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Pressure drop, liquid holdup and mass transfer in a graphite fibre bed with upward co-current gas-liquid flow Hodgson, Isaac O. A.

Abstract

The pressure drop, liquid holdup and overall mass transfer capacity have been studied in a graphite fibre electrode of porosity 0.90and fibre diameter 22 micrometer with cocurrent upward gas-liquid flow. A U-tube mercury manometer was used to measure the pressure drop in a graphite fibre bed 356 mm long by 38 mm wide by 3 mm thick. The gas and liquid were oxygen and water. For gas load 0 5 G 5 0.43kg/m2s and liquid load 1.46 5 L 5 7.30 kg/m2s, the pressure gradient ranged from 0.24 and 2.09 bar/m. The correlation for the pressure gradient is AP = L [ 0.36 + 1.182 (G/L ) 0.618 ]2 where AP = pressure gradient^bar/m L = liquid load^kg/m2s G = gas load^kg/m2s The quick closing valve method was used to measure the total liquid holdup in a graphite fibre bed 356 mm long by 38 mm wide by 3mm thick. Oxygen and 1M aqueous sodium hydroxide were the fluids used for the total liquid holdup measurements. For gas load 0 5 G 5 0.35 kg/m2s and liquid load 1.53 5 L 5 7.62 kg/m2s the liquid holdup ranged from 0.44 to 1.0. The correlation for the total liquid holdup is hL = 1 - 0.907 L 0.362 G 0.301 where hL = liquid holdup. The overall mass transfer capacity was determined by the electrochemical reaction method with the electro-reduction of oxygen to peroxide. The electrochemical reactor used consisted of graphite fibre cathode bed of dimension 89 mm long by 38 mm wide by3 mm thick. The cathode was separated from the anode by a cation membrane. Oxygen gas and 1M aqueous sodium hydroxide were the fluids used. For gas load 0.04 5 G 5 0.36 and liquid load 3.05 5L 5 7.62 the overall mass transfer capacity ranged from 3.4 to 9.0 -1 s . The correlation for the overall mass transfer capacity is Ka = 5 . 9 L0.371 G0.233 where K = overall mass transfer coefficient^m/s a = effective interfacial area for gas to solid^m-1 L = superficial liquid load^kg/m2s G = superficial gas load^kg/m2s

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