Experimental investigation of near-critical CO₂ tube-flow and Joule-Thompson throttling for carbon capture and sequestration

Flow of CO₂ in the vicinity of its critical point was studied experimentally in two different flow configurations. First, a 60cm long stainless steel pipe with 2.1mm inner diameter was used to study near-critical CO₂ pipe flow. In terms of raw flow data, the results indicated high sensitivity of pressure drop to mass flow rate as well as to inlet conditions; i.e. pressure and temperature. Remarkably though, when friction factor and Reynolds number were defined in terms of the inlet conditions, it was established that the classical Moody chart described the flow with satisfactory accuracy. This was rationalized using shadowgraphs that visualized the process of transition from a supercritical state to a two-phase subcritical state. During the transition the two phases were separated due to density mismatch and an interface was established that traveled in the direction of the flow. This interface separated two regions of essentially single-phase flow, which explained the effective validity of the classical Moody chart. Second, Joule-Thomson throttling was studied using a 0.36-mm-diameter orifice. For conditions relevant to carbon capture and sequestration, the fluid underwent Joule-Thompson cooling of approximately 0.5°C/bar. The temperature difference during the cooling increased with increasing inlet enthalpy. Discrepancies with previous computed and experimentally measured values of Joule-Thompson throttling were discussed in detail.