Phenomenological modelling of phase transitions with hysteresis in solid/liquid PCM

Abstract

Technical-grade and mixed solid/liquid phase change materials (PCM) typically melt and solidify over a temperature range, sometimes exhibiting thermal hysteresis. Three phenomenological phase transition models are presented which are directly parametrized using data from complete melting and solidification experiments. They predict hysteresis phenomena and are used to calculate effective PCM properties. Two models have already been implemented in commercial building simulation and/or multiphysics software, but not the third novel model. Applications are presented for two commercial PCM: a paraffin, and a salt water mixture with additives. Numerical implementation aspects are discussed, and significant differences in the predicted absorbed and released heat are highlighted when simulating consecutive incomplete phase transitions. The models are linked with energy balance equations to predict recorded PCM temperatures of a thermal energy storage. The cross-validation with data from 26 partial load conditions clearly indicate a superior predictive performance of the novel hysteresis model.

Identification of Phase Fraction–Temperature Curves from Heat Capacity Data for Numerical Modeling of Heat Transfer in Commercial Paraffin Waxes

“…It is assumed that the heat transfer in the PCM domain in the HEX can be computed by solution of a one-dimensional transient heat conduction problem with phase change (see [17] for details):…”

“…It is noted that not all of the reviewed models explicitly consider the liquid fraction as a system state. However, because of the direct relation between the liquid fraction and the heat capacity, [11,12,17] these models fall into the same category. The same applies for models defined by enthalpy-temperature curves, see e.g., [18].…”

“…These curves then correspond to data recorded during complete melting, complete solidification, or to intermediate curves between both, see e.g., [18,[21][22][23][24][25][26][27]. They are usually modeled e.g., by piecewise linear functions [28], probability distribution functions [12,17], cubic spline interpolating polynoms [29]. As an alternative, Franquet et al [30] propose to solve an inverse identification problem to identify parameters of a thermodynamical model of the sample's heat capacity.…”

“…PCM phase transition behavior is also scale dependent [35,36]. A direct strategy to account for this is the consideration of different phase transition models depending on the direction and rates of temperature changes in the studied application, e.g., [12,17,18,37]. Moreover, various extensions of the numerical methods have been proposed in order to account for (subcooling) supercooling phenomena, e.g., combining enthalpy curves for (super-)cooling with kinetic models for crystal growth [38,39], using punctionally negative apparent heat capacities to mimic the temperature growth in a recrystalling material [40], and considering an internal heat source in the PCM which is activated at a defined (supercooled) temperature [41].…”

Cooling System with PCM Storage for an Office Building: Experimental Investigation Aided by a Model of the Office Thermal Dynamics

“…In practice, due to the temperature gradient in the material, many PCMs change the phase over a certain temperature range. Moreover, an enthalpy–temperature characteristic h(T), usually used for the performance calculations, shows hysteresis [ 3 , 4 ]. That is why a theoretical estimation of the profits resulting from the use of PCMs in a real application is difficult to perform in a reliable way.…”