The development of a prototype Phase Change Material (PCM) storage tank necessitated the implementation of a comprehensive temperature monitoring system to ensure precise spatial temperature measurement across different sections of the tank. To achieve this, a distributed temperature sensing network was designed using Dallas DS18B20 digital temperature sensors, selected for their compatibility with OneWire communication and ease of serial installation. Two sensor configurations were evaluated: the first employed PCB boards measuring 500x9x5 mm with sensors positioned at 50 mm intervals, forming a continuous 2000 mm chain, while the second utilized flat three-core cables with sensors spaced at 100 mm intervals over the same length. For accurate thermal behavior assessment, five independent sensor chains comprising a total of 117 digital sensors were deployed within the thermal storage unit, ensuring detailed temperature monitoring across all critical regions.
Following the successful deployment of the temperature sensors, a heat exchanger was integrated into the tank to enable efficient thermal energy transfer between the PCM material and the heat transfer fluid circulating within the system. This heat exchanger was connected to an insulated piping network, which interfaced with a pump, resistance heater, and a series of control valves. The entire thermal management system was automated using a Siemens Simatic PLC, which continuously monitored key operational parameters, including heating circuit temperatures, flow rates, and other process variables. Temperature data from the sensor network inside the tank was acquired and analyzed using a LabVIEW-based monitoring system, facilitating real-time data acquisition and visualization.
The PCM material filling process was executed using a precision-controlled pump provided by the project partner BME. A total of 80 kg of molten PCM material was introduced into the tank, followed by the addition of 5 liters of water and minor quantities of supplementary components to achieve the desired thermophysical properties, as specified by BME. To enhance thermal retention and mitigate vapor losses, the upper section of the tank was sealed with liquefied wax. Throughout the filling process, the PCM material was maintained at approximately 90°C to ensure uniform distribution and homogeneous mixing within the tank. This temperature was achieved by preheating the PCM in dedicated thermal containers before pumping it into the storage unit, thereby minimizing heat losses during transfer. Following the installation, experimental operations began, implementing cyclic heating and cooling phases to evaluate the performance of the thermal storage system. This experimental framework enabled an in-depth analysis of the PCM material’s phase transition characteristics, as well as the overall efficiency of heat accumulation and release under real-world conditions. Furthermore, the system was subjected to supercooling scenarios, wherein sudden phase transitions facilitated the rapid release of stored thermal energy. The ongoing measurement campaigns provide critical insights into PCM material dynamics, phase change behaviors, and energy storage efficiency, thereby contributing to the optimization of PCM-based thermal storage solutions for future industrial and commercial applications
Text: Jan Zemánek, PhD student, R&D Engineer