LAUSR

Abstract Experimental data are reported for boiling water and a glycerol-water mixture at a free surface pressure of 50 mbar absolute on the shell-side of a thin slice model of an industrial boiler. The boiler test section was 1 m high, 0.75 m wide, 98 mm long and contained 36 electrically heated, horizontal tubes that were 28.5 mm in diameter. The design of the boiler ensured that the tubes were submerged in a liquid pool. The height of the liquid pool was set to 2 m, submerging the top of the tube bundle in 1.6 m of liquid. The heat flux was varied within the range 10–65 kW/m2. A near-symmetrical half of the tube bundle contained wall thermocouples. An additional 29 thermocouples were located throughout the liquid pool. For both fluids, the liquid temperature in the pool was found to be reasonably uniform and controlled by the pressure at the free surface. This led to subcoolings of up to 31 K on the tube surfaces. The reasonably uniform pool temperature suggests that the liquid re-circulates within it. For water, boiling was initiated in the heat flux range 25–40 kW/m2, whereas the glycerol-water mixture initiated boiled within the range 10–25 kW/m2. Below these heat flux ranges, both fluids were in natural convection, with the measured wall superheats in reasonable agreement with predictions from a correlation available in the open literature. The difference in the fluids’ boiling onset resulted from the natural convection, heat-transfer coefficients of the glycerol-water mixture being lower than that for water. The boiling wall superheats for water were reasonably well predicted by a correlation available in the open literature. Boiling glycerol-water mixture data, taken at atmospheric pressure and available in the open literature, was used to identify methods for correcting pure fluid boiling heat-transfer coefficients for mixture effects. Mixture boiling superheats were reasonably well predicted by some of these methods. The method that worked best at atmospheric pressure did not work best at low pressure. A method is identified that is reasonable at atmospheric and low pressures.