Optimus – Development, Optimization and Application of PCM Emulsions with High Thermal Storage Density

Duration: 05/2021 - 04/2023
Contracting Authority/ Sponsors: Bundesministerium für Wirtschaft und Energie (BMWi)
Project Partners: H&R Wax & Specialties GmbH, Hochschule RheinMain, Konvekta AG, IKS Industrielle KühlSysteme GmbH
Project Focus:  
PCM emulsion
© Fraunhofer ISE
PCM emulsion in a container .
Storage capacity and storage temperature of PCM emulsions
© Fraunhofer ISE
Storage capacity and storage temperature of PCM emulsions.
Storage density compared to water
© Fraunhofer ISE
Storage density compared to water.

In the "Optimus" project, we are working with industrial partners to develop new emulsions of phase change materials (PCMs) for use in buildings and industry, as well as for heat pump systems and battery cooling in motor vehicles.

We primarily use kerosenes with application-specific melting temperatures, which are dispersed or emulsified in water. Depending on the temperature range, storage densities are achieved that are about 3 to 4 times higher than those of water.

The aim of the development is, on the one hand, to achieve high thermomechanical stability and, on the other hand, large-scale production. After successful development, the PCM emulsions will be demonstrated in the addressed applications and characterized in comparison to the standard heat transfer medium used in each case.
 

PCM emulsions are high performance heat transfer fluids and offer high heat capacities especially at low temperature spreads. They are prepared by dispersing or emulsifying an organic phase change material (PCM) in water. Surfactants stabilize the PCM droplets finely dispersed in the water. Regardless of the aggregate state of the dispersed PCM, the PCM emulsion is liquid and can be conveyed through a hydraulic network. Thus, standard plate heat exchangers can be used for heat transfer into the PCM emulsion for loading and unloading, as well as comparatively simple storage tanks for storage, which overall reduces system costs compared to other PCM storage concepts.

At Fraunhofer ISE, we primarily use kerosenes as PCM with melting temperatures between 14 °C and 70 °C. We disperse between 30 and 45 wt.% kerosene in water and achieve storage densities that are 3 to 4 times higher than water, depending on the temperature spread. This is particularly advantageous for systems that are operated within a very narrow temperature spread. Compared with storage systems that use water as heat transfer and storage medium, the volume of the storage tanks can be reduced accordingly, which offers advantages in terms of space requirements and weight, especially in mobile applications. But there are also advantages in building applications due to the reduction of storage volumes, e.g. for cold storage tanks.

In the "Optimus" project, suitable PCMs are selected for each application (building, industry, heat pump, battery cooling) and corresponding formulations for the emulsion are developed. An important goal is to stabilize the emulsion of PCM and water, not only against segregation and phase separation of the emulsion, but also against the phase change in the PCM as well as against the high mechanical stresses caused in hydraulic circuits by pumps, valves, heat exchangers and other components.

Microscope image of a PCM emulsion
© Fraunhofer ISE
Microscope image of a PCM emulsion.
Prototype of a liquid-cooled battery, for which PCM emulsions could be used
© Fraunhofer ISE
Prototype of a liquid-cooled battery, for which PCM emulsions could be used.

Formulations are initially developed on a scale of up to about 0.5 liters in the laboratory. Promising formulations are then transferred to the larger manufacturing scale in several stages in cooperation with our partner H&R Wax & Specialties GmbH. As part of the "Optimus" project, PCM emulsions are to be manufactured up to a scale of about 20 m³, in order to ultimately demonstrate their performance also in larger storage systems at the end of the project, e.g. in cold storage systems for air conditioning in buildings or for process cooling in industry. 

More Information on this Topic:

Research Topic

Heat and Cold Storage

Research Topic

Thermal Energy Storage for Power Plants and Industry

Business Area

Energy-Efficient Buildings