Enclosure with metered air ducts for mounting and cooling modules

An enclosure for cooling device modules has metered air passages in an air duct system. The device modules which are of the form of air ducts are inserted into the air duct system of the enclosure and have exhaust air passages which are coupled to metered air passages in the air duct system of the enclosure. A source of reduced air pressure which is coupled to the air duct system of the enclosure draws air through the device module into the air duct system of the enclosure via the exhaust air passage of the device module and the metered air passage of the air duct system. The metered air passages are graduated in area as a function of their individual distances from the source of reduced air pressure to balance the air volume per unit of time at the respective metered air passages and are further sized in area to have a resistance to air flow which is greater than the air flow resistance of any of the device modules, to minimize changes in air volume rate in the air duct system whether or not device modules are in place in the air duct system of the enclosure.

CROSS REFERENCES TO RELATED APPLICATIONS 
Application of Guenter Schkrohowsky et al., Ser. No. 08/388,732, entitled 
Enclosure With Redundant Air Moving System, filed on the same date as this 
application and assigned to the Assignee of this invention. 
1. Field of the Invention 
This invention relates to enclosures for mounting and cooling various 
devices and in particular to enclosures for cooling electronic devices in 
which metered air passages in the air ducts control air flow volume rates 
in the air duct system. 
2. Background of the Invention 
Cooling of electronic devices mounted in enclosures has taken various 
forms, from the elementary, i.e., simply blowing or drawing air through 
the enclosure mounting the devices, to applying individual air streams to 
individual devices. Devices are frequently difficult to access in the 
enclosures, for servicing or replacement. Balanced air flows in the ducts 
of such systems are difficult to achieve. When a device is removed from a 
duct and the device slot is not refilled or plugged, the empty slot 
creates unacceptable air volume rate disturbances throughout the system, 
to the end that cooling is generally inadequate, necessitating system 
shutdown in extreme cases. 
Efforts to minimize such air flow disturbances have included the 
installation of plugs in air ducts from which devices are removed. But 
even this approach is unsatisfactory since the plug does not characterize 
the air flow dynamics of the removed device. 
Compensation for such disruption of air flow is frequently attempted in 
over design of the system which is not cost effective. 
SUMMARY OF THE INVENTION 
A solution to the problems aforesaid is provided, according to the best 
mode for practicing this invention, by mounting the devices to be cooled 
in modules which are an easily removable part of the air duct system of 
the enclosure and by providing metered air passages in the air duct system 
of the enclosure to control air flow between the module air duct and the 
air duct system of the enclosure. 
The metered air passages control air flow in the air duct at each module 
location whether or not the module is in place in the system. The metered 
air passages are also designed to substantially equalize the air volume 
rates across the metered air passages as a function of the distance of the 
metered air passages from the air pressure source of the system, in this 
case a source providing reduced air pressure. The pressure source 
initiates and maintains air movement in the air ducts. 
These metered air openings in the air ducts of the system control the air 
flow into the air duct from the modules, and the presence or absence of a 
module in the air duct system at a metered air passage has minimal effect 
upon the air volume rate across the metered air passage thereat. 
This invention, as applied in an enclosure for cooling pluralities of 
modules, functioned in the worst case situation when only a single module 
was plugged into the air duct system, to adequately cool the single 
module. 
According to the invention, metered air passages are placed in the walls of 
an air duct system both to balance air volume rates thereacross at 
differing distances from the air pressure source and to control air volume 
rates thereacross whether or not a module is in place thereat in the air 
duct system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A presently known best mode for practicing this invention is disclosed 
herein in the form of a two bay enclosure 1 for cooling device modules 
1A-4A, 1B-4B, which are mounted in respective bays A and B positioned in a 
side-by-side relationship in the enclosure 1. The four device modules 1A, 
2A, 3A and 4A, are disposed in a stack in bay A and the four device 
modules 1B, 2B, 3B and 4B, are disposed in a stack in bay B. Each device 
module has a slotted entrance air passage 3 in its front end through which 
air is admitted to the internal air duct system. 
The individual device modules 1A-4A, 1B-4B, are part of an air duct system 
(see also FIGS. 2, 3 and 4) which includes air ducts 5c and 7c in the side 
walls 5 and 7 and 9c in a central or common wall 9. The air ducts 5c, 7c 
and 9c open into an overhead air plenum 11a in an overhead structure 11 of 
the enclosure 1 which spans the side walls 5 and 7. Individual air movers 
13 and 15 located in the overhead structure 11 of the enclosure 1, above 
the air plenum 11a, communicate with the air plenum. The air movers in 
this application pull air from the air plenum 11a and exhaust it through 
the back of the enclosure 1. 
When the air pressure is reduced in the air plenum 11a, air is drawn into 
the air duct system through the slotted entrance air passages 3 in each of 
the device modules, 1A-4A, 1B-4B, passes therefrom via exhaust air 
passages 19 in the device modules through metered air passages 5d-5g, 
7d-7g and 9d-9g into the air ducts 5c, 7c and 9c in the side walls 5, 7 
and common wall 9 and into the air plenum 11a in the overhead structure 11 
and is exhausted to the atmosphere via the air movers 13 and 15. 
The device modules 1A-4A, 1B-4B, are of a width which spans the enclosure 
bays A and B between the side walls 5 and 7, respectively, to the central 
or common wall 9. 
While a two bay enclosure is shown, the invention may be practiced 
employing one or more bays. 
With one bay there being no central or common wall 9, the device modules 
span the distance between the side walls. 
With three bays the device modules in the central bay span the distance 
between the two common walls. 
FIGS. 2 and 3 depict this invention in greater detail. FIG. 2, which is 
fragmentarily in section, illustrates the device module 4A in cross 
section and illustrates the device module 4B in front elevation. Other 
device modules are not illustrated at this point, since they are not 
needed in describing this aspect of the invention. 
As seen in FIG. 2, the enclosure 1 comprises the pair of laterally spaced 
side walls 5 and 7, having inner wall surfaces 5a and 7a and an open end 
1a spanning the side walls 5 and 7. Laterally spaced wall sections 5a and 
5b, 7a and 7b, of the side walls 5 and 7 define therebetween air ducts 5c 
and 7c, respectively. The spaced wall sections 9a of the common wall 9 
define an air duct 9c therebetween. The air ducts 5c, 7c and 9c, at their 
upper ends, open into an air plenum 11a that spans the enclosure 1. The 
plenum 11a is defined between the bays A and B and an upper enclosure 
structure 11b which spans the side walls 5 and 7 and provides slots 11c 
and 11d which mount air mover modules 13 and 15. The air mover modules 13 
and 15 are of the same width as the device modules, 1A-4A, 1B-4B, and 
slide on tracks 11e, or other structural support, in the bases of the 
slots 11c, 11d. Each air mover module, 13, 15, comprises a centrifugal 
fan, 13a, 15a, each of which communicates with the air plenum 11a via an 
opening 13b, 15b. The centrifugal fans 13a, 15a draw air from the air 
plenum and exhaust the air through an exhaust air duct, 13c, 15c, (only 
the duct 150 is visible in FIG. 3) which opens through the back of the 
enclosure 1. An air pressure opened, gravity biased closed, flapper valve, 
13d, 15d, in the respective exhaust air ducts obviates reverse air flow 
into the air duct system in the event of failure of an air mover module 13 
or 15. 
The device modules 4A and 4B, as seen in FIG. 2 are rectangular in lateral 
cross section and are slidably fitted between the sidewalls 5 and 7 and 
the common walls 9 on tracks 21 which extend between the front and back 
ends of the enclosure 1. The tracks 21 position the modules, one above the 
other. The inner wall sections 5a and 7a of the sidewalls 5 and 7 and the 
opposite walls sections 9a of the common wall, are provided with metered 
air passages between the tracks 21. The metered air passages for the side 
wall 5 are, 5d, 5e, 5f and 5g. The metered air passages for the side wall 
7 are, 7d, 7e, 7f, and 7g. The corresponding metered air passages for the 
common wall 9 in the opposite wall sections 9a being identical, are 
identically identified, 9d, 9e, 9f and 9g. 
The metered air passages in FIGS. 2 and 3 are shown as comprising 
horizontal slots. The correspondingly numbered metered air passages in the 
best mode configuration of FIG. 4 each comprises 2 rows of slots both of 
which are vertically disposed. Either orientation is satisfactory. 
The air passages in FIGS. 2, 3 and 4 decrease in area from the bottom to 
the top of the enclosure, as seen in FIG. 2. This is accomplished by 
reducing the number of slots from device module space to device module 
space, proceeding in the upward direction. In these figures, the reduction 
is one slot per upward step to compensate the variation in air pressure as 
a function of the distance from the air pressure source. The reduction in 
the area of the metered air passage by one slot, stepping upwardly in the 
air duct, represents but one way of many ways of reducing metered air 
passage area. 
As seen in the device module 4B in FIG. 2, the slots in the end face of the 
device module 4B define the entrance air passage 3. The entrance air 
passage 3 admits air to the air ducts in the enclosure 1. The module 4A, 
being illustrated in section, reveals a device 17 therewithin. Such device 
may be a disk drive, for example, in a redundant array of inexpensive 
devices (RAID), or other device to be cooled. The modules, as represented 
by the device module 4A, define an air duct about the device 17. When 
inserted in the enclosure 1, the device modules 1A-4A, 1B-4B, become part 
of the air duct system within the enclosure 1. 
As seen in FIGS. 3 and 4, the modules are of rectangular configuration and 
are of a length which spans the enclosure 1 from the open end 1a at the 
front of the enclosure to a position at the back wall. An exhaust passage 
19 is formed in each of the opposite sides of the device modules at the 
back end of the device module. Being at the back end of the device module, 
the air entering the device module at the entrance air passage 3 travels 
the full length of the device module before exiting at the exhaust 
passages 19. The exhaust passages 19, as will be described in greater 
detail, are aligned with the metered air passages 5d-5g, 7d-7g and 9d-9g 
which communicate with the respective air ducts 5c, 7c and 9c. 
The exhaust passages 19 in each module are identical and are of an area 
which is at least equal to or greater than the area of the largest air 
duct passage in the air duct system. Air ducts 5c and 7c are defined 
within the side walls 5 and 7 of the enclosure 1. Air duct 9c is defined 
between the wall sections 9a of the common wall 9. 
The size or area of the metered air passages, as seen in FIGS. 2 and 3, is 
arbitrary, and is not intended to represent an actual or scaled size, but, 
rather to show the location of the metered air passages in the wall 
sections, 5a, 7a and 9a and to illustrate the progressively diminishing 
size of the metered air passages from the bottom metered air passage, 5d, 
7d and 9d, to the top metered air passage, 5g, 7g and 9g, in each air 
duct. Thus the bottom metered air passage, 5d, 7d and 9d, while not 
completely detailed in FIG. 2 and not seen in FIG. 3, lacking drawing 
space, in the progression of slots comprising these metered air passages, 
each comprise four slots, the metered air passages diminishing by one slot 
from the bottom to the top of the respective air ducts in the metered air 
passage progression. 
The air flow through the enclosure 1 is seen in FIGS. 2 and 3. When the 
centrifugal fans 13a, 15a in the air mover modules 13 and 15 are running, 
air is exhausted from the enclosure duct system through the exhaust ducts, 
13c, 15c, which open through the back wall of the enclosure 1. Air is now 
drawn into the enclosure duct system through the entrance air passages 3 
at the front ends of the modules, 1A-4A, 1B-4B, passing through the 
modules and transitioning through the module exhaust air passages 19 and 
aligned meter air passages, 5d-5g, 7d-7g and 9d-9g, into the air ducts, 
5c, 7c and 9c, and thence into the air plenum 11a. From the air plenum 11a 
the air is exhausted to the atmosphere via the centrifugal fans 13 and 15. 
By selecting the largest area of a metered air passage of all of the 
metered air passages, 5d-5g, 7d-7g and 9d-9g, so that the resistance to 
the air flow thereat is greater than the resistance to the air flow of any 
one of all of the device modules, each metered air passage predominately 
characterizes the air flow thereat into an air duct 5c, 7c or 9c whether 
or not a device module is present at that location, resulting in minimal 
air flow disturbance in the enclosure duct system regardless of the number 
of modules in the enclosure. 
By progressively scaling the area of the metered air passages as a function 
of the distance of the metered air passage from the air pressure source, 
the individual volumes of air flow per unit of time at the differing 
metered air passages are substantially equal. 
The cutaway isometric view of the best mode for practicing this invention, 
seen in FIG. 4, differs primarily in the detail of execution from the 
schematic depiction of the invention of FIGS. 2 and 3 by having vertical 
instead of horizontal slots. One such detail is seen in the slots which 
comprise the metered air passages into the air ducts 5c, 7c and 9c and the 
slots which comprise the exhaust air passages 19 of the device modules. 
Either the horizontal or vertical orientation of the slots is 
satisfactory. Each metered air passage comprises two rows of slots. The 
bottom metered air passage 5d, 7d and 9d, in each wall, comprises two 
rows of four slots. This is seen fragmentarily at 7d in the side wall 7. 
Proceeding upwardly to the next device module row, the metered air 
passages 5e, 7e and 9e, 5e being seen in the side wall 5, comprise seven 
slots. Proceeding upwardly to the next device module row the metered air 
passages 5f, 7f and 9f each comprise six slots, as seen in the metered air 
passage 9f in the common wall 9. This scaling of the metered air passages 
continues through the upper metered air passages to the upper most row 5g, 
7g and 9g where the slot count is five. 
Each device module is provided with exhaust air passages comprising two 
rows of four slots each. This is partially seen at 19 on the bottom device 
module 1B. The metered air passages of the air ducts 5c, 7c and 9c and the 
exhaust air passages 19 of the modules 1A-4A and 1B-4B are depicted 
approximately to scale. The device modules each slide on tracks or rails 
21 mounted to the respective side walls 5, 7 and 9. These rails are 
vertically spaced and precisely position the modules in the enclosure 1. 
The modules extend from the open front end of the enclosure 1 to the back 
of the enclosure. 
The front to back location of each of the modules is controlled by a 
pivoted latch mechanism 23 having a latch end 23a which engages a catch 
23b on the front end of each track 21, to latch the module in a precise 
longitudinal position. A latch handle 23c locks the pivoted latch in latch 
position. The details of this latch mechanism are not illustrated since 
they do not comprise a part of the invention which is claimed herein.