Patent Publication Number: US-2015068702-A1

Title: Dew condensation detecting device, cooling system and cooling medium flow rate controlling method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application filed under 35 U.S.C. 111(a) claiming benefit under 35 U.S.C. 120 and 365(c) of PCT International Application No. PCT/JP2012/065276 filed on Jun. 14, 2012, designating the U.S., the entire contents of the foregoing application are incorporated herein by reference. 
    
    
     FIELD 
     The embodiments discussed herein are directed to a dew condensation detecting device for detecting water droplets created by a dew condensation. 
     BACKGROUND 
     If a temperature of a component part of an electronic device reaches a temperature lower than a dew point of an atmosphere of the electronic device, a dew condensation occurs on the component part of the electronic device. Water droplets created by the dew condensation may cause a corrosion of a metal part of the electronic device or short-circuiting between electrodes of an electric circuit provided in the electronic device. Thus, a malfunction may occur in the electronic device due to the dew condensation. 
     Generally, a temperature and humidity of an environment, in which a liquid-cooling electronic device is located, and a temperature of a cooling liquid used in the liquid-cooling electronic device are controlled and managed in order to prevent an occurrence of a dew condensation in the liquid-cooling electronic device. However, if a failure occurs in an air-conditioner or a temperature abnormality occurs in a cooling-liquid outputting device, the temperature of the cooling liquid reaching the electronic device may become lower than the dew point, which results in the interior of the electronic device being set in a dew condensed state. Even in such a condition, there may be a case where a power of the electric device is turned on or the electronic device is continuously operated. Thus, if an amount of water droplets due to the dew condensation exceeds a certain amount in the electronic device, short-circuiting may occur between electrodes of an electric circuit in the electronic device. The short-circuiting in the electric circuit may cause a failure in the electronic device, such as a malfunction of the electric circuit, a burnout of the electric circuit, etc. 
     In order to prevent such a failure due to a dew condensation, it is suggested to provide a dew condensation sensor in an electronic device to detect a dew condensation in order to take measures for preventing a failure due to the dew condensation. That is, for example, if a dew condensation is detected by the dew condensation sensor, the electric device is prohibited from being turned on or the interior of the electronic device is subjected to a dehydration treatment. 
     There are several types of dew condensation sensors. There if known a dew condensed water detecting sensor that detects a dew condensation by detecting a water droplet, which is created by a dew condensation and flows to a detecting part. Such a dew condensed water detecting sensor generally includes a water droplet sensor (liquid sensor) and a measuring object formed of a metal on which a dew condensation tends to occur. The measuring object is provided to a cold water supply passage between a cold water supply apparatus and an electronic device so as to be cooled by cold water supplied from the cold water supply apparatus. Accordingly, if a temperature of the measuring object becomes lower than a dew point of the atmosphere, a dew condensation occurs on the measuring object. That is, the cold water supplied from the cold water supply apparatus first cools the measuring object of the dew condensed water detecting sensor, and, thereafter, the cold water is supplied to the electronic device so as to cool heat-radiating parts in the electronic device. 
     Because the heat capacity of the measuring object of the dew condensed water sensor is small and the measuring object does not generate heat, the temperature of the cold water entering the electronic device after cooling the measuring object is nearly equal to the temperature of the cold water supplied from the cold water supply apparatus to the measuring object. Thus, if a dew condensation occurs on the measuring object, a dew condensation may simultaneously occur on a cold water passage in the electronic device. 
     It is suggested, in Japanese Laid-Open Patent Application No. 2006-32515, to prevent a dew condensation in a device by causing a coolant temperature to rise by reducing an amount of flow of coolant to be supplied to the device when a dew condensation sensor provided to an external coolant equipment pipe detects a dew condensation. 
     Additionally, it is suggested, in Japanese Patent No. 3447257, to control a cold water supply apparatus by providing a dew condensation sensor on an uppermost stream side of a supply pipe that supplies cold water to a cooler panel. 
     Because the dew condensation sensor detects a dew condensation by detecting a water droplet due to the dew condensation, it takes a certain time from the time at which a dew condensation begins until the time at which an amount of a water droplet due to the dew condensation reaches a measurable amount. Accordingly, during the period from the time at which the dew condensation begins in the dew condensation sensor and the electronic device until the time at which the dew condensation sensor detects the dew condensation, water droplets may be created due to the dew condensation even in the electronic device. The water droplets due to the dew condensation in the electronic device may cause the above-mentioned failure. 
     SUMMARY 
     There is provided according to an aspect of the embodiments a dew condensation detecting device, including: a dew condensation detector provided to a supply pipe, which supplies a cooling medium from a cooling medium supply apparatus to a device to be cooled, the dew condensation detector detecting a dew condensation by detecting a water droplet due to the dew condensation; and a heat transfer part that transfers heat from the cooling medium flowing in a return pipe, which returns the cooling medium from the device to be cooled to the cooling medium supply apparatus, to the cooling medium flowing in the supply pipe between the dew condensation detector and the device to be cooled. 
     There is provided according to another aspect of the embodiments a cooling system including: a device to be cooled that incorporates an internal part to be cooled by a cooling medium; a cooling medium supply apparatus that creates the cooling medium supplied to the device to be cooled; a supply pipe that connects the device to be cooled to the cooling medium supply apparatus in order to supply the cooling medium from the cooling medium supply apparatus to the device to be cooled; a return pipe that connects the device to be cooled to the cooling medium supply apparatus in order to return the cooling medium from the device to be cooled to the cooling medium supply apparatus; a dew condensation detector provided in a middle of the supply pipe; and a heat transfer part that transfers heat from the cooling medium flowing in a return pipe to the cooling medium flowing in the supply pipe between the dew condensation detector and the device to be cooled. 
     There is provided according to a further aspect of the embodiments a cooling medium flow rate controlling method for controlling a flow rate of a cooling medium supplied to a device to be cooled, the cooling medium flow rate controlling method including: detecting a temperature of the cooling medium discharged from the device to be cooled; and comparing the detected temperature with a temperature threshold value and controlling the flow rate of the cooling medium supplied to the device to be cooled based on a result of the comparison. 
     The object and advantages of the embodiments will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary explanatory only and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an outline diagram illustrating an entire structure of an electronic device cooling system provided with a dew condensation detecting device according to a first embodiment; 
         FIG. 2  is an enlarged cross-sectional view of a heat transferring part; 
         FIG. 3  is an enlarged cross-sectional view of another heat transferring part; 
         FIG. 4  is a flowchart of a dew condensation detecting process; 
         FIG. 5  is an outline diagram illustrating an entire structure of an electronic device cooling system provided with a dew condensation detecting device according to a second embodiment; 
         FIG. 6  is an enlarged cross-sectional view of a portion A encircled by dashed line in  FIG. 5 ; 
         FIG. 7  is a perspective view of a connection pipe; 
         FIG. 8  is a cross-sectional view of a variation of the connection pipe; 
         FIG. 9  is a flowchart of a cold water flow amount controlling process; 
         FIG. 10  is an outline diagram illustrating an entire structure of an electronic device cooling system provided with a dew condensation detecting device according to a third embodiment; 
         FIG. 11  is a flowchart of a cold water flow amount controlling process performed in the electronic device cooling system illustrated in  FIG. 10 ; and 
         FIGS. 12(   a )-( e ) are time charts indicating operations and temperatures in the electronic device cooling system when the cold water flow amount controlling process illustrated in  FIG. 11  is performed. 
     
    
    
     DESCRIPTION OF EMBODIMENT(s) 
     A description will now be given, with reference to the drawings, of embodiments. 
       FIG. 1  is an outline diagram illustrating an entire structure of an electronic device cooling system provided with a dew condensation detection device according to a first embodiment. 
     An electronic device  10  illustrated in  FIG. 1  is an example of a device to be cooled. Specifically, the electronic device  10  is a liquid cooling type electronic device such as, for example, a computer, server, etc. A cold cooling water (hereinafter, referred to as the “cold water”) is supplied from a cold water supply apparatus  12  to the electronic device  10  to cool heat-generating parts provided in the electronic device  10 . The heat-generating parts include, for example, a semiconductor device, power supply circuit, etc. The cold water created by the cold water supply apparatus  12  is supplied to a cooling water passage (not illustrated in the figure) of the electronic device  10  through a cold water supply pipe  14 . The heat-generating parts are arranged in the middle of the cooling water passage in the electronic device  10  so that the heat-generating parts are cooled by the cold water, which absorbs heat from the heat-generating parts, while flowing through the cooling water passage. The cooling water warmed by cooling the heat-generating parts (hereinafter, referred to as the “warm water”), is returned from the cooling water passage of the electronic device  10  to the cold water supply apparatus  12  through a warm water return pipe  16 . 
     In the present embodiment, although the cold water supply apparatus  12  is a known cooling-water cooling apparatus provided with a refrigerating machine and a heat exchanger, a cold water supply apparatus having any structure may be used if it can supply cold water by cooling the warm water discharged from the electronic device  10 . 
     Additionally, although the cooling water is used as a coolant in the present embodiment, the coolant is not limited to the cooling water and a coolant such as a cooling liquid may be used. 
     Normally, the cold water supply apparatus  12  creates cold water of a predetermined temperature by cooling the warm water flowing out of the warm water return pipe  16 , and discharges the cold water to the cold water supply pipe  14  at a constant flow rate. Thus, the cold water supply apparatus  12  is provided with water temperature sensors  12   a  and  12   b  to detect the temperature of the warm water flowing into the cold water supply apparatus  12  from the warm water return pipe  16  and the temperature of the cold water supplied from the cold water supply apparatus  12  to the cold water supply pipe  14 , respectively. Further, the cold water supply apparatus  12  is provided with a flow rate controller  12   c  to adjust a flow rate of the cold water supplied to the cold water supply pipe  14 . The flow rate controller  12   c  may be a flow rate adjust valve provided to the flow path of the cold water, or may be a mechanism to adjust a flow rate by adjusting a revolution speed of a pump for delivering the cold water. 
     The cold water supply apparatus  12  is provided with a control part  12   d  for controlling the flow rate controller  12   c  based on the temperatures detected by the water temperature sensors  12   a  and  12   b . The control part  12   d  is configured by a microcomputer including a CPU, a memory, etc. Generally, a plurality of electronic devices  10  are provided to one cold water supply apparatus  12 . 
     The dew condensation sensor  20 , which is an example of a dew condensation detector, is provided in the middle of the cold water supply pipe  14  connecting the cold water supply apparatus  12  and the electronic device  40 . If the cold water supply pipe  14  is relatively short, the dew condensation sensor  20  may be provided at any position along the cold water supply pipe  14 . If the cold water supply pipe  14  is relatively long, the dew condensation sensor  20  is preferably arranged at a position close to (in the vicinity of) the electronic device  10 . This is because if an environment around the dew condensation sensor  20  is substantially equal to an environment inside the electronic device  10  or around the electronic device  10 , the dew condensation detection by the dew condensation sensor  20  can be regarded as a dew condensation detection in the electronic device  10 . 
     The dew condensation sensor  20  detects a water droplet due to a dew condensation on the measuring object and outputs a dew condensation detection signal. The dew condensation detection signal output by the dew condensation sensor  20  is supplied to a service processor  10   b  provided in a control part  10   a  of the electronic device  10 . The service processor  10   b  is a CPU performing a control for causing some functions even when the main power supply of the electric device  10  is shut off and the main function of the electronic device  10  is inactive. For example, if the dew condensation detection signal is supplied to the electronic device  10 , the service processor  10   b  can stop the operation of the electronic device by tuning off the main power of the electronic device  10 . 
     A heat transfer part  30 , which is an example of a heat transferring means to transfer heat from the warm water to the cold water, is provided between the dew condensation sensor  20  and the electronic device  10 . The heat transfer part  30  is provided to increase the temperature of the cold water entering the electronic device  10  by supplying heat to the cold water passed through the dew condensation sensor  20 . That is, the heat transfer part  30  is provided for raising the temperature of the cold water flowing into the electronic device  10  by a predetermined temperature (for example, 2° C.) by transferring a part of the heat of the warm water flowing out of the electronic device  16  to the warm water return pipe  16 . 
     In the present embodiment, as illustrated in  FIG. 2 , a metal member  40  is used as the heat transfer part  30 . The metal member  40  is formed by a metal as a heat transfer material such as, for example, copper, copper alloy, aluminum, aluminum alloy, etc. The metal member  40  has a shape, which can fits in a space between the cold water supply pipe  14  and the warm water return pipe  16 . Portions of the metal member  40  that contact with the cold water supply pipe  14  and the warm water return pipe  16  are joined to the cold water supply pipe  14  and the warm water return pipe  16 , respectively, by welding, brazing, soldering, etc., using a thermally meltable joining material. 
     In the part where the metal member  40  is attached, that is, in the heat transfer part  30 , the heat of the warm water is transferred from the warm water return pipe  16  to the metal member  40  and then transferred to the cold water supply pipe  14  and further transferred to the cold water flowing in the cold water pipe supply pipe  14  because the temperature of the warm water flowing in the warm water return pipe  16  is higher than the temperature of the cold water flowing in the cold water supply pipe  14 . Thus, the cold water flowing in the cold water supply pipe  14  is warmed by the transferred heat, and the cold water flowing into the electronic device  10  is raised. 
     For example, if the temperature of the cold water passing through the dew condensation sensor  20  is 21° C., a heat is supplied to the cold water of 21° C. to raise the temperature of the cold water to 23° C. so that the cold water of 23° C. is caused to flow into the electronic device  10 . The cold water after cooling the electronic parts by flowing through the electronic device  10 , is changed into the warm water of, for example, 33° C., and is discharged from the electronic device  10  to the warm water return pipe  16 . 
     Here, it is assumed that the environment in the server room in which the electronic device  10  is installed is maintained at a room temperature of 25° C. and a relative humidity of 50%, and the temperature of the cold water supplied from the cold water supply apparatus  12  is 21° C. In such an environment in the server room, a dew point in the dew condensation sensor  20  and electronic device  10  acquired from the psychrometric chart is 13.9° C. Accordingly, in such an environment, the temperature in the dew condensation sensor  20  (21° C. the same as the cold water) and also the temperature of the cooling water passage in the electronic device  10  (23° C. the same as the cold water warmed by the heat transfer part  30  serving as a heater) are equal to or lower than the dew point (13.9° C.). Thus, no dew condensation occurs in the dew condensation sensor  20  and the cooling water passage of the electronic device  10 . 
     Here, it is assumed that the environment in the server room is changed, for example, due to a failure of an air-conditioner of the server room, and the temperature and relative humidity in the server room are raised to 28° C. and 70%. In such a condition, the dew point in the environment of the server room is raised to 22° C., which is higher than the temperature 21° C. of the cold water. Accordingly, a dew condensation occurs in the dew condensation sensor  20  having the same temperature of 21° C. as the cold water. On the other hand, a dew condensation does not occur in the electronic device  10  because the cooling water passage in the electronic device  10  is at 23° C., which is the same as the temperature of the cold water heated by the heat transfer part  30 . 
     If the environment in the server room continues to change and the room temperature and relative humidity are continuously raised, the dew point is further raised from 22° C. Then, the dew point exceeds the temperature 23° C. of the cold water, a dew condensation occurs also in the electronic device  10 . 
     However, a certain period of time is passed from the time at which the dew point reaches the temperature of 21° C., which is the temperature of the dew condensation sensor  20 , until the time at which the dew point reaches the temperature of 23° C., which is the temperature of the cooling water passage in the electronic device  10 . During the period of time, the dew condensation progresses and water droplets grow, which results in a sufficient amount of water droplets detectable by the dew condensation sensor  20 . That is, a dew condensation is not initiated in the electronic device  10  and water droplets are not created in the electronic device  10  during the period from the time at which a dew condensation is initiated in the dew condensation sensor  20  until the time at which the dew condensation sensor  20  outputs the dew condensation detection signal. 
     Accordingly, by taking measures such as interrupting a power supply of the electronic device  10  upon reception of the dew condensation detection signal from the dew condensation sensor  20 , a failure of the electronic device  10  due to a dew condensation can be prevented. 
     The heat transfer part  30  is not limited to the metal part  40 , and the heat transfer part  30  may be formed by a material having an excellent heat transfer property, such as a ceramic material, thermo conductive plastic, thermo conductive rubber, etc. If the thermo conductive plastic is used, a thermo conductive adhesive may be used as a joining material. If the thermo conductive rubber is used, it is desirable to apply a thermo conductive grease or liquid on a connecting part. 
     The size and shape of the metal member  40  are determined according to an amount of heat to be transferred. The amount of heat to be transferred is, for example, an amount of heat that can raise the temperature of the cold water from 21° C. to 23° C. or an amount of heat that causes the temperature of the warm water to drop from 33° C. to 31° C. in the above description. The amount of heat transferrable by the metal member  40  is determined by the thermal conductivity of the metal member  40  and the heat transfer coefficient between the metal member  40 , cold water supply pipe  14  and warm water return pipe  16 . 
     Additionally, as another embodiment of the heat transfer part  30 , a structure illustrated in  FIG. 3  may be used. The heat transfer part  30  illustrated in  FIG. 3  includes a coupling cover  52  wound on the cold water supply pipe  14  and warm water return pip  16  to bundle the cold water supply pipe  14  and warm water return pip  16 . The coupling cover  52  is preferably formed by a thermo conductive material. For example, the coupling cover  52  is formed by a metal plate such as a copper plate, aluminum plate, etc. 
     A filling material  54  (heat transfer material) having a heat transfer property is filled in a space between the cold water supply pipe  14  and warm water return pipe  16  that are covered by the coupling cover  52 . The filling material  54  is a material having an excellent thermal conductivity, such as a thermal sheet, thermal compound, etc. If a sufficient amount of heat can be transferred by only the thermal conduction of the filling material  54 , the coupling cover  54  is not necessarily formed by a material having a heat transfer property, and may be formed by, for example, a plastic sheet, vinyl sheet, etc. 
     Moreover, the heat transfer property of the heat transfer part  30  may be improved by attaching the metal member  40  as illustrated in  FIG. 2  and further attaching the coupling cover  54  to the circumference of the portion attached with the metal member  40 . 
     A description is given below, with reference to  FIG. 4 , of a dew condensation detecting method in the electronic device cooling system.  FIG. 4  is a flowchart of a dew condensation detecting process. 
     When the dew condensation detecting process is started, first, the service processor  10   b  of the control part  10   a  of the electronic device  10  acquires a signal from the dew condensation sensor  20  (step S 1 ) when the electronic device  10  is operated to cool the heat-generating parts in the electronic device  10 . Subsequently, the service processor  10   b  of the electronic device  10  determines whether the signal from the dew condensation sensor  20  is a dew condensation detection signal, which indicates that a dew condensation is detected (step S 2 ). If it is determined in step S 2  that the signal from the dew condensation sensor  20  is not the dew condensation detection signal, the process returns to step S 1  to retrieve the signal from the dew condensation sensor  20 . 
     On the other hand, if it is determined in step S 2  that the signal from the dew condensation sensor  20  is the dew condensation detection signal, the process proceeds to step S 3 . In step S 3 , the service processor  10   b  performs a process for interrupting (turning off) the power of the electronic device  10 . At this time, a management person may be notified of the dew condensation state by the display apparatus. The notification may be made by issuing an alarm. Alternatively, instead of turning off the power of the electronic device  10 , a process for dehydrating inside the electronic device  10  may be performed. 
     While the above-mentioned dew condensation detecting process is performed, the temperature of the cold water after passing through the dew point sensor  20  and before entering the electronic device  10  is raised by the heat transferred by the heat transfer part  30 , and is set to a temperature higher than the temperature of the cold water in the dew condensation sensor  20 . Accordingly, during a period from an initiation of a dew condensation in the dew condensation sensor  20  until a detection of the dew condensation by the dew condensation sensor  20 , no dew condensation is initiated in the electronic device  10 . Thus, before a dew condensation is initiated in the electronic device  10 , measures for preventing a dew condensation such as turning off the power of the electronic device  10  may be taken to prevent an occurrence of a failure of the electronic device  10  due to a dew condensation in the electronic device  10 . 
     Although the dew condensation sensor  20  and the heat transfer part  30  are arranged outside and in the vicinity of the electronic device  10 , the dew condensation sensor  20  and the heat transfer part  30  may be provided in the electronic device  10  if a sufficient space can be reserved within the electronic device  10 . 
     A description is given below of a second embodiment.  FIG. 5  is an outline diagram illustrating an entire structure of the electronic device cooling system provided with a dew condensation detecting device according to the second embodiment. In  FIG. 5 , parts that are the same as the parts illustrated n  FIG. 1  are given the same reference numerals, and descriptions thereof will be omitted. 
     In the electronic device cooling system illustrated in  FIG. 5 , a coupling pipe  60  is used as the heat transfer part  30  for transferring heat to the cold water. That is, instead of transferring heat by the metal member  40 , a part of the warm water flowing in the warm water return pipe  16  is returned to the cold water supply pipe  14  through the coupling pipe  60  to mix the part of the warm water into the cold water to raise the temperature of the cold water. The coupling pipe  60  serves as the heat transfer part  30  because the coupling pipe  60  transfers the heat of the warm water flowing in the warm water return pipe  16  to the cold water flowing in the cold water supply pipe  14 . 
       FIG. 6  is an enlarged cross-sectional view of the part encircled by a dashed line A in  FIG. 5 . The coupling pipe  60  is provided between the cold water supply pipe  14  and the warm water return pipe  16  in a state where an end  60   a  of the coupling pipe  60  is inserted into the interior of the warm water return pipe  16  in the vicinity of the electronic device  10  and the other end  60   b  of the coupling pipe  60  is inserted into the interior of the cold water supply pipe  14  between the dew condensation sensor and the electronic device  10 . A flow-in opening  62  is provided in the end  60   a  of the coupling pipe  60   a  and a flow-out opening  64  is formed on the outer end  60   b  of the coupling pipe  60 . 
     The flow-in opening  62  is open toward an upstream of the flow of the warm water in the warm water return pipe  16 . The flow-out opening  64  is open toward a downstream of the flow of the cold water in the cold water supply pip  14 . Accordingly, when the warm water discharged from the electronic device  10  flows in the warm water return pipe  16 , a part of the warm water flowing in the warm water return pipe  16  flows into the flow-in opening  62  of the coupling pipe  60 . Then, the warm water flows through the coupling pipe  60  and flows into the cold water supply pipe  14  through the flow-out opening  64 . That is, a part of the warm water discharged from the electronic device  10  flows though the coupling pipe  60  and is mixed with the cold water immediately before the electronic device  10 . Thereby, the temperature of the cold water supplied to the electronic device  10  can be raised by the heat of the warm water mixed to the cold water. 
     For example, if the temperature of the cold water passing though the dew condensation sensor  20  is 21° C., the temperature of the cold water is raised to, for example, 23° C. by mixing the warm water so that the cold water of 23° C. enters the electronic device  10 . It is assumed that the cold water which has cooled the electronic parts by passing through the electronic device  10  is turned into the warm water of, for example, 33° C., and then discharged from the electronic device  10  to the warm water return pipe  16 . 
     For example, it is assumed that the environment in the serve room in which the electronic device  10  is installed is maintained at a room temperature of 25° C. and a relative humidity of less than or equal to 50%, and the temperature of the cold water supplied from the cold water supply apparatus  12  is 21° C. Moreover, it is assumed that a flow rate of the warm water (33° C.) flowing through the coupling pipe  60  is 450 ml/min. The warm water is supplied to the cold water after being passed though the dew condensation sensor  20  through the coupling pipe  60 . If the flow rate of the warm water (33° C.) flowing through the coupling pipe  60  is 150 ml/min, the cold water of 450 ml/min mixed with the warm water (33° C.) of 150 ml/min is supplied to the electronic device  10 . The temperature of the cold water supplied to the electronic device  10  is raised due to the joining of the warm water and turned to 23° C. Thus, the cold water (23° C.) of 600 ml/min is supplied to the electronic device  10 . 
     If an amount of heat generated by the electronic parts provided in the electronic device  10  is 420 W, the cold water of the temperature of 23° C. and the flow rate of 600 ml/min turns into the warm water of the temperature of 33° C. by absorbing the amount of heat of 420 W, and is discharged into the warm water return pipe  16 . A part of the warm water of 33° C. (150 ml/min as mentioned above) flows into the coupling pipe  60  immediately after being discharged from the electronic device  10 , and the rest of the warm water (33° C.) of 450 ml/min returns to the cold water supply device  12 . The cold water supply apparatus  12  cools the warm water (33° C.) of 450 ml/min to create the cold water (21° C.) of 450 ml/min, and supplies the created cold water to the cold water supply pipe  14 . 
     It is appreciated that if the above-mentioned environment is established in the server room, the dew point in the dew condensation sensor  20  and the electronic device is acquired as 13.9° C. from the psychrometric chart. Accordingly, in this environment, there is no dew condensation occurs in the dew condensation sensor  20  and also in the cooling water passage in the electronic device  10  because both the temperature in the dew condensation sensor  20  (21° C. which is the same as the cold water) and the temperature in the cooling water passage in the electronic device  10  (23° C. which is the same as the cold water heated by the heat transfer part  30  serving as a heater) are lower than the dew point (13.9° C.). 
     Here, it is assumed that the environment in the serve room is changed due to, for example, a failure in the air-conditioner of the server room and the room temperature is raised to 28° C. and the relative humidity is raised to 70%. In this condition, the dew point in the environment in the server room is raised to 22° C., which is higher than the temperature 21° C. of the cold water. Accordingly, a dew condensation occurs in the dew condensation sensor  20  having the temperature of 21° C., which is the same as the cold water. On the other hand, the cooling water passage in the electronic device  10  is at 23° C., which is the same as the temperature of the cold water, which is raised by the heat transfer part  30 . In this case, a dew condensation does not occur in the electronic device  10  because the temperature of the cooling water passage in the electronic device  10  (23° C.) is higher than the dew point 22° C. 
     If the environment in the server room is continuously changed and the room temperature and the relative humidity are continuously raised, the dew point is raised further from 22° C. Then, if the dew point exceeds the temperature 23° C. of the cold water, a dew condensation occurs also in the electronic device  10 . 
     However, it takes a certain period of time from the time at which the dew point reaches the temperature 21° C. of the dew condensation sensor  20  until the time at which the dew point reaches the temperature 23° C. of the cooling water passage in the electronic device  10 . During this period of time, the dew condensation progresses in the dew condensation sensor  20 , which results in a growth of the water droplets and finally an amount of water droplets detectable by the dew condensation sensor  20  is created. That is, no dew condensation is initiated and no water droplet is created in the electronic device  10  during the period of time from the time at which a dew condensation is initiated in the dew condensation sensor  20  until the time at which the dew condensation sensor  20  output the dew condensation detection signal. 
     As mentioned above, similar to the first embodiment, the temperature of the cold water after passing through the dew condensation sensor  20  can be raised in the present embodiment, thereby providing the same effect as the first embodiment. Accordingly, a failure of the electronic device  10  due to a dew condensation can be prevented by taking measures such as interrupting the power of the electronic device  10  upon receipt of the dew condensation detection signal from the dew condensation sensor  20 . 
     Although the coupling pipe  60  having the shape illustrated in  FIG. 7  is used as the heat transfer part  30 , the shape of the coupling pipe  60  is not limited to that illustrated in  FIG. 7 . There are many other shapes and configurations, which can take a part of the warm water flowing in the warm water return pipe  16  and supplies the warm water to the cold water supply pipe  14  other than the shape and configuration illustrated in  FIG. 7 . As an example, inclination plates  72  and  74  may be provided to both ends  70   a  and  70   b  of a cylindrical pipe  70  having open ends, respectively, as illustrated in  FIG. 8  so as to control a flow of the warm water. Alternatively, although not illustrated in the figures, both ends of the cylindrical pipe  70  may be cut obliquely and the cylindrical pipe  70  may be attached to the warm water return pipe  16  and cold water supply pipe  14  so that the obliquely cut surface is directed toward the upstream side of the flow of the warm water on the side of the warm water return pipe  16  and the obliquely cut surface is directed toward the downstream side of the flow of the cold water on the side of the cold water supply pipe  14 . 
     Here, in the above-mentioned first and second embodiments, if the amount of heat generated by the electronic parts, which are heat-generating parts, in the electronic device  10  is fixed, a difference in the temperature between the dew condensation sensor  20  and the electronic parts in the electronic device  10  is fixed. Accordingly, a period of time from the time at which a dew condensation is detected by the dew condensation sensor  20  until the time when a dew condensation occurs in the electronic device  10  is fixed. The electronic device  10  such as a server or the like may generate a different amount of heat depending on the type of the electronic device  10 . Moreover, the amount of heat generated by the same electronic device  10  may vary due to a fluctuation in a load applied to the electronic parts. 
     Thus, an appropriate temperature difference may be set by adjusting an amount of heat transferred by the heat transfer part  30  so that an operation of the electronic device  10  is stopped safely by interrupting a system power supply after the dew condensation sensor  20  detects a dew condensation and before a dew condensation occurs in the electronic device  10 . If an appropriate design is performed beforehand with respect to an electronic device having a small load fluctuation, measures for a dew condensation can be taken by merely providing the heat transfer part  30  as is in the first and second embodiments. 
     On the other hand, in an electronic device having a large load fluctuation such as, for example, a server or the like, if an amount of heat transferred by the heat transfer part  30  is set in accordance with a state where a load to electronic parts is smallest (a state where an amount of heat generation is small), cooling for the electronic parts is insufficient when the load is increased. Thus, an operating temperature of the electronic parts is raised, which may cause a reduction in the service life and an increase in the failure rate of the electronic parts. On the contrary, if the amount of heat transferred by the heat transfer part  30  is set in accordance with a state where the load to the electronic parts is largest, a temperature difference between the temperature of the dew condensation sensor  20  and the temperature inside the electronic device  10  is decreased. In such a condition, a period of time from the time at which the dew condensation sensor  20  detects a dew formation until the time at which a dew condensation occurs in the electronic device  10  is short, and there may be a case where the electronic device  10  cannot be stopped by reliably interrupting the system power supply. 
     In order to solve such a problem, a flow rate of the cold water supplied from the cold water supply apparatus  12  is controlled and adjusted based on the temperature of the warm water returning to the cold water supply apparatus  12  by flowing through the warm water return pipe  16 . That is, a measurement is taken for the temperature of the warm water returned to the cold water supply apparatus  12  to control a flow rate of the cold water created by the cold water supply apparatus  12  base on the measured temperature. In this case, an amount of supply of the cold water is set to a flow rate corresponding to a state where the load is smallest in the initial setting. If the temperature of the warm water exceeds a certain threshold value, the cooling capacity of the cold water with respect to electronic parts is increased based on an increase in the flow rate of the cold water supplied to the electronic device  10 , thereby suppressing the operating temperature of the electronic parts. Thereby, also the temperature difference between the temperature of the dew condensation sensor  20  and the temperature of the electronic parts can be maintained to fall within a fixed range. 
       FIG. 9  is a flowchart of a cold water flow rate controlling process for adjusting an amount of supply of the cold water. The cold water flow rate controlling process is performed repeatedly at each time interval. 
     When the cold water flow rate controlling process is started, first, the control part  12   d  of the cold water supply apparatus  12  acquires a temperature Tw of the warm water returned to the cold water supply apparatus  12  by flowing through the warm water return pipe  16  (step S 11 ). The temperature Tw of the warm water can be detected by a water temperature sensor  12   a.    
     Then, the control part  12   d  of the cold water supply apparatus  12  compares the acquired temperature Tw with a temperature threshold vale (step S 12 ). The temperature threshold includes an upper limit threshold value UTH and a lower limit threshold value LTH. If the temperature Tw of the warm water is lower than or equal to the upper limit threshold value UTH and higher than or equal to the lower limit threshold vale LTH, it is determined that the temperature of the warm water returned is an appropriate temperature and cooling for the electronic parts in the electronic device  10  is performed appropriately, and the process is ended. Although the cold water flow rate controlling process is repeatedly performed at a fixed time interval, the process may return to step S 11  so that a subsequent process is initiated immediately after the process is ended. 
     If the temperature Tw of the warm water is higher than the upper limit threshold temperature UTH, it is determined that the cooling of the electronic parts in the electronic device  10  is not sufficient, and the process proceeds to step S 13 . In step S 13 , the flow rate of the cold water (21° C.) supplied to the cold water supply pipe  14  (that is, the electronic device  10 ) from the cold water supply apparatus  12 ) is increased by a predetermined amount, and, thereafter, the process is ended. Although the cold water flow rate controlling process is repeatedly performed at a fixed time interval, the process may return to step S 11  after completing the process of step S 13  so that a subsequent process is initiated immediately after the process is ended. 
     If the temperature Tw of the warm water is lower than the lower limit threshold temperature LTH, it is determined that the cooling for the electronic parts in the electronic device  10  is too much, and the process proceeds to step S 14 . In step S 14 , the flow rate of the cold water (21° C.) supplied to the cold water supply pipe  14  (that is, the electronic device  10 ) from the cold water supply apparatus  12  is decreased by a predetermined amount, and, thereafter, the process is ended. Although the cold water flow rate controlling process is repeatedly performed at a fixed time interval, the process may return to step S 11  after completing the process of step S 14  so that a subsequent process is initiated immediately after the process is ended. 
     A description is given below of a third embodiment.  FIG. 10  is an outline diagram illustrating an entire structure of an electronic device cooling system provided with a dew condensation detecting device according to the third embodiment. In  FIG. 10 , parts that are the same as the parts illustrated in  FIG. 5  are given the same reference numerals, and descriptions thereof will be omitted. 
     In the electronic device cooling system illustrated in  FIG. 10 , similar to the second embodiment, the coupling pipe  60  is used as the heat transfer part  30  for transferring heat to the cold water. The metal member  40  may be used as the heat transfer part  30  as is in the first embodiment. 
     In the present embodiment, a heater  80  as an example of a heating part is provided between the dew condensation sensor  20  and the electronic device  10 . The heater  80  is provided for raising the temperature of the cold water entering the electronic device  10  by heating the cold water passed though the dew condensation sensor  20 . In the above-mentioned first and second embodiments, the temperature of the cold water passed through the dew condensation sensor  20  is raised by the heat transferred through the heat transfer part  30  so that the cold water becomes the cold water having a higher temperature by a predetermined temperature, and is supplied to the electronic device  10 . 
     However, if, for example, the electronic device  10  is set in a standby state and a load to the electronic parts becomes extremely small, there may be a case where the temperature of the warm water discharged from the electronic device  10  becomes extremely low. In such a case, the temperature difference between the temperature of the dew condensation sensor  20  and the temperature inside the electronic device  10  cannot be sufficient large. Thus, a period of time from the time at which a dew condensation is detected by the dew condensation sensor  20  until the time at which a dew condensation occurs in the electronic device  10  cannot be sufficiently large. 
     Accordingly, in the present embodiment, if the temperature of the warm water becomes extremely low, a dew condensation in the electronic device  10  is suppressed by raising the temperature of the cold water supplied to the electronic device  10  by driving the heater  80  to heat the cold water by the heat generated by the heater  80 . 
     Although the dew condensation sensor  20 , heat transfer part  30  (coupling pipe  60 ) and heater  80  are arranged outside the electronic device  10  but in the vicinity of the electronic device  10  in  FIG. 10 , the dew condensation sensor  20 , heat transfer part  30  (coupling pipe  60 ) and heater  80  may be arranged in the electronic device  10  if a sufficient space can be reserved in the electronic device  10 . 
     Moreover, although the heater  80  is provided between the coupling pipe  60  and the electronic device  10  in  FIG. 10 , the heater may be provided between the dew condensation sensor  20  and the coupling pipe  60 , or the heater  80  may be attached to the dew condensation sensor  20 . In this case, an insulating material is preferably provided between the heater and the dew condensation sensor  20  so that the heat of the heater  80  is not transferred to the dew condensation sensor  20 . As mentioned above, the heater  80  may be arranged at any position if it can raise the temperature of the cold water after exiting the dew condensation sensor  20  and before entering the electronic device  10 . The dew condensation sensor  20 , heat transfer part  30  (coupling pipe) and heater  80  together constitute a dew condensation detecting device. 
     Moreover, a heater that performs heating using an electric energy such as an electric heater (resistance heating heater) or conductive heater may be used as the heater  80 . Alternatively, instead of the heater  80 , heating may be performed using heat from a heating-radiating member of a peripheral device of the electric device  10 . 
       FIG. 11  is a flowchart of a cold water flow rate controlling process performed in the electronic device cooling system illustrated in  FIG. 10 . The cold water flow rate controlling process is performed repeatedly at a fixed time interval. In  FIG. 11 , steps that are the same as the steps illustrated in  FIG. 9  are given the same step numbers, and descriptions thereof will be omitted. 
     In the cold water flow rate controlling process illustrated in  FIG. 11 , if it is determined in step S 12  that the temperature Tw of the warm water is lower than the lower limit threshold value LTH, it is determined that the cooling for the electronic parts in the electronic device  10  is too much, and the process proceeds to step S 21 . In step S 21 , the control part  12   d  of the cold water supply apparatus  12  determines whether a flow rate of the cold water (21° C.) supplied from the cold water supply apparatus  12  to the cold water supply pipe  14  (that is, the electronic device  10 ) is higher than or equal to a flow rate lower limit value. 
     If the flow rate of the cold water supplied to the electronic device  10  is higher than or equal to the flow rate lower limit value (YES in step S 21 ), the process proceeds to step S 22 . In step S 22 , the flow rate of the cold water (21° C.) supplied from the cold water supply apparatus  12  to the cold water supply pipe  14  (that is, the electronic device  10 ) is reduced by a predetermined amount, and, thereafter, the process is ended. Although the cold water flow rate controlling process is repeatedly performed at a fixed time interval, the process may return to step S 11  after completing the process of step S 22  so that a subsequent process is initiated immediately after the process is ended. 
     On the other hand, if the flow rate of the cold water supplied to the electronic device  10  is less than the flow rate lower limit value (NO in step S 21 ), the process proceeds to step S 23 . In step S 23 , the flow rate of the cold water (21° C.) supplied from the cold water supply apparatus  12  to the cold water supply pipe  14  (that is, the electronic device  10 ) is maintained unchanged, and the heater  80  is activated. Thereby, the temperature of the cold water supplied to the electronic device  10  is raised by the heating by the heater  80 , which results in a sufficient temperature difference between the temperature of the dew condensation sensor  20  and the temperature inside the electronic device  10 . After the heater  80  is activated in step S 23 , the process is ended. Although the cold water flow rate controlling process is repeatedly performed at a fixed time interval, the process may return to step S 11  after completing the process of step S 23  so that a subsequent process is initiated immediately after the process is ended. 
       FIGS. 12(   a )-( e ) are time charts indicating changes in operations and temperatures of various parts when the cold water flow rate controlling process illustrated in  FIG. 11  is performed. 
     The electronic parts in the electronic device  10  are operated and a certain amount of heat is generated by the electronic parts, and the electronic parts are sufficiently cooled by a certain amount of the cold water supplied from the cold water supply apparatus  12  until time A. Accordingly, the temperature of the warm water discharged from the electronic device  10  (that is, the temperature of the warm water returning to the cold water supply apparatus  12 ) is maintained at a fixed temperature. Thus, a temperature difference between the temperature of the dew condensation sensor  20  and the temperature inside the electronic device  10  is maintained constant at a sufficient temperature difference. 
     The operating state of the electronic device  10  begins to change and the load to the electronic parts begins to decrease at time A, and, thereby, the amount of heat generated by the electronic parts decreases as illustrated in  FIG. 12(   a ). In this condition, as illustrated in  FIG. 12(   d ), the temperature of the warm water discharged from the electronic device  10  begins to fall with a slight time difference (slight time delay). Upon detection of the temperature fall of the warm water from the detection value of the water temperature sensor  12   a , the control part  12   d  of the cold water supply apparatus  12  causes, as illustrated in  FIG. 12(   b ), the amount of supply of the cold water (flow rate of the cold water) to decrease by a predetermined flow rate. As a result, as illustrated in  FIG. 12(   d ), the temperature of the warm water slightly falls and, then, rises and returns to the original fixed temperature. At this time, as illustrated in  FIG. 12(   e ) the temperature difference between the dew condensation sensor  20  and the temperature inside the electronic device  10  slightly decreases and then returns to the original temperature difference. The above-mentioned state changes are caused by the process of steps S 11 , S 12 , S 21  and S 22  in the flowchart of  FIG. 11 . 
     Subsequently, the operating state of the electronic device  10  begins to change and the load to the electronic parts begins to increase, and, thereby, as illustrated in  FIG. 12(   a ), the amount of heat generated by the electronic parts begins to increase at time B. In this condition, as illustrated in  FIG. 12(   d ), the temperature of the warm water discharged from the electronic device  10  begins to rise with a slight time difference (slight time delay). Upon detection of the temperature rise of the warm water from the detection value of the water temperature sensor  12   a , the control part  12   d  of the cold water supply apparatus  12  causes, as illustrated in  FIG. 12(   b ), the amount of supply of the cold water (the flow rate of the cold water) to increase by a predetermined flow rate. As a result, as illustrated in  FIG. 12(   d ), the temperature of the warm water slightly rises and, then, falls and returns to the original fixed temperature. At this time, as illustrated in  FIG. 12(   e ), the temperature difference between the dew condensation sensor  20  and the temperature inside the electronic device  10  slightly increases and then returns to the original temperature difference. The above-mentioned state changes are caused by the process of steps S 11 , S 12  and S 13  in the flowchart of  FIG. 11 . 
     Subsequently, the operating state of the electronic device  10  begins to change and the load to the electronic parts begins to greatly decrease, and, thereby, as illustrated in  FIG. 12(   a ), the amount of heat generated by the electronic parts begins to greatly decease at time C. In this condition, as illustrated in  FIG. 12(   d ), the temperature of the warm water discharged from the electronic device  10  begins to fall with a slight time difference (slight time delay). Upon detection of the temperature fall of the warm water from the detection value of the water temperature sensor  12   a , the control part  12   d  of the cold water supply apparatus  12  causes the amount of supply of the cold water (flow rate of the cold water) to decrease by a predetermined flow rate. 
     However, because the decrease in the amount of heat generated by the electronic parts is large, the temperature of the warm water continues to rise even after the amount of supply of the cold water is decreased, and, thereby, the amount of supply of the cold water is further decreased. Thus, the amount of supply of the cold water (the flow rate of the cold water) greatly decreases, and becomes smaller than the flow rate lower limit value as illustrated in  FIG. 12(   b ). Then, the heater  80  is turned on so that a voltage is applied to the heater  80 , as illustrated in  FIG. 12(   c ), in order to maintain the temperature difference by raising the temperature of the cold water. Thus, the heater  80  generates heat and the cold water supplied to the electronic device  10  is heated. 
     When the cold water to be supplied to the electronic device  10  is heated, the temperature of the warm water discharged from the electronic device  10  is raised again and returns to the original temperature difference as illustrated in  FIG. 12(   d ). Thereby, the temperature difference also increases and returns to the original temperature difference. Thus, a sufficient period of time from the time at which the condensation sensor  20  detects a dew condensation until the time at which a dew condensation occurs in the electronic device  10  can be reserved, which allows taking measures for preventing a dew condensation in the electronic device  10 , such as turning off the system power supply. 
     The state changes after time C correspond to the state changes due to the process of steps S 11 , S 12 , S 21 , S 22 , S 112 , S 12 , S 21  and S 23  in the flowchart illustrated in  FIG. 11 . 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed a being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relates to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present invention (s) has(have) been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.