Heat transfer and flow regimes during counter-flow steam condensation in flattened-tube air-cooled condensers

Experimental results for counter-flow steam condensation in a 5.7 m-long air-cooled condenser tube with a flattened-tube cross section are presented. The tube is inclined at upward inclination angles from 0.5° to 40°, with both the vapor inlet and liquid outlet at the lower end of the tube. The effect of inclination angle on flow regimes, void fraction, capacity and heat transfer coefficient is presented. In addition, a water-cooled test section provides local steam-side heat transfer coefficient along the tube circumference at increased accuracy to that determined in the air-cooled test section. The range of condensation pressures tested is 88–120 kPa and all tests have a mass flux of less than 4.2 kg m⁻² s⁻¹. Stratified flow is found for nearly all conditions and locations in the condenser. Flooding of this stratified condensate layer is found for tube inclination angles of 5° and lower. This flooding is found to reduce the condenser capacity. The results are compared to those for co-current flow in the same condenser tube. Capacity is found to be unaffected by the flow configuration (counter-flow vs. co-current) when flooding does not occur. Steam-side heat transfer coefficient is also found to be unaffected by flow configuration for all conditions tested.