Patent Application
20150292774
Harvesting of heat energy from a geothermal well (i.e., an underground region) can be useful for various purposes, including electrical energy generation, transferring heat to above ground systems for use in space heating, industrial or other processes, or other uses.
Aspects of the invention provide for heat harvesting from a geothermal well (i.e., an underground region) using one or more heat pipes. In some embodiments, one or more heat pipes may be arranged in a tree-type or other configuration and used to transfer heat from portions of the geothermal well to a heat exchanger and a heat receiving component, such as a heat exchange liquid, a thermoelectric device, or other component that receives heat, e.g., for use in generating electricity.
In one aspect of the invention, a geothermal heat harvesting system includes a heat exchanger arranged to receive heat from a geothermal well for transfer to a heat receiving component. The heat exchanger may include a cylindrical body or pipe that receives heat at its outer wall and transfers that heat to a working fluid, such as water or steam, in the heat exchanger. The heated fluid may be conducted out of the heat exchanger to a heat receiving component such as a thermal storage device, a thermal storage medium, and/or one or more thermoelectric or other power conversion devices, such as a steam turbine and generator.
One or more heat pipes may be arranged in the well to transfer heat from the well to the heat exchanger, e.g., heat pipes may be arranged around the heat exchanger and extend outwardly from the heat exchanger into hot rock or other medium of the geothermal well. The heat pipes may be arranged in one or more levels, e.g., a plurality of heat pipes may be arranged around the heat exchanger and extend radially into the geothermal well (e.g., 20 to 100 feet) at one or more vertical positions in the well. The one or more heat pipes may each have an evaporator section positioned within the geothermal well and distant from the heat exchanger, and a condenser section positioned adjacent the heat exchanger. Thus, heat received at the evaporator section may be transferred to the condenser section, which relays the heat to the heat exchanger. The heat pipes may be arranged in any suitable way, and may include a thermosiphon, a loop thermosiphon, a pulsating heat pipe, and/or an osmotic heat pipe. The heat pipes may have a length of 40 to 120 feet (or other suitable length such as up to 300 feet), and may have the condenser section aligned along a length of the heat exchanger. For example, the condenser section of the heat pipes may be uniformly spaced from the heat exchanger along a length of the condenser section of 2 to 20 feet. Thus, portions of the condenser section may be spaced from the heat exchanger to achieve a defined thermal gap or thermal resistance which helps to control the heat transfer rate between the heat pipes and the heat exchanger, allowing the heat pipe to operate at an optimal or other designed working temperature.
In some embodiments, a thermal gap material may be positioned in a thermal gap between the condenser section of the one or more heat pipes and the heat exchanger. The thermal gap material may provide a thermal coupling between the one or more heat pipes and the heat exchanger such that a desired temperature drop is incurred when heat is transferred between the one or more heat pipes and the heat exchanger via the thermal gap material. The thermal gap material may have a relatively low thermal conductivity, e.g., less than about 12 W/m-K or around 0.6 W/m-K, so as to meter heat transferred to the heat exchanger in comparison to a condition in which the heat pipe(s) are coupled to the heat exchanger by a steel or other relatively highly thermally conductive metal connection. A conduction length of the thermal gap and the thermal conductivity of the thermal gap material may be arranged to define a working temperature for the at least one heat pipe, which may be elevated above the operating temperature of the heat exchanger by 10 to 40% of the temperature difference between the heat exchanger and the geothermal resource and may allow the heat pipe(s) to harvest heat from the geothermal resource more efficiently than at lower temperatures. A majority of heat transferred between the heat pipe(s) and the heat exchanger may be transferred through the thermal gap material, e.g., 60%, 70%, 90%, 95% or more of heat transferred between the two may be transmitted through the thermal gap material.
In some embodiments, a heat spreader may be provided between the at least one heat pipe and the thermal gap material to help transfer heat from the heat pipe to the thermal gap material. Thus, the heat spreader may have a relatively high thermal conductivity, e.g., above 12 W/m-K, and be in direct thermal contact with the at least one heat pipe and with the thermal gap material. While the heat spreader may be arranged in different ways, the heat spreader may generally present a relatively smaller surface area to the heat pipe(s) for receiving heat and a relatively larger surface area to the thermal gap material. For example, the heat spreader may include a sleeve positioned over the heat pipe, and/or may include a plate with a partial cylindrical shell configuration that generally conforms to the outer periphery of a heat exchanger. The heat spreader may therefore effectively increase a surface area of the heat pipes for transferring heat to the thermal gap material.
In some embodiments, the heat pipe(s) may be mechanically coupled by a collar or other mounting component which also helps define the thermal gap between the heat pipe(s) and the heat exchanger. For example, a collar may engage with one or more heat pipes and be configured to receive the heat exchanger at an inner side of the collar, i.e., the collar may extend around the heat exchanger. The collar may help to position the one or more heat pipes from the heat exchanger so as to define a thermal gap, e.g., one or more spacer elements such as protrusions extending radially inwardly from the collar inner side may help maintain a desired distance between the heat pipe(s) and the heat exchanger. Two or more relatively short collars (e.g., 1 to 2 feet long, or more or less) may be employed, and may be spaced from each other along the condenser section of one or more heat pipes, e.g., at a distance of 10 to 20 feet or more (or less), so that portions of the heat pipes extending between the collars are suitably positioned from the heat exchanger to define a thermal gap. Alternately, a collar may have a relatively long length, e.g., of 10 to 20 feet or more (or less), and be arranged as a solid cylindrical shell, e.g., to control fluid flow in the thermal gap between the heat pipes and the heat exchanger along the length of the shell. In some embodiments, the collar may include one or more openings in the shell to permit fluid flow, e.g., to allow relatively hot fluid in the geothermal well to flow into the space between the collar and the heat exchanger and allow relatively cool fluid to exit. A collar or other mounting component may, or may not function as a heat spreader.
In one aspect of the invention, a heat pipe and mounting component apparatus for use with a heat exchanger in harvesting geothermal heat includes one or more heat pipes each having two end portions and an elongated central portion, and a mounting component dimensioned to engage and thermally couple with at least one heat pipe at or near one of the said end portions. The mounting component may be dimensioned to extend at least partially around a portion of a perimeter of the heat exchanger. For example, the mounting component may include a collar or sleeve arranged to receive a portion of a heat exchanger in the central opening of the collar, and/or may include a shoe or plate that extends around only a part of the heat exchanger. The portion of the mounting component that faces the heat exchanger may be shaped to generally conform to the shape of an adjacent portion of the heat exchanger, e.g., so that a generally uniform gap may be present between the mounting component and the heat exchanger. As will be understood by those of skill in the art, a uniform gap may provide for a uniform conduction length for heat passing between the mounting component and the heat exchanger, and thus uniform and predictable heat flow.
An interface material, or thermal gap material, may be positioned between, and thermally couple, the heat exchanger and the mounting component. The interface material may have a thermal conductivity that is less than the mounting component, and thus may provide a desired thermal gap or resistance to heat flow, e.g., to allow the one or more heat pipes to operate within an optimal working temperature range. As discussed in detail below, having a heat pipe operate in an optimal working temperature range may allow for more efficient heat harvesting. Thus, the thermal conductivity of the interface material may be selected to define an optimal heat pipe working temperature for use in harvesting geothermal energy, e.g., may be 0.5 to 12 W/m-K. Other characteristics of the thermal coupling of the heat pipe(s) to the heat exchanger, such as the surface area of the mounting component that faces the heat exchanger and the conduction length of the thermal gap, may be similarly selected to define, or otherwise be consistent with, an optimal heat pipe working temperature. In some embodiments, the optimal heat pipe working temperature may be higher than the temperature of the heat exchanger by an amount between 10% and 40% of the temperature difference between the heat exchanger and the geothermal resource. In contrast to the thermal gap material, the mounting component may have a relatively high thermal conductivity that is selected to promote heat spreading from the one or more heat pipes for transfer to the thermal gap material. As a result, a surface area of contact between the thermal gap material and the mounting component, and the thermal conductivity and thickness of the thermal gap material may be the primary controlling factors in defining a working temperature of the one or more heat pipes thermally coupled to the mounting component.
A surface area of the mounting component that faces the heat exchanger may define the surface area of contact between the thermal gap material and the mounting component, and so may help define heat flow characteristics of the heat pipe/heat exchanger thermal junction. In some embodiments, the mounting component may have a surface area facing the heat exchanger (i.e., a surface area that functions to transfer a majority of heat to the heat exchanger) that is larger than a surface area presented by the at least one heat pipe to the heat exchanger. That is, the mounting component may present a larger surface area for heat transfer to the heat exchanger than the heat pipe(s) would present in the absence of the mounting component. Such an arrangement may allow for higher heat flow rates, and/or better control over the heat flow rate of the thermal junction. In one embodiment, the surface area of the mounting component facing the heat exchanger may be at least 1 to 10 times the surface area presented by the at least one heat pipe to the heat exchanger.
The mounting component may also function to help deploy one or more heat pipes in a well and/or perform other functions. For example, the mounting component may include an upper collar portion and a lower collar portion, with the upper collar portion having one or more heat pipes fixed to the upper collar portion and the lower collar portion defining a heat pipe guide feature to receive at least one heat pipe that is fixed to the upper collar portion. The heat pipe(s) may move in a sliding relationship in the guide feature as the upper collar portion is moved toward the lower collar portion, e.g., to help guide the heat pipe(s) into side holes formed from a main well as the heat pipes are lowered into the main well bore.
In another aspect of the invention, a heat pipe and mounting component apparatus for use with a heat exchanger in harvesting geothermal heat includes one or more heat pipes each having two end portions and an elongated central portion, and a mounting component arranged and dimensioned to engage with an end portion of the one or more heat pipes and to position the end portion within a specified distance of a perimeter of the heat exchanger to define a thermal gap between the one or more heat pipes and the heat exchanger. The thermal gap may be filled by a thermal gap material that thermally couples the one or more heat pipes to the heat exchanger. The thermal gap material may have a thermal conductivity of 0.5 to 12 W/m-K that is less than the heat pipes, mounting component or heat exchanger outer surface, e.g., the thermal gap material may be water (including brine or water containing a variety of dissolved minerals and other substances) or a thermal grout, such as a cement-like substance with an engineered thermal conductivity. The mounting component may, or may not assist in transferring heat to the heat exchanger, e.g., may play a minor role in actual heat transfer. For example, a majority of heat transferred from a heat pipe to the heat exchanger may occur along portions of the heat pipe where no mounting component, heat spreader or other structure is located. In one embodiment, the mounting component includes an upper collar and a lower collar which are fixed to a set of heat pipes and are spaced from each other. Thus, an exposed portion of the heat pipes may extend between the collars and be spaced from the heat exchanger by a desired thermal gap. A bulk of heat transferred from the heat pipes to the heat exchanger may occur along the exposed heat pipe sections extending between the collars. In some embodiments, a heat spreader in the form of a sleeve may be arranged around the heat pipes, e.g., the heat pipes may include two concentric tubes with the outer tube functioning as a heat spreader.
In another aspect of the invention, a heat pipe deployment system may include one or more anti-buckling supports to assist in inserting one or more heat pipes in a geothermal well. For example, a geothermal well may be prepared for deployment of heat pipes by drilling or otherwise forming bores that extend radially outwardly from a main well bore. These bores may each receive at least one corresponding heat pipe, which is inserted into the bore from the main well bore and may have a length of 100 feet or more. To assist in inserting the heat pipe(s) into corresponding radial bores, one or more anti-buckling supports may be engaged with the heat pipe(s) to help keep the heat pipe(s) relatively straight when an axial load is applied to the pipe(s) to push the pipe(s) into the bore(s). The anti-buckling supports may disengage from the heat pipe(s) under particular conditions, such as when an axial force on the heat pipe(s) relative to the support exceeds a threshold. Thus, the anti-buckling supports may release from the heat pipes to allow their further insertion into a bore.
The system may additionally, or alternately include a heat pipe guide, or “kicker,” that helps to guide the heat pipe(s) into their respective bore. For example, the heat pipe guide may be arranged in the main well bore and include a flared or curved guide channel for one or more heat pipes. The guide channel may engage a heat pipe, e.g., at the distal end, and guide the heat pipe into a radially extending bore. The heat pipe guide may also be used to guide a tool that forms radially extending heat pipe bores, such as a rotary drilling tool, high pressure jet device, etc.
Thus, in one aspect of the invention, a heat pipe and mounting component apparatus for use with a heat exchanger in harvesting geothermal heat may include one or more heat pipes each having two end portions and an elongated central portion and an upper collar engaged with an end portion of the one or more heat pipes. An anti-buckling support, separate from the upper collar, may be attached to the one or more heat pipes at a location below and away from the upper collar. The anti-buckling support may be releasably attached to the one or more heat pipes to allow movement of the one or more heat pipes relative to the anti-buckling portion in a direction along a length of the one or more heat pipes, e.g., in response to an axial force on the heat pipe(s) relative to the anti-buckling support that exceeds a threshold.
In some embodiments, the anti-buckling support is attached to the one or more heat pipes by a frangible connection, such as a metallurgical joint or adhesive, that fixes the heat pipes relative to the anti-buckling portion until a force applied to the one or more heat pipes exceeds a threshold value. The frangible connection may fix the anti-buckling support relative to the heat pipes and the upper collar until a force moving the upper collar toward the anti-buckling portion exceeds the threshold value. For example, as a force is applied to the upper collar and/or heat pipes to push the heat pipes downwardly and into respective radial bores, the heat pipes and attached anti-buckling support may move downwardly together. However, at a specified point, such as where the anti-buckling support reaches the radial bores, the anti-buckling support may disengage from the heat pipes. In some embodiments, when the anti-buckling support disengages from the heat pipe(s), the anti-buckling portion may slide along the heat pipes such that the upper collar and anti-buckling portion move toward each other. In other embodiments, the anti-buckling portion may completely detach from the heat pipes.
In some embodiments, a lower heat pipe guide portion may also be provided which includes one or more heat pipe guides arranged to guide the one or more heat pipes in deployment in the geothermal well in directions away from the heat exchanger. For example, the anti-buckling portion may be positioned between the upper collar and lower guide portion, and the upper collar may be movable toward the lower guide portion to deploy the one or more heat pipes in the well, e.g., into radially extending bores from a main well bore. As noted above, two or more collars may be engaged with the heat pipes at an upper end, e.g., a lower collar may be engaged with the one or more heat pipes at a location below the upper collar and above the anti-buckling support. In some embodiments, the upper and/or lower collars, the anti-buckling support and/or the lower heat pipe guide may include two or more parts that are engagable with each other so as to receive a drill string or a portion of the heat exchanger between the two parts. For example, the components may be arranged in a clam shell or other configuration so that the components can be assembled over and around an existing drill string at the surface of the well.
In another aspect of the invention, a method for deploying one or more heat pipes in a geothermal well for use with a heat exchanger in harvesting geothermal heat includes providing one or more heat pipes each having a first portion engaged with an upper collar and a second portion engaged with an anti-buckling portion separate from the upper collar and attached to the one or more heat pipes at a location below the upper collar and above a distal end of the one or more heat pipes. The distal end of the one or more heat pipes may be inserted into a corresponding well bore, e.g., a bore that extends radially from a main well bore, and a force may be exerted on the one or more heat pipes so as to disengage the one or more heat pipes from the anti-buckling support. For example, the heat pipes may be forced downwardly into the main well bore such that the distal ends of the heat pipes move into a radially extending bore. The anti-buckling support may help keep the heat pipes generally straight in the main well bore (e.g., prevent buckling) until a certain point, such as when the anti-buckling support reaches a point where the heat pipes exit the main well bore and enter a radially extending bore. At this point, the heat pipes may detach from the anti-buckling support, allowing the one or more heat pipes to move in a direction along a length of the one or more heat pipes relative to the anti-buckling portion. The upper collar may be arranged adjacent a heat exchanger in the geothermal well, e.g., to position a condenser portion of the one or more heat pipes at a desired distance from the heat exchanger and thereby establish a desired thermal gap.
In another aspect of the invention, a geothermal heat harvesting system includes a heat exchanger arranged to transfer heat from a geothermal well to a heat receiving component, one or more heat pipes arranged in the well to transfer heat from the well to the heat exchanger, the one or more heat pipes having an evaporator section and a condenser section, a heat spreader in direct thermal contact with the condenser section of at least one heat pipe, and a thermal gap material positioned in a thermal gap between the heat spreader and the heat exchanger. The heat spreader may have a surface area and a first thermal conductivity, and the thermal gap material may have a second thermal conductivity that is less than the first thermal conductivity. As discussed above, a surface area of the heat spreader that functions to transfer a majority of heat to the heat exchanger, along with the thermal conductivity of the thermal gap material and a thickness of the thermal gap material (which defines the conduction length for heat moving between the heat spreader and the heat exchanger) may define a working temperature for the one or more heat pipes. In one embodiment, the heat spreader is metal and/or has thermal conductivity over 12 W/m-K, and the thermal gap material has a thermal conductivity of 0.5 to 12 W/m-K. The heat spreader may have a cylindrical shape, a partial cylindrical shell configuration, include a sleeve and/or a plate, etc., and may have a surface contour arranged to generally conform to a surface contour of a heat exchanger portion with which the heat spreader is thermally coupled. This arrangement may help define a uniform thermal gap between the heat spreader and the heat exchanger.
The geothermal heat harvesting system may be employed for any suitable purpose, e.g., the heat receiving component may include a heat exchange fluid, one or more conduits to conduct a heat exchange fluid, a thermal storage device, a thermal storage medium, and/or one or more thermoelectric or other power conversion devices. Also, heat pipes used in this or other embodiments may include a thermosiphon, a loop thermosiphon, a pulsating heat pipe, osmotic heat pipe and/or other possible specific configurations driven by other forces such as electro-osmotic, acoustic, electrical, and/or magnetic.
In another aspect of the invention, a method for deploying a thermal coupling for a geothermal device includes providing a heat exchanger in a geothermal well, providing one or more heat pipes in the geothermal well, each of the heat pipes including a condenser section located nearer the heat exchanger than an evaporator section of the heat pipe, providing a heat spreader thermally coupled to the condenser section of at least one heat pipe, the heat spreader having a first thermal conductivity, and providing a thermal gap material that extends between, and thermally couples, the heat spreader and the heat exchanger, the thermal gap material having a second thermal conductivity that is less than the first thermal conductivity. Components of the system, such as the heat spreader, thermal gap material, etc., may have any of those features described herein.
In yet another aspect of the invention, a method for designing a geothermal heat harvesting system includes determining an optimal working temperature range for one or more heat pipes used to transfer heat from portions of a geothermal well to a heat exchanger, determining a first surface area of a heat spreader to be thermally coupled to the heat exchanger based on the optimal working temperature range, the heat spreader being designed to provide heat to the heat exchanger via a thermal gap material having a thermal conductivity that is less than the heat spreader, and providing the heat spreader having the first surface area. The thermal conductivity of the thermal gap material and/or the thickness of the thermal gap material may also be determined based on the optimal working temperature range. In one embodiment, an optimal working temperature range may be determined by modeling fluid flow in the geothermal well in response to heat removal by the one or more heat pipes from portions of the geothermal well.
These and other aspects of the invention will be apparent from the following description and claims.
Aspects of the invention are described with reference to the following drawings in which numerals reference like elements, and wherein:
Aspects of the invention are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Other embodiments may be employed and aspects of the invention may be practiced or be carried out in various ways. Also, aspects of the invention may be used alone or in any suitable combination with each other. Thus, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.
It should also be understood that a geothermal well 1, as used herein, may include any underground region from which heat is harvested. In this embodiment, the well 1 is accessed by drilling using an above-surface drilling system, but the well 1 may be accessed in other ways, such as by digging a hole, providing below-ground system 100 components in the hole, and again filling the hole, whether with soil originally dug from the hole or other materials. Also, drilling to provide components in a well 1 may be done by rotating bit, fluid jet injection and/or any other suitable techniques, or combinations of such techniques.
In this embodiment, the geothermal well 1 includes fluid (such as underground water) that has at least some ability to flow in the well 1 (i.e., in a region around the below-ground components of the system 100), and therefore move heat in the well 1 by convection. However, embodiments described herein need not exchange fluid in the well 1 (e.g., underground water or steam) with fluid used by the heat harvesting system 100 to carry heat to the heat receiver 6. Instead, any fluid used by the system 100 to transport heat from the well 1 to the heat receiver 6 is generally isolated from rock, underground water and/or other features of the well. It should also be understood that aspects of the invention are not limited to such applications, however, but may be used in “dry” well 1 conditions in which fluid is not very free to flow in the well 1, or other well conditions.
The system 100 in
In accordance with an aspect of the invention, one or more heat pipes 5 are coupled with a mounting component 3 (in this example a collar or other support arranged to mount one or more heat pipes) that is positioned around at least part of an outer periphery of the heat exchanger 2 and that positions the heat pipes 5 for transfer of heat to the heat exchanger 2 via a thermal gap material 4. Thus, in this example, heat is harvested by the heat pipes 5 that extend radially from the mounting component 3 into portions of the geothermal well 1 surrounding a well bore in which the heat exchanger 2 is positioned. The harvested heat from the heat pipes 5 is transmitted to the thermal gap material 4, e.g., by conduction and/or convection, which in turn transfers heat to the heat exchanger 2. In some embodiments, heat may be conducted from the heat pipes 5 to the mounting component 3 which transfers heat to the thermal gap material 4 and into an outer wall or other suitable portion of the heat exchanger 2. Accordingly, a liquid or other fluid flowing in the heat exchanger 2 picks up the heat and transports it to the heat receiver 6. Although only two heat pipes are shown, any suitable number of such heat pipes assemblies may be arrayed along the length of the heat exchanger 2 to provide the required heat harvesting rate for a particular geothermal energy system 100. For example,
The mounting component 3 may support portions of the heat pipes 5 so that the heat pipes are spaced from the heat exchanger 2 by a thermal gap, i.e., a space of desired size and thickness to create the thermal resistance through which heat is transferred from the heat pipes 5 to the heat exchanger 2. In some embodiments, the thermal gap may be about ¼ inch to 2 inches, although other suitable spacing may be employed. Thus, the heat pipes 5 may be out of direct contact with the heat exchanger so that a majority of heat transferred to the heat exchanger is through a thermal gap material 4 located in the thermal gap, e.g., 60%, 70%, 80%, 90%, 95% or more of heat transfer may occur via the thermal gap material 4. The thermal gap material 4 may have a relatively low thermal conductivity, e.g., 0.5 to 12 W/m-K, at least as compared to a thermal conductivity of the material at the heat pipe 5 and/or heat exchanger 2 outer surface. As such, the thermal gap material 4 may meter heat transfer in a desired way, e.g., to allow the heat pipes 5 to operate at an optimal working temperature as discussed more below. The thermal gap material 4 may be or include a thermal grout, e.g., a cement-like material that is designed to have a desired thermal conductivity, or other material such as water (including water with dissolved minerals, salts and/or other material). Thus, the thermal gap material 4 may be a solid, liquid, semi-solid or other composite and may transfer heat by conduction and/or by convection.
In some embodiments, to achieve meaningful heat harvesting rates, the geothermal well should include a liquid pool or liquid-permeated porous rock so as to allow circulation of liquid within the volume of the geothermal well 1. Heat removal from the geothermal resource by the heat exchanger 2, and particularly by the heat pipes 5, cools the liquid of the well 1 and increases its density. As the denser, cool liquid sinks downwardly in the geothermal well 1, hotter liquid from below or elsewhere in or around the well 1 may move outwards and upwards to create large scale liquid circulation that may be necessary to deliver sufficient heat to the heat pipes 5 and the heat exchanger 2 for harvesting. This liquid already present in the geothermal well may itself, at least in part, function as a thermal gap material. Of course, other system 100 arrangements employing a lower heat harvesting rate need not exploit a liquid or liquid-permeated substrate and/or employ a large scale liquid circulation to operate properly. Also, although this embodiment shows the heat pipes 5 extending away from the mounting component 3 in a downward, curving arc, the heat pipes 5 may extend in a straight line and/or at any suitable angle(s) to the horizontal, including extending horizontally (or nearly so) in some embodiments.
In the gap between the mounting component 3/heat pipes 5 and the heat exchanger 2 is a thermal gap material 4, such as a thermal grout. As is explained in more detail below, the thermal conductivity of the thermal gap material 4 may be lower than the thermal conductivity of the mounting component 3 and heat pipes 5, and generally speaking, “meters” the flow of heat from the mounting component 3/heat pipes 5 to the heat exchanger 2 so that the heat pipe(s) 5 operate at an appropriate working temperature. In some embodiments, relatively little heat may be transmitted from the heat pipes 5 to the mounting component 3, so that a bulk of heat transfer from the heat pipes 5 to the heat exchanger 2 occurs directly from the heat pipes 5 to the thermal gap material 4 and then to the heat exchanger 2. However, in other embodiments, a significant amount of heat may be transferred from the heat pipes 5 to the mounting component 3, which is then transferred from the mounting component 3 to the thermal gap material 4. In this case, the mounting component 3 may function as a heat spreader, i.e., assisting to transmit heat from a first surface area of a heat pipe having a first size to a second surface area of the mounting component 3 that has a second size greater than the first size. As discussed more below, such heat spreading may assist in desired heat transfer to the heat exchanger, and to do so, a heat spreader may have a relatively high thermal conductivity, e.g., above 12 W/m-K. In some embodiments, a surface of the mounting component 3 that faces or otherwise thermally communicates with the heat exchanger 2 may be configured to generally conform to the shape of the heat exchanger portion that receives heat from the thermal gap material 4, e.g., so that a conduction length across the thermal gap material 4 may be maintained constant or otherwise controlled.
Many heat pipes are closed systems that rely on the counter flow of “liquid” and “vapor” phases of the “working fluid” within a sealed interior volume of the pipe to transport heat along the pipe. At the hot or “evaporator” end, heat is absorbed by evaporating or boiling the liquid inside the heat pipe into its vapor phase while at the cold or “condenser” end the vapor phase condenses back into a liquid and releases heat into the walls of the heat pipe. Vapor travels automatically from the hot end to the cold end by the pressure difference caused by small temperature differences between the hot and cold ends. Other forces, such as gravity, are used to return the condensed liquid from the cold to the hot end. Heat pipes that depend on gravity as the primary means to return condensed liquid from the cold end to the hot end are also called thermosiphons. Liquid and vapor flow in opposite directions in the heat pipe.
Because heat transport in heat pipes is mediated by the physical movement of liquid and vapor phases of the working fluid, the heat transport rate that can be achieved in heat pipes is limited by many mechanisms that apply to fluid flows. Some common limiting mechanisms are entrainment limit, flooding limit, sonic limit, boiling limit etc., but in short, the heat transport limit of heat pipes is strongly dependent on the temperature of the working fluid inside the heat pipe. (The liquid and vapor phases inside a heat pipe exist in near thermodynamic equilibrium so, for the purpose of this description, a single temperature is used to refer to both phases.)
In accordance with an aspect of the invention, the thermal gap (i.e., the conduction length or distance from the mounting component 3 (or other heat spreader) and/or the heat pipe 5 to the heat exchanger 2) and the thermal gap material 4 in the gap between the heat spreader/heat pipe 5 and the heat exchanger 2 may be arranged to conduct heat such that the heat pipe(s) 5 operate at a desired working temperature, and enable substantial heat harvesting from the geothermal resource via the heat pipe(s) 5. For example, if the heat pipes 5 were to be placed in direct and very intimate thermal contact with the heat exchanger 2, the operating temperature of the heat pipes would be low, close to the cold fluid temperature in the heat exchanger 2. Such cold heat pipes extending into the hot rock or other well 1 substrate could create a “high heat demand” from the well 1. However, at the “cold operating temperature,” the heat pipes 5 would have a “low heat transport capability” and would not be able to carry the heat that would want to flow into the heat pipe 5 from the hot rock or other well substrate.
On the other hand, if the thermal connection between the heat pipes 5 and the heat exchanger 2 is poor (such as if the heat pipes 5 are simply inserted into the holes drilled into hot rock around a main well bore and not thermally coupled to the heat exchanger 2 in any particular way), the heat pipe temperature would be high, closer to the high temperature of the hot rock. Such “hot heat pipes” would create a “low heat demand” from the rock even though the heat pipes 5 would have a “high heat transport capability” due to their high operating temperature. In both the above scenarios, the heat pipes 5 would not provide a suitably high heat harvesting rate, at least for some applications. By providing a suitable thermal gap characteristics (conduction length and thermal conductivity) between the heat pipes 5/heat spreader and the heat exchanger 2, the heat pipes 5 may operate at the desirable “in between” temperature such that a “relatively high heat demand” is placed on the hot rock and is well balanced against the “relatively high heat transport capability” of the heat pipes 5.
A further benefit of the “balanced high heat harvesting” rate of the heat pipes 5 is that more well fluid may be cooled to a higher density to drive a larger total convective circulation in the geothermal resource. In this way, embodiments configured in accordance with an aspect of the invention may operate such that the heat content of the geothermal well, or “reservoir,” is replenished at the same rate that heat is harvested for efficient and cost effective energy production over long term operation. Computer modeling of a geothermal well 1 having its heat harvested using three thermal transfer components (i.e., heat pipe/heat spreader/thermal gap material assemblies) positioned along the length of a vertical heat exchanger arrangement like that in
While the surface area of the heat pipes 5 and/or heat spreader is an important design consideration when arranging the system to operate such that the coupled heat pipe(s) 5 function at a desired working temperature, the distance between the heat pipes 5 and/or heat spreader and the heat exchanger 2 (or conduction length) may be another important factor. As noted above, the surface of the heat pipes 5 or heat spreader that faces the heat exchanger 2 may be shaped or contoured to match or conform with a counterpart surface of the heat exchanger 2. Thus, if the heat exchanger 2 has a cylindrically-shaped outer surface, the mounting component 3 or other heat spreader may include a corresponding cylindrically-shaped inner surface that faces the heat exchanger 2. Alternately, if the heat exchanger 2 includes a dimpled, grooved, or other shaped surface, the mounting component 3 or other heat spreader may have a corresponding shape. This arrangement may help maintain a thermal gap between the heat spreader and the heat exchanger 2 at a constant or otherwise known value, e.g., to help ensure that a conduction length of the thermal gap material 4 is constant or otherwise known across the thermal junction. In some embodiments, the distance between the mounting component 3 and the heat exchanger 2 may be defined in different ways, such as by standoffs, tabs, pins, annular rings or other structures that extend from the mounting component 3 toward the heat exchanger 2. These gap-defining elements may help ensure that there is a minimum (or maximum) distance between the mounting component 3/heat pipes 5 and the heat exchanger 2. The gap-defining elements may be made small enough or otherwise configured to contribute minimally to heat transfer between the heat spreader and the heat exchanger, or alternately, these gap-defining spacer elements may function as a non-trivial part of the heat transfer. If so, the gap between the heat spreader and the heat exchanger (conduction length), the thermal conductivity of the thermal gap material and/or the surface area of the heat spreader (i.e., the surface area facing the heat exchanger or that meaningfully contributes to heat transfer to the heat exchanger) may be designed to provide the desired heat transfer rate along with the gap-defining elements.
Deployment of a thermal gap material 4 in the space or gap between the mounting component 3/heat pipes 5 and the heat exchanger 2 may be done in a variety of ways. For example, the thermal gap material 4 may take the form of a flowable grout that can flow when deployed, and then may optionally harden after deployment. The grout may be pumped into place after the mounting component 3 and heat exchanger 2 are positioned relative to each other in the well 1, or may be applied to the heat exchanger 2 and/or to the mounting component 3 prior to positioning of the elements relative to each other. In other embodiments, the thermal gap material 4 may be present in the well 1 at or after the time of installing the heat exchanger 2 and/or heat pipes 5. For example, the thermal gap material 4 may be or include water (such as brine) in the well 1 that occurs naturally or is introduced, e.g., by pumping the water into the well 1. Thus, in some embodiments, the thermal gap material may include a liquid that can flow so as to accommodate convective heat transfer, as well as conductive heat transfer, between the heat pipes 5 and the heat exchanger 2.
In accordance with an aspect of the invention, one or more heat pipes may be engaged with a mounting component so that the assembled heat pipes and mounting component may be lowered into a well bore and the heat pipes deployed into corresponding well bores. For example,
In accordance with an aspect of the invention, the assembly may include one or more anti-buckling supports which may help support the heat pipes before and/or during deployment in the well 1. For example, as shown in
For example,
Another feature shown in
In accordance with another aspect of the invention, a heat pipe deployment system may include a heat pipe guide, or “kicker,” that helps to guide the heat pipe(s) into their respective bore in a well. For example, the heat pipe guide may be arranged in the main well bore and include a flared or curved guide channel for one or more heat pipes. The guide channel may engage a heat pipe, e.g., at the distal end, and guide the heat pipe into a radially extending bore. The heat pipe guide may also be used to guide a tool that forms radially extending heat pipe bores, such as a rotary drilling tool, high pressure jet device, etc. For example,
In accordance with another aspect of the invention, a portion of a mounting component, anti-buckling support and/or heat pipe guide may form part of the heat exchanger. That is, in the embodiments above, a portion of the mounting component is adjacent to, and spaced from, a portion of the heat exchanger and a thermal gap material serves to conduct heat from the heat spreader to the heat exchanger. However, in some embodiments, one or more portions of the heat pipe deployment system may function as part of the heat exchanger, and any thermal gap or other thermal link between heat pipes and the heat exchanger may be provided as part of the system. For example,
As a result, the portions 3a, 3b, 3c may be stacked onto each other when the heat pipes 5 are fully deployed into the well 1. As mentioned above, the portions 3a, 3b, 3c may be joined together, as shown in
Furthermore, the middle and lower portions 3c, 3b may include features that help align the portions in a rotational direction. For example, the lower portion 3b may include two heat pipe guide grooves located at 180 degrees from each other. To help align the heat pipes 5 with their respective guide grooves, the conical engagement surfaces may include complementary slots and protrusions that interact to align the middle and lower portions 3c, 3b rotationally. For example, the lower portion 3b may include one or more V-shaped slots in the conical engagement surface (with the wide end of the “V” facing upwardly) that received complementary V-shaped protrusions on the conical engagement surface (with the narrow end of the “V” facing downwardly) of the middle portion 3c. The complementary slots and protrusions may engage with each other to rotate the middle and lower portions 3c, 3b relative to each other, as necessary, so that the heat pipe 5 ends are suitably located relative to the guide grooves of the lower portion 3b. Those of skill in the art will appreciate that other engagement surface arrangements are possible to provide radial and/or rotational alignment of the middle and lower portions 3c, 3b. Moreover, such alignment features may be provided between adjacent middle portions 3c, and/or between a middle portion 3c and the upper portion 3a.
In another embodiment, if the saddles 33 are joined to the inner wall 31 with higher than desired thermal transfer capacity, a junction between the saddles 33 and the heat pipes 5 may be arranged to provide the desired thermal junction. For example, as shown in the close up view of the saddle 33 at the 9 o'clock position in
While in the embodiments above, a thermal gap material or other component is provided to control (e.g., limit) heat transfer between a heat pipe and a working fluid of the heat exchanger 2, such material is not always required, especially when the well temperature is low. For example,
The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”
The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified.
The use of “including,” “comprising,” “having,” “containing,” “involving,” and/or variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.
While aspects of the invention have been described with reference to various illustrative embodiments, such aspects are not limited to the embodiments described. Thus, it is evident that many alternatives, modifications, and variations of the embodiments described will be apparent to those skilled in the art. Accordingly, embodiments as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit of aspects of the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2013/071149 | 11/21/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61788074 | Mar 2013 | US | |
| 61728849 | Nov 2012 | US |
