The present research aims at buildingof a mathematical model using (Engineering Equation Solver) (EES) software to analyze the flow of the refrigerant R134a into two configurations of adiabatic capillary tubes (straight and helical coiled tubes) which are used widely in a household refrigerator, freezer and water cooler. The governing equations which depend on the conservation of mass, momentum, and energy have been coded in order to calculate the length of the single-phase flow region. Moreover, the two-phase regionhasbeen divided numerically depending on homogenous flow assumption after determining the boundary conditions and calculating the physical variables at each point of the numerical divisions by using successive substitution method using iteration loops. Finite difference scheme, the length of thetwo-phase region and the total length for the capillary tube have also been determined. The results show that the behavior of the flow is similar for both forms with regard to the distribution of variables (pressure and temperature drop, dryness fraction, velocity and entropy) over the whole length , while the helical coiled tube length for all cases is shorter than the straight tube at the same conditions. The main parameters that affect the size of capillary tube and the behavior of refrigerant through it have been shown. The tube length increased with the increase of (condenser temperature, degree of sub-cooling and tube diameter) and decreased with the increase of mass flow rate and roughness. The helical tube length increased by increasing coil diameter and coil pitch . The results of the present study agree with the experimental data of previous works with error not exceeding ±10% .
Keywords : Adiabatic capillary tube, Household refrigerators, R134a, EES, Helical, Two-phase flow.