Patent Publication Number: US-6698924-B2

Title: Cooling system comprising a circular venturi

Description:
RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 09/745,588 filed Dec. 21, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a cooling system, and more particularly, it relates to a venturi used in a closed-loop cooling system to facilitate cooling a heat-generating component by raising the pressure of the fluid in the system and, therefore, the boiling point of the fluid, with the increased pressure establishing that there is flow in the closed-loop system. 
     2. Description of the Prior Art 
     In many prior art cooling systems, the fluid is absorbing heat from a heat-generating component. The fluid is conveyed to a heat exchanger, which dissipates the heat, and the fluid is then recirculated to the heat-generating component. The size of the heat exchanger is directly related to the amount of heat dissipation required. For example, in a typical X-ray system, an X-ray tube generates a tremendous amount of heat on the order of 1 KW to about 10 KW. The X-ray tube is typically cooled by a fluid that is pumped to a conventional heat exchanger where it is cooled and then pumped back to the heat-generating component. 
     In the past, if a flow rate of the fluid fell below a predetermined flow rate, the temperature of the fluid in the system would necessarily increase to the point where the fluid in the system would boil or until a limit control would turn the heat-generating component off. This boiling would sometimes cause cavitation in the pump. 
     The increase in temperature of the fluid could also result in the heat-generating component not being cooled to the desired level. This could either degrade or completely ruin the performance of the heat-generating component altogether. 
     In the typical system of the past, a flow switch was used to turn the system off when the flow rate of the fluid became too low. FIG. 6 is a schematic illustration of a venturi which will be used to describe a conventional manner of measuring the flow rate. Referring to FIG. 6, the velocity at point B is higher than at either of sections A, and the pressure (measured by the difference in level in the liquid in the two legs of the U-tube at B) is correspondingly lower. 
     Since the difference in pressure between B and A depends on the velocity, it must also depend on the quantity of fluid passing through the pipe per unit of time (flow rate in cubic feet/second equals cross-sectional area of pipe in ft 2 × the velocity in ft./second). Consequently, the pressure difference provided a measure for the flow rate. In the gradually tapered portion of the pipe downstream of B, the velocity of the fluid is reduced and the pressure in the pipe restored to the value it had before passing through the construction. A pressure differential switch would be attached to the throat and an end of the venturi to generate a flow rate measurement. This measurement would then be used to start or shut the heat-generating component down. 
     In the past, a conventional pressure differential switch measured this pressure difference in order to provide a correlating measurement of the fluid flow rate in the system. The flow rate would then be used to control the operation of the heat- generating component, such as an X-ray tube. 
     Unfortunately, the pressure differential switch of the type used in these types of cooling systems of the past and described earlier herein are expensive and require additional care when coupling to the venturi. The pressure differential switches of the past were certainly more expensive than a conventional pressure switch which simply monitors a pressure at a given point in a conduit in the closed-loop system. 
     Another problem with the venturis of the past is that they were typically situated in line in a cooling system which caused the overall dimensions of the cooling system or portion thereof to increase because of the axial length of the venturi. 
     What is needed, therefore, is a system and method that facilitates using low-cost components, such as a non-differential pressure switch (rather than a differential pressure switch), which also provides a means for increasing pressure in the closed-loop system. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the invention to provide a system and method for improving cooling of a heat-generating component, such as an X-ray tube in an X-ray system. 
     Another object of the invention is to provide a closed-loop cooling system which uses a venturi and pressure switch combination, rather than a differential pressure switch, to facilitate controlling cooling of one or more components in the system. 
     Another object of the invention is to provide a closed-loop system having a venturi whose throat is set at a predetermined pressure, such as atmospheric pressure so that the venturi can provide means for controlling cooling of the heat-generating component in the system. 
     Still another object of the invention is to provide a circular venturi which reduces the overall axial length of the venturi by providing a venturi passageway which flows about the axis of the venturi. 
     In one aspect, the invention comprises a venturi having a first wall that lies in a first plane, said first wall comprising an outlet opening, a second wall that lies in a second plane substantially parallel to said first plane, a third wall situated between the first and second walls, the third wall lying in a third plane that is substantially perpendicular to the first plane, the third wall comprising an inlet opening and a throat opening; a fourth wall situated between the outlet opening and the third wall, the fourth wall having a first end secured to the third wall adjacent the inlet opening; the first, second, third and fourth walls cooperating to define a venturi passageway from the inlet opening, past the throat opening to the outlet opening. 
     Yet another aspect of this invention comprises a cooling system for cooling a component comprising a heat rejection component, a pump for pumping fluid to the heat-rejection component and the component, the pump comprising a venturi comprising a venturi inlet coupled to an outlet of the pump; the venturi comprising a first wall that lies in a first plane, the first wall comprising the venturi outlet, a second wall that lies in a second plane substantially parallel to the first plane, a third wall situated between the first and second walls, the third wall lying in a third plane that is substantially perpendicular to the first plane, the third wall comprising an inlet opening and a throat opening, a fourth wall situated between the venturi outlet and the third wall, the fourth wall having a first end secured to the third wall adjacent the inlet opening; the first, second, third and fourth walls cooperating to define a venturi passageway from the venturi inlet, past the throat opening to the venturi outlet opening, a conduit for communicating fluid among at least the component, the heat-rejection component and the pump. 
     Still another aspect of this invention comprises an x-ray system comprising an x-ray apparatus for generating x-rays, the x-ray apparatus comprising an x-ray tube situated in an x-ray tube casing and a cooling system for cooling the x-ray tube; the cooling system comprising a heat-rejection component coupled to the x-ray tube casing, a pump for pumping fluid to the heat-rejection component and the component; the pump comprising a conduit comprising a venturi having a predetermined pressure applied at a throat of the venturi, a conduit for communicating fluid among the x-ray tube casing, the heat-rejection component and the pump, the venturi comprising a first wall that lies in a first plane, the first wall comprising a venturi outlet, a second wall that lies in a second plane substantially parallel to the first plane, a third wall that lies in a third plane between the first and second walls, the third plane being generally circular and substantially perpendicular to the first and second planes, the third wall comprising an inlet opening and a throat opening, a fourth wall situated between the venturi outlet and the third wall, the fourth wall having a first end secured to said third wall adjacent the inlet opening, the first, second, third and fourth walls cooperating to define a venturi passageway from the venturi inlet, past the throat opening to the venturi outlet. 
     Yet another aspect of this invention comprises a venturi comprising a substantially planar first wall having a venturi outlet opening, a second wall coupled to the first wall and defining a cylindrical area, the second wall comprising a venturi inlet opening and a throat opening, a third wall situated within the cylindrical area and coupled to the substantially planar first wall in opposed relation to the second wall, the third wall comprising a first end coupled to the first wall adjacent the inlet opening, the substantially planar first wall, the second wall and the third wall cooperating with a fourth wall to define a passageway in communication with the venturi inlet opening, an outlet area at the venturi outlet area and a throat area adjacent the throat opening to define a predetermined pressure. 
     Yet another aspect of this invention comprises method for cooling a component situated in a system, the method comprising the steps of coupling a component to a pump for pumping a cooling fluid through heat-rejection component, pumping the cooling fluid through a circular venturi having a throat opening subject to a predetermined pressure, and increasing a boiling point of the cooling fluid, thereby increasing an operating temperature of the X-ray system. 
     Yet another aspect of this invention comprises a pump for pumping fluid comprising a pump motor comprising an axis, a circular venturi coupled to an outlet end of the pump, the circular venturi defining a venturi passageway that flows in a plane about the axis. 
     These and other objects and advantages of the invention will be apparent from the following description, the appended claims, and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF ACCOMPANYING DRAWING 
     FIG. 1 is a schematic view of a cooling system in accordance with one embodiment of the invention showing a venturi having a throat coupled to an expansion tank or accumulator whose bladder is exposed to atmospheric pressure; 
     FIG. 2 is a sectional view of the venturi shown in FIG. 1; 
     FIG. 3 is a plan view of the venturi shown in FIG. 2; 
     FIG. 4 are plots of the relationship between pressure and flow rate at various points in the system; 
     FIG. 5 is a table representing various measurements relative to a given flow diameter at a particular flow rate; and 
     FIG. 6 is a sectional view of a venturi of the prior art. 
     FIG. 7 is a schematic diagram of another embodiment of the invention illustrating use of the venturi in a closed-loop heat exchanger that uses fluid to cool another fluid; 
     FIG. 8 is a schematic view of a cooling system in accordance with a second embodiment of the invention showing a circular venturi; 
     FIG. 9 is a perspective view of the circular venturi; 
     FIG. 10 is a view taken in the direction of arrow P in FIG. 9, showing details of the circular venturi and venturi wall; 
     FIG. 11 is a view of the venturi wall; 
     FIG. 12 is a view of the motor and circular venturi, illustrating the compactness of the embodiment; 
     FIG. 13 is a sectional view taken along the line  13 — 13  in FIG.  10 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring now to FIG. 1, a cooling system  10  is shown for cooling a component  12 . While one embodiment of the invention will be described herein relative to a cooling system for cooling the X-ray tube  12  situated inside a housing  14 . It should be appreciated that the features of the invention may be used for cooling any heat-generating component in the closed-loop system  10 . 
     As mentioned, the cooling system  10  comprises a heat-generating component, such as the X-ray tube  12 , and a heat exchanger or heat-rejection component  16 , which in the embodiment being described is a heat exchanger available from Lytron of Woburn, Mass. 
     The system  10  further comprises a fluid pump  22  which is coupled to housing  14  via conduit  18 . In the embodiment being described, the pump  22  pumps fluid, such as a coolant, through the various conduits and components of system  10  in order to cool the components  12 . It has been found that one suitable pump  22  is the pump Model No. H0060.2A-11 available from Tark. Inc. of Dayton, Ohio. In the embodiment being described, the pump  22  is capable of pumping on the order of between 0 and 10 gallons per minute, but it should be appreciated that other size pumps may be provided, depending on the cooling requirements, size of the conduits in the system  10  and the like. 
     In the embodiment being described, the throat  36  of venturi  30  is subject to a predetermined pressure, such as atmospheric pressure. This predetermined pressure is selected to facilitate increasing the fluid pressure in the system  10  which, in turn, facilitates increasing a boiling point of the fluid which has been found to facilitate reducing or preventing cavitation in the pump  22 . 
     The system  10  further comprises a venturi  30  having an inlet end  32 , an outlet end  34  and a throat  36 . For ease of description, the venturi  30  is shown in FIG. 2 as having downstream port A, upstream port B, and throat port  40  that are described later herein. The venturi  30  is coupled to heat-rejection component  16  via conduit  26  and pump  22  via conduit  28 , as illustrated in FIG.  1 . In the embodiment being described, the throat  36  of venturi  30  is coupled to an expansion tank or accumulator  38  at an inlet port  40  of the accumulator  38 , as shown in FIG.  1 . The accumulator  38  comprises a bladder  42  having a first side  42   a  exposed to atmosphere via port  44 . A second side  42   b  of bladder  42  is exposed or subject to pressure Pt, which is the pressure at the throat  36  of venturi  30 , which is also atmospheric. 
     An advantage of this invention is that the venturi causes higher pressures and, therefore, a higher operating fluid temperature without boiling. This creates a larger temperature differential that maximizes the heat transfer capabilities of heat exchanger  16 . Stated another way, raising a boiling point of the fluid in the system  10  permits higher fluid temperatures, which maximizes the heat exchanging capability of heat exchanger  16 . These features of the invention will be explored later herein. 
     The system  10  further comprises a switch  46  situated adjacent (at port A in FIG. 2) venturi  30  in conduit  28 , as illustrated in FIG.  1 . In the embodiment shown in FIG. 1, the switch  46  is a non-differential pressure switch  46  that is located downstream of the venturi  30 , but upstream of pump  22 , but it could be situated upstream of venturi  30  (at port B illustrated in FIG. 2) if desired. As shown in FIG. 1, the switch is open, via throat  45 , to atmosphere and measures fluid pressure relative to atmospheric pressure. Therefore, it should be appreciated that because the pressure Pt at the throat  36  is also at atmospheric pressure, a difference in the pressure at throat  36  compared to the pressure sensed by switch  46  can be determined. This differential pressure is directly proportionally related to the flow in the system  10 . Consequently, it provides a measurement of a flow rate in the system  10 . 
     If necessary, either port A or port B may be closed after the switch is situated downstream or upstream, respectively, of said venturi  36 . It has been found that the use of the pressure switch, rather than a differential pressure switch, is advantageous because of its economical cost and relatively simple design and performance reliability. It should be appreciated that the switch  46  is coupled to an electronic control unit (“ECU”)  50 . The switch  46  provides a pressure signal corresponding to a flow rate of the fluid in system  10 . As mentioned earlier, the switch  46  may be located either upstream or downstream of the venturi  30 . This signal is received by ECU  50 , which is coupled to pressure switch  46  and component  12 , in order to monitor the temperature of the fluid and flow through component  12  in the system  10 . Thus, for example, when a flow rate of the fluid in system  10  is below a predetermined rate, such as 5 GPM. In this embodiment, then ECU  50  may respond by turning component  12  off so that it does not overheat. 
     Thus, the switch  46  cooperates with venturi  30  to provide, in effect, a pressure differential switch or flow switch which may be used by ECU  50  to monitor and control the temperature and flow rate of the fluid in the closed-loop system  10  in order to control the heating and cooling of component  12 . It should also be appreciated that the switch  46  may be a conventional pressure switch, available from Whitman of Bristol, Conn. 
     The expansion tank or accumulator  38 , which is maintained at atmospheric pressure, is connected to the throat  36  of venturi  30 , with the venturi  30  connected in series with the main circulating loop of the closed-loop system  10 . The venturi  30  and switch  46  cooperate to automatically control the pressure and temperature in the circulating system  10  by monitoring the flow of the fluid in the system  10 . The pressure differential between the throat  36  and, for example, the inlet end  32  of venturi  30  remains substantially constant, as long as the flow is substantially constant. 
     Because the pressure Pt at the throat  36  is held at atmospheric pressure, the subsequent pressure at outlet end  34  may be calculated using the formula (Vt−Ve)2/2 g, where Ve is a velocity of the fluid at, for example, end  34  of venturi  30  and Vt is a velocity of the fluid at the throat  36  of venturi  30 . 
     The ECU  50  may use the determined measurement of flow from switch  46  to cause the component  12  to be turned off or on if the flow rate of the fluid in system  10  is below or above, respectively, a predetermined flow rate. In this regard, switch  46  generates a signal responsive to pressure (and indicative of the flow rate) at end  34 . This signal is received by ECU  50 , which, in turn, causes the component  12  to be turned off or on as desired. Advantageously, this permits the flow rate of the fluid in the system  10  to be monitored such that if the flow rate decreases, thereby causing the cooling capability of the fluid in the closed-loop system to decrease, then the ECU  50  will respond by shutting the heat-generating component  12  off before it is damaged by excessive heat or before other problems occur resulting from excessive temperatures. 
     Advantageously, it should be appreciated that the use of the venturi  30  having the throat  36  subject to atmospheric pressure via the expansion tank  38  in combination with the pressure switch  46  provides a convenient and relatively inexpensive way to measure the flow rate of the fluid in the system  10  thereby eliminating the need for a pressure differential switch of the type used in the past. This also provides the ability to monitor the flow rate of the fluid in the closed-loop system  10 . 
     FIG. 4 is a diagram illustrating five locations describing various properties of the fluid as it moves through the closed-loop system  10 . 
     Neglecting minor temperature and pressure losses in the conduits  18 ,  20 ,  26  and  28 . The following Table I gives the relative properties (velocity, gauge pressure, temperature) when a flow rate of the fluid is held constant at four gallons per minute. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE I 
               
               
                   
               
               
                   
                   
                   
                 Gage 
                   
               
               
                   
                 Location 
                 Velocity 
                 Pressure 
                 Temperature 
               
               
                 GPM 
                 (FIG. 1) 
                 (fps) 
                 (psi) 
                 (F.) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 4 
                 32 
                 8 
                 26 
                 160 
               
               
                 4 
                 36 
                 64  
                 0 
                 160 
               
               
                 4 
                 34 
                 8 
                 24.7 
                 160 
               
               
                 4 
                 18 
                 8 
                 40 
                 160 
               
               
                 4 
                 20 
                 8 
                 35 
                 167 
               
               
                   
               
            
           
         
       
     
     The following Table II provides, among other things, different venturi  30  gauge pressures and fluid velocities resulting from flow rates of between zero to 4 gallons per minute in the illustration being described. Note that the pressure at the throat  36  of venturi  30  is always held at atmospheric pressure when the expansion tank  38  is coupled to the throat  36  as illustrated in FIG.  1 . 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE II 
               
               
                   
               
               
                 Loca- 
                   
                   
                   
                   
                   
                   
               
               
                 tion 
                 32 
                 32 
                 36 
                 36 
                 34 
                 34 
               
               
                 (FIG. 1) 
                 Inlet 
                 Inlet 
                 Throat 
                 Throat 
                 Outlet 
                 Outlet 
               
               
                 Flow 
                 Velocity 
                 Pressure 
                 Velocity 
                 Pressure 
                 Velocity 
                 Pressure 
               
               
                 rate 
                 (ft/sec) 
                 (psi) 
                 (ft/sec) 
                 (psi) 
                 (ft/sec) 
                 (psi) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 1 
                 2 
                 1.7 
                 16 
                 0 
                 2 
                 1.6 
               
               
                 2 
                 4 
                 7 
                 32 
                 0 
                 4 
                 6.65 
               
               
                 4 
                 8 
                 26 
                 64 
                 0 
                 8 
                 24.7 
               
               
                   
               
            
           
         
       
     
     Note from the Tables I and II that when there is no flow, the fluid pressure throughout the closed-loop system  10  is that of the expansion tank or atmospheric pressure. In the closed-loop system  10 , Table I shows the fluid at a minimum pressure at the venturi throat  36  and maximum on a discharge or outlet side  22   a  of pump  22 . There is a pressure loss after entering and leaving the heat-generating component  12 , such as the X-ray tube, heat exchanger  16  and venturi  30 . Velocity is held substantially constant throughout the system  10  because the inner diameter of the conduits  18 ,  20 ,  26  and  28  are substantially the same. Fluid velocity changes only when an area of the passage it travels in is either increased or decreased, such as when the fluid is pumped from ends  32  at  34  towards and away from throat  36  of venturi  30 . 
     If the system  10  is assumed to reach a steady state, then a temperature of the fluid in the system  10  will increase from a value before the heat-generating component  12  to a higher value after exiting the heat-generating component  12 . The higher temperature fluid will cool back down to the original temperature after exiting the heat exchanger  16 , neglecting small temperature changes throughout the conduits  18 ,  20 ,  26  and  28  of the system  10 . 
     FIGS. 2 and 3 illustrate various features and measurements of the venturi  30  with the various dimensions at points D 1 -D 16  identified in the following Table III: 
     
       
         
           
               
               
               
             
               
                   
                 TABLE III 
               
               
                   
                   
               
               
                   
                 Dimension 
                 Size 
               
               
                   
                   
               
             
            
               
                   
                 D1  
                 1.5″ 
               
               
                   
                 D2  
                 1.71″ 
               
               
                   
                 D3  
                 0.84″ 
               
               
                   
                 D4  
                 1.5″ 
               
               
                   
                 D5  
                 9.5″ 
               
               
                   
                 D6  
                 0.622″ 
               
               
                   
                 D7  
                 10.5E 
               
               
                   
                 D8  
                 2.0″ 
               
               
                   
                 D9  
                 1.172″ 
               
               
                   
                 D10 
                 0.2″ 
               
               
                   
                 D11 
                 0.188″ 
               
               
                   
                 D12 
                 4.145″ 
               
               
                   
                 D13 
                 0.622″ 
               
               
                   
                 D14 
                 3E 
               
               
                   
                 D15 
                 ¼″ 
               
               
                   
                   
                 NPIF hole at 3 locations 
               
               
                   
                 D16 
                 0.1″ through hole at 3 locations 
               
               
                   
                   
                 concentric with D15 holes 
               
               
                   
                   
               
            
           
         
       
     
     It should be appreciated that the values represented in Table III are merely representative for the embodiment being described. 
     Table IV in FIG. 5 is an illustration of the results of another venturi  30  (not shown) at various flow rates using varying flow rate diameters at the throat  36  (represented by dimension D 11  in FIG.  2 ). 
     It should be appreciated that by holding the pressure at the throat  36  at the predetermined pressure, which in the embodiment being described is atmospheric pressure, the velocity of the fluid exiting end  34  of venturi  30  can be consistently and accurately determined using the pressure switch  46 , rather than a differential pressure switch (now shown) which operates off a differential pressure between the throat  36  and the inlet end  32  or outlet end  34 . Instead of using a differential pressure device (not shown) to measure flow in the system, the expansion tank, when attached to the throat  36  of venturi  30 , causes the fluid in the system  10  to be at atmospheric pressure when there is zero flow. For any given flow rate, the pressure at the throat  36  of venturi  30  remains at atmospheric pressure, but a fluid velocity is developed for each cross-sectional area in the closed-loop system  10 . Since the venturi throat  36  of venturi  30  is smaller than the venturi inlet  32  and the venturi outlet  34 , the velocity at the throat will be higher than the velocity at the inlet  32  or outlet  34 . This velocity difference creates a pressure difference between the venturi throat  36  and the ends  32  and  34 , which mandates that the pressure at the throat  36  be lower than the pressure at the ends  32  and  34 . Stated another way, the pressure at the ends  32  and  34  must be higher than the pressure at the throat  36  which is held at atmospheric pressure. 
     Consequently, the pressure at the ends  32  and  34  must be greater than atmospheric pressure when there is flow in the system  10 . This phenomenon causes the overall pressure in the system  10  to increase, which in effect, raises the effective boiling point of the fluid in the system  10 . Because the boiling point of the fluid in the system  10  has been raised, this facilitates avoid cavitation in the pump  22  which occurs when the fluid in the system  10  achieves its boiling point. 
     Another feature of the invention is that because the boiling point of the fluid is effectively raised in the closed-loop system  10 , the higher fluid temperature creates a larger temperature differential and enhances heat transfer for a given size heat exchanger  16 . In the embodiment being described, the specific volume of vaporized fluid is reduced by an increase in the system pressure. By way of example, water&#39;s specific volume is 11.9 ft.3/lbs. at 35 psia and 26.8 ft.3/lbs. at atmospheric pressure. Thus, increasing the system pressure results in a reduction of the specific volume of the vaporized fluid. In the embodiment being described, the fluid is a liquid such as water, but it may be any suitable fluid-cooling medium, such as ethylene glycol and water, oil or other heat transfer fluids, such as Syltherm available from Dow Chemical. 
     Advantageously, the higher pressure enabled by venturi  30  permits the use of a simple pressure switch  46  to act as a flow switch. This switch  46  could be placed at the venturi outlet  34  (for example, at port A in FIG.  2 ), as illustrated in FIG. 1, or at the inlet  32  (for example, at port B in FIG.  2 ). 
     Note that a single pressure switch whose reference is atmospheric pressure is preferable. Because its pressure is atmospheric pressure, it does not need to be coupled to the throat  36 , which is also at atmospheric pressure. Once the pressure is determined at the outlet  34  or inlet  32 , a flow rate can be calculated using the formula mentioned earlier herein, thereby eliminating a need for a differential pressure switch of the type used in the past. A method for increasing pressure in the closed-loop system  10  will now be described. 
     The method comprises the steps of situating the venturi in the closed-loop system  10 . In the embodiment being described, the venturi is situated in series in the system  10  as shown. 
     A predetermined pressure, such as atmospheric pressure in the embodiment being described, is then established at the throat  36  of the venturi  30 . The method further uses the pump  22  to cause flow in the system  10  in order to increase pressure in the system, thereby increasing a flow rate of the fluid in the system  10  such that the pressure at the inlet  32  and outlet  34  relative to the throat  36 , which is held at a predetermined pressure, such as atmospheric pressure, is caused to be increased. 
     In the embodiment being described, the predetermined pressure at the throat  36  is established to be the atmospheric pressure, but it should be appreciated that a pressure other than atmospheric pressure may be used, depending on the pressures desired in the system  10 . Advantageously, this system and method provides an improved means for cooling a heat-generating component utilizing a simple pressure switch  46  and venturi  30  combination to provide, in effect, a switch for generating a signal when a flow rate achieves a predetermined rate. This signal may be received by ECU  50 , and in turn, used to control the operation of heat-generating component  12  to ensure that the heat-generating component  12  does not overheat. 
     Referring to FIGS. 8-13 another embodiment of the invention is illustrated wherein like elements to those described with reference to the previous embodiment are labeled with the same reference numerals, except that a prime (“′”) mark has been added to the numerals shown in FIGS. 8-13. As illustrated in FIGS. 8 and 12, the system  10 ′ comprises a fluid pump  101 ′ having an impeller  103 ′ (FIG. 12) for pumping fluid, such as a coolant, received from an inlet conduit  113 ′, through an opening or outlet  105   a ′ of a circular venturi  105 ′, and through an outlet conduit  107 ′. 
     In the embodiment being described, the circular venturi  105 ′ comprises an inlet conduit  113 ′ receives fluid from the conduit  26 ′ and from the heat-rejection component  16 ′, as best illustrated in FIG.  8 . The circular venturi  105 ′ further comprises a throat conduit  109 ′ (FIGS. 8,  9  and  10 ) that defines a throat opening  110 ′. 
     As best illustrated in FIGS. 12 and 13, the circular venturi  105 ′ comprises a first planer wall  112 ′ that lies in a first plane FP (FIG. 12) and a second wall  114 ′ that lies in a second plane SP. Note that the second plane SP is substantially parallel to the first plane FP, as illustrated in FIG.  12 . 
     The circular venturi  105 ′ further comprises a third wall  116 ′, which in the embodiment being defines an outer wall of the venturi  105 ′. Note that the third wall  116 ′ comprises an inlet opening  113   a ′ (FIG. 13) defined by inlet conduit  113 ′ and the throat opening  110 ′ defined by the throat conduit  109 ′. Note that the third wall  116 ′ lies in a circular plane CP that is substantially perpendicular to the first plane FP and second plane SP as best illustrated in FIG.  9 . 
     The venturi  105 ′ further comprises a fourth wall  118 ′ situated between the outlet opening  105   a ′ defined by the wall  105   b ′ (FIGS.  9  and  13 ). Notice that the fourth wall  118 ′ has a first end  118   a ′ which is coupled to the wall  116 ′ adjacent the inlet opening  113   a ′ defined by the inlet conduit  113 ′, as best illustrated in FIGS. 9 and 10. Notice that the second end  118   b ′ terminates between the wall  116 ′ and outlet opening  105   a ′. Note that the walls  112 ′,  114 ′,  116 ′ and  118 ′ cooperate (as best illustrated in FIGS. 9-11) to define a venturi passageway  121 ′ comprising a venturi inlet area  120 ′, a venturi throat area  122 ′, and venturi outlet area  124 ′. Note that in the sectional view illustrated in FIG. 13, the venturi passageway  121 ′ is defined by at least a portion of walls  112 ′,  114 ′,  116 ′ and  118 ′ in cross section, when viewed in a direction that is perpendicular to a direction of the fluid flow as defined by the walls  112 ′,  114 ′,  116 ′ and  118 ′. Thus, it should be appreciated that the fourth wall  118 ′ cooperates with the walls  112 ′- 116 ′ to define the venturi passageway  121 ′ which functions in a manner that is similar to the venturi  30  illustrated in the first embodiments shown in FIGS. 1-7. In this embodiment, the conduits  107 ′,  109 ′,  113 ′ and the walls  112 ′- 116 ′ are fastened, secured or fixed together by suitable means, such as welding or any other suitable means. Once assembled, the venturi  105 ′ is situated into the system  10 ′, as illustrated in FIG.  8 . 
     As best illustrated in FIG. 8, the throat conduit  109 ′ is coupled to the accumulator  38 ′ which functions in the manner described earlier herein relative to the embodiment described in FIGS. 1-7. The system  10 ′ of the embodiment described in FIGS. 8-13 comprises the switch  46 ′ and ECU  50 ′, which is coupled to the switch  46 ′, motor  101 ′, and the heat-generating component, such as the x-ray tube  112 ′. The ECU  50 ′ may use the determined measurement of flow from switch  46 ′ to cause the component  12 ′ to be turned off or on if the flow rate of the fluid in system  10 ′ is below or above, respectively, a predetermined flow rate. In this regard, switch  46 ′ generates a signal responsive to pressure (and indicative of the flow rate) from the heat-rejection component  16 ′. This signal is received by ECU  50 ′ which, in turn, causes the component  12 ′ to be turned off or on as desired. As with the embodiment described earlier herein, this permits the flow rate of the fluid in the system  10 ′ to be monitored such that if the flow rate decreases, thereby causing the cooling capability of the fluid in the closed-loop system  10 ′ to decrease, then the ECU  50 ′ will respond by shutting the heat-generating component  12 ′ off before it is damaged by excessive heat or before other problems occur resulting from excessive temperatures. 
     In this embodiment, the throat area  122 ′ of venturi  105 ′ is subject to a predetermined pressure, such as atmospheric pressure through accumulator  38 ′. This predetermined pressure is selected to facilitate increasing the fluid pressure in the system  10 ′ which, in turn, facilitates controlling a boiling point of the fluid in the system  10 ′. Controlling the boiling point facilitates reducing or preventing cavitation in the pump  101 ′. 
     As with the embodiment described earlier herein, the throat area  122 ′ of venturi  105 ′ is coupled to the expansion tank or accumulator  38 ′ at an inlet port  40 ′ of the accumulator  38 ′ which is coupled to the throat conduit  109 ′, as best illustrated in FIG.  8 . The accumulator  38 ′ comprises a bladder  42 ′ having a first side  42   a ′ exposed to atmosphere via port  44 ′. A second side  42   b ′ of bladder  42 ′ is exposed or subject to pressure PT 2  which is the pressure at the throat  122 ′ of the venturi  105 ′. 
     As mentioned earlier, the system  10 ′ comprises the switch  46 ′ that is situated between the inlet conduit  113 ′ and the heat-rejection component  16 ′ in the embodiment now being described and as illustrated in FIG.  8 . It should be appreciated that, as with the embodiment described earlier herein, the switch  46 ′ is a non-differential pressure switch  46 ′ that is located upstream of the venturi  105 ′, but downstream of the heat-rejection component  16 ′, but it could be situated downstream of the venturi  105  ′, if desired. As shown in FIG. 8, the switch  46 ′ is open, via throat  45 ′, to atmosphere and measures fluid pressure relative to atmospheric pressure. Therefore, it should be appreciated that because the pressure T 2  at the throat  122 ′ is also at atmospheric pressure a difference in the pressure at  122 ′ compared to the pressure sensed by switch  46 ′ can be determined. This pressure differential is directly proportionally related to the flow in the system  10 ′. As with the embodiment described earlier, this provides a measurement of a flow rate in the system  10 ′. 
     As with the embodiment described earlier herein, the use of the venturi  105 ′ having the throat  122 ′ subject to atmospheric pressure via the expansion tank  38 ′ in combination with the switch  46 ′ provides a convenient and relatively inexpensive way to measure the flow rate of the fluid in the system  10 ′, thereby eliminating the need for pressure differential switch of the type used in the past. This also provides the ability to monitor the flow rate in the closed-loop system  10 ′ to shut down the heat-generating component in the system  10 ′ if necessary. For ease of illustration, minor temperature and pressure losses in the conduits  18 ′,  20 ′, and  26 ′ the following Table IV gives the relative properties (velocity, gauge pressure, temperature) when a flow rate of a fluid is held constant at 4 gallons per minute: 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE IV 
               
               
                   
               
               
                   
                   
                   
                 Gage 
                   
               
               
                   
                 Location 
                 Velocity 
                 Pressure 
                 Temperature 
               
               
                 GPM 
                 (FIG. 8) 
                 (fps) 
                 (psi) 
                 (F.) 
               
               
                   
               
             
            
               
                 4 
                 120′ 
                 5.5 
                 15 
                 160° F. 
               
               
                 4 
                 122′ 
                 47.0  
                  0 
                 160° F. 
               
               
                 4 
                 121′ 
                 5.5 
                 12 
                 160° F. 
               
               
                 4 
                 107′ 
                 5.3 
                 27 
                 160° F. 
               
               
                 4 
                  20′ 
                 5.3 
                 23 
                 160° F. 
               
               
                   
               
            
           
         
       
     
     The following Table V provides, among other things, different venturi  105 ′ gauge pressure and fluid velocities resulting from flow rates of between 0-4 gallons per minute in the illustration being described. Note that the pressure at the throat  122 ′ of venturi  105 ′ is always held at atmospheric pressure in the expansion tank  38 ′ is throat  122 ′ as illustrated in FIG.  8 . 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE V 
               
               
                   
               
               
                 Loca- 
                   
                   
                   
                   
                   
                   
               
               
                 tion 
                 120′ 
                 120′ 
                 122′ 
                 122′ 
                 121′ 
                 121′ 
               
               
                 (FIG. 8) 
                 Inlet 
                 Inlet 
                 Throat 
                 Throat 
                 Outlet 
                 Outlet 
               
               
                 Flow 
                 Velocity 
                 Pressure 
                 Velocity 
                 Pressure 
                 Velocity 
                 Pressure 
               
               
                 rate 
                 (ft/sec) 
                 (psi) 
                 (ft/sec) 
                 (psi) 
                 (ft/sec) 
                 (psi) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 1 
                 1.3 
                 1 
                 12 
                 0 
                 1.3 
                 1.0 
               
               
                 2 
                 2.6 
                 4 
                 24 
                 0 
                 2.6 
                 3.0 
               
               
                 4 
                 5.5 
                 15 
                 47 
                 0 
                 5.5 
                 12 
               
               
                   
               
            
           
         
       
     
     Note from the Tables IV and V that when there is no flow, the fluid pressure throughout the closed-loop system  10 ′ is that of the expansion tank or atmospheric pressure. In the closed-loop system  10 ′ the Table IV shows the fluid at a minimum pressure at the venturi throat  122 ′, and a maximum on a discharge or outlet end  107 ′ of pump  101 ′. There is a pressure loss after entering and leaving the heat-generating component  12 ′ such as the x-ray tube heat exchanger  16 ′, and venturi  105 ′. Velocity is held substantially constant throughout the system  10 ′ because an inner diameter of the conduits  18 ′,  20 ′,  26 ′, conduits  107 ′ and  109 ′ and diameter of wall  105   b ′ (FIG. 9) are substantially the same. The fluid velocity changes only when an area of the passage it travels in is either increased or decreased, such as when the fluid is pumped between conduits  107 ′ and  113 ′ towards and away from throat  122 ′ of venturi  105 ′. 
     FIGS. 10 and 11 illustrate features and dimensions of the venturi  105 ′ at various points F 1 -F 21  identified in the following Table VI: 
     
       
         
           
               
               
               
             
               
                   
                 TABLE VI 
               
               
                   
                   
               
               
                   
                 Dimension 
                 Size 
               
               
                   
                   
               
             
            
               
                   
                 F1 
                 164° 
               
               
                   
                 F2 
                 2.42″ 
               
               
                   
                 F3 
                 0.37″ 
               
               
                   
                 F3a 
                 0.37″ 
               
               
                   
                 F4 
                 0.63″ 
               
               
                   
                 F5 
                 0.07″ 
               
               
                   
                 F6 
                 0.19″ 
               
               
                   
                 F7 
                 2.90″ 
               
               
                   
                 F8 
                 8.33″ 
               
               
                   
                 F9 
                 0.043″ 
               
               
                   
                 F10 
                 25° 
               
               
                   
                 F11 
                 68° 
               
               
                   
                 F12 
                 76° 
               
               
                   
                 F13 
                 3.50″ dia. 
               
               
                   
                 F14 
                 10° 
               
               
                   
                 F15 
                 1.34″ 
               
               
                   
                 F16 
                 0.70″ 
               
               
                   
                 F17 
                 117° 
               
               
                   
                 F19 
                 0.05″ 
               
               
                   
                 F20 
                 1.51″ 
               
               
                   
                 F21 
                 0.55″ 
               
               
                   
                   
               
            
           
         
       
     
     It should be appreciated that the values represented in Table VI are merely representative for the embodiment being described. 
     As with the embodiment described earlier herein, note that by holding the pressure at the throat  122 ′ at the predetermined pressure, which in the embodiment being described is atmospheric pressure, the velocity of the fluid entering conduit  113 ′ at venturi  105 ′ can be consistently and accurately determined using the pressure switch  46 ′, rather than a differential switch (not shown) which operates off a differential pressure between the throat  122 ′ and the inlet conduit  113 ′ and venturi outlet  105   a ′. Consequently, the pressure at the outlet  105   a ′ and inlet conduit  113 ′ must be greater than atmospheric pressure when there is flow in the system  10 ′. As mentioned earlier, this phenomenon causes the overall pressure system in the system  10 ′ to increase, which in effect, raises the effective boiling point of fluid in the system  10 ′. Because the boiling point of the fluid in the system  10 ′ has been raised, this facilitates avoiding cavitation in the pump  101 ′, which can occur when the fluid in the system  10 ′ achieves its boiling point. As with the embodiment described earlier, another feature of the invention is that because the boiling point of the fluid is effectively raised in the closed-loop system  10 ′, the higher fluid temperature creates a larger temperature differential and enhances heat transfer for a given size exchanger  16 ′. In the embodiment being described, the specific volume of vaporized fluid is reduced by an increase in the system pressure which results in a reduction of the specific volume of the vaporized fluid, as explained earlier herein. 
     In the embodiment being described, the fluid is a liquid such as water, but may be any suitable fluid-cooling medium, such as ethylene glycol and water, oil, water or other heat transfer fluids, such as Syltherm available from Dow Chemical. Also, the pump  101 ′ is a Model No. HDD60.8A-11 available from Tark, Inc. Advantageously, the higher pressure enabled by venturi  30 ′ permits the use of a single pressure switch  46 ′ to act as a flow switch. 
     Advantageously, providing a circular venturi having a venturi passageway of flow path that flows about an axis of the pump  101 ′ provides a convenient means and method for reducing the overall space requirements of the pump  101 ′ and the venturi  105 ′ because the length of the venturi  105 ′ is reduced. Thus, note the axial dimension of F 4  (FIG. 13) of venturi  105 ′ of the second embodiment is considerably shorter than the axial dimension D 5  (FIG.  3 ). This makes the circular venturi  105 ′ advantageous when axial space requirements of the system  10 ′ are a concern. 
     While the method herein described, and the form of apparatus for carrying this method into effect, constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to this precise method and form of apparatus, and that changes may be made in either without departing from the scope of the invention, which is defined in the appended claims. For example, while the systems  10  and  10 ′ have been shown and described for use relative to an X-ray cooling system of the type used in, for example, CT Scanners, Diagnostic X-Ray tube used in “C”-Arms, and industrial X-Ray tubes used in non-destructive testing and bomb scanners, it is envisioned that the systems  10  and  10 ′ may be used with an internal combustion engine, cooling system, a hydronic boiler or any closed loop heat exchanger that uses a fluid to cool another fluid. The embodiments illustrated in FIGS. 1-6 and  8 - 13 , may be used with the system  100  illustrated in FIG.  7 . As illustrated in FIG. 7, the system  100  comprises a heat exchanger  102 , such as a liquid to air heat exchanger, and a liquid-to-liquid heat exchanger  104  for cooling a fluid, such as oil, from a heat-generating component  106 . A venturi and switch  49 ,  49 ′ (FIGS. 1 and 7) couples the heat rejection component  104  to the pump  108 . Note that either the venturi  30  or venturi  105 ′ may be provided to achieve the advantages described earlier herein. For example, the venturi  30  of the first embodiment of FIGS. 1-7 or venturi  105 ′ of the embodiment shown in FIGS. 8-13 enables higher system pressure and higher operating fluid temperatures that maximize heat transfer capabilities of heat exchangers  102  and/or  104 . This design also facilitates bringing system pressure back to atmospheric pressure at substantially the same time as when the flow rate is reduced to zero.