Yu Seshimo

Forced Air Heat Sink with New Enhanced Fins

A forced-air-cooled heat sink with new enhanced fins was developed. The fin has many perforations and is bent to form a trapezoidal shape. The fin was enhanced in heat transfer by a breathing effect, a phenomenon by which the fluid is injected and sucked through the trapezoidal perforated fins. The thermal conductance of the heat sink at the same pumping power was about 1.6 times that of a similar heat sink with conventional plain fins, and also about 3 times at the same Reynolds number. A heat sink with the new enhanced fins designed for practical use was also shown.

Study of a Cooling System for the Telecommunication Base Site (Performance Analysis of a Cooling System Using Natural-circulation Loop)

New cooling system with a natural-circulation loop has been developed to reduce energy consumption of a cooling system for the telecommunication base site. The cooling system consists of two refrigeration units ; vapor compression refrigeration unit and pre-cooling unit with a natural-circulation loop. A simulation which calculates pressure drop, heat transfer and refrigerant charge has been developed and the experiments were carried out to evaluate the cycle performance of the pre-cooling unit using HFC refrigerants. The measured cooling capacity and operating pressure agreed with the simulation results within ± 10% in the various experimental conditions. In addition, the experimental results indicated that the cooling capacity of R 410 A is approximately 30% larger than that of R 407 C at the temperature difference of 20 K. Also the cooling capacity took a maximum value at the range of refrigerant charge of 2.0-3.0 kg. Furthermore, the cooling capacity slightly increased as the height difference between the evaporator and the condenser increased. These experimental results were in good agreement with the simulation results.

Characteristics of air-cooled heat exchanger with frost formation.

In order to clarify the effects of frost formation on the performance of an air-cooled heat exchanger, analyses by a uniform frost formation model and experiments were performed. Using this model, frost thickness and frost density can be estimated from the increase of the pressure drop of the heat exchangers. It is found that the heat transfer characteristics under frost formation can be grasped in the same manner as the case of no frost formation and that the analogy of heat and mass transfer holds in the practical application.