수직 미세관에서의 공기-물 이상유동의 압력강하에 관한 연구

Abstract

The two-phase flow is encountered in nature and many industrial applications such as the evaporators and condensers of refrigeration and air-conditioning systems, the conventional steam power plants, the nuclear power plants, and the chemical processing systems.

Recently, on the increase of heat flux due to a high-integrated electric circuit using in the computer, it is impossible to cool the electric circuit by the forced convection cooling method with air. So the phase-change heat transfer has been proposed.

The phase-change heat transfer can be adopted to design the cooling of electric circuit, narrow-gap boiling in nuclear power plants and compact heat exchanger.

In this case, the tube size is less than 5.0 mm inner diameter but until now, the two-phase research have been performed in greater than 10.0 mm inner diameter.

If working fluid and the shape of tube change, the characteristics of the heat transfer and flow patterns will be changed and it can't be adopted to the small diameter tubes.

In the present study, single-phase and two-phase experiments were performed to develop the pressure drop correlation, the flow regime map, and flow characteristics in 2.0, 4.0, 6.0, 10.0 mm inner diameter under the assumption of phase-change heat transfer.

Working fluid were air and water.

Single-phase flow experiments were performed to check the conventional prediction method for single-phase flow and the reliability of the experimental apparatus before two-phase flow experiments.

The conventional method to predict the friction factor in single-phase turbulent flow is the Blausius equation.

In case of 6.0 and 10.0 mm inner diameter, the friction factor agreed very precisely with the Blausius equation but in case of 2.0 and 4.0 mm inner diameter, the friction factor not agreed and were lower than the Blausius eqution.

From the experimental results, the new friction factor equation at the Reynolds number greater than 2,000 in turbulent flow region were obtained.

The total two-phase flow pressure drop consists of three components such as a frictional, a gravitational, and an acceleration (or deceleration) component.

The frictional pressure drop of two-phase flow was calculated by subtracting gravitational pressure drop from the measured total pressure drop. The acceleration pressure drop was neglected because of no phase change, constant void fraction, quality and cross sectional area.

The void fraction was calculated and compared by homogeneous model, drift flux model, and Hibiki correlation as a function of inner diameter.

The frictional pressure drop of two-phase flow was calculated and compared by Chisholm parameter, Hibiki correlation and new fricton factor obtained from single-phase flow.

The mechanism of the pressure drop in small tubes was discussed and new prediction method was proposed.