Cooling system

Abstract: This system includes grooved guide plates (11, 12, 18, 19) forming part of subracks (9, 10) and making thermal contact with horizontal portions of flat box-shaped heat pipes (25, 26, 27) having the shape of an L. The grooved guide plates have associated excentric members (15, 16, 22, 23) to fix the thermal drains of circuit boards (17, 24) in their grooves (13, 14, 20, 21). The horizontal portions of each guide pipe collect the heat from circuit boards and convey it via their vertical portions to a heat exchanger (31).

Description: COOLING SYSTEM The present invention relates to a cooling system for a plurality of circuit boards each having a substantially planar thermally conductive thermal drain having longitudinal sides and in thermal contact with a plurality of electronic components dissipating heat, said cooling system including a heat exchanger to deliver heat to a cooling medium and heat pipe means to transfer heat from said thermal drains to said heat exchanger. Such a cooling system is already known from EP-A-0461114 which falls under Article 54(3) EPC and which corresponds to WO-A-9110346 first filed by Applicant on December 28,1989. Therein the heat pipe means comprises sets of heat conductive metal rails housing heat pipes. More particularly, two sets of first metal rails arranged in two parallel planes and housing first heat pipes make thermal contact with respective opposite longitudinal sides of the thermal drains of the circuit boards. Two sets of second metal rails including second parallel heat pipes and mounted in a plane perpendicular to those containing the first metal rails makes thermal contact therewith. Finally, a third metal rail housing third heat pipes and mounted in a plane perpendicular to those containing the first and second metal rails makes thermal contact with the second rails and leads to the heat exchanger. A drawback of this known cooling system is that the thermal resistance between the thermal drains and the heat exchanger is still relatively high, especially due to the fact that the heat transfer between these elements does not take place directly via the heat pipes but through the intermediary of a plurality of metal rails which thermally link the thermal drains, heat pipes and heat exchanger and which present a relatively high thermal resistance especially at their junctions. An object of the present invention is to provide a cooling system of the above known type, but presenting a reduced thermal resistance. From EP-A- 0 231 456 there is further known a cooling system having means to transfer heat from thermal drains to an heat exchanger. The means to transfer heat from the thermal drains are integrated with the heat exchanger in a closed circuit with evaporators at the side of the thermal drains, a condensor at the side of the heat exchanger, and a network of pipes interconnecting the evaporators and the condensor. According to the invention, the above object is achieved due to the fact that the heat pipe means includes at least one flat box-shaped heat pipe of which at least one part is in thermal contact with the longitudinal sides of said thermal drains of said circuit boards. Heat from the thermal drains is thus collected and transferred by a single flat box-shaped heat pipe, thus reducing the thermal resistance of the cooling system. Compared with the known system the flat box-shaped heat pipe thus replaces the first and second heat pipes thermally coupled by metal rails. Another characteristic feature of the present cooling system is that said longitudinal sides of said thermal drains are located in grooves making thermal contact with said flat box-shaped heat pipe. Still another characteristic feature of the present cooling system is that it further includes a guide plate provided with said grooves and in thermal contact with said heat pipe. The grooved guide plate thus collects heat from the thermal drains and transfers it to the single flat box-shaped heat pipe and may be thermally coupled via a rail containing a heat pipe and leading to the heat exchanger. Compared with the above known system the grooved guide plate thus replaces the first and second rails. The cooling system according to the invention is also characterized in that said flat box-shaped heat pipe has another part substantially perpendicular to said one part and leading to said heat exchanger In this way the flat box-shaped heat pipe conveys the heat collected from the thermal drains directly to the heat exchanger. Compared with the known system there is no need to use third rails housing heat pipes. The above mentioned and other objects and features of the invention will become more apparent and the invention itself will be best understood by referring to the following description of embodiments taken in conjunction with the accompanying drawings wherein : Fig. 1 is a cross-sectional front view of a rack to which a first embodiment of a cooling system according to the invention is associated; Fig. 2 is a perspective view of a part of the flat plate heat pipe 26 and associated flat guide plates 12 and 18 of Fig. 1; Fig. 3 is a perspective view of a second embodiment of a cooling system according to the invention. Principally referring to Fig. 1 the rack shown therein includes a metal frame structure constituted by a plurality of interconnected frame members such as 1 to 8. Two like subracks 9 and 10 are secured to the rack in a not shown but obvious way and such that some free space is left at both the lower and upper sides of these subracks. Subrack 9 comprises two parallel guide plates 11 and 12 which extend over the width and depth of the rack and each of which has a plurality of parallel grooves such as 13 and 14. Each of these guide plates moreover carries a plurality of pivoted excentric members such as 15 and 16 which are for instance of the type disclosed in the above mentioned PCT patent application. They are used to fix circuit boards such as 17 in the grooves. As also described in this patent application the circuit board 17 is of the type having a substantially planar thermally conductive thermal drain for a plurality of electronic components mounted on the circuit board and dissipating heat. To simplify the drawing the circuit board and its thermal drain are represented by a single element 17. The longitudinal sides of each such thermal drain 17 are fixed in a pair of grooves such as 13, 14 by means of the excentric members 15, 16 which fermly press the longitudinal sides against side walls of the grooves. Subrack 10 likewise comprises two parallel flat guide plates 18 and 19 which extend over the width and depth of the rack. Each of these flat plates 18, 19 has a plurality of grooves, such as 20 and 21, and carries pivoted excentric members such as 22 and 23 to fix the longitudinal sides of the thermal drain of a circuit board 24 in these grooves. The cooling system associated to the above frame structure includes the above guide plates and three L-shaped flat box-shaped heat pipes 25, 26 and 27, each with two perpendicular flat first and second portions. The first portions of the pipes 25, 26 and 27 are horizontally mounted below subrack 9, between subracks 9 and 10 and above subrack 10 respectively. The second flat portions of the pipes 25, 27 extend vertically along the frame member 4 and lead to cooling elements such as 28, 29 and 30 of a heat exchanger 31. Likewise, the second flat portion of the heat pipe 26 extends vertically along the frame member 3 and leads to other elements 32 and 33 of this heat exchanger 31. A cooling medium, e.g. water, circulates in these elements 28, 29, 30, 32, 33. Part of the flat box-shaped heat pipe 26 of Fig. 1 is shown in perspective in Fig. 2, together with the associated flat guide plates 12 and 18 of the subracks 9 and 10 respectively. The above cooling system functions as follows : heat dissipated by components (not shown) mounted on the various circuit boards is collected by the thermal drains, such as 17, 24, thereof, and is directly collected by the horizontal portions of the flat box-shaped heat pipes 25, 26, 27 and conveyed to the heat exchanger 31 via the vertical portions of these pipes. Instead of being made in the guide plates such as 11, 12, 18, 19 the grooves 13, 14, 20, 21 could also be provided directly in corresponding upper/lower walls of the box-shaped heat pipes, thus eliminating the need for using separate guide plates. Reference is now made to Fig. 3 which schematically represents part of a cooling system to be mounted in a cabinet or constituting a cabinet itself. It comprises a pair of vertically mounted flat box-shaped heat pipes 34 and 35 united by plates 36 and 37 to form a firm structure. The heat pipes 34 and 35 lead to a heat exchanger (not shown) and have associated grooved guide plates 38 and 39 which are of the same type as those represented in Figs. 1 and 2. The grooves enable a printed circuit such as 40 to be horizontally mounted and such that the longitudinal sides of its thermal drain are in thermal contact with the heat pipes 38 and 39. While the principles of the invention have been described above in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention as defined in the claims.

Claims: Cooling system for a plurality of circuit boards each having a substantially planar thermally conductive thermal drain (17, 24, 40) with longitudinal sides and in thermal contact with a plurality of electronic components dissipating heat, said cooling system including a heat exchanger (31) to deliver heat to a cooling medium and heat pipe means (25, 26, 27, 34, 35) to transfer heat from said thermal drains (17, 24, 40) to said heat exchanger (31), characterized in that said heat pipe means includes at least one flat box-shaped heat pipe (25, 26, 27, 34, 35) of which at least one part is in thermal contact with the longitudinal sides of the thermal drains (17, 24, 40) of said circuit boards. Cooling system according to claim 1, characterized in that said longitudinal sides of said thermal drains (24) are located in grooves (20) making thermal contact with said flat box-shaped heat pipe (26). Cooling system according to claim 2, characterized in that it further includes a guide plate (18) provided with said grooves (20) and in thermal contact with said heat pipe (26). Cooling system according to claim 2, characterized in that said box-shaped heat pipe (25, 26, 27) is provided with said grooves (20). Cooling system according to claim 1, characterized in that said flat box-shaped heat pipe (25, 26, 27) has another part substantially perpendicular to said one part and leading to said heat exchanger (31). Cooling system according to claim 1, characterized in that said flat box-shaped heat pipe (26) is in thermal contat with the longitudinal sides of the thermal drains (17, 24) of two adjacent sets of circuit boards.

Inventors: LEYSSENS FRANCOIS JEANNE CHARL, ROMBOUTS HENDRIKUS MARTINUS JO, LEYSSENS, FRANCOIS JEANNE CHARLES, ROMBOUTS, HENDRIKUS MARTINUS JOANNES, Leyssens, François Jeanne Charles
Applicants: BELL TELEPHONE MFG, BELL TELEPHONE MANUFACTURING COMPANY NAAMLOZE VENNOOTSCHAP
Application year: 1991
Main classification: H05K7
IPC codes: H05K7, G12B15, F25D9