Fluid flow and heat transfer in micro-channel has received attention in developing electronic element cooling systems and in designing thermal elements of micro machines and refrigerators. In the present experiment, pressurized water in the chamber flushed out of a vertical capillary tube of 0.5mm in inner diameter and 1150mm in length. The outer surface of the tube was insulated. The chamber excess pressure was changed from 0.1 MPa to 0.6 MPa and also the inlet water temperature was widely varied. At low excess pressures, the flow is liquid single-phase flow but at high excess pressures, phase change (flushing) takes place inside and/or near the exit end of the tube and the flow becomes two-phase flow of oscillatory or intermittent. Mass flow rate as well as tube wall temperature (distribution and fluctuation) were measured, and the aspect of flushing at the tube exit end was observed using high-speed video movie. It is found that the flow regime can be classified into three (single-phase, two-phase and transient flow regimes) depending on the chamber excess pressure.

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