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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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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."

Research roundup: New way to measure specific heat capacity; PCM underfloor heating; metal foams; more

Ben Welter - Tuesday, February 14, 2017

New proposed methodology for specific heat capacity determination of materials for thermal energy storage (TES) by DSC [Journal of Energy Storage]

Thermal diffusivity measurement of erythritol and numerical analysis of heat storage performance on a fin-type heat exchanger [Applied Thermal Engineering]

Benefits of PCM underfloor heating with PCM wallboards for space heating in winter [Applied Energy]

Non-steady experimental investigation on an integrated thermal management system for power battery with phase change materials [Energy Conversion and Management]

Experimental investigation on heat transfer characteristics during melting of a phase change material with dispersed TiO2 nanoparticles in a rectangular enclosure [International Journal of Heat and Mass Transfer]

Numerical method and model for calculating thermal storage time for an annular tube with phase change material [Journal of Central South Florida]

Stratified Laboratory Thermal Energy Storage (LabTES) Tank Experiments: Sensible Only and Sensible Augmented with PCM-Filled Tubes [University of Cincinnati master's thesis]

Development and optimization of PCM-based technology for cooling applications for improvement of fuel efficiency in commercial vehicle [SAE World Congress Experience]

Establishment and experimental verification of TRNSYS model for PCM floor coupled with solar water heating system [Energy and Buildings]

Thermal Performance Enhancement of Phase Change Materials (PCMs) by Using Metal Foams [Al-Nahrain Journal for Engineering Sciences]

Research roundup: Encapsulation techniques for inorganic PCM; effects of flake graphite nanoparticles; more

Ben Welter - Monday, February 13, 2017

From Renewable and Sustainable Energy Reviews:

A review on encapsulation techniques for inorganic phase change materials and the influence on their thermophysical properties
Phase equilibrium in the design of phase change materials for thermal energy storage: State-of-the-art

From Applied Thermal Engineering:

Investigating the impact of Cp-T values determined by DSC on the PCM-CFD Model
Performance of a Finned, Latent-Heat Storage System for Solar Thermal Power Application

From Applied Energy:

Impact of periodic flow reversal of heat transfer fluid on the melting and solidification processes in a latent heat shell and tube storage system
The effects of flake graphite nanoparticles, phase change material, and film cooling on the solar still performance
A quick-fix design of phase change material by particle blending and spherical agglomeration

From Journal of the Taiwan Institute of Chemical Engineers:

Phase-change heat transfer in a cavity heated from below: The effect of utilizing single or hybrid nanoparticles as additives

From Energy:

Field evaluation of microencapsulated phase change material slurry in ground source heat pump systems

From Renewable Energy:

Numerical studies on thermal and electrical performance of a fully wetted absorber PVT collector with PCM as a storage medium
Glass encapsulated phase change materials for high temperature thermal energy storage

From SAE World Congress Experience:

Integration and Validation of Thermal Energy Storage System for Electric Vehicle Cabin Heating

From Engineering Technology International Conference 2016:

Preparation and characterization of form-stable paraffin/polycaprolactone composites as phase change materials for thermal energy storage

Sunamp joins RAL Quality Association PCM

Ben Welter - Monday, February 13, 2017

Sunamp Ltd. of Scotland has joined the RAL Quality Association PCM, a European-based organization established in 2004 to develop standards for the phase change material industry. 

"Sunamp is delighted to join RAL PCM, the world's leading quality association for phase change materials," said Sunamp CEO Andrew Bissell. "We have extremely stable and long-lived, high energy density PCM that we deliver in high-power heat batteries. We look forward to working with RAL PCM and the other members to further develop PCM and Heat Battery standards, and to have our products certified."

RAL PCM has two key objectives: Promote the use of high-quality PCMs and influence the political landscape in the European Union in favor of PCMs. Other RAL members are Croda, BASF, Rubitherm, EMCO, va-Q-tec, PCM Technology, Global Energy Systems Europe, Sasol, Pluss Advanced Technologies and Entropy Solutions.

Technically speaking, PCM-infused lingerie line radiates an air of mystery

Ben Welter - Monday, February 13, 2017

Giapenta's beautiful new line of PCM-infused lingerie features soft, breathable mesh, delicate appliques and natural, moisture-wicking fabrics. As far as technical details, though, the brand’s founder is leaving much to the imagination.

Giapenta modelThe Florida startup, which launched a Kickstarter campaign last month to cover costs of its first production run, says the TempPro fabric used in the lingerie “proactively” pulls heat away to cool the body. Giapenta’s message to consumers:

“Just as you start to get warm, the phase changing materials in the fabric actively pull heat away from your body. Overheating and sweating are reduced. If you do start to get cold, stored heat is released back to you, when you need it the most.”

The company was founded by Kris Strouthopoulos, who managed Sleep Number mattress and bedding stores for 10 years. That’s where she became familiar with temperature-regulating fabrics and materials.

“Women especially would always come up to me to tell me how amazing and life changing the fabric was for them,” she said. “I always thought that if they were getting such an amazing benefit from this technology all night long, why not get the same effects during the day from their undergarments? So that is how we initially got into the lingerie industry and built a team dedicated to infusing technology and smart design solutions into garments to help improve the lives of others.”

TempPro fabric illustrationShe and her sister, Marketing VP Elena Strouthopoulos, have been working on the brand for two years. The Kickstarter campaign met its modest target of raising $25,000 in just one day, putting the company on a path to complete the production run in Canada by April and ship the first orders in May.

I contacted Kris Strouthopoulos to learn more about the TempPro fabric, which the company says is used throughout the line. What type of phase change material is used? What is its melt point? How is it encapsulated? She politely declined to answer any questions of a technical nature, saying such information is proprietary. Fair enough. We'll leave that to your imagination.

PCM briefing: California utility will buy up to 100 Ice Bears for residential use; Malouf unveils new graphite-PCM pillow

Ben Welter - Thursday, February 09, 2017

Ice Energy will join forces with the Southern California Public Power Authority to provide up to 100 Ice Bear 20 cooling units for residential use within utility's 12 member territories in 2017. Installations will begin in June. The Ice Bear 20 stores cooling energy during off-peak hours by freezing water in an insulated tank. During peak hours, the company says, the stored ice delivers up to four hours of cooling, reducing the typical peak load by 95 percent. The new deployment is designed to demonstrate the Ice Bear 20's grid value to utilities. The units will be installed in single-family homes chosen by Ice Energy based on site visits. Homes that need 4-, 5- or 6-ton air-conditioning systems replaced are the likely targets. The utilities pay for the Ice Bears; it's unclear at this point who will pay installation costs. If all 100 Ice Bear 20s are purchased, the total cost to the utilities will be $1.33 million (not including installation).

Malouf CarbonCool pillow• Bedding maker Malouf's new CarbonCool Plus OmniPhase pillow combines the temperature-regulation properties of graphite and microencapsulated phase change material. "At the molecular level," Furniture Today reports, "the material inside the capsules changes from a solid to a liquid when the temperature is high and vice versa when the temperature is low. This continuous cycle is designed keep the pillow surface between 87 and 91 degrees, which research shows is the ideal skin temperature range for deep sleep." The queen size shown here retails for $299.99.

• New from Absolute Reports: "United States Advanced Phase Change Materials (PCM) Market By Manufacturers, States, Type And Application, Forecast To 2022"

SPX Flow's new FLEX Series refrigerated air dryer uses phase change material to tightly regulate temperatures and reduce compressor cycling.

Prongo insulin bagPluss Technologies' PronGo bag, introduced last year for consumers to transport frozen and chilled food and beverages, is  now being promoted as a way to keep insulin at the right temperature for up to 10 hours. The 3-liter bag comes with two sets of PCM cooling packs. It's available on Amazon.in for about $52. In an interview with Express Pharma, company director Samit Jain talked about the Prongo and another new product, Celsure, a passive shipper designed to keep pharma products "at the right temperature for 96 hours and beyond at the tropical temperatures that countries like India, South East Asia and Africa have."

1414 Degrees, the Australian company that has developed a way to store electricity as thermal energy by heating and melting containers full of silicon, is now scaling up the technology and plans to launch the first commercial systems this year. Executive Chairman Kevin Moriarty said the company is waiting for AusIndustry, a division of Australia's Department of Industry, Innovation and Science, to sign off on the 10MWh project in February so manufacture can begin.

Sunamp is thinking big with commercial-scale heat battery

Ben Welter - Monday, February 06, 2017

Sunamp Ltd. continues to seek financing to fund development of its commercial-scale heat battery, the SunampCube. The device is designed to store energy generated by wind, solar and other renewable sources, as well as harvest excess heat generated by waste-treatment facilities.

Sunamp CEO Andrew BissellThe Scottish company is in negotiations to use the technology to transport waste heat by barge from the Avonmouth waste processing facility to Bristol for use in the district heating system under construction there. The batteries would be stored in 16 shipping container units, each holding 2 MWh of heat.

"We have built and tested a number of cells that will be used to build the full-scale device," says CEO Andrew Bissell. "Each one is a single cell storing 45-50 kWh."

What type of phase change material is being used?

"It's a salt hydrate ... our own tweak on sodium acetate trihydrate with both a nucleator and a stability enhancer," Bissell says. "58C melt and freeze points - almost no subcooling or hysteresis. And very cycle stable. We have cycled a test heat battery over 26,000 times with no loss of capacity or degradation in any metric."

Bissell says the company is working on financing for the project's next phase.

http://www.sunamp.com/products/sunampcube/

PCM briefing: New denim features phase change material; Sasol 'back on the expansion trail'

Ben Welter - Monday, February 06, 2017

• Thinking about attending BiobasedWorld 2017 in Cologne, Germany, this month? Sorry, the trade show was canceled a few months ago due to the industry's "challenging economic environment." A related show is on the horizon: Bio-Based Live Europe in Amsterdam, May 31-June 1. The focus will be on "Process Innovation and Technology" and "Sustainable Products." Speakers include Freek Snieders, managing director, Croda International; and Jean Luc Dubois, scientific director, Arkema.

Oak Ridge National Laboratory takes a look at how University of Michigan researchers used a Cray XK7 Titan supercomputer to study melting in two-dimensional systems. Deeper understanding of the process, Oak Ridge says, "could yield insights into surface interactions in materials important to technologies like solar panels, as well as into the mechanism behind three-dimensional melting." 

• The cold chain packaging class developed by Sonoco ThermoSafe’s ISC Labs will be offered at the Cold Chain GDP & Temperature Management Logistics Global Forum in San Diego in May. The all-day session on May 25 will cover the design, development and qualification of temperature-controlled packaging. The conference agenda is available for download.

Biznews.com reports that chemicals giant Sasol is "back on the expansion trail, seeking out suitable acquisitions."

• Among the new fabrics on display at the Munich Fabric Start trade show this week: Cordura denim combined with Schoeller phase change material. 

• The University of the West of England has installed two Monodraught Cool-Phase hybrid units in the university's Estates Management Office in Bristol. Monodraught says its PCM-equipped systems have been shown to "use up to 90% less energy than traditional a/c systems."  

• The 12th Conference on Advanced Building Skins, scheduled for Oct. 2-3 in Bern, Switzerland, has issued a call for papers. Possible topics include financial models, new products, advanced design and building performance. The deadline is Feb. 10. 

Pelican BioThermal has announced that its new passive pallet shipper system, Crēdo Cargo, is now available to rent or buy. The reusable bulk shipper uses phase change material cooling panels to maintain temperature ranges +2C to +8C and +15C to +25C.