Cooling system for an x-ray source

The present invention is directed to a cooling system and apparatus for use in radiographic devices having high output x-ray tubes. In operation, the x-ray tube generates large amounts of heat that must be removed so as to prevent damage to the tube. In the present invention, the x-ray tube is disposed within an x-ray tube housing that is connected within a closed fluid circuit through which circulates a coolant fluid. The fluid circulates through the x-ray tube housing and absorbs heat dissipated by the x-ray tube. Also connected within the closed fluid circuit is a heat exchange which cools the coolant fluid before it is recirculated back to the x-ray tube housing. Also connected within the closed fluid circuit is a centrifugal pump which continuously circulates the coolant fluid between the x-ray tube housing and the heat exchange device. The pump includes as an integral part a deformable bellows that accomodates any volume changes with the closed fluid system due to increases in temperature.

FIELD OF THE INVENTION 
The present invention relates to an apparatus and system for removing 
excess heat generated by electrical components. More particularly, the 
present invention is directed to a cooling system for removing heat 
dissipated by a high power, high intensity x-ray source, such as x-ray 
tubes used in systems such as CT scanners and the like. 
BACKGROUND OF THE INVENTION 
In system utilizing electrical components, heat is often generated when 
electrical power is supplied to the component. With some components, the 
amount of heat generated can be substantial. In such an environment, the 
dissipated heat must be continuously removed so as to prevent overheating 
and damage to the component and/or surrounding electrical circuitry. 
One common example of an electrical system in which overheating can be 
problematic is in systems utilizing high power x-ray tubes for commercial 
or medical applications. Such tubes are commonly found in various 
radiographic devices used, for instance in CT (computerized tomographic) 
scanning for x-ray imaging, x-ray lithography for producing integrated 
circuits, x-ray diffraction for analyzing materials, and the like. In such 
devices and applications, a high power, high intensity x-ray tube is 
arranged to direct radiation through a targeted region. Depending on the 
particular application, the radiation can be used in various ways. For 
instance, in a CT scanner, the radiation can be detected after it has 
passed through the region of interest of a patient's body with one or more 
detectors, and then analyzed to determine the distribution of absorption 
of the radiation. In the course of such a procedure, much heat is 
generated by the x-ray tube as a by-product of the x-ray energy generated. 
This heat must be continuously removed to prevent damage to the tube (and 
any other adjacent electrical components) and to increase the x-ray tube's 
overall service life. 
Typically, heat is dissipated in such a device with a coolant liquid or 
fluid, such as a dielectric oil. In a cooling system of this sort, the 
x-ray tube is usually disposed within an x-ray tube housing, and a pump is 
used to continuously circulate the coolant fluid through the housing. 
Then, as heat is dissipated by the x-ray tube during its operation, at 
least some of it is absorbed by the coolant fluid. The heated coolant 
fluid is then passed to some form of heat exchange device, such as a 
radiative surface in the form of a heat exchanger. Air is passed over the 
heat exchange (usually with a fan or fans) and, since the air is at a 
lower temperature than the heated fluid, a portion of the heat is 
dissipated from the fluid to the outside air. The fluid is then 
recirculated by the pump back into the x-ray tube housing and the process 
repeated. 
The cooling system of the sort described above is typically implemented 
with the x-ray tube housing, the pump, and the radiator all interconnected 
within a closed circulation system, i.e., the fluid circuit for the 
coolant fluid is not open to the atmosphere. Thus, when heat is generated 
by the x-ray tube, both the temperature and the volume of the coolant 
fluid within the closed system increase. As such, the closed system must 
provide some ability for accommodating volume within in the closed 
circulation system. Typically, the mechanism that provides this ability is 
a separate component, often referred to as an accumulator. Usually, an 
accumulator includes an expandable material, such as a rubber bladder or 
diaphragm, and a housing or similar structure for protecting the bladder 
or diaphragm. In known implementations, the accumulator is configured as a 
separate and discrete component that is interconnected somewhere within 
the closed circulation system. Consequently, it must include suitable 
fluid fittings and conduits so that it can be physically connected within 
the closed system. In operation, as the coolant fluid is heated, and the 
fluid volume within the closed system increases, the expandable 
bladder/diaphragm correspondingly expands and thereby maintains the 
integrity of the closed system. Conversely, a decrease in temperature and 
volume is also accommodated by a corresponding contraction of the flexible 
diaphragm. 
As noted, in the prior art the accumulator is designed as a component 
separate and distinct from the rest of the components within the closed 
system. Such an approach has resulted in several undesirable 
characteristics, primarily due to the need for additional fluid connection 
points to physically connect the accumulator within the closed system. 
This gives rise to a need for additional parts and for additional assembly 
time and complexity, resulting in a system that is difficult to install, 
replace and repair. Moreover, additional fluid fitting interconnection 
points raise the probability that the system will leak coolant fluid 
during operation. 
As such, there is a need for a system in which the accumulator is not 
implemented as a separate and discrete component within the closed system. 
This would eliminate the need to have additional fluid connection points 
within the closed system, and reduces the number of parts present. A 
reduction in parts reduces the overall complexity of the system, as well 
as the time needed for its initial assembly and subsequent servicing. In 
addition, reduction in fluid connection points reduces the chance for part 
failure and fluid leakage, and would provide a more reliable system. 
SUMMARY OF THE INVENTION 
The foregoing problems in the prior state of the art have been successfully 
overcome by the present invention, which is directed to a system for 
removing heat dissipated by a high intensity x-ray source, such as an 
x-ray tube used in radiographic equipment such as a CT scanner and the 
like. In the preferred embodiment, the cooling system operates within a 
closed circulation circuit and functions so as to continuously circulate a 
coolant liquid or fluid to the x-ray tube, which is disposed within an 
x-ray tube housing. The coolant then absorbs at least some of the heat 
dissipated by the tube during its operation as the coolant passes through 
the tube housing. The heated coolant is then preferably circulated through 
a means for removing heat from the coolant, such as a radiant surface 
implemented as a heat exchanger, at which point a portion of the heat 
present in the coolant is released to the air. The resulting coolant 
fluid, which has a lower temperature, is then recirculated back to the 
x-ray tube housing, and the process repeated. 
In the preferred embodiment, the cooling system includes a means for 
pumping the coolant fluid in a predetermined direction through the closed 
circulation circuit, such as a centrifugal pump device. Because the 
coolant is circulated within a closed system (i.e., not open to 
atmosphere), when the tube heats the coolant, the coolant volume increases 
within the system. As such, the preferred embodiment also includes a means 
for accommodating volume changes within the closed circulation system. 
This volume accommodation means is preferably comprised of an accumulator 
fashioned as a bellows constructed with a flexible, deformable material. 
Moreover, the accumulator is formed as an integral part of the centrifugal 
pump, and in a manner so as to be in fluid communication with the coolant 
liquid. As coolant is circulated through the pump, the deformable 
accumulator thus accommodates for any coolant volume increase (or 
decrease) within the closed system by expanding and contracting as needed. 
Integrating the accumulator as an integral component of the pump provides 
several key advantages. First, integration of the components eliminates 
the need to connect a separate accumulator within the closed circulation 
circuit, thereby eliminating the need for additional, fluid conduit 
connection points between the accumulator and the rest of the circuit. 
This reduces the overall complexity and number of parts within the cooling 
system, and simplifies its assembly and repair. Moreover, the reduction in 
fluid connection points reduces the chance of fluid leakage within the 
circuit, thereby increasing the overall reliability of the system. 
Additional objects, features and advantages of the invention will be set 
forth in the description which follows, and in part will be obvious from 
the description, or may be learned by the practice of the invention. The 
objects and advantages of the invention may be realized and obtained by 
means of the instruments and combinations particularly pointed out in the 
appended claims. These and other objects and features of the present 
invention will become more fully apparent from the following description 
and appended claims, or may be learned by the practice of the invention as 
set forth hereinafter.

DETAILED DESCRIPTION OF THE INVENTION 
Reference is now to the drawings, in which reference numerals are used to 
designate parts throughout the various figures. FIG. 1 illustrates an 
example of the sort of radiographic device, the computerized tomography 
(CT) scanner, that typically utilizes the type of high intensity x-ray 
tube that requires continuous heat removal, and in which the current 
invention finds particular application. It will be appreciated that while 
embodiments of the invention are described in connection with a CT 
scanner, the current invention could also be used in connection with other 
similar devices that use similar x-ray tubes and in which heat removal is 
of particular concern. 
The CT scanner of FIG. 1, designated generally at 10, includes a patient 
region 12 in which a patient assumes a stationary position during a CT 
scanning procedure. The scanner 10 also includes a gantry 14, which is 
mounted and positioned for rotation about the patient region 12 during 
operation of the scanner. Mounted on the gantry 14 is an x-ray tube 
housing 16, which contains a high intensity x-ray tube (not shown), and a 
cooling system 18. The housing 16 and cooling system 18 are interconnected 
in a closed circulation circuit by way of fluid tubing, shown as outlet 
fluid conduit 20 and an inlet fluid conduit 22. While the illustrated 
embodiment shows a CT scanner having the x-ray tube housing 16 and the 
cooling system 18 both mounted on the rotating gantry 14, it will be 
appreciated that the invention can be employed in CT scanners which 
instead have the x-ray tube housing mounted on the gantry and the cooling 
system located at a stationary point on the scanner. Alternatively, the 
x-ray tube housing assembly and the cooling system could be integrated as 
a single unit. Different mounting schemes could also be utilized if the 
present invention were utilized in radiographic equipment other than a CT 
scanner. 
During a typical CT scanning procedure, the high intensity x-ray tube 
generates a planar beam of radiation through an x-ray port (not shown) to 
the patient region 12. This beam of radiation is then rotated around the 
patient's body by rotating the gantry 14. Radiation detectors 26, which 
are disposed about the patient region 12, are then used to detect the 
intensity of the resultant radiation beam. This information can then be 
used to generate an image slice of the patient's body in a manner that is 
well known in the art. 
As already discussed in the background section, in the course of generating 
radiation beams, an extreme amount of heat is dissipated by the x-ray tube 
as a by-product. In the embodiment illustrated, this heat is removed by 
way of the cooling system 18. During operation, the cooling system 18 
continuously circulates a coolant, such as a dielectric oil or any other 
suitable coolant liquid or fluid, through the x-ray tube housing 16 by way 
of the inlet fluid conduit 22 and the outlet fluid conduit 20. As the 
x-ray tube generates heat, it is absorbed by the coolant fluid present 
within the housing 16. The heated coolant is then circulated out from the 
x-ray tube housing 16 back to the cooling system 18, and then cooled (in a 
manner described in more detail below). The coolant is then recirculated 
by the cooling system 18 back to the x-ray tube housing 16. This process 
is continued throughout the operation of the CT scanner. 
FIG. 2 shows additional details of the coolant fluid flow within the closed 
circulation system circuit, which is designated generally at 30. As is 
indicated by the fluid flow arrows, during operation of the CT scanner 10, 
the coolant is continuously circulated between the cooling system 
(represented as at the dotted box indicated at 18) and the x-ray tube 
housing 16. 
FIG. 2 further illustrates that in one preferred embodiment of the 
invention, the cooling system 18 is comprised of a means for pumping the 
coolant fluid, such as a dielectric oil, in a predetermined direction 
through the closed circulation circuit, and a means for removing heat from 
the coolant fluid. By way of example and not limitation, the pumping means 
is comprised of a centrifugal pump, designated at 32 (discussed in more 
detail below), and the heat removal means is comprised of a radiative 
surface in the form of a heat exchange (such as a radiator), which is 
designated at 34. In operation, the coolant fluid is received at an inlet 
port 40 of the pump 32 and then forwarded under positive pressure out of 
pump outlet port 42 to heat exchange 34. While any one of a number of 
different cooling schemes could be utilized, in the illustrated embodiment 
the heated coolant is passed through the heat exchange 34, and air is 
passed over the heat exchange 34 surface so as to dissipate heat from the 
coolant fluid. A fan, or fans (not shown) can be used to increase the 
efficiency of the heat exchange by passing cool air over the heat exchange 
34 and then facilitating the removal of the dissipated heat to an external 
location. Once cooled, the coolant fluid is then circulated out heat 
exchange 34 and cooling system 18 via outlet port 44 and returned back to 
the x-ray tube housing 16. The circulation process continues so as to 
maintain the temperature of the x-ray tube below a maximum temperature. 
Reference is next made to FIG. 3, which illustrates in further detail an 
example of a preferred embodiment of the pump 32 shown in FIG. 2. Pump 32 
includes a cylindrical outer housing 50 that serves to enclose and 
hermetically seal the interior components of the pump 32. Enclosed within 
the pump housing 50 is an electrical pump motor 51 that drives a standard 
pump impeller 52. In the preferred embodiment the centrifugal pump 32 
utilizes a pump motor with a wetted stator and rotor. In will be 
appreciated that other designs can also be used, including a motor with a 
wet rotor and a dry stator, or an impeller and rotor functioning as one 
component and/or a wet or dry stator. 
In the illustrated embodiment, the pump motor 51 receives electrical power 
through an electrical connection provided via a hermetically sealed 
electrical wiring harness and plug arrangement, which is designated at 54. 
Any pump designs incorporating a dry stator would not require a 
hermetically sealed electrical wiring arrangement. 
In the example embodiment, the pump housing 50 is in the form of a cylinder 
that is open on both ends. A first end 53 includes a small round opening 
through which the above-mentioned hermetic electrical connector 54 is 
passed. The opposite end 55 of the cylindrical housing 50 forms a hollow 
interior space 57. Pump 32 further includes a pump inlet 40 that is formed 
through the wall of the pump housing 50, and which is in fluid 
communication with the inlet conduit 20 in FIG. 2, so as to be capable of 
receiving coolant fluid from the x-ray tube housing 16. The pump 32 also 
includes a discharge outlet 42, also formed through the wall of the pump 
housing 50. In operation, the impeller 52 portion of the pump rotates in a 
manner so as to discharge the coolant fluid out of the discharge port 42 
of the pump under pressure, in a manner that is well known in the art. 
In the preferred embodiment, the pump 32 also includes an impeller plate 
80, which functions to prevent the coolant fluid from being circulated 
between the inlet 40 and the discharge outlet 42 of the pump 32. Impeller 
plate 80 has formed therein an inlet hole 78. In operation, as coolant 
fluid enters inlet 44, it flows into the inlet chamber 76 formed within 
the hollow interior space 57 of the pump 32. The fluid then enters the 
impeller 52 chamber of the pump via the inlet hole 78, and is discharged 
through the discharge port 42 by the rotating impeller 52. 
As was noted in the background section above, when an x-ray tube is 
generating radiation, both the temperature, pressure and the volume of the 
coolant fluid within the closed circulation system increase. Thus, the 
closed circulation system must include a facility to accommodate the 
volume changes in the closed system. Thus, the preferred embodiment of the 
invention includes means for accommodating volume changes within the 
closed circulation system illustrated in FIG. 2. Moreover, the volume 
accommodation means is formed as an integral part of the pump means. By 
way of example, and not limitation, one example of a volume accommodation 
means is shown in FIG. 3 as comprising an accumulator bellows 56, which is 
disposed within the pump housing 50. The bellows 56 is cylindrical in 
shape, and is constructed from a flexible material so as to be deformable 
and thereby accommodate any increases in volume within the closed 
circulation system such as would occur when the coolant is heated. In the 
illustrated embodiment the bellows 56 is formed from a rubber material, 
but could also be constructed from any other material or combination of 
materials that expands under pressure. For instance, a bellows constructed 
from metal could be utilized if it were configured so as to expand when 
the coolant volume is increased. 
In the illustrated example, the bellows 56 includes a molded integral 
O-ring 58 formed around the base of the cylindrical bellows 56. Formed 
around the circumference of the cylindrical opening formed by the pump 
housing 50 is an shoulder region 74 having a slightly larger diameter that 
the rest of the pump housing cylinder 50. The interior of the shoulder 
region 74 forms an O-ring gland 73. When positioned within the pump 
housing 50, the O-ring 58 is seated within the O-ring gland 73. This is 
shown in greater detail in FIG. 4. In the preferred embodiment, the 
bellows 56 is then secured within the pump housing 50 by way of two 
accumulator retainers, shown at 60 and 62. The accumulator retainers 60, 
62 each include a retaining lip 63, 65 that functions so as to compress 
and retain the molded O-ring 58 portion within the O-ring gland 73. 
Moreover, when retained in this fashion, the O-ring 58 forms a fluid-tight 
seal. 
While other securing means could be utilized, in the illustrated embodiment 
the retainers 60, 62 are each secured to the pump housing 50 in a manner 
so as to retain the bellows 56 by way of a pump housing cover plate 66 
that is placed over the open end 55 of the pump housing 50. The cover 
plate 66 is held in place with screws 68, 70 that are inserted through 
corresponding threaded holes on the cover plate 66 and the shoulder region 
74 of the housing 50. 
Referring again to FIG. 3, since the bellows 56 disposed within the pump 32 
is deformable, the illustrated embodiment further includes a means for 
preventing the bellows from blocking the coolant fluid from entering the 
pump impeller 52. In the illustrated embodiment, this is accomplished by 
way of a round plate 82 which is secured to the interior of the pump 
housing 50 walls. The plate 82 includes an oil bleed-through hole 84, 
through which fluid can pass between the inlet pump chamber 76 and the 
bellows 56. In operation, an increase in fluid volume within the closed 
fluid circuit can be easily accommodated by the cooling system of the 
present invention. Specifically, coolant fluid can pass through the 
bleed-through hole 84 formed in plate 82. To the extent extra volume 
within the closed system is required, the bellows 56 will deform in an 
appropriate manner. Moreover, expansion and contraction of the bellows 
will not impede fluid flow through the closed system. 
As can be seen, the present invention provides a cooling system in which 
increases in fluid pressure and volume that occur as a result of increased 
heat dissipation are easily accommodated. The function is provided by way 
of a pump having an integrated accumulator, which eliminates the need for 
a separate and discrete accumulator component within the closed system. 
This simplifies the overall system due to a reduction of parts, and 
further enhances the reliability of the overall system because the 
potential for fluid leaks is reduced. 
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 illustrated 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.