Visualization Study of the Relationship between the Orientation of Tube and the Flow Regimes near the Expansion Valve

Several types of noise exist in automobiles. The flow-induced noise in the expansion device can be very disturbing since the expansion device is located near the occupants. In many researches, the flow-induced noise is found to be mitigated when the orientation of the tube is changed. However, no study explores the reason why flow-induced noise changes when the orientation of the tube is changed. The flow-induced noise varies along with the flow regimes near the expansion devices. In this paper, an experimental based research is used to study how the tube orientation changes the flow regimes under the same operating conditions. A pumped R134a system with transparent tubes (1/4-inch ID) is used to visualize the flow regimes near the manual expansion valve. The transparent tube is a continuous connection of horizontal tubes, 45^o inclined tubes, and vertical tubes. It is interesting to find that the flow regimes can be very different at the same mass flux, the same quality, and the same pressure when the tube orientation is changed. When the horizontal flow is stratified-wavy flow, the downward vertical flow will either be annular flow or wavy, which depends on the mass flow rate in the system. The upward vertical flow will either be churn flow or plug flow. The 45^o inclined downward flow can be wavy flow, while the 45^o inclined upward flow can be either intermittent flow or wavy flow. The noise variation for different tubes with the same conditions is also explored in this paper. The results show that the flow regimes, the mass flux, and the vapor mass fraction jointly affect the level of annoyance of flow-induced noise. The vapor mass fraction influences the loudness of the noise, while the flow regimes influence the sharpness of the noise. The higher mass flux makes the flow more turbulent and therefore increases the total annoyance of noise. In the paper, the vertical upward tube installation is found to be the best.