Characterization of Phase Change Materials for a real Thermal Energy Storage Application

Introduction and Project Background

Phase change materials (PCMs) are substances that absorb, store and release large amounts of latent heat when undergoing phase transitions, such as melting and solidification, at a nearly constant temperature. This makes PCMs very promising for thermal energy storage (TES) applications. One commercially available (from Rubitherm GmbH) organic PCM alternative is RT57HC, a bio-based material with a melting point around 57°C. This PCM and several other alternatives are currently considered in the horizon project HYSTORE, by Energy Technology, KTH, for a pilot-scale PCM-TES system that will be designed, installed and operated (c.f. details) in KTH live-in-Lab.

To accurately design latent heat thermal energy storage (LHTES) systems and their heat exchangers, using PCMs, it is critical to accurately know their key thermo-physical properties. Especially their specific heat capacity, latent heat of fusion, viscosity and thermal conductivity across their operating temperature ranges covering both solid and liquid phases. For the PCM alternatives for this project, while some data is available from the manufacturer, there is a need for additional independent testing to validate and complement this data and fill in any gaps.

In this thesis project, the aim is to experimentally measure the specific heat capacity and latent heat of fusion, dynamic viscosity and thermal conductivity of chosen PCMs (1 to 2) using state-of-the-art instruments available in the Applied Thermodynamics and Refrigeration (ETT) division lab at Energy Technology, KTH. These include, as shown in Figure 1, Micro-DSC (Setaram), Hot-Disk Thermal constants analyser (TPS 2500S), Viscometer (Brookfield) and specific gravity cups (VWR International). Each of these instruments allows measurements of the PCM property across a wide temperature range concerning both solid and liquid phases.

Project Description

In this project, two students will work in-parallel and together, dividing relevant scientific tasks between each other, to bring own specific contributions to the project. The students will work closely with the supervisors and research group on this project. Starting with a comprehensive literature review on the topic, characterization methodologies and comparable PCMs, optimal analysis procedures will be established, while also closely discussing with the supervision team. The experimental thermophysical characterization of the chosen PCM(s) will be then performed using the micro-DSC, TPS, Viscometer, and additionally e.g. simple physical property tests, e.g. specific density (using specific gravity cups). The results obtained through these experiments should be critically analysed by comparing them with available literature data. Iterative analyses might be also necessary upon analysing a given batch of data, as needed. The implications of the results will be used to improve the design and modelling of PCM-based thermal energy storage. A comprehensive MSc thesis report along the KTH and Energy Technology’s guidelines should be delivered at the project's end, closely working with the supervisors and the research team. A final key outcome of the project is a set of reliable and accurate thermophysical property data of the chosen PCM(s) that will greatly benefit the TES design. In the project report, you need to critically and comparatively discuss these results on the contexts of LHTES, TES, as well as sustainability.

The project is meant for 2 students. The objectives and tasks can be discussed, distinguished and planned accordingly.

Project learning objectives

After the project is performed, the student should be able to/should be:

• Knowledgeable and with hands-on experience in performing thermo-physical characterization of PCM properties: specific heat capacity, latent heat of fusion, thermal conductivity, viscosity and density using e.g., the micro-DSC, TPS, Viscometer and specific gravity cups

• Knowledgeable and self-sustained (upon initial training) in conceptualizing and then performing experimental measurements in the stated instruments and apparatus, for the intended TES application conditions and for varied conditions to realize measurement-specific requirements (e.g. thermal equilibrium in the samples) within the safety margins of the instruments

• Identify the relevant fundamental theory and phenomena (e.g. mass transfer and heat transfer) for each respective instrument/method, the relevant governing each equations and calculate the intended thermophysical properties therein

• Process, analyze, report and critically and comparatively discuss the obtained experimental results, including uncertainty analysis, and compare findings to available literature data on the thermal properties of the chosen PCM and similar PCMs for a similar/ comparable temperature range.

• Generalize the obtained results and their derived parameters into the contexts of TES and sustainability

• Seek advice effectively and perform the research tasks independently when necessary, and take initiatives as necessary for the progress of the project

• Draw key scientific and design conclusions based on the critical analysis of the obtained results, and therein, propose relevant future work to improve the presented results, methods and thermo-physical properties testing and characterization of PCMs.

Methodology

The proposed methodology for this thesis work includes the following. It should start with a comprehensive review of relevant literature on the intended thermophysical property characterizations, concerning, methods (procedures, relevant standards and underlying theory and concepts) and other comparable PCMs’ data. Thereafter, full engagement in an experimental campaign of thermophysical characterizations of the chosen PCM(s) is expected. This includes the planning and safe execution of the intended experimental analyses to measure the specific heat capacity and latent heat of fusion (with micro-DSC), viscosity (with a viscometer), thermal conductivity (with a TPS Hot Disk instrument) and density (using specific gravity cups) of the chosen PCM samples. The data obtained should be appropriate post-processed using the relevant theoretical frameworks to obtain the intended property data, while also estimating the respective measurement uncertainties. The estimated property data should be compared and critically discussed also against available comparable literature-data. The project concerning the topic as a whole should also be critically discussed in-terms of its suitability aspects. Overall engineering and scientific conclusions should be drawn, in the end. The report writing must be a continuous process parallel to the project work, from the very beginning to the end.

The project report should be written in English and the students should have sufficiently good writing skills to write a clear and a comprehensible report.

Each student must show their sufficient and respective contributions to the report.

Pre-requisites

• Knowledge and preferably experience in the involvement in experimental analyses and/or laboratory-related projects.

• Fundamental knowledge on heat and mass transfer and thermodynamics

Advantages of being engaged in the project

• A wide variety of hands-on experience on several key experimental measurement instruments widely used in TES design

• Possibility to collaborate with a Horizon project team, and particularly with a leading PCM supplier

• The potential to write a conference or even a journal scientific article based on the obtained results, together with the project team

Project main supervisor, examiner and contact

Project co-supervision/ collaboration team