A one dimension homogeneous steady model of adiabatic capillary tubes in CO

2

transcritical refrigeration systems was established to evaluate the performance and the flow characteristics of capillary tubes. The simulation results by using three different friction factor correlations(Churchill

Colebrook

Bittle

&

Pate)were compared with each other. The distributions of temperature

pressure

enthalpy and entropy along the tube length were investigated. The influences of four parameters(inner diameter

inlet pressure

inlet temperature

back pressure)on the mass flow rate were explored

and the chocking phenomenon was analyzed. The results show that the Churchill correlation and the Colebrook correlation predict 92% of the refrigerant mass flow rates with

an error of less than 10% while the Bittle

&

Pate correlation may be unsuitable for simulating the flow in CO

2

capillary tubes due to its neglect of the inner wall roughness of capillary tubes. The back pressure has slight influence on the mass flow rate. In addition

the rate of mass flow without chocking is approximately equal to that with chocking.