Experimental research of viscosity of microencapsulated PCM slurry at the phase change temperature

With the advancement of technological progress it is possible to close Phase Change Material inside capsules of the order of micro- and even nano-meters. Microcapsules added to a base liquid can be used as latent functionally thermal fluid (LFTF) in active heat exchange systems. Accurate recognition of the rheological properties of the resulting suspension, especially at the phase change temperature of the PCM, is essential for the planned practical application of the fluid. Knowledge of viscosity is one of the key parameters as this is reflected in both flow resistance and, for example, convective heat exchange. This paper presents the results of detailed tests on the viscosity change of the microencapsulated PCM slurry (Micronal (R) DS 5039 X - BASF product) at unsteady state conditions. The effect of the temperature increase rate (0.1-1.2 degrees C/min), mPCM concentration (80%, 90% of Micronal (R) DS 5039 X in water and pure Micronal (R) DS 5039 X) and the influence of spindle speed (50 RPM and 150 RPM) on mPCM slurry apparent viscosity was examined. Because the main peak melting temperature of the product is around 23 degrees C the temperature range of experiment was 15-30 degrees C. On the basis of the conducted tests, it was found that in general the temperature increase of the suspension causes a decrease of its viscosity, however a temporary increase in the viscosity of the slurry was observed when the PCM contained in the microcapsules undergoes a phase transition. (C) 2019 Elsevier Ltd. All rights reserved.