Disclosed embodiments relate generally to X-ray tube devices. In particular, embodiments relate to cooling systems that employ a heat sink to increase the rate of heat transfer from X-ray tube components to a coolant.
X-ray producing devices are used in a wide variety of applications, both industrial and medical. Such equipment is commonly used in applications such as diagnostic and therapeutic radiology, semiconductor manufacture and fabrication, and materials testing. While used in a number of different applications, the basic operation of an X-ray tube is similar. In general, X-rays, or X-ray radiation, are produced when electrons are produced, accelerated, and then impinged upon a material of a particular composition.
Regardless of the application in which they are employed, X-ray devices typically include a number of common elements including a cathode, or electron source, and an anode situated within an evacuated enclosure in a spaced apart arrangement. The anode includes a target surface oriented to receive electrons emitted by the cathode. In operation, an electric current applied to a filament portion of the cathode causes electrons to be emitted from the filament by thermionic emission. The electrons then accelerate towards a target surface of the anode under the influence of an electric potential applied between the cathode and the anode. Upon approaching and striking the anode target surface, many of the electrons either emit, or cause the anode to emit, electromagnetic radiation of very high frequency, i.e., X-rays. The specific frequency of the X-rays produced depends in large part on the type of material used to form the anode target surface. Anode target surface materials with high atomic numbers (“Z” numbers) are typically employed. The X-rays exit the X-ray tube through a window in the tube, and enter the x-ray subject. As is well known, the X-rays can be used for therapeutic treatment, X-ray medical diagnostic examination, or material analysis procedures.
Some of the electrons that impact the anode target surface convert a substantial portion of their kinetic energy to x-rays. Many electrons, however, do not produce X-rays as a result of their interaction with the anode target surface, but instead impart their kinetic energy to the anode and other X-ray tube structures in the form of heat. As a consequence of their substantial kinetic energy, the heat produced by these electrons can be significant. The heat generated as a consequence of electron impacts on the target surface must be reliably and continuously removed or otherwise managed. If left unchecked, it can ultimately damage the x-ray tube and shorten its operational life. Moreover, removal of excessive heat allows for a proportional increase in the power capacity of the X-ray tube system, thereby increasing image quality.
A more particular description of the claimed invention will be rendered by reference to example embodiments, which are illustrated in the appended drawings. It is appreciated that these drawings depict only example embodiments and are therefore not to be considered limiting of its scope.
In the following detailed description of the embodiments, reference is made to the accompanying drawings that show, by way of illustration, example embodiments of the invention. In the drawings, like numerals describe substantially similar components throughout the several views. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical and electrical changes may be made without departing from the scope of the present invention. Moreover, it is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described in one embodiment may be included within other embodiments. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.
Referring first to
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In operation, an electrical current is supplied to the cathode 106, such as a filament component (not shown), which causes a cloud of electrons (denoted at “e” in
As is shown in the example embodiment, although not required, a shield structure 110 may be positioned between the cathode 106 and the anode 200 within vacuum enclosure. The shield 110 may define an aperture (denoted at 114) that is sized and shaped so as to substantially prevent errant electrons from impacting anode 200 other than at target surface 204. The shield 110 may also include an electron collection surface, denoted at 112, formed at one end of aperture 114, which is shaped (here, concave) so as to function to collect electrons that rebound from the target surface 204 (sometimes referred to as “backscattered” electrons) thereby minimizing such electrons from re-impacting anode 200 or other areas within the evacuated enclosure so as to avoid further heat generation and/or off-focus radiation.
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Any one of a different types of coolants can be used to provide adequate heat transfer into the coolant. For example, a 50% water/50% glycol combination can be used as a cooling fluid. Pure (or deionized) water may also be used, but due to a closed loop cooling system a bacterial growth inhibitor (such as glycol) can be added. If needed, a coolant with dielectric proprieties can be used if the coolant is used as part of the electrical insulation of the x-ray tube, such as a dielectric oil (e.g., Shell Diala Oil AX and Syltherm 800). It will be appreciated that the coolant could comprise any other appropriate coolant that is capable of performing the functions of heat absorption and removal, as enumerated herein. Note that, as contemplated herein, “coolant” includes, but is not limited to, both liquid and dual phase coolants.
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In the illustrated embodiment, the thermal structure 208 is cylindrical in shape, and forms a fluid passageway reservoir 211 that is configured to receive coolant, as will be described in further detail below. In one embodiment, the outer periphery of the thermal structure 208 is approximately the size and shape of the periphery denoted by the line at 209 in
As noted, the thermal structure 208 is configured to define at least one fluid passageway, which in the illustrated example is denoted at 211. As is illustrated, the fluid passageway may be a configured so as to form a single contiguous reservoir. Alternatively, the thermal structure may define two or more passageways. Further, while the illustrated example shows a single contiguous passageway, in alternative embodiments there may be fins, partial walls, or other similar structures formed within the one or more passageways.
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This recirculation of coolant through the fluid passageway reservoir 211 may be continuous, thereby enhancing the removal of heat that is generated at the target surface 204 (or other regions of the anode 200). In particular, heat generated 220 at the target surface 204 is thermally conducted to the thermal structure 208 and absorbed by the coolant entering (denoted at 352) and then circulating through the fluid passageway reservoir 211. The heated coolant is returned (denoted at 350) to the external cooling unit 300, and the process repeated.
To enhance the removal of thermal energy, embodiments further include a thermally conductive porous matrix that is disposed within the fluid passageway reservoir 211. The thermally conductive porous matrix acts to facilitate and enhance the transfer of heat generated at the target surface to the coolant that is circulating within the fluid passageway 211. For example, inclusion of the conductive porous matrix increases the relative effective surface area between the coolant and the heated surfaces that are conducting heat generated in the anode regions, such as the target surface 204. Moreover, the porous nature of the matrix facilitates improved heat transfer from the anode to the coolant due to the increased velocity of coolant flow, which is at least partially a function of the cross-sectional area of the passageways provided by the porous matrix. For a constant rate of flow, the velocity of the coolant increases as the cross-sectional area of the passageways (formed by the porous configuration) decreases. Accelerating a flow of coolant and then impinging the accelerated coolant on the surface(s) of the porous matrix is a more efficient method of convective cooling.
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In one embodiment, the individual particles are comprised of copper spheres that are approximately 0.5-1.0 millimeters (mm) in diameter. Other sizes (or combinations of sizes and shapes) can also be used, depending on, for example, porosity desired for a given fluid flow, heat transfer, and the like.
By way of example, the operation of an X-ray tube of the sort denoted at 100 proceeds generally as follows. External cooling unit 300 directs a flow of coolant 352 via conduit 304 into X-ray tube 100. The flow of coolant 352 is directed to a fluid passageway 211 formed within a thermal structure 208 via a fluid inlet channel 214 and inlet port 210 that is operatively connected to conduit 304. As the coolant enters the fluid passageway 211, it passes through a thermally conductive porous matrix. Since the thermal structure 208 is interfaced with anode 200, thermal energy 220 generated at the anode (particularly the target surface 204) conducts to the thermally conduct porous matrix, and is transferred to the circulating coolant. The heated coolant exits the passageway reservoir 211 via the fluid outlet channel 216 and the outlet port 212 and back to the external cooling unit 300 via fluid conduit 302 (flow denoted at 350). Heat is removed from the coolant by the cooling unit 300, and then recirculated.
To enhance convective cooling within the thermal structure 208, coolant may be circulated by pump disposed within the cooling unit 300 at appropriate fluid flow rate and/or pressure. Adjusting the flow rate through porous structure results in different rates of heat removal. In one embodiment, flow rates between about 0.4 and 0.62 gallons per minute (g.p.m) (between about 1.514 and 2.347 liters per minute) are used to prevent boiling of the fluid in the porous structure, and to prevent damage to the porous structure due to overly high delivery pressure or flow rate. Other fluid flow rates or fluid pressures may be used depending on the structural integrity of the porous structure, thermal characteristics, the type of coolant used, and the like.
By way of summary, disclosed embodiments are directed to an X-ray tube having improved cooling characteristics, particularly in the region of the anode. Example embodiments include an X-ray tube having a vacuum enclosure within which is disposed an electron source and anode. The anode, which in one disclosed embodiment is of a stationary type, includes a target surface positioned to receive electrons that are emitted by the electron source, for example, a filament disposed within a cathode head. As electrons strike the target surface, X-rays are generated. In addition, heat is generated in the region of the target surface. To assist in the removal of at least some of this heat, a thermal structure is interfaced directly with the anode. In one example, the thermal structure defines a fluid passageway that is configured to circulate a coolant, such as water, to absorb heat. In addition, a thermally conductive porous matrix is disposed within the fluid passageway so as to facilitate the transfer of heat generated at the target surface to the coolant circulating through the passageway. In some embodiments, a pump is used to continuously circulate the coolant through the fluid passageway, and a heat exchange device removes heat from the coolant before it is recirculated back to the thermal structure. Although various configurations can be used, the porous matrix is comprised of a thermally conductive material that is arranged in a porous matrix that permits circulation of the coolant through the passageway, and that increases the transfer of heat to the coolant. In one embodiment, the porous matrix is comprised of thermally conductive particles that are suitably interconnected or attached so as to provide the porous matrix.
Simulation data demonstrates that implementations using the above cooling techniques result in much improved thermal capacities and operational capabilities. For example, utilizing a thermal structure with a porous matrix allows for operation of the x-ray tube at higher energy inputs, and larger focal spot sizes (electron impact on the target surface), resulting in improved image quality.
The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
This application claims priority to U.S. Provisional Application No. 62/426,487, filed Nov. 26, 2016, titled HEAT SINK FOR X-RAY TUBE ANODE, which is incorporated herein by reference in its entirety.
Number | Date | Country | |
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62426487 | Nov 2016 | US |