Recently, latent heat thermal energy storage system has been used in order to utilize the middle-temperature (100 - 200 °C ) factory-waste heat. In the range of middle temperature, erythritol is a suitable PCM, which has melting point at 119 °C , and latent heat of 340 kJ ⁄ kg . In this experiment, silicon oil as a heat transfer fluid injects from the nozzle plate of the bottom of a heat storage vessel. It flows to the upper direction through PCM region and heat is directly transfered between PCM and oil. In this study, the melting and solidification behavior between oil and PCM were visualized in order to investigate the characteristics of heat storage and release at difference flow rate of heat transfer fluid (1.0 - 4.0 kg ⁄ min ) and packed height of PCM (0.23, 0.45, 0.60 m ). The experimental result shows that the amount of heat storage and release is influenced by the flow rate of oil and the packed height of PCM. It is found that the volumetric overall heat transfer coefficient increases when the flow rate of the oil increases. During solidification process, the volumetric overall heat transfer coefficient decreases with increasing the packed height of PCM, while, it is not different in the melting process.

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Cooling characteristic of the thermosiphon type heat pipe by adding the surfactant to pure water is examined. Sodium myristate which has good hydrophilicity and foamability is used as a surfactant. The experimental results show reduction of total thermal resistance for surfactant solution is about 10~40 % with concentration of 30ppm compared to pure water. Reduction of thermal resistance of condenser is primal effect on the reduction of total thermal resistance. On the other hand, thermal resistance of evaporator is not changed with surfactant concentration so much compared to pure water. However, the start-up characteristic of heat pipe at low temperature operating condition is improved with addition of surfactant due to activated bubble formation.

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Unsteady measurement of convective heat transfer was performed to a water flow in a horizontal acrylic circular pipe with inner diameter of D = 20.4 mm for Reynolds number from 1000 to 30000. The velocity distribution in the pipe measured by LDV was laminar at Re ≤ 2000 and turbulent at Re ≥ 3000. The test surface for the heat transfer measurement was fabricated from a titanium foil of 22 μm thick coated with black paint. The titanium foil was heated electrically under conditions of constant heat flux. The time-spatial distribution of the heat transfer coefficient was evaluated from the temperature fluctuation on the test surface measured using a high-speed infrared thermograph (~800 Hz ). The time-averaged heat transfer coefficient measured here agreed well to the conventional empirical correlation. As a result of the present measurement, the dynamic feature of the thermal streak in a circular pipe was revealed, which elongated along the streamwise direction and flowed downstream with some meanderings. The statistic values of the spatio-temporal characteristics, such as the mean spanwise wavelength of the thermal streak and the rms value of the fluctuating heat transfer, were investigated and compared with those of the previously published literature.

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