Boiling Heat Transfer of Butanol Aqueous Solution

Boiling heat transfer of some aqueous solutions is enhanced by adding a small amount of high-carbon alcohol such as butanol. Such solutions show nonlinear surface tension dependence on liquid temperature and are sometimes called as “self-rewetting liquid”. In recent years, such liquids are applied to thermal devices such as heat pipes. However, the characteristics of boiling heat transfer of self-rewetting liquids are not fully understood. In the present research, by employing butanol aqueous solution as a test solution, a fundamental boiling experiment is performed on a heated wire with special attention to critical heat flux (CHF) augmentation and to address fundamental issues. In the experiment, the solution density and the subcooling of liquid were changed in a wide range. From the experiment, it is found that CHF of saturated boiling is enhanced from 2 to 3 times when compared with that of pure water and that generating bubbles are very small, large in number and are difficult to coalescence. It is also found that the dependence of CHF on liquid subcooling is peculiar. Namely, with increasing subcooling, CHF decreases first, takes minimum and then increases. In order to find the reasons for such characteristics, the component density of bulk liquid as well as evaporated vapor is measured by gas-chromatography. As the related topics, the results of the tests of transient cooling and flow boiling inside a mini-channel are shown.