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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.




Research roundup: Self-luminous wood composite; palmitic acid/mullite composite; corrosion sensitivity of metal alloys; more

Ben Welter - Tuesday, February 12, 2019

From Energy Storage Materials:

Self-luminous wood composite for both thermal and light energy storage

From International Journal of Refrigeration:

The thermal performances of a refrigerator incorporating a Phase Change Material

From Renewable Energy:

Enhanced thermal conductivity of palmitic acid/mullite phase change composite with graphite powder for thermal energy storage
An experimental study on the corrosion sensitivity of metal alloys for usage in PCM thermal energy storages

From Energy Conversion and Management:

Sorption thermal energy storage: Hybrid coating/granules adsorber design and hybrid TCM/PCM operation
Novel hybrid microencapsulated phase change materials incorporated wallboard for year-long year energy storage in buildings

From Thermochimica Acta:

Experimental Investigation on Thermal Properties of Sodium Acetate Trihydrate based Phase Change Materials for Thermal Energy Storage
The preparation of AgI/Au/foam-Cu as a framework of composite for water-based cool storage phase-change material with low supercooling

From Energy and Buildings:

Nano-encapsulation of phase change materials: from design to thermal performance, simulations and toxicological assessment
Investigation of phase change materials integrated with fin-tube baseboard convector for space heating

From Journal of Energy Storage:

Nano-enhancement of phase change material in a shell and multi-PCM-tube heat exchanger

From Applied Energy:

Numerical investigation of phase change material thermal storage for space cooling

From Journal of Materials Chemistry A:

Vertically aligned carbon fibers as supporting scaffolds for phase change composites with anisotropic thermal-conductivity and good shape-stability

Patent application: Aliphatic materials in heating and cooling applications

Ben Welter - Wednesday, February 06, 2019

U.S. patent application 20190033009 (applicant Elevance Renewable Sciences Inc., Woodridge, Ill.):

"Aliphatic materials and their use in passive heating and cooling applications are generally disclosed. In some embodiments, dibasic acids and esters (diesters) thereof and their use in passive heating and cooling applications are disclosed. In some embodiments, C18 dibasic acids and esters thereof are disclosed, including their use in passive heating and cooling applications. In some embodiments, various olefins, including alkenes and olefinic acids and esters, are disclosed, including their use in passive heating and cooling applications."

PureTemp introduces temperature-control fabric coating

Ben Welter - Wednesday, January 23, 2019

PureTemp LLC has developed a fabric coating engineered to provide an effective buffer against ambient temperature swings in consumer products such as apparel, footwear, bedding, safety, medical, workwear and industrial applications.

Scanning electron microscope image of PureTemp fabric coating Through a proprietary process, PureTemp's biobased phase change material is enclosed in spherical microcapsules and bound to the surface of the fabric. PCMs absorb, store and release thermal energy as they cycle between solid and liquid states. The PCM coating interacts continuously with the unique microclimate of the human body, storing and releasing energy to balance body temperature and increase comfort.

PureTemp honeycomb pattern coatings are available for knit, woven, interlock, circular knits, nonwoven, cotton, polyester and other blends. The photo above shows what PureTemp coated fabric looks like under a scanning electron microscope.

The Minnesota company began producing the world’s first 100 percent biobased PCMs in 2007. PureTemp PCMs, developed in three years of research sponsored by the U.S. Department of Agriculture, are used in a wide variety of temperature-control applications, from cooling vests and warming blankets to shipping containers and coffee mugs.

PureTemp's Dan Keller is directing the business initiative. For more information on PureTemp coated fabrics, contact him via or visit

Research roundup: Solar storage tank; concentric PCM module; supercooling degree improvement; more

Ben Welter - Monday, January 21, 2019

From Journal of Thermal Science:

Energy Storage Performance of a PCM in the Solar Storage Tank

From International Journal of Applied Engineering Research:

Numerical assessment of suitability of phase-change materials in a concentric PCM-module for thermal storage applications [pdf]

From International Journal of Energy Research:

Experimental measurements and numerical computation of nanofluid and microencapsulated phase change material in porous material

From IOP Conference Series: Materials Science and Engineering:

Nano-enhanced phase change material effects on the supercooling degree improvement: A review

From Renewable Energy:

Potential of ventilation systems with thermal energy storage using PCMs applied to air conditioned buildings

From Journal of Mechanical Engineering and Technology:

Thermal performance analysis of nano enhanced paraffin wax and myristic acid

From Solar Energy:

Synthesis and characterization of microencapsulated phase change materials with comb-like acrylic co-polymer shell as thermal energy storage materials
Sensible and latent heat energy storage systems for concentrated solar power plants, exergy efficiency comparison

From Solar Energy Materials and Solar Cells:

Thermal energy storage characteristics of myristic acid-palmitic eutectic mixtures encapsulated in PMMA shell

From Thermal Science and Engineering Progress:

Parametric analysis and optimization of an underfloor solar assisted heating system with phase change materials

From International Journal of Heat and Mass Transfer:

The improved enthalpy-transforming based lattice Boltzmann model for solid-liquid phase change

From Applied Energy:

Innovative design of superhydrophobic thermal energy-storage materials by microencapsulation of n-docosane with nanostructured ZnO/SiO2 shell

From AIP Conference Proceedings:

Preparation and characterization of nanoparticle blended polymers for thermal energy storage applications

Research roundup: Hydrophobic lauric acid; paraffin in heat exchanger; EnergyPlus vs. IES; more

Ben Welter - Thursday, January 10, 2019

From Journal of Energy Storage:

Preparation of hydrophobic lauric acid/SiO2 shape-stabilized phase change materials for thermal energy storage

From Applied Thermal Engineering:

Development of paraffin wax as phase change material based latent heat storage in heat exchanger

From Renewable Energy:

Characterization and stability study of a form-stable erythritol/expanded graphite composite phase change material for thermal energy storage

From Journal of Building Engineering:

Comparison of EnergyPlus and IES to model a complex university building using three scenarios: Free-floating, ideal air load system, and detailed

From 4th International Conference on Renewable Energies for Developing Countries :

Phase Change Materials in a Domestic Solar Hot Water Storage Tank of the Lebanese Market
Numerical and experimental investigations of a PCM integrated solar chimney
Integrating a High Solar Combi-Plus System using PCM Storage in a Smart Network: KSA Case Study

From International Journal of Advanced Research In Applied Sciences, Engineering and Technology:

Solar Cooker with Heat Storage System: A Review [pdf]

From Energy and Buildings:

From Solar Energy Materials and Solar Cells:

Bio-based poly (lactic acid)/high-density polyethylene blends as shape-stabilized phase change material for thermal energy storage applications

From Construction and Building Materials:

Microstructure-guided numerical simulation to evaluate the influence of phase change materials (PCMs) on the freeze-thaw response of concrete pavements

From Energy Conversion and Management:

Thermal management of Li-ion battery pack with the application of flexible form-stable composite phase change materials
Experimental investigation on cylindrically macro-encapsulated latent heat storage for space heating applications

From International Communications in Heat and Mass Transfer:

Experimental investigation on using a novel phase change material (PCM) in micro structure photovoltaic cooling system
Experimental investigation on a novel composite heat pipe with phase change materials coated on the adiabatic section

From Journal of Cleaner Production:

PCM-equipped infant warming mat set for large-scale trial in Rwanda

Ben Welter - Monday, January 07, 2019

Dr. Anne HansenAn infant warming mat developed at Lawrence Berkeley National Laboratory in California is undergoing approval for a six-month trial at 10 hospitals in Rwanda beginning next fall. The DREAM infant warmer uses biobased phase change material to keep newborns warm in places where electricity is unavailable or unreliable. Dr. Anne Hansen, medical director of the neonatal intensive care unit at Boston Children's Hospital, helped develop the mat and is directing the trial. In an interview, she provided background on the device and explained how it works.

Q: Tell me about the need for this device. What problem does it solve?

A: In low- and middle-income countries, hypothermia is a contributing cause in about one million infant deaths per year. Newborn babies, especially babies who are low birth weight or preterm or both, tend to cool to the temperature of their environment. Therefore even in warm climates like that of sub-Saharan Africa, newborns can become dangerously cold. It's rare for hypothermia to be the primary cause of death, but hypothermia in newborns can contribute to respiratory problems, glucose regulation, immune system function, and most importantly growth, including brain growth, and therefore neuro-developmental outcome. This can perpetuate the cycle of poverty.

Q: Why is this a particular problem for babies born in lower-income countries?

A: Babies born in a rich country receive a heat chain that protects them all the way from the delivery room until they go home from the hospital. This includes electric warming tables and incubators. In poor countries, this heat chain is more difficult to ensure. The supply of electricity can be inconsistent at best, the expensive warmers and incubators may be unaffordable. If they can be acquired, the nurses may not have the training to work these complex medical devices, causing hypo- and hyperthermia, as well as raising infection control concerns given how hard they can be to clean between uses. Finally, unless the facility has advanced biomedical engineers to provide the maintenance and repairs, the warmers do not last long. Because of all these problems, ensuring that newborns in resource-limited settings have access to a consistent heat chain requires a lot of workarounds. 

The World Health Organization recommends skin-to-skin care, where you put a newborn directly on the mother's chest and she provides the external heat source. Skin-to-skin is great; we are total fans of skin-to-skin. The problem is that there are times where it's not very feasible, when the mother is sick or the mother dies in childbirth or if she has twins or triplets. If the baby is sick and requires medical assessment and treatments, the skin-to-skin positioning may not be feasible. Also, importantly, it's hard to be a human incubator for weeks to even months while a preterm baby gets old enough and mature enough to not need this external heat source. So providing heat by continuous skin-to-skin all day, all night for a long time, mothers just can't do that. They need to bathe, they may need to cook over a fire, or take care of their other children. So they have to stop; they put the baby down on a regular bed and then the baby gets cold. Finally, for the smallest babies, skin-to-skin may not provide enough heat; they're only getting heat from the part of their skin that is in direct contact with the mother's chest, but they aren't getting any heat from their backs.

We set out to design a warmer both to complement to skin-to-skin care when a mother wants to put her baby down, that could also be additive to skin-to-skin care when it is not providing enough heat. It needed to be electricity-free, inexpensive, intuitive to use, requiring minimal training, easily washed and reused with a goal of a thousand cycles.

Q: What was your role in the development of the device?

A: I've been working with Partners In Health (called Inshuti Mi Buzima in Rwanda) for almost 10 years. They work in very close collaboration with the Rwanda Ministry of Health. When I first went there in 2010, we helped them to develop and implement their national standards for newborn medicine. One of the problems that really stood out for me was that the options for thermoregulation were not working. When I came home, I partnered with Lawrence Berkeley National Lab to think about some other alternatives. We looked at a lot of ideas and ultimately settled on this phase change approach because it's so simple and straightforward.

DREAM warming mat thermosThe engineers did the actual design work, but we worked closely with them over many years to fine-tune it, figuring out how long it needed to be, how heavy it could be, how much people were willing to pay for it. From the outset we worked hand in glove with both Rwandan clinicians and the Ministry of Health. For example, the warmer is heated in thermos that holds boiling water to melt the PCM. The Ministry of Health was insistent that the thermos be wide-based and stable so that it wouldn't tip over when it was being filled with the boiling water and present any risk of burns.

We have completed two clinical studies of the warmer in Rwanda and it has performed extremely well. We are just gearing up to do what I hope will be a definitive large study with 10 hospitals in Rwanda this year. The Rwanda Ministry of Health has been amazing through all of this, supporting and facilitating all of our studies. We' want to have the warmer approved by the Rwandan Standards Bureau, which is like their FDA. They have also expressed interest in sponsoring the warmer for an international approval process, but we are going to wait on this until after we have the results from our large trial that we will be conducting later this year.

Q: Describe how the device functions.

DREAM warming mat packsA: We use your phase change material, PureTemp 37, configured as a set of 12 candles, each in its own plastic sleeve. The mat measures about 45.7 cm, by 25.4 cm, by 1.91 cm thick and contains about 1.2 kilograms of PCM. This arrangement allows the mat to be rolled up for charging or storage. Boiling water is used to charge the mat. All human civilizations know how to heat water, whether it is using a tea kettle with electricity or coal without. You heat 1.7 liters of water to boiling temperature, which provides the exact amount of energy needed to melt all the wax. The mat has a little temperature indicator that shows when it is cool enough to be safe to use. Once it has cooled, you dry it off and slip it in a little insulating pad. Then you put the baby, ideally naked, on the pad. This tends to be a population that does not have diapers, so a critical piece of the design was to avoid any fabric, Velcro or anything else that couldn't easily be cleaned with standard hospital cleanser. Ideally you give the baby a hat, and socks if you've got them, and then you wrap the baby and the warmer up in a blanket. The warmer stays hot for up to six hours, exactly at skin temperature.

Q: What's the projected price for a single unit?

A: Our goal is to keep it well under $100.

Q: Tell me about the upcoming study.

A: We're going to start this study in September of 2019 and it will run for six months. It's a complex study design called a step wedge study, specifically chosen to avoid the ethical conflict of having control patients such that one cold baby gets the warmer and another in the next bed does not. Instead, we will collect pre-data prior to introducing the warmer and this will serve as our control data. Then we will introduce the warmer, and use our post-data as our treatment data. Our hope is that we will find a reduction in hypothermia, hospital length of stay, and mortality, with improvement in growth. If so, then we we'll move to full-scale production, first for distribution across the rest of Rwanda and then in other appropriate countries in the sub-Saharan Africa.

Q: Where does the mat stand as far as approval processes in Africa?

A: We are still really at the prototype phase. We met this summer with a representative of the Rwandan Standards Bureau in Kigali. He said that, based on the results of our two preliminary pilot studies with 204 uses, it would be appropriate to for us to submit the paperwork for approval. We have not done that yet because they want to approve the absolutely final design, and we are still doing a bit more work, finding a more robust plastic and temperature indicator. Once we have our final design, we will submit the paperwork to the Rwandan Standards Bureau, sponsored by the Ministry of Health. Based on our feedback from this summer's meeting I am optimistic that they will approve it.

Rwandan twins on warming mat

Q: What's been the most satisfying part of this project for you?

A: That is the easiest question. It is absolutely 100 percent the mothers. I will never forget the very first patients that we enrolled, a pair of twins. When we walked into the hospital that very first day, we had just explained to the nurses how to prepare the warmer, we were ready to enroll our first patients, and there was this mother with these twins. She looked so tired, not smiling or really interacting. Through a translator I asked her if she would like to have her babies enrolled in this study. She learned what it was, and signed the consent form.

One of the babies was so cold that we did the combination of the skin-to-skin and warmer across the back, and the other baby went straight on the warmer. She looked at the babies and she saw them getting warm. She just had this unbelievable look of relief - she was so happy. She said, "This is the first time that I've seen my babies look comfortable since they were born."

Research roundup: Thermally modulated fiber sorbents; metamaterial-based radiative cooling; stearic–capric acid/porous nanoceramics; more

Ben Welter - Friday, January 04, 2019

From Industrial & Engineering Chemistry Research:

Development of Phase-Change-Based Thermally Modulated Fiber Sorbents

From ChemistrySelect:

Preparation and Thermal Properties of 1‐Hexadecanol‐Palmitic Acid Eutectic Mixture/Activated Carbon Composite Phase Change Material for Thermal Energy Storage

From Energies:

Thermal Conductivity Enhancement of Phase Change Materials for Low-Temperature Thermal Energy Storage Applications [pdf]
Metamaterial-Based Radiative Cooling: Towards Energy-Free All-Day Cooling [pdf]

From Renewable and Sustainable Energy Reviews:

A review and evaluation of thermal insulation materials and methods for thermal energy storage systems

From Materials Letters:

Stearic–capric acid/porous nanoceramics as a novel form-stable composite phase change material (FSPCM) for thermal energy storage

From International Refrigeration and Air Conditioning Conference:

Analysis of TES with PCM (Solid/Liquid) Integrated in a Residential System
Experimental Study on Portable Air-Conditioning System with Enhanced PCM Condenser

Research roundup: Dynamic building envelope; multilayer glazing facades; spherical capsule with pin-fins; more

Ben Welter - Wednesday, December 05, 2018

From Applied Energy:

Form-stable and thermally induced flexible composite phase change material for thermal energy storage and thermal management applications
Influence of the storage period between charge and discharge in a latent heat thermal energy storage system working under partial load operating conditions
Dynamic building envelope with PCM for cooling purposes – Proof of concept

From Air Force Research Laboratory:

High Energy Advanced Thermal Storage (HEATS) [pdf]

From Solar Energy:

Synthesis and characterization of sensible thermal heat storage mixture containing phosphate compound of cobalt and sodium
Thermal performance of non-ventilated multilayer glazing facades filled with phase change material

From Applied Thermal Engineering:

Charging nanoparticle enhanced bio-based PCM in open cell metallic foams: An experimental investigation
Thermal performance analysis and optimization of a spherical PCM capsule with pin-fins for cold storage
A phase change material with enhanced thermal conductivity and secondary heat dissipation capability by introducing a binary thermal conductive skeleton for battery thermal management

From Materials:

Characterization of MgCl2·6H2O-Based Eutectic/Expanded Perlite Composite Phase Change Material with Low Thermal Conductivity

From Solar Energy Materials and Solar Cells:

Size controlled lauric acid/silicon dioxide nanocapsules for thermal energy storage

From Energy Procedia:

Life Cycle Assessment of thermal energy storage materials and components

From MATEC Web of Conferences:

A Numerical Method for Analysing Heat Conduction in Composites Containing Encapsulated Phase Change Materials [pdf]

From Journal of Building Engineering:

Research roundup: Thermo-regulating bamboo fabric; PCM emulsions; nanoparticle-enhanced composite; more

Ben Welter - Friday, November 30, 2018

From Journal of Cleaner Production:

Autonomous greenhouse microclimate through hydroponic design and refurbished thermal energy by phase change material

From Journal of Energy Storage:

Development of heat accumulation unit based on heterogeneous structure of MF/PCM for cogeneration units

From Textile Research Journal:

Preparation and evaluation of thermo-regulating bamboo fabric treated by microencapsulated phase change materials

From International Journal of Clothing Science and Technology:

Development of thermo-regulating fabrics using PCM microcapsules with poly(methyl methacrylate-co-2-hydroxy ethyl methacrylate) shell and n-alkane core

From Canadian Society for Mechanical Engineering International Congress:

Preparation and Properties of Nanoparticle-enhanced Composite Phase Change Material with Ceramic Porous Media

From Solar Energy Materials and Solar Cells:

A comprehensive review on phase change material emulsions: Fabrication, characteristics, and heat transfer performance

From 59th Conference on Simulation and Modelling:

Convective Melting Modeling Approach for Phase Change Materials with Variable Boundary Heating

From Energy Conversion and Management:

Simultaneous energy storage and recovery in the triplex-tube heat exchanger with PCM, copper fins and Al2O3 nanoparticles

From International Journal of Energy Research:

Operation strategies guideline for packed bed thermal energy storage systems [pdf]

From Journal of Molecular Liquids:

Solidification process of hybrid nano-enhanced phase change material in a LHTESS with tree-like branching fin in the presence of thermal radiation

From Energy:

Experiment study on thermal performance of building integrated with double layers shape-stabilized phase change material wallboard

Patent application: Cables made of phase change material

Ben Welter - Thursday, November 29, 2018

U.S. patent application 20180334775 (applicant E.I. du Pont de Nemours and Co., Wilmington, Del.):

"A phase change material (PCM) is useful for thermal management in various applications such as automotive, building, packaging, garments, and footwear, and in devices such as wires and cables. The cable described herein comprises a core and a PCM layer surrounding the core. The PCM layer comprises a PCM composition, which in turn comprises a 1,3-propanediol fatty acid ester. The core consists of a yarn, strand or wire made of a natural or synthetic polymeric material or a metal."