US20090004961A1

US20090004961A1 - Cooling the air exiting a computer

Info

Publication number: US20090004961A1
Application number: US11/772,205
Authority: US
Inventors: Rajiv Mongia
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-06-30
Filing date: 2007-06-30
Publication date: 2009-01-01

Abstract

Methods and arrangements for cooling the air exiting a computer are discussed. Embodiments include a method and apparatus to cool the air exiting a computer. The embodiments may also include blowing air out of an exhaust fan past one or more dilution air vents in the chassis of a computer. The embodiments may include pulling in air outside the chassis through the one or more dilution air vents, mixing the air pulled in from outside the chassis and the air blown through the exhaust fan, and blowing the mixed air through an exit vent. Other embodiments are described and claimed.

Description

FIELD

The present invention is in the field of computer cooling systems and, more particularly, systems for cooling exhaust air.

BACKGROUND

Constraints on the temperature of the air exiting a notebook or other computer may limit the amount of power available for use on the notebook or other computer. The notebook's use of power in components such as the processor, power supply, hard drive, wireless card and the like, may generate heat. A fan may dissipate the heat by blowing air past the components of the notebook and eventually out of the case of the notebook. The components may include a heat exchanger, which absorbs heat from other components. The exhaust air cannot be too hot. Otherwise, it may feel uncomfortable to a user. In addition, a user may believe that the notebook is not performing correctly, and may contact technical support or seek a refund.
The dissipation of heat may be limited by the form factor of the notebook. A notebook may produce a large amount of heat in a small volume of space, and its components may be crowded together. The dissipation of heat may also be limited by the fan performance that can be achieved within an acoustic constraint. While a more powerful fan may produce a greater volume of air flow, and therefore a cooler exhaust air temperature, it may produce more noise. Therefore, there is often a maximum fan flow rate that is achievable for a given form factor notebook. In consequence, to achieve an exhaust air temperature acceptable to a user, it may be necessary to limit the power usage of the notebook.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which like references may indicate similar elements:

FIG. 1 is a diagram of an embodiment of a cooling system for a notebook;

FIG. 2 is a flow diagram of an embodiment of air used to cool a computer;

FIG. 3 is a chart of an embodiment of the effect of the shape of a nozzle on air flow rate and pressure; and

FIG. 4 is a flowchart of an embodiment of a method to cool the air exiting a computer.

DETAILED DESCRIPTION OF EMBODIMENTS

The following is a detailed description of embodiments of the invention depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
Generally speaking, methods and arrangements for cooling the air exiting a notebook or other computer are contemplated. Embodiments include a method and apparatus to cool the air exiting a notebook or other computer. The embodiments may also include blowing air out of an exhaust fan past one or more dilution air ducts in the chassis of a computer. The embodiments may include pulling in air from outside the chassis through the one or more dilution air ducts, mixing the air pulled in from outside the chassis and the air blown through the exhaust fan, and blowing the mixed air through an exit duct.
In further embodiments, there may be a pair of dilution air ducts on opposite sides of the chassis, such as the top and bottom. In many embodiments, a dilution air duct may consist of one to five slits. In several embodiments, the slits may be approximately 1 mm to 3 mm wide. In some embodiments, the slits may be approximately 20 mm to 80 mm long. In several embodiments, the mixed air may travel a distance of 5 mm to 15 mm to the exit duct.
In a few embodiments, the air may blow through at least one nozzle located between the fan and the dilution air ducts. Traveling through the nozzle may increase the velocity of the air, and may therefore increase the amount of outside air pulled in through the dilution air ducts. While specific embodiments will be described below with reference to particular configurations, those of skill in the art will realize that embodiments of the present invention may advantageously be implemented with other substantially equivalent configurations.
FIG. 1 is a diagram of an embodiment of a cooling system for a notebook 100. The notebook 100 includes case 105, fan case 110, dilution air duct 120, dilution air vent 125 and exhaust vent 130. Fan case 110 includes fan 115. Fan 115 may draw air past the components of notebook 100 (not shown), in order to cool them. The components may include a heat exchanger. Heat may flow by conduction from other hot components to the heat exchanger, thereby cooling the other components. Arrow 135 shows the direction of flow of exhaust air from the fan. The air may blow past the components of notebook 100, and through dilution air duct 120, passing over dilution air vent 125, and through exhaust vent 130, thereby exiting the computer.
Air is the mixture of gases making up the Earth's atmosphere. Air contains roughly 78% nitrogen, 21% oxygen, 1% argon, 0.04% carbon dioxide, trace amounts of other gases, and a variable amount of water vapor which averages around 1%. The air inside and around a computer may be cooler than some of the components of the computer, and may cool the components by contact with them.
The ability of fan 115 to cool notebook 100 may be limited by human factors. The air exiting a computer cannot be too hot, or it will feel uncomfortable to a user. The power of a fan may be limited by the amount of noise it may produce. In addition, many notebooks may be densely packed with components, generating large amounts of heat and making cooling difficult.
Dilution air vent 125 is an opening in the case of notebook 100 through which outside air may be drawn. Dilution air vent 125 may consist of a series of slits. In some embodiments, the slits may be approximately 1 mm to 3 mm wide, and approximately 20 mm to 60 mm long. In many embodiments, a dilution air vent 125 may consist of 1 to 5 slits. The slits may be perpendicular to the direction of the exhaust air 135 from the fan 115.
The exhaust air 135 passing through the dilution air duct 120 may draw air from outside case 105 into the notebook through dilution air vent 125. This drawing of air may be caused by a difference in the static pressure of the flowing exhaust air 135 relative to the stationary outside air. It follows from Bernoulli's equation that flowing air has lower static pressure than stationary air. Therefore, by locating dilution air vents 125 in the dilution air duct 120 in the path of the exhaust air 135, cold ambient air can be drawn into the exhaust stream 135. Arrow 140 shows the direction of flow of this entrained air 140 which is drawn through dilution air vent 125. Arrow 145 shows the direction of flow of entrained air which may be drawn through a dilution air duct on the top of the computer case 105 (not pictured). The region of computer 100 into which entrained air is drawn is the dilution section of computer 100.
The entrained air 140 and 145 and exhaust air 135 may mix as they travel to the end of the case 105 and exit computer 100 through exhaust vent 130. The mixing occurs in the dilution air duct 120 between dilution air vent 125 and the exhaust vent 130. In some embodiments, this mixing section may be approximately 5 to 15 mm long. Because space may be at a premium in a notebook, a longer mixing section may be uneconomical. As a result of the mixing of the cooler outside air with the heated exhaust air 135 which has been used to cool components of the computer 100, the temperature of the air exiting the computer 100 is lowered.
A test rig may be constructed to experiment with the shape of dilution air vents such as dilution air vents 125. The test rig may include movable baffles to restrict internal flow, movable baffles to control external air intake, and an exhaust thermocouple bank to measure the temperature of exit air. The test rig can be operated at various settings for internal flow and external air intake, and the temperature of the exit air determined. In one set of experiments, the simulation of dilution air ducts with the movable baffles produced a reduction on the order of 5° C. in temperature. Equivalently, the use of dilution air ducts may enable the use of an additional 10 W or so of platform power within a thin system, or approximately 15% higher power, with no increase in the temperature of the exhaust air. This greater power is achieved with no additional noise or significant bill of materials cost. The only requirement for the more efficient cooling of exhaust air may be approximately 5 to 15 mm of space downstream of the heat exchanger in order to add the dilution air vent 125.
The cooling system of FIG. 1 is for explanation, not for limitation. Systems useful for cooling exhaust air according to various embodiments of the present invention may include additional components or may omit some of the components shown. In some embodiments, a cooling system for a notebook or other computer may contain multiple dilution air vents, rather than the single dilution air vent shown in FIG. 1. In further embodiments, the cooling system may contain a pair of dilution air vents on opposite sides of the case, such as on the top or bottom. In many embodiments, a dilution air duct may be omitted. In order to enhance mixing of exhaust air 135 and the entrained air 140 and 145 there may be included mixing structures within the dilution duct 120. These mixing structures may be passive, assisting in the mixing; or active, helping to perform mixing.
In some embodiments, the exhaust air from a fan may flow through a nozzle downstream of the fan upstream of a dilution air vent. The flow through the nozzle may to generate a jet pump. The nozzle may constrict the flow of air through it, causing the air exiting the nozzle to travel at a higher velocity than the air entering the nozzle. The increased velocity may cause the air leaving the nozzle draw in more outside air as it passes the dilution air vents. As a result, more dilution air may mix with the exhaust air from the fan, and the temperature of the air exiting the notebook or other computer may be cooler.
In some embodiments, the ambient substance may be a liquid or gas other than air. For instance, a computer may operate in a rocket, on another planet, or in a special environment. In all of this other environments, a fan may push the ambient substance, and draw in more of the substance from outside the computer as one of ordinary skill would appreciate based upon the teachings described herein.
Turning to FIG. 2, illustrated is a flow diagram 200 of air used to cool a computer such as a notebook. Flow diagram 200 includes components of a computer through or over which air flows, including a case 210, a fan 220, a heat exchanger 230, and a jet pump 240. The arrows in FIG. 2 (250, 260, 270, 280, and 290) represent air flow.
In flow diagram 200, air 250 may flow from outside the computer into computer case 210. The outside air may be cooler than the inside of the computer, and the computer may exchange heat with outside air 250. Exhaust fan 220 may draw in air 260 from the interior of the computer and force it out. The fan exhaust air 270 may blow past a heat exchanger 230, and may cool the heat exchanger 230. The heat exchanger may absorb heat from other components of the computer, and may thereby cool the other components.
Air passing the heat exchanger 230 (air 280) may then enter jet pump 240. Jet pump 240 may increase the speed of air flowing through it. Jet pump 240 includes nozzle 243. Nozzle 243 constricts the air 280 flowing through it. Nozzle 243 includes inlet 245 and exit 248. The area of the inlet 245 is larger than the area of the exit 248. As a result of the constriction, the velocity of the air 290 exiting the nozzle is larger than the velocity of the air 280 entering the nozzle 243. The air 290 may then flow past dilution air vents such as dilution air vent 250 in FIG. 1. Because of its higher velocity, air 290 may generate greater suction in pulling outside air through the dilution air ducts. As a result, the addition of jet pump 240 may increase the amount of dilution air from outside of a computer that mixes with air blown from a fan.
The flow diagram of FIG. 2 is for explanation and not limitation. In other embodiments of a cooling system, a nozzle of a jet pump may have the narrowest portion in a location other than the exit, or may otherwise be of a design known to those of skill in the art.
The narrowing between inlet 245 and exit 248 in FIG. 2 may be limited to preserve air flow through fan 220. Turning to FIG. 3, shown is a chart 300 depicting the effect of the area ratio of a nozzle on air flow rate and pressure. The horizontal axis represents the narrowing of the nozzle, measured by the ratio of the inlet area to the throat (smallest) area. The ratio varies from approximately 0.4 at the left of the horizontal axis to 1.0 at the right. Thus, points to the right represent a less constricted nozzle than points on the left. The vertical axis represents both pressure in mm of H ₂0 and flow rate in cubic feet per minute (CFM). Solid lines represent pressure and dashed lines represent flow rates. Chart 300 includes lines 310, 330, 350, and 360, which indicate the air flow pressure at various locations of a notebook or other computer. Line 310 indicates fan exit pressure, line 330 indicates the pressure at the heat exchanger, line 350 indicates the pressure at the nozzle exit, and line 360 indicates the pressure at the fan inlet. Chart 300 indicates a diminution of pressure at the fan exit (line 310) and at the heat exchanger exit (line 330) as the nozzle approaches a ratio of 1.0 (no constriction). These lines (310 and 330) gradually slope downward. Chart 300 indicates a slight increase of pressure at the nozzle exit (line 350) and slight decrease of pressure at fan inlet (line 360) as the nozzle becomes unconstricted. These lines (350 and 360) are nearly flat, indicating only a slight change in pressure with a change in the constriction of a nozzle.
Chart 300 also includes lines 320 and 340, which indicate the effect of constriction on air flow rate. Line 320 is the total flow rate through the exit of the computer. This is a measure of the amount of dilution air flowing through a notebook or other computer. The amount of dilution air flow is closely related to the temperature of air exiting a computer. Mixing increased volumes of outside air with fan exhaust air may the lower the temperature of the air exiting the computer. As indicated by line 320, constricting the nozzle increases dilution air flow. At a ratio of 1.0 (no constriction), the total flow rate is approximately 3.5 CFM. At a ratio of about 0.4, the total flow rate rises to almost 5.0 CFM. At a ratio of approximately 0.6, the CFM is approximately 4.0. Constricting the nozzle has, however, the opposite effect on fan flow rate. The fan flow rate is approximately 3.5 CFM with no constriction from the nozzle, and approximately 3.2 CFM at a ratio in the range of 0.4.
In the circumstances depicted by chart 300, a ratio of approximately 0.6 might produce significantly more dilution air while leaving fan flow rate at almost its maximum value. At this ratio, the total flow rate is about 4.0 CFM, a gain on the order of 20% over the approximately 3.5 CFM with no constriction, but the fan flow rate is almost its maximum value of 3.5. Thus, in the circumstances represented by chart 300, a ratio of approximately 0.6 between the inlet area of a nozzle and the throat of a nozzle may produce significant additional amounts of dilution air while not interfering with the air flow produced by the fan. The data depicted in chart 300 may be generated analytically, by simulations or formulas or both, or experimentally.
FIG. 4 depicts a flowchart 400 of an embodiment of a method to cool a computer. The method of flowchart 400 may be carried out by a cooling system for exhaust air such as the cooling system of the computer 100 depicted in FIG. 1. The method includes blowing air out of an exhaust fan (element 410). The method may include blowing air through a nozzle (element 420). The nozzle may constrict the flow of air blown through it, because the throat of the nozzle may be narrower than the inlet. The narrowing may increase the velocity of the air flowing through the nozzle. The shape of the nozzle may be designed to balance increasing the velocity and maintaining the flow of air from the fan. A smaller ratio of throat area to inlet area may produce a greater velocity of the air, but too small a ratio may reduce the flow of air from the fan.
The method of flowchart 400 includes blowing the air past one or more dilution air vents in the chassis of the computer. Under the Bernouilli principle, the air moving past the dilution air ducts is under lower pressure than the stationary air outside the computer. As a result, the air moving past the dilution air vents may pull in air outside the chassis of the computer through the one or more dilution air vents (element 440). This outside air may be cooler than the air blowing out of the exhaust fan, because the exhaust air was used to cool the components of the computer.
The dilution air vents may lie downstream of the nozzle. As a result, the velocity of the air blown past the one or more dilution air vents may be increased by flowing through the nozzle. The increased velocity may lead to drawing in greater volumes of dilution air through the dilution air vents. In some embodiments, a dilution air vent may consist of 1 to 5 slits. In further embodiments, the slits may lie perpendicular to the air flow, may be approximately 1 mm to 3 mm wide, and may be approximately 20 mm to 80 mm long. In many embodiments, there may be a pair of vents on opposite sides of the computer, such as the top and bottom.
The dilution air and the exhaust air leaving the fan may mix (element 450) in the dilution duct. The mixture may be cooler than the air blown out of the exhaust fan. The mixed air may be blown through an exit vent of the computer (element 460), such as in the rear of the computer. In some embodiments, the mixed air may travel a distance of approximately 10 mm before exiting. Because space may be at a premium inside the computer, a longer distance may not be available.
The flowchart of FIG. 4 is for explanation and not limitation. Other embodiments of cooling the air exiting a computer may include additional steps, omit steps shown in FIG. 4, or perform the steps in a different order, as may be known to those of skill in the art.
It will be apparent to those skilled in the art having the benefit of this disclosure that the present invention contemplates methods and arrangements for cooling the air exiting a computer. It is understood that the form of the invention shown and described in the detailed description and the drawings are to be taken merely as examples. It is intended that the following claims be interpreted broadly to embrace all the variations of the example embodiments disclosed.
Although the present invention and some of its advantages have been described in detail for some embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Although an embodiment of the invention may achieve multiple objectives, not every embodiment falling within the scope of the attached claims will achieve every objective. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Claims

1. A method of cooling the air exiting a computer, the method comprising:

blowing air out of an exhaust fan past one or more dilution air vents in the chassis of a computer, the blowing air pulling in dilution air from outside the chassis through the one or more dilution air vents;

mixing the air pulled in from outside the chassis and the air blown through the exhaust fan; and

blowing the mixed air through an exit vent.

2. The method of claim 1, wherein blowing air out of an exhaust fan comprises blowing air through a nozzle.

3. The method of claim 2, further comprising:

determining the area ratio of the nozzle, the determining based upon cooling the mixed air blown through the exit vent and based upon cooling components of the computer.

4. The method of claim 1, wherein blowing air out of an exhaust fan past one or more dilution air vents comprises blowing air out of an exhaust fan past a pair of dilution air vents, the pair of dilution air vents lying on opposite sides of the computer.

5. The method of claim 1, wherein blowing the mixed air through an exit vent comprises blowing the mixed air a distance of 5 mm to 15 mm between the fan exit and the exit vent.

6. The method of claim 1, wherein blowing air out of an exhaust fan past one or more dilution air vents comprises blowing air out of an exhaust fan past a dilution air vent, the dilution air vent comprising one to five slits, the slits approximately 1 mm to 3 mm wide.

7. The method of claim 1, wherein blowing air out of an exhaust fan past one or more dilution air vents comprises blowing air out of an exhaust fan past a dilution air vent, the dilution air vent comprising one or more slits, the slits approximately 20 mm to 80 mm long.

8. An apparatus to cool the air exiting a computer, the apparatus comprising:

a dilution section comprising one or more dilution air vents in the chassis of a computer, the dilution section to pull in air from outside the chassis in response to the blowing of air past the one or more dilution air vents;

an exhaust fan to blow air past the one or more dilution air vents;

a mixing section to mix the air pulled in from outside the chassis and the air blown past the one or more dilution air vents by the exhaust fan; and

an exit vent for the mixed air to exit the computer.

9. The apparatus of claim 8, further comprising a nozzle, the nozzle located between the exhaust fan and the dilution section, the nozzle for air blown through the exhaust fan to blow through the nozzle.

10. The apparatus of claim 8, wherein the dilution section comprises a pair of dilution air vents lying on opposite sides of the computer.

11. The apparatus of claim 8, wherein the dilution section comprises one or more dilution air ducts comprising one to five slits, the slits approximately 1 mm to 3 mm wide.

12. The apparatus of claim 8, wherein the dilution section comprises one or more dilution air vents comprising one or more slits, the slits approximately 20 mm to 80 mm long.

13. The apparatus of claim 8, wherein the mixing section comprises a mixing section from 5 mm to 15 mm in length.

14. The apparatus of claim 8, further comprising a dilution air duct to carry air over the one or more dilution air vents.

15. The apparatus of claim 14, further comprising a mixing structure within the mixing section to perform active or passive mixing, wherein the mixing structure lies within the air duct.