Block style heat exchanger for heat pipe reactor

A block style heat exchanger for a heat pipe reactor having a plurality of heat pipes extending from a reactor core. The heat exchanger includes a plurality of primary channels, each for receiving heat transferred from the core via one of the heat pipes. The primary channels extending within a block of one or more materials. The heat exchanger also includes a plurality of secondary channels defined within the block for transmitting a flow of the secondary heat transfer medium through the heat exchanger from an inlet to an outlet. The block is formed from one or both of: a plurality of plates bonded together, with each plate defining at least a portion of one or more of the plurality of primary channels and/or the plurality of secondary channels, and/or a unitary piece of material formed from an additive manufacturing process.

BACKGROUND

The present invention pertains generally to heat exchangers and, more particularly, to block style heat exchangers particularly suited to transfer heat from a primary heat source to a secondary medium through a number of heat pipes.

2. Related Art

Supercritical carbon dioxide (sCO2) is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure. Carbon dioxide usually behaves as a gas in air at standard temperature and pressure, or as a solid called dry ice when frozen. If the temperature and pressure are both increased from standard temperature and pressure to be at or above the critical point for carbon dioxide, it can adopt properties midway between a gas and a liquid. More specifically, carbon dioxide behaves as a supercritical fluid above its critical temperature (304.25 K, 31.10° C., 87.98° F.) and critical pressure (72.9 atm, 7.39 MPa, 1,071 psi), expanding to fill its container like a gas but with the density like that of a liquid.

sCO2is chemically stable, reliable, low-cost, non-toxic, non-flammable and readily available, making it a desirable candidate for a working fluid. Further, due to its superior thermal stability and non-flammability, direct heat exchange from high temperature sources is possible, permitting higher working fluid temperatures and therefore higher cycle efficiency. Unlike two-phase flow, the single-phase nature of sCO2eliminates the necessity of a heat input for phase change that is required for the water to steam conversion, thereby also eliminating associated thermal fatigue and corrosion. Despite the promise of substantially higher efficiency and lower capital costs, the use of sCO2presents material selection and design issues. Materials in power generation components must display resistance to damage caused by high-temperature, oxidation and creep. Candidate materials that meet these property and performance goals include incumbent alloys in power generation, such as nickel-based superalloys for turbomachinery components and austenitic stainless steels for piping. Components within sCO2Brayton loops suffer from corrosion and erosion, specifically erosion in turbomachinery and recuperative heat exchanger components and intergranular corrosion and pitting in the piping.

Prior to this point, no feasible primary heat exchanger design and manufacturing route has been conceived to integrate a sCO2secondary cycle into a heat pipe reactor. Most designs assume a block style heat exchanger with shell and tube style headers on either end of the heat exchanger, along the path of the heat pipes. This type of design requires the heat pipes to be protected from the high pressure sCO2in the open headers, although there is limited space between heat pipes. Integrating protective heat pipe sleeves into the header chambers and heat exchanger block section becomes difficult, if not impossible, due to the limited space available for connecting or welding the chamber and sleeves to the heat exchanger section and remaining real estate for the sCO2channels into the heat exchanger block. Thicker protective material around the heat pipe also reduces the heat transfer capability of the heat exchanger substantially. Accordingly, it is an object of this invention to provide an integrated block style heat exchanger design that will practicably enable the heat output of a heat pipe reactor to be effectively transferred to a sCO2secondary side and operate with a minimum of maintenance.

SUMMARY

These and other objects are achieved in one aspect of the invention by an integrated block style heat exchanger for use with a heat pipe reactor having a plurality of heat pipes extending from a reactor core. The heat exchanger comprises: a plurality of primary channels each structured to receive heat transferred from the core via a corresponding one of the plurality of heat pipes, the plurality of primary channels defined within a block of one or more materials, each primary channel extending in a first direction along a longitudinal axis of the heat exchanger from a first end of the heat exchanger to a second end of the heat exchanger; and a plurality of secondary channels defined within the block, each secondary channel being structured to transmit a flow of the secondary heat transfer medium through the heat exchanger from an inlet to an outlet of the heat exchanger, each secondary channel comprising: a first portion extending from the inlet to adjacent at least one of the primary channels; a second portion extending along, being situated in heat exchange proximity to, and separated from, at the at least one of the primary channels; and a third portion extending from the second portion to the outlet, wherein each of the first portion and the second portion is disposed at a non-zero angle with respect to the second portion, and wherein the block comprises one or both of: a plurality of plates bonded together, with each plate defining at least a portion of one or more of the plurality of primary channels and/or the plurality of secondary channels, and/or a unitary piece of material formed from an additive manufacturing process.

The second portion of each secondary channel may comprise a plurality of separate sub channels, each spaced around the at least one of the primary channels and extending between the first portion and the third portion of the secondary channel.

The block may comprise the plurality of plates bonded together.

The plurality of plates may be arranged in a stack prior to, or as they are bonded together.

The plurality of plates may be bonded together via one or more of: diffusion bonding, brazing or hot isostatic pressing.

The portion of the one or more of the plurality of primary channels and/or the plurality of secondary channels may be formed via one or more of: machining, laser cutting, chemical etching, electrical discharge machining, electro-chemical machining, and/or stamping.

The block may comprise the unitary piece of material formed from the additive manufacturing process.

At least one of the inlet and/or the outlet may comprise a circumferential header cavity structured to transmit the flow of the secondary heat transfer medium to or from each secondary channel of the plurality of secondary channels.

The circumferential header cavity may extend along only a portion of a circumference of the heat exchanger.

The circumferential header cavity may extend along an entire circumference of the heat exchanger.

At least one of the inlet and the outlet may comprise an integral header.

The integral header may be a flanged header.

The plurality of secondary channels may exit the block via multiple plates.

The plurality of secondary channels may exit the block via a single plate.

As another aspect of the invention, a nuclear reactor comprises: a core; a block style heat exchanger such as described herein; and a plurality of heat pipes, each heat pipe extending from the core to a corresponding primary channel of the heat exchanger, wherein each heat pipe is structured to transfer heat from the core to the corresponding primary channel of the heat exchanger.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the present invention provide block style heat exchanger arrangements that enable the integration of a sCO2secondary cycle into a heat pipe reactor. The block style heat exchanger is generally formed from a block (of any suitable shape) of material (generally referred to herein as “the block”) contains channels for the heat pipes coming from the reactor along with smaller channels for the sCO2defined/formed therein. The smaller channels extend between inlets and outlets and are positioned around and extend along the heat pipes. The center heat exchanger portion of the block is made up of thin sheet metal shims or plates, which contain through holes for both the heat pipe channels and the sCO2channels. The shims or plates may be produced, for example, without limitation, by machining, laser cutting, chemical etching, EDM (Electrical Discharge Machining), ECM (Electro-Chemical Machining), stamping or other metal fabrication methods. The end sections of the block can also be made from similar shims, which contains holes and channels, produced, for example, by laser cutting, machining, EDM, ECM or chemical etching, to create sCO2flow paths perpendicular to the heat pipe, in order for the sCO2channels to collect in headers on the periphery of the block. The entire plate portion of the heat exchanger is bonded into a single block using, for example, diffusion bonding, brazing or hot isostatic pressing. The heat exchanger headers may be internal chambers, slots or channels within the block that are cut/formed in the individual shims, or chambers that are attached to the outside of the main heat exchanger block.

Alternatively, the block style heat exchangers described herein may be produced entirely or in sections using various additive manufacturing technologies including large scale powder bed fusion, directed energy deposition, binder jetting, ultrasonic, friction stir and/or hybrid additive manufacturing. As used herein, the phrase “and/or” shall mean either one, or both of the items separated by such phrase (i.e., something including A and/or B may include A alone, B alone, or both A and B.

FIG. 1illustrates a partially schematic perspective view of a portion of a heat pipe nuclear reactor2having a reactor core4and a plurality of heat pipes6, each heat pipe6extending from core4to a block style heat exchanger10in accordance with one example embodiment of the present invention. Heat exchanger10is formed generally as a block of material of materials (such as the cylindrically shaped block ofFIG. 1) and includes a plurality of primary channels12defined therein that extend generally in a first direction along a longitudinal axis A of heat exchanger10. Each of primary channels12is formed generally as a tubular member that is structured to transmit a flow of a primary heat transfer medium through heat exchanger10. In the example embodiment illustrated inFIG. 1, each heat pipe6extends from core4to a corresponding primary channel12. Each heat pipe6is structured to transfer heat from core6to the corresponding primary channel12of heat exchanger10. Heat exchanger10also includes a plurality of smaller secondary channels14defined in the block of material, with each secondary channel14being structured to transmit a secondary heat transfer medium (e.g., sCO2) between a circumferential inlet header16and a circumferential outlet header18. In the example illustrated inFIG. 1, each secondary channel14extends from inlet header16along a first portion20to adjacent a corresponding primary channel12, where secondary channel14then transitions from first portion20to a second portion22that is disposed along the primary channel12over a heat exchange portion of the heat exchanger10. Second portion22of each of secondary channels14is in heat exchange proximity to, but spaced from, the corresponding primary channel12. As will be appreciated from the examples discussed herein, second portion22of each secondary channel14may consist of a single channel running along primary channel12or may be a plurality of (i.e., two or more) sub-channels positioned around primary channel12. At the lower end of the heat exchange portion of heat exchanger10each secondary channel14transitions from second portion22to a third portion24that extends from near primary channel12to outlet header18. In the example shown inFIG. 1, second portions22of secondary channels14are positioned generally vertically along longitudinal axis A while first and third portions20and24of secondary channels14are positioned generally normal (i.e., generally at 90°) to axis A, however, it is to be appreciated that first and third portions20and24of secondary channels14may be oriented at any non-zero angle with respect to second portions22without varying from the scope of the present invention.

Continuing to refer toFIG. 1, circumferential inlet and outlet headers16and18may extend completely around heat exchanger10, such as illustrated by the outlet header18inFIG. 1, or may extend only partially around the heat exchanger10, as illustrated by the inlet header16inFIG. 1. Circumferential headers16and18may be formed as separate components and attached to the heat exchanger10via any suitable means (e.g., without limitation, mechanically or by welding) or may be formed integrally with heat exchanger10via any suitable means.

FIG. 2illustrates another heat exchanger10in accordance with a second embodiment of the present invention that includes integral inlet and outlet headers16and18instead of the circumferential inlet and outlet headers16and18shown inFIG. 1. In all other respects, heat exchanger10, illustrated inFIG. 2, is the same as the heat exchanger10illustrated inFIG. 1.

FIG. 3shows a partially exploded view of a portion of outlet header18of heat exchanger10ofFIG. 2, showing third portions24of secondary channels14that extend from adjacent primary channels12to the outlet header18with second portions22of secondary channels14traversing multiple layers of the block segments26, which are also referred to herein as shims or plates. Though the upper segment28and the lower segment30ofFIG. 3are shown as thick portions of the heat exchange portion, each of the segments28and30may be, and preferably are, made up of multiple layers of plates26that are bonded together. Each of the secondary channels14may be formed by any suitable machining process, or by chemical or laser etching. From such view it is to be appreciated that in such example second portions22of each secondary channel14consist of a plurality of small conduits or sub-channels circumferentially spaced around the respective primary channel12.

FIG. 4shows a similar arrangement asFIG. 3except the arrangement ofFIG. 4can interface with circumferential headers16and18such as those illustrated inFIG. 1, rather than the integrated headers16and18such as illustrated inFIGS. 2 and 3.

FIGS. 5 and 6show a similar arrangement to that shown inFIGS. 3 and 4except third portions24of secondary channels14are only defined in, and extend in one layer of the plates26, rather than through the tiered layers such as shown in the arrangement ofFIG. 3. Note that in such example the layer26housing third portions24of secondary channels14is much thicker than the other layers of plates26in order to accommodate a sufficient volume of the secondary heat transfer medium.

While the heat exchanger arrangements described herein are especially suited for interfacing a heat pipe reactor to a sCO2secondary cycle, it is to be appreciated that the arrangements are applicable to other applications where the primary fluid would transverse the primary channels12and the secondary fluid would traverse the secondary channels14. Various shim (i.e., plate or block segment) manufacturing and bonding options enable multiple design feature options, including heat exchanger size, length, primary channel size, secondary channel size, shape, and path, and header size, shape and location. Alternatively, or in addition to, the heat exchangers could be produced with a variety of additive manufacturing techniques, including powder bed fusion, binder jetting, directed energy deposition or hybrid additive manufacturing, in a similar layered approach. The layered approach enables automation during manufacturing, such as laser cutting, CNC (Computer Numerical Control) machining, forming process and plate stacking and handling automation process, which enables automated fabrication of nuclear reactors.

While specific embodiments of the invention have been described in detail herein, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.