Numerical simulation and validation of a stepped capillary tube using as throttling device in residential heat pump systems

作者：Garcia Valladares O^*

来源：Applied Thermal Engineering, 2015, 84: 27-33.

DOI：10.1016/j.applthermaleng.2015.03.029

• Capillary tubes
• Refrigeration
• Two-phase flow
• Expansion devices
• New design

A stepped capillary tube is a new design proposed by Zhao et al. that consist of two serial-connected capillary tubes with different diameter as an alternative in order to reduce the manufacturing cost of the typical assembly of two capillary tubes and a by-pass check valve widely used to achieve different mass flow rates in residential heat pump systems.
In previous works, one-dimensional numerical modeling of fluid-flow inside capillary tubes and short tube orifices were performed, and successfully validated against a wide range of mass flow rate measurements reported for different refrigerant and mixtures. In this article, the model is applied to stepped capillary tubes (expansion devices). Governing equations (continuity, momentum, energy, and entropy) for describing the fluid flow have been solved by using a fully implicit step-by-step method. A numerical treatment has been codified for considering thermodynamic and flow transitions (subcooled liquid region, metastable liquid region, metastable two-phase region and equilibrium two-phase region). Sudden contraction and enlargement were also considered. A comparison and validation analyses of the simulation results were carried out by using mass flow rate experimental data (N-0 = 30), which have been recently reported in the literature for R-22. Linear relationships between mass flow rate (predicted) and experimental mass flow rate data were statistically demonstrated. Average deviation error of +/- 3.2% was consistently computed between numerical model and experimental data, which demonstrates the good capability of the model developed for predicting the fluid flow processes.
These results demonstrate a new and robust application of the model developed to predict reliably the mass flow rate through stepped capillary tubes, which enable this tool to be reliably used for the design of this kind of systems.

• 出版日期2015-6-5