Abstract
A detailed experimental freezing study, designed for undergraduate students, has been carried out to evaluate the heat transfer performance of a solid/liquid phase-change thermal energy storage system. The test vessel system, experimental procedure and results, and analytical solutions are discussed. The phase-change material (PCM) is contained in a vertically oriented test cylinder that is cooled at its outside boundary, resulting in radially inward freezing. Detailed quantitative time-dependent volumetric temperature distributions and freeze-front motion and shape data were experimentally obtained. To fully understand the behavior of the eicosane, four freezing tests were performed with different temperature set points as low as 10°C. In the analysis, results of a test in which molten eicosane, initially at 50°C, was solidified and brought to a final temperature of 10°C are presented. In the freezing case study, a mathematical model based on a one-dimensional analysis, which considered heat conduction as the only mode of heat transfer was developed. The phase-change medium, 99% pure eicosane (C20H42) was chosen as the PCM. Eicosane is desirable because its fusion temperature is just slightly higher than ambient temperature (36.5°C), which is convenient for phase-change experimentation. Low-temperature heating can be used to melt the PCM and ambient-temperature cooling can be used to re-freeze it. To evaluate the inward radius of fusion, several analytical and experimental approaches were considered. These approaches were (1) experimental method; (2) conduction model; (3) integral method; and (4) cumulative heat transfer method. Comparison of these methods reveals excellent agreement. In most cases, the heat transfer estimated from the freezing-front analysis was slightly higher than the heat transfer evaluated from the time-series data. The largest discrepancy occurs at fifty minutes into the experiment (10.7%).