Capillaries are important throttling elements widely used in small cooling and heating devices. R32 is an environmentally friendly refrigerant and is extensively employed in household air conditioning. In this study

a mathematical model of adiabatic capillary tubes was first developed on the basis of homogeneous flow

energy conservation

momentum conservation

and mass conservation equations. The model affords a formula for calculating the capillary lengths in the subcooling and two-phase regions. The concept of choked flow was introduced into the model

and the critical flow was used to assess whether choked flow occurred. The incorporation of the choked flow concept improved the accuracy and stability of the model. Next

a capillary tube test platform using R32 was built to verify the accuracy of the simulation model. The mass flow rates of two capillary tubes with an inner diameter of 1 mm and lengths of 0.5 and 1 m under a condensing pressure of 2.4–3.2 MPa and a subcooling degree of 5–20 °C were obtained. Finally

a nomogram of the R32 capillary was drawn using extensive data points obtained from the simulation model.