Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention disclosed and claimed herein generally pertains to an apparatus and method for controlling the flow of liquid coolant to a liquid flow through (LFT) heat exchanger, such as a heat exchanger used to provide cooling for one or more electronic devices. More particularly, the invention pertains to an apparatus and method of the above type, wherein a component located proximate to a heat exchanger regulates coolant flow automatically, in response to changes in coolant temperature. 
     2. Description of the Related Art 
     High performance computing systems are using ever-increasing amounts of power, at higher power densities. As a result, it has become common to meet system cooling requirements by means of LFT heat sink and heat exchange technologies. Also, semiconductor electronic devices that have very different cooling requirements from each other, because of different size or duty cycle, may be located on the same PCB assembly, or may otherwise be adjacent to each other. This situation presents a further challenge. 
     Conventional heat sink and heat exchange technologies have generally carried out their tasks in the static domain. That is, a heat exchanger typically cannot actively control or adjust its own cooling profile. If such active control were to be achieved, it could permit the operational function of maintaining the multiple devices which were adjacent to one another at the same temperature. Alternatively, such active control capability could permit the temperatures of different device types, such as processors, memories and voltage regulator modules, to be selectively offset from one another. 
     SUMMARY OF THE INVENTION 
     In embodiments of the invention, a system for providing coolant to a number of heat exchangers, each adjacent to one or more different electronic devices, includes the same number of valves. Each valve is located proximate to one of the heat exchangers, and automatically controls the flow of coolant thereto based on the temperature local to that valve. Each of the valves comprises a device such as a bi-metallic actuator, or a shape memory alloy (SMA) which has a metallic component that changes shape in response to temperature. One embodiment of the invention is directed to coolant flow control apparatus, in association with an LFT heat exchanger situated to remove heat from one or more electronic devices. The apparatus comprises a first input channel for carrying liquid coolant to a first input of the heat exchanger, and further comprises a flow control device positioned along a flow path that includes the first input channel. The flow control device is provided with a gating element supported for selected movements across the flow path, in order to selectively vary the amount of coolant moving through the flow path. The apparatus further includes an actuator located in the flow control device that comprises a metal component which is directly tied to the gating element. The metal component changes its shape in response to specified changes in coolant temperature, and a given change in the shape of the metal component acts to selectively move or displace the gating element with respect to the flow path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an embodiment of the invention. 
         FIG. 2  is a schematic diagram depicting a thermally actuated valve for the embodiment of  FIG. 1  that uses a bimetallic actuator. 
         FIG. 3  is a schematic diagram showing a heat exchanger for the embodiment of  FIG. 1  in greater detail. 
         FIG. 4  is a block diagram illustrating a further embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown a configuration of LFT heat exchangers  102   a - c ,  106   a - b , and  110   a - q  that are grouped together. Each of the heat exchangers is placed upon a corresponding electronic device, to selectively remove heat therefrom. For example, each of the heat exchangers  102   a - c  is positioned to provide cooling or heat removal for a voltage regulator module (VRM)  104 , as shown in connection with heat exchanger  102   c . Heat exchangers  106   a - b  are each similarly positioned to provide cooling or heat removal for a processor  108 , as shown in connection with heat exchangers  106   a  and  b . Heat exchangers  110   a - q  are each positioned to provide cooling for a dynamic random access memory (DRAM)  112 , as shown in connection with heat exchanger  110   b . These electronic devices are respectively mounted upon a common platform or carrier, such as a PCB  100 . 
     It is to be emphasized in regard to embodiments of the invention that one or more of the heat exchangers shown in  FIG. 1  could, if desired, provide heat removal for multiple corresponding devices, and are thus not limited to cooling only a single device. For example, heat exchanger  110   a  could be mounted upon the two DRAMS  112 , rather than a single DRAM, and provide cooling for both DRAMS. 
     Referring further to  FIG. 1 , it is shown that each of the LFT heat exchangers has at least two input channels or lines, for receiving a coolant fluid such as water, and also has one or more output channels. For example, heat exchanger  102   a  has input channels  116  and  118  and output channels  128 - 134 ; heat exchanger  102   b  has input channels  120  and  122 , and output channels  136 - 140 ; and heat exchanger  102   c  has input channels  124  and  126 , and output channels  142 - 146 . 
     Moreover, as an essential feature of embodiments of the invention, a temperature responsive flow control device is placed in one of the coolant input channels of each of the heat exchangers shown in  FIG. 1 . Thus, flow control devices  130   a - c  are positioned to control or modulate coolant flow through each of the channels  118 ,  122 , and  126 , to inputs of heat exchangers  102   a - c , respectively. Each of the flow control devices comprises a thermally actuated valve. 
     In a configuration of electronic devices as disclosed by  FIG. 1 , different types of devices can dissipate very different amounts of thermal power. Also, different devices of the same type can dissipate different amounts of thermal power, such as when they have different duty cycles, and a particular device can dissipate different amounts of thermal power at different times. Accordingly, in embodiments of the invention thermally actuated valves as referred to above are distributed among a network of coolant flow paths of a heat exchanger arrangement, so that each valve is proximate or local to a heat exchanger which is provided for one of a plurality of electronic devices. The valve for a particular heat exchanger is responsive to changes in coolant temperature at its heat exchanger, to selectively increase or decrease the flow of coolant thereto. 
     As a further important feature of embodiments of the invention, each of the coolant flow devices, or thermally actuated valves, comprises a mechanism having a metal component that changes or shifts its shape, in response to an adjacent change in temperature or thermal energy. One type of such mechanism uses a bimetallic member, as described hereinafter in connection with  FIG. 3 . Another type, such as a shape memory alloy (SMA), employs a memory metal. By using a device of such type for the thermally actuated valves, each valve will operate automatically, in response only to local temperature change, to vary the coolant flow to its heat exchanger. Each such valve or coolant flow device thus needs no other direction or regulation. 
     By incorporating the above capabilities, embodiments of the invention provide a cooling system which dynamically configures system components to adjust or vary coolant flow, such as to direct more coolant flow to regions where electronic devices are running hotter and producing more thermal energy. These system embodiments operate automatically, and have no need of any external logic to manage their cooling performance or function. 
     As a useful feature for certain embodiments of the invention, each of the heat exchangers of  FIG. 1  also receives coolant from a coolant input channel that is not regulated or modulated by a flow control device or valve, of the type described above. For example,  FIG. 1  shows heat changers  102   a - c  receiving coolant from unmodulated input channels  116 ,  120 , and  124 , respectively. Since different types of electronic devices can have very different cooling requirements, the unmodulated input channels can be used to provide different amounts of static cooling to the different devices. Also, use of the unmodulated coolant input channels provides a measure of safety, such as to prevent overheating in the event that one of the thermally actuated valves malfunctions. In some embodiments of the invention, the unmodulated coolant input channels would not be needed. 
     Referring further to  FIG. 1 , there is shown heat exchangers  110   a - d  receiving coolant from unmodulated channel  128 , and also receiving coolant from channel  132  through respective flow control devices  154 . Heat exchangers  110   n - q  receive coolant from unmodulated channel  146 , and also receive coolant from channel  144  through respective flow control devices  154 . 
     Heat exchanger  106   a  receives coolant from two unmodulated channels  134  and  136 , and has an output channel  148 . Heat exchanger  106   b  likewise receives coolant from two unmodulated channels  140  and  142 , and has an output channel  150 . Both heat exchangers  106   a  and  106   b  receive coolant from input channel  138  through two flow control devices  152 . 
       FIG. 1  further shows heat exchangers  110   e - g  receiving coolant from unmodulated channel  148 . Heat exchangers  110   h - j  receive coolant from unmodulated channel  138 , and heat exchangers  110   k - m  receive coolant from unmodulated channel  150 . Heat exchangers  110   e - m  also receive coolant from channel  138 , through respective flow control devices  154 . 
       FIG. 1  additionally shows an output channel  156 , which is positioned to carry coolant away from respective heat exchangers of  FIG. 1 . 
     Referring to  FIG. 2 , there is shown a thermally actuated valve  200  which may usefully be employed in embodiments of the invention as a coolant flow device that is responsive to temperature changes, such as devices  130   a - c  described above.  FIG. 2  shows flow device  200  in two different modes of operation, referenced as modes (A) and (B). Each mode shows device  200  provided with a housing or case  202 , and with a gate  204 . Gate  204  is mounted for linear movement with respect to housing  202 , or for upward and downward movement as viewed in  FIG. 2 . 
     Coolant flow device  200  is usefully placed within the coolant fluid chamber of a heat exchanger, such as heat exchanger  102   a  of  FIG. 1  by way of example, and is immersed in the coolant fluid contained in the heat exchanger. Flow device  200  is thus able to readily respond to changes in coolant temperature, such as when the heat exchanger receives increased thermal energy from its associated electronic device. Flow device  200  is also positioned to selectively close or seal an input port  206  of the heat exchanger, wherein port  206  passes coolant into the heat exchanger from an input channel, e.g. channel  118  of  FIG. 1 . 
     Referring further to  FIG. 2 , there is shown a circular aperture  208  formed through gate  204 . When aperture  208  is at least partially aligned with port  206 , coolant can flow into the heat exchanger through the port  206 . Thus, the amount of coolant flow allowed by device  200  can be varied, by moving gate  204  upward or downward as viewed in  FIG. 2 . In mode (A) of  FIG. 2 , a portion  210   a  of aperture  208  is aligned with port  206 . This alignment enables an amount of coolant to flow into the heat exchanger which is 15% of the maximum amount which would flow if the entire area of aperture  208  was aligned with port  206 . Mode (B) of  FIG. 2  shows a portion  210   b  of aperture  208  aligned with port  206 , wherein this alignment enables 85% of the maximum coolant amount to flow into the heat exchanger. It is to be emphasized that both the 15% and 85% amounts are given by way of example only, and do not in any way limit the scope of the invention. 
     In order to linearly move gate  204  and aperture  208  automatically, and in response to local coolant temperature change within the heat exchanger, a bimetallic strip  212  is joined to gate  204 . A bimetallic strip generally is used to convert a temperature change into mechanical displacement, and comprises two strips of metal that have different coefficients of thermal expansion (CTE). Thus, bimetallic strip  212  comprises strips  212   a  and  212   b , wherein by way of example one of the strips could be formed of steel and the other of copper or brass. Strips  212   a  and  212   b  are rigidly bonded to each other along their respective lengths. 
     Mode (A) of  FIG. 2  shows strips  212   a  and  212   b  in a relaxed condition, at some temperature. In Mode (B), the temperature of coolant adjacent to device  200  has increased. This causes strips  212   a  and  212   b  to both expand. However, because of the difference in CTE of the two strips, the combined structure  212  is caused to bend. This, in turn, moves gate  204  and aperture  208  to increase the flow of coolant into the heat exchanger, through port  206 . 
     It is anticipated that a wide range of design choices is available, in embodiments of the invention that employ flow control device  200  of  FIG. 2 . For example, gate  204  could be moved to control coolant flow over a range of 0% to 100% of the possible maximum amount. Alternatively, the range could be designed to lie between 15% and 85% of the maximum, as depicted by Modes (A) and (B), respectively, of  FIG. 2 . Flow control device  200  could also be designed for binomial, linear or non-linear operation, to implement a selected functional relationship between temperature and coolant flow. 
     In other embodiments of the invention, a shape memory alloy (SMA) could be used instead of the bimetallic strip of  FIG. 2 . An SMA is an alloy that remembers its original cold forged shape, and returns to its predeformed shape when heated. 
     Referring to  FIG. 3 , there is shown one of the heat exchangers of the embodiment of  FIG. 1 . More particularly,  FIG. 3  depicts an overhead view of heat exchanger  110   b , with a section broken away to illustrate a flow control device  302  located within heat exchanger  110   b . Device  302  includes a gate  304 , which is pivotable about a hinge  306  to selectively close or seal a port  310 , and thus prevent coolant flow into heat exchanger  110   b  from input channel  132 . Gate  304  may be pivoted further to enable pre-determined amounts of coolant to flow into heat exchanger  110   b  from channel  132 . 
       FIG. 3  further shows gate  304  moved by an actuating mechanism  308  that comprises a bimetallic coil. Coil  308  is contained within the coolant chamber of heat exchanger  110   b , and is designed to respond to rising temperature therein by moving gate  304  to open port  310 , to enable or increase coolant flow into heat exchanger  110   b  from channel  132 . Coil  308  responds to falling temperatures by moving gate  304  to prevent or reduce the flow of coolant from input channel  132 . Bimetallic coil  308  comprises a strip formed of two metal strips with different CTEs, as described above, which is wound into the form of a spiral or the like. Usefully, gate  304  is covered with a layer of insulating material  312 , to provide a thermal barrier between coolant in the chamber of heat exchanger  110   b , and the coolant in input channel  132 . 
     The rate of opening or closing the flow control device  302  could be a design variable. The flow control could be configured to open around a particular temperature, or could begin to open upon reaching a specified narrow temperature range. By judicious selection of the materials for the bimetallic strips as well as their respective CTEs, their thicknesses and three dimensional shapes, flow control device  302  may be selectively tuned, in order to provide a minimum temperature at which the input coolant port begins to open, and the rate at which it opens. 
     Multiple flow control devices may also be constructed in accordance with embodiments of the inventions, for use with different heat exchangers that are adjacent to one another. Different flow controls may be tuned so that they are offset from each other, that is, they respond to different respective temperatures. The flow control devices could also be designed for binomial, linear and non-linear operation. 
     Referring to  FIG. 4 , there are shown a number of the LFT heat exchangers of  FIG. 1 , respectively mounted on a PCB  400  or the like, to illustrate a further embodiment of the invention.  FIG. 4  thus includes heat exchangers  102   a - b ,  106   a  and  110   a - j , which each provides cooling for a corresponding electronic device as described above. Each of the heat exchangers shown in  FIG. 4  has at least two coolant output channels, and one or more coolant input channels. Accordingly, heat exchanger  102   a  has input channels  116  and  118 , and output channels  402 ,  404  and  406 . Segments of channels  402  and  404  respectively serve as input and output channels for heat exchangers  110   a - d.    
     Similarly, heat exchanger  102   b  has input channels  120  and  122 , and output channels  408  and  410 . Segments of channel  410  respectively serve as input and output channels for heat exchangers  110   h - j . Channels  406  and  408  are coolant input channels for heat exchanger  106   a , and a segment of channel  406  comprises an output channel therefor. Segments of channel  406  respectively serve as input and output channels for heat exchangers  110   e - g.    
     Referring further to  FIG. 4 , it is seen that a coolant flow control device of the type describe above is placed in one of the coolant channel outputs of each heat exchanger. Thus, flow control devices  412  are positioned to control coolant flow out from heat exchangers  102   a  and  102   b , through channels  402 ,  406  and  408 . In this configuration, respective flow control devices may limit or regulate coolant flow to downstream heat exchangers. For example, the flow control device  412  in channel  402  can impact coolant flow to each of the heat exchangers  110   a - d . Moreover, each of the heat exchangers  110   a - j  has a flow control device  414  at one of its output channels, and thus can likewise impact downstream heat exchangers. 
       FIG. 4  further shows heat exchanger  106   a  having a coolant flow device  416  in its output channel  406 . Also, each of the heat exchangers has at least one output coolant channel that is unmodulated or not controlled. Thus, heat exchangers  102   a - b  have unmodulated output channels  404  and  410 , respectively, and heat exchanger  106   a  has unmodulated output channels  418  and  420 . Heat exchangers  110   a - d ,  110   e - g  and  110   h - j  have unmodulated output channels  404 ,  418  and  422  respectively. 
       FIG. 4  further shows the embodiment thereof provided with a coolant output channel  424 . 
     In embodiments of the invention, modulated and unmodulated channels can be of different aperture sizes with respect to each other. Also, channels can be straight, serpentine or comprise a cavity within a heat exchanger. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

Technology Category: 5