Abstract:
A leak detection apparatus includes one or more detection devices that envelope the various pipe joints of a liquid circulation cooling system. In one approach, the detection devices include a pair of conductors separated by a wicking material impregnated with a crystalline salt that provides a low resistance electrical path between the conductors in the presence of a leak. In another approach, the detection devices include a pair of dissimilar metal mesh electrodes separated by an electrolyte-impregnated wicking material to form a water-activated battery that energizes an alarm in the presence of a leak. In either case, the electrodes and wicking material may be encased with a water-activated sealing material that hardens in the presence of a leak to contain the leakage.

Description:
TECHNICAL FIELD 
     The present invention is directed to liquid circulation cooling systems for electronic devices and the like, and more particularly to apparatus for detecting, locating and isolating coolant leaks at the pipe joints of such systems. 
     BACKGROUND OF THE INVENTION 
     Liquid cooling is finding increased application in the electronics industry due to the limited heat dissipation capability of forced air cooling systems and the desire to minimize cooling system noise levels. FIG. 1 depicts a liquid cooling system  10  for one or more heat producing electronic devices  12 . The device  12  is typically mounted on a circuit board  14 , and its upper surface is secured to a cold plate  16  of cooling system  10  by thermal paste, thermal interface material or other means so that heat generated by the device  12  is conducted to the cold plate  16 . The cold plate  16  is provided with inlet and outlet pipes  16   a ,  16   b  through which a liquid coolant such as water or a water-glycol solution is circulated. The coolant is stored in a tank or reservoir  18 , and a pump  20  draws coolant out of tank  18  for delivery to the cold plate inlet pipe  16   a . Heated fluid exiting cold plate  16  through outlet pipe  16   b  is supplied to a heat exchanger  22  before being returned to the tank  18 . A cooling fan  24  driven by electric motor  26  forces ambient air through the heat exchanger  22 , so that the heat transferred from device  12  to the fluid in cold plate  16  is subsequently transferred from the fluid in heat exchanger  22  to circumambient air. 
     The potential for fluid leaks is a significant concern, particularly in electronic systems where the leaked fluid can damage various electronic devices and potentially create a risk of electrocution or fire. As in any liquid (single phase or multi-phase fluid) circulation system, the most likely sources of leakage in the system  10  are the pipe joints. In the system of FIG. 1, for example, the inlet  16   a ,  18   a ,  20   a ,  22   a  of each device  16 ,  18 ,  20 ,  22  is coupled to the outlet  16   b ,  18   b ,  20   b ,  22   b  of another device by a connecting pipe  28 ,  30 ,  32 ,  34 , and there is a pipe joint at each such coupling. In the system of FIG. 1, the connecting pipes  28 ,  30 ,  32 ,  34  have an inside diameter that matches the outside diameter of the inlet or outlet pipe to which it is coupled, and a clamp  36  prevents the pipes from becoming uncoupled. Other possible coupling configurations are depicted in FIGS. 2-4, described herein. Although the coupled pipes can be soldered or otherwise sealed to prevent fluid leakage, the possibility of fluid leakage remains due to sealing defects or imperfections that occur over time. 
     Various systems have been devised to address the aforementioned leakage concerns, most of which include one or more leak detection devices and an alarm or other warning device to alert an operator upon detection of leakage. The detection device typically takes the form of a pair of electrodes separated by an absorbent material that is insulative in the absence of fluid but which dissolves or becomes conductive in the presence of fluid. A circuit responsive to the resistance between the electrodes activates the alarm when a change in resistance indicative of fluid leakage is detected. See, for example, the U.S. Pat. Nos. 4,922,232; 4,974,739; 5,172,730; 5,176,025; and 5,918,267 which pertain to leak detection in pipelines, and the U.S. Pat. Nos. 4,870,477 and 5,086,829, which pertain to leak detection for liquid circulation cooling systems. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved leak detection apparatus that is particularly suited to liquid circulation cooling systems having pipe joints, including detection devices that envelope the various pipe joints of the cooling system. According to a first embodiment, the detection devices comprise a pair of conductors separated by a wicking material impregnated with a crystalline salt that provides a low resistance electrical path between the conductors in the presence of a leak. According to a second embodiment, the detection devices comprise a pair of dissimilar metal mesh electrodes separated by an electrolyte-impregnated wicking material to form a water-activated battery that energizes an alarm in the presence of a leak. Both embodiments optionally are encased with a water-activated sealing material that hardens in the presence of a leak to contain the leakage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a diagram of a Prior Art liquid circulation cooling system for electronic devices. 
     FIG. 2 depicts a leak detection and containment device for a pipe joint of the system of FIG. 1, including a pair of radially displaced conductor sleeves. 
     FIGS. 3 and 4 depict a leak detection and containment device for a pipe joint of the system of FIG. 1, including a pair of laterally displaced conductor bands. The device of FIG. 3 is depicted in the context of a butt-type pipe joint with an internal sleeve, and the device of FIG. 4 is depicted in the context of a barb-type pipe joint. 
     FIGS. 5A and 5B depict a patch-type leak detection and containment device according to this invention. FIG. 5A depicts a plan view, while FIG. 5B depicts a cross-sectional view taken along line I—I in FIG.  5 A. 
     FIG. 6 depicts a leak detection circuit used in connection with the leak detection and containment devices of FIGS. 2,  3 ,  4  and  5 A- 5 B. 
     FIGS. 7A and 7B depict a wrap-type leak detection device according to this invention including a water-activated battery and alarm. FIG. 7A depicts an exploded view of the water-activated battery, and FIG. 7B depicts the water-activated battery of FIG. 7A as applied to a pipe joint of the system of FIG.  1 . 
     FIGS. 8A and 8B depict a block-type leak detection device according to this invention including a water-activated battery and alarm. FIG. 8A depicts an exploded view of the water-activated battery and a pipe joint, and FIG. 8B depicts the water-activated battery of FIG. 7A as applied to the depicted pipe joint. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is described in the context of a circulated water cooling system generally of the type designated by the reference numeral  10  in FIG.  1 . However, it will be appreciated by those skilled in the art that the embodiments described herein are also applicable to other types of circulated liquid cooling systems, and also to systems with stagnant fluid as in pool-boiling. 
     The embodiments depicted in FIGS. 2 and 3 are particularly applicable to cooling system pipe joints of the abutment type in which two similarly sized pipes  40  and  42  separated by a small gap  43  are joined by an internal sleeve  44  having an outside diameter equal to or slightly larger than the inside diameter of the pipes  40  and  42 . Although not depicted in FIGS. 2-3, the sleeve  44  or the pipes  40 ,  42  may be coated with a sealing material that is compressed between the sleeve  44  and the pipes  40 ,  42  to prevent leakage of fluid circulated therethrough. 
     Referring particularly to FIG. 2, the reference numeral  50  designates a leak detection and containment apparatus where the electrodes are defined by the radially spaced metal screens  52  and  54 . The screens  52  and  54  may be formed of copper or aluminum for example, and are coupled to an external circuit such as depicted in FIG. 6 by the external conductors  56  and  58 , respectively. The screens  52  and  54  are separated from the pipes  40 ,  42  and from each other by intervening layers of a wicking material  60  that absorbs coolant that may ooze from the pipe joint and acts to soak up and hold the oozing coolant until the joint can be repaired. The wicking material  60 , which may be formed of felt for example, is preferably impregnated with a crystalline salt such as sodium-bicarbonate or sodium-chloride. When dry, the wicking material  60  is insulative in nature to establish a high-resistance electrical path between the screens  52  and  54 ; when moistened by leaking coolant at the pipe joint, the crystalline salt dissolves, forming a highly ionic low-resistance electrical path between the screens  52  and  54 . In systems where the coolant itself is highly conductive, impregnation of the wicking material with crystalline salt can be omitted. If desired, the wicking material  60  can additionally be impregnated with a dry dye material such as cobalt chloride that is dissolved by leaking coolant; in such event, the dye produces a visible stain on the detection apparatus  50 , allowing a user to visually identify the location of a detected leak. Optionally the screens  52 ,  54  and wicking material  60  are enveloped by a superincumbent layer of sealing material  62  designed to harden and seal the leak on contact with the coolant. If the coolant is water, for example, the sealing material may be a water-activated material such as hydrophobic polyurethane foam or resin, epoxy resin, sodium-polyacrylate gel, or simple plaster-of-paris. The apparatus  50  is preferably manufactured in the form of a rectangular strip that is wrapped around some or all of the pipe joints of the cooling system  10 , particularly those joints located in proximity to sensitive electronic devices or other electrical equipment where a leak would cause damage and/or pose an electrical hazard. 
     Referring to FIG. 3, the reference numeral  70  designates a leak detection and containment apparatus where the electrodes are defined by the axially spaced metal bands  72  and  74 . The bands  72  and  74  may be formed of copper or aluminum for example, and are coupled to an external circuit such as depicted in FIG. 6 by the external conductors  76  and  78 , respectively. A sleeve of wicking material  80  surrounds the pipes  40 ,  42  in the vicinity of the gap  43 , and the bands  72  and  74  are secured to opposite axial ends of the wicking material  80  as shown. As in the embodiment of FIG. 2, the wicking material  80  separates the bands  72  and  74  from the pipes  40 ,  42  and from each other; and additionally in this embodiment, the bands  72 ,  74  serve as clamps to hold the wicking material  80  in place. As discussed above, the wicking material  80  may be formed of felt for example, and is impregnated with a dry dye material and crystalline salt to facilitate both visual and electrical detection of coolant leakage. And as with the embodiment of FIG. 2, the bands  72 ,  74  and wicking material  80  are optionally enveloped by a superincumbent layer of sealing material  82  designed to harden and seal the leak on contact with the coolant. 
     Referring to FIG. 4, the reference numeral  90  designates a leak detection and containment apparatus essentially as shown in FIG. 3, but as applied to a barb-type pipe joint between different sized pipes  92  and  94 . As in the embodiment of FIG. 3, a sleeve of wicking material  96  surrounds the pipes  92 ,  94  in the vicinity of the pipe joint, and metal bands  98  and  100  are secured to opposite axial ends of the wicking material  96 . Conductors  102  and  104  connect the bands  98  and  100  to an external circuit such as depicted in FIG.  6 . And as with the embodiments of FIG. 2-3, the bands  92 ,  94  and wicking material  96  are optionally enveloped by a superincumbent layer of sealing material  106  designed to harden and seal the leak on contact with the coolant. 
     Referring to FIGS. 5A-5B, the reference numeral  110  generally designates a patch-type version of the above-described pipe joint leak detection devices that is particularly adapted for detecting leaks from a flat surface in the liquid cooling loop of cold plate  16 . A sheet of metal foil tape  112  has a rectangular central opening  112   a  covered by a sheet of wicking material  114  that is somewhat larger than the opening  112   a  so that the margins of the wicking material  114  adhere to the foil tape  112 . First and second conductor bars  116 ,  118  are adhered to foil tape  112  oppositely about the wicking material  114 , so that the electrical resistance between conductor bars  116  and  118  is determined by the combined resistance of the intervening wicking material  114  and the marginal portions  112   b ,  112   c  of the foil tape  112 . As the wicking material  114  moistens due to a coolant leak, the combined electrical resistance decreases, and a circuit such as depicted in FIG. 6 coupled to the conductor bars  116 ,  118  via wires  120 ,  122  detects the resistance drop as an indication of coolant leakage. As with the previously discussed embodiments, the wicking material  114  may be impregnated with dry dye and crystalline salts to facilitate visual and electrical leak detection, and the apparatus may be optionally enveloped by a superincumbent layer of sealing material  124  designed to harden and seal the leak on contact with the coolant. 
     FIG. 6 depicts a leak detection circuit designed to interface with the above-described leak detection devices, designated in FIG. 6 by the detector  140 . A power source such as battery  142  is coupled to a relay coil  144  via a Darlington transistor pair  146  comprising the individual transistors  148  and  150 . When the Darlington pair  146  is conductive, the relay coil  144  is energized to activate a set of contacts  156  that in turn activate an alarm to alert the operator that a coolant leak has been detected. The resistor  154  and leak detector  140  couple the base of transistor  148  to the positive terminal of battery  142 , while the pull-down resistor  152  couples the base of transistor  148  to the negative terminal of battery  142 . The normal resistance of detector  140  is relatively high so that the pull-down resistor  152  biases the Darlington pair  146  non-conductive. In the event of a coolant leak, however, the resistance of detector  140  drops precipitously, biasing the Darlington pair  146  conductive to activate the alarm. Advantageously, the circuit elements  144 - 154  may be replicated to provide a detection circuit for each leak detector present in a system  10 . 
     FIGS. 7A-7B and  8 A- 8 B depict leak detection devices having an integral coolant-activated battery that interfaces directly to an alarm device, thereby eliminating the need for remote resistance detection circuitry and batteries that must be periodically replaced. 
     FIGS. 7A-7B depict a detection apparatus  160  in the form of an elongated strip that is intended to be wrapped around a pipe joint as depicted in FIG.  7 B. When the integral battery is activated, an alarm  178  (such as a piezoelectric sounder) coupled to the apparatus  160  via the wires  174  and  176  sounds to alert the operator or user of the coolant leakage. Referring to FIG. 7A, the apparatus  160  comprises first and second electrode strips  162  and  164  separated by a strip of wicking material  166 , and upper and lower strips of porous fabric  168 ,  170  covering the electrode strips  162 ,  164 . The porous fabric layers  168 ,  170  serve to protect the respective electrode strips  162 ,  164 , and also to insulate the electrode strips  162 ,  164  from pipe  172 , and from each other if the wrapping results in any overlap. The electrode strips  162 ,  164  are formed of a screen or mesh material so that leaked coolant soaks into the wicking material  166 , and the wicking material is impregnated with crystalline electrolyte that is non-conductive in its dry state. In the illustrated mechanization, one of the electrode strips  162 ,  164  is formed of aluminum, while the other is formed of copper, so that an aluminum-copper cell is activated in the event of coolant leakage to produce an output voltage of approximately 1.2 volts across lines  174 ,  176 . The current produced by the cell is proportional to the active area of the electrodes  162 ,  164 , which increases as leaked coolant soaks into the wicking material  166 . Other electrode combinations such as copper and magnesium are also possible. 
     FIGS. 8A-8B depict a detection apparatus  180  comprising first and second blocks  182  and  184  that are clamped together about a butt-joint of two equal diameter pipes  186 ,  188 . As depicted in FIG. 8A in respect to block  182 , each of the blocks  182 ,  184  comprises a stack of plates that form one or more coolant activated battery cells. The exterior periphery of the stack is covered by an insulative layer  190 , and each stack has a semi-cylindrical recess that is complementary to the exterior periphery of the pipes  186 ,  188 . A porous insulative layer is also applied to the pipes  186 ,  188  in the event that the pipes  186 , 188  are conductive. Each battery cell includes an aluminum plate  192 , a layer of wicking material  194  and a copper plate  196  in succession, and each cell is separated by an insulator plate  198 . The various aluminum plates  192  are electrically coupled by internal inter-connects, as are the various copper plates  196 . As shown in FIG. 8B, a pair of conductors  200 ,  202  couple the battery cells of blocks  182  and  184  in parallel, and the wires  204 ,  206  couple the battery cells to the alarm  208 , which may be a piezoelectric sounder as mentioned above. As with the embodiment of FIGS. 7A-7B, the wicking material  194  is impregnated with crystalline electrolyte that is dissolved by leaked coolant to activate the battery cells. 
     In summary, the present invention provides a reliable and cost-effective means of quickly detecting and locating leaked coolant in a liquid-circulated cooling system  10 . While the invention has been described in reference to the illustrated embodiments, it will be understood that various modifications in addition to those mentioned herein will occur to those skilled in the art. For example, the size and shape of the detection apparatus may be varied to suit a given application, materials other than those mentioned herein may be used, and so forth. Additionally, it is possible to apply two or more staged detection devices to a single location; in such a mechanization, initial coolant leakage is detected by a first detection device, and leakage detection by the second and subsequent detection devices indicates the extent of the leak. Also, the alarm circuitry may be effective to perform auto-shutdown or other functions in response to detection of a coolant leak Moreover, the leak detection apparatus may be applied as extensively in a system as desired, and need not be confined solely to the pipe joints. Thus, it will be understood that devices incorporating these and other modifications may fall within the scope of this invention, which is defined by the appended claims.