BACKGROUND OF THE INVENTION Ultrahigh-pressure fluid has numerous uses. For example, ultrahigh- pressure fluid, generated by an ultrahigh-pressure pump, may be directed through a nozzle to form an'ultrahigh-pressure fluid jet, which may or may not be mixed with abrasive material. Depending on the characteristics of the ultrahigh-pressure fluid jet, the jet may be used to cut or clean a variety of surfaces and objects, as is understood in the art. Ultrahigh- pressure fluid may also be directed to a pressure vessel to pressure-treat a substance. For example, it is known in the art that pathogens and microorganisms in substances, for example food, may be inactivated by exposing the substances to high pressure. While generating an ultrahigh-pressure fluid jet with fluid at ambient temperature provides acceptable results in many applications, applicants believe that it may be desirable in some situations to provide pressurized fluid for use at a selected temperature, above or below ambient. The present invention is therefore directed to selectively heating or cooling ultrahigh-pressure fluid.

SUMMARY OF THE INVENTION Briefly, the present invention provides ultrahigh-pressure fluid at a selected temperature for use in any application that calls for the use of ultrahigh-pressure fluid. In preferred embodiments, the fluid is heated or cooled after it is pressurized. This is in contrast to heating or cooling the fluid prior to pressurization, which applicants believe

may negatively affect the performance of an ultrahigh-pressure pump, particularly at extreme temperatures.

In a first preferred embodiment, ultrahigh-pressure fluid flows from its source, for example an ultrahigh-pressure pump, to its point of use, through ultrahigh- pressure tubing. The ultrahigh-pressure tubing is passed through a plurality of thermally conductive blocks, each block having a first bore through which the tubing passes. Each thermally conductive block is provided with a second bore, into which is positioned a source of heating or cooling. For example, a cartridge heater may be inserted into the second bore and set to a selected temperature. Alternatively, fluid at a selected temperature may be circulated through the second bore. In this manner, each thermally conductive block works as a heat exchanger, to create a heat flux across the ultrahigh-pressure tubing, thereby increasing or decreasing the temperature of the ultrahigh-pressure fluid, as desired.

In a preferred embodiment, a thermocouple is provided in each block to sense the temperature of the block and/or the outer surface of the ultrahigh-pressure tubing, and provide feedback to a control loop, that in turn adjusts the temperature of the source of heating or cooling.

In another preferred embodiment, electrical resistance is used to heat the ultrahigh-pressure fluid as it flows through ultrahigh-pressure tubing. More particularly, a plurality of electrodes are coupled to an outer surface of the ultrahigh-pressure tubing and to a source of current. Preferably, a high current with a low voltage is used to reduce the likelihood of electric shocks. By passing a large current through the tubing, the entire cross section of the tubing effectively becomes the heat source. Without limiting the invention in any way, this invention may be particularly well suited to applications where heating to a high temperature is desired.

It will be understood that the number of blocks used and the arrangement of the blocks will be selected based on design parameters and the task at hand. For example, in a preferred embodiment, the number of blocks and the temperature of each block is selected based on the desired temperature of the ultrahigh-pressure fluid at the point of use, and the flow rate through the tubing.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic cross-sectional view of a device for heating or cooling fluid in ultrahigh-pressure tubing in accordance with a preferred embodiment of the present invention.

Figure 2 is a schematic cross-sectional view of an alternative device for heating and cooling provided in accordance with the present invention.

Figure 3 is a schematic elevational view of an alternative device provided in accordance with the present invention.

Figure 4 is a top plan view of an assembly for heating or cooling fluid in ultrahigh-pressure tubing in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION As described previously, the present invention provides ultrahigh-pressure fluid at a selected temperature. In preferred embodiments, the temperature of the fluid is changed from ambient after the fluid is pressurized to the desired pressure and is discharged from the source of pressure 20 through ultrahigh-pressure tubing. In a preferred embodiment, as illustrated in Figure 1, an apparatus 10 for changing the temperature of ultrahigh-pressure fluid includes a block 12 of thermally conductive material. While any thermally conductive material may be used, in a preferred embodiment, block 12 is made of aluminum. The block 12 is provided with a first bore 13 through which the ultrahigh- pressure tubing 11 passes. The block 12 is further provided with a second bore 14, which is provided with a source of heating or cooling. While any source of heating or cooling may be used, in a preferred embodiment, a cartridge heater 16 is positioned in the second bore 14. While any cartridge heater may be used, an example of an appropriate cartridge heater 16 is manufactured by Omega, item CIR-5069/240. Alternatively, as illustrated in Figure 2, fluid 15 at a selected temperature is circulated through tubing 17 positioned in a circuit through second bore 14.

It will be understood that ultrahigh-pressure tubing 11 is thick walled and typically made of steel. In order to get the desired heat flux across the tubing 11 to the

ultrahigh-pressure fluid flowing within it, it is desirable to monitor the system and adjust the temperature of the blocks as necessary to ensure that the ultrahigh-pressure fluid reaches the desired temperature. Although this may be accomplished in a variety of ways, in a preferred embodiment, a temperature sensor 18 such as a thermocouple is positioned on the block 12 to sense the temperature of the block and/or an outer surface of the tubing 11, and provide feedback to a control loop 19. A feedback control look 19 may in turn regulate the temperature of the source of heating or cooling, for example by adjusting the power supply to the cartridge heater. Alternatively, a temperature sensor may be positioned to sense the temperature of the fluid itself and provide feedback to the system accordingly. Monitoring the temperature of the block and/or an outer surface of the ultrahigh-pressure tubing may also be useful to ensure that the integrity of the tubing is not compromised. For example, stainless steel 316 ultrahigh-pressure tubing available from Autoclave Engineers, having an outer diameter of 3/8 inch and an inner diameter of 1/8 inch, can be taken up to approximately 450°F with a loss of approximately 10% of its fatigue life. It would therefore be an objective of the system, when in use with this particular ultrahigh-pressure tubing, to ensure that the temperature of the outer surface of the tubing does not exceed 450°F.

In an alternative embodiment, as illustrated in Figure 3, the ultrahigh- pressure fluid is heated as it flows through the ultrahigh-pressure tubing 11 using resistance heating. More particularly, as illustrated in Figure 3, electrodes 23 are placed on an outer surface of the ultrahigh-pressure tubing 11, and connected to a source of current. By passing a large current through the tubing 11, the entire cross section effectively becomes a heat source. To eliminate the risk of electric shock, a low-voltage high current is used, for example 16 volts and 3000 amps to provide a 48 kW heating system. By placing a positive electrode in the center of the tubing and a grounded negative terminal on either side of it, the risk of electric shock is further reduced. Conventional transformers may be used to provide the desired level of current.

In a preferred embodiment, as illustrated in Figure 4, a plurality of blocks 12 are provided along a length of the ultrahigh-pressure tubing 11. Each block 12 has a

construction and operation as described above. The exact number and layout of the number of blocks may be selected based on the particular application. In a preferred embodiment, the blocks 12 are mounted in a box 21 provided with insulation 22.

In operation, therefore, a volume of fluid is pressurized, for example, via an ultrahigh-pressure pump 24 shown schematically in Figure 4. Ultrahigh-pressure pumps are commercially available, for example from Flow International Corporation, the assignee of the present invention. As the pressurized fluid flows through the ultrahigh-pressure tubing 11, it passes through the plurality of thermally conductive blocks 12, in which the source of heating or cooling has been activated. By the time the ultrahigh-pressure fluid reaches an outlet 26 of the ultrahigh-pressure tubing 11, it is at a desired temperature. The ultrahigh-pressure fluid at the selected temperature is then used as desired. For example, it may be discharged through a nozzle 25, shown schematically in Figure 4. It will be understood that the ultrahigh-pressure fluid at a selected temperature may be discharged to any commercially available system for forming an ultrahigh-pressure fluid jet, for example those manufactured by Flow International Corporation. Depending on the application, the ultrahigh-pressure fluid jet at the selected temperature may be used to cut or clean, and may further entrain abrasives, depending on the desired application. Alternatively, the ultrahigh-pressure fluid at a selected temperature may be discharged to a pressure vessel to pressurize a substance contained in the pressure vessel. As described and claimed in a co- pending patent application entitled"Method and Apparatus for High-Pressure Treatment of Substances Under Controlled Temperature Conditions,"serial no., it may be desirable to pressure-treat substances, such as food, with a heated pressure media. This co-pending application is owned by Flow International Corporation, the assignee of the present invention, and the application is incorporated by reference into the present application.

As described previously, in a preferred embodiment, the temperature of one or more of the ultrahigh-pressure tubing 11, thermally conductive blocks 12, or the pressurized fluid, is measured, and the temperature of the source of heating or cooling is adjusted as needed to increase or reduce the temperature of the ultrahigh-pressure fluid. In

a preferred embodiment, the thermally conductive blocks are heated or cooled to a selected temperature that is determined as a function of the flow rate of pressurized fluid through the ultrahigh-pressure tubing 11 and the desired change in temperature of the ultrahigh- pressure fluid. For example, in the system illustrated in Figure 4, a three-phase electric power supply is used, such that eighteen thermally conductive blocks and two blanks are arranged in a grid. Extrapolating test data obtained from a four-block system, applicants believe that the temperature rise of the ultrahigh-pressure fluid may be defined by the following equation: Temperature rise = (-. 3B + 41) q +. 86B-102 where capital B is the block temperature in degrees Fahrenheit and q is the flow rate through the ultrahigh pressure tubing, in gallons per minute. It will be understood that the system shown in Figure 4 and the above equation is merely illustrative of numerous systems that may be configured in accordance with the present invention, and an assembly may be configured in accordance with the present invention using any number of blocks.

From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.