1. Field of the Invention
The present invention relates to a cooling system and an evaporator thereof, and more particularly to a two-stage expansion cooling system and an evaporator thereof.
2. Related Art
Currently, an electronic device in the market is generally formed by various electronic components. As the performance of the computer has been increasingly enhanced, more and more heats are generated by the electronic components. Among these components, the central processing unit (CPU) operates even faster, and thus becomes the electronic component that generates the most heats per unit time within the electronic device. On the other aspect, besides the increased heat generated by the electronic components, as the size of the electronic device is gradually reduced, the heat dissipation effect of the electronic device is deteriorated due to the allocation of these components within an increasingly reduced space. Based upon such a developing trend of the electronic device, after working for a long time, the temperature of the working environment in the electronic device is greatly raised due to the heat generated by the CPU. As a result, the excessively high-temperature working environment may affect the normal operation of the electronic device, and thus the failure and damage rates of the electronic device will be increased. Therefore, it is a tough problem to be solved by manufacturers about how to rapidly and effectively dissipate the heat from the CPU.
In the prior art, in order to solve the heat dissipation problem of the CPU, a heat dissipation module is mounted on the CPU to dissipate the heat generated thereby, so as to prevent the CPU getting overheated. The conventional heat dissipation module has a base attached to a surface of the CPU and a plurality of heatsink fins connected to the base. The heat generated by the CPU is conducted from the CPU to the base, and then from the base to the heatsink fins. As the heatsink fins contact the outside air at a large contact area, the heat is rapidly dissipated to the ambient environment. When the heat dissipation module cannot satisfy the heat dissipation requirement, a fan is further added to the heat dissipation module in the prior art to enhance the heat dissipation effect. However, as the CPU generates more and more heat, the technology of dissipating heat through the base and a fan has gradually come to a bottleneck.
Accordingly, a water-cooling system is provided in the prior art. The water-cooling system includes an evaporator, a condenser, a conduct pipe, and a pump. The cooling water is circulated in the water-cooling system. The evaporator thermally contacts the CPU. The evaporator, the heat sink, and the pump are communicated with each other via the conduct pipe. The cooling water is driven by the pump to circulate among the evaporator, the heat sink, and the pump via the conduct pipe. The condenser is used to remove the heat from the cooling water. Based on the above system, the heat generated by the CPU is absorbed by the cooling water in the evaporator when passing through the evaporator. After the above heat absorption process, the cooling water is driven by the pump to enter the condenser via the conduct pipe, and the heat absorbed by the cooling water is then released through the condenser. Then, after the heat dissipation process, the cooling water is again driven by the pump to enter the evaporator, thereby completing a cooling circulation.
However, as for the water-cooling system in the prior art, when the cooling water flows through the evaporator, the temperature of the cooling water rises due to the absorption of the heat generated by the CPU. However, during the whole heat absorption process, the cooling water remains in a liquid state. Therefore, if the heat generated by the CPU is increased abruptly, and as the size of the electronic device has been continuously reduced, the heat dissipation performance of the water-cooling system has gradually come to a bottleneck.
Typical implementations of the low temperature designs are thermoelectrics and refrigeration. Among them, refrigeration is capable of operating in high-temperature ambient, yet it is also quite reliable and cost-effective. Moreover, its COP (coefficient of performance) is well above the present thermoelectrics system. There are also other advantages for exploiting the refrigeration cooling, such as maintenance of low junction temperatures while dissipating high heat fluxes, potential increases in microprocessor performance at lower operating temperatures, and increased chip reliability. However, there are several major concerns in the application of refrigeration systems to cool electronics include condensation of the evaporator cold plate where the electronics components are mounted. The first one is associated with the condensation on the surfaces when the temperature is below the dew point temperature of the surrounding air and the second concern is the systems lagging response to applied load at the evaporator. The presence of water condensate can bring hazards to the electronic system and must be avoided all the time. Typical solutions to the first concern may involve clumsy insulation or using heater to vaporize condensate outside the cold plate. The former requires considerable space that is often quite limited in practice and is apt to reduce the overall system performance due to blockage of the air flow. The later design not only raises problem in control but is also sceptical to additional energy consumption. In summary of these two designs, one can see there is a need for novel design to employ the refrigeration cooling in electronic cooling. It is therefore the objective of this invention. We have proposed a novel design that can completely eliminate the concern in condensate formation.