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Modeling of flow along adiabatic capillary tubes - comparison between transient and Quasi-Steady models

Grant number: 14/02934-3
Support type:Scholarships in Brazil - Scientific Initiation
Effective date (Start): April 01, 2014
Effective date (End): September 30, 2014
Field of knowledge:Engineering - Mechanical Engineering
Principal Investigator:André Luiz Seixlack
Grantee:José Augusto Ignácio da Silva
Home Institution: Faculdade de Engenharia (FEIS). Universidade Estadual Paulista (UNESP). Campus de Ilha Solteira. Ilha Solteira , SP, Brazil

Abstract

Capillary tubes are expansion devices extensively used in small refrigeration and air conditioning systems. It is proposed in this research project the steady state adiabatic flow simulation along capillary tubes, from the numerical solution of the governing equations: mass conservation, momentum and energy conservation. The flow is divided in a single-phase region, where the refrigerant is in the subcooled liquid state, and a region of two-phase flow. The capillary tube is considered straight and horizontal. The analysis of the dynamic behavior of the flow is significant since the capillaries tubes are used in refrigeration systems generally controlled by on-off method. The flow is taken as one-dimensional and is divided in a single-phase region, where the refrigerant is in the subcooled liquid state, and a region of two-phase flow. The capillary tube is considered straight, horizontal, with constant diameter and the metastable flow phenomena are neglected. The homogeneous model is employed for the two-phase flow region. The system of differential equations is solved using a 4th order Runge-Kutta method. It is proposed to evaluate aspect of the steady and transient flow regimes and compare the results with experimental data available in the literature and with those calculated by other authors. It is also proposed to evaluate the influence of the transient terms of the governing equations, comparing the results obtained with the transient quasi-steady model, on which the dynamic behavior is defined only by the time variation of the boundary conditions.