| Cooling electronics via two-phase tangential jet impingement in a semi-toroidal channel -> Monitor Keywords |
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Cooling electronics via two-phase tangential jet impingement in a semi-toroidal channelRelated Patent Categories: Refrigeration, Structural Installation, With Electrical Component CoolingCooling electronics via two-phase tangential jet impingement in a semi-toroidal channel description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060162365, Cooling electronics via two-phase tangential jet impingement in a semi-toroidal channel. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of provisional patent application Ser. No. 60/621,894, filed 2004 Oct. 22 by the present inventors. FEDERALLY SPONSORED RESEARCH [0002] Not Applicable SEQUENCE LISTING OF PROGRAM [0003] Not Applicable BACKGROUND OF THE INVENTION [0004] 1. Field of Invention [0005] This invention relates to cooling electronics, specifically to spray-cooling of two-phase fluid on a heated surface contained within a conventional refrigeration loop. [0006] 2. Prior Art [0007] The problem addressed in this invention is removal of high thermal dissipation flux from electronic devices such as amplifier gate arrays, laser diodes, etc. [0008] Heat flux from electronics is now in the range of 100 to 1,000 Watts per square centimeter (W/cm.sup.2). Thermal literature refers to this as the high-flux range, and ultra-high flux being from 10.sup.3 to 10.sup.5 W/cm.sup.2 and describes a number of ways to remove the heat. If the heated surface is in the interior of an electronics package it can be removed only by circulation of a fluid against the heated surface. [0009] Fluids commonly available for this are air, water and fluorochemicals (generally called "refrigerants", although they may be used in high temperature applications), and the means of circulation can be natural convection, single-phase forced (mechanically pumped) convection, and boiling (2-phase pumped flow). The heat transfer coefficient Watts per centimeter-squared and degree centigrade (W/cm.sup.2-C) defines the rate of heat removal from a surface for a given temperature difference between the surface and the cooling liquid, and is highly dependant on the type of fluid and the means of circulation. Air is a poor choice for any type of circulation because of its low mass and low thermal conductivity. Water will have a coefficient about an order of magnitude greater than a refrigerant. Natural convection with water reaches only about 0.1 W/cm.sup.2-C, so this process cannot be considered for use with a refrigerant for high flux needs. In single-phase forced convection flow refrigerants reach about 1 W/cm.sup.2-C and water 10 W/cm.sup.2-C, and in boiling heat transfer refrigerants reach about 10 W/cm.sup.2-C and water over 100 W/cm.sup.2-C. In single-phase flow, water would require a temperature difference of 100C to carry away 1 kW/cm.sup.2, limiting the practical approach in most cases to boiling heat transfer. A further, key advantage of phase change flow is that only a modest increase in heated surface temperature results in a large increase in heat flux, and in certain situations such as freezing environments only a refrigerant can be used in the two-phase system. [0010] There are several phase change cooling schemes available: micro- and mini-channel cooling, jet impingement cooling and spray cooling. In all of these the upper limit of heat transfer is set by critical heat flux (CHF) which is the point at which liquid cannot reach the heated surface fast enough to prevent dryout of the surface. Micro-channel and mini-channel refer to flow devices having hydraulic diameters of 10 to several hundred micro-meters, and one to a few millimeters, respectively. Typically the channels are rectangular grooves cut in a metal plate on which the thermally dissipating element is mounted. High heat transfer coefficients, inversely proportional to the Reynolds Number, are achieved by the thinness of the liquid channel in laminar flow. Drawbacks include the limitations of the minimum size of the hydraulic diameter necessary to avoid flow clogging, and high streamwise pressure drops that can cause flow choking as the fluid suddenly evaporates. This latter problem limits the size of the cooling device. In addition, there will be thermal resistance to the flow of heat through the fins to the heated baseplate. Typical values for heat transfer coefficient with refrigerant fluids are 3 to 5 W/cm.sup.2-C. Conventional Jet impingement cooling (FIG. 2a) is done by directing a stream of liquid orthogonally against a heated flat plate. Heat transfer from plate to liquid is enhanced by the thinness of the boundary layer at the jet's small area of impingement, and then by the high velocity of the liquid moving tangential for two or three jet radii along the heated surface. Problems here are first the smallness of the effective cooling area and the necessity for very high jet velocities. In particular for two phase flows, the vapor bubbles formed on the plate's surface tend to push the liquid film away from the surface. There is also a loss in liquid momentum by the orthogonal impact on the plate, and areas of sub-saturated pressure directly under and near the impinging jet that may cause surface bubbles at this region. Heat transfer coefficients are in the range of 2 to 3 W/cm.sup.2-C. Spray cooling produces a peak heat transfer rate about half that of jet impingement, but cools a larger area. A problem with spray cooling is maintenance of the nozzles. [0011] There are three other relevant two-phase phenomenon that must be listed. The first is flow in a curved channel where the concave surface is heated. Here the g-forces generated by the flow velocity on the curved heated surface tend to force bubbles to move away from the heated surface and so prevent the bubbles from blocking access of liquid to the surface. Another flow regime of interest is annular flow in a pipe (FIG. 3). Heat transfer texts show this can produce the highest heat transfer rates in pipe flow boiling. In annular flow, there is a thin liquid film moving along the pipe wall, with the vapor moving down the center of the pipe at very high velocity. The high velocity of vapor relative to that of the liquid creates turbulence in the liquid film much higher than that created by flow of the liquid against the pipe wall. This can increase the heat transfer coefficient by more than an order of magnitude. However, the high turbulence quickly causes the liquid film to break up into what is called mist flow, so CHF is exceeded and the heat transfer coefficient falls back sharply. A third flow phenomenon is called the Coanda effect. This is the tendency for a flowing liquid to remain attached to a convex surface, with the result that unevenness in film thickness is eliminated as the pressure head in the thicker film areas pushed the fluid toward thinner areas. This is seen in water flowing over an apple held under a faucet. [0012] The following prior-art patents describe specific attempts to solve he problem of high thermal flux removal. [0013] Chu (U.S. Pat. No. 6,519,151) discloses a jet impingement thermal control device consisting of a nozzle that directs a fluid to strike perpendicular to, and at the bottom center of, a (bowl-shaped) concave conic-sectioned heated surface, so the liquid flows radially outwards along the surface of the bowl and exits the apparatus in a direction generally opposite to the incoming jet (FIG. 2b). Several such assemblies may be located in parallel to cool a large surface. The liquid film thins as it expands from the point of impact, and, combined with a high-g centrifugal force, this causes the fluid velocity to increase while the velocity in conventional flat plate jet impingement rapidly decreases by flow friction as it moves from the impact point. The combination of high velocity and thin, stable liquid film in Chu's invention causes an increase in efficiency over conventional jet impingement cooling. However, the perpendicular impact will cause momentum and velocity loss in the liquid stream as it turns a right angle to flow along the curved surface. Further, the radial velocity of the liquid is highest where it moves away in a direction perpendicular from the jet, so if there is any initial circumferential difference in film thickness there will not be sufficient time for the film to come to even thickness. The extent of the radial flow is limited because eventually the flow friction overcomes the momentum in the liquid film when the film becomes very thin. Hocker (Application 2002/0062945 A1) shows the same concept as Chu cited above. [0014] Rini et al. (U.S. Pat. No. 6,571,569) shows a design of an evaporative cooling system wherein the refrigeration expansion valve (nozzle) directs fluid directly against the flat plate having the heat dissipating elements on its opposite side. This approach suffers from the same problems described above in spray cooling. This patent further describes a means for a mechanical pump to force a high velocity vapor steam into the stream of liquid refrigerant to increase its velocity and cooling effectiveness. This approach adds to the weight and complexity of the cooling system. [0015] Remsburg (U.S. Pat. Nos. 5,864,466 and 6,064,572) shows a conic-sectioned plate in a heat exchange apparatus. However, the function of the curved piece is to create a themosyphon action to direct liquid flow against a heated flat plate. The flow is then convectional to that heat transfer coefficients will be very low. Searight (U.S. Pat. No. 4,108,242) shows a means to inject fluid jets into a cylindrical cavity to induce swirling flow in general flow along the axis of the cavity. Here the heated surface has a single axis of curvature so the flow is not accelerated by motion along the curved surface nor is a thin flow film created. Lynch (U.S. Pat. No. 4,140,302) shows a water-cooled blast-furnace tuyeres nozzle having a number of liquid jets at high speed directed against the contoured inner surface of the nozzle. The jet impinges the surface at low angle to avoid momentum loss, but the curved surface shown is only to direct flow against a heated surface that is flat. Further, in this design the water passages are filled with liquid, so this arrangement does not produce a thin film liquid flow nor does the single-axis curved surface provide an acceleration of flow. Bemisderfer (U.S. Pat. No. 5,056,586) shows a spray system whereby the liquid is directed against cusp-shaped surfaces to increase turbulence. This does not produce a thin film nor accelerate flow. Tilton (20030172669) shows transverse thin-film evaporative spray cooling. The spray nozzle directs droplets down a narrow channel on whose side(s) are electronic devices to be cooled. This does not create a continuous liquid film, nor does it provide uniform cooling of the devices. [0016] Niggeman (U.S. Pat. No. 4,643,250) shows a heat exchanger whereby a conical surface is used as a means to separate cryogenic liquid from vapor phase, and then to condense the vapor phase in a heat exchanger wherein the liquid phase is the heat sink. This is not possible since the two phases will be at the same temperature at the entrance to the apparatus. OBJECTS AND ADVANTAGES [0017] Several objects and advantages of the present invention are: [0018] to provide a means to direct a coolant fluid jet against a heated surface without loss of velocity or momentum after contact with the surface; [0019] to provide a means to enable the coolant fluid jet to form into a thin, high-velocity liquid film of consistent thickness on the heated surface to create a high value of convection heat transfer coefficient and significant increase in critical flux; [0020] to provide a means to maintain velocity of a cooling liquid film over a heated surface to a distance significantly longer than conventional jet impingement devices; [0021] to increase the effectiveness of the coolant fluid jet beyond what is available from the thermodynamic refrigeration system's expansion valve jet but without addition of a mechanical system; [0022] to create an equivalent of circular pipe annular flow over the heated surface to increase the heat flux removal rate. BRIEF SUMMARY OF THE INVENTION [0023] In accordance with the present invention a coolant fluid jet directed against a doubly-curved, semi toroidal surface located in a conductive plate on whose the opposite face are thermally dissipating electronic devices. Continue reading about Cooling electronics via two-phase tangential jet impingement in a semi-toroidal channel... Full patent description for Cooling electronics via two-phase tangential jet impingement in a semi-toroidal channel Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Cooling electronics via two-phase tangential jet impingement in a semi-toroidal channel patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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