Simultaneous, noninvasive measurements of convective heat transfer and solid volume fraction at the wall of an entrained gas-solid suspension

We describe an instrument for local, instantaneous, noninvasive, simultaneo us measurements of solid volume fraction and convective heat transfer at th e wall of a vertical tube containing a relatively dense, entrained suspensi on of gas and fine solids. The instrument combines a small platinum coil an d a guarded capacitance sensor. The capacitance sensor records instantaneou s solid volume fraction in the near vicinity of the wall. The coil is maint ained at constant temperature by a rapid anemometer bridge circuit. The ves sel is wrapped in electric heaters to avoid artificially high rates associa ted with developing heat transfer and to minimize conduction losses from th e coil. Using a model capturing these losses, convective heat transfer rate s are inferred from the power input to the coil. The instrument is tested i n a cold circulating fluidized bed riser. The temporal response of the ther mal sensor is faster than 30 ms. (C) 2000 American Institute of Physics. [S 0034-6748(00)02807-0].