Short-term superheating of hydrocarbon liquids: heat transfer enhancement due to micro-additives of water

The practical application of small-size devices with pulsed heat generation requires the search for passive methods of removing heat fluxes over a wide range of wall temperature variations. In the context of such a request, this study focuses on interpretation of the physical picture of the phenomenon of puzzling increase in heat transfer from the micro-heater to the hydrocarbon (base) liquid, caused by the introduction of small, at the level of tens of mg/kg, moisture additives. This interpretation is based on the hypothesis that the onset of liquid motion occurs in the course of its short-term superheating with respect to the liquid-vapor equilibrium line. Water clusters serve as the source of this motion. They initiate premature (relative to the attainable superheating of a pure base liquid under the given experimental conditions) nucleation of the vapor phase and the motion of subcritical bubbles of the base fluid in a temperature gradient field. A model for enhancement of the heat transfer coefficient from a pulse-heated wall to superheated hydrocarbon/water additive system has been developed. The modeling results are consistent with the experimental data on pulsed (millisecond) heating of saturated hydrocarbons using a wire heater. They help to clarify the specific features of heat transfer at confined scale of spatiotemporal variables.