2026 ASEE Annual Conference & Exposition

Thermal energy storage (TES) systems that incorporate phase change materials (PCMs) offer significant potential for reducing carbon dioxide emissions by capturing waste heat and enabling peak load shifting. Among the available TES configurations, the helical coiled heat exchanger is one of the most widely studied heat exchanger. Despite its straightforward geometry, its design process remains challenging due to the complex transient behavior of PCMs. To help undergraduate students understand and address these challenges, a heat transfer laboratory session was developed featuring a lab scale helical coiled heat exchanger containing PCM.
The apparatus consists of a helical copper coil surrounded by PCM and enclosed within a 76.2 mm long transparent glass cylinder, enabling direct visualization of the phase change process. Water acts as the working fluid and flows through the copper coil with its inlet temperature and flow rate controlled by a chiller. Tubes connect the test section to the chiller, and T valves create a bypass loop used to preheat the water to achieve a 330 K inlet temperature for the heat exchanger loop during melting. Thermocouple probes measure the inlet and outlet water temperatures as well as the PCM temperature at mid height. A digital flowmeter records the water flow rate. Data acquisition is performed using the InstaCal interface, and a Python script running in Jupyter Notebook records time series temperature data in CSV format.
By varying the inlet temperature and mass flow rate, students examine the effects of temperature gradient and Reynolds number on convective heat transfer and PCM phase change behavior. On the fluid flow side, they evaluate the heat transfer rate, account for heat loss to the surroundings, and analyze heat exchanger performance and effectiveness, including pumping power at different Reynolds numbers. For the melting and freezing of PCM, both sensible and latent heat can be assessed using temperature–time curves that reveal phase transition plateaus. Students also quantify measurement uncertainties and identify sources of error.
Through this activity, students gain early exposure to TES and PCM technologies, which are expected to play an important role in future thermal management and energy system applications. Additionally, the experiment provides practical insight into forced convection, natural convection, and phase change phenomena through hands on experience and data analysis.