Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

“Reverse Engineering” Materials for More Efficient Heating and Cooling

29.10.2014

A new way to calculate the electrical properties of individual components of composite materials could open a path toward more energy-efficient medical refrigerators, air-conditioned car seats and more

If you’ve ever gone for a spin in a luxury car and felt your back being warmed or cooled by a seat-based climate control system, then you’ve likely experienced the benefits of a class of materials called thermoelectrics. Thermoelectric materials convert heat into electricity, and vice versa, and they have many advantages over more traditional heating and cooling systems.


Tristan Day/Caltech

Researchers at Caltech devised a way to calculate the electrical properties of individual components of a composite material by testing the material’s response in a range of magnetic fields. This image shows the material wired in a sample holder designed to measure its electrical properties.

Recently, researchers have observed that the performance of some thermoelectric materials can be improved by combining different solid phases -- more than one material intermixed like the clumps of fat and meat in a slice of salami. The observations offer the tantalizing prospect of significantly boosting thermoelectrics’ energy efficiency, but scientists still lack the tools to fully understand how the bulk properties arise out of combinations of solid phases.

Now a research team based at the California Institute of Technology (Caltech) has developed a new way to analyze the electrical properties of thermoelectrics that have two or more solid phases. The new technique could help researchers better understand multi-phase thermoelectric properties – and offer pointers on how to design new materials to get the best properties.

The team describes their new technique in a paper published in the journal Applied Physics Letters, from AIP Publishing.

An Old Theory Does a 180

Because it’s sometimes difficult to separately manufacture the pure components that make up multi-phase materials, researchers can’t always measure the pure phase properties directly. The Caltech team overcame this challenge by developing a way to calculate the electrical properties of individual phases while only experimenting directly with the composite.

“It’s like you’ve made chocolate chip cookies, and you want to know what the chocolate chips and the batter taste like by themselves, but you can’t, because every bite you take has both chocolate chips and batter,” said Jeff Snyder, a researcher at Caltech who specializes in thermoelectric materials and devices.

To separate the "chips" and "batter" without un-baking the cookie, Snyder and his colleagues turned to a decades old theory, called effective medium theory, and they gave it a new twist.

“Effective medium theory is pretty old,” said Tristan Day, a graduate student in Snyder’s Caltech laboratory and first author on the APL paper. The theory is traditionally used to predict the properties of a bulk composite based on the properties of the individual phases. “What’s new about what we did is we took a composite, and then backed-out the properties of each constituent phase,” said Day.

The key to making the reversal work lies in the different way that each part of a composite thermoelectric material responds to a magnetic field. By measuring certain electrical properties over a range of different magnetic field strengths, the researchers were able to tease apart the influence of the two different phases.

The team tested their method on the widely studied thermoelectric Cu1.97Ag0.03Se, which consists of a main crystal structure of Cu2Se and an impurity phase with the crystal structure of CuAgSe.

Temperature Control of the Future?

Thermoelectric materials are currently used in many niche applications, including air-conditioned car seats, wine coolers, and medical refrigerators used to store temperature-sensitive medicines.

“The definite benefits of using thermoelectrics are that there are no moving parts in the cooling mechanism, and you don’t have to have the same temperature fluctuations typical of a compressor-based refrigerator that turns on every half hour, rattles a bit and then turns off,” said Snyder.

One of the drawbacks of the thermoelectric cooling systems, however, is their energy consumption.

If used in the same manner as a compressor-based cooling system, most commercial thermoelectrics would require approximately 3 times more energy to deliver the same cooling power. Theoretical analysis suggests the energy efficiency of thermoelectrics could be significantly improved if the right material combinations and structures were found, and this is one area where Synder and his colleagues’ new calculation methods may help.

Many of the performance benefits of multi-phase thermoelectrics may come from quantum effects generated by micro- and nano-scale structures. The Caltech researchers’ calculations make classical assumptions, but Snyder notes that discrepancies between the calculations and observed properties could confirm nanoscale effects.

Snyder also points out that while thermoelectrics may be less energy efficient than compressors, their small size and versatility mean they could be used in smarter ways to cut energy consumption. For example, thermoelectric-based heaters or coolers could be placed in strategic areas around a car, such as the seat and steering wheel. The thermoelectric systems would create the feeling of warmth or coolness for the driver without consuming the energy to change the temperature of the entire cabin.

“I don’t know about you, but when I’m uncomfortable in a car it’s because I’m sitting on a hot seat and my backside is hot,” said Snyder. “In principle, 100 watts of cooling on a car seat could replace 1000 watts in the cabin.”

Ultimately, the team would like to use their new knowledge of thermoelectrics to custom design ‘smart’ materials with the right properties for any particular application.

“We have a lot of fun because we think of ourselves as material engineers with the periodic table and microstructures as our playgrounds,” Snyder said.

The article, "Determining conductivity and mobility values of individual components in multiphase composite Cu1.97 Ag0.03Se," is authored by Tristan W. Day, Wolfgang G. Zeier, David R. Brown, Brent C. Melot, and G. Jeffrey Snyder. It will be published in the journal Applied Physics Letters on October 28, 2014 (DOI: 10.1063/1.4897435). After that date, it can be accessed at: http://scitation.aip.org/content/aip/journal/apl/105/17/10.1063/1.4897435

The authors of this paper are affiliated with the California Institute of Technology (Caltech) and the University of Southern California.

ABOUT THE JOURNAL

Applied Physics Letters features concise, rapid reports on significant new findings in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology. See: http://apl.aip.org

Jason Socrates Bardi | newswise

More articles from Materials Sciences:

nachricht Decoding cement's shape promises greener concrete
08.12.2016 | Rice University

nachricht Scientists track chemical and structural evolution of catalytic nanoparticles in 3-D
08.12.2016 | DOE/Brookhaven National Laboratory

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Closing the carbon loop

08.12.2016 | Life Sciences

Applicability of dynamic facilitation theory to binary hard disk systems

08.12.2016 | Physics and Astronomy

Scientists track chemical and structural evolution of catalytic nanoparticles in 3-D

08.12.2016 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>