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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]

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: 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

Patent application: TES facility with heat storage and heat release functions

Ben Welter - Thursday, February 02, 2017

U.S. patent application 20170030656 (applicant SFI Electronics Technology Inc., Taiwan):

SFI patent drawing"A thermal energy storage facility for use in heat storage and heat release comprises a heat storage/release mechanism constituted by multiple heat storage/heat exchange units stacked up, each unit at least comprises a heat storage board having parallel grooves for loading phase-change material (PCM) therein and a heat exchange plate having micro-channel groups for heat transfer fluid (HTF) flowed through to exchange heat with the PCM; particularly two or more the thermal energy storage facilities can be worked together by combination in series or/and in parallel to input of thermal energy, absorption of thermal energy and both simultaneously from the PCM, and the thermal energy storage facility capably operating at a heat storage temperature higher than 1200° C. is suited for use in solar thermal power generation system to improve overall efficiency of solar thermal power to reach 35-40%."

http://www.freepatentsonline.com/20170030656.pdf

Research roundup: PU-PCM in refrigerated vehicle; indirect solar dryer; triplex tube heat exchangers; more

Ben Welter - Thursday, February 02, 2017

Experimental and numerical study of insulation walls containing a composite layer of PU-PCM and dedicated to refrigerated vehicle [Applied Thermal Engineering]

Development and experimental validation of a CFD model for PCM in a vertical triplex tube heat exchanger [Applied Thermal Engineering]

Recycled additions for improving the thermal conductivity of concrete in preparing energy storage systems [Construction and Building Materials]

Thermal behavior of indirect solar dryer: nocturnal usage of solar air collector with PCM [Journal of Cleaner Production]

Solar still with latent heat energy storage: A review [Innovative Food Science & Emerging Technologies]

2-D numerical investigation of melting of an impure PCM in the arbitrary-shaped annuli [International Journal of Thermal Sciences]

Melting enhancement in triplex-tube latent heat energy storage system using nanoparticles-metal foam combination [Applied Energy]

A concept of a thermal comfort system with energy storage in structure of the building [Problemy Eksploatacji]

Impact of Sodium Silicate Pentahydrate as Phase Change Material in Concrete Cubes for Enhancing the Thermal Comfort [pdf]
[International Journal of Civil Engineering and Technology]

Patent application: Enclosure temperature control system

Ben Welter - Thursday, January 19, 2017

U.S. patent application 20170013789 (applicant Sustainable Energy & Agriculture Technology, Sahuarita, Ariz.):

SEAT patent application drawing"An enclosure temperature control system utilizes a renewable power source and a thermal sink to reduce the overall power requirements from a power grid. A renewable power source, such as a solar panel may provide power that drives the components required to maintain the greenhouse temperature within upper and lower limits, including a HVAC system and/or a heat transfer system coupled with a thermal sink. The thermal sink includes a phase change material that releases heat when it solidifies and this heat can be used to heat the greenhouse. Likewise, the phase change material absorbs heat during the day to reduce the temperature within the greenhouse. A heat transfer system may be coupled with the phase change material and a solid conductor component within the tank of a phase change material may increase thermal transfer rate."

http://www.freepatentsonline.com/20170013789.pdf