Heat transfer to tubes in freeboard space of fluidized-bed combustors. Progress report, August 1, 1981-January 31, 1982

The heat transfer experiments and data reduction were completed. A schematic of the test setup is shown. The static bed height was held constant at 36 cm, except for the experiments for the effects of static bed height. The heat transfer tube was placed to the heights of 1.25, 19, 58, 147 and 224 cm above the bed. The 1.25 cm tube elevation was the one when the lower side of the tube just touched the top of the static bed. Immersed tube heat transfer coefficients were also measured (for glass beads of d = 300, 850 ..mu..m) to compare with the heat transfer coefficients in freeboard region. Glass beads with 300, 850 ..mu..m mean diameters and sand with 285, 465 ..mu..m mean diameters were used as fluidizing particles. High gas velocities were reached up to 3.5 m/sec. The heat transfer probe was capable of measuring local heat transfer coefficients at eight locations that are 45/sup 0/ apart from each other. The average heat transfer coefficients were then calculated by integrating the local values. A sample of experimental results for the variation of local heat transfer coefficient around the heat transfer tube for glass beads with mean diameter 300 ..mu..m is shown for low and high air flow rates. These experiments were also carried out for 850 ..mu..m mean diameter glass beads and 285 and 465 ..mu..m mean diameter sand. Average heat transfer coefficients were calculated from above mentioned local experimental data. Effects of tube elevation and gas flow rate on average heat transfer coefficient is shown for glass beads with mean diameter of 300 ..mu..m. Experimental results for average heat transfer coefficient versus tube elevation are shown for two different gas flow rates. Effect of static bed height on heat transfer coefficient was also investigated by changing the static bed height