Slot jet cooler and method of cooling

A cooling device for cooling a cooled surface includes a manifold having a number of inlet slots for directing fluid into an enclosed volume or chamber, toward the cooled surface. The manifold has a number of exit ports for receiving the fluid from the enclosed volume or chamber after it has impinged upon the cooled surface. The inlet slots and exit ports may be rectangular, or may be otherwise elongated, so as to provide substantially spatially uniform heat removal from the cooled surface. The cooling device may be used for a wide variety of applications, for example for cooling small devices such as integrated circuits or other devices involving electronics.

TECHNICAL FIELD

The invention relates to cooling devices and methods, and in particular to cooling devices and methods utilizing a coolant or cooling fluid.

BACKGROUND OF THE RELATED ART

Device thermal management is increasingly associated with large distributed heat loads, very high localized heat fluxes, stringent temperature control requirements, and/or difficult-to-meet platform compatibility requirements. Prior approaches to solving these problems include cooling schemes such as pool boiling, detachable heat sinks, channel flow boiling, micro-channel and mini-channel heat sinks, jet impingement, and spray cooling. However, none of these prior approaches has proved uniformly successful in device thermal management. Accordingly, there is a need for thermal management or cooling devices that provide improved performance.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a cooling device for cooling a cooled surface includes: a manifold; and one or more side walls. The manifold, the side wall(s), and the cooled surface together define an enclosed volume. The manifold and the cooled surface are on opposite sides of the enclosed volume. The manifold has plural inlet slots therein for directing fluid at the cooled surface. The inlet slots are substantially parallel to each other.

According to another aspect of the invention, a method of cooling a cooled surface includes the steps of directing a cooling fluid into an enclosed volume through a plurality of substantially-parallel inlet slots toward a major surface of the cooled surface; transferring heat from the cooled surface to the cooling fluid; and removing the cooling fluid from the enclosed volume through exit ports, wherein adjacent pairs of the inlet slots have respective substantially-parallel exit ports therebetween.

According to still another aspect of the invention, a method of designing a slot jet cooling device includes the steps of: selecting a cooling fluid; selecting a desired operating regime; performing a parametric study calculating parameters for a variety of geometries; and selecting a cooling device design based on results of the parametric study.

DETAILED DESCRIPTION

A cooling device for cooling a cooled surface includes a manifold having a number of inlet slots for directing fluid into an enclosed volume or chamber, toward the cooled surface. The manifold has a number of exit ports for receiving the fluid from the enclosed volume or chamber after it has impinged upon the cooled surface. The inlet slots and exit ports may be rectangular, or may be otherwise elongated, so as to provide substantially spatially uniform heat removal from the cooled surface. The cooling device may be used for a wide variety of applications, for example for cooling small devices such as integrated circuits or other devices involving electronics.

Referring initially toFIG. 1, a cooling device10for cooling a heat source or surface to be cooled12includes a manifold14, and one or more side walls16. The heat source12may be any of a variety of heat-generating devices or devices to be cooled, or may be a device or surface that is thermally coupled to a heat-generating device or device to be cooled. The heat source12, the manifold14, and the side walls16all serve to define an enclosed volume or chamber in the interior of the cooling device10. The manifold receives a cooling fluid from a fluid inlet20. The fluid is then directed within the manifold14into the enclosed volume, toward the heat source12. The fluid impinges upon the surface of the heat source12, removing heat from the heat source12. Heated fluid is removed from the enclosed volume, and is output from the manifold14via a fluid outlet22. The cooling device10may be hooked up to a circuit for recirculating the cooling fluid, for example, by use of a suitable pump.

Turning now toFIGS. 2 and 3, details of the interior configuration of the cooling device10are discussed. The manifold14may include a plenum28that is in communication with, and supplies cooling fluid to, multiple fluid inlet slots30that allow pressurized fluid to be introduced into an enclosed volume or chamber32, directed at a major surface34of the heat source12. The plenum28may be sized and positioned so as to achieve substantially the same rate of flow in each of the inlet slots30.

Between adjacent pairs of the fluid inlet slots30, the manifold14has fluid exit ports36. In addition, the manifold14may have side fluid exit ports38distal from the outermost of the fluid inlet slots30. The cooling fluid enters the chamber32through the fluid inlet slots30and impinges on the major surface34of the heat source12. The fluid flow then turns and exits the chamber32through the fluid exit ports36and38.

The manifold14may be made of any of a variety of suitable materials, such as stainless steel, aluminum, or polycarbonate. The side walls16may also be made of stainless steel, for example. Alternatively, the side walls16may be of a structurally strong, low thermal conductivity material, for example such as NEMA Grade G-10 glass epoxy laminate sheet.

As shown inFIG. 3, the inlet slots30and the exit ports36and38are separated from one another in a first direction42. In addition, the inlet slots30and the exit ports36and38may be elongated in a second direction40. The inlet slots30and the fluid exit ports36and38may for example be substantially rectangular in shape. The inlet slots30and the fluid exit ports36and38may have an aspect ratio, of distance in the second direction40, relative to distance in a first direction42that is perpendicular to the second direction40, of equal to or greater than one. That is, a length Ljetof the inlet slot30may be equal to or greater than a width Wjetof the inlet slot30. Alternatively, the length Ljetmay be at least about twice that of the width Wjet. As a further alternative, the length Ljetmay be at least five times as large as the width Wjet. The length-to-width aspect ration may be even higher, such as 10:1, 20:1, 30:1, 50:1, or even higher than 50:1. The inlet slots30and the exit ports36and38may be substantially rectangular, although for durability and ease of manufacture the slots30and the exit ports36and38may have rounded corners, for example. It will be appreciated that the inlet slots30and the exit ports36and38may have other suitable elongated shapes.

There also may be a variety of values of the ratio between Hjet(FIG. 2), the distance between the manifold14and the surface to be cooled12, and the inlet slot width Wjet. The ratio of Hjetto Wjetmay be greater than about 1, and may be greater than about 3. The ratio of Hjetto Wjetmay be even higher, for example being greater than about 5, greater than about 10, or greater than about 20.

The inlet slots30may all be substantially parallel to one another. In addition, the exit ports36and38may also be substantially parallel to the inlet slots30. The interior fluid exit ports36may each be placed substantially evenly between an adjacent pair of the fluid inlet slots30, offset substantially the same distance from each of the inlet slots30. The outer fluid inlet slots38may be placed offset from the adjacent fluid inlet slots30approximately the same distance that the fluid exit ports36are between the fluid inlet slots30. As best seen inFIG. 3, the outer fluid exit ports38may have approximately half the width of the inner fluid exit ports36. This is because the inner fluid exit ports36each receive approximately half the flow from a pair of adjacent fluid inlet slots30, while the outer fluid exit ports38receive approximately half the flow from only one of the fluid inlet slots30.

The inlet slots30may be narrower in width than the fluid exit ports36and38. Having the inlet slots30narrower than the exit ports36and38may be desirable when some boiling occurs within the chamber32, to thereby accommodate the increased volume rate of flow due to vaporization of some of the cooling fluid. The ratio of exit port width to inlet slot width may range from about 1 to 10, although it will be appreciated that other ratios may be used. More specifically, the ratio may be from about 1 to 5, and may be about 3.

The fluid inlet slots30and the fluid exit ports36and38may be located within the manifold14so as to provide a relatively smooth flow path within the enclosed volume or chamber32. Referring to the fluid flow path streamlines50shown inFIG. 2, fluid flow out from the fluid inlet slots30may impinge on the major surface34of the heat source12. The fluid may then make an approximately 180° turn, and exit the enclosed volume32through the fluid exit ports36and38. Heat is transferred to the fluid from the heat source12, and is carried away by the fluid. The flow of the fluid of each of the inlet slots30may be substantially confined to respective fluid flow cells52within the enclosed volume32. This is not to say that fluid flow from the inlet slots30do not mix with one another, since some intermixing of fluids from different fluid inlet slots30may be expected.

The rectangular or otherwise elongated fluid inlet slots30, and the similarly-elongated exit ports36and38, provide a high degree of cooling uniformity in the transverse direction, the second direction40. In addition, the placement of the fluid exit ports36and38substantially parallel to and interspersed with the fluid inlet slots30allows turning of the flow in a small space, inhibiting growth of thermal boundary layers. This allows a high degree of cooling uniformity in the streamwise direction, the first direction42.

The slot jet cooling device10may utilize either single-phase or two-phase heat transfer. In a single-phase mode, subcooled liquid enters the enclosed volume32from the fluid inlet slots30, is heated but still remains a liquid, and exits through the fluid exit ports36and38. In two-phase mode operation, subcooled or saturated liquid is introduced into the enclosed volume32through the inlet slots30. Upon impinging on the major surface34of the heat source12the impinging liquid undergoes a phase change, for example, via nucleate or another type of boiling. A single-phase or two-phase mixture then exits the enclosed volume32via the fluid exit ports36and38. Vapor that exits through the fluid exit ports36and38may be condensed elsewhere in the flow loop that the slot jet cooling device10forms a part of. Although the two modes of operation just described are the most likely modes to achieve high levels of heat transfer, and thus high levels of cooling, it will be appreciated that the cooling device10may be operable in other modes, for example, involving gas flow, film boiling, or introduction of a two-phase mixture through the inlet slots30.

The cooling device10may be utilized with a large variety of suitable fluids. Examples of suitable fluids include fluorocarbons, alcohols, water, and ammonia. An embodiment of the cooling device10has been demonstrated to dissipate more than 100 W/cm2using fluorocarbons and more than 300 W/cm2using ethyl alcohol, over a heated surface area of 3 cm2, with a temperature uniformity of ±1° C.FIG. 4shows a plot of heat flux as a function of a temperature difference between the temperature of the major surface34of a heat source12, and the inlet temperature of the bulk cooling fluid. Heat flux plot is shown for a cooling device having a surface area of 3 cm2, a height of the enclosed volume32of 1 mm, and using ethyl alcohol as the cooling fluid.FIG. 4shows the heat transfer performance of the slot jet cooler in both single-phase and nucleate boiling regimes.FIG. 4shows a critical heat flux (CHF) at which nucleate boiling transitions to film boiling.

It will be appreciated that the manifold14may have any of a large variety of suitable configurations. For example, there may be a greater or lesser number of inlet slots and exit ports, than is shown in the illustrated embodiment. Additionally, if the plenum28is included in the manifold14, it may be positioned above or to the side of the inlet slots30. It will also be appreciated that fluid may be pumped into and out of the manifold14in any of a variety of suitable directions and/or configurations. For example, the fluid may be introduced into the inlet slots30from the top of the cooling device10, and drawn out from the exit ports36and38through a side of the manifold14. Alternatively, the cooling fluid may be introduced into the manifold14on one side of the manifold14and drawn out from the fluid exit ports36and38on a different side of the manifold. It will be appreciated that there are a variety of other possible configurations.

FIGS. 5 and 6illustrate two configurations of the manifold14, showing a pair of possible configurations. InFIG. 5the cooling fluid is introduced from above the manifold14directly into the inlet slots30. A channel60connects the fluid exit ports36and38to a fluid exit62along a side of the manifold14.FIG. 6illustrates a side-side configuration for introducing and removing fluid from the manifold14. Fluid enters through an entry port70, and proceeds through a channel72to the inlet slots30. The fluid inlet70is on one side of the manifold14, on a side of the manifold14opposite from the fluid outlet channel60and fluid outlet62, which may be similar to that shown inFIG. 5. It will be appreciated that other configurations are possible, such as where the cooling fluid enters the manifold by a side channel, and exits through the top of the manifold.

With reference now toFIG. 7, the cooling device or slot jet cooler10may be part of a flow loop80. Cooling fluid may be pumped through the flow loop by a suitable pump82, with the outlet of the pump82coupled to the fluid inlet of the manifold14of the cooling device10. After flow circulates through the cooling device10, and in particular through the enclosed volume or chamber32of the cooling device10, flow exits the cooling device or slot jet cooler10and proceeds through the flow loop80to a heat exchanger or condenser84, which may be used to vent or otherwise expel heat to the environment or another cold source. The heat exchanger84may have any of a variety of suitable configurations, for example, involving a serpentine flow path, fins, or forced convection, such as from a cooling fan. It will be appreciated that the flow loop80illustrated inFIG. 7is but one of a wide variety of possible configurations for providing cooling fluid to the slot jet cooler10and for removing heat from the cooling fluid provided to the slot jet cooler10.

The slot jet cooling device10disclosed herein offers significant potential advantages relative to other devices used in the past, such as circular jets and spray cooling. The cooling device10may provide high heat transfer rates in a small size. In addition, the heat transfer over the exposed portion of the heated surface12may be highly uniform, especially when the slot jet cooler operates in a nucleate boiling regime. Although the cooling device10offers the potential of high heat transfer rates in a small size, it will be appreciated that the cooling device10may be scalable to cool much larger areas.

In one example embodiment, the inlet slots30have a length of 10 mm (0.394 inches) and a width of 1 mm (0.039 inches). The exit slots36and38have the same length, with the exit slots36having a width of 3 mm (0.118 inches) and the exit slots38having a width of 1.5 mm (0.059 inches). The centerline-to-centerline spacing of the inlet slots30and the exit slots36is 5 mm (0.197 inches).

With reference now toFIG. 8, a method100for designing the slot jet cooler10is described. The method100involves selecting a design giving desired heat flux and operating temperature conditions. The method100starts in step102with selection of a suitable cooling fluid (coolant). Then in step104, a desired operating regime, such as single-phase flow or nucleate boiling, is selected. In step106various operating parameters, such as maximum allowable pressure drop, maximum flow rate, and coolant inlet temperature are selected. These operating parameters may be selected so as to conform with the flow and heat transfer available from the flow loop80.

In step108, a parametric study is performed. A parametric study may involve calculation of parameters such as heat transfer rate, pressure drop, and critical heat flux, for a range of geometries (length, width, and/or shape) of the inlet slots30. The following equations have been found suitable for use in such a parametric study:

Nu_LPrf1/3=3.060⁢⁢Re0.50+0.118⁢⁢Re0.694⁡(L-WW)0.694(1)where⁢⁢Nu_L=h_L⁢Lkf⁢⁢and⁢⁢Re=U⁡(2⁢W)vfqs″=μf⁢hfg⁡[g⁡(ρf-ρg)σf]1/2⁡[cpf⁢Δ⁢⁢TeCsf⁢hfg⁢Prfn]3(2)qCHF″ρg⁢Uhfg=0.0919⁡[ρfρg]2/3⁡[1+cpf⁢Δ⁢⁢Tsubhfg]1/3⁡[1+0.034⁢ρf⁢cpf⁢Δ⁢⁢Tsubρg⁢hfg]2/3(3)[σρf⁢U2⁡(L-W)]0.157⁡[WL-W]0.331Δ⁢⁢p=(f⁢LeqDh+∑K)⁢ρf⁢V22(4)
Equation (1) provides heat flux for single-phase heat transfer, Equation (2) provides heat flux for nucleate boiling, Equation (3) provides the critical heat flux, and Equation (4) provides pressure drop. In the above equation, Csfis an empirical constant associated with nucleate boiling, Dhis hydraulic diameter, f is a friction factor, K is a loss coefficient, L is the length of the heater surface corresponding to one inlet slot, Leqis the equivalent length, n is an empirical constant associated with nucleate boiling, U is the inlet slot velocity, and W is the inlet slot width.

Finally, in step110, an optimum design is selected based on the results of the parametric study. The optimum design may include the dimensions and shape of the inlet slots30, the number and spacing of the inlet slots30, and the dimensions and placement of the fluid exit ports36and38.

FIG. 9shows an additional embodiment cooler10, in which the cooled surface or heat source12has a number of fins or extended surfaces112thereupon. The fins112may be substantially perpendicular to the inlet slots30and the manifold14. It will be appreciated that the fins112may increase the heat transfer from the cooled surface12to the cooling fluid, without significantly altering the turning flow of the cooling fluid.

FIG. 10shows the manifold14of another additional embodiment of the cooler10. The manifold14has inlet slots30and exit ports36that alternate in a pair of substantially perpendicular directions. A given inlet slot30may be between a pair of the exit ports36on both sides, as well as being between another pair of the exit ports36on both ends.

FIGS. 11 and 12show further embodiments of the cooler10, with different configurations of the manifold14.FIG. 11illustrates a manifold configuration in which the inlet slots30are in communication with channels130, and the exit ports36and38pass through the manifold14from bottom to top.FIG. 12illustrates another manifold configuration, one in which the exit ports36and38do not pass through the manifold14from bottom to top, but rather form channels that may exit the manifold14from a side of the manifold14.