Abstract
Experimental studies of hydrodynamics and the heat transfer crisis were carried out for a two-phase stratified flow in a mini-channel with intensive heating from a heat source of 1x1 cm2. It has been established that as the heat flow increases, the total area of dry spots on the heater increases, but when a certain temperature of the heater surface reaches ≈100 °C, the area of dry spots begins to decrease. With the help of high-speed visualization (shooting speed 100000 frames per second), several stages of formation of a dry spot (a typical size of the order of 100 microns) were isolated. It was found that at a heat flux of 450 W/cm2 about 1 million dry spots per 1 second are formed and washed on the surface of the heater (1 cm2). The speed of the contact line when dry spot is forming reaches 10 m/s.
Highlights
One of the most important problems of thermal physics today is the cooling of microelectronic equipment
In the visual analysis the following stages of the liquid film rupture were identified with an increase in the heat flux. 1 – formation of a dry spot below the heater. 2 – increase in the dimensions of the first dry spot and the achievement of the surface of the heater. 3 – increase of dry spots on the surface of the heater. 4 – decrease in the area of dry spots on the surface of the heater; 5 – in the pre-crisis moment, the liquid film again covers practically the entire surface of the heater with rapidly appearing and vanishing dry spots on it
The places of the heater on which the dry spots formed were assigned a white color and their area in pixels was further considered, knowing the characteristic scale, the area of the dry spots was translated into mm2, the total area of dry spots, Sspot, on the surface of heater was plotted in relation to the surface area of the heater, Sheater, from the heat flux density q
Summary
One of the most important problems of thermal physics today is the cooling of microelectronic equipment. In local areas from 100 μm to several square millimeters, the heat flux density reaches values of 1 kW/cm or even higher (IBM). In [9,10,11], studies were carried out that showed the possibility of removing heat fluxes of density up to 1200 W/cm from the heating area 1x1 cm by means of a thin film moving under the action of the gas flow in the channel. In [14], heat transfer was studied in a liquid film moving in a channel with an extended heater (at relatively low heat fluxes). Systematic experimental studies of the flow and rupture of a water film moving in a channel are considered when heated from a local heat source 1x1 cm. The dynamics of dry spots is investigated using a high-speed camera with the frequency of up to 100 000 frames per second
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