Satoru Gima

Indirect Cooling of IC Chips Using a Two Phase Closed Thermosyphon Loop

This paper reports on indirect cooling of high-power IC chips of notebook computers using a two phase closed thermosyphon loop with Fluorinert (FC-72) as the working fluid. The experimental set-up consists of an evaporator and a condenser connected by flexible tubing. The evaporator corresponds to a high-power IC chip, and the condenser represents a cooling plate located behind the display of notebook computer. The evaporator and the condenser have the outer dimensions of 50mm x 50mm x 20mm and 150mm x 200mm x 20mm, respectively. The effects of the heat input Q and the charged volume of Fluorinert liquid F on the heat transfer characteristics of the cooling system were studied experimentally. Further, the experiment for the evaporator with plate fin to enhance the boiling in the evaporator was carried out. It has been confirmed that the heater surface temperature for the evaporator with plate fin reduces about 10% in comparison with those for the evaporator without fin. It is found that enhancing the boiling in the evaporator is very effective to reduce the surface temperature of heater. In the case of the evaporator with the plate fin, the temperature difference between the heater surface and ambient is kept around 60K for the highest heat input Q=30W in the present experiments.

AN EXPERIMENTAL STUDY OF MASS TRANSFER FROM FLUTTERING FLAGS

Mass transfer from a whole flag with free trailing edge fluttering vigorously with large amplitude in vertical wind and from parts of flags fluttering with arc-shapes between fixed leading edges and nodes was experimentally investigated in the ranges of the Reynolds number Re = 3 × 10 4 -4. 5 × 10 4 and 1 × 10 4 -5 X 10 4 , respectively. The arc-shape fluttering causes an increase in the Sherwood number only by 15% whereas it has fluttering frequencies much larger than the vigorous fluttering with the free trailing edge, which causes a rapid increase in the Sherwood number with wind velocity up to 3.2 times what is measured for the flags being still in the wind. The abrupt 14-fold increase in the drag of flags due to fluttering and the smoke flow visualization presented by Taneda and the 2-6-fold increase in heat transfer from a flat surface due to flow separation and reattachment measured by Ota and Kon strongly indicate that flow separation and reattachment occur on the vigorously fluttering flag to cause the 3.2-fold increase in the Sherwood number