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EFFECT OF PHYSICAL PROPERTIES ON HEAT TRANSFER AND FLOW REGIMES IN BUBBLE COLUMNS
تأثير الخواص الفيزيائية على انتقال الحرارة وانظمة التدفق في الاعمدة الفقاعية

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Abstract

This work discusses the effect of superficial gas velocity and liquid properties (viscosity μ, surface tension σ, thermal conductivity k , density ρ , specific heat Cp ) on the heat transfer coefficient and gas holdup investigated in a bubble column. Experiments were carried out in a Plexiglass column (0.15 m diameter and 1.5 m height). A perforated plate was used as a gas distributor, having 84 holes of 1mm diameter, and 0.37% opening area. The heat transfer coefficient was measured for the air-liquid systems in bubble column of four types of liquid (water, 60%ethanol, 35% glycerol, and 65% glycerol) covering a range of surface tension and viscosity values, while the gas phase is atmospheric air. The superficial gas velocity, UG, was varied in rang of (0.0037-0.094) m/sec. For all sets of experiments the height of liquid phase was maintained constant at 0.8 m above the gas distributor. From experimental, data it is found that the values heat transfer coefficient for aqueous glycerol solutions decrease with increasing concentration of glycerin and are lower than those for 60%ethanol and water solutions. This is attributed to the combined effects of surface tension, viscosity, specific heat, and thermal conductivity of the liquid. The overall gas holdup for all liquids increases with an increase in superficial gas velocity, the liquid property has an impact on gas holdup. An increase in liquid viscosity results in large bubbles and thus higher bubble rising velocities and lower gas holdup. A correlation based on dimensionless groups for the prediction of heat transfer coefficient is proposed and found to be in good agreement with available data.Keywords: heat transfer coefficient; liquid properties; bubble column

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