1. Field of the Invention
The present invention relates to a cooling apparatus boiling and condensing refrigerant, capable of absorbing heat generated from high-temperature medium such as a heating body of semiconductor devices or electric devices, to cool the high-temperature medium.
2. Description of Related Art
There have been known cooling apparatuses boiling and condensing refrigerant, for cooling heat generated from a heating body as high-temperature medium. Among those known cooling apparatuses, as disclosed in JP-A-56-147457, there is a cooling apparatus capable of preventing a flooding of ascending refrigerant which has been boiled and vaporized and liquid refrigerant which has been cooled in a radiator and is returning to a refrigerant tank, within the apparatus, i.e., a phenomenon in which both collide with each other, to perform a heat exchanging operation efficiently.
The cooling apparatus disclosed in JP-A-56-147457 includes a refrigerant tank for containing a refrigerant to be boiled and evaporated by heat generated by a heating body, an inflow passage having a substantially uniform diameter communicating with the refrigerant tank, a radiator having a plurality of radiating passages communicating with the inflow passage, and an outflow passage through which the refrigerant condensed and liquefied in the radiator is returned to the refrigerant tank.
According to this cooling apparatus, in a normal operation (an amount of radiating heat is small), bubbles of the refrigerant blow up and the refrigerant flows through the inflow passage in a gas-phase to transfer heat. That is, the gas-phase refrigerant comes into direct contact with walls defining the radiating passages so that heat is transferred directly to the walls (condensation heat transfer).
However, as the amount of radiating increases, bubbles of the refrigerant blow up greatly and part of the refrigerant flows in a liquid-phase through the inflow passage, so that heat is transferred by both the gas-phase and the liquid-phase refrigerant. The liquid refrigerant transfers heat not by condensation but by forced convection, i.e., by the heat transfer of the liquid refrigerant with the wall of the radiating passages. The efficiency of heat transfer by forced convection is 1/10 to 1/20 of that of heat transfer by condensation.
Since the inflow passage communicating with the refrigerant tank of the cooling apparatus disclosed in JP-A-56-147457 has a substantially uniform diameter, a relatively large amount of liquid refrigerant flows into the radiating passages, which results in a problem that the radiating characteristics of the whole cooling apparatus deteriorates remarkably.
Further, since the inflow passage communicating with the refrigerant tank of the cooling apparatus disclosed in JP-A-56-147457 has a substantially uniform diameter, the flow resistance in the inflow passage is relatively low. Therefore, the gas-phase refrigerant which rises up and reaches the inflow passage is likely to stay at an end portion of the inflow passage apart from the inlet of the inflow passage and hence the end portion of the inflow passage is heated at a high-temperature. Even if the cooling apparatus is provided with a plurality of radiating passages, the temperatures of portions of the radiating passages, which are away from the end portions are relatively low and hence heat cannot be radiated efficiently. Consequently, the radiating performance of the cooling apparatus is low as compared with the size of the radiator.