Heat transfer coefficients in a high-pressure bubble column

Time-averaged local heat transfer coefficients were studied in a 0.16 m inner diameter high-pressure air-water bubble column. The effects of the superficial gas velocity (up to 0.30 m/s), pressure (up to 10 bar), probe position, and probe orientation were investigated. The heat transfer coefficients increased with superficial gas velocity, and the values in the center of the column were 9-16% greater than those near the wall region under atmospheric pressure (1 bar). With the increase in pressure, the heat transfer coefficients decreased due to combined effects of bubble size decreasing, gas holdup increasing, and bubble number increasing. The heat transfer coefficients at 10 bar were about 6-17% lower than those at 1 bar for the studied conditions, where the radial profile of the heat transfer coefficients became flat with increasing pressure. The orientation of the probe qualitatively indicated the flow direction in different radial positions of the column.