Heat transfer and liquid motion of forced convective boiling in a mini-tube for aqueous solutions with nonlinear surface energy

The value of the surface tension of aqueous solutions of some alcohol, such as butanol, increases from above some temperature when the solution is heated. Evaporation heat transfer of such a nonlinear solution was experimentally investigated. Butanol aqueous solution was adopted as the test fluid. The direction of thermocapillary force in liquid film of a nonlinear surface energy solution on a heated surface acts in the same direction to solute Marangoni force. The surface tension effects are expected to be marked in small-scale systems. The aim of the present study is to investigate the effect of the nonlinear surface tension of butanol aqueous solution on the liquid motion and heat transfer in convective boiling in a single mini channel. The quartz tube whose ID was 1 mm was applied as the test mini tube. The mass flux of the butanol solution was 1.96 kg/m2s. Prior to the experiments, the measurement of the surface tension of the butanol aqueous solution was performed by Wilhelmy's method to compare to the ethanol solution and pure water. From the convective boiling experiments, it was found that the temperature of the outer surface of the tube was much lower in the case of the butanol aqueous solution, at the region where the vapor quality was unity, than in the case of pure water. The liquid droplet motions were also observed by CCD video camera system.