Abstract The addition of microencapsulated phase-change material (mPCM) to the base liquid initiated the emergence of a new type of fluid from the group of latent functional thermal fluid (LFTF). Intensive research is underway to determine the physical, rheological and thermal properties of mPCM slurries. Despite extensive research, there is lack of detailed information on changes in the density of the slurry, especially when the PCM encapsulated in the microcapsule melts and whether the existence of the capsule limits the changes in the volume of PCM during its phase transformation. The article presents the results of detailed experimental studies carried out in a narrow temperature range (10–30 °C) of an aqueous slurry of mPCM. The slurry was made by mixing the product under the trade name MicronalⓇ DS 5039 X (the main peak melting temperature ~ 25 °C) with distilled and deionized water. Four slurry samples had a mass fraction of mPCM in water of 2.15%, 4.30%, 6.45% and 8.60%, respectively. Samples were heated very slowly and their density was measured and recorded every 5 sec. The obtained test results were compared with the theoretical calculations. For calculations, it was assumed that each of the components of the slurry (water, PCM coating and PCM alone) behave like emulsion components - i.e. they occur separately and do not limit changes in volume. It was found that the results of calculations practically coincide with the results of experimental tests, which allowed to exclude the effect of the coating on the expansion of PCM enclosed in it. In addition, it was found that the change in slurry's density during the PCM phase transition is dominated by this process, despite the fact that the mass of PCM in the slurry is only at the level of 1.82 - 7.31%.

中文翻译：

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相变温度下mPCM浆料密度的实验研究

摘要 在基液中加入微囊化相变材料 (mPCM) 引发了潜功能热流体 (LFTF) 组中一种新型流体的出现。正在进行深入的研究，以确定 mPCM 浆料的物理、流变和热性能。尽管进行了广泛的研究，但缺乏关于浆料密度变化的详细信息，特别是当封装在微胶囊中的 PCM 熔化时，以及胶囊的存在是否限制了相变过程中 PCM 体积的变化。本文介绍了在 mPCM 水性浆液的狭窄温度范围 (10–30 °C) 中进行的详细实验研究的结果。通过将商品名 MicronalⓇ DS 5039 X（主峰熔化温度 ~ 25 °C）下的产品与蒸馏水和去离子水混合制成浆液。四个浆液样品在水中的 mPCM 质量分数分别为 2.15%、4.30%、6.45% 和 8.60%。样品加热非常缓慢，每 5 秒测量和记录一次其密度。将获得的测试结果与理论计算进行了比较。为了计算，假设浆料的每个组分（水、PCM 涂层和单独的 PCM）表现得像乳液组分——即它们单独出现并且不限制体积变化。发现计算结果实际上与实验测试结果一致，这允许排除涂层对包裹在其中的 PCM 膨胀的影响。此外，