Heat carriers play an important role in many different applications in the industrial and domestic sector, e.g. for heating and cooling of production lines or technical components or for heat transfer in solar installations. Regardless of the actual volumes required, thermal fluids are usually formulated on the basis of water–propylene glycol mixtures. For some applications in the industrial sector expensive silicon oils are used as task-specific thermal fluids.
The use of ionic liquids as heat carriers can be traced back to the group of R. D. Rogers at the University of Alabama (USA). Although it has been found that thermal stabilities of 400°C and above as initially reported cannot be achieved in long-term, a number of systems have now been identified that display good long-term thermal stability at up to 250°C. Even without any structural optimisation, many of these ionic liquids already show relatively high heat capacities and heat storage densities. These characteristics in addition to the fact that they have a negligible vapour pressure make ionic liquids promising candidates for the use as thermal fluids that could be superior to conventional ones.
In this context the possibility of using ionic liquids in domestic solar installations was tested in collaboration with the University of Bremen's Insitute of Environmental Research and Technology (UFT), the Fraunhofer Institute of Solar Energy Systems (FhG ISE) and a commercial partner during a recent feasibility study funded by the Deutsche Bundesstiftung Umwelt e.V. (DBU) and coordinated by IoLiTec (http://www.dbu.de/123artikel25625_335.html). It was found that some of the selected ionic liquids show interesting technical properties. However, considering both technical and economic aspects, the study concluded that neat ionic liquids are not suitable for use in such installations, but they have great potential as additives. This assessment is based on recent problems encountered with the use of conventional heat carriers in modern and highly efficient vacuum tube collectors of domestic solar installations. These systems have to be emptied during the so-called stagnancy phases. Residues and decomposition products of conventional heat carriers can lead to blocked tubes which can cause the need for costly repairs.
A prime goal of IoLiTec's current research activities in this field is tuning the properties of high-performance heat carriers for solar installations for requirements of vacuum tube collectors by using ionic liquid-based additives. Apart from enhanced performance and lower susceptibility to plugging, the introduction of such products can lead to a reduced need to use propylene glycol, a petroleum product. The additives are currently being developed, and will be commercialised under the brand name IoLiTive®.
Another field of use for ionic liquid-based heat carriers with a variety of very specific applications is their employment as high-performance thermal fluids. Various suppliers offer a number of products based on different materials containing product-specific additives. Typical examples are based on mineral oil, polyglycols, aromatic hydrocarbons or silicon oil. Some suppliers also offer tailor-made formulations for specific requirements.
IoLiTec can offer high-performance heat carriers for special applications on the basis of selected ionic liquids with good long-term thermal stability. These products are the result of research carried out in the course of the above-mentioned feasibility study. Compared to other products already on the market, these new IoLiTherm® materials are advantageous due to their enhanced stability, low vapour pressure, non-flammability and low health risk which opens up new applications.
If you have any questions regarding our activities, applications or products in this field please feel free to contact us.