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Anthropogenic release of carbon dioxide (CO2) is a major contribution to manmade increase in global warming. Carbon capture and storage (CCS) is a necessary technology for lowering CO2 emissions to an acceptable level that limits global warming to below 2 °C. Liquefaction of CO2 is a key process both in capture technologies and in conditioning before ship transport. The efficiency of this process can be remarkably enhanced by promoting dropwise CO2 condensation on cooling surfaces, yet this remains largely unexplored. Here, using molecular dynamics (MD) simulations, we report for the first time the contact angle and condensation behavior of CO2 droplets on a smooth solid surface. The contact angle of the condensed CO2 droplet is greatly dependent on the CO2–solid characteristic interaction energy, but this does not hold true for the sum of condensed molecules. In contrast, the sum of condensed molecules for the filmwise condensation regime increases monotonically at first, but then remains constant as the...

Phase-change processes such as condensation are efficient means of heat transfer. However, condensation is also an energy-intensive process and extensive research is conducted to increase the heat transfer efficiency. Increasing the effective heat transfer area in terms of surface structures on macro or microscale is one such technique of heat transfer enhancement. In this work, we have studied micro- and nanostructured surfaces for their potentials in increasing heat transfer during condensation of CO2. Three Cu-based surfaces on which CuO nanoneedles have been grown, have been investigated. We hypothesize three competing mechanisms govern the overall heat transfer on structured surfaces: 1) increased heat transfer area, 2) lower thermal conductivity of oxides, and 3) condensate flooding of the structures. Our study has shown that in some cases, the effect of these mechanisms can be neutralized. More importantly, the results show that superior heat transfer can be achieved by optimizing the surface structure. The best of the structured surfaces resulted in a heat transfer coefficient 66% higher than that of the unstructured surface. This is an open access article distributed under the terms of the Creative Commons CC-BY license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Understanding condensation of CO2 is essential for e.g designing compact heat exchangers or processes involved in Carbon Capture and Storage. However, a consistent experimental campaign for condensation of CO2 on common materials is lacking. In this work, we present an experimental method and an associated laboratory setup for measuring the heat transfer properties of CO2 condensation on materials commonly used in heat exchangers for the liquefaction of CO2. We have investigated the heat transfer during CO2 condensation on copper, aluminum, stainless steel (316) to reveal the heat transfer dependency on surface properties. The experiments are conducted at three saturation pressures, 10, 15, and 20 bar and at substrate subcooling between 0 and 5k. The results show that the heat transfer coefficients decrease with increasing surface subcooling. It was also found that increasing the saturation pressure increases the heat transfer coefficient. The results indicate that surface roughness and surface energy affect the condensation heat transfer coefficient, and an increased roughness results in reduced heat transfer coefficients. The highest heat transfer coefficient is found for condensation on copper, for which the lowest surface roughness has been measured.

CO2 capture by dropwise CO2 condensation on cold solid surfaces is a promising technology. Understanding the role of the nanoscale surface and topographical features of CO2 droplet wetting characteristics is of importance for CO2 capture by this technology, but this remains unexplored as of yet. Here, using large-scale molecular dynamics (MD) simulations, the contact angle and wetting behaviors of CO2 droplets on pillar-structured Cu-like surfaces are investigated for the first time. Dynamic wetting simulations show that, by changing the strength of the solid-liquid attraction [Formula: see text] a smooth Cu-like surface offers a transition from CO2-philic to CO2-phobic. By periodically pillared roughening of the Cu-like surfaces, however, a higher contact angle and a smaller spreading exponent of a liquid CO2 droplet are realized. Particularly, a critical crossover of CO2-philic to CO2-phobic can appear. The wetting of the pillared surfaces by a liquid CO2 droplet proceeds non-uniformly. A liquid CO2 droplet is capable of exhibiting a transition from the Cassie state to the Wenzel state with increasing [Formula: see text] increasing inter-pillar distance, and increasing pillar width. The wetting morphologies of the metastable Wenzel state of a CO2 droplet are very different from each other. The findings will inform the ongoing design of CO2-phobic solid surfaces for practical dropwise condensation-based CO2 capture applications.

Liquefaction of vapor is a necessary, but energy intensive step in several important process industries. This review identifies possible materials and surface structures for promoting dropwise condensation, known to increase efficiency of condensation heat transfer. Research on superhydrophobic and superomniphobic surfaces promoting dropwise condensation constitutes the basis of the review. In extension of this, knowledge is extrapolated to condensation of CO2. Global emissions of CO2 need to be minimized in order to reduce global warming, and liquefaction of CO2 is a necessary step in some carbon capture, transport and storage (CCS) technologies. The review is divided into three main parts: 1) An overview of recent research on superhydrophobicity and promotion of dropwise condensation of water, 2) An overview of recent research on superomniphobicity and dropwise condensation of low surface tension substances, and 3) Suggested materials and surface structures for dropwise CO2 condensation based on the two first parts. This is a submitted manuscript of an article published by Elsevier Ltd in Advances in Colloid and Interface Science, 29 March 2018.

In the Enabling Low-Emission LNG Systems project, SINTEF Energy Research and NTNU have since 2009 been developing knowledge and tools with the aim to enable environmental safe, cost-effective, and energy efficient LNG processes. The project has employed a multilevel approach, where studies of fundamental phenomena, component modeling, and process optimization have been performed in parallel. Detailed models for two-phase flow in heat exchangers (HXs) have been developed, and falling films and droplet behavior relevant for LNG HXs have been studied experimentally. Further, the project work has generated robust and accurate HX models that can describe instabilities and include geometrical considerations. Finally, the project has improved the basis for optimization of LNG process through investigating of optimization tools and careful analysis and formulation of the optimization problem.

Liquefaction of vapor is a necessary, but energy intensive step in several important process industries. This review identifies possible materials and surface structures for promoting dropwise condensation, known to increase efficiency of condensation heat transfer. Research on superhydrophobic and superomniphobic surfaces promoting dropwise condensation constitutes the basis of the review. In extension of this, knowledge is extrapolated to condensation of CO

Accurate thermophysical data for the CO2-rich mixtures relevant for carbon capture, transport and storage (CCS) are essential for the development of the accurate equations of state (EOS) and models needed for the design and operation of the processes within CCS. Vapor-liquid equilibrium measurements for the binary system CO2 + O2 are reported at 218, 233, 253, 273, 288 and 298 K, with estimated standard uncertainties of maximum 8 mK in temperature, maximum 3 kPa in pressure, and maximum 0.0031 in the mole fractions of the phases in the mixture critical regions, and 0.0005 in the mole fractions outside the critical regions. These measurements are compared with existing data. Although some data exists, there are little trustworthy literature data around critical conditions, and the measurements in the present work indicate a need to revise the parameters of existing models. The data in the present work has significantly less scatter than most of the literature data, and range from the vapor pressure of pure CO2 to close to the mixture critical point pressure at all six temperatures. With the measurements in the present work, the data situation for the CO2 + O2 system is significantly improved, forming the basis to develop better equations of state for the system. A scaling law model is fitted to the critical region data of each isotherm, and high accuracy estimates for the critical composition and pressure are found. The Peng-Robinson EOS with the alpha correction by Mathias and Copeman, the mixing rules by Wong and Sandler, and the NRTL excess Gibbs energy model is fitted to the data in the present work, with a maximum absolute average deviation of 0.01 in mole fraction. Preprint submitted to Fluid Phase Equilibria

A new setup for the measurement of vapor-liquid phase equilibria of CO2-rich mixtures relevant for carbon capture and storage (CCS) transport conditions is presented. An isothermal analytical method with a variable volume cell is used. The apparatus is capable of highly accurate measurements in terms of pressure, temperature and composition, also in the critical region. Vapor-liquid equilibrium (VLE) measurements for the binary system CO2+N2 are reported at 223, 270, 298 and 303 K, with estimated standard uncertainties of maximum 0.006 K in the temperature, maximum 0.003 MPa in the pressure, and maximum 0.0004 in the mole fractions of the phases. These measurements are verified against existing data. Although some data exists, there is little trustworthy data around critical conditions, and our data indicate a need to revise the parameters of existing models. A fit made against our data of the vapor-liquid equilibrium prediction of GERG-2008/EOS-CG for CO2+N2 is presented. At 223 and 298 K, the critical region of the isotherm are fitted using a scaling law, and high accuracy estimates for the critical composition and pressure are found. © 2015 Elsevier B.V. All rights reserved. This is the authors' accepted and refereed manuscript to the article. Locked until 2017-09-25.

A facility designed for precise measurements of phase equilibria of CO2-rich mixtures relevant for CCS conditioning and transport is demonstrated. The setup aims for high accuracy in pressure, temperature, and composition measurements for pressures between 4 and 200 bar and temperatures between -60 and 150 °C. In this paper, the test measurement of the N2 / CO2 system in the vicinity of the critical point for CO2, have shown the ability to produce measurements with the high accuracy and repeatability in temperature, pressure and composition © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).