Enhanced heat transfer characteristics of upward flow boiling of kerosene in a vertical spirally internally ribbed tube

摘要

Experiments of upward flow boiling of kerosene in a vertical spirally internally ribbed tube and a vertical smooth tube were conducted, respectively, in the present study. The spirally internally ribbed tube has an inner diameter of 11 mm (an equivalent inner diameter of 11.6 mm) and an outer diameter of 22 mm. The smooth tube has an inner diameter of 15 mm and an outer diameter of 19 mm. The test tubes were uniformly heated by passing an electrical current along the tubes with an available heated length of 2500 mm. At the outlet of the test section, the experimental pressure was 3 bars. The experimental heat flux ranged from 28.5 to 93.75 kW/m(2). The experimental mass flux was 410, 6 10, and 8 10 kg/m(2)s, respectively. Both local and average flow boiling heat transfer coefficients were measured in the test tubes. The enhanced heat transfer characteristics of the flow boiling of kerosene in the spirally internally ribbed tube are presented by comparing the experimental heat transfer coefficients with those obtained in the smooth tube. It shows that the flow boiling heat transfer coefficients in the spirally internally ribbed tube are 1.6 to 2 times greater than those in the smooth tube. The physical mechanisms of the enhanced heat transfer characteristics of flow boiling in the spirally internally ribbed tube are analyzed. According to the experimental data, an expression for the flow boiling heat transfer coefficient of kerosene was found in terms of the Martinelli number for the spirally internally ribbed tube. The correlation is applicable to the design of heat exchange equipment, using the spirally internally ribbed tube as a heat transfer element under these test conditions.