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.
Magnus Aa. Gjennestad joins the team
Magnus Aa. Gjennestad, shown in the picture below, wants to understand how to more accurately describe multi-phase flow in porous media as well as their thermodynamic properties. Fluids in porous media can exist in a diverse set of heterogeneous structures such as adsorbed droplets, free droplets, films or bubbles. Thermodynamics can give answer to what configurations that are most likely to find, i.e. those that result in the lowest energy of the respective ensemble.
Magnus is also my colleague at SINTEF who is now on leave to pursue his PhD. We already have two articles together from our work at SINTEF, on the spinodals and present challenges with modern equations of state. Together with Prof. A. Hansen and Prof. S. Kjelstrup, I have now become part of his team of supervisors at the Porelab center of excellence in Trondheim. We are currently working hard to complete a first article that gives new and valuable insight into the rich heterogeneous phase state of pores.
Visitor from the University of Lorraine in France
The 24th of April, we were so fortunate to have visitors from the University of Lorraine in France, Prof. Jean Noël Jaubert and Ass. Prof. Silvia Lasala. In a seminar, they shared with us new insight on their recent research and progress on consistent alpha-correlations for cubic equations of state, classification of binary mixtures with the scheme of van Konynenburg and Scott, comparison of PC-SAFT and cubic equations of state and a consistent derivation of residual excess Helmholtz energy based mixing rules. Altogether, a very insightful and interesting seminar. A well deserved beer at Heidis Bier Bar at the "sunny-side" of Trondheim afterwards (see picture below). From the left, the picture shows Morten Hammer, myself, Jean Noël and Silvia.
New article gives insight about the highway
Our article entitled Minimum entropy generation in a heat exchanger in the cryogenic part of the hydrogen liquefaction process: On the validity of equipartition and disappearance of the highway has just been accepted for publication in the International Journal of Hydrogen Energy.
In the paper, we use optimal control theory to minimize the total entropy production of a heat exchanger in the cryogenic part of the hydrogen liquefaction process. The heat exchanger is also a reactor, as catalyst is placed in some of the layers to speed up to conversion between the two spin-isomers of hydrogen, ortho- and para-hydrogen.
In recent literature, there has been a discussion about whether it is beneficial to invoke a higher operation pressure than 20 bar in the hydrogen liquefaction process. Inspired by this discussion, we investigate two reference cases; one where the feed stream enters at 20 bar, and one where it enters at 80 bar. The optimal refrigeration strategies give a reduction of the total entropy production of 8.7% in the 20-bar case and 4.3% in the 80-bar case. The overall heat transfer coefficient and duty is higher in the 20~bar case, which compensates for the increase in entropy production due to a thermal mismatch that is avoided in the 80-bar case. This leads the second law efficiency of the 20-bar case (91%) to be similar to the 80 bar case (89%).
We demonstrate in the article that equipartition of the entropy production and equipartition of the thermal driving force are both excellent design principles for the process unit considered, with total entropy productions deviating only 0.2% and 0.5% from the state of minimum entropy production. We find that both heat transfer and the spin-isomer reaction contribute significantly to the entropy production throughout the length of the process unit. Unlike previous examples in the literature, the process unit considered in this work is not characterized by a ``reaction mode'' at the inlet followed by a ``heat transfer mode''. Therefore, it does not follow a highway in state space, i.e. a band that is particularly dense with energy efficient solutions. By artificially increasing the spin-isomer conversion rate, the highway appears when the conversion rate becomes sufficiently high (see figure below).
The work is an outcome of the thesis work of my previous Msc. student, Ragnhild Hånde from the Department of Physics (see picture below), who delivered her thesis last year. She is now working as a software developer.
Presenting about hydrogen liquefaction at the Cryogenics conference in Prague
This week, I was travelling to Prague in the Check Republic to the 15th Cryogenics conference together with two of my colleagues from SINTEF, Stian Trædal and David Berstad. Me and David were both presenting recent progress on technology related to liquefaction of hydrogen. David presented recent research from dynamic modelling of a liquid hydrogen loading cycle from onshore storage to a seaborne tanker (see picture below). The insight gained from this research will be very important to realize large-scale transport of liquid hydrogen, as the transport between tanks represents a critical part of the value-chain, with large potential for exergy losses if not done properly. I presented research performed together with my colleague, Geir Skaugen, on design and evaluation of novel, catalyst-filled spiral wound heat exchangers which hold the potential to further improve the efficiency in the bottom part of the hydrogen liquefaction process. A paper is under development on this topic.
Vilde Bråten will improve the understanding of thermodynamic for nano-systems in her PhD
Vilde Bråten started her PhD in the autumn of 2018. In her PhD, she will bring new insight on the thermodynamics of nano-systems. It is well known that the thermodynamics of nano-systems differs from bulk-behavior, and this is often referred to as finite-size effects. Thus far, the finite-size effects have been undesired e.g. in molecular simulations. However, with the introduction of nanotechnology comes the need to understand the behavior of small systems and these finite-size effects. In her PhD, Vilde will build on the work by T. Hill on the thermodynamics of small systems, and the ultimate aim is to develop thermodynamic methodology and understanding of molecular machines in order to explore the potential of these devices in technological and scientific applications.