orifice tube, flow induced noise, CFD, natural frequency, vortex shedding frequency
Flow-induced noise in expansion devices is always a severe problem in HVAC&R applications, such as the TXV noise in an automobile where users are sensitive to noise emissions. This paper introduces a CFD based model for exploring the geometry optimization of an orifice tube using R134a. Relevant parameters including diameter and internal geometry features are discussed in the paper. When the flow is going through the constrained section, liquid R134a turns into vapor. In this paper, the internal fluid flow is solved separately as large eddies and small scales with 3D large eddy method. Phase change that happens in the orifice is computed using mass transfer between liquid R134a and vapor R134a that is similar to what happens in cavitation. The cavitation model is used together with a simplified multiphase model – mixture model. The fluid model and structure model interact with each other with two interactive surfaces within each solving step. Natural frequency describes the vibration of the orifice tube when the interior flow is going through, while vortex shedding frequency is generated when internal flow hits bluff geometry features. The modification of internal geometry significantly mitigates the flow-induced noise by reducing the turbulence of flow field. Increasing the tube wall thickness also weakens the flow-induced noise by lowering resonance with structure vibration. The results are references for geometry optimization of other types of expansion devices, such as manual expansion valve and TXV.