This page contains news about my research such as new publications, new project grants, happenings, collaborations, or other topics of significance which I think could be of interest to others.
Article about the spinodal and how it can be used in development of equations of state
Our paper entitled: The spinodal of single- and multi-component fluids and its role in the development of modern equations of state has been accepted for publication in Fluid Phase Equilibria. The spinodal represents the limit of thermodynamic stability of a homogeneous fluid. In this work, we present a robust methodology to obtain the spinodal of multicomponent fluids described even with the most sophisticated equations of state (EoS) available. We elaborate how information about the spinodal and its uncertainty can contribute both in the development of modern EoS and to estimate their uncertainty in the metastable regions. Inequality constraints are presented that can be exploited in the fitting of modern EoS of single-component fluids to avoid inadmissible pseudo-stable states between the vapor and liquid spinodals. We find that even cubic EoS violate some of these constraints. With the use of a selection of EoS representative of modern applications, we compare vapor and liquid spinodal curves, superheat and supersaturation limits from classic nucleation theory (CNT), and available experimental data for the superheat limit. Computations are performed with pure species found in natural gas, binary mixtures, as well as a multi-component natural gas mixture in order to demonstrate the scalability of the approach. We demonstrate that there are large inconsistencies in predicted spinodals from a wide range of EoS such as cubic EoS, extended corresponding state EoS, SAFT and multiparameter EoS. We demonstrate that a large part of the metastable domain of the phase diagram is currently unavailable to experiments (the area between the solid red (spinodals) and the green dashed lines (CNT) in the figure below, which shows the pressure of methane as a function of density and temperature). Novel techniques, experimental or with computational simulations, should be developed to characterize the thermodynamic properties in these regions, and to identify the thermodynamic states that define the spinodal. The work was performed in in collaboration with Peder Aursand, Magnus Aa. Gjennestad, Eskil Aursand and Morten Hammer from SINTEF Energy Research.
Popular scientific article about the magical reindeer nose
Our article on the energy efficient reindeer nose entitled: "The Nasal Geometry of the Reindeer Gives Energy-Efficient Respiration" has been picked up by several national media outlets such as Gemini, Teknisk Ukeblad, Forskning.no, Computerworld, and international media outlets such as Sciencedaily, Arabian Post (Newspaper in the United Arab Emirates) , Obwaldner Zeitung (Newspaper in Germany), DR (Broadcaster in Denmark), Before Its News, Daily Express (Newspaper in the UK), and several other webpages. The article has also received significant attention at twitter and facebook. We (the authors) are very happy for this!
Article about using thermoelectric generators for harnessing waste heat during metal casting
Our paper entitled: Exploring the potential for waste heat recovery during metal casting with thermoelectric generators: On-site experiments and mathematical modeling has been accepted for publication in Energy. Since casting of metals like silicon occurs at a very high temperature (about 1750 K), much heat disappears into the surroundings by radiation. Thermoelectric generators are scalable and simple systems that can be used to convert heat to electrical power by exploiting the coupling between transport of heat and electrical charge. In our work, we combined on-site measurements at Elkems silicon casting plant at Salten in Norway (see picture below) and a mathematical model to study the potential for power generation with this technology from heat available during casting of silicon. We implemented a bismuth-tellurium based thermoelectric generator in the casting area of a silicon plant. The measured peak power was 160 W/m2, however, we predicted a large potential to increase the power generated beyond the measured values. One of the main findings was the concept of "less for more", where a higher power output could be obtained by using fewer thermoelectric modules per surface area. This work is the first in an ongoing effort to understand the potential of thermoelectric generators in recovering waste heat, and how to optimize their performance. The work was performed in in collaboration with Marit B. Takla, Odne S. Burheim and Signe Kjelstrup from NTNU.
Article about ion selective membranes available
Our paper entitled: The Permselectivity and Water Transference Number of Ion Exchange Membranes in Reverse Electrodialysis has been accepted for publication in the Journal of membrane science. Ion exchange membranes are the main components of equipment to perform reverse electrodialysis, i.e. to produce electricity from the mixing of fresh-water (from rivers) and sea-water. In the article, we show that the water transference number of ion exchange membranes plays an important role in deciding their selectivity, and hence the efficiency of cells for reverse electrodialysis. We have measured the transport numbers of sodium, chloride and water in ion exchange membranes from Fumatech. Using the measured transport numbers, we demonstrate that a route to improve the selectivity of ion exchange membranes, and hence the performance of cells for reverse electrodialysis is to have a water transference number as close to zero as possible. This can possibly be achieved by constructing hydrophobic membranes. The work is an important step towards making saline power available, and was performed in collaboration with Agnieszka Zlotorowicz, Robin V. Strand, Odne S. Burheim and Signe Kjelstrup from NTNU.
Article about the amazing reindeer nose available online
Our paper entitled: "The Nasal Geometry of the Reindeer Gives Energy-Efficient Respiration" has been accepted for publication in the Journal of nonequilibrium thermodynamics. In the article, we show that the complicated geometry and internal structure of the nose of arctic reindeer help them to survive in the harsh arctic climate by making breathing more energy-efficient. In particular, we found that in comparison to a simple "cylindrical-like" reference nose (similar to that of humans), the reindeer nose became increasingly more efficient the lower the temperature got. The work was a combination of theory and experiments, in which we developed and solved a distributed, time-dependend mathematical model of the reindeer nose with input from experiments and measurements on a real reindeer nose. The work was done in collaboration with Elisa Magnanelli and Signe Kjelstrup at NTNU, and Mario Acquarone and Lars. P. Folkow at the department of Arctic and Marine Biology at the University of Tromsø.
Employed part-time as Professor at NTNU
I have now started to work as a part-time Professor (called Professor II in Norway) at the Department of Electrical Engineering and Renewable Energy at NTNU. I am employed in a strategic research area called ENERSENSE, which has focus on the nexus of energy efficiency, energy storage and sensor technologies, including automation. My position is within process systems engineering with emphasis on energy efficiency. I look very much forward to embark on the duties as well as the possibilities that come with this position.
Received prize for best PhD thesis
I received the prize for the best PhD thesis at the faculty of natural sciences at NTNU, 2016. I am very honored by this. Unfortunately, I was abroad and could not receive the prize myself. Fortunately, my good friend and close colleague Dr. Anders Lervik received the prize on my behalf (the good-looking guy in the middle of the picture below).
Paper about transport across the water interface receives attention in media
Our article on how to describe transport of heat and mass across the vapor-liquid interface of water entitled: "Coherent description of transport across the water interface: From nanodroplets to climate models" has been picked up by several national media outlets such as Gemini, Teknisk Ukeblad, Forskning.no, as well as international media outlets such as Sciencedaily, Nanotechnology now, Phys.org, Terradaily, Science magazine, Chemeurope (German), and several other webpages. The article has also received significant attention at twitter and facebook. We (the authors) are very happy for this!
Our article was selected to be Editors choice in J. Chem. Phys. for 2015!
The Journal of Chemical Physics is, in my opinion, the best "regular" journal to publish research on topics within chemical physics. A total of 2544 articles, communications, perspectives etc. were published there in 2015. Among these, our paper entitled "Tolman length and rigidity constants of the Lennard-Jones fluid" was chosen as one out of 65 articles to be the Editors choice for 2015! This work was performed in collaboration with Prof. David Reguera at the University of Barcelona in Spain and Prof. Dick Bedeaux from NTNU in Norway. According to the Journal of Chemical Physics , this means that our paper has been hand-selected by the editors as one of the most innovative and influential articles of 2015. In addition, the article is freely available to download through the end of 2016 and a short summary of the article will be published at the facebook page of J. Chem. Phys. All three of us are very happy and honored by this!
New paper accepted for publication in Phys. Chem. Chem. Phys.
Our paper entitled "Heat transport through a solid-solid junction: the interface as an autonomous thermodynamic system" has been accepted for publication in the journal, Physical Chemistry Chemical Physics. The work was performed in collaboration with Dr. Riccardo Rurali from the Materials Science Institute of Barcelona, Prof. Dr. Luciano Colombo from the Department of Physics at the University of Cagliari, Prof. Dr. Xavier Cartoixà from the Department of Electronic Engineering at the Autonomous University of Barcelona, and my national colleagues, Dr. Thuat T. Trinh, Prof. Dr. Dick Bedeaux and Prof. Dr. Signe Kjelstrup from NTNU. In the work, we demonstrate with nonequilibrium molecular dynamics simulations that the interface of a nanowire solid-solid junction can be considered to be an autonomous system at local equilibrium. In the paper, we show this for the first time for an interface between two solids. The practical consequence of this is that the Kapitza resistance (rK) of a solid-solid junction can be regarded as an interfacial property. For the nanowire junction, this means that we can tabulate the Kapitza resistance as a function of only the surface temperature, (TS) and the Kapitza resistance is thus independent of the applied thermal bias. The figure below shows the Kapitza resistance of a nanowire junction as a function of the surface temperature for many applied thermal biases.
New paper accepted for publication in the J. Membr. Sci.
Our paper entitled "Enhancing the understanding of heat and mass transport through a cellulose acetate membrane for CO2 separation" has been accepted for publication in the Journal of membrane science.The work has been done in collaboration with PhD candidate Elisa Magnanelli, whom I am co-supervising together with Dr. Eivind Johannessen (Statoil) and Prof. Signe Kjelstrup (NTNU). In the paper, we present a detailed theoretical model to describe heat and mass transport across a cellulose acetate membrane for CO2 separation. Some of our findings contradict previous results in the literature, in that we document that the Joule-Thomson effect gives a negligible transmembrane temperature drop. However, The accumulated Joule-Thompson effect can be significant along the membrane unit. We use nonequilibrium thermodynamics to account for coupling between heat and mass fluxes in the system. In conventional membranes, the support limits the possibility of using a temperature difference to enhance the performance. With thinner or better conductive support layers, we estimate that is possible to exploit coupling effects to enhance both permeation and selectivity by 14% and 8% respectively with a transmembrane temperature difference of 20 K. The possibility of using a thermal driving force to enhance the membrane performance is appealing, as a large amount of waste heat is typically available at the natural gas extraction site.
New paper accepted for publication in Phys. Rev. E
Our paper entitled "Coherent description of transport across the water interface: From nanodroplets to climate models" has been accepted for publication in Physical Review E. The work has been done in collaboration with Dr. T. T. Trinh, Dr. A. Lervik, Prof. S. Kjelstrup and Prof. D. Bedeaux, all from NTNU and Dr. V. K. Badam from India. In the paper, we have found the necessary coefficients to describe transport of heat and mass across the vapor-liquid interface of water with nonequilibrium thermodynamics. For the first time, one can now describe this transport across flat interfaces as well as across interfaces of bubbles and droplets or of water structures with complicated geometries. We believe the results can be used to improve weather forecasts and climate models and they represent a significant advance of the understanding and description of the water interfaces. The figure below shows an outline of how transport across the interface occurs.
New paper accepted for publication in J. Chem. Phys.
Our paper entitled "A new truncation correction for the configurational temperature extends its applicability to interaction potentials with a discontinuous force" has been accepted for publication in the Journal of Chemical Physics. The work has been done in collaboration with Prof. E. M. Blokhuis at the University in Leiden in the Netherlands, Dr. A. Lervik from NTNU and Dr. T. T. Trinh from NTNU. In the paper, we present a new truncation correction (triangles) for the configurational temperature which, unlike previous corrections (squares), works for the truncated and shifted LJ-potential within the accuracy of the simulations. The most important outcome of the work is that we show that the expression for the configurational temperature is valid also for interaction potentials with a discontinuous force, given that the discontinuity is properly taken into account. The figure below shows an example from the paper.
My PhD thesis defense
My PhD thesis entitled: "Equilibrium and Nonequilibrium Thermodynamics of Planar and Curved Interfaces" was successfully defended. The picture to the right was taken after the defense. From left to right: Prof. Bjørn Hafskjold (thesis administrator), Prof. Maria Fernandino (3rd Opponent), Prof. E. M. Blokhuis (2nd Opponent), me, Prof. D. Frenkel (1rst Opponent), Prof. S. Kjelstrup (my thesis advisor), Prof. D. Bedeaux (my thesis advisor).