Cooling electronics via two-phase tangential jet impingement in a semi-toroidal channel

Abstract

A two-fluid-phase cooling device for absorbing high thermal flux from electronics devices and other thermally dissipating devices. It consists of a thermally conductive plate with thermally dissipating elements on one face and a semi-toroidal cavity in the opposite face with the cavity's axis perpendicular to the face of the plate, a liquid refrigerant supply tube ending in a thermodynamic cycle's refrigeration expansion valve that directs jets of liquid to impact the conical surface in the center region of the semi-toroidal cavity in a direction along the cavity's axis and tangent to the conical surface, a second plate with a semi-toroidal protrusion extending into the semi-toroidal cavity to form a thin, semi-toroidal channel between the two plates, and a seal between the liquid supply tube and the second semi-toroidal plate. In operation liquid refrigerant jets strike the conical surface generally tangential to the surface and flow at high velocity in a thin film on the surface of the semi-toroidal cavity from its center radially to the outer edge of the toroidal channel, absorbing heat and boiling as it does so. The high radial acceleration forces caused by the liquid film moving at high velocity on the cavity's concave surface force the liquid film against the surface and create a pressure gradient that biases evaporation toward the liquid/vapor interface. The vapor moves parallel to the liquid flow radially outwards between the liquid film and the surface of the semi-toroidal protrusion at very high velocity, causing extreme turbulence in the liquid film and highly augmented heat transfer between the heated plate and the liquid film, while the liquid film nevertheless remains intact and forced against the heated surface by radial acceleration and carried to a distance significantly greater than in conventional jet impingement systems. The device may also be composed of wedge-shaped sections of the semi-toroidal plates. It may further have two expansion valves in series in the liquid supply line, the first generating a small amount of vapor (increase in quality) so the resulting increase in flow volume greatly increases the velocity through the second expansion valve toward the heated surface to further enhance heat transfer.

1 . A cooling device comprising: a thermally conductive solid such as a plate with thermally dissipating elements attached to one face and a semi-toroidal cavity in the opposite face, the cavity formed by cutting in the material face, and about an axis perpendicular to the face, a groove of generally semi-circular shape of radius r 1 , with the center of radius r 1  at a radius C from the axis of the circle to the center of the groove, so that setting the radius r 1  equal to radius C causes the semi-toroidal cavity to form an apex point that lies both on the center line of the cavity and in the plane of the plate in which the cavity is cut, so the surface is, to a distance from its centerline to the radius C, convex in a direction circumferential to the axis of the cavity and concave in a direction radial from the axis of the cavity, and past the radius C is concave both in circumferential direction and radial direction; and a second plate having a semi-toroidal protrusion in the shape of a circular ridge of semi-circular cross-section of radius r 2 <r 1 , with the center of radius r 2  located at radius C from the axis of the circular protrusion, and the protrusion located concentric with and extending into the semi-toroidal cavity so a semi-toroidal channel exists between the cavity wall surface and the protrusion wall surface; and a nozzle on the centerline of the circular protrusion and parallel to its axis, passing through and sealed to the plate containing the protrusion, and containing several orifices that direct streams of a volatile fluid in a direction generally parallel to the axis of the semi-toroidal cavity to strike the upper surface of the cavity immediately below the centerline apex of its surface and in a direction generally tangent to the cavity surface, and flows outward in the semi-toroidal channel and exits the channel in a direction generally opposite that of the fluid streams directed from the nozzle.  
   
   
       2 . The cooling device of  claim 1  wherein the nozzle acts as the expansion valve in a thermodynamic cooling cycle, so that a volatile compressed liquid at subcooled temperature forced through the nozzle drops to a saturated temperature and pressure causing a fraction of the liquid to flash to vapor so a mix of cooled liquid and vapor enters the semi-toroidal channel.  
   
   
       3 . The cooling device of  claim 1 , wherein the fluid striking the upper surface of the cavity directly below its centerline apex in a direction generally tangent to the surface does so virtually without loss of momentum and velocity.  
   
   
       4 . The cooling device of  claim 1  where the velocity of the liquid on the cavity surface immediately below the impact point has a relatively small component in a direction perpendicular to the axis of the cavity, so the liquid film has negligible axial velocity and so thins rapidly in this region giving the film time to coalesce into an even thickness in the circumferential dimension about the axis of the cavity by flowing in the convex direction of the surface under the Coanda effect.  
   
   
       5 . The cooling device of  claim 1  wherein the volatile liquid film flowing in the semi-toroidal channel experiences very high centripetal acceleration that forces the film against the concave cavity wall of the channel, so the liquid and vapor phases of the fluid are separated with liquid against the cavity wall and vapor between the liquid film and the semi-toroidal protrusion wall surface above it, creating a high pressure gradient in the liquid film with the minimum value equal to the saturation pressure at the liquid/vapor interface, so that when the liquid is heated by the thermally dissipating elements the boiling is biased toward the vapor/liquid interface that is at saturation pressure, and any bubbles forming on the cavity surface are immediately pushed to the liquid/vapor interface thereby increasing the efficiency of the heat transfer process.  
   
   
       6 . The cooling device of  claim 1  wherein the rate of thinning of the liquid film as it expands outwards in the channel is increased by the evaporation of liquid from the film, so the heat transfer coefficient between cavity wall and liquid film increases more rapidly and generally in inverse proportion to the thinness of the liquid film.  
   
   
       7 . The cooling device of  claim 1  wherein the vapor formed by the expansion valve process combines with the vapor formed by the energy input from the dissipating elements to expand radially outwards in the semi-toroidal channel at a great velocity relative to the velocity of the liquid film moving in the same direction, so that the vapor creates extreme turbulence in the liquid film to increase the heat transfer from the cavity wall to the liquid film, and the vapor pushes the liquid film to overcome the flow friction between wall and film so the film increases its velocity, over that rate of increase naturally afforded by the effect of centripetal acceleration on the thinning film, even when the film becomes extremely thin, and maintains this velocity to provide cooling over an area much larger than state of art jet impingement, while the centripetal acceleration forces on the liquid film prevent the film from being broken up by the vapor into mist flow that would decrease the heat transfer rate as occurs in annular pipe flow.  
   
   
       9 . The cooling device of  claim 1  wherein the expansion valve is formed by extending the refrigerant liquid supply tube over the apex of the semi-toroidal cavity until a narrow annulus is created between tube and cavity surface, at which point the tube expands orthogonally to create irreversible flow conditions in the fluid and then blends into the semi-toroidal protruding surface  
   
   
       10 . The cooling device of  claim 1  wherein the semi-toroidal protruding surface is removed so the vapor is not channeled above the semi-toroidal cavity, but the vapor emitted from the nozzle flows above and in a general direction tangential to the liquid film flowing on the surface of the semi-toroidal cavity so that some increased turbulence is created in the liquid film on the surface of the semi-toroidal cavity and heat transfer is enhanced.  
   
   
       11 . The cooling device of  claim 1  wherein the liquid refrigerant supply tube has an orifice upstream of the nozzle, acting to create irreversible flow to cause a small amount of liquid refrigerant to flash to vapor so that the volume flow rate through nozzle directed at the semi-toroidal cavity is greatly increases to increase the heat transfer of the system.  
   
   
       12 . A cooling device wherein a flow channel with a rectangular cross-section is located below a surface on which is mounted a generally elongated thermally dissipating device, with the entrance and exits of the channel in directions generally orthogonal to the plane on which the dissipating devices are located and the connecting channel curved in a convex direction toward the dissipating elements, the wall of the channel in opposition to the dissipating devices being initially convex in the cross-sectional view at the entrance, changing to flat and then concave with increasing distance along the channel; and a nozzle sealed around the entrance to the channel and directing a jet of volatile liquid into entrance of the channel.  
   
   
       13 . The cooling device of  claim 12  wherein the a jet of volatile liquid strikes the convex surface at the entrance to the channel in a direction generally tangential to the surface, spreads out in the convex direction of the surface to form a film of even thickness and maintains an even thickness by means of the gradual change of the cross-sectional shape of the surface from convex to concave, the liquid film being held against the wall by the centripetal force caused by the concave shape of the shape in the flow direction.  
   
   
       14 . A cooling device wherein a number of semi-toroidal channels and nozzles are located in a face of a conductive plate to increase the effective heat-gathering area of the apparatus.  
   
   
       15 . The cooling device of  claim 14  wherein cooling channels are composed of a number of alternately placed wedge-shaped sections of the semi-toroidal surface so that heat may be evenly absorbed from a large rectangular surface, and the dividing walls between the alternately placed channels act as structural support ribs in the plate to allow the thickness of the plate between the thermally dissipating elements and the cavity surfaces to be minimized to enhance heat transfer.