Abstract:
The “venturi fan” comprises a series of “half-venturi” shaped profiles incorporated into the periphery of a cylindrical fan, for use with a cylindrical heat sink. In one embodiment, the half-venturis are open, in another the half-venturis are enclosed so that the outer surface of the fan is smooth so that it is not a hazard to intruding fingers and the like. A leading edge deflector keeps hot compressed air in front of the venturi out of the heat sink fins.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a provisional application of a provisional patent Ser. No. 60/481,179 of the same name, filed Aug. 5, 2003. Priority to that date is claimed. 

   BACKGROUND OF INVENTION 
   U.S. Pat. Nos. 5,297,617 and 5,445,215, both entitled FAN WITH HEAT SINK, and owned by the same entity as this patent application, teach that the area surrounding the fan blade tips in an axial flow fan has high velocity, very turbulent air, and that the periphery of an axial flow fan is an excellent heat sink, particularly if the inside of the fan duct and/or the fan blade are modified as taught therein to enhance the heat sinking. These are modified axial flow fans, and the air flow through them may be partly or completely redirected to fins or other features in the periphery of the fan duct, to remove heat therefrom. These patents are incorporated herein by reference. 
   Other related patent applications are: a provisional patent application entitled FAN WITH HEAT SINK USING STAMPED HEAT SINK FINS, Ser. No. 60/062,171, filed 16 Oct., 1997; a utility patent application of the same name, Ser. No. 09/174,374, filed 15 Oct., 1998 and issued as U.S. Pat. No. 6,125,920 on 3 Oct., 2000; a utility patent application of the same name, Ser. No. 09/678,424 filed 2 Oct., 2000; a utility patent application of the same name, Ser. No. 10/064,071 filed 6 Jun., 2002, a utility patent application entitled FAN WITH HEAT SINK, Ser. No. 10/064,060 filed 5 Jun., 2002, and a patent application Ser. No. 10/710,794 entitled WAVE-FANS AND WAVE-FANS WITH HEAT SINKS filed 3 Aug., 2004. 
   It is well known that a plurality of closely spaced fins makes an excellent heat sink. However, there is a boundary layer that is a very persistent viscous layer of air on the surfaces of the heat sink fins, requiring very high velocity and turbulent air flow to dissipate the boundary layer for heat flow into the air. In prior art heat sinks, this required very large, powerful and noisy fans. 
   In the patent applications referenced above, air is not blown through the fins, as in going in one surface and out another, but rather, air is agitated between the fins on a single surface with no separate exit air path. The air in the vicinity of a plurality of fan blades is very turbulent and has a oscillating component as each of the fan blades passes any point on fins. Air is thus scrubbed in and out of the fins with very high local velocities to break up the boundary layer and transfer heat to the air. These fins can be on an inner surface, with internal fan blades, or on an external surface with external fan blades or both, or on a circular array of buttresses or posts rising from a plate. In the latter, there may be some air flow through the fins as well, but this is incidental. High velocity and turbulent air is needed to break up the boundary layer, but a modest movement of air is sufficient to transport the heat away. The rotation of the fan blades causes enough incidental air motion around the fan with heat sink to accomplish this. Thus a fan of low or moderate power can cause more vigorous local air movement immediately on the heat sink fins if the fan blades are very close than even a very powerful fan that is spaced apart. The fans and heat sinks of these inventions are smaller, lighter, much quieter and consume much less power than prior art fans and heat sinks of the same heat capacity. 
   A wave-fan comprises a wavy surface, generally sinusoidal in the direction of rotation, which rotates in close proximity to the fins of a heat sink. 
   The heat sink fins may comprise a flat coil spring like strip of metal, similar to the familiar “Slinky” toy, placed in or on a cylinder of metal, or it may be like a closely pitched “clock spring” bonded onto a plate. Alternatively, the heat sink fins may comprise a stack of stamped metal rings pressed on or in a cylinder of metal. Alternatively, the heat sink fins may comprise a formed strip of metal that has been wrapped around a metal cylinder or attached to a flat plate. These may rest on the surface or may be pressed into complementary grooves in the surface. 
   SUMMARY OF INVENTION 
   The fans of this invention do not comprise a plurality of blades, or airfoils, as in a conventional fan. The “venturi fan” comprises a series of “half-venturi” shaped profiles incorporated into the periphery of a cylindrical fan, for use with a cylindrical heat sink. In one embodiment, the half-venturis are open, in another the half-venturis are enclosed so that the outer surface of the fan is smooth so that it is not a hazard to intruding fingers and the like. A similar arrangement is adapted for flat fans and flat heat sinks. 
   This arrangement has a number of benefits, among them a compact, low profile design, high efficiency, low noise and less susceptibility to dirt in the air. In some embodiments of the invention, the outer exposed surface is smooth, so they may be used in exposed locations without guards or housings. In the preferred embodiments of the invention, the centrifugal force on the air flowing through the fan is such that any contaminants tend to be thrown away from the heat sink, to greatly reduce the tendency of dust and so forth to clog the heat sink and reduce or eliminate the need for inlet air filters. Because the net air flow through the fan is much lower than in prior art fans, operation is very quiet and they requires less power. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  shows a venturi. 
       FIG. 2  shows a half venturi. 
       FIG. 3  shows a half venturi with a heat sink. 
       FIG. 4  shows a half venturi with a cylindrical heat sink. 
       FIG. 5  shows a venturi fan rotating about a cylindrical heat sink. 
       FIG. 6  shows another view of the venturi fan of  FIG. 5 . 
       FIG. 7  shows a venturi with a center piece. 
       FIG. 8  shows a half venturi with a half center piece. 
       FIG. 9  shows a half venturi with a half center piece and with a heat sink. 
       FIG. 10  shows a half venturi with a half center piece and with a cylindrical heat sink. 
       FIG. 11  shows a venturi fan rotating about a cylindrical heat sink. 
       FIG. 12  shows another view of the venturi fan of  figure 11 . 
       FIG. 13  shows a flat venturi fan rotating above a flat heat sink. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a section of a venturi  1  having a venturi wall  3 . Airflow, shown by arrows, may pass through the venturi. If it does, the well known Bernoulli effect teaches that the airflow must accelerate in narrow section of the venturi  1 , resulting in a pressure drop. Boyle&#39;s law teaches that if the pressure drops, the temperature drops, and this is known to apply to venturis, as they feel cold and icing is a common problem in carburetors (particularly in aircraft engines). 
   The venturi is often round, but the same principles apply if it has a rectangular profile, and that is the configuration used in the venturi fans, as further explained and illustrated below. 
     FIG. 2  shows that a venturi  11  having a venturi wall  13  can be divided along its axis of symmetry, the axis of symmetry being replaced by a dividing wall  15 . For half the airflow, all characteristics are otherwise the same. 
     FIG. 3  shows a half-venturi  21  having a venturi wall  23 . With reference to  FIG. 2 , the dividing wall  15  is replaced by a leading section  25  and a trailing section  19 . In between a heat sink  27  has been introduced into the airflow. The left end of the heat sink  27  is closed, else it would suck in air due to the reduced pressure in the venturi. 
   Assuming the airflow is propelled by an external air pump source, not shown, at the inlet side of the venturi, the venturi represents a restriction to the airflow, and there is a higher pressure on the inlet side. By Boyle&#39;s law, if air is compressed, it is hotter. However within the throat of the venturi, the air is greatly accelerated, and by Bernoulli&#39;s principle, the pressure will drop. Boyle&#39;s law teaches that air at a reduced pressure is cooler. Therefor the heat sink  27  is placed in the region of accelerated air. As the air expands, the pressure will return to ambient pressure and the temperature will recover. This takes place above and beyond the heat sink  27 . 
   In  FIGS. 4 through 6 , a fan and heat sink  41  comprises a venturi fan  53  rotating around a cylindrical heat sink  49 . The venturi fan  53  comprises a plurality of venturis  43 – 43  having a half venturi profile as its outer periphery. The cylindrical heat sink  49  comprises an active heat dissipating surface comprising a plurality of heat sink fins  47  in good thermal contact with a metal cylinder  51  which, in turn, is in good thermal contact with a base plate  59  that is a cold plate. 
   Whereas in  FIG. 3  the air is moved into the venturi  21 , in the venturi fan  53  a plurality of venturis  43 – 43  are moved into the air as the fan  53  rotates as indicated by the arrow. As the fan  53  rotates, air is moved into the venturis  43 – 43 , but as they are restrictions, there is a pressure increase ahead of the venturis  43 – 43 . By Boyle&#39;s law, the temperature will increase, and it is desirable to keep the heated air out of the heat sink  49  to the extent possible. Accordingly, deflector pieces  45 — 45  block the air from the heat sink  49  ahead of each of the venturis  43 — 43 . 
   As the air continues into the venturis  43 — 43 , it is accelerated. Undisturbed (in the absence of the rotating venturis  43 — 43 , the air within the heat sink  49  is static. However, as the fan  53  rotates counterclockwise as shown, the air will accelerate to have a clockwise movement under the venturis  43 — 43 . This air is moving rapidly, with a reduced pressure and temperature, ideal conditions for removing heat from the heat sink  49 . Not only does the air have a high velocity to scrub away the boundary layer, it also has a reduced temperature. As the venturis  43 — 43  move on, the air will decelerate, the pressure will recover and the temperature will rise. However, this will happen mostly in the space outside the heat sink  49 . 
   As the plurality of venturis  43 — 43  move through the air around the heat sink  49 , the air in the central portion of the venturi is forced into the space between the fins of the heat sink  49 . Due to the decreased cross sectional area, the air is accelerated within the central portion of the venturi and the heat sink  49  is exposed to this air in this central portion of the venturi for improved heat removal from the heat sink  49 . In  FIG. 4 , it may appear that this region has an increased area as compared to the throat of the venturi, but the fins of the heat sink  49  occupy a significant volume so the space remaining for air continues to be restricted within the heat sink  49 . The air can expand decelerate and the pressure can recover only in the space behind the venturis. 
   In  FIG. 6 , it can be seen that the space between the venturis  43 — 43  is open. Due in part to the centrifugal forces due to the rotation of the fan  53  and in part to the agitation of the air by the venturis  43 — 43 , the air is well mixed with ambient air and the exhaust heat is well dissipated. 
     FIG. 7  shows a venturi  101  having a venturi wall  103  and a center piece  105 . Center pieces are fairly common in venturis, often as the location point for a pressure sensor or for introducing a fluid into the air stream. It also serves to further restrict the air flow and thus further accelerate the airflow within the venturi. 
     FIG. 8  shows a half venturi  111  having a venturi wall  113  and a dividing wall  119  as well as half a center piece  115 . 
     FIG. 9  shows the introduction of a heat sink  127  into a half venturi  121  having a venturi wall  113  and a partial dividing wall  129 . The half of a center piece  115  of  FIG. 8  carries forward as a leading edge air foil  125 . The part of the heat sink  127  that is outside of the venturi  121  on the leading edge is sealed to prevent ambient air from being sucked in. Operation is similar to that of the venturi  21  of  FIG. 3 . 
     FIGS. 10 through 12  show a fan and heat sink  141  comprising a venturi fan  153  rotating around a cylindrical heat sink  149 . The heat sink  149  comprises a plurality of heat sink fins  147  in good thermal contact with a metal cylinder  151  which, in turn, is in good thermal contact with a base plate  159  that is a cold plate. 
   The principle of operation of the fan and heat sink  141  is similar to the operation of the fan and heat sink  41  of  FIGS. 4 through 6  with the following differences. The leading edge deflectors  145 — 145  are airfoils, and the periphery of the fan  153  is a smooth closed surface except for plurality of vents  157 — 157 . The deflector plates  145 — 145  have a thicker section, for more strength, and the thicker sections are shaped as airfoils to reduce drag. They still serve the function of deflecting the compressed air ahead of the venturis  143 — 143  from the heat sink  149 . 
   Because the periphery of the fan  153  is closed, air is admitted into the fan  153  through a plurality of vents  137 – 157 . The air will flow generally radially due to centrifugal force, and generally flow to the bottom of the fan and exit between the venturis  143 — 143 , carrying away the heated air in the process. This air path and the centrifugal force of the rotating fan  153  will prevent any debris or contamination in the air from getting into the heat sink  149 . 
   Because the outer surface of the fan  153  is smooth, it is not a hazard to intruding fingers and the like, so the fan and heat sink  141  may be operated without guards or enclosures. 
     FIG. 13  shows a flat venturi fan with heat sink  171  comprising a flat venturi fan  173  and a flat heat sink  179 . The venturi fan  173  and the heat sink  179  are not “flat” in the sense that a sheet of paper is flat, but rather the term “generally flat” is used to express that the lowest points of the flat venturi fan  173  lie in a plane, and the highest points of the flat heat sink  179  also lie in a plane, and the planes are closely proximate. 
   The venturi fan  173  may be rotated by a motor shaft  181  that in turn is rotated by a motor means (hidden). Usually the motor means is located in the center of the heat sink  179 , but it could be separate, acting through a shaft and gears, pulleys couplings and so forth. In  FIG. 13 , the motor means may be powered by electrical wires  183  and  183 . The heat sink  177  may further comprise a base plate  189  that may be a cold plate. 
   On the lower surface of the venturi fan  173 , in a radial pattern entirely around the venturi fan  173  there are a plurality of half venturis  177 — 177 , each of which further comprises a deflector plate  175 — 175 . Operation is just as described above.