The measurement of heat transfer from hot surfaces to non-wetting droplets

An experimental method to measure the heat transfer between a hot surface and a non-wetting droplet is reported in this paper. By means of transient, high resolution, infrared microscopy, surface temperature measurements with spatial and temporal resolutions of ∼100 μm and ∼4 ms, respectively, are obtained, by observing a thin metallic layer from beneath through an infrared-transparent substrate. Data from the infrared camera is generated at each time-step in the form of a set of temperatures, at closely-spaced locations on the surface of the infrared transparent plate. Subsequent solution of the transient thermal conduction equation within the substrate permits all thermal quantities (heat flux, energy, etc.) to be determined. As a typical result, the heat transferred by a 1.5 mm droplet is measured to be 0.19 J, with the heat flux peaking at 3.5 MW/m2 during the 10 ms it spends in the vicinity of the surface, and with a peak transient surface temperature reduction of 47 °C. Error analysis indicates that the uncertainty in this measurement of heat transfer is about 15%.