Science Current Events | Science News | Brightsurf.com
 

Controlling heat flow with atomic-level precision

April 23, 2012
CHAMPAIGN, Ill. - Through a combination of atomic-scale materials design and ultrafast measurements, researchers at the University of Illinois have revealed new insights about how heat flows across an interface between two materials.

The researchers demonstrated that a single layer of atoms can disrupt or enhance heat flow across an interface. Their results are published this week in Nature Materials.

Improved control of heat exchange is a key element to enhancing the performance of current technologies such as integrated circuits and combustion engines as well as emerging technologies such as thermoelectric devices, which harvest renewable energy from waste heat. However, achieving control is hampered by an incomplete understanding of how heat is conducted through and between materials.

"Heat travels through electrically insulating material via 'phonons,' which are collective vibrations of atoms that travel like waves through a material," said David Cahill, a Willett Professor and the head of materials science and engineering at Illinois and co-author of the paper. "Compared to our knowledge of how electricity and light travel through materials, scientists' knowledge of heat flow is rather rudimentary."

One reason such knowledge remains elusive is the difficulty of accurately measuring temperatures, especially at small-length scales and over short time periods - the parameters that many micro and nano devices operate under.

Over the past decade, Cahill's group has refined a measurement technique using very short laser pulses, lasting only one trillionth of a second, to probe heat flow accurately with nanometer-depth resolution. Cahill teamed up with Paul Braun, the Racheff Professor of Materials Science and Engineering at the U. of I. and a leader in nanoscale materials synthesis, to apply the technique to understanding how atomic-scale features affect heat transport.

"These experiments used a 'molecular sandwich' that allowed us to manipulate and study the effect that chemistry at the interface has on heat flow, at an atomic scale," Braun said.

The researchers assembled their molecular sandwich by first depositing a single layer of molecules on a quartz surface. Next, through a technique known as transfer-printing, they placed a very thin gold film on top of these molecules. Then they applied a heat pulse to the gold layer and measured how it traveled through the sandwich to the quartz at the bottom.

By adjusting just the composition of the molecules in contact with the gold layer, the group observed a change in heat transfer depending on how strongly the molecule bonded to the gold. They demonstrated that stronger bonding produced a twofold increase in heat flow.

"This variation in heat flow could be much greater in other systems," said Mark Losego, who led this research effort as a postdoctoral scholar at Illinois and is now a research professor at North Carolina State University. "If the vibrational modes for the two solids were more similar, we could expect changes of up to a factor of 10 or more."

The researchers also used their ability to systematically adjust the interfacial chemistry to dial-in a heat flow value between the two extremes, verifying the ability to use this knowledge to design materials systems with desired thermal transport properties.

"We've basically shown that changing even a single layer of atoms at the interface between two materials significantly impacts heat flow across that interface," said Losego.

Scientifically, this work opens up new avenues of research. The Illinois group is already working toward a deeper fundamental understanding of heat transfer by refining measurement methods for quantifying interfacial bonding stiffness, as well as investigating temperature dependence, which will reveal a better fundamental picture of how the changes in interface chemistry are disrupting or enhancing the flow of heat across the interface.

"For many years, the physical models for heat flow between two materials have ignored the atomic-level features of an interface," Cahill said. "Now these theories need to be refined. The experimental methods developed here will help quantify the extent to which interfacial structural features contribute to heat flow and will be used to validate these new theories."

Braun and Cahill are affiliated with the Frederick Seitz Materials Research Laboratory at the U. of I. Braun is also affiliated with the department of chemistry and the Beckman Institute for Advanced Science and Technology. The Air Force Office of Scientific Research supported this work.

University of Illinois at Urbana-Champaign


Related Heat Flow Current Events and Heat Flow News Articles


Study proposes common mechanism for shallow and deep earthquakes
Earthquakes are labeled "shallow" if they occur at less than 50 kilometers depth.

The fearsome foursome: Technologies enable ambitious MMS mission
It was unprecedented developing a mission that could fly four identically equipped spacecraft in a tight formation and take measurements 100 times faster than any previous space mission -- an achievement enabled in part by four NASA-developed technologies that in some cases took nearly 10 years to mature.

Tunneling across a tiny gap
Conduction and thermal radiation are two ways in which heat is transferred from one object to another: Conduction is the process by which heat flows between objects in physical contact, such as a pot of tea on a hot stove, while thermal radiation describes heat flow across large distances, such as heat emitted by the sun.

Folic acid may help elderly weather heat waves
Supplemental folic acid can enhance blood vessel dilation in older adults, according to Penn State researchers, suggesting that folic acid supplements may be an inexpensive alternative for helping older adults to increase skin blood flow during heat waves and reduce cardiovascular events.

Squeezing out new science from material interfaces
With more than five times the thermal conductivity of copper, diamond is the ultimate heat spreader. But the slow rate of heat flow into diamond from other materials limits its use in practice.

The 2 faces of Mars
The two hemispheres of Mars are more different from any other planet in our solar system. Non-volcanic, flat lowlands characterise the northern hemisphere, while highlands punctuated by countless volcanoes extend across the southern hemisphere.

Earth's most abundant mineral finally has a name
An ancient meteorite and high-energy X-rays have helped scientists conclude a half century of effort to find, identify and characterize a mineral that makes up 38 percent of the Earth.

New form of crystalline order holds promise for thermoelectric applications
Since the 1850's scientists have known that crystalline materials are organized into fourteen different basic lattice structures.

Miranda: An Icy Moon Deformed by Tidal Heating
Miranda, a small, icy moon of Uranus, is one of the most visually striking and enigmatic bodies in the solar system. Despite its relatively small size, Miranda appears to have experienced an episode of intense resurfacing that resulted in the formation of at least three remarkable and unique surface features -- polygonal-shaped regions called coronae.

Resolving apparent inconsistencies in optimality principles for flow processes in geosystems
Optimality principles have been used, in a holistic approach, to describe flow processes in several important geosystems. Optimality principles refer to the state of a physical system that is controlled by an optimal condition subject to physical and/or resource constraints.
More Heat Flow Current Events and Heat Flow News Articles

Numerical Heat Transfer and Fluid Flow (Hemisphere Series on Computational Methods in Mechanics and Thermal Science)

Numerical Heat Transfer and Fluid Flow (Hemisphere Series on Computational Methods in Mechanics and Thermal Science)
by Suhas Patankar (Author)


This book focuses on heat and mass transfer, fluid flow, chemical reaction, and other related processes that occur in engineering equipment, the natural environment, and living organisms. Using simple algebra and elementary calculus, the author develops numerical methods for predicting these processes mainly based on physical considerations. Through this approach, readers will develop a deeper understanding of the underlying physical aspects of heat transfer and fluid flow as well as improve their ability to analyze and interpret computed results.

Engineering Flow and Heat Exchange

Engineering Flow and Heat Exchange
by Octave Levenspiel (Author)


The third edition of Engineering Flow and Heat Exchange is the most practical textbook available on the design of heat transfer and equipment. This book is an excellent introduction to real-world applications for advanced undergraduates and an indispensable reference for professionals. The book includes comprehensive chapters on the different types and classifications of fluids, how to analyze fluids, and where a particular fluid fits into a broader picture. This book includes various a wide variety of problems and solutions – some whimsical and others directly from industrial applications.Numerous practical examples of heat transferDifferent from other introductory books on fluidsClearly written, simple to understand, written for students to absorb material quicklyDiscusses...

Two-phase Flow and Heat Transfer in the Power and Process Industries

Two-phase Flow and Heat Transfer in the Power and Process Industries
by A. E. Bergles (Author)




Crustal Heat Flow: A Guide to Measurement and Modelling

Crustal Heat Flow: A Guide to Measurement and Modelling
by G. R. Beardsmore (Author), J. P. Cull (Author)


Crustal Heat Flow: A Guide to Measurement and Modelling is a handbook for geologists and geophysicists who manipulate thermal data, particularly for petroleum exploration. In theory and with practical examples, the book discusses the sources of heat within the crust, describes how to maximize the accuracy of temperature data, covers the measurement of the thermal properties of rocks, and explains a number of maturity indicators. The second part covers a range of thermodynamic models of the lithosphere and shows how these can be used to reconstruct the thermal history of individual sedimentary basins.

Fluid flow and heat transfer formulae: for Chemical and Mechanical Engineering

Fluid flow and heat transfer formulae: for Chemical and Mechanical Engineering
by Dr Nadimpalli Sankara Srinivas (Author)


This book covers the equations or correlations on Fluid statics, Fluid dynamics, Newtonian and non-Newtonian fluids, Manometers, Flow measuring instruments, Laminar flow, Turbulant flow, Flow through pipes, Flow through packed beds, Flow through fluidized beds, Laminar and turbulant boundary layers over flat plates, Conduction heat transfer, Convection heat transfer, Forced convection and Natural convection, Internal heat generation, Heat exchangers, Condensation, Boiling, Evaporation and Radiation.

Fundamentals of the Finite Element Method for Heat and Fluid Flow

Fundamentals of the Finite Element Method for Heat and Fluid Flow
by R. W. Lewis (Author), Perumal Nithiarasu (Author), Kankanhalli Seetharamu (Author)


Heat transfer is the area of engineering science which describes the energy transport between material bodies due to a difference in temperature. The three different modes of heat transport are conduction, convection and radiation. In most problems, these three modes exist simultaneously. However, the significance of these modes depends on the problems studied and often, insignificant modes are neglected. Very often books published on Computational Fluid Dynamics using the Finite Element Method give very little or no significance to thermal or heat transfer problems. From the research point of view, it is important to explain the handling of various types of heat transfer problems with different types of complex boundary conditions. Problems with slow fluid motion and heat transfer can be...

Introduction to Compressible Fluid Flow, Second Edition (Heat Transfer)

Introduction to Compressible Fluid Flow, Second Edition (Heat Transfer)
by Patrick H. Oosthuizen (Author), William E. Carscallen (Author)


Introduction to Compressible Fluid Flow, Second Edition offers extensive coverage of the physical phenomena experienced in compressible flow. Updated and revised, the second edition provides a thorough explanation of the assumptions used in the analysis of compressible flows. It develops in students an understanding of what causes compressible flows to differ from incompressible flows and how they can be analyzed. This book also offers a strong foundation for more advanced and focused study. The book begins with discussions of the analysis of isentropic flows, of normal and oblique shock waves and of expansion waves. The final chapters deal with nozzle characteristics, friction effects, heat exchange effects, a hypersonic flow, high-temperature gas effects, and low-density flows. This...

Boiling Heat Transfer And Two-Phase Flow (Series in Chemical and Mechanical Engineering)

Boiling Heat Transfer And Two-Phase Flow (Series in Chemical and Mechanical Engineering)
by L S Tong (Author), Y S Tang (Author)


Completely updated, this graduate text describes the current state of boiling heat transfer and two-phase flow, in terms through which students can attain a consistent understanding. Prediction of real or potential boiling heat transfer behaviour, both in steady and transient states, is covered to aid engineering design of reliable and effective systems.

The flow of heat

The flow of heat
by Keith Cornwell (Author)




Motion Mountain - vol. 1 - The Adventure of Physics: Fall, Flow and Heat (Volume 1)

Motion Mountain - vol. 1 - The Adventure of Physics: Fall, Flow and Heat (Volume 1)
by Christoph Schiller (Author)


How high can animals jump? What are the fastest thrown balls? How fast can aeroplanes and butterflies fly? What does the sea level tell us about the sun? What are temperature and heat? What is self-organization? This free colour pdf on introductory physics guarantees to be entertaining, surprising and challenging on every page. The text presents the best stories, images, movies and puzzles in mechanics, gravity and thermodynamics - with little mathematics, always starting from observations of everyday life. This first volume also explains conservation laws and the reversibility of motion, explores mirror symmetry, and presents the principle of cosmic laziness: the principle of least action. This popular series has already more than 160 000 readers. If you are between the age of 16 and...

© 2015 BrightSurf.com