Cheaper slurries for cooling processes
In order to reduce the cost of PCM storages, scientists develop new slurries and materials for cold storages. The aim of the project KOLAN is to develop an emulsion with a very high heat capacity. At a temperature difference of 6 Kelvin it should store about four times more heat than water.
|Project status||Near completion|
|Type of storage||Latent heat storage|
|Research objective||storage material (e. g. reinforced pastics, above ground or underground), components for charging and discharging (PCM emulsions (slurries), macroencapsulated materials)|
|Storage time||short (hours to days)|
|Number of cycles||1-few/day|
|Charging temperature||10 to 30 °C|
|Discharging temperature||6 to 25 °C|
|Energy storage density||100 kJ/m3|
|Project duration||October 2013 until September 2017|
Water is mainly used as the storage medium in thermal storage systems. Since cooling applications often have only small temperature differences, the usage of water results in the very large storage volumes. In this context Phase change materials (PCMs) are particularly suitable as storage materials since they show high storage densities at low temperature changes due to their quasi isothermal phase change behaviour. Dispersing a PCM into a carrier fluid forms an emulsion which is commonly referred to as a phase change slurry (PCS). PCS enables pumping through hydraulic systems independent of the phase state of the PCM. Thus conventional heat exchanger can be used for charging the PCM and tanks can be used for storage. Therefore storage and power unit of a PCS system can be dimensioned independently. In this project PCS based on emulsiones will be developed with a high storage capacity and good stability. Furthermore, PCM storage based on macroencapsulated PCM or new composite materials will be developed.
Optimized phase change material
The overall objective of this project is to increase the storage capacity of PCM storage systems compared to the state of the art in PCM slurries (PCS) and reduce costs. For macroencapsulated PCM or composite material storages especially the costs are to be reduced. At the end of the project, the PCS will be demonstrated in a pilot plant. The newly developed materials are intended for cooling, pre-cooling and pre-heating in the building sector and for cooling in the technical field, eg manufacturing machines. The goal is to reduce energy consumption for cooling in the two sectors and thus to contribute to climate change goals.
Due to the lower viscosity greater heat capacity is reached
In the project "Development of cold storage based on phase change fluids and macroencapsulated phase change materials" between 2007 and 2010 PCS based on microencapsulated paraffin were developed. A capsule concentration up to 30 wt.-% in water could be achieved. With higher concentrations viscosity increases sharply, which greatly restricts the achievable heat capacity in the temperature range of the phase change. Emulsions exhibit lower viscosities which basically allows higher PCM concentrations and larger heat capacities per unit volume can be achieved. The objective of the project is to develop PCM emulsions having a heat capacity which can store 4 times more than water, having a temperature difference of 6 K.
In addition, new PCM composite materials will be developed in this project, which offer new solutions for thermal storage based on makroencapsulated PCM. The objective is to lower the cost of PCM storages.
The duration of the project is three years. The project startet on 1.10.2013 and is currently in the first phase, in which PCM materials and emulsifiers for producing emulsions are selected and characterized. Different PCMs of the project partner Sasol, which have a phase change temperature in the range 6 °C - 30 °C were thermally characterized at Fraunhofer ISE and evaluated in terms of possible applivations. First PCM composites were produced and their dimensional stability investigated. Emulsions were formulated using various emulsifiers and examined in terms of separation and shear stability.
Sub-project A (macroencapsulation and system integration): In this subproject simulations are used to study the integration of PCM solutions to specific technical applications. Both, the phase-change properties as well as the system parameter will be varied to integrate a PCS or PCM macrocapsules with its specific performance characteristic into a thermal system. Furthermore, macrocapsule systems and PCM composite systems will be experimentally investigated and thier charge and discharge characteristic will be determined. In addition, the PCM emulsions will be simulated in a 5m³ storage systemn and afterwards tested in a pilot plant under real conditions.
In Sub-project B, new organic PCM materials in the temperature range 6°C to 30°C are developed or modified so that their phase change properties meets the requirements of an application (Project A and C, simulation). Emulsifiers are tested for their potential to stabilize the dispersed organic PCM. For this purpose, various classes of emulsifiers, and different functional groups will be tested and investigated with regard to the stability of the emulsions. In addition, PCM composite materials are produced.
In Project C simulations are used to study the influence of the melting and crystallization temperature on the efficiency of a cooling application. For this purpose, different applications will be analized in terms of their potential for PCM emulsions as a storage and heat transfer medium. A selected application is displayed in a simulation environment and the most appropriate phase change temperature will be identified by parameter variation. Furthermore, emulsifiers are investigated in close alignment with sub-project B to accelarate the development time for the PCM emulsions. The emulsions prepared in all sub-projects will be characterized in terms of their capacity , their melting behavior and their flow behavior. In pump- and storage test facilities the stability of the PCM emulsions as well as the storage behaviour will be examined in the 100 liter scale.