A finite element model was used to estimate the refrigerant flow through flexible short-tubes for two refrigerants and three moduli of elasticity. The short-tubes were 14.5 mm (0.57 in.) in length with an inlet diameter of 2.06 mm (0.081 in.) and an outlet diameter of 2.46 mm (0.097 in.). The study included two refrigerants: R-134a and R-410a, and short-tubes with three moduli of elasticity: 5513, 7084, and 9889 kPa (800, 1025, and 1434 psi). A finite element model was developed using a commercially available software package. The model captured deformation by coupling the fluid/short-tube structural interaction in the shorttube. Upstream pressures were set to correspond to typical condensing temperatures for each refrigerant. The upstream subcooling was held at a constant value of 16.7°C (30°F).

The model estimated tube deformation and refrigerant flow as a result of upstream pressure changes. The internal short-tube shape resembled the shape of a converging-diverging nozzle. A chamfered-like shape was seen at both the inlet and outlet of the short-tube. This shape reduced the large pressure drop at the vena contracta downstream of the tube inlet found in rigid short-tubes. However, flexible short-tubes showed a second pressure drop at approximately 4 mm (0.157 in.) from the inlet of the tubes. This second pressure drop was a consequence of the tube deformation and increased as the modulus of elasticity decreased. For a condensing temperature of 46°C (129°F), the operating upstream pressure of R-410a was 140% higher than that of R-134a. R-410a had a larger tube
deformation than that of R-134a.

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