GB1561689A - Air cooled electrical apparatus - Google Patents

Description

(54) AIR COOLED ELECTRICAL APPARATUS (71) We, INTERNATIONAL BUSINESS MACHINES CORPORATION, a Corporation organized and existing under the laws of the State of New York in the United States of America, of Armonk, New York 10504, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to electrical apparatus and is more particularly concerned with such apparatus including means for cooling the heat generating electrical components or circuitry of the apparatus. The invention is applicable to air-cooled electronic equipment having components densely mounted on printed-circuit boards or other planar elements carrying or comprising electrical circuitry and/or components.

The invention provides electrical apparatus comprising a main frame; a multiplicity of electrical circuit boards or other planar elements carrying or comprising electrical circuitry and/or components; a subframe hingedly mounted on the main frame for movement between two angularly spaced positions, said sub-frame comprising first means supporting at least a group of the circuit boards or other planar elements in a row, the planar elements in the row being positioned one behind the other in parallel planes and being spaced apart so as to form air flow passages between their major surfaces, and an elongate plenum chamber tapering from a wider end to a narrower end and having a flat wall aligned with and adjacent to the row of planar elements, said wall lying in a plane perpendicular to the planes of the planar elements and having a row of parallel slots through it at a spacing such that the slots register respectively with the air passages between the planar elements, each slot being provided with a lip or flange extending from the wall outwardly of the chamber towards the air passages; and blower means for supplying cooling air to the plenum chamber at or adjacent the wider end thereof, at least some of which air passes from the plenum chamber through the slots and into the air flow passages between the circuit boards or planar elements.

Electrical apparatus embodying the invention will now be described by way of example, with reference to the accompanying drawings, in which: FIGURE 1 is a simplified perspective view of a part of a sub-frame of the apparatus, and FIGURE 2 is a top plan view of the electrical apparatus showing the sub-frame of Figure 1 in its open position.

In Figure 1, numeral 100 denotes generally the sub-frame which comprises a socalled "gate member" having a frame moulded as a single piece in structural foamed plastics material. An L-shaped rear bay 110 has an upstanding wall 111 and a floor 112 having moulded lugs 113 for fastening a power-supply module (not shown in Figure 1).

Housing 120, integrally moulded with the rest of gate 100, provides an enclosed chamber 121 (Fig. 2) of a conventional "scroll" design which, with a squirrel-cage blower rotor 122, form air blower means. The rotor 122 is driven by a motor (not shown) mounted on the bottom surface 123 of housing 120. Inlet aperture 124 is surrounded by upstanding walls 125, 126 and 111. A plenum chamber 130 is partially defined by walls 137, 138, 139 (Fig. 2) moulded in with the gate 100 and communicating with the housing 120.

Chamber 130 is covered by a stamped metal sheet 132 having a front wall 135 containing a series of slots 133 and outturned lips 134 formed by the material removed from the slots. The sheet 132 has side flange 1351 fastened to wall 138. In the illustrative embodiment shown, the lips and slots are generally trapezoidal, having bases of 4.6 and 4.1 cms, and a width of 0.8cm. The slot-to-slot spacing is about 1.6cm. The rectangular cross section of plenum chamber 130, decreases uniformly in area from its wider entrance end 140 to its narrower forward end 136. This decrease in area is achieved entirely by decreasing the width between sheet 132 and side wall 137, while the height between upper and lower walls 138, 139 remains constant. Sheet 132 is slightly shorter than the length of chamber 130, to provide a final air exit at 1331.

Finally, gate 100 includes an integrally molded structure defining a front bay 140.

Wall 141 is attached at one end to end 136 of plenum chamber 130 and to bar 142, shown broken away for clarity. Wall 143 has one end attached to wall 141; its other end is attached to wall 111. The upper surfaces of wall 141 and bar 142, along with ledges formed in walls 143 and 111, form a mounting surface 144 for a backplane 161 (Fig. 2) containing sockets for a number of circuit boards 163.

Figure 2 is a top plan view of a desktop data processor 200 including the gate 100 shown in Figure 1. Since gate 100 is in its "open" position in Figure 2, it is seen from the bottom, i.e. upside down with respect to Figure 1.

Figure 2 shows a simplified outline of a power-supply module 150 mounted in rear bay 110. Broadly speaking, module 150 comprises a number of component packages, such as 151-154, mounted on a support board 155. Board 155 is in turn fastened to lugs 113, Figure 1. A solid metal safety cover 114 is attached to the side and bottom of wall 111, as it appears in Figure 2. Cover 114 is also fastened to the left end of floor 112 and to walls 125 and 126.

Figure 2 also shows an electronics assembly 160 mounted in front bay 140. Backplane 161 is stiff horizontal board mounted on surface 144, Figure 1. It contains a number of parallel edge-connector sockets such as 162 into which circuit boards such as 163 may be inserted in a conventional manner.

In this illustrative embodiment, boards 163 are printed-circuit boards each holding many components and modules. Backplane 161 merely provides physical support and electrical isolation for sockets 162; inter-socket electrical connections are provided by wires wrapped on posts (not shown) on each socket to the rear of backplane 161 as seen in Figure 2, and/or by printed-circuit wiring (not shown) on backplane 161. Sockets 162 are disposed parallel to each other and are aligned with respective ones of the lips 134 on plenum-chamber sheet 132, such that circuit boards 163 are coplanar with lips 134 but separated therefrom by a small distance e.g. less than about 1.5 cm. The height of plenum chamber 130 (i.e., in the direction out of the plane of Figure 2) is less than half the height of boards 163.

Gate 100 is attached to a structural foamed-Dlastics lower housing 210 of processor 200 by hinge means 220. A conventional "invisible" hinge 221 is fastened between arms 222 molded in gate 100 and vertical posts 223 molded into lower housing 210. Another hinge 224 is fastened between posts 225 in gate 100 and posts 226 in housing 210. This arrangement allows gate 100 to swing up to 180C about a horizontal axis, from the position shown in Figure 2 to a "closed" position in which gate 100 lies fully within lower housing 210.

In the closed position, metal brackets 101 and 102 may be screwed to upstanding posts 211 and 212 molded in housing 210. The upper edges of circuit boards 163 rest against a resilient foam-rubber cushion 213 on a raised platform 214 molded into the bottom of housing 110.

In this way, gate 100 and its cooling system and electronics components are rigidly secured within housing 110 in the closed position. At the same time, the interboard wiring on backplane 161 is easily accessible for servicing from above. Then, when gate 100 is opened and laid flat on the same surface upon which housing 110 rests, the power supply 150 and the individual circuit boards 163 are immediately accessible. Processor 200 may continue to operate indefinitely in the open position, since full cooling is retained.

Lower housing 210 also holds other electronics modules, shown in outline form to illustrate their spatial relationship to gate 100. Keyboard 270 is positioned to one side of a slightly sloping vertical panel 230.

Magnetic-tape unit 240 and cathode-ray tube (CRT) display 250 abut panel 230.

Control panel 260 is for use by service personnel, and is accessible in both the open and closed positions of gate 100. When gate 100 is closed, a louvered upper housing (not shown) may be fitted over lower housing 210 to the rear of panel 230.

In operation, squirrel-cage blower rotor 122 draws inlet cooling air through a Bshaped opening in the rear of bay 110 into blower housing 120. This relatively highvolume low-velocity air flows across power supply 150 to cool components 151-154 before being drawn into blower housing 120.

Rotor 122 propels air into plenum chamber 130, preferably at a lineal velocity of about 15 meters per second in the present embodiment. The air then proceeds through slots 133 and between circuit boards 163 in bay 160.

The combination of the uniformly decreasing cross section of plenum chamber 130, the uniformly spaced slots 133 and the perpendicular out-turned lips 134 produces a stream of cooling air of substantially constant volume from slot to slot along the length of sheet 132 and flowing perpendicularly thereto. These characteristics are substantially independent of the cooling load, that is, independent of the number of circuit boards 163 actually present in bay 140.

Each slot 133 presents a higher airflow impedance than that of the space between two adjacent boards 163. Lips 134, although they lie wholly outside of chamber 130, are effective to deflect the airflow through a complete right angle, whether or not a circuit board is inserted in the corresponding socket 162. For the aforementioned air velocity of 15 m/sec., this directional change is best accomplished when each lip 134 is downstream from its associated slot 133.

At higher velocities, such as about 30 m/ sec., however, the lips are more effective when positioned at the upstream sides of the slots.

The cooling air exiting slots 133 has a high normal velocity component. Very little backsplash occurs when the lips and boards are less than about 1.5 cm. apart. Therefore, the areas above and below boards 163 need not be sealed in order to maintain proper air flow. Moreover, adequate cooling is achieved even though the vertical height of boards 163 is much greater than that of lips 134. Lips 134 in turn need not be taller or wider than slots 133 and do not extend into chamber 130, so that these lips may be easily fabricated by merely bending out the interiors of the slots. These characteristics also result in a small size for the entire cooling system, in relation to the size of the cooling load.

Another advantage of the embodiment shown in Figures 1 and 2 is that the cooling air is drawn into and exhausted from processor 200 at relatively large distances from blower rotor 122. This configuration reduces blower noise sufficiently that other acoustic absorption materials are unnecessary.

WHAT WE CLAIM IS:- 1. Electrical apparatus comprising a main frame; a multiplicity of electrical circuit boards or other planar elements carrying or comprising electrical circuitry and/or components; a sub-frame hingedly mounted on the main frame for movement between two angularly spaced positions, said sub-frame comprising first means supporting at least a group of the circuit boards or other planar elements in a row, the planar elements in the row being positioned one behind the other in parallel planes and being spaced apart so as to form air flow passages between their major surfaces, and an elongate plenum chamber tapering from a wider end to a narrower end and having a flat wall aligned with and adjacent to the row of planar elements, said wall lying in a plane perpendicular to the planes of the planar elements and having a row of parallel slots through it at a spacing such that the slots register respectively with the air passages between the planar elements, each slot being provided with a lip or flange extending from the wall outwardly of the chamber towards the air passages; and blower means for supplying cooling air to the plenum chamber at or adjacent the wider end thereof, at least some of which air passes from the plenum chamber through the slots and into the air flow passages between the circuit boards or planar elements.

2. Apparatus as claimed in claim 1, in which the blower means comprise a blower mounted on the sub-frame and having a pressure outlet registering with the wider, inlet end of the plenum chamber.

3. Apparatus as claimed in claim 2, in which the sub-frame comprises second means supporting further heat generating electrical equipment in an air duct through which ambient air is drawn by the blower into its air inlet.

4. Apparatus as claimed in claim 1, 2 or 3, in which the wall is formed of sheet material and in which each slot is formed by bending a strip of the material out of the plane of the sheet, the strip providing the lip or flange.

5. Electrical apparatus as claimed in claim 1, 2, 3 or 4, in which the sub-frame is substantially as hereinbefore described with reference to and as shown in Figure 1 of the accompanying drawings.

6. Electrical apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. boards 163 actually present in bay 140. Each slot 133 presents a higher airflow impedance than that of the space between two adjacent boards 163. Lips 134, although they lie wholly outside of chamber 130, are effective to deflect the airflow through a complete right angle, whether or not a circuit board is inserted in the corresponding socket 162. For the aforementioned air velocity of 15 m/sec., this directional change is best accomplished when each lip 134 is downstream from its associated slot 133. At higher velocities, such as about 30 m/ sec., however, the lips are more effective when positioned at the upstream sides of the slots. The cooling air exiting slots 133 has a high normal velocity component. Very little backsplash occurs when the lips and boards are less than about 1.5 cm. apart. Therefore, the areas above and below boards 163 need not be sealed in order to maintain proper air flow. Moreover, adequate cooling is achieved even though the vertical height of boards 163 is much greater than that of lips 134. Lips 134 in turn need not be taller or wider than slots 133 and do not extend into chamber 130, so that these lips may be easily fabricated by merely bending out the interiors of the slots. These characteristics also result in a small size for the entire cooling system, in relation to the size of the cooling load. Another advantage of the embodiment shown in Figures 1 and 2 is that the cooling air is drawn into and exhausted from processor 200 at relatively large distances from blower rotor 122. This configuration reduces blower noise sufficiently that other acoustic absorption materials are unnecessary. WHAT WE CLAIM IS:-

1. Electrical apparatus comprising a main frame; a multiplicity of electrical circuit boards or other planar elements carrying or comprising electrical circuitry and/or components; a sub-frame hingedly mounted on the main frame for movement between two angularly spaced positions, said sub-frame comprising first means supporting at least a group of the circuit boards or other planar elements in a row, the planar elements in the row being positioned one behind the other in parallel planes and being spaced apart so as to form air flow passages between their major surfaces, and an elongate plenum chamber tapering from a wider end to a narrower end and having a flat wall aligned with and adjacent to the row of planar elements, said wall lying in a plane perpendicular to the planes of the planar elements and having a row of parallel slots through it at a spacing such that the slots register respectively with the air passages between the planar elements, each slot being provided with a lip or flange extending from the wall outwardly of the chamber towards the air passages; and blower means for supplying cooling air to the plenum chamber at or adjacent the wider end thereof, at least some of which air passes from the plenum chamber through the slots and into the air flow passages between the circuit boards or planar elements.

2. Apparatus as claimed in claim 1, in which the blower means comprise a blower mounted on the sub-frame and having a pressure outlet registering with the wider, inlet end of the plenum chamber.

3. Apparatus as claimed in claim 2, in which the sub-frame comprises second means supporting further heat generating electrical equipment in an air duct through which ambient air is drawn by the blower into its air inlet.

4. Apparatus as claimed in claim 1, 2 or 3, in which the wall is formed of sheet material and in which each slot is formed by bending a strip of the material out of the plane of the sheet, the strip providing the lip or flange.

5. Electrical apparatus as claimed in claim 1, 2, 3 or 4, in which the sub-frame is substantially as hereinbefore described with reference to and as shown in Figure 1 of the accompanying drawings.

6. Electrical apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.