Abstract:
Systems and methods for cooling a component within a housing adapted for subsurface disposal using a vortex tube. The housing contains a first pressure chamber; a vortex tube coupled to the first pressure chamber; a cooling chamber coupled to the vortex tube; and a second pressure chambercoupled to the cooling chamber; wherein the pressure chambers are adapted to stimulate a cool fluid flow from the vortex tube into the cooling chamber. A cooling method entails disposing the component to be cooled within the cooling chamber and adapting the system pressure chambers to stimulate a cool fluid flow from a vortex tube into the cooling chamber.

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates generally to cooling systems and techniques using vortex tubes. 
   2. Background Art 
   The use of vortex tubes (also know as the “Ranque Tube”, “Hilsch Tube”, “Ranque-Hilsch Tube”, and “Maxwell&#39;s Demon”) to implement systems for emitting colder and hotter gas streams is well known (See U.S. Pat. Nos. 1,952,281, 3,208,229, 4,339,926). A vortex tube offers a simple method of cooling using compressed air. Compressed air at high pressure is passed through a nozzle that sets the air in a vortex motion inside the vortex tube. A valve at one end of the tube allows the warmed air from this first vortex to escape. Some of the air that does not escape heads back up the tube as a second vortex inside the low pressure inner area of the larger first vortex. The inner vortex loses heat and exits through the other end of the tube as a cold air stream. Further description of vortex tubes can be found on the World Wide Web (See http://www.exair.com/vortextube/vt_page.htm). Thus the vortex tube takes compressed air as an input and outputs two streams of air, one heated and the other cooled. 
   In hydrocarbon exploration operations, there is a need to use electronic devices at temperatures much higher than their rated operational temperature range. With oil wells being drilled deeper, the operating temperatures for these devices keeps increasing. Besides self-generated heat, conventional electronics used in the computer and communications industry generally do not have a need to operate devices at high temperatures. For this reason, most commercial electronic devices are rated only up to 85° C. (commercial rating). 
   Modern tools or instruments designed for subsurface logging operations are highly sophisticated and use electronics extensively. In order to use devices that are commercially rated in a subsurface or downhole environment, it is highly desirable to have a cooling system capable of maintaining the electronics within their operational range while disposed downhole. Conventional logging techniques include instruments for “wireline” logging, logging-while-drilling (LWD) or measurement-while-drilling (MWD), logging-while-tripping (LWT), coiled tubing, and reservoir monitoring applications. These logging techniques are well known in the art. 
   Several approaches to extending the life of electronics in hot environments have been proposed in the past. U.S. Pat. No. 4,400,858 describes retainer clips that serve as heat sinks to conduct heat from the electronics to the tool housing to minimize temperature rise in the devices. U.S. Pat. No. 4,722,026 describes a method for reducing the temperature rise of critical devices by placing them in a dewar. U.S. Pat. No. 4,513,352 describes a dewar combined with heat conducting pipes to reduce the heating of electronics in a geothermal borehole. U.S. Pat. No. 4,375,157 describes a downhole refrigerator to protect electronics in the drilling environment. U.S. Pat. No. 5,720,342 proposes the use of a thermoelectric cooler attached directly to a multi chip module to cool the module. U.S. Pat. No. 5,730,217 describes a thermoelectric cooler used to cool electronics disposed in a vacuum to reduce heat gain from the ambient environment. Other methods to cool electronics using thermoelectric coolers are proposed in U.S. Pat. Nos. 5,931,000, 5,547,028 and 6,424,533. U.S. Pat. No. 6,341,498 proposes a cooling system including a container for a liquid and a sorbent to transfer heat from the electronics to the wellbore. U.S. Pat. No. 6,401,463 describes a cooling and heating system using a vortex tube to cool an equipment enclosure. 
   Vortex tubes have also been implemented in downhole instruments for cooling purposes. U.S. Pat. No. 2,861,780 describes a system using vortex tubes to cool the cutters of drill bits. U.S. Pat. No. 4,287,957 describes another system using a vortex tube to cool tool components. A drawback of the system proposed in the &#39;957 patent is the need for a pressurized gas source at the surface for continuous gas feed, making the system impractical for many subsurface operations. 
   There remains a need for improved cooling techniques to maintain components at a temperature below the ambient temperatures experienced in hot environments, particularly electronics housed in instruments adapted for subsurface disposal, where rapid temperature variations are encountered. 
   SUMMARY OF INVENTION 
   The invention provides a vortex tube cooling system. The system including a housing adapted for subsurface disposal, the housing containing a first pressure chamber; a vortex tube coupled to the first pressure chamber; a cooling chamber coupled to the vortex tube; and a second pressure chambercoupled to the cooling chamber; wherein the pressure chambers are adapted to stimulate a cool fluid flow from the vortex tube into the cooling chamber. 
   The invention provides a vortex tube cooling system. The system includes a housing adapted for subsurface disposal, the housing containing: a first pressure chamber adapted to sustain high fluid pressure; a vortex tube coupled to the first pressure chamber; a cooling chamber coupled to the vortex tube; a second pressure chamber coupled to the cooling chamber and adapted to sustain lower fluid pressure in relation to the first pressure chamber; at least one valve linked between the first pressure chamber and the cooling chamber to regulate fluid flow to stimulate a cool fluid flow from the vortex tube into the cooling chamber. 
   The invention provides a method for cooling a component within a housing adapted for subsurface disposal. The method includes equipping the housing with: a first pressure chamber; a vortex tube coupled to the first pressure chamber; a cooling chamber coupled to the vortex tube; a second pressure chambercoupled to the cooling chamber; disposing the component to be cooled within the cooling chamber; and adapting the pressure chambers to stimulate a cool fluid flow from the vortex tube into the cooling chamber. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
       FIG. 1  shows a downhole instrument disposed in a borehole and equipped with a vortex tube cooling system in accord with the invention. 
       FIG. 2  is a schematic diagram of an active vortex tube cooling system including a compressor in accord with the invention. 
       FIG. 3  is a schematic diagram of a passive vortex tube cooling system in accord with the invention. 
       FIG. 4  is a schematic diagram of another passive vortex tube cooling system in accord with the invention. 
       FIG. 5  is a schematic diagram of an active vortex tube cooling system providing an extended operational capability in accord with the invention. 
       FIG. 6  illustrates a flow chart of a process for cooling a component within a housing adapted for subsurface disposal in accord with the invention. 
   

   DETAILED DESCRIPTION 
   The disclosed cooling systems are based on a vortex tube to provide cooling. These cooling techniques are not limited to any particular field, they apply to any application where cooling is desired. 
     FIG. 1  shows an instrument designed for subsurface logging operations including a vortex tube cooling system  50  of the invention. The downhole tool  28  is disposed in a borehole  30  that penetrates an earth formation. The cooling system  50  includes a cooling chamber  48  adapted to house the component(s)  49  (e.g. electronics) to be cooled. The tool  28  also includes a multi-axial electromagnetic antenna  46 , a conventional source/sensor  44  array for subsurface measurements (e.g., nuclear, acoustic, gravity), and an circuit junction  42 . The tool housing  40  may be any type of conventional shell, such as a metallic, non-metallic, or composite sleeve as known in the art. The tool  28  is shown supported in the borehole  30  by a multi-wire cable  36  in the case of a wireline system or a drill string  36  in the case of a while-drilling system. 
   With a wireline tool, the tool  28  is raised and lowered in the borehole  30  by a winch  38 , which is controlled by the surface equipment  32 . Logging cable or drill string  36  includes conductors  34  that connect the tool&#39;s electronics with the surface equipment  32  for signal and control communication. Alternatively, these signals may be processed or recorded in the tool  28  and the processed data transmitted to the surface equipment  32 .  FIG. 1  exemplifies a typical logging tool configuration implemented with a vortex tube system of the invention. It will be appreciated by those skilled in the art that other types of downhole instruments and systems may be used to implement the invention. 
   For clarity of illustration, the vortex tube cooling systems  50  of the invention are shown schematically. Conventional components, connectors, valves and mounting hardware may be used to implement the cooling systems  50  as known in the art. It will also be appreciated by those skilled in the art that while the component couplings and operational designs of the cooling systems of the invention are specifically disclosed, the actual physical layout of the systems may vary depending on the space constraints of the particular implementation. 
     FIG. 2  shows a cooling system  50  of the invention. The system includes a compressor  52  to pump a fluid from a low-pressure chamber  54  to a high-pressure chamber  56  to maintain these chambers within a desired operational range. The Cooling systems  50  of the invention may be implemented using compressible fluids (e.g. air or gaseous mixtures), and in some cases the use of incompressible fluids (e.g. liquids) may also be possible. An optional high-pressure cutoff switch  55  may be added to the high-pressure chamber  56  as an added safety feature. An intermediate chamber  58  is also disposed between the high-pressure chamber  56  (where the pressure is P 1 ) and the vortex tube  60 . In this embodiment, the intermediate chamber  58  is kept at pressure P 2 , which may be the optimal desired intake pressure for the vortex tube  60 . The pressure P 2  in the intermediate chamber  58  is regulated via a control valve  62 . The fluid flow into the vortex tube  60  from the intermediate high-pressure chamber  58  is controlled via a control valve  64  to maintain the component(s)  49  within the cooling chamber  66  at the desired temperature. The valve  64  can be opened to allow fluid flow and cooling when the cooling chamber  66  temperature rises above a minimum value of a desired operating temperature for the cooling chamber  66  component(s)  49 . The valve  64  can be closed and cooling stopped if the temperature falls below the minimum. This type of control may require some hysteresis to prevent chattering. 
   Pressure in the cooling chamber  66  is maintained at a desired optimal pressure P 3  for the vortex tube  60  outlet via a control valve  68 . When the pressure in the cooling chamber  66  rises above P 3 , control valve  68  is opened to allow fluid flow into the low-pressure chamber  54  until the pressure falls back to P 3 . The compressor  52  maintains the low-pressure chamber  54  at pressure P 4 , which is less than P 3 . In some embodiments, the low-pressure chamber  54  may be of sufficient size such that in order to have the pressure in the low-pressure chamber  54  approach P 3 , the pressure in the high-pressure chamber  56  must fall far below P 1  to trigger the compressor  52 . The hot fluid stream out of the vortex tube  60  is directed to a heat exchanger  70  where the heat gained in the vortex tube is rejected to the ambient and the fluid stream is cooled down to ambient temperature before it is routed into the low-pressure chamber  54 . 
   As known in the art, downhole tools used for while-drilling applications are typically powered by turbines that are operated via the borehole fluid (“mud”) flowing through the tool. These tools generally have a battery power backup to keep the tools operational when mudflow is stopped periodically for various reasons. The vortex tube cooling system  50  described in  FIG. 2  may be implemented in a while-drilling downhole tool  28 . In such an embodiment, the compressor  52  used to generate high pressure for the vortex tube  60  can be operated either directly via the mud turbine or by having it powered electrically as known in the art (not shown). 
   An advantage of using a vortex tube for downhole while-drilling applications is that it enables holdover capability. That is, when the mud pumps are switched off and the compressor  52  stops, for a limited period of time the vortex tube  60  can continue to cool the cooling chamber  66  due to the pressure built up in the high-pressure chamber  56 . This can be very useful as the tool  28  generally sees the highest temperatures when the mud pumps are switched off. The holdover capabilities can be increased by increasing the size of the system chambers (e.g. the high  56  and low-pressure  54  chambers). 
   In applications where exposure to high temperatures is only for a limited period of time, cooling is similarly required for a brief period of time. A passive vortex tube cooling system is suitable for such applications.  FIG. 3  shows a passive cooling system  50  embodiment of the invention. In this embodiment, the compressor  52  (see  FIG. 2 ) does not exist. The low-pressure chamber  54  is evacuated and the high-pressure  56  chamber is prepressurized. During operation, the vortex tube  60  provides cooling until the pressure in the low-pressure chamber  54  becomes too high for adequate fluid flow through the vortex tube  60 . The control valves  64 ,  68  serve the same purpose as described with respect to  FIG. 2 . The hot fluid stream from the vortex tube  60  is routed to the ambient environment.  FIG. 4  shows another passive cooling system  50  embodiment of the invention. This embodiment is similar to that of  FIG. 3 , with the addition of a heat exchanger  70  and an intermediate high-pressure chamber  58  as described with respect to  FIG. 2 . The control valves of these embodiments serve the same purpose. 
   The passive vortex tube cooling systems  50  described in  FIG. 3  and  FIG. 4  are suitable for downhole wireline tool applications. In such applications, the high-pressure chamber  56  can be pressurized at the surface prior to subsurface disposal. While it may be advantageous to use a passive cooling system for wireline applications in instances where tool space is premium, other wireline embodiments can be implemented with a compressor ( 52  in  FIG. 2 ) powered through the tool  28  power supply. As described above, wireline tools are powered through a multi-wire cable that is attached to the tool  28  from the surface. 
   A limitation on the holdover capability (the period of time the vortex cooler can continue to cool with the compressor off) of the cooling systems of the invention is the pressure buildup in the low-pressure chamber  54 . Once the pressure in the low-pressure chamber  54  rises above what is acceptable for the cooling chamber  66  or the maximum outlet pressure that the vortex tube  60  can operate at efficiently, cooling is effectively stopped. The high-pressure side of the systems faces no such limitation. The pressure in the high-pressure chamber  56  can be built up very high, allowing for a compressed fluid supply for an extended period of time. 
     FIG. 5  shows an embodiment of the invention that provides a way to extend the holdover capability of the cooling system  50 . The high-pressure supply of the high-pressure chamber  56  is used to operate essentially a small turbine  72 , which turns a small secondary compressor  74  to pump fluid from an intermediate low-pressure chamber  76  to the low-pressure chamber  54 . In this embodiment, the additional intermediate low-pressure chamber  76  enables the cooling chamber  66  and the heat exchanger  70  to be maintained at an optimal pressure for an extended period of time. The small turbine  72  compressor  74  pair can be a pair of fans on the same shaft with one set of blades causing the fan to turn through the fluid flow into the vortex tube  60  while the other set of blades pump fluid out of the intermediate low pressure chamber  76  to the low pressure chamber  54 . The system of  FIG. 5  also includes a double-walled cooling chamber  66 . By passing the cool fluid stream from the vortex tube  60  through the annular space between the chamber  66  walls, the chamber&#39;s contents are thereby shielded from pressure. Double-walled chambers may be used for any implementation of the invention. 
   The same holdover extension can be added to the passive cooling systems of the invention to increase the amount of time the passive systems can operate. Since the pressure in the low-pressure chamber  54  will be higher than that in the intermediate low-pressure chamber  76  when operating passively, a one-way valve (not shown) between these two chambers may be used to allow fluid flow only from the intermediate low-pressure chamber  76  to the low-pressure chamber  54 . 
   When implemented in downhole tools for subsurface disposal, the cooling systems of the invention provide several benefits. Minimal moving parts in the cooling system (the vortex tube itself has no moving parts) provide a major advantage in qualifying the instruments for shock and vibration. The use of air for the working fluid minimizes environmental and other concerns with using the systems in the downhole environment. The systems also have the capability to operate passively for a period of time, which is particularly useful in applications where power is not supplied or interrupted. 
     FIG. 6  shows a flow chart illustrating a process for cooling a component within a housing adapted for subsurface disposal according to the invention. At step  100 , the process begins by equipping the housing with: a first pressure chamber; a vortex tube coupled to the first pressure chamber; a cooling chamber coupled to the vortex tube; and a second pressure chamber coupled to the cooling chamber. The component  49  to be cooled is then deposed within the cooling chamber (at step  105 ). Then the pressure chambers are adapted to stimulate a cool fluid flow from the vortex tube into the cooling chamber as described herein (at step  110 ). For example, in passive systems the pressure chambers are adapted by pressurizing the high-pressure chamber and evacuating the low-pressure chamber at the surface prior to subsurface disposal. 
   While the invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate that other embodiments can be devised which do not depart from the scope of the invention. For example, the pressure chambers of the cooling systems may be insulated using conventional insulating materials or Dewar flasks if desired (shown at  69  in  FIG. 3 ). It will also be appreciated that with some modification the cooling systems of the invention may be used as heating systems or combined cooling-heating systems by appropriate routing of the fluid streams from the vortex tube.