Patent Publication Number: US-11024450-B2

Title: Controllable magnetorheological fluid temperature control device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 14/833,223, filed Aug. 24, 2015, which is a continuation of co-pending U.S. patent application Ser. No. 14/818,733, filed Aug. 5, 2015, which is related to U.S. patent application Ser. No. 14/818,722, titled “Controllable Magnetorheological Fluid Temperature Control Device,” filed Aug. 5, 2015. The aforementioned related patent applications are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     The present invention relates to a method and apparatus to control heat transfer between two objects, and more specifically, a method and apparatus to control heat transfer using a system of manipulating magnetorheological fluid. 
     Electronic devices perform tasks, which are becoming more complicated and computationally intensive with each passing year. In response to the requirements placed on these electronic devices, semiconductor die need to perform at ever-increasing levels of performance. To provide the increased performance, successive generations of electronic devices include semiconductor die having smaller design rules which enable higher data speeds with the tradeoff of generating more heat in successively smaller spatial volumes. Further, as semiconductor die to the larger electrical device becomes more densely packed. This dense interconnection circuitry may become a physical obstacle to remove heat from the semiconductor die and contributes to the heat generated by the electrical device. Heat is often removed from the electrical device as materials making up the electrical device may be altered by temperatures above a certain threshold and these temperatures may adversely change electrical characteristics of the materials. For example, power leakage through transistors on logic circuitry may occur as the temperature is increased and data integrity issues may occur when memory cells are exposed to temperatures outside their operating range. Also, removing heat may reduce extreme temperature fluctuations in the electrical device, which can damage components through expansion and contraction when power is cycled on and off. 
     Conventional heat transfer approaches for semiconductor die include passive air convection, forced air conduction, and/or thermal sinks. However, these approaches are becoming less effective given the greater amounts of heat being generated in reduced spatial volumes. A known inefficiency in server and other electronic cooling is the underutilization of heat sinks based on chip usage. For example, when one processor is being used at fully capacity and another adjacent processor is not being used, the heat sink volume of the unused processor is being wasted. 
     Thus, an apparatus and method for heat to be transferred between two objects when desired are needed. 
     SUMMARY 
     According to one embodiment, a method includes providing a first current through a first electromagnet to align particles in a magnetorheological fluid to conductively couple a first conductive element to a second conductive element and providing a second current through a second electromagnet to align the particles in the magnetorheological fluid to conductively uncouple the first conductive element from the second conductive element. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIGS. 1A-1C  illustrate one embodiment of a temperature control device during different stages of a current being supplied therein. 
         FIG. 2  illustrates one embodiment of the magnetic flux lines generated through the temperature control device of  FIGS. 1A-1C . 
         FIG. 3  illustrates another embodiment of a temperature control device, as disclosed herein. 
         FIG. 4  illustrates a method of controlling temperature using the temperature control device of  FIGS. 1A-1C , according to one embodiment. 
         FIGS. 5A-5D  illustrate one embodiment of a temperature control device during different stages of a current being supplied therein. 
         FIG. 6  illustrates one embodiment of the magnetic flux lines generated by the first electromagnet and the second electromagnet of the temperature control device illustrated in  FIGS. 5A-5D . 
         FIG. 7  illustrates a method of controlling temperature using the temperature control device of  FIGS. 5A-5D , according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  illustrates one embodiment of a temperature control device  100  to control heat transfer between two objects. The temperature control device  100  may include a container  102 , at least one biasing element, an electromagnet  108 , and a plurality of conductive elements  110 ,  112 . The container  102  includes a first end  114  and a second end  116 . The first conductive element  110  is disposed at the first end  114  of the container  102 . The second conductive element  112  is disposed at the second end  116  of the container  102 . In some embodiments, the first and second conductive elements  110 ,  112  impinge on the container  102 . 
     In one embodiment, the temperature control device  100  includes a first biasing element  104  and a second biasing element  106 . While embodiments of the present disclosure are described having two biasing elements, it is noted that other embodiments may include any number of biasing elements in a variety of configurations and arrangements, such as more than two biasing elements, only one biasing elements, or even no biasing elements. The first biasing element  104  is coupled to the first conductive element  110 . The first biasing element  104  is configured to move the first conductive element  110  relative to the container  102 . The second biasing element  106  is coupled to the second conductive element  112 . The second biasing element  106  is configured to move the second conductive element  112  relative to the container  102 . In the embodiment shown in  FIG. 1 , the first and second biasing elements  104 ,  106  are coaxial with the first and second conductive elements  110 ,  112 . The temperature control device  100  may further include a third conductive element  122  and a fourth conductive element  124 . The third conductive element  122  may be coupled to the first biasing element  104 , opposite the first conductive element  110 . The fourth conductive element  124  may be coupled to the second biasing element  106 , opposite the second conductive element  112 . The first conductive element  110 , the first biasing element  104 , the second conductive member  112 , and the second biasing member  106  form compliant sections that permit the ends  114 ,  116  to move closer together. 
     The electromagnet  108  is disposed about the container  102 . In one embodiment, the electromagnet  108  may be a solenoid disposed around the container  102 , although other embodiments are possible. The electromagnet  108  is coupled to a power source  210 . The power source  210  is configured to provide a current through to the electromagnet  108  to generate a magnetic field about the container  102 . For example, the generated magnetic field may be parallel to the container  102 . 
     The container  102  may contain a fluid  118 . The fluid  118  may be a magnetorheological fluid (MR fluid)  118 . The MR fluid  118  contains a plurality of ferromagnetic particles  126 . Initially, the particles  126  are randomly distributed throughout the MR fluid. The particles  126  are configured to align with magnetic flux lines of a magnetic field when a magnetic field is generated about the container  102 . The alignment of the particles  126  is configured to conductively couple the first conductive element  110  to the second conductive element  112  such that heat may be transferred through the temperature control device  100 . For example, when the power source  210  provides a current to the electromagnet  108  to generate a magnetic field about the container with magnetic flux lines parallel to the container, the particles  126  in the MR fluid  118  will align with the magnetic flux lines in a parallel arrangement to conductively couple the first conductive element  110  to the second conductive element  112 . The container  102  may be a flexible container that is configured to be constricted responsive to movement of the first conductive element  110  and the second conductive element  112  against the first end  114  and the second end  116 , respectively. 
     In the embodiment shown in  FIG. 1A , the biasing elements  104 ,  106  are in a relaxed initial position. The biasing elements  104 ,  106  are in the relaxed positions because no current is provided to the electromagnet  108 . When no current is provided to the electromagnet  108 , particles  126  in the MR fluid  118  are not aligned. Thus, the first conductive element  110  is not conductively coupled with the second conductive element  112 . 
       FIG. 1B  illustrates one embodiment of the temperature control device  100  when a current, I, is provided to the electromagnet  108 . In operation, the power source  210  provides a current, I, to the electromagnet  108 . Responsive to providing current I to the electromagnet  108 , a magnetic field is generated within the container  102 . 
       FIG. 2  shows an enlarged view of the container  102  of the temperature control device  100  depicting the magnetic field. The magnetic field generated within the container  102  contains flux lines  202  parallel to the container  102 . The particles  126  in the MR fluid  118  align with the flux lines  202  to create a parallel arrangement of particles  126 . The alignment of the particles  126  in the direction of the magnetic field increases the heat transfer in the axial direction due to the different in thermal conductivity of the MR fluid  118 . 
     Referring back to  FIG. 1B , the magnetic field pulls the first biasing element  104  towards the first end  114  of the container  102  and the second biasing element  106  towards the second end  116  of the container  102 . As a result, the first biasing element  104  biases the first conductive element towards the first end  114  of the container  102  and the second biasing element  106  biases the second conductive element towards the second end  116  of the container  102 . The biasing of the conductive elements  110 ,  112  constricts the flexible container  102 . Constricting the flexible container  102  reduces an initial area  148  of the flexible container  102  between the first conductive element  110  and the second conductive element  112 . A reduced area  150  results in an increased concentration of particles  126  in the MR fluid  118 . 
     The magnetic field generated by the electromagnet  108  influences the particles  126  to align with the magnetic flux lines. The magnetic field, in addition to the reduced area  150 , creates a plurality of chains  128  of particles  126  in the MR fluid  118 . The chains  128  are aligned with the magnetic flux lines, parallel to the container  102 , and coaxial to the conductive elements  110 ,  112 . The chains  128  conductively couple the first conductive element  110  to the second conductive element  112 . By conductively coupling the first conductive element  110  to the second conductive element  112 , heat is transferred through the temperature control device  100 . For example, heat may be transferred in the direction illustrated by line  130 . In  FIG. 1B , the rate of heat transfer is not at its maximum. As illustrated, a plurality of particles  126  remain scattered in the MR fluid  118  because only moderate current is provided to the electromagnet  108 . 
       FIG. 1C  illustrates the temperature control device  100  according to one embodiment. In  FIG. 1C , maximum current is provided to the electromagnet  108 . The maximum current increases the strength of the generated magnetic field. The increased magnetic field pulls the first biasing element  104  further towards the first end  114  of the container  102  and the second biasing element  106  further towards the second end  116  of the container  102 . The first biasing element  104  biases the first conductive element  110  further towards the first end  114  of the container  102  and the second biasing element  106  biases the second conductive element  112  further towards the second end  116  of the container  102 . The additional biasing of the conductive elements towards the ends  114 ,  116 , respectively, further constricts the flexible container  102 . Further constricting the flexible container  102  reduces the area  150  of the flexible container to an area  152 . The reduced area  152  results in a larger concentration of particles  126  in the MR fluid  118  as compared to the concentration of particles  126  in the MR fluid  118  in areas  148 ,  150 . 
     The increased magnetic field generated by the electromagnet  108  influences more particles  126  to align with the magnetic flux lines. The magnetic field, in addition to the reduced area  152 , creates a greater plurality of chains  128  of particles  126  in the MR fluid  118 . The increased number of chains  128  increases the conductive coupling between the first conductive element  110  and the second conductive element  112 . At maximum current, heat transfer is at its greatest and the number of particles  126  scattered is minimized. 
     The current provided to the electromagnet  108  may be reduced to decrease the rate of heat transfer through the temperature control device  100 . Reducing the current through the electromagnet  108  reduces the strength of the magnetic field. The first and second biasing elements  104 ,  106  begin to relax when the strength of the magnetic field is reduced. The first conductive element  110  and the second conductive element  112  move back to the initial positions. The container  102  expands, thus increasing the reduced area  152  back to the initial area  148 . The expansion of the container  102  breaks the chains  128  of particles  126  in the MR fluid  118 . The rate of heat transfer through the temperature control device  100  is decreased because breaking the chains of particles  126  in the MR fluid conductively uncouples the first conductive element  110  from the second conductive element  112 . To stop heat transfer through the temperature control device  100 , the power source  210  provides no current to the electromagnet  108  resulting in the biasing elements  104 ,  106  moving back to an initial relaxed position and the reduced area  152  of the container  102  expanding back to the initial area  148 , and returns to the state depicted in  FIG. 1A . 
     The embodiments shown in  FIGS. 1A-1C  illustrate a certain level of displacement between the conductive elements via the biasing elements. However, those skilled in the art will appreciate that in another embodiment, it may be preferred to accept a lower maximum displacement. This may be done by including only one biasing element. 
       FIG. 3  illustrates another embodiment of a temperature control device  300 . It should be understood that other configurations of the temperature control device may be utilized. For Example,  FIG. 3  illustrates another embodiment of the temperature control device wherein the biasing elements need not be axially aligned with the conductive member  110 ,  112 . The temperature control device  300  includes a plurality of biasing elements  302 ,  304 ,  306 ,  308 . The first biasing element  302  and the second biasing element  304  are coupled to the first conductive element  110 . The biasing elements  302 ,  304  are not axially aligned with the conductive element  110 . The third biasing element  306  and the fourth biasing element  308  are coupled to the second conductive element  112 . The biasing elements  306 ,  308  are not axially aligned with the conductive element  112 . The biasing elements  302 ,  304  are configured to bias the first conductive element  110  relative to the container  102 . The biasing elements  306 ,  308  are configured to bias the second conductive element  112  relative to the container  102 . 
       FIG. 4  illustrates a method  400  of transferring heat through a temperature control device, such as the temperature control device of  FIGS. 1A-1C . The method begins at block  402 . At block  402 , a power source provides a current to an electromagnet disposed around a container containing MF fluid. The electromagnet generates a magnetic field about the container. The magnetic field causes a first biasing element to bias a first conductive element positioned on one end of the container towards the container, and a second biasing element to bias a second conductive element positioned on a second end of the container towards the container. The movement of the first conductive element and the second conductive element constricts the container. Particles in the MR fluid align themselves with the magnetic flux lines in the magnetic field to form chains of particles. The constriction of the container increases the concentration of the chains in the MR fluid. The alignment of the particles conductively couples the first conductive element to the second conductive element. The conductive coupling allows heat to transfer through the temperature control device. The amount of heat transfer may be controlled by adjusting the current provided to the electromagnet. 
     At block  404 , the current provided to the electromagnet is reduced to reduce heat transfer through the temperature control device. Reducing the current weakens the strength of the magnetic field about the container. The decreased strength results in the biasing elements biasing the first and second conductive elements away from the container. The concentration of chains of particles in the MR fluid is reduced due to the reduction in magnetic flux lines and the expansion of the container holding the MR fluid. The amount of heat transferred through the temperature control device may be reduced to zero if current is no longer provided to the electromagnet. When current is no longer applied to the electromagnet, the first and second conductive elements are moved back to their initial positions. Additionally, the chains of particles in the MR fluid are broken, and the particles are randomly scattered. As such, there is no longer a conductive coupling between the first and second conductive elements. 
     Blocks  402 - 404  may be repeated to vary the amount of heat transferred through the temperature control device. 
       FIG. 5A  illustrates one embodiment of a temperature control device  500  to control heat transfer between two objects. The temperature control device  500  may include a container  502 , a plurality of conductive elements  504 ,  506 , a first electromagnet  508 , and second electromagnet  510 . The container  502  includes a first end  512  and a second end  514 . The first conductive element  504  is disposed at the first end  512  of the container  502 . The second conductive element  506  is disposed at the second end  514  of the container  502 . 
     The electromagnet  508  is disposed about the container  502 . The electromagnet  508  may be, for example, a solenoid disposed about the container  502 . The electromagnet  508  is coupled to a power source  520 . The power source  520  is configured to provide a first current to the electromagnet  508  to generate a magnetic field about the container  502 . For example, the generated magnetic field may be parallel to the container  502 . 
     The container  502  may be a flexible container that is configured to be constricted responsive to movement of the first conductive element  504  and the second conductive element  506  against the first end  512  and the second end  514 , respectively. The container  502  may contain a fluid  516 . For example, the fluid  516  may be an MR fluid. The MR fluid  516  contains a plurality of particles  518 . The particles  518  may be magnetic. Initially, the particles  518  are randomly distributed through the fluid  516 . The particles  518  are configured to align with magnetic flux lines of a magnetic field when the magnetic field is generated about the container  502 . The alignment of the particles  518  is configured to conductively couple the first conductive element  504  and the second conductive element  506  such that heat may be transferred through the temperature control device  500 . For example, when the power source  520  provides a current to the electromagnet  508  to generate a magnetic field about the container with magnetic flux lines parallel to the container, the particles  518  in the MR fluid  516  will align with the magnetic flux lines in a parallel arrangement to conductively couple the first conductive element  504  to the second conductive element  506 . 
     The second electromagnet  510  is positioned perpendicular to the electromagnet  508 . In the embodiment shown in  FIGS. 5A, 5B, 5C, and 5D , the second electromagnet  510  is positioned above the electromagnet  508 . The second electromagnet  510  is coupled to the power source  522 . The power source  522  is configured to provide a current through the second electromagnet  510  such that a magnetic field is generated. The magnetic field generated by the second electromagnet  510  is orthogonal to the magnetic field generated by the electromagnet  508 . In one embodiment, the second electromagnet  510  may be replaced with a permanent magnet. 
     In the embodiment shown in  FIG. 5A , a current has not been provided to the electromagnet  508 . When no current is provided to the electromagnet  508 , the particles  518  in the MR fluid  516  are randomly scattered and not aligned. Thus, the first conductive element  504  is not conductively coupled with the second conductive element  506 . As such, heat cannot be transferred through the temperature control device  500 . 
       FIG. 5B  illustrates one embodiment of the temperature control device  500  when a current, I 1 , is provided to the electromagnet  508 . The power source  520  provides the current I 1  to the electromagnet  508 . Responsive to providing a current to the electromagnet  508 , a magnetic field is generated through the electromagnet  508 . 
       FIG. 6  shows an enlarged view of the container  502  of the temperature control device  500  depicting the first magnetic field  600 . The first magnetic field  600  contains flux lines  602  parallel to the container  502 . The particles  518  in the MR fluid  516  will align with the flux lines  602  to create a parallel arrangement of particles  518 . Referring back to  FIG. 5B , the magnetic field influences the particles  518  to align in the direction of the flux lines  602 . The particles  518  form a plurality of chains  524  that conductively couple the first conductive element  504  to the second conductive element  506 . By conductively coupling the first conductive element  504  to the second conductive element  506 , heat may be transferred through the temperature control device  500 . The direction of heat transfer is illustrated by line  526 . Because only moderate current has been provided to the electromagnet  508 , a plurality of particles  518  remain scattered in the MR fluid  516 . Thus, the rate at which heat is transferred in  FIG. 5B  is not at its maximum. 
       FIG. 5C  illustrates the temperature control device  500 , according to one embodiment. In  FIG. 5C , maximum current is provided to the electromagnet  508  by the first power source  520 . The maximum current increases the strength of the magnetic field about the container  502 . The number of chains  524  of particles  518  formed in the MR fluid  516  is at its maximum, and the number of particles  518  that remain scattered are minimized. The increased number of chains  524  increases the conductive coupling between the first conductive element  504  and the second conductive element  506 . At maximum current, heat transfer through the temperature control device  500  is at its greatest. 
       FIG. 5D  illustrates the temperature control device  500 , according to one embodiment. The power source  520  reduces the current provided to the electromagnet  508  to decrease the rate of heat transfer through the temperature control device  100 . To reduce alignment of the particles  518  in the MR fluid  516 , the power source  520  reduces the current I 1  in conjunction with providing a current I 2  to the second electromagnet  510 . The power source  522  provides the current I 2  to the second electromagnet  510  to generate a magnetic field substantially perpendicular to the magnetic field generated by the electromagnet. 
       FIG. 6  illustrates an enlarged view of the container  502  with both the first and second magnetic fields provided through the container  502 . The second magnetic field  604  contains magnetic flux lines  606 . The magnetic flux lines  606  are substantially perpendicular to the magnetic flux lines  602 . 
     Referring back to  FIG. 5D , the current I 2  may be pulsed to the second electromagnet  510  during a gap in the current I 1  provided to the electromagnet  508 . Pulsing the current I 2  forces some or most of the particles  518  in the MR fluid  516  out of alignment from the chains  524 . The decrease in current I 1  provided to the electromagnet  508  continues to move the particles  518  to a lesser state of alignment. When the current I 1  provided to the electromagnet  508  is zero, the particles  518  in the MR fluid  516  will align with the magnetic flux lines  606 , to form chains  528 . The chains  528  conductively uncouple the first conductive element  504  from the second conductive element  506 . Heat transfer through the temperature control device  500  is thus decreased. For example, heat transfer through the temperature control device  500  may be reduced by 50%. 
       FIG. 7  illustrates a method  700  of controlling heat transfer through a temperature control device, such as the temperature control device  500  as illustrated in  FIGS. 5A-5D . The method  700  begins at block  702 . At block  702 , the power source provides a first current to an electromagnet. The electromagnet is disposed about a container holding MR fluid. The electromagnet generates a magnetic field about the container. A first conductive element is positioned on a first end of the container. A second conductive element is positioned on a second end of the container. When the magnetic field is generated, magnetic particles in the MR fluid align themselves with the magnetic flux lines of the magnetic field. The alignment of the particles in the MR fluid creates a plurality of chains. The plurality of chains in the MR fluid conductively coupled the first conductive element to the second conductive element. As such, heat may be transferred through the temperature control device. The amount of heat transfer may be controlled by adjusting the current provided to the electromagnet. 
     At block  704 , a power source provides a second current to a second electromagnet. The second electromagnet is disposed perpendicular to the first electromagnet. The second electromagnet generates a second magnetic field. The second magnetic field is perpendicular to the first magnetic field. To reduce the amount of heat transfer through the temperature control device, the second current is pulsed to the second electromagnet during a gap in the first current provided to the first electromagnet. The pulsing of the current forces most of the particles in the plurality of chains out of alignment. The first current provided to the first electromagnet is decreased to continue to move the particles to a lesser state of alignment. The first conductive element is conductively uncoupled from the second conductive element when the first current goes to zero, and the plurality of particles for a plurality of horizontal chains, aligning with the magnetic flux lines of the second magnetic field. 
     Blocks  702 - 704  may be repeated to vary the amount of heat transferred through the temperature control device. 
     EXAMPLE 
     An example using the temperature control device  100  of  FIGS. 1A-1C  is disclosed herein. The temperature control device is used to control the heat transfer between a central processing unit (CPU) heat sink connected to a heat sink on a Peripheral Component Interconnect Express (PCIe). The temperature control device may be connected between the CPU heat sink and the PCIe. When the CPU is being used at full capacity and the PCIe is not being used, the full volume of the heat sink connected to the PCIe is not being used. It is desirable for the CPU to use the extra surface area of the PCIe heat sink while the PCIe is not being used. 
     The temperature control device allows the CPU to use the extra surface area of the PCIe heat sink by transferring heat from the CPU heat sink to the PCIe heat sink. For example, the CPU heat sink may be coupled to the third conductive element of the temperature control device and the PCIe heat sink may be connected to the fourth conductive element of the temperature control device. When it is desirable to use the extra surface area of PCIe heat sink, the first power source provides a first current to the electromagnet. The electromagnet then generates a magnetic field, which influences the first and second biasing elements to bias the first and second conductive elements towards the first and second ends of the container holding MR fluid. The particles in the MR fluid align with the magnetic flux lines of the magnetic field to form chains of particles. The chains conductively couple the first conductive element to the second conductive element so that heat may transfer through the temperature control device. Thus, the heat generated by the CPU can be transferred to the PCIe heat sink to utilize the extra surface area of the PCIe heat sink. 
     When the PCIe card usage is increased, the amount of heat transferred from the CPU to the PCIe heat sink may be decreased. To decrease the amount of heat transferred, the current provided to the electromagnet may be reduced to decrease the number of chains of particles formed in the MR fluid and to expand the container of MR fluid. By alternating between increasing and decreasing the current provided to the electromagnet, the user may more effectively control the heat transfer from both the CPU heat sink to the PCIe heat sink and back from the PCIe heat sink to the CPU heat sink. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.