Abstract:
An apparatus and a method for thermal management of a component in a first region, wherein an interconnector connects the component thermally to a second heat region, wherein a thermally conducting heat shield encloses the interconnector from a position within the first region in close proximity to the component to the second region, and that at least one heat unit is thermally connected to the interconnector within the second region. The heat units may be heat sources and/or heat sinks, and the invention may manage the component at a higher or lower temperature than the surrounding first region. When heat enters the heat shield from a hot surrounding first region, e.g. hot gas, the heat shield conducts heat more efficiently than the medium encapsulated by the heat shield. Thus, the heat tends to follow the path provided by the heat shield. Areas of use include providing efficient particle deposition by thermophoresis or heat a component in a cold environment.

Description:
[0001]    The present invention concerns an apparatus and a method for thermal management of a component in a first region, which may be hot or cold compared to a surrounding second region. 
       BACKGROUND OF THE INVENTION 
       [0002]    There is sometimes a need to cool or heat a device or component locally in a first region which is hotter or cooler than the temperature in a second, ambient region. Some examples are:
       Particle detection by thermophoresis, where particles, e.g. soot, is deposited on a sensor area when the sensor area is significantly cooler than the surrounding hot fluid flow. Applications include detecting soot in the exhaust gases from a combustion engine or from a combustion oven.   Regenerating a sensor by burning off deposited particles.   Cooling electronic and other components for a proper and reliable operation in hot environments, e.g. in wells for production of hydrocarbons or geothermal industry.   Heating a frozen, movable component, in particular where use of electricity for heating is impractical or prohibited.       
 
         [0007]    It is noted that the above applications may involve thermal management in corrosive, hot and/or otherwise harsh or hostile environments. 
         [0008]    An example is drawn from the automotive industry and a project to detect soot particle content in the exhaust gas system of diesel engines (Soot sensors for a healthy environment, SootSens, MNT ERA-Net TRANSNATIONAL CALL 2007). The sensor concept is based on the physical phenomenon thermophoresis. Thermophoretic deposition of particles in a gas is driven by the temperature gradient (Messerer et. al. “Thermophoretic deposition of soot aerosol particles under experimental conditions relevant for modern diesel engine exhaust gas systems”, Journal of Aerosol Science, April 2003). The theory states that soot particles are drawn towards colder regions in the gas and finally deposit onto a cold surface, if present. Soot deposited on top of a common finger electrode structure changes the electrical resistance of the electrode, which can be monitored, i.e. soot can be detected. This information can be used in a monitoring system to indicate when a filter is full or damaged and regeneration or replacement is required. 
         [0009]    The particle velocity for thermophoresis is directly proportional to the temperature gradient between the hot gas and the cooler sensor area. Thus, a high temperature gradient in the sensor vicinity is believed to increase the sensitivity of a sensor in a low soot concentration environment, as more soot will be deposited. Preliminary results show that a temperature difference of 50-70° C. between the sensor surface and the hot gases is sufficient for a thermophoresis based soot sensor to work. 
         [0010]    The exhaust pipe may provide an excellent heat sink for a thermophoresis based sensor disposed in the hotter gases within the pipe. However, a reasonably good thermal conductor e.g. a alumina sensor substrate, when inserted through the exhaust wall and directly exposed to the exhaust gas flow, will typically not transfer sufficient heat for soot sense applications based on thermophoresis. In other words, an alumina sensor substrate quickly accumulates heat from the ambient gas, and approach the gas temperature. The resulting temperature gradient within the substrate will be sharp and located close to the exhaust pipe wall. Hence the remaining parts, including the sensor surface at the substrate tip inside the pipe and away from the pipe wall, will have a temperature very close to that of the gas. Thus, even when the sensor substrate is a reasonably good heat conductor, and even if the temperature difference between the exhaust gases and the exhaust pipe is considerably greater than the 50-70° C. required for a thermophoresis based sensor to work, the substrate alone will not provide the cooler surface required for such a sensor. 
         [0011]    Insulating parts of the substrate from direct exposure to the gas has shown that the temperature gradient within the alumina extends further away from the exhaust pipe wall. I.e. the sensor surface temperature, at the tip, will be reduced. 
         [0012]    Conventional heat insulation, e.g. steel wool wound around the sensor substrate (i.e. thermal interconnector), has been shown inadequate to maintain a 50-70° C. temperature difference between the hot exhaust gas and the sensor area. The required volume of insulation for sufficient performance is significant. An exhaust pipe has limited space available for a sensor application, hence bulky insulation or cooling equipment will simply not be an option. 
         [0013]    Thermophoresis can also be used to detect particle contents in the exhaust gases from a combustion oven, as it is a suitable method to detect low particle concentrations in hot gases. In this application, the exhaust gas temperature may exceed 300° C., and the pipe diameter and other dimensions are generally larger than in the previous example. Still, a sensor needs to be put into the hot gases away from a colder exhaust conduit. The sensor must provide a cool surface, and there is still limited space available for any bulky insulation or cooling equipment. Local active cooling may be expensive and/or inadequate with respect to size requirements. 
         [0014]    In another example, thermal management can be employed in the process to regenerate the sensor surface from the above examples: When soot deposits, the soot sensor looses its sensitivity. However, reliable and accurate measurements over time may be required in applications such as long time monitoring of a particular filter status, for monitoring a diesel engine exhaust gas system, etc. Particles can be removed by cremation, i.e. by increasing the sensor surface temperature to transform the particles to combustion gases and ash, e.g. to a surface temperature above 600° C. Conducting the required power through the sensor and/or sensor electronics may burn off sensor elements and/or wiring as well as soot and other particles. 
         [0015]    Thus, a temperature increase in the sensor area is required without increasing the temperature in the wires above the melting point of the electrical insulation materials, the bonding etc. In other words, a substantial amount of the supplied heat energy should be provided by a secondary heat path. Additional heat may be supplied locally through the sensor area, as long as it does not exceed the limits for the sensor and/or the electronics, etc. 
         [0016]    Another example involve a movable component that needs a temporary motion in an icy environment, e.g. a ship in the Arctic, where sea spray and temperatures below 0° C. build layers of ice on rigging and deck equipment. 
         [0017]    Ice will hamper movable parts from operating properly. Water has a considerable heat capacity, impeding the progress of melting. Obviously, the melting process can be speeded up and energy consumption held at a minimum by heating the components locally. This can be achieved by local thermal management, in particular by heating the component to a temperature above 0° C. while the surrounding ice is exposed to minimal heat transfer from the supplied power. 
         [0018]    Electric resistors of various forms are typically used for such local heating applications. An electric resistor emits heat when an electric current passes though, and can generally be adapted to the application at hand in an easy manner. However, special care must be taken when using electricity in applications like this. Among other things, proper electric insulation must be provided to ensure that no part of the electric circuit comes into contact with water at any point in time. In areas with explosion hazard, use of electricity may be prohibited. 
         [0019]    In other words, thermal management of the component from a region outside the cold area, including the ice, without use of electricity, will be highly advantageous for this type of application. In particular, local thermal management with a minimum of power losses will be advantageous. 
         [0020]    Lab-on-a-chip applications were local precision heating without electrical connection or where space is limited is also an area of application for this invention. 
         [0021]    Thus, an objective of the present invention is to provide thermal management of a component mounted on an interconnector, where the component, e.g. a sensor or a moving part, is disposed in a first thermal region and thermally connected to a second thermal region by the interconnector. 
         [0022]    Further objectives include provision for a simple and cost effective design with focus on reliable and durable operation, with the option to easily miniaturize the thermal management system. 
         [0023]    Areas of use include providing efficient particle deposition by thermophoresis and other applications where a comparatively small region it to be managed thermally with respect to its surroundings. 
       SUMMARY OF THE INVENTION 
       [0024]    This objective is achieved by providing an apparatus and a method for thermal management of a component in a first region, wherein an interconnector connects the component thermally to a second heat region, wherein a thermally conducting heat shield encloses the interconnector from a position within the first region, in close proximity to the component, to the second region, and that at least one heat unit is thermally connected to at least one of the heat shield and the interconnector within the second region. 
         [0025]    The basic idea behind the invention is to utilize the relative thermal resistance of different parallel heat paths. 
         [0026]    When heat enters the heat shield from a hot surrounding first region, e.g. hot gas, the heat shield conducts heat more efficiently than the medium encapsulated by the heat shield. Thus, the heat tends to follow the path provided by the heat shield i.e. the path with low thermal resistance, rather than dissipating through it and enter the encapsulated region, where an interconnector is to be kept at a lower temperature. The heat from the heat shield is dissipated through a proper heat unit, in this case a heat sink, at a suitable location in connection with the second region, rather than heating the encapsulated region. Thus, the need for bulky insulation is significantly reduced. 
         [0027]    When a heat unit in the form of a heat source provides the thermally conductive heat shield with heat, e.g. for cremation of deposited particles as discussed above, heat is conducted through the heat shield to the component location. In this case, heat is also radiated from the heat shield to the surrounding environment, and in one embodiment, the top face of the heat shield can have a parabolic shape that concentrates radiation from the heat shield to the sensor area, heating the sensor surface. It is noted that in a practical soot sensor, all or part of the heat required to burn off soot may be provided through the interconnector, and that providing heat through the heat shield in the above example is for illustrative purposes only. 
         [0028]    Another way of heating the component within the first region, is by connecting a heat source in the second region to the interconnector, which conducts heat to the component. This assumes that the thermal conductivity of the interconnector is sufficient to provide enough energy transport to the component. In this case, the heat shield will shield the interconnector from the first region, which is now a cold region relative to the hotter second region. This may be an energy efficient way of heating a component to a desired temperature, e.g. the movable part encapsulated in ice or burning soot off of a sensor surface as discussed above. Further, as heat is transferred as heat, there is no need for electrical heating in the first region, with its adherent limitations, as mentioned previously. 
         [0029]    When the heat shield is disposed in a first region which is colder than the second region, e.g. when the heat shield is enclosed in ice, heat emanated from a hot interconnector enters the heat shield from the inside. If the heat shield conducts heat more efficiently than the surrounding medium, e.g. ice, the heat is again conducted to a proper heat sink. In this case the heat could be used to heat the interconnector, rather than, for example, unnecessary melting of the ice. 
         [0030]    These and other features and benefits are properly disclosed in the accompanying claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The invention will be better understood from the following detailed description with reference to the accompanying drawings, where like numerals refer to similar, but not necessarily equal, parts throughout the several figures, and where: 
           [0032]      FIG. 1  is a perspective view of a heat shield and interconnector assembly 
           [0033]      FIG. 2  indicates the interior of the assembly in  FIG. 1 . 
           [0034]      FIG. 3   a,b  are side views of the assembly in  FIG. 1 , seen from angles 90° apart 
           [0035]      FIG. 4  is a top view of the assembly of the previous figures 
           [0036]      FIG. 5  shows a cross section taken along the line A-A in  FIG. 4   
           [0037]      FIG. 6   a - c  are schematic views of a first embodiment 
           [0038]      FIG. 7   a - c  are schematic views of a second embodiment 
           [0039]      FIG. 8  is a schematic view showing convection in a heat shield 
           [0040]      FIG. 9   a, b  are schematic views of a third embodiment 
           [0041]      FIG. 10  is a schematic view of an embodiment with extra support 
           [0042]      FIG. 11  is a perspective view of the embodiment in  FIG. 10   
           [0043]      FIG. 12  is an enlarged, cross sectional view of a detail on  FIG. 2   
       
    
    
     DETAILED DESCRIPTION 
       [0044]      FIGS. 1-5  illustrates preferred embodiments of the present disclosure through several views and cross sections viewed from different angles. The component to be thermally managed is represented by  120 , and is mounted on or is a part of an interconnector  110 . A thermally conducting heat shield  130  encloses the interconnector  110  up to the component  120  that is required to be exposed to a first region. As used herein, the terms first and second region refer to distinct thermal regions, i.e. regardless whether the regions are otherwise connected and regardless of their other properties. 
         [0045]    The part referenced by  220  in  FIG. 1  is a fitting, which can either be a thermal conductor or insulator in the context of thermal management and this disclosure. The main purpose for fitting  220  is to mechanically connect the interconnector  110  to the heat shield  130  and/or provide a seal, separating the first region from the interior of the heat shield. In other contexts, the parts represented by numeral  220  throughout the description, claims and drawings have different functions like; fastening or sealing one part to another, e.g. the heat shield  130  to the interconnector  110  Parts, e.g.  220 , can be provided to allow for use of materials with different coefficients of thermal expansion (CTE), and for this purpose be, e.g., an elastomer, a sheet of ceramic paper or a small gap. In general, an insulator, or more precisely an element with a low thermal conductivity, may intentionally be inserted between elements to reduce thermal flow e.g. between the heat shield and the interconnector. However, for simplicity, parts acting as thermal resistors in the context of thermal management are here collectively referenced by numeral  210 , regardless of their other functions as adhesives, sealants, adaptors for thermal expansion, lids, other structural elements, etc. 
         [0046]    It is noted that impact from CTE mismatch will decrease with a decrease in contact area and length. In the present disclosure, the contact area at the interconnection between the heat shield and the component and/or the interconnector can be small or even omitted from the design. The present invention therefore provides a viable way to minimizing or eliminating CTE mismatch. 
         [0047]    The first region can be the interior of a conduit or container for a hot or cold flowing or stationary fluid, in which the component  120  is inserted. For illustrative purposes, the figures show a part of a conduit wall  200  separating the first and second thermal regions. Thus, in the figures, the first region is simply the region above the conduit wall  200 , and the second region is the area below the conduit wall  200 . However, it should be understood that the component  120  to be thermally managed can be enclosed in a solid, e.g. ice or an alloy, in which case there is no need for a physical wall  200 . Further, a physical container or conduit would obviously have some structured design and a temperature gradient separating the first and second regions. As this structure and temperature gradient are irrelevant for the present disclosure, they are simply not shown. 
         [0048]      FIGS. 6   a - c  is schematic views of various embodiments, in which the heat shield  130  is open towards the second region. This is mainly meant to indicate that the ambient fluid can provide sufficient thermal insulation between the interconnector  110  and the heat shield  130 . In some applications, this ambient fluid will be air or some other gas. However, any ambient fluid could enter the cavity within the open heat shield in  FIGS. 6   a - c . For example, in the introduction chapter, an oil well application is mentioned, where a component  120  might be disposed in fluid, represented by the first region, having a pressure of several hundred bars. A typical well tool, represented by the second region, may be filled with a clean liquid, e.g. mineral oil. The clean mineral oil will be mechanically isolated from the surrounding oil well, while the pressure can be, but does not have to be balanced to that of the surrounding fluids. The liquid within the well tool (second region) will have low compressibility and is expected to provide sufficient thermal insulation for the purposes of the concrete application of the present invention. 
         [0049]    In  FIG. 6   a , the interconnector  110  and heat shield  130  share a heat unit  300 , which may be a heat sink or a heat source depending on the application; heating or cooling the component. A thermal resistor  210  is shown between the heat shield  130  and the conduit wall  200 , to indicate that the heat may not flow effectively to the conduit wall  200  in all applications. In fact, the conduit wall may not even exist in all applications. This is the case when, for example, a heat shield is enclosed in ice. 
         [0050]    For clarity, the thermal resistor  210 /fitting  220  shown in  FIG. 1  and several other thermal resistors and/or fittings are omitted from the schematic views in  FIG. 6   a - 9   b . However, in a physical embodiment, parts may be joined by an adhesive or a mechanical connection, or require some means to allow for differences in thermal expansion coefficient, both of which change the thermal resistance. See also the description of  FIG. 1 . 
         [0051]      FIG. 6   b  illustrates a combination in which the interconnector  110  and heat shield  130  are connected to separate heat units  300  and  301 . Either of the heat units  300 ,  301  may be a heat sink or a heat source. Thus, in the example of a movable frozen part in an icy environment, from the introduction chapter, the heat unit  301 , connected to the interconnector  110 , would be a heat source providing heat to melt the ice around the component  120 , and the heat unit  300 , connected to the heat shield  130 , would be a heat sink to dissipate excess heat, to prevent unintentional and energy consuming melting of ice. If the medium or lack of medium (vacuum) enclosed by the heat shield  130  is transparent to heat radiation (IR), the interior surfaces may be surface treated to reduce heat from being transferred by radiation between them, e.g. polish them to be reflective. 
         [0052]      FIG. 6   c  shows a special case of  FIG. 6   b , in which the conduit wall  200  doubles as a heat unit  300  for the heat shield  130 . In the example with a soot sensor from the introduction chapter, the component  120  would be the sensor area required to be kept 50-70° C. below the ˜300° C. of the exhaust gases. The first region would be the interior of the exhaust pipe, or strictly speaking, the region where the sensor element  120  is inserted into the gas flow, some distance away from the exhaust pipe wall. The second region would be the general region from the exhaust pipe and radially outwards from it. Thus, in this example, the heat unit  301  would be a heat sink to cool the component  120  rather than a heat source to heat the component as in the previous example. The exhaust pipe, represented by the conduit wall  200 , may be an excellent heat sink  300  for the heat shield  130  because
       a) it typically has a temperature well below the exhaust gas temperature, e.g. 120° C. vs the first regions 300° C.   b) the exhaust pipe has a large heat capacity compared to the sensor assembly  110 ,  120 .   c) the heat from the exhaust pipe  200 ,  300  is readily dissipated into the second region, e.g ambient air and nearby metallic parts.       
 
         [0056]      FIGS. 7   a - c  show configurations similar to the ones in  FIGS. 6   a - c  respectively, but where the heat shields in  FIG. 7  are closed towards the second region. Typically the interior is escaped to generate a substantially lower pressure, or “vacuum”. The walls inside the cavity are typically polished to be reflective. Both the vacuum and the reflective surfaces provide a reduction of heat transfer between the heat shield and the interconnector. 
         [0057]    In particular,  FIG. 7   a  illustrates a configuration with low thermal resistance between the interconnector  110  and the heat shield  130 , whereas  FIGS. 7   b  and  7   c  show a thermal resistor or insulator between the interconnector  110  and the heat shield  130 . As noted, a fitting  220  or a thermal resistor or insulator  210  may be present between the interconnector and heat shield in the upper part of the schematic views, including  FIGS. 6   a - 9   b.  Such fittings, resistors or insulators are merely not shown in the schematic figures. 
         [0058]    As discussed in connection with  FIG. 6 , the heat shield can be filled with a gas or a liquid.  FIG. 8  is intended to illustrate that the fluid can be circulated within the cavity of the heat shield  130  when required. The circulation may be provided by a pump (not shown) circulating fluid, e.g. a fan circulating air in an open configuration as shown in  FIGS. 6   a - c  or a pump circulating a liquid in a closed configuration as shown in  FIGS. 7   a - c . Boundary conditions at the interconnector  110  and heat shield  130  can also cause natural convection in the cavity, When the configuration is closed, it is important that too much heat does not accumulate within the circulating fluid. Hence, an external heat sink would typically be provided to cool the circulating fluid as it passes the bottom lid in  FIG. 8 , and the bottom wall would preferably be good heat conductor rather than the insulator indicated in  FIG. 8 . 
         [0059]    It should also be noted that the circulation may be in the opposite direction of the one that shown in  FIG. 8 , i.e. into the cavity adjacent the interconnector  110  and in the outward direction along the heat shield  130 . 
         [0060]      FIGS. 9   a, b  illustrates that the interior of the heat shield can be a medium or combination of any media of any phase, including solid or granular media. The requirement for a solid medium may be determined by a structural mechanics point of view, e.g. to withstand extensive mechanical loads. For example, if the temperature in the first region is time dependent or transient, the interior can be filled with a mechanically strong solid or granular medium with a large heat capacity, e.g. titanium. In this way, a large, but short temperature change in the first region will only slightly affect the overall temperature of the encapsulated medium. 
         [0061]      FIGS. 10 and 11  show the embodiment of  FIGS. 1-5  with a support  140  disposed between the interconnector  110  and the heat shield  130  in order to provide mechanical stability or rigidity to the structure. It is readily understood that several such supports may be disposed if needed. 
         [0062]      FIG. 12  is an enlarged view of the top of the heat shield/interconnector assembly. In particular, the fitting  220  between the interconnector  110  and the heat shield  130  is apparent. Also, the reference numeral  120  points to a sensor assembly covered by an extension of the shield  130 . In some applications, the sensing surface can be in contact with the gases. In other applications, the component, including a sensor, may be entirely encapsulated. It should be noted that any sensor  120  may be protected by a cover and/or an extension of the shield  130  in this manner. 
         [0063]    If the temperature at the component is requested to be stable, a medium with a large heat capacity, will act as a method to control and reduce temperature fluctuations within the component. 
         [0064]    From the discussion above, it should be clear that, any combination of a heat shield  130  open or closed to a surrounding second region, filled with air, another gas, liquid, a solid or granular material can be used in different applications. Any of these combinations can further be configured with a heat shield  130  connected to a heat sink or heat source  300 ,  301 . The heat sink  300 ,  301  may be, but does not have to be, the heat sink  300 ,  301  that dissipate heat from an interconnector  110 , or heat source  300 ,  301  that provide heat to an interconnector  110  and/or a heat shield  130 . Any of these variants may, in turn, be combined with any interconnector  110  and component  120  which is to be thermally managed. Further, the medium within the heat shield  130  is generally chosen to avoid heat transfer between the interconnector  110  and the heat shield  130 , but may be chosen to inhibit thermal exchange between the interconnector  110  and the heat shield  130 . Elements  210  and  220  with a different thermal conductivity than adjacent elements may be required between any elements of the structure, e.g. to compensate for differences in thermal expansion. Surface treatment may be used to minimize heat transfer between the interconnector  110  and the heat shield  130  e.g. reflecting surfaces. Obviously, the application determines the exact embodiment of the invention. 
         [0065]    Although the present invention has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art are also within the scope of the invention. Accordingly, the scope of the invention is intended to be defined only by reference to the appended claims. While variations have been described and shown, it is to be understood that these variations are merely exemplary of the present invention and are by no means meant to be limiting.