Performance comparison of three models for thermal property determination from experimental phase change data

Abstract

The characterization of thermal properties continues to be a challenge facing the development of composite phase change materials. To overcome the practical issues of current techniques a new experimental method was developed. The system is modelled using two fundamental models and a simplified analytical representation.Pure myristic acid is used for validation and a performance comparison based on time, accuracy and stability. All three approaches perform comparatively well in terms of accuracy with an average prediction error of less than one third of a degree and all thermal properties in line with expectations. The enthalpy model is susceptible to instability while the effective heat capacity method does not show any such behaviour. In addition, due to the choice of a smooth function for the transition from liquid to solid, this method delivers more realistic behaviour. The effective heat capacity method is faster than the enthalpy method by a factor of three, but the analytical approach is the fastest. However for a more robust and comprehensive representation the effective heat capacity method is preferred.

The use of graphite foams for simultaneous collection and storage of concentrated solar energy

“…During the transition from solid to liquid energy is stored and then recovered during the reverse transformation. However, the low thermal conductivity of these materials is a significant issue [30,31]. To overcome this limitation recent research has increasingly focused on developing composites with graphite foams, to improve the thermal performance of the PCMs [32][33][34][35].…”

Critical analysis of the T-history method: A fundamental approach

“…A similar approach was recently proposed by Badenhorst [27]. In this case, a 318 cubic polystyrene container (13x13x13 cm) with low thermal conductivity (0.024 319 W•m -1 •K -1 ) is used.…”

“…To achieve this it may be assumed that the convective resistance of the system should be less than 5% of that of the conductive. Using the standard expressions for these variables [33] it may be shown that for an enclosure using the polystyrene 573 material mentioned earlier [27] (k~0.024 W.m -1 .K -1 ), a will thickness of 32 mm would be required. For this case the convective heat transfer coefficient is assumed to be 15 W.m -2 .K -1 in accordance with the average, measured natural convection values.…”

“…Unfortunately the simplicity of the measurement and the lack of a standardized methodology have led to a proliferation of alternatives and adaptations [21][22][23][24][25][26][27], both in terms of the setup used and the manner in which the data is employed to obtain the final property values [28]. This in turn presents an abundance of options for measurement but no clear method for distinguishing between the quality and accuracy of the techniques.…”

A novel heat exchanger concept for latent heat thermal energy storage in solar power towers: Modelling and performance comparison

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