Abstract:
The present invention provides for repeatedly pulsing coolant through a first channel exposed to heat-generating computer components. The pulsing involves a relatively low baseline coolant flow rate with repeated excursions to a relatively high expulsion coolant flow rate.

Description:
BACKGROUND OF THE INVENTION 
     Computer components, especially microprocessors, can generate considerable heat that must be removed from the computer, least it cause damage to computer components, burn or at least cause discomfort to users, or ignite a fire. Most computers rely on some form of coolant fluid, typically air, to remove heat. Most often, the coolant, is air forced by fans through a computer system. The fans, for the most part, provide a consistent flow of coolant. In some systems, the coolant flow rate can be regulated as a function of the temperature, either internal temperature, or a combination of internal and external temperature. Some systems turn the fans off when the internal temperature is low and speed up a fan as temperature increases. 
     As widely used as fans are, they are not always sufficiently effective at removing heat. Some systems supplement or replace airflow with liquid heat exchange, but this can be an expensive solution. What is needed is a more-effect yet economical approach to heat removal. 
     Herein, related art is described to facilitate understanding of the invention. Related art labeled “prior art” is admitted prior art; related art not labeled “prior art” is not admitted prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures depict implementations/embodiments of the invention and not the invention itself. 
         FIG. 1  is a combination of a schematic representation of a blade server system and a flow chart of a heat removal method used with the system in accordance with an embodiment of the invention. Note that in the figures, the fans are drawn orthogonal to their actual orientation. 
         FIG. 2  is a schematic illustration of a single-computer system in accordance with another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the course of the present invention, it was recognized that the laminar flow produced by cooling fans can leave dead spots and limit heat absorption. The present invention provides for pulsed coolant flow along a channel through a computer system. In other words, the coolant flow speed alternates between relatively low (or no) speed and relatively high speed. The relatively “calm” sub-periods facilitate heat absorption by the air, while the relatively “windy” sub-periods help reduce dead spots. In the latter case, the high speed, more turbulent, coolant flow can entrain heated fluid that would (in a laminar flow system) be less likely to be exhausted. 
       FIG. 1  depicts a blade-server computer system AP 1  in which four blades  11 ,  12 ,  13 , and  14  are inserted into a chassis  15 . Whereas a standard rack-mount server can exist with (at least) a power cord and network cable, blade servers have many components removed for space, power and other considerations while still having all the functional components to be considered a computer. A blade enclosure provides services such as power, cooling, networking, various interconnects and management—though different blade providers have differing principles around what should and should not be included in the blade itself (and sometimes in the enclosure altogether). The present invention provides embodiments for all these variations and for any number of blades, as well as other forms of modular and non-modular computer systems. 
     Blades  11 - 14  include processors  16 , media  17  (e.g., solid-state and disk-based memory), and communications devices  18  (e.g., I/O devices, network interface cards), all of which generate heat. Power for the blades is provided via chassis  15 . Six fans  20 , installed in chassis  15 , provide for drawing coolant into and exhausting coolant out of blades  11 - 14 . Of course, other numbers of types of fans can be used. Tubes  21 - 24 , couple respective blades  11 - 14  to a common plenum  27  located adjacent fans  20 . Each combination of tube and blade defines a coolant flow channel  31 - 34  in which flowing coolant can contact computer components  16 - 18  to remove heat therefrom. 
     Each tube includes a barn-door valve  35 - 38  that can be switched from an open position, which minimally restricts coolant flow through the respective channel  31 - 34 , and a closed position, which maximally restricts coolant flow through the respective channel. A coolant flow controller  39  controls valves  35 - 38  so that they open and close in an alternating staggered pattern, as shown in the timing diagram at the right in  FIG. 1 . Coolant flow controller  39  can be responsive to internal (to the blades) temperature via thermometers  19  and an ambient temperature via ambient thermometer  41 . At cooler temperatures, fans  20  can be shut off and valves  35 - 38  left open. At moderate temperatures, a constant coolant flow can be provided with valves  35 - 38  open. 
     At higher temperatures, the staggered pattern can be used with fans  20  at a relatively high speed. Each channel  31 - 34  is then subjected to short sub-periods  43  of turbulent windy conditions separated by longer sub-periods  45  of relatively calm laminar flow. During the calm sub-periods  45 , there is sufficient opportunity for heat to be absorbed by the coolant; during the windy sub-periods  43 , the coolant is whisked away, entraining coolant that was contained in relatively stagnant pockets during the respective preceding calm sub-periods  45 . 
     In general, the windy sub-periods  43  should be shorter than the calm sub-periods, with the ratio being 2:3 or more extreme. In  FIG. 1 , the ratio is 1:4 so that one valve is closed at all times, but the total coolant flow through channels  31 - 34  is essentially constant. The amount the total coolant flow varies in volume per unit time is less than the amount the coolant flow varies in each of the channels  31 - 34 . Thus, coolant flow controller  39  can achieve the pulsed flow without changing fan speeds. 
     Coolant-flow controller  39  can close barn-door valves  35 - 38  entirely for maximum turbulence or leave them slightly open so that at least a minimal coolant flow exists at all times as long as fans  20  are running. Instead of using valves  35 - 38 , coolant-flow controller  39  can control the speed of fans  20  to pulse all four channels synchronously. Varying fan speed to control coolant flow has the advantage that it works with single as well as multiple channels. Coolant-flow controller  39  can pulse the fan speed and valve positions in various ways and even alternate degrees and types of control so that different turbulence patterns are generated. Thus, if one type of control leaves certain stagnant areas in place, another type of control might be able to entrain the previously stagnant air. 
     A method ME 1  of the invention is flow charted in the lower portion of  FIG. 1 . At method segment MS 1 , coolant flow is pulsed to create cycles with calm and windy sub-periods  45  and  43 . Typically, the windy sub-periods  43  are on a duty cycle of 40% or less. If there are multiple channels, the windy sub-periods can be the reciprocal of the number of channels. During the relatively long calm sub-periods  45 , the relatively slow moving coolant absorbs heat from exposed computer components in the respective channel at method segment MS 2 . During the relatively short windy sub-periods  43 , heat is expelled with the coolant that absorbed it. 
     The invention provides alternative means for producing pulsed coolant flow. Of course, controlled pumping into the channel intake can be used instead of pulling at the exhaust. Coolant flow can be diverted from a single channel and dumped before entering the channel during calm periods. Another approach is to change the cross section or volume of a channel while maintaining a constant volume per time coolant flow. 
     In  FIG. 2 , a computer system AP 2  has many components that correspond to parts of computer system AP 1 , so like components are given the same numbers. System AP 2  eschews the valves of system AP 1  for opposing baffles  60 , which operate in the manner of an audio subwoofer. Each baffle includes a frame  61 , a coil  63 , and a baffle membrane  65 . Airflow controller  67  drives these baffles  60  sinusoidally to vary the pressure in plenum  27 . This causes baffle membranes  65  to move in toward each other than out away from each other; this in turn alters the effective volume of plenum  27  periodically, which in turn causes the air pressure in plenum  27  to vary periodically. 
     When the fan speed is constant, the amount of coolant in volume per time stays constant, so the speed at which coolant flows changes with the channel volume. Airflow controller  67  controls this volume to alternate calm and turbulent sub-cycles within server blades  11 - 14 . This has the effect of allowing heat to be absorbed during calm sub-periods and causing stagnant heated coolant to be entrained for exhaust during turbulent sub-periods. Baffles  60  are driven synchronously so that their motions oppose, minimizing net motions to computer system AP 2 . 
     The pulse period or signal frequency can vary according to the topology of the computer system, heat characteristics of components, and ambient conditions. In general, enough calm time should be allotted to permit heat to be absorbed, but not so long that heat builds up unacceptably. Enough time should be allotted to the windy sub-period to allow a full exchange of air or other coolant, but not so much longer so as to not waste opportunity to absorb heat. The higher the baseline flow (e.g., the flow rate during a calm sub-period), the longer the calm sub-period can be without heat buildup. In general, the frequency can be anywhere from 0.01 Hz to 100 Hz. A variety of shapes can be used as can be gleaned from a comparison of  FIGS. 1 and 2 . Noise from a sinusoidal waveform is easy to filter for purposes of minimizing radio frequency noise. 
     While the coolant can be air, especially for systems in which the coolant gas is not contained, other fluids can be used, including other gases, liquids, and fluids that change phase as heat is absorbed in the computer system. Heated exhaust air can be dumped to the ambient air surrounding computer system AP 1 . However, this can heat the ambient air and reduce its ability to cool. The ambient air can be cooled, e.g., using air conditioning or heat exchange so that it retains its cooling effectiveness. Alternatively, air or other coolant gas can be contained in a closed system with heat removed using a heat exchanger external to computer AP 2 . 
     In some multi-channel embodiments, such as the embodiment of  FIG. 1 , the coolant flow through individual channels can vary considerably even though the total coolant flow through the channels collectively remains essentially constant. Of course, some variation in the total flow can still occur. For the most part, however, the amount of variation in the total volume-rate flow can be less than the amount of variation in the volume-rate flows for the individual channels. 
     The calm period can involve positive coolant flow (in the same direction as the exhaust), negative coolant flow (e.g., intake and exhaust through same port, as in breathing) or zero coolant flow. Zero coolant flow can be achieved by closing intake and/or exhaust openings. Negative coolant flow can be achieved by reversing fan direction, either by changing the direction the fan blades rotate (e.g., clockwise versus counterclockwise) or by rotating the fans 180° so they face in the opposite direction. The invention can apply to various types of blade systems, other types of modular computer systems including rack-mount systems, self-standing computers, etc. These and other modifications to and variations upon the illustrated embodiments are provided for by the present invention, the scope of which is defined by the following claims.