Balanced flow cooling

There is described a modular electronic circuit wherein a series of electronics modules are penetrated by a passageway having an air-permeable wall, and cooling air is supplied to the passageway at a pressure above that obtaining in the modules, so that each module receives a supply of air passing out through the wall of the passageway. The passageway is constituted by a plurality of aligned tubular sleeves mounted in respective modules. There is also described a ventilation module including blowers to pressurize the passageway. A second passageway may be provided, at a reduced pressure, to extract air from the modules.

FIELD OF INVENTION

The present invention relates to modular electronic circuits, and is particularly concerned with the provision of cooling air flows through electronic circuit modules.

BACKGROUND OF THE INVENTION

Complex electronic circuits are frequently implemented by assembling a plurality of individually cased circuit modules in a supporting rack, with electrical interconnection between the modules being effected by cabling.

The electronic components within each module require cooling, and to provide such an airflow cooling fans are often installed on the front and/or back faces of each module so that air is drawn into the module through openings in the front face and is expelled through openings in the rear face.

When the modules are assembled into a rack, only the front and rear faces are accessible. As the circuit modules become more complex, the rear face of the module is increasingly taken up by the provision of connectors for linking the modules together, and the front face is increasingly occupied by devices such as indicator lights, disc drives, setting switches, etc. This increasing number and complexity of components mounted on the front and rear faces of the module leaves little room for ventilation fans or ventilation openings.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide cooling air flows over the electronic components of the modules of a rack-mounted system, without taking up space on the front and/or rear faces of the modules for cooling fans or openings.

According to a first aspect of the present invention, there is provided a modular assembly for containing an electronic circuit, the assembly comprising a supporting structure, a number of circuit modules, and at least one ventilation module. The ventilation module comprises a plurality of air inlet openings on its front and/or rear face, and a ventilator or fan to move air through the cooling module from the inlet openings to an air supply opening on an upper or lower face of the ventilation module. Each of the circuit modules comprises openings on its upper and lower faces positioned so as to be in vertical alignment with the air supply opening of the ventilation module when the modules are assembled in the supporting structure. Extending between the openings of each module is a tubular permeable membrane. Air is supplied to the interiors of the tubular membranes, and passes out through the membranes in to the circuit modules to establish a cooling airflow over components housed in the modules.

The circuit modules may also comprise air exhaust openings in their respective upper and lower faces, arranged to be in vertical alignment when the modules are mounted in the supporting structure. The aligned exhaust openings may be provided with tubular membranes within each module to form a tubular exhaust manifold. The ventilation module may be provided with an air aspiration opening in its upper or lower face to communicate with the exhaust manifold, and extractor fans on its front and/or rear faces to draw in air through the aspiration opening and expel it through exhaust openings on the front and/or rear faces of the ventilation module.

In a combined supply and exhaust ventilation module, the interior of the ventilation module is divided into two regions, one of which communicates with an air supply opening and optionally has fan means to draw air into the module and expel it through the air supply opening, and the other region has an air exhaust opening and optionally exhaust fans to draw air into the module through the aspiration opening and expel it through exhaust openings in the front or rear face of the module. In one embodiment, the ventilation module has two sets of fans so that air is both blown out of the air supply opening and sucked in through the aspiration opening of the ventilation module.

A further aspect of the invention provides a housing for an electronic module for use in the assembly, the housing comprising upper and lower surfaces having aligned openings, and a tubular pressure control membrane extending within the module between the upper and lower surfaces of the module, to delimit an internal region of the module containing the upper and lower openings.

A yet further aspect of the invention provides for a “dummy” module to replace an electronics module in a rack while the electronics module is removed for servicing, the dummy module having mounting elements to cooperate with the rack, and ducts to provide a sealed connection between the air inlet and/or outlet openings of the electronics modules adjacent the removed module. Cooling air supply to the remaining modules is preserved by the presence of the dummy module, whose ducts replace the membranes of the removed module, so that the remaining electronics modules may continue to operate without overheating.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring now to the drawings, in which like parts will be given like reference numerals,FIG. 1shows a modular assembly1comprising a supporting structure or rack2, a plurality of circuit modules3mounted in a vertically-extending array in the rack2, and a ventilation module4mounted below the array of circuit modules3. The front faces of the circuit modules3are visible inFIG. 1, and components5of the electronic circuits contained within the circuit modules3are mounted to the front faces of the modules. The components5may be switches, indicator devices, media drives, or other components to which access is required during operation or maintenance of the circuits contained in the modular assembly.

The ventilation module4has mounted to its front face a number of fans6and an indicator panel7. The indicator panel7may comprise indicator lights to show the operational states of the fans6of the ventilation module4.

FIG. 2is a perspective view of the ventilation module4. The module4comprises a front face4fto which the fans6and indicator panel7are mounted, and a rear face4rto which a plurality of extractor fans8are mounted. The interior of the module4is divided into front and rear regions4aand4bby a bulkhead9, which extends between side walls10and11of the ventilation module4. The side walls and bulkhead may be formed of any suitable impervious material, such as plastics or metal sheet.

The upper surface of the ventilation module4is formed with two openings, positioned on either side of the bulkhead9. Adjacent the front face4fof the ventilation module is an air supply opening13communicating with front region4aof the interior of the module4, and adjacent the rear face4rof the ventilation module is an aspiration opening14communicating with the rear region4b. In operation, the fans6draw air in through the front face4fof the ventilation module, pressurising the front region4a. This pressurised air is delivered through the air supply opening13. Similarly, extractor fans8expel air from within the rear region4bof the ventilation module through the rear face4r, and this results in air being drawn into the module through the aspiration opening14. Filter membranes formed from mesh or non-woven fabric may be provided adjacent the fans6and/or the fans8, to catch airborne particles.

On the upper surface12of the ventilation module4, resilient sealing elements15are provided to surround the air supply opening13and the aspiration opening14, and will be described later in detail.

The indicator panel7of the ventilation module may include one or more indicator devices associated with each of the fans6and extractor fans8, so that a malfunction of the fans6or extractor fans8will be indicated on the panel7.

Referring now toFIGS. 3 and 4, there is shown a circuit module3, comprising a substantially air tight casing housing a number of electronics components5mounted to its front and rear faces, and internal electronics components5a. The wiring connecting the electronic components5and5ahas been omitted, for clarity. The casing may be formed from sheet metal, or from synthetic plastics material with or without fibre reinforcement.

The upper surface16and the lower surface17of each circuit module3are each formed with two openings16a,16band17a,17bcorresponding in position to the air supply opening13and the air aspiration opening14of the ventilator module4, respectively. The circuit module3therefore comprises two pairs of vertically-aligned openings, one pair being aligned with the air supply opening13, and the other pair being aligned with the aspiration opening14when the circuit module is placed above the ventilator module4.

A tubular mesh sleeve18f,18rextends between the upper and lower surfaces16and17of the circuit module3, between the openings of each vertically-aligned pair. The sleeves18f,18rmay be formed from fine wire or plastics mesh, or may be formed from a thin layer of open-cell foam material or non-woven fabric, or from a textile material. The sleeves18f,18rare sealed to the upper and lower surfaces16,17of the module by substantially airtight joints.

A respective seal member15surrounds each of the openings in the upper surface16of the circuit module3, and extends above the upper surface16of the circuit module3.

The modular assembly1ofFIG. 1is assembled by placing a ventilation module in the lowermost position in the supporting structure or rack2and arranging a number of circuit modules3into the supporting structure2vertically above the ventilation module4. The vertical spacing between adjacent modules is such that the seals15on the upper surface of each module can form an air tight seal with the undersurface of the module above. With the modules assembled in the rack, the seals15of the uppermost module engage a top surface19of the supporting structure2, effectively closing off the openings in the upper surface of the topmost module. The top surface19may be formed from metal sheet, or plastics material, or any other suitably impervious sheet material able to withstand the pressure difference between ambient and the pressure within the sleeves18fand18r.

As can be seen inFIG. 5, the air supply opening13in the ventilation module4communicates with the lower end of a vertically-extending passageway bounded by the mesh sleeves18adjacent the front faces of the circuit modules3, while the aspiration opening14is in communication with the lower end of a passageway formed by the mesh sleeves18adjacent the rear faces of the circuit modules3. The sleeves may, in one embodiment, comprise a skeletal frame formed from resilient material such as metal or plastics, with snap-engaging formation to cooperate with one or both of the upper and lower surfaces16,17of the module. The mesh, foam or fabric filter material of the sleeves18f,18rmay be bonded to the frame or clamped thereto. The sealing elements15may be integrated with the mesh sleeves18.

In operation, the fans6draw air into the ventilation module4, pressurising the front region4aof module and the space within the tubular sleeves18above the air supply opening13to a superambient pressure. Air within this space then passes out through the mesh sleeves into the interiors of the circuit modules3, providing a cooling air flow over the electronic components. The fans6may generate a superambient pressure in the front region4aand within the sleeves18fthat is from 0.001 to 0.005 bar above the surrounding atmosphere, i.e. above the pressure within the interior of the module3. The area and permeability of the membrane from which sleeve18fis formed is chosen for each module so that the overpressure within the sleeve provides an air flow rate through the sleeve adequate to cool the components in that module. The area and permeability of the membrane may be chosen to provide a volumetric flow of air of from 0.5 to 100 m3/hour, preferably from 10 to 50 m3/hour into the module.

The fans6provide substantially the same super-atmospheric pressure within all of the sleeves18f. If the sleeves18fall have the same surface area and are all made from the same material, then equal amounts of air will be delivered to the interiors of the circuit modules3. If the cooling requirements of one circuit module3exceed those of the others, then the cross-sectional are of the sleeve18fof that circuit module may be enlarged to provide a greater surface area to the sleeve and therefore a greater mass flow of air into the module3, or the sleeve may be made more permeable for example by using a larger mesh or a more open-celled foam.

The rear region4bof the ventilation module4is connected, via the aspiration opening14, to the interiors of the sleeves18rof the circuit modules3, and thus the operation of the extractor fans8reduces the pressure within the sleeves18rto below ambient, drawing air into the sleeves18rfrom the interiors of the circuit modules. The sleeves18rmay be made from a material which is more porous than that of the sleeves18f, and thus presents less resistance to the flow of air therethrough.

Where extractor fans8are provided, the fans8may be arranged to reduce the pressure in the region4band within the sleeves18rfrom 0.001 to 0.005 bar below the pressure within the circuit modules3.

The area and permeability of the membranes of sleeves18r may be adjusted for each module so that the pressure drop across the sleeve18ris greater than or the same as that across the sleeve18fof the module. This arrangement provides a slight pressurisation of to the module3above ambient so that any air leakage from module3is outward, preventing ingress of dust. Where mesh is used for sleeves18fand18r, the openings in the mesh may be from 0.05 to 1 mm2in area.

FIG. 6illustrates in perspective view a circuit module3in which the sleeve18fis generally rectangular in cross-section, and has a cross-sectional area substantially greater than that of the opening in the undersurface17of the module3. Extending away from the sleeve18fis a deflector plate20, which deflects the flow of air issuing through the sleeve18ftowards a component requiring a particularly high flow of cooling air. It will be understood that the sleeve18fmay have any convenient cross-sectional shape, and the deflector plate20may be straight, curved or angular. A number of deflector plates20of plastics or metal sheet may be provided to collect the air flowing out of the sleeve18fand direct it to components5arequiring particularly high cooling flows.

In the embodiment shown inFIG. 6, the sleeve18ris omitted, and the lower surface17of the module is simply formed with an opening which aligns with an opening in the upper surface of the next module below. Since the ingress of dust through the exhaust openings will be prevented by the nett outflow of air, the mesh sleeves18fcan be relied upon to effectively filter the incoming cooling air. Alternatively, air filters may be provided adjacent to the fans6in the ventilation module4, to prevent the sleeves18ffrom becoming clogged. The absence of sleeves18rremoves the need for extractor fans8in the ventilation module4, since the resistance to flow of air out of the module3is decreased. Permeable sleeves18rmay be provided, however, to produce a slight resistance to exhaust air flow and thus produce a slight pressurisation of the interior of the module to counter inward air leakage.

The ventilation module4is shown in the foregoing embodiment positioned below the circuit modules3. By providing additional air supply and aspiration openings in the undersurface of the ventilation module4, the ventilation module4may be placed at any position within the vertical array of circuit modules. Removable blanking plates, of material similar to the material of the module casing21may be provided in the ventilation module4to cover any unused openings in the upper or lower surfaces of the ventilation module4.

It is also possible, by placing the blanking plates21over the openings in the upper surface of the ventilation module4, to mount the ventilation module4as the uppermost module with the circuit modules3mounted below. In such an arrangement, the openings in the lower surface of the lowermost circuit module may be provided with blanking plates to close them off.

The ventilation module may be provided with removable blanking plates21for all its air supply and exhaust openings13and14, and such blanking plates as are unused may be stored internally within the regions4aand4bof the ventilation module, or externally by attaching them to the upper of lower faces of the module.

If a module3is to be removed from the assembly for maintenance, the continuity between the sleeves18fand18rof the remaining modules3may be provided for by inserting an impermeable tubular component to bridge the gap left by the absent module. Alternatively, a “dummy” module3having no electronics components and having impermeable tubular sleeves may be inserted in place of a removed module, to enable the remaining modules to continue in operation without overheating.FIG. 7shows such a dummy module, which comprises a baseplate30and mounting rails31for mounting the baseplate30to a rack. The baseplate30has openings32and33aligned with the openings13,14of the ventilation module4and with openings16a,16bof the module3. Impermeable tubular sleeves34and35surround the openings32and33and extend above the baseplate30by the height of a module3. Sealing elements15are provided at the tops of sleeves34and35.

When a module3is removed from the supporting structure or rack for maintenance, the dummy module ofFIG. 7is inserted into the slot vacated by the removed module. The baseplate30of the dummy module engages the seals15of the module below, and the seals15of the dummy module engage the undersurface of the next module above, so that sleeves34and35replace the sleeves18fand18r, respectively, of the removed module and cooling air supply to all the remaining modules3is assured, and their operation may continue uninterrupted.

When the removed module3is repaired, then dummy module7is removed from the slot and the repaired module replaced.