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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.




Hybrid sensible-latent heat storage concept achieves high energy densities

Ben Welter - Tuesday, October 31, 2017

Christoph Zauner of AITChistoph Zauner, a research scientist at the Austrian Institute of Technology, has been investigating the use of phase change material for a variety of applications since 2010. His most recent papers include “Experimental characterization and simulation of a hybrid sensible-latent heat storage,” published earlier this year in Applied Energy. He discussed his work in an email interview. 

Q: How did you first become interested in phase change material?

A: I worked for quite some time in the field of solar thermal energy and was especially focusing on industrial application with non-standard solar collector, so-called medium temperature collectors. This more efficient class of collectors (concentrating and non-concentrating) can produce temperature up to 250° C heating pressurized water, oil and generate steam. In order to achieve high solar fractions (i.e. cover much more than 10% of the total required process energy by solar energy), one needs to store energy. Standard storages (steam, oil, water) have limitations and latent storage certain advantages. Thus, we started developing such storages. In the meantime, we want to use it for a much broader range of applications (not only solar thermal).

Q: Describe the hybrid sensible-latent heat storage concept you have been working on.

Inverted shell and tube heat exchanger

A: In our new concept, we place the PCM inside the tubes of a modified shell-and-tube heat exchanger [shown above]. This is in contrast to the well-known approach of placing it outside. On the shell side we use a heat transfer fluid (in our first prototype we used oil) which at the same time serves as a sensible storage medium. Thus, we achieve a hybrid sensible-latent heat storage, which offers several opportunities:

• Heat transfer fluid (in our case oil) and PCM fractions can be varied over a wide range, i.e. a hybrid sensible-latent heat storage is realized. Advantages of both domains can be exploited, such as high energy density of the PCM and high power density of sensible storages

• Fewer weld seams as for the standard concept (PCM outside many small tubes) leads to storage cost reduction

• Larger heat transfer area between tubes and PCM enables higher storage power

• Our tubes serve as a macroencapsulation of the PCM, which serves as protection and increases storage lifetime.

Q: Is HDPE in use as a PCM in any commercialized application?

A: HDPE is a so-called commodity plastics. It is the kind of polymer used most out of all polymers. As such it is produced in a multi-million-ton scale each year. Also a versatile recycling industry is in place, which allows for further cost reduction potential (we know which types are suitable and which ones are not). Usually HDPE is used to contain PCMs only. There are no commercial applications yet, where HDPE is used as PCM. Currently we are investigating various possible applications.

Q: How do you anticipate the viscosity of the PCM affecting the thermal modeling? At what point does this significantly contribute to the internal convection in the tube?

A: Convection plays a minor role for our HDPE grade. This may be somewhat different for other grades and was analyzed in our lab. Our models can be adapted to incorporate convection, too. If necessary, we also have 3d-CFD models available.

AIT test tank
A 40 kWh, 100 kW peak power hybrid latent-sensible storage system was successfully tested at AIT labs at temperatures up to 200 °C.
Q: Beyond manufacturing costs, what are the benefits of the inverted shell-and-tube in comparison to other geometries such as a packed bed?

A: Apart from the advantages mentioned above, there is one particular key advantage over packed beds: packing density. Our storage can achieve up to 90% PCM volume density, whereas the theoretical limit for ideally packed spheres is 74%. In a packed bed, however, one does not have “ideal packing,” but the situation of “random packing,” where PCM volume fractions of 64% are achieved.

We found a certain way, which we do not disclose, how to actually fill up the whole tubes even for the crystallized (shrinked) PCM. Usually, PCM macroencapsulations are filled up to 100% only in the molten state, which further reduces the final volume PCM fraction of the whole storage (i.e. kWh/m3).

So summing up: We achieve much higher energy densities. 

Q: How was the DSC data implemented into the thermal modeling?

A: Actual measurement data can be easily implemented in our Dymola model. We use different approaches for the two models described in the paper (Stefan-model, cp(T)-model).

However, it is important to emphasize that one has to perform the DSC measurement “in the correct way.” This means one has to use the correct DSC parameter sets. By comparing the data obtained from different DSC settings to experimental storage data, we found out that very often DSC measurements are done in the wrong way. Wrong DSC settings lead to incorrect material values (especially melting temperature, sub-cooling and phase change enthalpy). However, we know now how to do it correctly and implemented the corresponding curves in the models.
Q: Would a sharper phase change peak be advantageous to the proposed application? How would this also affect the Stefan model?
A: We already designed storages for different applications (various combinations of low/high power, low/high capacity, different temperature levels). Sometimes it is very important to actually have a PCM with a sharp peak and sometimes even large subcooling doesn’t matter. It depends on the application.

Of course, one has to be careful by applying the various models (not only the Stefan model) and not to spoil the underlying assumptions. We learned a lot in that direction by comparing experimental storage data to simulations and know now very well where the limits are.
Q: What are the next steps in your investigation of this storage concept for district heating networks and industrial processes? How close is it to possible commercialization?

A: It is important to emphasize that AIT is not a university, but more like a real company which has to do “real business” and earn “real money.” We do business in various ways and offer different business models.

This ranges from material characterization or simulations directly done (and paid) by customers. We also offer storage engineering using our models and experimental know-how to storage manufacturers. We also demonstrate storages at real demo sites (currently we have projects in polymer extrusion and aluminum die casting) and evaluate their potential in various companies (e.g. we are currently investing a specific process in steel industry using a PCM-steam-storage concept).

We can provide various services or even serve as a “one-stop-shop” for energy optimization of industrial processes using storages. This starts from analyzing the process in detail (incl. monitoring), designing the storage (including integration), organization of storage manufacturing, integration at the plant and commissioning. Also this includes financing aspects (contracting, subsidies, R&D projects etc.).

The storages are permanently optimized but can be bought right away as we are only using industrially available PCMs (we also tested [PureTemp PCMs] and might use them, of course) and heat exchanger/storage manufacturing techniques.

Q: What other projects are you working on that might be of interest to the PCM community?

A: We also work on “overheating solutions” using PCM. Some articles have been published in that direction already, including “High temperature phase change materials for the overheating protection of facade integrated solar thermal collectors.” Also, we employ PCMs in car batteries and developed concepts there. We simulated and tested various prototypes of real batteries.

A related topic is development of new insulations, especially aerogel-based. This is very much needed for storages and also for energy efficiency in industries (“stop wasting energy first, then re-use it!”). 

[For more examples, see]

We are very much looking for partners for new PCMs. We do not produce them on our own. However, we do some development with partners on organic PCMs.

Research roundup: Metal corrosion rate assessment; industrial heat storage; erythritol, glycerol and olive oil; more

Ben Welter - Monday, October 30, 2017

A Review of Phase Change Materials as an Alternative for Solar Thermal Energy Storage [Materials Today]

Step by Step Methodology for the Assessment of Metal Corrosion Rate with PCMs Suitable for Low Temperature Heat Storage Applications [Materials Today]

Investigation of the effect on the efficiency of phase change material placed in solar collector tank [Thermal Science and Engineering Progress]

Generalized diagrams of energy storage efficiency for latent heat thermal storage system in concentrated solar power plant [Applied Thermal Engineering]

Thermal energy storage with phase change materials to increase the efficiency of solar photovoltaic modules [Energy Procedia]

Development of industrial PCM heat storage lab prototype [Energy Procedia]

High Power Latent Heat Storages With 3D Wire Structures – Numerical Evaluation Of Phase Change Behavior [Energy Procedia]

Experimental comparison of two heat exchanger concepts for latent heat storage applications [Energy Procedia]

Erythritol, glycerol, their blends, and olive oil, as sustainable phase change materials [Energy Procedia]

PCM briefing: Survey finds chemists think field is short on innovation; Lufthansa Cargo partners with va-Q-tec

Ben Welter - Monday, October 30, 2017

• A recent survey by Reaxys found that many chemists don’t think the field is innovative enough. Eighty percent said there is too much emphasis on research with industrial applications, which is stifling innovation. Reaxys is a chemistry research tool developed by Elsevier

Min Zhu, assistant professor of textile development and marketing at the Fashion Institute of Technology, will speak about the future of phase change materials at a textiles conference in New York City Nov. 8. 

Lufthansa Cargo has partnered with va-Q-tec AG to offer the temperature-controlled specialist's va-Q-tainer thermal containers across the German carrier’s global network.

• Scientists investigating how scavenging animals are adapting to the monoculture palm oil plantations in Borneo were surprised by what turned up in their traps. "In the jungles and border regions, the team found animals such as civets, otters, mongooses and pigs," Oils & Fats International magazine reports. "But the closer they got to the plantations where the land had been disturbed and human activity was frequent, the fewer species they found until only one stood out – the Southeast Asian water monitor." The big lizards are thriving, thanks to a plentiful supply of food and less competition from mammalian scavengers and predators. 

• Researchers at the University of Maryland have developed a thermally conductive and strong textile from fibers of aligned boron nitride nanosheets embedded in a polymer matrix that can cool a person down by up to 2° C.  

Patent application: Method and apparatus for absorbing thermal energy

Ben Welter - Friday, October 27, 2017

U.S. patent application 20170268829 (applicant Rini Technologies Inc., Oviedo, Fla.):

"The subject invention pertains to a method and apparatus for storing thermal energy. The subject thermal energy storage apparatus can function as a heat absorber in a cooling system. A cooling system can incorporate a cooling cycle that utilizes thermal energy storage and has two coolant loops. The primary cooling loop acquires the waste heat from a heat source, such as an electronic device, by heat transfer to the primary coolant via, for example, a sensible heat process (where sensible heat is heat absorbed or transmitted by a substance during a change in temperature which is not accompanied by a change of state) or by evaporating the primary coolant through a latent heat phase change process. The waste heat absorbed by the primary coolant is transferred to the host material of the heat absorber. The subject invention uses a high thermal conductivity host material to house a lower thermal conductivity phase change material, in order to achieve a thermal energy absorber that has a high effective thermal conductivity."

PCM briefing: Thermal storage capacity on the rise; clinical trial for prosthetics liner

Ben Welter - Friday, October 27, 2017

• Thermal energy storage exceeds the capacity of battery storage now in operation, according to a new report from the International Renewable Energy Agency. Greentech Media reports that a recent resurgence in concentrated solar power development promises to increase that advantage.

• New from QYResearch Group: "Global Thermal Energy Storage Market Size, Status and Forecast 2022"

• New from Persistence Market Research: "Advanced Phase Change Material (PCM) Market - Global Industry Analysis and Forecast to 2020"

Alpha SmartTemp liner• The effectiveness of a PCM-infused prosthetics liner made by Ohio Willow Wood Co. will be put to the test in a two-year clinical trial. The liner is designed to absorb heat and reduce sweating where a prosthesis meets skin. The study, funded by a $140,000 Department of Defense grant, will be conducted by the University of Pittsburgh and Widener University.

• Registration is open for "2-8°C Solutions: Design variables and constraints," the next webinar in Sonoco ThermoSafe's temperature assurance packaging series. Frank Butch, director of engineering at Sonoco ThermoSafe, and Lisa Barbieri Moher, North American head of distribution packaging and graphics at Sanofi, will lead the one-hour class, to be held Nov. 14.

Sonoco ThermoSafe's development of the LD7 Quarter PMC pallet shipper won first place for Excellence in Collaboration at the Cold Chain GDP & Temperature Management Global Forum in Chicago last month. ThermoSafe's ChillTech reusable PCM system was runner-up in the Excellence in Technological Innovation category.

In a recent interview with Innovation in Textiles, CEO Dirk Van Hyning of PCM-maker Alexium International discussed U.S. efforts to curb the use of halogenated flame retardants.

Patent application: Economized cycle with thermal energy storage

Ben Welter - Friday, October 27, 2017

U.S. patent application 20170307266 (applicant Carrier Corp., Farmington, Conn.):

"In one aspect, an air conditioning system is provided. The air conditioning system includes a refrigeration circuit having a refrigerant and an economizer circuit, and a subcooling circuit thermally coupled to the refrigeration circuit, the subcooling circuit including a thermal energy storage (TES) unit and a phase change material (PCM) for thermal exchange with the refrigerant."

Patent application: Heat retaining dish assembly

Ben Welter - Friday, October 27, 2017

Patent application 20170303710 (applicant Tempra Technology Inc., Bradenton, Fla.):

"A dish assembly for serving food includes a dish housing that defines a surface, upon which the food can be placed, and an inner compartment, a phase-change material within the inner compartment, and an electrically-conductive element inside the inner compartment and thermally coupled to the phase-change material. In a typical implementation, the phase-change material is adapted to melt in response to the electrically-conductive element being heated by an electromagnetic induction heater. The thus heated dish assembly can facilitate getting hot food to a table while it is still hot, and once at the table, keeping that hot food at least warm for quite some time, while it is consumed."

RAL Quality Association PCM welcomes Microtek, bids farewell to BASF

Ben Welter - Thursday, October 26, 2017

The RAL Quality Association PCM, meeting in Germany last week, welcomed its newest member, Microtek Labs, and said goodbye to one of its founding members, BASF. 

Microtek CEO Tim Riazzi introduced his company with a brief overview of its history, research efforts and products. He said Microtek may seek RAL certification for its phase change materials, including the new Nextek line of microencapsulated PCMs. Microtek, which purchased BASF's Micronal line of microencapsulated phase change material earlier this year, will officially assume BASF's RAL membership on Jan. 1, 2018.

Samit Jain, managing director of Pluss Advanced Technologies, was also attending his first RAL meeting. Jain, right, presented an overview of Pluss R&D efforts and its PCM product line, which is focused on addressing four challenges: vaccine waste, food spoilage, neonatal deaths and energy inefficiency in buildings. 

Other member organizations attending the meeting in Dusseldorf were Croda, va-Q-tec AG, Rubitherm, ZAE Bayern, Fraunhofer ISE, Sasol Germany GmbH, Sunamp Ltd., EMCO, PCM Technology and Entropy Solutions. Discussion topics included RAL-GZ 896 quality and testing specifications; registration of the new RAL quality mark; efforts to integrate PCM in the German Energy Saving Ordinance; ISSO publication 111 PCM in Netherlands; and the new Phase Change Materials Industry Association of North America.

As the meeting drew to a close, Prof. Bernd Boiting, chairman of the quality association, thanked BASF's Marco Schmidt for his contributions. As Micronal's head of business management at BASF, Schmidt played a key role in many RAL initiatives, including the development of a Google map that will showcase PCM building projects around the world.

RAL's next meeting is scheduled for March 1, 2018, in Dusseldorf. 

Sunamp expands factory, warehouse space

Ben Welter - Thursday, October 26, 2017

Sunamp Ltd. is moving its phase change production unit into a 15,000-square-foot factory and warehouse space near the company's headquarters in East Lothian, Scotland. The new space is three times the size of Sunamp's current production space and will allow the company to bring in test rigs and a vehicle lift to meet the needs of its automotive division. Sunamp says the move will free up "much needed lab space at headquarters to expand our current chemical material and HVAC product R&D operations."

Other recent developments at Sunamp:

Sunamp EV• The company showcased its cooling system for refrigerated vans at the Cenex Low Carbon Vehicle event in Millbank, England, last month. The system, developed with bodybuilder Paneltex, route optimization software maker Route Monkey and the Low Carbon Vehicle Partnership, integrates low-temperature PCMs in electric delivery vans for supermarket deliveries. It was among the winners in a proof of concept competition sponsored by the Office for Low Emission Vehicles and Innovate UK.

• Along with other companies involved in the Smart Islands Energy Systems (SMILE) initiative, Sunamp is gearing up for the implementation phase of the Orkney pilot project, starting in November. Sunamp's heat batteries are among nine smart-grid technologies to be demonstrated in the four-year SMILE project, launched in May 2017 and funded under the European Union’s Horizon 2020 program.

• Sunamp's PCM heat batteries were featured this week on the UK television show "Grand Designs."

Research roundup: TES in Toronto high-rises; rotary desiccant cooling systems; natural convection characterization; more

Ben Welter - Tuesday, October 24, 2017

Experimental investigation of latent thermal energy storage in high-rise residential buildings in Toronto [Energy Procedia]

Study on the Performance of Heat Storage and Heat Release of Water Storage Tank with PCMs [Energy and Buildings]

Design of effective fins for fast PCM melting and solidification in shell-and-tube latent heat thermal energy storage through topology optimization [Applied Energy]

Integrating photovoltaic thermal collectors and thermal energy storage systems using phase change materials with rotary desiccant cooling systems [Sustainable Cities and Society]

Development of thermal energy storage cementitious composites (TESC) containing a novel paraffin/hydrophobic expanded perlite composite phase change material [Solar Energy]

Experimental analysis of solar photovoltaic unit integrated with free cool thermal energy storage system [Solar Energy]

Natural convection characterization during melting of phase change materials: Development of a simplified front tracking method [Solar Energy]

Thermal behavior of latent thermal energy storage unit using two phase change materials: Effects of HTF inlet temperature [Case Studies in Thermal Engineering]

Experimental Investigation of a New Passive Thermal Management System for a Li-Ion Battery Pack Using Phase Change Composite Material [Electrochimica Acta]