Liquid coolant circulating system

Abstract: A liquid coolant circulating system includes a discharge pump (103), a cooling tank (107), a recovery pump (108), a heat exchanger (106), a detector (109), and a controller (111). The cooling tank (107) is filled with liquid coolant for immersing an object (105) to be cooled. The discharge pump (103) is on the inlet side of the cooling tank, and supplies liquid coolant to the cooling tank at a predetermined flow rate. The recovery pump (108) is on the outlet side of the cooling tank, and recovers liquid coolant from the cooling tank. The heat exchanger (106) is on the outlet side of the recovery pump, and cools heated liquid coolant to a predetermined temperature and supplies cooled liquid coolant to the discharge pump, e.g. via a buffer tank (101). The detector (109) detects a value related to a pressure in the cooling tank. The detected value may, e.g. be the pressure in the cooling tank, the level in the buffer tank or in a buffer tank between the cooling tank and the recovery pump, or the flow rate or the pressure at the input and/or outlet of the cooling tank, or combinations thereof. The controller (111) controls the recovery pump in response to a signal from the detector.

Description: The present invention relates to a liquid coolant circulating system for an immersion cooling system. Fig. 3 shows a conventional coolant circulating system. This is a system for circulating and supplying a liquid coolant to an object to be cooled such as a liquid-cooled electronic part. In Fig. 3, reference numeral 1 denotes a buffer tank for absorbing the variation in volume of a coolant 2 caused by a change in temperature; 3, a discharge pump for supplying the coolant 2 in the buffer tank 1 to an object 5 to be cooled, such as an electronic part, through a pipe 4; 6, a heat exchanger for cooling the coolant 2 which is heated by cooling the object 5 such as an electronic part to a predetermined temperature and returning the coolant 102 to the buffer tank 1; and 7a, a cooling tank with the object 5 in it. Note that a constant flow rate valve for obtaining a predetermined flow rate for the liquid coolant may be arranged on the outlet side of the discharge pump 3 as needed. The operation of the coolant circulating system will now be described. The coolant 2 in the buffer tank 1 is supplied to the cooling tank 7a by the discharge pressure of the discharge pump 3 through the pipe 4 to cool the object 5. Thereafter, the coolant 2 is cooled to a predetermined temperature by the heat exchanger 6 and returned to the buffer tank 1. Fig. 4 shows another conventional coolant circulating system. In Fig. 4, reference numeral 7b denotes a cooling tank filled with an insulating liquid coolant 2. In the coolant circulating system with this arrangement, the object 5 to be cooled, such as an electronic part, is immersed in the insulating liquid coolant 2 and cooled by boiling the coolant 2. Although this insulating liquid coolant 2 is circulated from the output of the buffer tank 1 back to the buffer tank 1 through a pipe 4, the cooling tank 7b, and a heat exchanger 6, by the discharge pressure of a discharge pump 3, the insulating liquid coolant 2, the temperature of which rises, can by cooled to a predetermined temperature by the heat exchanger 6. Note that a cooling scheme using a nucleate boiling scheme is used in the cooling tank 7b to increase the cooling efficiency. In the conventional liquid coolant circulating system described above, however, since only the discharge pump 3 is used as a means for circulating the coolant 2, a discharge pump having a high discharge pressure must be used. In the coolant circulating system shown in Fig. 4, a circulating system consists of only the discharge pump 3. For this reason, the so-called return pressure of the coolant path extending from the outlet of the coolant tank 7b to the buffer tank 1 through the heat exchanger 6 is charged on the coolant in the coolant tank 7b. As a result, since the boiling point of the coolant in the cooling tank 7b rises, boiling is not promoted, and a sufficient cooling effect cannot be obtained. In addition, since the pressure charged on the flow path is also increased, the withstanding pressure of the cooling tank 7a, the heat exchanger 6 and the like, constituting the flow path, must be excessively increased. The present applicant's copending European patent application no: 91309381.1 (EP-A-0480750), which forms part of the state of the art for the present application according to article 54(3) EPC, discloses a liquid cooling system for LSI packages comprising a cooling tank in which are sealed the packages to be cooled. A discharge pump discharges coolant liquid through a series of nozzles arranged in the cooling tank onto the packages to be cooled. The coolant is withdrawn from the tank by a recovery pump and returned to the discharge pump through a heat exchanger. Detection means are provided to detect the pressure in the tank and control means control the recovery pump in response to the detected pressure. The present invention in its various aspects is defined in the appended claims, to which reference should now be made. The invention will be described in more detail, by way of example, with reference to the drawings, in which: Fig. 1 is a view showing an arrangement of a liquid coolant circulating system according to an embodiment of the present invention; Fig. 2 is a view showing an arrangement of a liquid coolant circulating system according to another embodiment of the present invention; Fig. 3 (referred to above) is a view showing an arrangement of a conventional liquid coolant circulating system; and Fig. 4 (referred to above) is a view showing an arrangement of another conventional liquid coolant circulating system. Fig. 1 shows a liquid coolant circulating system according to an embodiment of the present invention. In Fig. 1, reference numeral 101 denotes a buffer tank; 103, a discharge pump; 106, a heat exchanger; 107, a cooling tank; 108, a recovery pump; and 111, a recovery pump controller. The buffer tank 101 absorbs variations in the volume of coolant 102 caused by changes in temperature. The discharge pump 103 supplies the coolant 102 in the buffer tank 101 to an object to be cooled 105 such as an electronic part through a pipe 104. The heat exchanger 106 cools the coolant 102, which is heated by cooling the object 105, for example an electronic part, to a predetermined temperature, and the heat exchanger 106 returns the coolant 102 to the buffer tank 101. The cooling tank 107 immerses the object 105 in the coolant 102 consisting of an insulating liquid. Reference numeral 113 denotes a second buffer tank connected to the outlet side of the cooling tank 107, and reference numeral 114 denotes a liquid-level sensor having a high liquid-level float 115 for detecting a high liquid-level of the coolant 102 in the second buffer tank 113 and a low liquid-level float 116 for detecting a low liquid-level. The liquid-level sensor 114 detects these floats and outputs a detection signal to the recovery pump controller 111 through a detection line 110. The recovery pump controller 111 receives the liquid level detection signal, controls a recovery amount of the coolant 102 of the recovery pump 108 such that the pressure in the cooling tank 107 is set at the predetermined pressure, and outputs a control signal to the recovery pump 108 through a control line 112 to prevent the boiling point of the coolant 102 from rising. Arrows indicate the direction of flow of the coolant 102. Note that an inverter-controlled pump capable of continuously varying the coolant transfer amount is used as the recovery pump 108. The operation of the liquid coolant circulating system with the above arrangement will now be described. The object 105 to be cooled, such as an electronic part, is immersed in the coolant 102 in the cooling tank 107 and cooled by boiling the coolant 102 in a nucleate boiling scheme. This coolant 102 is supplied from the buffer tank 101 to the cooling tank 107 through the pipe 104 by the discharge pump 103 at a predetermined flow rate. When the liquid level of the coolant 102 in the second buffer tank 113 rises to reach a high liquid level, the liquid-level sensor 114 detects the high liquid-level float 115 and outputs a detection signal to a recovery pump controller 111 through the detection line 110. When the recovery pump controller 111 sends a control signal to the recovery pump 108 through the control line 112, the recovery pump 108 is operated to take out the coolant 102 from the second buffer tank 113. When the liquid level of the coolant 102 in the second buffer tank 113 falls to reach the low liquid level, the liquid-level sensor 114 detects the low liquid-level float 116 and outputs a detection signal to the recovery pump controller 111 through the detection line 110. At this time, the recovery pump controller 111 sends a control signal to the recovery pump 108 through the control line 112 to stop the operation of the recovery pump 108. In this manner, since the liquid level of the coolant 102 in the second buffer tank 113 can be controlled between the levels of the high liquid-level float 115 and the low liquid-level float 116, the pressure in the cooling tank 107 can be kept almost at the predetermined pressure, (for example, atmospheric pressure) and the boiling point of the coolant 102 can be prevented from rising, thereby obtaining efficient cooling performance by boiling. The heated coolant 102 is sent to the heat exchanger 106 by the recovery pump 108, cooled to a predetermined temperature, and returned to the buffer tank 101. Fig. 2 shows an arrangement of a liquid coolant circulating system according to another embodiment of the present invention. In Fig. 2, reference numeral 117 denotes a second recovery pump controller for receiving a detection signal from a liquid-level sensor 114 through a detection line 118; and 119, a second recovery pump for receiving an output signal from the second recovery pump controller 117 through a control line 120. The liquid-level sensor 114 is arranged on a second buffer tank 113 which is arranged on the outlet side of the heat exchanger 106. The operation of the liquid coolant circulating system with the above arrangement will now be described. An object 105 to be cooled, such as an electronic part, is immersed in the coolant 102 in a cooling tank 107 and cooled by boiling the coolant 102. This coolant 102 is supplied from a buffer tank 101 to the cooling tank 107 through a pipe 104 by the discharge pump 103 at a predetermined flow rate. A pressure sensor 109 detects the pressure in the cooling tank 107 and outputs a pressure detection signal to the recovery pump controller 111 through the detection line 110. When the recovery pump controller 111 send a control signal to the recovery pump 108 through the control line 112, the recovery pump 108 is operated, and the recovery amount of the coolant 102 in the cooling tank 107 is continuously controlled to always set the pressure in the cooling tank 107 to the predetermined pressure, thereby preventing the boiling point of the coolant 102 from rising. The heated coolant 102 is supplied to the heat exchanger 106 by the recovery pump 108, cooled to a predetermined temperature, and supplied to the second buffer tank 113. When the liquid level of the coolant 102 in the second buffer tank 113 rises to reach the high liquid level, the liquid-level sensor 114 detects the high liquid-level float 115 and outputs a detection signal to the second recovery pump controller 117 through the detection line 118. When this second recovery pump controller 117 sends a control signal to the second recovery pump 119 through the control line 120, the second recovery pump 119 is operated to supply the coolant 102 in the second buffer tank 113 to the buffer tank 101. When the liquid level of the coolant 102 in the second buffer tank 113 falls to reach the low liquid level, the liquid-level sensor 114 detects the low liquid-level float 116 and outputs a detection signal to the second recovery pump controller 117 through the detection line 118. At this time, the second recovery pump controller 117 sends a control signal to the second recovery pump 119 through the control line 120 to stop the operation of the second recovery pump 119. In this manner, the liquid level of the coolant 102 in the second buffer tank 113 can be controlled between the levels of the high liquid-level float 115 and the low liquid-level float 116. In addition, since the pressure in the cooling tank 107 can be kept at the predetermined pressure, the boiling point of the coolant 102 can be prevented from rising, thereby obtaining stable cooling performance by boiling. In this embodiment, the heat exchanger 106 is connected to the inlet of the second buffer tank 113. However, the embodiment is not limited to this arrangement, and the heat exchanger 106 may be connected to the outlet of the second buffer tank 113. As described above, in a liquid coolant circulating system embodying the present invention, a pressure in a cooling tank in which an object to be cooled is immersed is directly or indirectly detected by various sensors or measuring instruments, and the operation of a recovery pump is controlled by a detection signal to control discharging of a coolant from the cooling tank. For this reason, the pressure in the cooling tank can be kept at the atmospheric or predetermined pressure, and a stable cooling ability by boiling can be obtained. In addition, the withstanding pressure of the cooling tank and the like constituting the flow path can be advantageously set to be low. The sealed liquid coolant circulating system is capable of providing a sufficient and stable cooling effect by boiling, and does not require a high capacity discharge pump.

Claims: A liquid coolant circulating system comprising: a cooling tank (107) filled with a liquid coolant (102) for immersing an object (105) to be cooled; a discharge pump (103), arranged on an inlet side of said cooling tank, for supplying liquid coolant to said cooling tank at a predetermined flow rate; a recovery pump (108), arranged on an outlet side of said cooling tank, for recovering liquid coolant from said cooling tank; a heat exchanger (106), arranged on an outlet side of said recovery pump, for cooling heated liquid coolant to a predetermined temperature and supplying cooled liquid coolant to said discharge pump; control means (111) for controlling the ability of said recovery pump; a buffer tank (113) arranged between said cooling tank and said recovery pump and filled with a liquid coolant; and a liquid-level sensor (114, 115, 116) for detecting a high liquid-level and a low liquid level of the liquid coolant in said buffer tank, and wherein said control means operates said recovery pump by a high liquid-level detection output from said liquid-level sensor to recover the liquid coolant in said cooling tank and stops operation of said recovery pump by a low liquid-level detection output to stop a recovering operation of the liquid coolant. A liquid coolant circulating system comprising: a cooling tank (107) filled with a liquid coolant (102) for immersing an object (105) to be cooled; a discharge pump (103), arranged on an inlet side of said cooling tank, for supplying liquid coolant to said cooling tank at a predetermined flow rate; a recovery pump (108), arranged on an outlet side of said cooling tank, for recovering liquid coolant from said cooling tank; a heat exchanger (106), arranged on an outlet side of said recovery pump, for cooling heated liquid coolant to a predetermined temperature and supplying cooled liquid coolant to said discharge pump; detecting means (109) for detecting a value related to a pressure in said cooling tank; control means (111) for controlling the ability of said recovery pump in response to a detection signal from said detecting means; a pressure sensor (109), used as said detecting means, for detecting a pressure in said cooling tank and outputting a detection signal to said control means; a buffer tank (113) arranged on an outlet side of said recovery pump (108) and filled with a liquid coolant; a second recovery pump (119) arranged on an outlet side of said buffer tank (113); a liquid-level sensor (114) for detecting a high liquid level and a low liquid level of the liquid coolant in said buffer tank (113); and a second control means (117) for controlling operation of said second recovery pump (119) by an output from said liquid-level sensor (114). A method of cooling an object, preferably an electronic part, comprising the steps of: providing a liquid coolant circulating system as claimed in claim 1, including a discharge pump, a cooling tank, a buffer tank filled with a liquid coolant, a liquid-level sensor for detecting a high liquid level and a low liquid level of the liquid coolant in the buffer tank, a recovery pump and a heat exchanger arranged in a closed circuit; inserting the object in the cooling tank; operating the pumps such that the object in the cooling tank is cooled by nucleate boiling; and controlling the recovery pump in response to the high liquid level detection output value from the liquid level sensor to recover the liquid coolant in said cooling tank and stop operation on detection of a low liquid level output to stop recovering operation of the liquid coolant. A method of cooling an object, preferably an electronic part, comprising the steps of: providing a liquid coolant circulating system as claimed in claim 2, including a discharge pump, a cooling tank, a first recovery pump, a buffer tank filled with a liquid coolant, a liquid-level sensor for detecting a high liquid level and a low liquid level of the liquid coolant in the buffer tank, and a heat exchanger and a second recovery pump arranged in a closed circuit; inserting the object in the cooling tank; operating the pumps such that the object in the cooling tank is cooled by nucleate boiling; detecting a value related to the pressure in the cooling tank; and controlling the second recovery pump in response to the high liquid level detection output value from the liquid level sensor to recover the liquid coolant and stop operation on detection of a low liquid level output to stop recovering operation of the liquid coolant.

Inventors: MIZUNO TSUKASA C O NEC CORPORA, MIZUNO, TSUKASA, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1992
Main classification: H05K7
IPC codes: H05K7, H01L23