Patent Application
20080230210
1. Field of the Invention
The subject invention relates to a thermosiphon boiler plate assembly for dissipating heat generated by an electronic device, and more specifically, to a low profile thermosiphon boiler plate assembly having a high plate strength.
2. Description of the Prior Art
Boiler plates have traditionally been used in electronic apparatuses to dissipate heat from electrical components. A boiler plate is a device that attaches directly to an electrical device to enhance the dissipation of heat therefrom. A boiler plate is generally designed with a base for contacting an electrical device and a means for dissipating the heat transferred from the device to the boiler plate. An example of such a boiler plate is disclosed in U.S. Pat. No. 6,179,046 to Hwang et al. The Hwang et al. patent discloses a base having a top surface and a bottom surface and a plurality of spaced fins disposed on the top surface of the base. The spaced fins are disposed radially around a circumference of a circular central portion of the base and extend radially outward from the circumference of the circular central portion along the top surface of the base. Heat is transferred from an electrical device to the base, and the base transfers the heat from the fins to the exterior environment.
An additional example of a boiler plate is disclosed in U.S. Pat. No. 6,140,571 to Kitahara et al. The Kithara et al. patent discloses a base having a top surface and a bottom surface. The base has a longitudinal axis extending along the top surface of the base equidistant from a pair of width edges and a latitudinal axis extending along the top surface of the base equidistant from a pair of length edges and perpendicular to said longitudinal axis. A first partition plate is disposed on the top surface extending along the longitudinal axis and a second partition plate is disposed on the top surface extending along the latitudinal axis intersecting the first partition plate. A fan is disposed above the top surface of the base to propel air towards the top surface of the base. The partition plates restrict the path of the propelled air to the outside of the heat sink to prevent a reduction of the cooling efficiency by the mutual collision of the cooling air.
Recent advances in electrical components have led to decreasing device size and increasing capabilities which has resulted in an increasing of package densities and heat generation rate. In recent electronic apparatuses, the increasing package densities have led to a decreasing package size allowing for a diminishing amount of space to effectively dissipate heat generated by the electrical components within the electronic apparatuses. The available space for dissipating heat has become narrower, and the heat radiation within electronic apparatuses has become an increasingly difficult problem.
The present invention provides for a thermosiphon boiler plate assembly for dissipating heat generated by an electronic device comprising a base having a top surface and a bottom surface for absorbing heat generated by the electronic device, a plurality of widthwise ribs disposed on the top surface of the base, and a plurality of lengthwise ribs disposed on the top surface of the base. The lengthwise ribs intersect the widthwise ribs on the top surface of the base to define a plurality of pockets on the top surface completely surrounded by the lengthwise and widthwise ribs to increase the widthwise and lengthwise area moment of inertia of the assembly for resisting deflection of the assembly.
The present invention provides a thermosiphon boiler plate assembly that has a low profile, high heat transfer rate, high plate strength, and low plate mass.
Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein the FIGURE is a perspective view of a thermosiphon boiler plate assembly.
Referring to the FIGURE, wherein like numerals indicate corresponding parts throughout the several views, a thermosiphon boiler plate assembly 20 is generally shown for dissipating heat generated by an electronic device 22.
The thermosiphon boiler plate assembly 20 comprises a base 24 generally indicated having a top surface 26 and a bottom surface 28 and a rectangular periphery thereabout. The bottom surface 28 contacts the electronic device 22 to absorb heat generated by the electronic device 22. The periphery is defined be a pair of length edges 30 and a pair of width edges 32 extending between the surfaces 26, 28. In an embodiment of the invention as shown in the FIGURE, the length edges 30 and the width edges 32 are equal in length defining the periphery of the base 24 as a square.
The length edges 30 and the width edges 32 define a base thickness tb between the surfaces 26, 28. The base thickness tb is proportional to a thermal resistance R of the base 24 as defined by the equation:
R=t
b/(kA)
where “k” is the thermal conductivity of the material of the base 24 and “A” is the surface area of the base 24. In the preferred embodiment, the thermal resistance R of the base 24 should be as low as possible to establish a high heat transfer rate to effectively dissipate heat. The base thickness tb is preferably in the range of 0.5 to 1 millimeters.
A chamber 34 is disposed about the top surface 26 of the base 24 for containing a refrigerant 36 for liquid-to-vapor transformation. Heat generated by the electronic device 22 is absorbed by the base 24 and transferred to the refrigerant 36 contained within the chamber 34. The refrigerant 36 is evaporated by the heat and the resultant vapor is later condensed and returned to the chamber 34.
As shown in the FIGURE, the base 24 has a latitudinal axis Ax extending along the top surface 26 equidistant from the width edges 32 and perpendicular to the length edges 30. The base 24 also has a longitudinal axis Ay extending along the top surface 26 equidistant from the length edges 30 and perpendicular to the width edges 32 and perpendicular to the latitudinal axis Ax.
A plurality of widthwise ribs 38 are disposed on the top surface 26 of the base 24 to reinforce the assembly 20. Widthwise ribs 38 of various densities can be used to match the heat flux footprint of the heat generating device. The widthwise ribs 38 preferably extend parallel to the latitudinal axis Ax in spaced relationship to each other between the length edges 30. In an embodiment as shown in the FIGURE, one of the widthwise ribs 38 extends axially along the latitudinal axis Ax and each of the widthwise ribs 38 are spaced from adjacent widthwise ribs 38 a widthwise distance sy. Each of the widthwise ribs 38 first adjacent each of the width edges 32 are spaced the widthwise distance sy from the adjacent width edges 32 as shown in the FIGURE. The widthwise distance sy can be varied to vary a widthwise elastic constant Dx of the assembly 20. The widthwise elastic constant Dx of the assembly 20 is defined by the equation:
D
x
=E/(12(1−v2))*EIy/sy
where “E” is Young's modulus, “v” is Poisson's ratio, and “IY” is a lengthwise area moment inertia of the assembly 20 expressed as:
I
y
=t
2(h2+tB/2)3/12
where “t2” is a second rib thickness and “h2” is a second rib height. The widthwise distance sy divided by the base thickness tb is a first distance ratio preferably in the range of 1 to 6 as a factor in the widthwise elastic constant Dx of the assembly 20. The significance of the widthwise elastic constant Dx is that it is an elastic parameter which determines the deflection of the assembly 20 along the latitudinal axis Ax. The greater the value of the widthwise elastic constant Dx, the greater the resistance of the assembly 20 to deflection along the latitudinal axis Ax. The deflection of the assembly 20 along the latitudinal axis Ax is inversely proportional to the widthwise elastic constant Dx.
Each of the widthwise ribs 38 have a rib cross-section defining a first rib height h1 and a first rib thickness t1. The first rib height h1 and the first rib thickness t1 can be varied to vary a widthwise area moment of inertia Ix of the assembly 20. The widthwise area moment of inertia Ix of the assembly 20 is defined by the equation:
I
x
=t
1(h1+tb/2)3/12
and the first rib thickness t1 divided by the base thickness tb is a first thickness ratio in the range of 1 to 2 as a factor in the widthwise area moment of inertia Ix of the assembly 20. The first rib height h1 divided by the base thickness tb is a first height ratio greater than 0 and not greater than 4 as a factor in the widthwise area moment of inertia Ix of the assembly 20.
A plurality of lengthwise ribs 40 are disposed on the top surface 26 of the base 24 intersecting the widthwise ribs 38 on the top surface 26 of the base 24 to define a plurality of pockets 42 on the top surface 26 completely surrounded by the lengthwise and widthwise ribs 40, 38 to reinforce the assembly 20. The plurality of pockets 42 defined by the intersection of the lengthwise and widthwise ribs 40, 38 are completely surrounded on all sides as shown in the FIGURE. Lengthwise ribs 40 having various densities can be used to match the heat flux footprint of the heat generating device.
The lengthwise ribs 40 preferably extend parallel to the longitudinal axis Ay in spaced relationship to each other between the width edges 32. In an embodiment as shown in the FIGURE, one of the lengthwise ribs 40 extends axially along the longitudinal axis Ay and each of the lengthwise ribs 40 are spaced from adjacent lengthwise ribs 40 a lengthwise distance sx. Each of the lengthwise ribs 40 first adjacent each of the length edges 30 are spaced the lengthwise distance sx from the adjacent length edges 30 as shown in the FIGURE. In an embodiment as shown in the FIGURE, the lengthwise distance sx is equal to the widthwise distance sy defining each pocket 42 as being a square. The lengthwise distance sx can be varied to vary a lengthwise elastic constant Dy of the assembly 20. The lengthwise elastic constant Dy of the assembly 20 is defined by the equation:
D
y
=E/(12(1−v2))+EIx/(sxtb3)
where “E” is Young's modulus and “v” is Poisson's ratio. The lengthwise distance sx divided by the base thickness tb is a second distance ratio preferably in the range of 1 to 6 as a factor in the lengthwise elastic constant Dy of the assembly 20. The significance of the lengthwise elastic constant Dy is that it is an elastic parameter which determines the deflection of the assembly 20 along the longitudinal axis Ay in that the lengthwise elastic constant Dy is inversely proportional to the deflection of the assembly 20 along the longitudinal axis Ay. The deflection of the assembly 20 is inversely proportional to the square root of the widthwise elastic constant Dx times the lengthwise elastic constant Dy.
Each of the lengthwise ribs 40 have a rib cross-section defining the second rib height h2 and the second rib thickness t2. In the embodiment shown in the FIGURE, the second rib height h2 is equal to the first rib height h1 and the second rib thickness t2 is equal to the first rib thickness t1. In alternative embodiments, the second rib height h2 and the second rib thickness t2 can be varied to vary the lengthwise area moment of inertia Iy of the assembly 20. The lengthwise area moment of inertia Iy of the assembly 20 is defined by the equation:
I
y
=t
2(h2+tB/2)3/12.
The second rib thickness t2 divided by the base thickness tb is a second thickness ratio in the range of 1 to 2 as a factor in the lengthwise area moment of inertia Iy of the assembly 20. The second rib height h2 divided by the base thickness tb is a second height ratio greater than 0 and not greater than 4 as a factor in the lengthwise area moment of inertia Iy of the assembly 20.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
