抄録
Small, high-performing heat transport devices are required for the effective cooling of electronic devices and equipment. Devices that utilize oscillatory flow technology are currently considered prime candidates for this function. In oscillatory flow, longitudinal heat transport occurs due to an interaction between a nonuniform axial velocity profile and effective lateral heat transfer. Therefore, to enhance longitudinal heat transport, lateral heat transfer effects must be introduced. The present paper describes an experimental study of longitudinal heat transport by an oscillatory flow using a microencapsulated phase change material suspension (MPCMS). Heat transport experiments were conducted for several oscillating heat transport tubes (length, 500 mm; inner diameter, 3.0, 6.0, and 13.5 mm). The working fluid was MPCMS consisting of microencapsulated paraffin (diameter, 10 μm; melting point, 32 °C) and water. The MPCMS mass concentration was varied from 0 (water only) to 5 wt%. An oscillation generator installed at one end of the tube generated sinusoidal oscillatory flow, and MPCMS working fluid with a uniform temperature of 9 °C flowed into the tube. At the other end of the tube, a coil heater was installed to maintain the temperature at 40 °C. Frequency and displacement amplitude of oscillatory flow were varied from 0.5 to 2.0 Hz and 0.057 to 0.19 m, respectively. The longitudinal heat transport was evaluated by determining the effective thermal conductivity based on the measured cycle-averaged heat transport rate and temperature gradient. The results confirmed that MPCMS enhances longitudinal heat transport in oscillatory flow depending on the flow conditions. The effective thermal conductivity increased at lower frequencies of 0.5-1.0 Hz, middle displacement amplitudes of 0.10-0.15 m, and a larger particle diameter of 13.5 mm; at its maximum, the value was 1.4 times greater than that of water only. It was also found that MPCMS without phase changes (melting point of 5 °C) does not enhance longitudinal heat transport. This suggests that the storage and release of latent heat due to phase changes play an important role in enhancing longitudinal heat transport.
