A Study of Critical Heat Flux of Butanol Aqueous Solution

Some alcohol aqueous solution such as butanol shows nonlinear surface tension dependence. Namely, contrary to ordinary liquid or solution, surface tension increases with temperature at the range of high liquid temperature. At the triple-phase point on a heated surface, the thermo-capillary force acts for the liquid to wet the heated surface, so the solutions are sometimes called as “self-rewetting liquid”. Self-rewetting liquids may prohibit the dry-out of a heated surface so that the heat transfer performance would be enhanced. For this reason, applications of self-rewetting liquids to heat transfer devices such as heat pipes are actively studied in recent years. However, the heat transfer characteristics of boiling of self-rewetting liquids are not fully understood. In the present research, a boiling experiment of butanol aqueous solution was performed on a heated wire in order to make clear the fundamental heat transfer characteristics, especially Critical Heat Flux (CHF), by changing solution concentration density and liquid temperature in a wide range. Bubbling aspects were observed by high-speed video camera with the rate of 1000 frames per second. It is found from the experiment that CHF is generally enhanced when compared to the case of pure water. CHF increases with concentration density at any temperatures. CHF generally increases with subcooling but at low subcooling region, it once decreases and then increases after taking a minimum. It is also found that peculiar boiling takes place where many tiny bubbles generate and bubbles are unlikely to coalesce. At high subcoolings, the mode of boiling similar to the so-called MEB (Micro-bubble Emission Boiling) was observed. These results of the present experiment indicate a possible application of butanol aqueous solution to high-performance-cooling-devices utilizing micro-channels because generating bubbles are small enough so that the pressure loss of the coolant may be small and the heat transfer rate is sufficiently high even at the saturated condition.