Condensation of ethylene glycol on pin-fin tubes: Effect of circumferential pin spacing and thickness

New experimental data are reported for condensation of ethylene glycol at atmospheric pressure and low velocity on five three-dimensional pin-fin tubes. The only geometric parameters varied were circumferential pin spacing and thickness, since these have been shown to have a strong effect on condensate retention on pin-fin tubes. Heat-transfer enhancement was found to be strongly dependent on the 'unflooded' area enhancement i.e. on the parts of the tube and pin surface not covered by condensate retained by surface tension. For all the tubes, vapour-side, heat-transfer enhancements were found to be approximately 2.5-3 times the corresponding unflooded area enhancements. An increase in the vapour-side, heat-transfer enhancement is noticed with decreasing values of pin spacing. The best performing pin-fin tube gave a heat-transfer enhancement of 4.9; equal to those obtained from an 'optimised' two-dimensional fin-tube reported in the literature and about 20% higher than the 'equivalent' two-dimensional integral-fin tube (i.e. with same fin-root diameter, longitudinal fin spacing and thickness and fin height).