Development of a Negative Thermal Expansion Capsular Object Using Phase Change Material

Driving device for heat transfer enhancement in a fluid layer heated from above was developed. The device was composed of two closed vessels of which the size differs. They are flexible in axial direction, and the lager vessel is filled with air and the smaller one is filled with phase change material (PCM). By the change of the steam pressure of the PCM, the device shrinks and sinks under water when it is hot, and it expands and floats on water when it is cold. The device has a negative thermal expansion behavior, so the authors named it negative thermal expansion capsular object, NTE capsule for short. In this study, the NTE capsule using phase change material (PCM) was developed. It was composed of the large vessel enclosing the air and small vessel enclosing the PCM. Perfluorocyclobutane (RC318) was used for the PCM. The vapor pressure of the PCM changes widely according to the temperature. The motion characteristics of the NTE capsule using PCM were investigated experimentally. As a result, it was confirmed that the new NTE capsule falls downward and rises upward spontaneously in a fluid layer heated from above.