Air-water two-phase flow through U-bend, sudden expansion and sudden contraction in rectangular mini-channels

Abstract

The evaluation of pressure loss in gas-liquid two-phase flow through singularities is important for designing compact heat exchangers such as cooling devices in electronic equipment. However, the accurate evaluation methods are scarce especially for mini-channel flow. In the present study, air-water twophase flow and water single-phase flow experiments were conducted at room temperature using three kinds of horizontal rectangular mini-channels each with a U-bend, sudden expansion, and sudden contraction. The width and depth of the rectangular cross-section of the channel with U-bend were 3 mm by 3 mm, while those with sudden expansion and/or sudden contraction were 3 mm by 3 mm and 6 mm by 3 mm. The flow regimes covered were bubble, slug and annular flows. Reynolds number range for water was from 240 to 9300, while that for air from 17 to 3200. The local pressures upstream and downstream from the singularity were measured with calibrated pressure sensors to determine the frictional pressure drop in the channels upstream and downstream from the singularity, together with the pressure drop at the singularity. Video photography of flows was also conducted to determine flow regime, bubble velocity and void fraction. In the analysis, the frictional pressure drop data and the pressure drop data at the singularity were compared with calculations by various correlations in literatures. Results of such experiment and analysis are described in the present paper.

Single Phase and Two Phase Pressure Drops Across Sudden Contraction in Horizontal Rectangular Minichannel

“…Sadatomi et al [3] investigated flow regime, pressure drop, bubble velocity and void fraction for air-water two phase flow through U-bend, sudden expansion and sudden contraction in rectangular minichannel. Kusumaningsih et al [5] conducted experimental investigations on nitrogen gasliquid (distilled water, ethanol 49 wt% aqueous solution, pure ethanol and HFE 7200) two-phase flows in two kinds of rectangular microchannels with the widths of in the larger channels upstream of the contraction 0.53 or 0.78 mm (0.240 mm in height), while 0.240 mm (0.240 mm in height) the smaller ones.…”

“…In particular, the small and narrow channels are widely adopted in compact heat exchangers [2]. Recently, such a flow through singularity in micro and minichannels ranged from 100 μm to 10 mm becomes popular because compact heat exchangers with phase change, such as cooling devices of electronic equipment and refrigerators, are miniaturized [3].…”

Passage of a Liquid Taylor Drop through Successive Bends in a Rectangular Channel

“…Usui et al have studied possible flow patterns occurring at different velocities of gas and liquid and their mutual transformation while passing through a return U bend. Later, several researchers proposed different correlations for the calculation of pressure drop along U bends considering different fluid combinations. − Sadatomi et al carried out experiments for different flow rates of air–water and observed their effect along a channel with a U bend, a sudden contraction and expansion. Yadav and Mehta have explained the effect of the radius of curvature of a U bend on the flow patterns and the hydrodynamics behind the Taylor bubble flow.…”

Non-Newtonian Two-Phase Flow Characteristics across Sudden Expansion in Horizontal Rectangular Minichannel

“…A number of researches have been reported on two-phase flows in small channel with singularities. Among them, Sadatomi et al [2] investigated flow regime, pressure drop, bubble velocity and void fraction for air-water two phase flow through U-bend, sudden expansion and sudden contraction in rectangular minichannel. Kawahara et al [3] conducted experimental investigations on gas-liquid two-phase flows in two kinds of rectangular microchannels with the width of in the larger channels upstream from the contraction were 0.53 or 0.78 mm at 0.230 mm in height, while that in the smaller ones was 0.270 mm at 0.230 mm in height.…”