Experimental investigation of near-critical CO 2 tube-flow and Joule–Thompson throttling for carbon capture and sequestration Farzan Kazemifar a,b , Dimitrios C. Kyritsis a,b,c,⇑ a Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 W. Green St., Urbana, IL 61801, USA b International Institute for Carbon Neutral Energy Research (WPI-I 2 CNER), Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan c Khalifa University of Science Technology and Research, Abu-Dhabi, UAE article info Article history: Received 30 July 2013 Received in revised form 28 November 2013 Accepted 28 November 2013 Available online 11 December 2013 Keywords: Carbon capture and sequestration Supercritical CO 2 Visualization Joule–Thomson throttling abstract Flow of CO 2 in the vicinity of its critical point was studied experimentally in two different flow configu- rations. First, a 60 cm long stainless steel pipe with 2.1 mm inner diameter was used to study near-critical CO 2 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 shadow- graphs 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. Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction Geological media and specifically depleted hydrocarbon reser- voirs and saline aquifers are the top candidates as storage sites for carbon sequestration [1,2]. Since most oil and gas reservoirs are not close to its primary sources, CO 2 needs to be transported in pipelines from the source to the storage site [1]. The transition from atmospheric pressure and high temperature of a flue gas stream to the low temperatures and high pressures of transport and storage can potentially pass near the critical point of CO 2 at 73.8 bar and 31 °C. Also, depending on reservoir pressure and tem- perature, which are determined by the geological characteristics of the site, CO 2 can be stored as supercritical fluid, liquid, or compressed gas [1]. CO 2 flow in the vicinity of its critical point is thus of particular interest because of the abrupt changes in thermophysical and transport properties in this region. Even small fluctuations in pressure and temperature can affect the fluid properties, and hence the flow behavior. Studying of two-phase CO 2 flow has gained attention in the past two decades due to the increased popularity of CO 2 as a refrigerant [3,4]. Heat transfer and flow of supercritical CO 2 in pipes and chan- nels have been studied in transcritical refrigeration cycle applica- tions where heat rejection takes place at a supercritical state [5,6]. Similar studies have also been performed in the context of nu- clear reactor cooling systems [7–9]. In these studies, the main focus was the determination of the heat transfer coefficient. However, an investigation of the underlying flow fundamentals is still missing. In terms of flow visualization, the only relevant previous works were conducted by Pettersen [10] and Yun and Kim [11]. Pettersen studied two-phase flow patterns of CO 2 during vaporization in a horizontal glass tube at 0 °C and 20 °C (corresponding saturation pressure: 3.5 MPa and 5.7 MPa). Yun and Kim studied the flow boiling of CO 2 in a horizontal narrow rectangular channel at 4.0 MPa (corresponding saturation temperature: 5.3 °C). These pressures and temperatures are relevant to the evaporation process in air-conditioning systems. In both studies, high-speed visualization was employed to study the distribution of the two phases in the flow. Distinct flow regimes were identified and flow pattern maps were created based on quality (vapor mass fraction) and mass flux. The thermodynamic state of the fluid in these studies was relatively far from the critical point and thus may not represent the behavior of the flow of a ‘‘near-critical’’ fluid. 0894-1777/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.expthermflusci.2013.11.026 ⇑ Corresponding author at: Khalifa University of Science Technology and Research, Department of Mechanical Engineering, Al Saada Street, Abu Dhabi 127788, UAE. Tel.: ++971 2 4018168; fax: ++971 2 4472442. E-mail address: kyritsis@illinois.edu (D.C. Kyritsis). Experimental Thermal and Fluid Science 53 (2014) 161–170 Contents lists available at ScienceDirect Experimental Thermal and Fluid Science journal homepage: www.elsevier.com/locate/etfs