1. Field of the Invention
The present invention relates to an evaporator that forms a looped heat pipe system with a condenser, a vapor transport line, and a liquid transport line, and a method of manufacturing the evaporator, and more particularly, to an evaporator for a looped heat pipe system, including an additional layer, in which a plurality of through hole pores are formed, and that is formed on an vaporization surface of a sintered wick inside the evaporator, so that a working fluid may flow a relatively long distance and under a relatively high heat flux condition.
2. Description of the Related Art
Electronic components such as a central processing unit (CPU) or a semiconductor chip, used in various electronic devices such as computers generate a lot of heat during operation. The electronic components are designed to perform their functions usually at room temperature, and thus if the heat generated during operation is not effectively dissipated, not only is performance of the electronic components degraded but the electronic devices are damaged in some circumstances.
Examples of methods of cooling electronic components may be a thermal conduction method using a heat sink, a method using natural air convection and radiation, a forced convection method using a fan, a method using liquid circulation, and a submerged cooling method.
However, as electronic products are reduced in size to be slim, installation intervals between electronic components thereof that generate heat during operation are continuously reduced, and thus, currently, the heat generated during use of the electronic products is not properly dissipated. Also, due to the high integration degree and high performance of the electronic components, a heat generation load of the electronic components is continuously increasing, and thus it is difficult to cool the electronic components using the above-described conventional cooling methods.
As a new technology for solving this problem, a phase change heat transport system capable of cooling electronic components having a highly thermal density has been introduced. One example of the phase change heat transport system is a cylindrical heat pipe.
As illustrated in FIG. 1, a typical cylindrical heat pipe 100 is used to perform cooling as a working fluid is circulated using a capillary pumping force of a sintered wick 102 installed on an inner wall of the cylindrical heat pipe 100.
Upon receiving heat from a heat source 101, the working fluid contained in the sintered wick 102 is evaporated and is transferred along an arrow 103 denoting a vapor flow, and then heat of the working fluid is taken away by a heat sink 104, and the working fluid is condensed again and flows through the sintered wick 102 along an arrow 105 denoting a liquid flow, by a capillary pumping force, to thereby circulate.
However, although dependence of a heat pipe on a gravity field is low, there are still limitations regarding arrangement of components; for example, if a condensation section is located below an evaporation section in a gravity field, heat transport capability of the heat pipe decreases greatly. Thus, if the heat pipe is applied as a cooling system in an electronic product, the heat pipe may be a restriction on a structure of the electronic product.
In addition, since a vapor and a liquid flow in opposite directions in a straight cylindrical heat pipe, the vapor and the liquid mix in a middle portion of the pipe. Through the mixture, an amount of heat to be transferred is substantially reduced compared to a heat amount that can be transferred theoretically.
A looped heat pipe (LHP) system is suggested as an ideal heat transfer system to solve the problems due to the structure restriction and the mixing of a vapor and a liquid.
An LHP system is a type of capillary pumped loop heat pipe (CPL) developed by NASA of the US in order to dissipate large amounts of heat generated in communication devices or electronic devices for artificial satellites.
FIG. 2 is a schematic conceptual diagram of a conventional LHP system 110. The conventional LHP system 110 includes a condenser 112, an evaporator 114, and a vapor line 116 and a liquid line 118 that connect the condenser 112 and the evaporator 114 to one another to thereby form a loop.
FIG. 3 is a schematic conceptual diagram illustrating an operation of the LHP system 110 of FIG. 2.
The evaporator 114 includes a compensation chamber 112 that accommodates a working fluid that is to be liquefied before permeating into a sintered wick 120 included in the evaporator 114, to buffer the working fluid. In the LHP system 110, the sintered wick 120 is installed only in the evaporator 114, unlike the conventional straight heat pipe 100 (see FIG. 1).
The LHP system 110 having the above-described structure operates according to the following principle.
First, when a heating plate 124 of the evaporator 114 contacting a heat source such as a heat generating component is heated, a working fluid permeated into the sintered wick 120 is heated to a saturation temperature by heat transmitted from the heating plate 124, and is changed into a vapor.
The generated vapor is transferred to the condenser 112 along a vapor line 116 connected to a side of the evaporator 114. Next, as the vapor passes through the condenser 112 and dissipates heat to the outside, the vapor is condensed, and the condensed working fluid is moved to the evaporator 114 again along a liquid line 118 connected to the condenser 112, thereby repeating the above-described operation to cool the heat source 101.
As illustrated in FIG. 3, the sintered wick 120 is bonded to an inner circumferential surface of the evaporator 114, and a space formed by the inner circumferential surface of the sintered wick 120 forms a vapor passage through which the working fluid is changed into a vapor and moves to the vapor line 116.
Meanwhile, the working fluid in a liquid state is changed into a vapor on a surface of the sintered wick 120. Accordingly, this surface is referred to as an evaporation interface or a vapor-liquid interface.
The working fluid circulates while passing by points denoted by P1 through P7. The working fluid is evaporated at the point P1, and the evaporated working fluid moves to the point P2 through the vapor path inside the evaporator 114, and then moves to the point P3 along the vapor line 116. By passing from the points P3 and P4 at an inlet to the point P5 at an outlet of the condenser 112, the working fluid in a vapor state is condensed again. The working fluid in a liquid state passes by the point P6 at the inlet of the evaporator 114 along the liquid line 118 and passes a compensation chamber 122 and is absorbed by the sintered wick 120 at the point P7 to move to the point P1 again.
Meanwhile, in the LHP system 110, a force that causes movement of the working fluid is a capillary pumping force of the sintered wick 120. The capillary pumping force is related to a diameter of pores formed in the sintered wick 120.
That is, if the diameter of pores formed in the sintered wick 120 is reduced, a capillary pumping force is increased. However, at the same time, as the size of pores is reduced, permeability of the sintered wick 120 decreases. Thus, it is difficult to obtain desired cooling performance just by adjusting a size of pores in the sintered wick 120.
Consequently, a sintered wick included in an evaporator used in an LHP system needs to be configured such that a capillary pumping force is increased but permeability is not decreased, so that a working fluid may be effectively circulated.