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- Paberit, Robert, 1987, et al.
(författare)
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Cycling stability of Poly(Ethylene Glycol) of six molecular weights: influence of thermal conditions for energy applications
- 2020
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:11, s. 10578-10589
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Tidskriftsartikel (refereegranskat)abstract
- Utilizing energy storage technologies is beneficial for bridging the gap between supply and demand of energy, and for increasing the share of renewable energy in the energy system. Phase change materials (PCM) offer higher energy density and compact storage design compared to conventional sensible heat storage materials. Over the past years, polyethylene glycol (PEG) gained attention in the PCM field, and several new composites of PEGs are developed for thermal energy storage purposes. PCMs are investigated at a given heating/cooling rate to evaluate their phase change temperature and enthalpy. In the case of PEG, some molecular weights show a melting behavior that depends on the thermal history, such as the crystallization conditions. This study investigates the relationship between the molecular weight of PEGs (400 to 6000 g/mol), cooling/heating rates, and the behavior during phase transitions. To evaluate the performance of PEGs as a PCM under various thermal conditions. Experiments were performed using differential scanning calorimeter (DSC) and the transient plane source method (TPS). All PEG molecular weights were subjected to the same cooling and heating conditions, cooling and heating rate and number of cycles, to decouple the thermal effects from molecular weight effects. The behavior of phase transition for different thermal conditions was thoroughly analyzed and discussed. It was found that the melting temperature range of PEGs with different molecular weight was between 5.8 °C and 62 °C (at 5 °C/min). Each PEG showed unique responses to the cooling and heating rates. Generally, the behavior of the crystallization is changing most between the thermal cycles, while the melting peak is stable regardless of the molecular weight. Finally, it is recommended that the characterization of PEGs and their composites should be conducted at a heating and cooling rate close to the thermal conditions of the intended thermal energy storage application.
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| 2. |
- Göhl, Johan, 1989, et al.
(författare)
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Manipulation of phase transition temperatures and supercooling of sugar alcohols based Phase Change Materials (PCMs) by urea
- 2016
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Ingår i: Proceedings of the INNOSTORAGE conference, Beer Sheva, Israel.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this work we have investigated the possibility to change the thermal characteristics of the sugar alcohols erythritol and mannitol by use of urea as additive. The results show that even small amounts of urea have a great influence on the thermal properties of the sugar alcohols, which in turn implies large structural differences between the different compositions. For both sugar alcohols both smaller and higher fractions of urea result in two melting peaks, whereas a eutectic composition is obtained at intermediate urea fractions. However, not all compositions undergo crystallization on cooling.
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| 3. |
- Johansson, Pär, 1986, et al.
(författare)
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Evaluation of PCM activation using changes in physical properties during phase transition for visualization of passive building envelope technologies
- 2016
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Ingår i: Proceedings of the 9th International Conference on Indoor Air Quality Ventilation & Energy Conservation In Buildings, IAQVEC 2016, October 23-26, 2016, Songdo, Incheon, Republic of Korea.
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Konferensbidrag (refereegranskat)abstract
- There is a large potential to use passive technologies for increasing the thermal comfort and reducing the energy use for heating and cooling in buildings. In many cases the occupants of the building lack good practical understanding and knowledge on how these passive technologies function. Therefore, there is a challenge to utilize their full potential. For instance, the potential energy savings for space heating and cooling is 5-21 % with phase change materials (PCMs) integrated in building envelopes (e.g. encapsulated in the plaster board). Consequently, there is a pedagogical problem to explain how and when PCMs are active in regard to passive adjustment to changes in the indoor environment. The reason for this is the lack of proper tools. Temperature sensors alone or numbers on the energy use is not enough to give the occupants information on how to use the passive technologies in the most efficient way. One aim of this study is therefore to explore properties that can be used as a foundation for the development of technologies for visualizing the phase transition. Laboratory experiments are used to evaluate three methodologies based on density, viscosity and optical properties that change when a PCM undergoes a phase transition. The results are compared to phase transition measurements by DSC. The methods are tested on a type of organic PCMs, polyethylene glycol (PEG), of different molecular weights. From the results it is obvious that all three methods can be used to differentiate the phases even if there remains challenges before practical implementation in buildings is possible.
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