Numerical Simulation of Capillary-Tube Behaviour Working With Pure and Mixed Refrigerants Under Adiabatic and Non-Adiabatic Flow Conditions

Abstract

Abstract A detailed numerical method for analysing the thermal and fluid-dynamic behaviour of capillary tube expansion devices working with pure refrigerants and mixtures has been developed by means of a one-dimensional analysis of the governing equations (continuity, momentum and energy). Metastable both liquid and two-phase regions have been taken into account. The discretized governing equations are coupled using an implicit step by step method. In order to minimise computational cost, a special treatment has been implemented to solve the control volume that contains transition between regions and a special mesh distribution has been used. All the flow variables together with the thermophysical properties are evaluated at each point of the grid in which the domain is discretized. The numerical model allows analysis of aspects such as geometry, type of fluid, critical or non-critical flow conditions, metastable regions, adiabatic or non-adiabatic capillary tubes and transient aspects. The accuracy of the detailed simulation model is demonstrated by comparison with experimental data from the technical literature for adiabatic capillary tubes and also for concentric capillary tube-suction line heat exchanger.