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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.

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Research roundup: Enthalpy-temperature plots; solar wall collector; vertical U-tube heat exchanger; more

Ben Welter - Monday, November 20, 2017

From Journal of Energy Storage:

Enthalpy-temperature plots to compare calorimetric measurements of phase change materials at different sample scales
Preparation and enhanced thermal performance of novel (solid to gel) form-stable eutectic PCM modified by nano-graphene platelets

From International Journal of Heat and Mass Transfer:

An implicit algorithm for melting and settling of phase change material inside macrocapsules

From Energy Procedia:

Experimental study of a solar wall collector with PCM towards the natural ventilation of model house
Experimental Study of Solar - Phase Change Material Wall for Domestic Hot Water Production under the Tropical Climate

From Applied Thermal Engineering:

Efficiency analysis of utilizing phase change materials as grout for a vertical U-tube heat exchanger coupled ground source heat pump system

From Sustainable Cities and Societies:

PCM Thermal Energy Storage in Solar Heating of Ventilation Air—Experimental and Numerical Investigations

From International Communications in Heat and Mass Transfer:

Evaluation of thermophysical properties of refrigerant clathrates with additives

From Solar Energy:

A comprehensive study on the effect of hot water demand and PCM integration on the performance of SDHW system

Agenda set for 5th Swiss Symposium Thermal Energy Storage

Ben Welter - Monday, November 20, 2017

The 5th Swiss Symposium Thermal Energy Storage will be held at the Lucerne University of Applied Sciences and Arts on Jan. 26, 2018.

This year's symposium will focus on the importance of energy storage in energy systems and industrial processes; the economic aspects of thermal storage; and recent findings about new storage materials. Eleven presentations, all in English, are scheduled:

• "Macro-encapsulated Phase Change Materials for Thermal Energy Storage," Dieter Brüggemann, University of Bayreuth, Germany

• "Fast Loadable Phase Change Heat Storages for Multiple Applications," Sven Kunkel, Matthias Rädle, University of Applied Science Mannheim, Germany

• "Future Directions in Thermal Energy Storage Systems and Applications," Ibrahim Dinçer, University of Ontario Institute of Technology, Ontario, Canada 

• "Applying PCM Beyond the Building Sector," Esther Kieseritzky, Rubitherm Technologies GmbH, Germany

• "Thermal Recuperation with CrodaTherm PCM Using Axiotherm Heat Storage Technology," Yvonne Reimann, Croda GmbH, Germany; Dirk Büttner, Axiotherm GmbH, Germany

• "Integration of Variable Renewable Energy in Switzerland – Implications for Storage Technologies and System Flexibility," Tom Kober, Paul Scherrer Institute, Switzerland

• "Thermal Heat and Renewable Energy Integration in the Industry," François Maréchal, École polytechnique fédérale de Lausanne, Switzerland

• "Experimental and Numerical Investigation of Horizontal Packed Bed Thermal Energy Storages," Marco Prenzel, Vladimir Danov, Siemens AG, Germany

• "Seasonal Heat Storage, the Underestimated Pillar of our Future Energy System, Examples of Realized Projects," Stefan Brändle, Simon Büttgenbach, Amstein + Walthert AG, Switzerland 

• "Large Thermal Energy Storage for Large Cities – A New Dimension," Hannes Poier, TU Graz / S.O.L.I.D. Gesellschaft für Solarinstallation und Design GmbH, Austria

• "Ecological Comparison of Thermal and Electrical Storages for Load Shifting in PV and Heat Pump Systems," Michel Haller, Hochschule für Technik Rapperswil, Switzerland

The registration fee is 300 Swiss francs. Lunch is included. To register, visit https://www.hslu.ch/en/lucerne-school-of-engineering-architecture/campus/veranstaltungen/2018/01/26/sstes-2018.

Research roundup: Cascaded cold storage unit with multiple PCMs; evolution of global heat transfer coefficient; more

Ben Welter - Tuesday, November 07, 2017

Evolution of global heat transfer coefficient on PCM energy storage cycles [Energy Procedia]

Thermal performance analysis of a cascaded cold storage unit using multiple PCMs [Energy]

An experimental investigation of discharge/solidification cycle of paraffin in novel shell and tube with longitudinal fins based latent heat storage system [Energy Conversion and Management]

An alternative approach for assessing the benefit of phase change materials in solar domestic hot water systems [Solar Energy]

Organic-inorganic hybrid shell microencapsulated phase change materials prepared from SiO2/TiC-stabilized pickering emulsion polymerization [Solar Energy Materials and Solar Cells]

Preparation of phase change material emulsions with good stability and little supercooling by using a mixed polymeric emulsifier for thermal energy storage [Solar Energy Materials and Solar Cells]

Optimal design of PCM thermal storage tank and its application for winter available open-air swimming pool [Applied Energy]

Research roundup: Biocatalysts combined to make new PCMs; tankless solar heating system; dual PCM gypsum board; more

Ben Welter - Thursday, November 02, 2017

Combining biocatalysts to achieve new phase change materials. Application to non-edible animal fat [Molecular Catalysis]

Performance evaluation of dual phase change material gypsum board for the reduction of temperature swings in a building prototype in composite climate [Energy and Buildings]

Study on a tankless solar heating system using phase-change material plaster [Building and Environment]

Performance Enhancement of a Building-Integrated Photovoltaic Module Using Phase Change Material [Energy]

Low cracking ratio of paraffin microcapsules shelled by hydroxyl terminated polydimethylsiloxane modified melamine-formaldehyde resin [Colloids and Surfaces A: Physicochemical and Engineering Aspects]

Numerical and experimental research of cold storage for a novel expanded perlite-based shape-stabilized phase change material wallboard used in building [Energy Conversion and Management]

Comparative study in the identification of liquid to solid transition phase with DSC, Raman spectra analysis and chemiometrics methods applied to phase change materials used for icing-delay in civil engineering infrastructures [Applied Thermal Engineering]

Thickness Determination of a Three-layer Wall with Phase Change Materials in a Chinese Solar Greenhouse [Procedia Engineering]

Experimental Study on Thermal Performance Improvement of Building Envelopes Integrated with Phase Change Materials in an Air-conditioned Room [Procedia Engineering]

Phase Change Humidity Control Material and its Application in Buildings [Procedia Engineering]

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 www.ait.ac.at/en/research-fields/sustainable-thermal-energy-systems/projects/storeitup-if.]

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.

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. 

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]

Patent application: Controlled release microcapsules

Ben Welter - Wednesday, October 11, 2017

U.S. patent application 20170281985 (applicant Encapsys LLC, Appleton, Wis.):

"A method of forming microcapsules having improved physical properties and release control as well as the microcapsules formed by the process wherein the capsule wall is formed by the concurrent polymerization of monomers, oligomer and/or prepolymers on the inside of the capsule wall and different monomers, oligomers and/or prepolymers on the exterior of the capsule wall as it forms. ... Microcapsules containing phase change materials according to the present invention are prepared using a process with a two-part water phase and a single core phase."

http://www.freepatentsonline.com/20170281985.pdf

Research roundup: Graphene oxide; PV/PCM integration in glazed building; porous plaster board; more

Ben Welter - Friday, September 29, 2017

Microencapsulated phase change material modified by graphene oxide with different degrees of oxidation for solar energy storage [Solar Energy Materials and Solar Cells]

PV-PCM integration in glazed building. Co-simulation and genetic optimization study [Building and Environment]

Performance study on different location of double layers SSPCM wallboard in office building [Energy and Buildings]

Facile Preparation of Porous Plaster Board Containing Phase Change Capsules Using Gel Template [Energy and Buildings]

Preparation and properties of capric-stearic acid/White Carbon Black composite for thermal storage in building envelope [Energy and Buildings]

Development of a hybrid solar thermal system with TEG and PEM electrolyzer for hydrogen and power production [International Journal of Hydrogen Energy]

Research roundup: Silk hydrogel as packaging material; interfacial polymerization; ecodesign of cladding system with PCM; more

Ben Welter - Wednesday, September 27, 2017

Silk hydrogel illustration

Temperature buffering capacity of silk hydrogel: A useful packaging material [Materials Letters]

Preparation and Characterization of Cross-linked Polyurethane Shell Microencapsulated Phase Change Materials by Interfacial Polymerization [Materials Letters]

Environmental and spatial assessment for the ecodesign of a cladding system with embedded Phase Change Materials [Energy and Buildings]

Novel shapeable phase change material (PCM) composites for thermal energy storage (TES) applications [Solar Energy Materials and Solar Cells]

Novel approaches and recent developments on potential applications of phase change materials in solar energy [Renewable and Sustainable Energy Reviews]

Study of thermal conductive enhancement mechanism and selection criteria of carbon-additive for composite phase change materials [International Journal of Heat and Mass Transfer]

Natural aging of shape stabilized phase change materials based on paraffin wax [Polymer Testing]

Multiphase transport phenomena in composite phase change materials for thermal energy storage [13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics]

Numerical investigation of cylindrical and spherical encapsulated thermal energy storage system with phase change materials [Transylvania Review]

Temperature Dependence of the Enthalpy of Alkanes and Related Phase Change Materials [Enthalpy and Internal Energy: Liquids, Solutions and Vapours]

Heat transfer enhancement of phase change materials by fins under simultaneous charging and discharging [Energy Conversion and Management]