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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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Research roundup: PCM compatibility with metals, plastic; desiccant packet for cooling vest; paraffin viscosity; more

Ben Welter - Thursday, March 23, 2017

Investigation of the corrosive properties of phase change materials in contact with metals and plastic [Renewable Energy]

Preparation and thermal properties of SAT-CMC-DSP/EG composite as phase change material [Applied Thermal Engineering]

A numerical study on the usage of phase change material (PCM) to prolong compressor off period in a beverage cooler [Energy Conversion and Management]

Abilities and limitations of thermal mass activation for thermal comfort, peak shifting and shaving: A review [Building and Environment]

Corrosion effect of phase change materials in solar thermal energy storage application [Renewable and Sustainable Energy Reviews]

A review for phase change materials (PCMs) in solar absorption refrigeration systems [Renewable and Sustainable Energy Reviews]

Sodium nitrate – Diatomite composite materials for thermal energy storage [Solar Energy]

Innovative PCM-desiccant packet to provide dry microclimate and improve performance of cooling vest in hot environment [Energy Conversion and Management]

Heat transfer study of phase change materials with graphene nano particle for thermal energy storage [Solar Energy]

Energy performance evaluation of heat-storage gypsum board with hybrid SSPCM composite [Journal of Industrial and Engineering Chemistry]

Empirical equation to estimate viscosity of paraffin [Journal of Energy Storage]

Yearly energy performance of a photovoltaic-phase change material (PV-PCM) system in hot climate [Solar Energy]

Research roundup: Microcapsule-based composites; porous cellulose acetate films; underfloor heating; more

Ben Welter - Tuesday, March 07, 2017

Experimental study on effective thermal conductivity of microcapsules based phase change composites [International Journal of Heat and Mass Transfer]

Multi-objective RSM Optimization of Fin Assisted Latent Heat Thermal Energy Storage System Based on Solidification Process of Phase Change Material in Presence of Copper Nanoparticles [Applied Thermal Engineering]

Buildings cooling: An experimental study of phase change materials storage for low-energy buildings [2017 International Conference on Communication, Control, Computing and Electronics Engineering ]

Aluminum Mesh and Phase-Change Characteristics of n-Octadecane for Thermal Energy Storage [Journal of Thermophysics and Heat Transfer]

Analytical analysis of latent heat thermal energy storage model for solar thermal power plants [14th International Bhurban Conference on Applied Sciences and Technology]

Analysis of graphene-encapsulated polymer microcapsules with superior thermal and storage stability behavior [Polymer Degradation and Stability]

Experimental and numerical investigations on the thermal performance of building plane containing CaCl2·6H2O/expanded graphite composite phase change material [Applied Energy]

Fabrication and characterization of porous cellulose acetate films by breath figure incorporated with capric acid as form-stable phase change materials for storing/retrieving thermal energy [Fibers and Polymers]

In-situ preparation of a shape stable phase change material [Renewable Energy]

Proposal of a PCM Underfloor Heating System Using a Web Construction Method [pdf] [International Journal of Polymer Science]

Finland's Team HeatStock is developing a novel PCM designed to lock in solar, waste heat for later use

Ben Welter - Monday, March 06, 2017

Researchers in Finland are developing a novel phase change material that combines sugar alcohols and sodium polyacrylate, the superabsorbent polymer used in disposable diapers. The material is designed to store solar heat collected in summer and release it for use in winter. The material could also be used to store industrial waste heat.

Team HeatStock, whose members include chemists, energy engineers and physicists from three universities, is one of 20 semifinalists in the 2017 Helsinki Challenge. Finalists, to be selected in June, will compete for a share of 375,000 euros in research funds. The winners will be announced in December.

Team HeatStock PCMTeam HeatStock presented its technology at the Helsinki Challenge pitch night last month.

“The charging of our storage happens by melting the active material of our solution,” said Aalto University research scientist Salla Puupponen. “However, when the melt material starts to cool, it doesn’t release the heat on crystallization as conventional phase change materials, but instead we can keep our material as low temperatures as we want, as long time as we want without losing the stored energy.”

In an interview with Phase Change Matters, team leader Ari Seppälä, a senior scientist at Aalto, describes the technology in further detail.

Q: On the Helsinki Challenge website, you mention that the material will be used to store heat from "solar collectors.” That’s solar thermal, not photovoltaic, correct?

A: Yes, that meant solar thermal collectors. But that is just a one possibility. Other options include such as storing waste heat from industrial processes and storing the surplus heat produced by CHPs (combined heat and power plants) during summertime. As CHPs are often linked with district heating systems (at least in Nordic countries) delivering hot water to residents, the surplus heat could also be exploited for charging the storages of residential buildings during summer for wintertime use.

Q: How is the project being funded now?

A: We have Aalto University strategic funding (Aalto Energy Efficiency Program) and also funding from Fortum Foundation. However, our funding ends during this year. Currently we are looking for new funding possibilities. We are also looking for more collaborators and community members for the research and the competition. So, experts, scientists, companies and organizations who are interested in our research are most welcome to join us!

Q: Your PCM sounds like a composite. What are its components and how are they combined?

A: Our PCM can be classified more likely as a mixture than as a composite. It is composed of a polyol in a cross-linked polyelectrolyte matrix.

Q: What is the PCM's melting point?

A: The melting point is about 100º C.

Q: What is the PCM’s thermal energy capacity in joules per gram?

A: The heat of melting is 180-280 J/g depending on the composition. The heat of crystallization of the material is currently approximately 140-170 J/g. We aim at developing the latent heat of our material further.

Q. You have describe the material as having “phase-change properties that had never been seen before with any material.” What are those properties?

A: Operation of our novel material is based on so-called cold-crystallization, in which the conventional melt-crystallization on cooling is prevented and the material crystallizes only on heating. Supercooled PCM does not seem to crystallize even with a seed crystal below the cold-crystallization temperature. Anomalously, the PCM seems to be stable also above the glass-transition temperature. The novel operation principle enables long-term storing of thermal energy, and discharge of the storage by a small heat pulse.

Cold-crystallization is previously observed also for hydrated polymers, in which water is absorbed by hydrophilic polymers. However, in these cases the amount of cold-crystallizing water is small and the crystallization properties are not conserved in the repeated melting-crystallization cycles. Our material instead can consist up to 90 percent of actual PCM and can be cycled without notable changes in phase change properties.

In addition, the cold-crystallization temperature can be adjusted by the changing the material composition.

Q: What are the key steps in your scale-up plans?

In the beginning, we aim at scaling-up our sample size from tens of milligrams to a kilogram scale. In the scale-up, it is crucial that the material properties, especially the stability of supercooled state, remain unaltered. That is of course an open question, as it is well known that the stability of metastable states decreases with increasing volume of the sample. However, our small, deeply supercooled samples did not crystallize even with seeds and thus the operation of our material differs substantially from conventional materials. After the scale-up process, we will study the triggering of the crystallization by the heat pulse. We also aim at building a practical demo linked with a heat loading and releasing system.

We will later also look for creating similarly behaving materials based on different PCMs.

Q: Have you published research papers on the material?

A: There are no published papers concerning this new material so far. The manuscript on this material, (Puupponen and Seppälä, Cold-crystallization of polyelectrolyte absorbed polyol for long-term storing of thermal energy) has just been submitted for review and a patent application is pending.

Here are links to recent journal papers related to our other PCM studies:

PCM for long-term storage:

Puupponen S, Mikkola V, Ala-Nissilä T, Seppälä A, (2016) Novel microstructured polyol–polystyrene composites for seasonal heat storage, Applied Energy 172 96–106.

Thermodynamics of solidification and melting:

Seppälä A., Irreversibility of solidification and of a cyclic solidification-melting process, (2012), International Journal of Heat and Mass Transfer, 55 1582-1595.

Heat transfer nanofluids with PCM particles:

Puupponen, S., Seppälä, A., Vartia, O., Saari, K., Ala-Nissilä, T., Preparation of paraffin and fatty acidphase changing nanoemulsions for heat transfer (2015), Thermochimica Acta, 601, 33-38

Mikkola V, Puupponen S, Saari K, Ala-Nissila T, Seppälä A., Thermal properties and convective heat transfer of phase changing paraffin nanofluids, (2017), accepted for publication in International Journal of Thermal Sciences.

PCM briefing: Sunamp, University of Glasgow partner on Chinese power plant project; Reaxys PhD Prize entries due March 13

Ben Welter - Monday, March 06, 2017

Sunamp Ltd. is teaming up with Glasgow University and partners in China to boost the performance of Organic Rankine Cycle power plants that use renewable heat sources for distributed heat and power supply in China. The joint project has been awarded 2 million pounds in funding from the China-UK Research and Innovation Bridges program. Sunamp's PCM heat batteries will be integrated with ORC plants to store heat energy for power generation when the sun doesn’t shine. 

• Submissions for the 2017 Reaxys PhD Prize close on March 13. The international competition is open to Ph.D. students or recent graduates conducting innovative research in synthetic chemistry. Forty-five finalists will present their research at the Reaxys Prize Symposium in Shanghai in October. Three winners will be selected, with each earning a $2,000 award.

• In an interview with Energy Storage Report, Ice Energy CEO Mike Hopkins says his company is looking to tie up partnerships with solar installers in regions where net metering is being phased out.

• Global chemicals production started the first quarter on a strong note, according to the American Chemistry Council. The council’s Global Chemical Production Regional Index showed that that headline global production rose 0.6 percent in January after a similar gain in December.

• Packaging giant Sonoco has again made Fortune magazine's list of most-admired companies, ranking second in the packaging/containers category. 

Alexium International has appointed Dirk Van Hyning as CEO, effective June 30. He will replace Nicholas Clark, who remains on the board and assumes a new role as executive director strategy. Former U.S. congresswoman Karen Thurman has joined Alexium's board as a non-executive director.  

Carnegie Mellon researchers have developed a thermally conductive rubber material that they’ve nicknamed “thubber.” The new material, which can stretch more than six times its initial length, is an electrically insulating composite. Potential applications include soft robotics and athletic wear.

• New from Wise Guy Reports: "Global Thermal Energy Storage (TES) Market Research Report 2017"

Research roundup: Novel PCM plaster; chitosan-derived carbon aerogel; carboxylic esters; Trnsys simulation; more

Ben Welter - Thursday, March 02, 2017

Thermal effects of a novel phase change material (PCM) plaster under different insulation and heating scenarios [Energy and Buildings]

Form-stable phase change material embedded with chitosan-derived carbon aerogel [Materials Letters]

Investigation of Unbranched, Saturated, Carboxylic Esters as Phase Change Materials [Renewable Energy]

A simulation study of a solar collector using phase change materials for air heating application needs [AIP Conference Proceedings]

Intensification of monostearin (phase change material) synthesis in infrared radiated rotating reactor: Optimization and heterogeneous kinetics [Energy Conversion and Management]

Preparation research of novel composite phase change materials based on sodium acetate trihydrate [Applied Thermal Engineering]

The quasi-enthalpy based lattice Boltzmann model for solid-liquid phase change [Applied Thermal Engineering]

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

Synthesis of epoxy-loaded poly(melamine-formaldehyde) microcapsules: effect of pH regulation method and emulsifier selection [Colloids and Surfaces A: Physicochemical and Engineering Aspects]

Dual-encapsulation of octadecanol in thermal/electric conductor for enhanced thermoconductivity and efficient energy storage [Materials Chemistry Frontiers]

A Trnsys simulation of a solar-driven ejector air conditioning system with an integrated PCM cold storage [AIP Conference Proceedings]

PCM briefing: Encapsulation market projected to hit $17.9 billion; report casts shadow on solar-plus-storage

Ben Welter - Monday, February 27, 2017

• The global microencapsulation market is expected to reach $17.94 billion by 2025, according to a new report from Grand View Research. Microtek Laboratories, Encapsys, BASF and Aveka Inc. are among the companies profiled in the report, "Microencapsulation Market Estimates & Trend Analysis By Application (Pharmaceutical, Household Product, Agrochemical, Food Additive, Phase Change Material), By Region (North America, Europe, Asia Pacific, RoW), And Segment Forecasts, 2014 - 2025"

• A Rochester Institute of Technology study casts a shadow on the economics of residential solar-plus-storage. The conclusion: A customer must face high electricity bills and unfavorable net metering or feed-in policies for "grid defection" to work. 

• New from Transparency Market Research: "Reusable Ice Packs Market - Global Industry Analysis, Size, Share, Growth, Trends and Forecast 2016-2024"

• New from QYResearch: "China Bio-Based Phase Change Materials Market Research Report 2017"

A one-day workshop on energy storage for building, solar and wind sectors will be held March 4 at Anna University in Chennai, India. Topics include integration of PCMs for passive cooling in buildings, energy-efficient cool thermal energy storage systems and thermal energy storage technologies for solar applications. 

The National Law Review has posted a detailed update on implementation of the newly revised Toxic Substances Control Act. A key takeaway: Resource and budgetary constraints under the Trump administration could have an impact on the Environmental Protection Agency’s ability to implement the new provisions.

• The latest issue of Chemical & Engineering News features a piece on “natural catalysts” derived from wild plants, mud and earthworms. 

Samit Jain, director at Pluss Advanced Technologies, talks about his company’s pharma logistics products in an interview with India's Financial Express.

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]

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."