Experimental study on the flow boiling oscillation characteristics in a rectangular multiple micro-channel

摘要

Multiple micro-channels can be used as heat sink components of many electronic devices due to high heat transfer capacity. In this paper, the flow boiling oscillation characteristics of a multiple micro-channel test section made of six rectangular micro-channels with an equivalent hydraulic diameter of 526.2 mu m were experimentally studied. The experiments were operated with heat flux q(eff) 11.58-99.56 kW/m(2), mass flux G 20.40-107.04 kg/m(2).s and inlet temperature T-in = 55 degrees C. The flow pattern evolution process in the multiple micro-channel was visually studied and analyzed. Also, the pressure drop characteristics of the multiple microchannel test section and two individual channels of the multiple micro-channel were measured and studied with time domain and frequency domain analyses, and the relationship between amplitude-frequency characteristics of test section pressure drop and q(eff)/G under typical working conditions was gained. The results showed that under oscillation conditions different flow pattern evolution modes may occur for different micro-channels due to the coupling effects of inertial force, the evaporation momentum, heating wall etc. During boiling, reverse flow of bubbles could be observed, and liquid may also be pushed upstream by the bubbles. The differences of oscillation waveform, frequency, phase position as well as the interaction effects of individual channels were found to get smaller with an increase of outlet equilibrium quality. Based on the amplitude-frequency characteristics, five flow boiling patterns were identified as boiling developed, i.e. the single phase pattern, the boiling onset pattern, the reverse flow onset pattern, the reverse flow infecting pattern, and the complete reverse flow pattern. The boundaries of the flow boiling patterns were very clear from a view of oscillation amplitude-frequency characteristics, and it was found that the boundaries can be roughly determined with parameter q(eff)/G.