Experimental study on condensation heat transfer characteristics of steam on horizontal twisted elliptical tubes

An experimental research was conducted to investigate the heat transfer characteristics of steam condensation on horizontal twisted elliptical tubes (TETs) with different structural parameters. Experiments were carried out at the steam saturation temperature of around 100.5°C with the wall subcooling from around 2°C to 14°C. Experimental results indicate that the condensation heat transfer coefficients for all the tubes reduce with the increase of wall subcooling, while the enhancement factor of each TET is almost constant. Not all the tested TETs have better condensation heat transfer performance than the smooth circular tube, the average enhancement factors provided by the five TETs range from 0.87 to 1.34. Condensation heat transfer coefficients increase with the rise of the tube ellipticities. The TET No. 3 with the largest ellipticity of 0.86 has the highest condensation heat transfer coefficient augmentation of around 34%. The TET with a twist pitch of 192mm has a better condensation performance than the smooth circular tube when its ellipticity exceeds 0.77. A smaller twist pitch leads to a lower condensation heat transfer coefficient. The condensation heat transfer enhancement mechanism of the TETs has also been analysed.