Session: Research Posters

Paper Number: 113269

113269 - Thermal Behavior of PCMs During Phase Transitions With Phase Change Hysteresis: Experimental Setup Development and Problems of Model Validation 

Several models and modeling approaches for phase transitions of phase change materials (PCMs) have been proposed in recent years. However, many of these models have not been thoroughly validated with experimental data. This is particularly the case of the models for thermal hysteresis and partial phase transitions of PCMs. An experimental set-up for the acquisition of data for the validation of phase change models have been proposed and assembled. The primary scope of research activities is the development and validation of methods and techniques for identification of PCM properties from inverse heat transfer problems. The first case study experiment is based on the monitoring of heat flux and temperature distribution in a PCM contained in a rectangular cavity with a heated/cooled wall. A positive or negative heat flux was introduced at one of the vertical cavity walls in a way to minimize (ideally to avoid) natural convection in the melted PCM (only a small amount of PCM was fully melted). Unlike in similar experiments, where a heat transfer fluid (HTF) or resistance electric heaters were used to introduce the heat flux at the wall, the Peltier cells are used in the present experimental set-up for this purpose. Also, most experiments reported in the literature only address the melting process (heating of a PCM) with the positive heat flux introduced at the wall. The Peltier cells allow for switching between the positive and negative heat fluxes (heating/cooling), making it possible to investigate both complete and incomplete phase change cycles in a PCM (depending on the distance from the wall). A rectangular cavity filled with a PCM was 30 mm high, 250 mm long (in the horizontal direction along the heated/cooled wall) and 45 mm deep (perpendicular to heated/cooled wall). The heated/cooled wall is made of a 15 mm thick aluminum plate with three embedded RTD (Pt 100) temperature sensors for wall temperature monitoring and two heat flux sensors monitoring the heat flux to/from the PCM. The temperature distribution (profile) in the PCM is monitored with seven RTD (Pt 100) temperature sensors. The first set of experiments was carried out with the RT35HC paraffin-based PCM, which exhibits very noticeable thermal hysteresis of phase transitions. The acquired experimental results were compared with the results of a numerical model. Due to the expected symmetry of the investigated scenario, one dimensional conductive heat transfer model was used in the first step. Despite a relatively small height of the cavity, natural convection developed in the melted PCM, significantly influencing the temperature distribution in the PCM. As a result, the numerical model (which neglected the convection) overestimated the temperature in the vicinity of the heated surface (wall), while underestimating the PCM temperature further inside the cavity. For future research, the thickness of the rectangular cavity will be reduced in order to mitigate the effect of natural convection.

Presenting Author: Martin Zálešák Brno University of Technology

Presenting Author Biography: Researcher and a Ph.D. candidate at the Department of Thermodynamics and Environmental Engineering, Faculty of Mechanical Engineering, Brno University of Technology, city of Brno, Czech Republic. Area of interest: computer modeling of complete and incomplete phase transitions of PCMs considering phase change hysteresis.
https://www.vut.cz/lide/martin-zalesak-162098

Authors:

Martin Zálešák Brno University of Technology
Pavel Charvát Brno University of Technology
Lubomír Klimeš Brno University of Technology
Ondřej Pech Brno University of Technology
Patrik Bouchal Brno University of Technology