Kenichi Inaba

Phase change cooling for energy-efficient ICT systems

Data center businesses are growing rapidly, along with their power consumption. Approximately one half of the power consumed at a data center is used to maintain the temperatures of ICT equipment and server rooms. Increasing the energy efficiency has been one of the most critical issues when building and operating these energy consuming infrastructures important for the modern society, and effective management of the airflow in data center holds the key to increasing the efficiency. The present study reviews phase change heat transfer and a cooling module for 1U servers developed to minimize airflow through these most commonly used type of equipment at data centers. Using the thickness of about 44mm, the phase change cooling module allows natural circulation of its coolant with gravity. The cooling module is so efficient that it reduces more than 30 percent of airflow than conventional technology, thereby reducing the cooling power by 70 percent. The application of this cooling module is verified numerically for a large-scale data center to reduce the airflow, and the power consumption is estimated to be reduced by more than 20 percent.

Management of thermal interfacial resistance for a reparable thermal interface

Thermal interfacial resistance is characterized with state-of-the-art thermal interface materials (TIMs), including a grease, a phase change material (PCM) and a graphite-enhanced sheet (GES). A test bench has been developed to control the holding pressure with a built-in heating and cooling system. Pressures and temperatures are measured at multiple locations along the interface to be able to examine the effects of imbalance on the thermal resistance. Results indicate that the GES has a low thermal resistance of about 26 K-mm2/W at 330 kPa while the phase change material has a value of 34 K-mm2/W at a comparable pressure. The grease has a low value of 20 K-mm2/W, but the interface would not be reparable. The PCM and the GES have a metal foil on one of the surfaces, allowing them to construct a reparable interface. The effect of imbalance in holding pressure has also been examined. An imbalance in temperature grows with pressure, and a mechanical inclination of binding surfaces relative to each other is suggested as a cause of the temperature variation.