Phase change materials (PCM) are capable to store thermal energy in a small temperatures range due to their high latent heat. In the simulations of Thermal Energy Storage (TES) systems with PCMs, in many cases the natural convection is not considered, maybe causing possible differences between the numerical and the experimental results. Since the natural convection depends on the viscosity of the melting or melted region, it is important to determine this property in PCMs accurately. The paper presents different measurements carried out with a pure substance: octadecane. Both rotational and oscillatory tests have been accomplished and the influence of the gap and the heating and cooling rate on the results have been analyzed. A first approach of the measurement methodology for the obtaining of its viscosity during the phase change and melting is proposed, when using a plate as geometry and a Peltier plate as temperature controller.
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