Dry spots dynamics in shear-driven thin liquid films under intensive local heating

Development of the modern microelectronic equipment requires the effective cooling solutions because it is necessary to remove high heat fluxes of up to 1 kW/cm(2) and higher from the local hot spots of the processor. Thin and ultra-thin (less than 10 mu m in thickness) liquid films, moving under the action of a forced gas flow in a mini-channel, are promising for the use in the temperature control systems of the modern semiconductor devices. Here we report results of systematic experimental studies of the flow and rupture of a water film, shear-driven in the channel, under intense heating from a local heat source with size of 1x1 cm(2). To carry out high-speed visualization of the process, the FASTCAM SA1.1 CCD camera is used (with the speed of up to 100 000 frames per second). The camera is equipped with an optical system of high spatial resolution (2.5 mu m per 1 pixel of the camera sensor). With the help of high-speed imaging, it was found that the maximum intensity of heat removal from the heater is achieved in the mode, when the film flow continuity is broken. The heater is covered with dry spots having typical size on the order of 10-100 mu m and typical lifetime on the order of 0.1-1 ms. At that, the number of dry spots that exist simultaneously on 1 cm(2) of the heater surface can reach several hundred. During 1 s up to 1 million dry spots appear and disappear at the area of the heater.