DESIGN OF STABLE STEAM INJECTORS FOR CONTINUOUS HEATING

Continuous direct steam injection systems are used in industry to rapi dly raise the temperature of process streams either for heating or for sterilization purposes. High heat transfer rates can be achieved usin g this method, as compared with other methods e.g. shell and tube heat exchangers. Currently, there are no rational procedures available for designing steam injectors for stable operation. Flow visualization st udies and pressure measurements have shown that three flow regimes; bu bbling, jetting and intermittent steam/water flow exist, in direct ste am injection into continuously flowing water. These flow regimes are a function of process conditions and orifice diameter. A semi-quantitat ive flow regime map for a range of process conditions has been drawn u p. Bubbly flows give rise to the highest levels of noise due to bubble oscillations. This type of flow should therefore be avoided. The most stable flow regime, in terms of noise levels generated and hydrodynam ic considerations is the jetting regime. Models have been derived for each flow regime; good agreement is found between experimental and the oretical data. A dimensionless number (Bubble/Jet number) has been def ined, which can be used to predict transitions between bubbling and je tting flows. This dimensionless number, together with the flow regime map can be used to design stable, relatively quiet steam injection sys tems.