Improved equation of CO2 Joule-Thomson coefficient

The Joule-Thomson coefficient is a key parameter in the calculation of temperature and pressure and the prediction of the phase state and physical parameters. However, owing to different temperature and pressure conditions, CO2 presents different states: vapor, liquid, supercritical, etc. A set of experimental apparatus for the measurement of the CO2 Joule-Thomson coefficient measurement of was designed, which accurately measures the Joule Thomson coefficient of CO2 in the ranges 283-423 K, 2-40 MPa. Based on the experimental results, the absolute average errors of the CO2 Joule-Thomson coefficient predicted by the state equations are relatively low in vapor and supercritical states, but larger errors appear near the CO2 critical point and liquid state. According to the study findings, the CO2 Joule-Thomson coefficient is affected by the phase and varies dramatically at vapor, liquid, and supercritical states. However, the commonly used CO2 Joule-Thomson coefficient prediction methods do not exhibit good accuracy at all phase states. In order to accurately predict the CO2 Joule-Thomson coefficient at different phase states, a 25-parameter CO2 Joule-Thomson coefficient prediction equation is proposed in a temperature range of 283-423 K and a pressure range of 2-40 MPa, which can accurately describe the drastic change near the critical point. The error analysis of the CO2 Joule-Thomson coefficient experimental data determined that the absolute average errors at the vapor, liquid, and supercritical states are 1.52%, 4.59% and 3.08%, respectively. This work is expected to facilitate the engineering applications of CO2.