- Published on 15 July 2019
Numerical simulations of the thermodiffusion effect within falling film absorbers reveal that thin films composed of liquid mixtures with negative thermodiffusion coefficients enhance the efficiency of heat recycling
Absorption heat transformers can effectively reuse the waste heat generated in various industries. In these devices, specialised liquids form thin films as they flow downward due to gravity. These liquid films can absorb vapour, and the heat is then extracted by a coolant so that it can be used in future processes. So far, however, there has been little research into how the performance of these films is influenced by the thermodiffusion effect – a behaviour seen in mixtures, where different types of mixture respond differently to the same temperature gradient. In a study recently published in EPJ E, researchers from the Fluid Mechanics group at Mondragon University and Tecnalia in Spain, led by M. M. Bou-Ali at Mondragon University, pooled their expertise in transport phenomena and absorption technology. Together, they explored for the first time the influence of the thermodiffusion property on the absorption, temperature and concentration profiles of falling films.
- Published on 11 July 2019
Diffusive processes are ubiquitous in daily life and in natural processes, playing a key role in the transformation and mixing of fluid mixtures, and there is considerable scientific and industrial interest in such mixing processes. One consequence of diffusion is the development of non-equilibrium fluctuations in liquid mixtures, particularly when fluids are exposed to a thermal gradient. This is easier to observe in weightlessness, as gravity dampens this phenomenon on Earth especially for large fluctuations.
- Published on 28 June 2019
Active fluids are living matter or biologically inspired systems, consisting of self-propelled units that burn stored or ambient energy and turn it into work, eventually giving rise to systematic movement. In a new Topical Review paper published in EPJE, authors from groups in Bari (University of Bari, INFN, and the Istituto Applicazioni Calcolo, CNR) and the Center for Life Nano Science, La Sapienza, Rome describe the use of Lattice Boltzmann Methods (LBM) in the study of large scale properties of active fluids.
- Published on 04 June 2019
Hydrocarbons trapped within porous media are easier to model with computer simulations than researchers previously assumed – a discovery that opens up new possibilities for thermodynamics research.
Hidden deep below our feet, petroleum reservoirs are made up of hydrocarbons like oil and natural gas, stored within porous rock. These systems are particularly interesting to physicists, as they clearly show how temperature gradients between different regions affect the gradients of fluid pressures and compositions. However, because these reservoirs are so hard to access, researchers can only model them using data from a few sparse points, meaning many of their properties can only be guessed at. In a new study published in EPJ E, physicists from France and Vietnam, led by Guillaume Galliero at the University of Pau, have found that this guesswork actually isn’t necessary. They show that if the right choices are made when constructing models, no assumptions are needed in order to calculate the impact of temperature gradients on pressure and composition gradients.
- Published on 03 June 2019
The orientation of the ordered molecules that make up nematic liquid crystals can change under electric fields, and can be used to detect subtle electrical effects.
You may not know it, but you probably spend several hours a day looking at nematic liquid crystals; they are used in virtually every smartphone, computer and TV screen. They are liquids composed of elongated molecules, which in some situations can be oriented in a curious way termed the 'dowser texture', which is sensitive to external conditions. Physicists Pawel Pieranski of the Universite Paris-Sud, Paris, France and Maria Helena Godinho of Universidade Nova de Lisboa, Lisbon, Portugal have now published a paper in EPJ E that shows that the dowser texture responds to electric fields in different ways in different nematic materials.
- Published on 08 May 2019
A new study suggests the pattern of fibres in tissues is similar to the petals of a flower
Collagen fibrils are a major component of the connective tissues found throughout the animal kingdom. The cable-like assemblies of long biological molecules combine to form tissues as varied as skin, corneas, tendons or bones. The development of these complex tissues is the subject of a variety of research efforts, focusing on the steps involved and the respective contributions of genetics and physical chemistry to their development. Now, two researchers at the Universite Paris-sud in Orsay, France, have shed new light on how complex collagen fibrils form. In a new study published in EPJ E, the authors focus on one of the hierarchical steps, in which molecules spontaneously associate in long and dense axisymmetric fibres, known as type I collagen fibrils.
- Published on 26 April 2019
A new model of red blood flowing through narrow capillaries shows that the cells change shape and alignment, allowing plasma to flow down the sides
Blood consists of a suspension of cells and other components in plasma, including red blood cells, which give it its red colour. When blood flows through the narrowest vessels in the body, known as the capillaries, the interactions between the cells become much more important. In a new study published in EPJ E, a team of researchers led by Ignacio Pagonabarraga from the University of Barcelona, Spain, has now developed a mathematical model of how red blood cells flow in narrow, crowded vessels. This could help design more precise methods for intravenous drug delivery, as well as 'microfluidic chips' incorporating artificial capillaries, which could offer faster, simpler and more precise blood-based diagnoses.
- Published on 03 April 2019
Using computational models to investigate how liquid drops behave on surfaces
Whether we're aware of it or not, in day-to-day life we often witness an intriguing phenomenon: the breakup of jets of liquid into chains of droplets. It happens when it rains, for example, and it is important for inkjet printers. However, little is known about what happens when a liquid jet, also known as a liquid filament, breaks up on top of a substrate. According to a new study, the presence of a nearby surface changes the way the filament breaks up into smaller droplets. In a new paper published by Andrew Dziedzic at the New Jersey Institute of Technology in Newark, New Jersey, USA, and colleagues in EPJ E, computer simulations are used to show that a filament is more likely to break up near a surface.
EPJ E Topical Review: Gyrotactic phytoplankton in laminar and turbulent ﬂows: A dynamical systems approach
- Published on 20 March 2019
Biological and geophysical fluids host a sea of microorganisms many of which are motile. An often overlooked aspect of the life of such microorganisms is that the fluids where they are suspended are not still but flowing. In this brief review published in EPJ E, the authors aim to describe some of the interesting phenomena that can emerge due to the modification of the microorganisms' swimming direction by velocity gradients, which affect both the individual motion of microorganisms and their spatial distribution in dilute suspensions.
- Published on 06 February 2019
Moving around small objects using capillary forces is a phenomenon that has stimulated scientists trying to understand the fundamental mechanisms at play. It is also important for many industrial, technological and analytical processes, for example micro-fluidics, oil and gas displacement, mineral flotation, miniature robot and biomechanics. In this EPJ E topical review article Jianlin Liu and Shanpeng Li present a critical review of capillarity-driven migration in which many examples are presented and explained. The small objects in question are non-deformable objects, such as particles, rods, disks and metal sheets as well as soft objects, such as droplets and bubbles. The authors clarify some misunderstandings on the conventional views on these systems.