Experimental design and investigation on a thermal energy storage system using phase change materials
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Journal Title
Journal ISSN
Volume Title
Insinööritieteiden korkeakoulu |
Master's thesis
Authors
Date
2020-08-17
Department
Major/Subject
Sustainable Energy Conversion Processes
Mcode
ENG3069
Degree programme
Master's Programme in Advanced Energy Solutions (AAE)
Language
en
Pages
59 + 3
Series
Abstract
Last years have proved that energy storages will have a paramount importance within future energy systems. These storages facilitate the sustainable use of renewable energy resources and also promotes waste reduction. Thermal energy storages are not unknown concepts, but technologies and materials they rely on yet need improvements. Waste heat arise as by-product of many activities and processes. This thesis investigates the possibility to recover waste heat from 5G smart poles designed within the LuxTurrim5G project. While the amount of waste heat generated by one pole is not very significant, a network of such smart poles already represents a considerable energy source. The digital ecosystem designed by the LuxTurrim5G project incorporates such a smart 5G pole infrastructure which can be considered a significant thermal energy source. The thesis assesses the functionality of a thermal battery to recover and store for later use the waste heat coming from the mentioned LuxTurrim5G 5G poles. The thermal energy storage was designed to use phase change material as storage material. The thermal storage conceived and tested during this thesis is planned to be integrated as one of the possible heat sources of a low-temperature district heating network designed within the same LuxTurrim5G project. In the first part of the thesis, review of the available and feasible phase change materials has been carried out. The state of art of heat storage technologies is also discussed and presented. The second part refers to the experimental study and analysis of the results. Experimental study has relied on thermal charging and discharging processes involving two distinct heat exchanger type. In this thesis both heat exchangers were 3D printed out of aluminum. The first was a single plate i.e. planar heat exchanger without any extended surfaces, meanwhile the other employed an extensive mesh system. The role of the surface extrusions was to improve the heat transfer rate between water, transporting waste heat from LuxTurrim5G’s 5G poles, and the storage material of the thermal battery. The heat exchangers were embedded into phase change materials. Experiments used two different phase change materials namely paraffin and myristic acid. Tests had similar experimental conditions which allowed the assessment of extended surface efficiency and to compare two, similar thermophysical properties bearing potential storage material. Storage charging processes have been visually documented as well to better understand when and how the phase change of the materials occurs. As a main result of this thesis, a new thermal battery concept, based on PCM-heat exchanger combination, has been explored and demonstrated. Based on the results, we show that the planar heat exchanger without surface extrusions leads to very inefficient power charging process. With the planar heat exchanger, the mean charging power was about 84 W and the time needed to charge the thermal storage i.e. to melt the 1800 g of storage material was 250 minutes. The amount of energy that was stored in the thermal storage was 555 kJ. In contrast we show that the heat exchanger with surface extrusions has increased the power of the thermal battery to 571 W which is almost seven times higher than for the planar heat exchanger. The charging time of the thermal battery was reduced to 23 minutes, while the amount of stored energy was reduced to 430 kJ. By increasing the mass flow of hot thermal fluid with 20-30% did not bring significative increase in heat transfer rate. It was noticed that the most important parameter was the temperature difference between the hot thermal fluid and storage material. Further optimization of the extended surfaces could lead to bigger energy storage volume yet satisfying powerful thermal battery. Additionally, it was demonstrated that both phase change materials behave consistently during thermal processes and are suitable materials for thermal storage applications.Description
Supervisor
Vuorinen, VilleThesis advisor
Saari, KariYazdani, Roza
Keywords
latent heat of fusion, thermal energy storage, phase change material, heat transfer