Visualization Study of the Relationship between Tube Orientation and Two-phase Refrigerant Flow Regime near the Expansion Valve Aimed at Noise Reduction 2020-01-1256
Flow-induced noise in the expansion device of an automotive evaporator can be very disturbing since the TXV is located in the close vicinity of the vehicle occupants. In many researches, the flow-induced noise can be mitigated when the orientation of the fluid carrying tubes is changed. However, no study explores the reason why the flow-induced noise changes when the orientation of the tubes is changed. The flow-induced noise varies along with the flow regimes near the expansion device. In this paper, an experimental approach is used to study how the orientation of tubes changes the two-phase refrigerant flow regimes under otherwise identical operation conditions. A pumped R134a loop with transparent tubes (1/4 inches ID) is used to visualize the flow regimes near the manual expansion valve. The transparent tube is a continuous connection of horizontal tubes, 45 degree inclined tubes, and vertical tubes. It is interesting to find that for the same mass flux, vapor quality, and pressure, the flow regimes can be influenced when the tube orientation is changed. When the horizontal flow is stratified-wavy, the downward vertical flow will either be annular flow or wavy which largely depends on the mass flux in the system. The upward vertical flow will either be churn flow or plug flow. The 45 degree inclined downward flow can be wavy flow, while the 45 degree inclined upward flow can be either intermittent flow or wavy flow. The noise variation for different tubes with same mass flow rate, vapor quality, and pressure is also explored in this paper. The results explain how the flow-induced noise changes when the orientation of tube changes.