Experimental investigation of bubble jet flow, sweeping and rotation on horizontal or inclined micro-wire during subcooled boiling

The generation and departure of bubbles are closely related to the boiling heat transfer efficiency. To investigate the bubble boiling characteristics on a heated micro-wire, platinum wires with diameter of 0.1 and 0.2 mm were used as the experimental material. The bubble dynamics over a horizontal heated wire and an inclined heated wire were investigated by a high-speed camera and an electronic microscope. The influences of heat flux and subcooled condition on the bubble departure diameter and the departure frequency were analyzed. The results showed that three kinds of bubble motion track were observed over the heated micro-wires under subcooled condition, including jet flow, sweeping, and rotation. The multi-jet flow phenomenon could be seen over the bubble on the heated 0.2 mm wire under the conditions of heat flux of 1.7 x 10(5) W m(-2) and mainstream temperature of 36 degrees C. As the diameter increased, the bubbles grown on the lower side of the heated wire would gradually rotate over the wire. There were three phenomena observed on the 0.1 mm wire when two bubbles collided under conditions of 2.9 x 10(5) W m(-2) heat flux and 34 degrees C mainstream temperature. For an inclined micro-wire with the inclined angle of 25 degrees, the movement of the bubble would only move along the wire to the tip and eventually break away. When the mainstream temperature was 40 degrees C, the bubbles departure diameter and the frequency increased with the increase in heat flux. When the heat flux was 3.0 x 10(5) W m(-2), the bubble departure diameter and frequency increased with the increase in temperature.