capillary, expansion, isobutane, homogeneous, parameter
In this work a homogenous capillary tube model using R600a (isobutane) as refrigerant is presented. The capillary tube model underlies common restrictions; it is assumed to be adiabatic, straight with constant cross section and operates under steady state conditions. Different empirical correlations for friction and two-phase-viscosity are applied, and the resulting mass flow rates for given boundary conditions are compared with experimental data, available in open literature. The computational scheme comprises cell-wise iterative solution of conservation equations for mass, momentum and energy on a non-uniform, one-dimensional grid. Invariability-studies follow, where the number of computational cells is varied and the impact on the mass flow is investigated. In a next step, parameter variations of length, diameter, wall roughness, subcooling, inlet pressure, outlet pressure, friction laws, viscosity relations and the influence of gravity are investigated under different working conditions (choked and non-choked) with respect to the mass flow.