A mechanism by which light-weight heaters can more effectively boil water is identified by researchers in the USA. Increasing the rate at which a fluid is heated is hampered by the formation of a layer of vapor on the surface of a heater, which prevents heat flow. This is particularly problematic for small heaters such as those required in space applications. Boris Khusid and his colleagues from the New Jersey Institute of Technology now demonstrate a new boiling regime that takes advantage of an air-vapor bubble that forms on a smaller heater. This bubble drives cold water to the surface and improves the flow of heat. This effect was investigated both under normal gravity and in a low-gravity environment created by parabolic flights, with gravity exhibiting only a negligible influence on the rate of heat transfer.
Research Highlights: Physical Sciences
Explore our collection of research highlights in the physical sciences from npj Microgravity. The collection includes articles on engineering, physics, and materials science.
To support oil and gas exploration, researchers sent hydrocarbon mixtures into space to obtain accurate data on how each component behaves. The group—led by Guillaume Galliero from the University of Pau and Pays de l’Adour, France—wanted to study the effect of temperature on the movement of individual hydrocarbons in mixtures under typical reservoir conditions. Eliminating the effects of gravity allowed them to collect more accurate data than has previously been obtained. The team showed that thermodiffusion has a large impact on the distribution of hydrocarbon reservoirs under the ground. They state that thermodiffusion should therefore be considered in computer models that assess analytical data collected at potential underground reservoirs. This would allow oil and gas companies to more accurately predict the suitability of the hydrocarbons at potential drilling sites.
Swing-like pool boiling on nano-textured surfaces for microgravity applications related to cooling of high-power microelectronics
As microelectronics get smaller, there is an urgent need to develop efficient methods to keep them cool without extra power input. Under normal gravity, excess heat can be removed by vapor bubbles rising through a coolant. In space however, due to the lack buoyancy force, vapor bubbles remain attached to the submerged heater and prevent heat removal. Prof. Alexander Yarin, at the University of Illinois at Chicago, and his team show that in heaters mimicking high-power microelectronics, the thrust of vapor bubble release (the vapor recoil force, which exists irrespective of gravity) helps shedding merger vapor bubbles by generating a swing-like motion of the heater. Moreover, they demonstrate how nanofiber coatings can increase heat transfer by providing more bubble nucleation sites, and thus enhance the swing-like motion.
US scientists are developing and testing an instrument for trapping and cooling ultracold atoms in preparation for the launch of the device to the International Space Station (ISS). Quantum mechanical effects are enhanced at temperatures near absolute zero, and the microgravity conditions of the ISS will allow atom traps to decompress to a new regime of picokelvin temperatures and ultra-low densities. David Aveline and colleagues from the Jet Propulsion Laboratory at the California Institute of Technology present a status of the Cold Atom Lab (CAL) instrument’s ground development and test progress. The team demonstrates the system capabilities by creating Bose-Einstein condensates of rubidium atoms with microwave-based evaporative cooling and quantum gas mixtures of rubidium and potassium in a magnetic trap formed by current carrying wires on a compact chip.
Microgravity provides a better environment to study how grains move when agitated, scientists in Germany show. Philip Born and co-workers from the Institute of Materials Physics in Space demonstrate that microgravity analogue conditions enable studies on particle dynamics at packing densities not achievable on the ground. Dense granular media under external agitation tends to partially arrest on the ground due to particle collision and settling caused by gravity. This diverseness of the medium makes it hard to develop a theory that can describe the general behavior. Born and colleagues use diffusing-wave spectroscopy to compare the spatial homogeneity and microscopic dynamics of granular media on the ground and in drop towers. They show that unlike on the ground, granular media in microgravity conditions can reach a homogeneous state without partial arrest at high packing densities.
Retained free energy as a driving force for phase transformation during rapid solidification of stainless steel alloys in microgravity
A model that describes the atomic-structure changes in a steel alloy as it rapidly changes from a molten to a solid state is developed by a scientist in the USA. Steel solidifies very quickly after being welded, during which process the atomic structure of the solid alloy can change multiple times. For example, an alloy of iron, chromium and nickel transforms from a ferrite atomic structure to one known as austenite. Classical nucleation theory does not explain this so-called double recalescence. Douglas Matson at Tufts University has developed a novel physical model to describe this microstructural evolution that is based on viewing the transformation as an accumulation of defects. The model predicts the time delay of the transformation, which Matson compares to observed values determined by microgravity experiments.
Faraday forcing of high-temperature levitated liquid metal drops for the measurement of surface tension
A novel method for measuring the surface tension of droplets of liquid metal is developed by researchers in the USA and Japan. Many of the techniques used to investigate the properties of an interface between liquid and air are not applicable to very high temperature fluids. The method now demonstrated by Nevin Brosius, Kevin Ward, and Ranga Narayanan from the University of Florida and collaborators from NASA and Japanese Aerospace Exploration Agency (JAXA), which they call Faraday forcing, employs a continuous periodic electrostatic force that causes a levitating drop to vibrate. The amplitude of these vibrations reaches a maximum when the driving frequency equals the natural frequency of the drop. This value can then be used to calculate the surface tension. The team demonstrate the viability of their technique with pure zirconium and an alloy of titanium, zirconium, and nickel.
Gravity is shown to influence the shape of a small drop of water on a surface in a theoretical model developed by a researcher in Germany. Alfredo Calvimontes from BSH Hausgeräte GmbH demonstrates the importance of the droplet geometry in determining the interfacial energies. Surface tension strongly influences a water drop’s shape, but it was thought that gravity played little role for very small drops. However, recent experimental work has suggested that this might not be true. Calvimontes develops a theoretical model that differs from the conventional approach of the two hundred- years-old Young’s equation in that it assumes a thermodynamic equilibrium of the interfaces, rather than a balance of forces, on the solid-liquid-gas contour line. The model was supported by high-speed-camera images of droplets on various surfaces in free fall using a three-meter drop tower that allows quantifying the change of shape from normal gravity to microgravity.
A way to measure the motion of tiny particles of different sizes on the International Space Station is developed by researchers in the USA. Jacinta Conrad, Peter Vekilov, and their colleagues from the University of Houston demonstrate that this can be achieved using a technique called differential dynamic microscopy. Colloidal systems can contain particles of a wide variety of sizes, all moving at different rates. Conrad and the team demonstrate that differential dynamic microscopy has the ability to resolve the motion of polystyrene particles of two different sizes suspended together in water. The equipment required for their experiment is readily available on the International Space Station, and so the approach could help to better understand how potentially a microgravity environment affects complex dynamics in a variety of systems.