The energy demand for cooling applications has been steadily increasing in recent years. Using thermal energy storages is an efficient way to reduce the increasing electricity consumption and to shift peak loads. Conventional cold storage and distribution systems use water or brines as heat transfer fluids to store or transfer energy with the sensible heat capacity of water. Due to the typically small temperature difference between the forward and return flow, these systems usually have a high flow rate and a large storage volume. Multifunctional heat transfer fluids consisting of a latent heat storage material as the dispersed phase and a carrier fluid as the continuous phase, known as Phase Change Slurries (PCSs), have been studied to increase the storage capacity. PCSs have a higher energy density than water by using both the sensible and latent heat capacity of the materials.

The goals of this project are to develop stable and suitable PCSs for comfort cooling applications in a temperature range of 0-20°C and to investigate the application as cold storage medium for solar cooling systems with the highest efficiency. The PCSs studied within this project are paraffin/water emulsions and hydrate slurries as well as the combination of them. Paraffin/water emulsions are colloid systems where fine paraffin droplets are dispersed in water by a surfactant. CO2 hydrates are crystalline compounds formed from water and CO2 molecules. CO2 hydrates in emulsion and/or associate of hydrates with paraffin-water emulsion will be studied in order to enhance the amount of heat stored in the resulting slurry. These PCSs will be investigated in view of formation kinetics, stabilities, thermophysical properties, rheological behaviour and ecological aspects.

Application tests of PCSs as cold storage media will be conducted in a solar cooling plant to evaluate their application potential. A charge state sensor will be developed and integrated into the demonstration plant to determine the solid content of the PCSs which indicates the energy density of the PCSs at different temperatures. As a result the control and the efficiency of the system can be improved by using this sensor. Additionally the performance of the PCSs will be simulated and analyzed. The knowledge of creating these PCSs gained during the project could be used to design new heat transfer fluids for many different applications.