Pex.<60 psia), and primarily directed toward subcooled, local boiling (hex<hsatliq.)-Two types of instability were recognized: The first, a non-recurring excursive instability, and the second, an oscillatory instability in which the operating point varies in a sustained, repetitive way around the original condition. The excursive behavior was predicted on the basis of a comparison of the slopes of the pressure drop vs. flow rate curve of the heated section and the external system. The criterion for stability was simply that the slope of the external system characteristic be more strongly negative than that of the heated section. This was verified experimentally. This excursion was found to be the limiting condition on the heat flux in a parallel channel system.

Modelling of Passive Heat Removal Systems: A Review with Reference to the Framatome BWR Reactor KERENA: Part II

“…The results of the experimental investigations contain the following main statements to stabilized the two-phase flow in general, which are also summarized by [78]:…”

“…Detailed studies of the nonrecurring excursive instabilities with experimental background are published by Maulbetsch and Griffith [78], Bouré et al [8] and Padki et al [77]. Padki et al discovered that the static Ledinegg instability is caused by a saddle-node bifurcation [77].…”

Operational Flexibility of Two-Phase Flow Test Rig for Investigating the Dynamic Instabilities in Tube Boiling Systems

“…The horizontally oriented test tube with water as a test fluid is very rare. Maulbetsch and Griffith (1965) studied the influence of the compressible volume on the PWO and DWO with water driven by forced circulation in horizontal orientation pipe and (Karsli et al, 2002) investigated the amplitudes and periods of the DWOs in a horizontal pipe with inserts.…”

Experimental research on hydrodynamic instabilities during condensation of the pro-ecological refrigerant R1234yf in tubular minichannels

“…The first discovered instability was the Ledinegg's flow excursion [15] -the pressure drop versus flow rate (or the N-curve) for heated channels may have up to 3 different points of operation. The occurrence of instabilities depends on the flow rate, heat flux and medium conditions at the inlet (like quality, superheating or subcooling) [16] and system characteristics (like the presence of internal compressible volumes) [17]. The instabilities mainly affect flow distribution in parallel channels [18], flow pattern [19] and pressure drop [20].…”