Heat transfer to nonmiscible liquid-liquid mixtures flowing in a vertical tube

✍ Scribed by P. Lang; H. Auracher

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 813 KB
• Volume: 12
• Category: Article
• ISSN: 0894-1777
• DOI: 10.1016/0894-1777(95)00127-1

✦ Synopsis

Phase distribution and heat transfer measurements were carried out in an n-heptane-water mixture flowing upward in a vertical stainless steel tube of 16-mm inner diameter. For the phase distribution measurement a very high frequency impedance probe was used with a tip diameter of 0.58 mm. The volumetric phase fraction of n-heptane was varied between 0 and 1, the mixture velocities between 0.5 and 2.3 m/s, and the temperature between 30 and 80°C. By means of a high-speed data acquisition board implemented in a personal computer, two methods for signal conditioning were tested: level thresholding and derivative thresholding. Derivative thresholding proved to be advantageous because it is insensitive to baseline drift and allows detection of droplets of the discontinuous phase. Heat transfer to the liquid-liquid mixture depends on the phase distribution in the boundary layer at the wall. It was found that the change from waterdominated heat transfer to n-heptane-dominated heat transfer occurs nearly abruptly at n-heptane volumetric phase fractions between 0.6 and 0.7. An estimate of the heat transfer coefficient as a function of the mean volumetric fraction e by a linear interpolation between the heat transfer coefficients at ens = 0 and ens = 1 would therefore lead to significant errors. The few correlations available in the literature are also not suitable to predict heat transfer to water-n-heptane mixtures. Therefore a preliminary prediction method is proposed based on the experimental data for phase distribution near the heated wall.