The Aqueous Solutions With Nonlinear Surface Energy and Their Application to Flow Boiling in a Mini/Micro Tube

The temperature dependency of surface tension of aqueous solutions of some alcohol such as butanol and pentanol behaves in a nonlinear manner. Namely, the value of surface tension increases from some temperature when the solution is heated. Since this was discovered about 30 years ago, several experimental studies were done about the liquid motion focusing on the difference from the normal fluids. At the same time several ideas have been attempted in the application to heat pipes and so on to promote the heat transfer. The direction of thermocapillary force in liquid film of the nonlinear solution on a heated surface acts in the same direction to solute Marangoni force. This characteristic will be much marked in small scale systems such as mini/micro channels. In this talk the author surveys the research about the special aqueous solutions and their applications until now. Moreover, the author will report the new measurement results about the nonlinearity of the temperature dependency of the surface tension of the solutions. Also the author will present the result of flow boiling and the liquid motion when the nonlinear aqueous solution was used as test fluid for mini channel of 1 mm ID. The mini/micro channel was a single quartz tube with thin film heater coated on its outer surface. When the channel was mini channel of 1 mm ID, the dryout position was not much different from the case when pure water was used as test fluid. But the liquid motion was much different. The experiments when the channel was smaller micro channel (for example, 500 μm ID), are being done in the authors’ laboratory. Moreover, the author is also doing the experiments about the boiling heat transfer in regard to the increase of CHF when the nonlinear solution was used as test fluid.