Phase conversion cooler and mobile equipment

The present application claims priority from Japanese patent application serial No. 2009-084013, filed on Mar. 31, 2009, which further claims priority from Japanese patent application serial No. 2008-112688, filed on Apr. 23, 2008, the contents of which are hereby incorporated by reference into this application.

1. Field of the Invention

The present invention relates to a small lightweight phase conversion type cooler with high cooling efficiency and mobile equipment.

2. Description of Related Art

A forced heat dissipation means is provided instead of natural heat dissipation, in high-level heat-generating parts among parts provided in a computer. For example, in an LSI (Large Scale Integrated circuit) such as a CPU (Central Processing Unit), since heat generation causes a serious problem in accordance with degree of integration and/or processing speed, a heat dissipation means is absolutely necessary.

A phase conversion cooler is known as a cooler used for the heat dissipation applicable to such electronic parts, as disclosed in Japanese laid-open publication Nos. 2004-85186, Hei 7-142886 and 2006-125718.

As shown in FIG. 7, a conventional phase conversion cooler 101 has a cooling head 102 having a first side (which is faced toward the rear side of the drawing in FIG. 7) in contact with a cooled object, a first circular port 103 provided to a second side 102b not opposite to the first side of the cooling head 102, a second circular port 104 provided to a third side 102c not opposite to the first side and the second side 102b of the cooling head 102, a first pipe 105 whose one end is connected to the first circular port 103 as an outlet port, a condenser part 106 connected to another end of the first pipe 105 and placed in a heat dissipation environment, and a second pipe 107 whose one end is connected to the condenser part 106 and another end is connected to the second circular port 104 as inlet port. The phase conversion cooler 101 has a refrigerant circular system for a refrigerant changeable in liquid phase/vapor phase.

The cooling head 202 is a metal container with high thermal conductivity having an approximately rectangular parallelepiped shape. The first side (the front surface on the rear side of the drawing) of the cooling head 102 is in contact with a heat radiating surface of an LSI as an object to be cooled.

The first pipe 105 connected to the first circular port 103 is extended by a sufficiently long length in a direction orthogonal to the second side 102b of the cooling head 102 and connected to the condenser part 106. In the status shown in the figure, as the second side 102b of the cooling head 102 is positioned as an upper side of the cooling head 102, the first pipe 105 is extended upward.

The condenser part 106 has a surface area widened by e.g. folding back a metal pipe with high thermal conductivity plural times. The condenser part 106 is placed in a heat dissipation environment sufficiently away from the cooled object. The heat dissipation environment means an environment appropriate to heat dissipation such as an environment easily exposed to atmosphere, an environment adjacent to a member with high thermal conductivity exposed to atmosphere or an environment around which any heat source or member with low heat-resistance does not exist.

The second pipe 107 connected to the second circular port 104 is extended by a comparatively short length part in a direction orthogonal to the third side 102c of the cooling head 102, then other part is bent toward the condenser part 106, then extended by a long length in parallel with the first pipe 105 and connected to the condenser part 106. In the status shown in the figure, as the third side 102c of the cooling head 102 is positioned as a vertical side of the cooling head 102, the second pipe 107 is laterally extended and then extended upward vertically.

The first pipe 105, the condenser part 106 and the second pipe 107 can be formed as one continuous pipe.

The phase conversion cooler 101 contains a refrigerant in its internal space formed from the cooling head 102 through the first pipe 105, the condenser part 106 and the second pipe 107, again to the cooling head 102.

In the phase conversion cooler 101, heat from the cooled object is thermal-conducted to the cooling head 102, and the refrigerant in the cooling head 102 is vaporized (boiled) into gas phase by the heat. The refrigerant in gas phase flows upward in the cooling head 102 into the first pipe 105 via the first circular port 103 and flow into the condenser part 106. The refrigerant in gas phase is heat-dissipated with the condenser part 106 then liquefied (condensed) into liquid phase. The refrigerant in liquid phase flows downward in the second pipe 107 from the condenser part 106 into the cooling head 102 via the second circular port 104. In this manner, in the conventional phase conversion cooler 101, the refrigerant absorbs the heat of the cooled object by vaporization, then the condenser part 106 dissipates the heat outside the system (atmosphere or the like), and then the refrigerant in liquid phase returns to the cooling head 102, i.e., the circulation of the refrigerant is repeated. This achieves continuous forced-cooling of the cooled object.

In the phase conversion cooler 101 which is smaller and simpler in comparison with a cooling fan to do air-cooling to a cooled object, a pump mechanism to do forced circulate of a refrigerant with a mechanical force is not required.

The percentage of the liquid phase in the entire phase conversion cooler (in the internal space from the cooling head 102 through the first pipe 105, the condenser part 106 and the second pipe 107, again to the cooling head 102) is 20 to 30% to total amount of the refrigerant by volume. In the cooling head 102, the refrigerant exists in appropriate percentages of liquid phase and gas phase.

The refrigerant in liquid phase is stored in a lower part of the cooling head 102, and a liquid surface (s) of the refrigerant is above the second circular port 104. The refrigerant in gas phase occupies space higher from the liquid surface (s). The first circular port 103 is positioned above the space. Accordingly, the volume of refrigerant in gas phase is increased by vaporization, the refrigerant in gas phase easily flows into the first pipe 105, and further, the refrigerant in gas phase flows only into the first pipe 105. Further, the refrigerant in liquid phase changed from gas phase to liquid phase with the condenser part 106 flows into the second pipe 107 in accordance with gravity and returns to the cooling head 102. In this arrangement, the refrigerant in gas phase flows upward from the cooling head 102 into the condenser part 106, then the refrigerant in liquid phase flows downward from the condenser part 106 into the cooling head 102, i.e., the circulation of the refrigerant is promoted smoothly.

The conventional phase conversion cooler 101 is provided to a desktop type personal computer or the like. However, a problem occurs when this phase conversion cooler 101 is provided in a portable device (mobile equipment) such as a cellular phone or a notebook-sized personal computer.

Since the housing of mobile equipment is smaller than that of fixed type equipment such as a desktop type personal computer and its inner space is small, a phase conversion cooler to be provided to such mobile equipment must be further downsized and thinned in comparison with the conventional phase conversion cooler.

In the conventional phase conversion cooler 101, for the purpose of improvement in thermal exchange efficiency with the cooled object, the cooling head 102 is entirely made of a metal material. Further, as the cooling head 102 serves as a refrigerant container, it is necessary for the cooling head 102 to have a hollow and airtight structure. The cooling head 102 is more particularly formed by so-called sheet metal processing of three-dimensionally assembling metal plates and sealing the jointed portions with welding.

In order to join the metal plates with high airtightness, it is necessary to prepare metal plates having a predetermined or relatively greater thickness. If using thin metal plates to be welded, the shape of the metal plates may be distorted or hole(s) may be formed. Accordingly, in the conventional phase conversion cooler, the metal plates of the cooling head have relatively great thickness. The thickness is more particularly about 1 mm. Generally, the limit of thickness of copper plates to welding is equal to or greater than 0.5 mm. Accordingly, the external dimensions of the cooling head 102 become greater. The limitation of the thickness of the metal plates disturbs the downsizing of the cooling head 102 and the ensuring of refrigerant container space.