Study of Thermal Oscillations at the Dryout Front in Half Heated Tubes

Abstract

In this work thermal oscillations at the dryout front in an electrically heated composite tube of inconel and glass have been studied experimentally and analytically. The tube has an inside diameter of 17.2 mm, and a heated length of 1913 mm. The thickness of the inconel half tube is 0.89 mm. In the experiments deionized water and Freon-113 were used as the test liquids while the pressure at the exit of the tube was one atmosphere. The dryout front was established at a predetermined height from the inlet. The frequency and magnitude of the wall temperature oscillations in the vicinity of the dryout front has been obtained from the temperature-time history. The most probable time period obtained from the probability distributions has been correlated with dimensionless groups formed with mass velocity, tube diameter and the physical properties of the test liquid. Normalized probability distributions for the time period have been found to be represented by a modified gamma-distribution. The magnitude and the nature of the temperature oscillations has been predicted by solving the energy equation for the heated tube and the mass conservation equation for the liquid film left on the wall during upward movement of the dryout front. The predictions have been compared with the data.