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The award-winning Phase Change Matters blog tracks the latest news and research on phase change materials and thermal energy storage. E-mail tips and comments to Ben Welter, communications director at Entropy Solutions. Follow the blog on Twitter at @PureTemp. Subscribe to the weekly PCM newsletter. Or join the discussion on LinkedIn.

Two Entropy advisors, Dr. Mohammed Farid and Lucas B. Hyman, are pleased to take your questions about PCMs and thermal energy storage. Send your questions to bwelter@puretemp.com. We'll select the best and post the answers here each week.

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PCM makers discuss formation of North American association

Ben Welter - Friday, February 24, 2017

Representatives of several U.S.-based PCM makers held a conference call this week to begin discussion of a proposed North American PCM manufacturers association. 

Entropy Solutions, Insolcorp, Phase Change Energy Solutions, Microtek Laboratories and representatives of companies in related industries, including Cold Chain Technologies, were among the participants. 

The effort, initiated at a thermal mass workshop in Florida last fall, is spearheaded by Dr. Jan Kosny of the Fraunhofer Center for Sustainable Energy Systems. He is compiling a list of all potential member companies. Please contact him at jkosny@cse.fraunhofer.org if you wish to join the discussion.

Patent application: Refrigeration system with PCM heat exchanger

Ben Welter - Friday, February 24, 2017

U.S. patent application 20170051954 (applicant Coca-Cola Co., Atlanta, Georgia):

Coca-Cola patent drawing"The present application provides a refrigeration system. The refrigeration system may include a compressor and a condenser downstream of the compressor. The condenser may include a refrigerant tube (550), an outer jacket (510) surrounding the refrigerant tube, and a phase change material positioned between the refrigerant tube and the outer jacket and in contact with the refrigerant tube. ... The phase change material heat exchanger (500) may include a heat source, a phase change material surrounding the heat source in whole or in part, and an outer jacket surrounding the phase change material. The phase change material removes heat when the heat source is on by melting and releases heat to the ambient when the heat source is off by solidifying." 

http://www.freepatentsonline.com/20170051954.pdf

Research roundup: 2 promising PCM candidates; calcium carbonate shell; thermocapillary effects; more

Ben Welter - Tuesday, February 21, 2017

Thermal properties characterization of two promising phase change material candidates [Journal of Thermal Analysis and Calorimetry]

Self-assembly synthesis and properties of microencapsulated n-tetradecane phase change materials with calcium carbonate shell for cold energy storage [ACS Sustainable Chemistry and Engineering]

Thermal Analysis of a Thermal Energy Storage Unit to Enhance a Workshop Heating System Driven by Industrial Residual Water [Energies]

Effect of a low-cost parabolic reflector on the charging efficiency of an evacuated tube collector/storage system with a PCM [Solar Energy]

Numerical study on free-surface jet impingement cooling with nanoencapsulated phase-change material slurry and nanofluid [International Journal of Heat and Mass Transfer]

Heat transfer performance and melting dynamic of a phase change material subjected to thermocapillary effects [International Journal of Heat and Mass Transfer]

Evaluation and optimization of melting performance for a latent heat thermal energy storage unit partially filled with porous media [Applied Energy]

Carbon nanotube/paraffin/montmorillonite composite phase change material for thermal energy storage [Solar Energy]

Synthesis and thermal properties of novel solid-solid phase change materials with comb-polyurethane block copolymer structure for thermal energy storage [Thermochimica Acta]

Synthesis and Properties of Polyurethane/Coal-Derived Carbon Foam Phase Change Composites for Thermal Energy Storage [Acta Physico-Chimica Sinica]

Patent application: PCMs comprising alkanolamides and diesters and methods of making and using them

Ben Welter - Monday, February 20, 2017

U.S. patent application 20170044414 (applicant Entropy Solutions LLC, Plymouth, Minn.):

"This invention generally relates to thermoregulation and temperature stabilization, thermal protection and insulation, and nucleating agents. In particular, in alternative embodiments, provided are organic phase change materials comprising diesters and alkanolamides. In alternative embodiments, provided are Phase Change Material (PCMs) compositions comprising diesters and alkanolamides, and methods for making and using them. In alternative embodiments, the Phase Change Material (PCMs) compositions are used for thermal energy management, including energy storage and/or temperature stabilization, in various applications such as building, automotive, packaging, garment and footwear, textiles, fabrics, synthetic fibers, foods, microcapsules and other energy storage systems."

http://www.freepatentsonline.com/20170044414.pdf

Patent application: Heated or cooled dishware and drinkware and food containers

Ben Welter - Monday, February 20, 2017

Ember patent drawingU.S. patent application 20170042373 (applicant Ember Technologies Inc., Westlake Village, Calif.):

"An actively heated or cooled food container can have a lid movable between an open and a closed position and an insulated body to which the lid can be attached. The insulated body can have a sidewall that defines a perimeter of the container body and a base, the sidewall and base defining one or more chambers that can be sealed by the lid. ... The heating and cooling system comprises a cooling element comprising a phase change material disposed in a chamber that surrounds at least a portion of the inner sidewall so that the phase change material is in thermal communication with at least a portion of the inner sidewall of the portable body, the phase change material configured to transition from one phase to a second phase at a predetermined temperature."

http://www.freepatentsonline.com/20170042373.pdf

Patent application: Cables made of phase change material

Ben Welter - Monday, February 20, 2017

U.S. patent application 20170045301 (applicant E.I. Du Pont De Nemours and Co., Wilmington, Del.):

"Disclosed is a cable comprising a core and a PCM layer surrounding the core wherein the PCM layer consists of a PCM composition wherein the PCM composition comprises a PCM and an ethylene copolymer; and the core consists of a yarn, strand, or wire each made of a natural or synthetic polymeric material or a metal. The invention is useful for thermal management in a variety of applications in such as, for example, automotive, building, packaging, garments, and footwear."

http://www.freepatentsonline.com/20170045301.pdf

Thanks to PCM insert, luxury chocolates melt in your mouth, not in the box

Ben Welter - Monday, February 20, 2017

In hot climates, chocolates bought at retail shops can end up melting on the way home. Pluss Advanced Technologies of India has introduced a packaging insert to keep the sweets in solid form during transit.

Pluss PCM insertDeveloped for ITC’s Fabelle line of premium chocolates, the insert features inorganic phase change material contained in a non-woven film. Vishnu Sasidharan, vice president of new product initiatives at Pluss, says the PCM was customized to keep the chocolate between 3º and 9º Celsius. The insert, designed for one-time use, measures about 170mm x 70mm. The goal is to maintain product quality and texture for one to two hours.

“The product was launched about five months back,” Sasidharan says. “It was available only in one hotel chain within ITC group of hotels. The boutique has gained much traction only in the last few months with ITC expanding it to not only within their group but in all the 5 star/7 star hotels across India.”

Pluss is working with other chocolate/confectionary companies to offer similar solutions for premium temperature-sensitive products.

A look inside an undergraduate team's solar thermal storage project

Ben Welter - Friday, February 17, 2017

The Solar Owl team

From left: Brandon Koyanagi, Will Wilson, Gerardo Rojo and Michelle Zdanowski

For their senior undergraduate project, four engineering students at Southern Illinois University Edwardsville developed a heat storage system designed to collect thermal energy from the sun and release it at night.

The Solar Owl combines water-based sensible heat storage in an insulated tank and latent heat storage through use of a hydrated salt phase change material. The PCM is contained in a continuous, multiple-coil vessel within the tank.

SIUE TES tankThe team – Brandon Koyanagi, Will Wilson, Gerardo Rojo and Michelle Zdanowski – designed, analyzed, built and tested a scale prototype of the apparatus.

“At full size,” Wilson says, “the tank would be capable of heating an average American home through the evening and night, fourteen hours, using heat accumulated from solar thermal collectors during a typical St. Louis-area winter day. The Solar Owl reduces the size of the heat storage tank by 40 percent when compared to a sensible-only storage solution.”

The team earned an A on the project and will continue to develop the system in graduate studies. Aside from securing a patent on the design elements and a trademark on the name, the team has no immediate plans to commercialize the system.

Here’s a Q&A with Wilson, who was selected as Outstanding Senior in the university’s Mechanical Engineering Department this year.

Q: Why did the team choose sodium acetate trihydrate as the phase change material? 

A: SAT fit our needs in four important ways. (1) SAT's latent heat of fusion is high enough to keep tank size adequately small. (2) SAT, and the necessary additives, are readily availability at low to mid cost. (3) SAT exhibits low toxicity and is environmentally friendly. (4) The melting point of 58 C lends itself well to our application. This melting point is low enough to be completely melted by heat collected from a standard flat-plate solar thermal collector, while also providing a good temperature delta for most hydronic loop appliances.

Q: What is the source of the SAT you're using? 

A: We utilized SIUE chemistry lab space to synthesize a custom solution of lab-grade hydrated sodium acetate crystals with a small amount of additional water to slightly lower the temperature needed for complete melting. Carboxymethyl cellulose (CMC) was added to mitigate phase separation and potassium sulfate to minimize supercooling.

Q: SAT typically exhibits supercooling. Is that a problem in your application? 

A: As the system is not intended to be a long-term heat store, supercooling was not desirable for our design. To reduce supercooling, we added potassium sulfate to the solution as a nucleating agent.

Q. Unmodified SAT's latent heat of fusion is typically 264–289 joules per gram, with a melt point of 58 C. Does your SAT fit those specs? 

A: Our SAT did fit within that range per gram of SAT in solution. Of course, the latent heat of fusion for the solution overall, including the extra water and additives, was somewhat lower.

Q: What triggers the release of the heat?

A: Heat is released as the tank temperature falls below the melting point (plus a correction for minimal supercooling, approximately 5 degrees Celsius).

Q: What heat transfer fluid is used between the solar collectors and the tank?

A: I should note that, since the storage tank was the focus of our project, our prototype simulated solar collectors using an electrically heated water bath with submerged heat transfer coil. The transfer fluid from the “collector” to the tank, and between the tank and the testing radiators, is a solution of propylene glycol. This was chosen for (1) its low environmental toxicity and (2) its sensible heat capacity, which is high enough to help maintain tank temperature, but low enough to facilitate an appropriate heat transfer rate.

Q: What are the key design elements of the container, and what material is it made of?

A: The PCM container is a set of interconnected concentric helical coils constructed from standard PEX tubing. A set of likewise interconnected helical heat transfer coils is interspersed between the PEX coils, allowing proximity of the heat source to melt the PCM during the day, with enough space between coils to allow free convective heat transfer to the surrounding water in the tank. This configuration has the following advantages:

• It holds a relatively large amount of PCM with large surface area for heat transfer to the water in the tank.

• The tubing diameter is small enough to allow for an adequate heat rejection rate from the PCM (given SAT’s low heat conductivity).

• The thermal conductivity of PEX is higher than many plastics, such that it does not present a bottleneck to the release of PCM heat. 

As far as our research informs us, our design also stands out in that the PCM solution may be readily drained and filled for system maintenance. According to the data we could locate, an SAT solution experiencing daily phase cycling has a predicted useful life of around 10 years. Allowing easy access to flush the PCM container and refill is therefore critical for long-term maintenance and also for the case where the SAT formulation fails early, becomes contaminated, or requires testing or monitoring.

For more on the project, see:

http://www.theintelligencer.com/news/article/Students-design-heat-storage-system-10865688.php

Research roundup: Heat transfer enhancement; gypsum incorporated with diatomite/paraffin composite; more

Ben Welter - Friday, February 17, 2017

Heat transfer enhancement of phase change materials for thermal energy storage applications: A critical review [Renewable and Sustainable Energy Reviews]

Melting enhancement in triplex-tube latent thermal energy storage system using nanoparticles-fins combination [International Journal of Heat and Mass Transfer]

Mixed mill-heating fabrication and thermal energy storage of diatomite/paraffin phase change composite incorporated gypsum-based materials [Applied Thermal Engineering]

Definition of a new set of parameters for the dynamic thermal characterization of PCM layers in the presence of one or more liquid-solid interfaces [Energy and Buildings]

PCM briefing: Underground heat storage proposed for Hamburg; Solar Decathlon entry will have PCM in ceilings

Ben Welter - Wednesday, February 15, 2017

• The water utility in Hamburg, Germany, wants to build an underground thermal heat storage system that could supply about 25 percent of the city's heating needs with waste heat from industrial and power plants. A huge saltwater aquifer below the city is seen as an ideal "thermal battery" in which to store heat for use in winter.

• The University of Nevada-Las Vegas entry in the 2017 Solar Decathlon will feature phase change material in the ceilings of the 900-square-foot home.

Sonoco has announced a 10 percent price increase on all expanded polystyrene components used in its temperature-assurance packaging products. The company said the increase reflects the rising cost of polystyrene, the key raw material in EPS products.

University of Colorado engineers have developed a metamaterial that can cool objects even under direct sunlight with zero energy and water consumption. The glass-polymer hybrid material measures just 50 micrometers thick and can be manufactured economically on rolls, making it potentially viable for large-scale residential and commercial applications.

StoCalce Functio, a wall covering material developed by the Swiss research institute Empa together with the building specialist Sto, manages interior humidity by absorbing, storing and releasing moisture. Perhaps PCMs could be added to the material to manage temperatures as well. [German]

Alexium International, maker of Alexicool phase change material, is one of nine companies planning to attend Gabelli & Company's 8th annual Specialty Chemicals Conference in New York City on March 22.

Axiom Exergy co-founders Anthony Diamond and Amrit Robbins, who made Forbes' "30 Under 30" in the energy sector this year, shared advice for other young entrepreneurs on energy.gov. Said Robbins: “If you want to build a business, go out and get third party validation for your technology, team and product-market fit."