Patent Description:
Supercritical carbon dioxide (sCO<NUM>) 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 (<NUM>, <NUM>, <NUM> °F) and critical pressure (<NUM> atm, <NUM> MPa, <NUM>,<NUM> psi), expanding to fill its container like a gas but with the density like that of a liquid.

sCO<NUM> is 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 sCO<NUM> eliminates 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 sCO<NUM> presents 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 sCO<NUM> Brayton 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 sCO<NUM> secondary 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 sCO<NUM> in 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 sCO<NUM> channels into the heat exchanger block. Thicker protective material around the heat pipe also reduces the heat transfer capability of the heat exchanger substantially.

<CIT> discloses a heat exchanger according to the preamble of claim <NUM> and describes a heat exchanger formed from a plurality of very thin layers affixed to one another and formed via additive manufacturing. Such additive manufacturing enables the configurations of the heat exchanger's flow channels and the arrangements of such flow channels to be optimized for improved heat transfer performance, for improved resistance to thermal and mechanical stresses, and for optimization based upon other factors such as the environment in which the heat exchanger will be situated.

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 sCO<NUM> secondary side and operate with a minimum of maintenance.

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 for receiving 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 third portion is disposed at a non-zero angle with respect to the second portion, and the second portion of each secondary channel comprises a plurality of separate sub channels 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 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 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.

Another aspect of the invention is achieved by a nuclear reactor according to claim <NUM>.

A further understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:.

Embodiments of the present invention provide block style heat exchanger arrangements that enable the integration of a sCO<NUM> secondary 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 sCO<NUM> defined/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 sCO<NUM> channels. 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 sCO<NUM> flow paths perpendicular to the heat pipe, in order for the sCO<NUM> channels 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> illustrates a partially schematic perspective view of a portion of a heat pipe nuclear reactor <NUM> having a reactor core <NUM> and a plurality of heat pipes <NUM>, each heat pipe <NUM> extending from core <NUM> to a block style heat exchanger <NUM> in accordance with one example embodiment of the present invention. Heat exchanger <NUM> is formed generally as a block of material of materials (such as the cylindrically shaped block of <FIG>) and includes a plurality of primary channels <NUM> defined therein that extend generally in a first direction along a longitudinal axis A of heat exchanger <NUM>. Each of primary channels <NUM> is formed generally as a tubular member that is structured to transmit a flow of a primary heat transfer medium through heat exchanger <NUM>. In the example embodiment illustrated in <FIG>, each heat pipe <NUM> extends from core <NUM> to a corresponding primary channel <NUM>. Each heat pipe <NUM> is structured to transfer heat from core <NUM> to the corresponding primary channel <NUM> of heat exchanger <NUM>. Heat exchanger <NUM> also includes a plurality of smaller secondary channels <NUM> defined in the block of material, with each secondary channel <NUM> being structured to transmit a secondary heat transfer medium (e.g., sCO<NUM>) between a circumferential inlet header <NUM> and a circumferential outlet header <NUM>. In the example illustrated in <FIG>, each secondary channel <NUM> extends from inlet header <NUM> along a first portion <NUM> to adjacent a corresponding primary channel <NUM>, where secondary channel <NUM> then transitions from first portion <NUM> to a second portion <NUM> that is disposed along the primary channel <NUM> over a heat exchange portion of the heat exchanger <NUM>. Second portion <NUM> of each of secondary channels <NUM> is in heat exchange proximity to, but spaced from, the corresponding primary channel <NUM>. As will be appreciated from the examples discussed herein, second portion <NUM> of each secondary channel <NUM> may consist of a single channel running along primary channel <NUM> or may be a plurality of (i.e., two or more) sub-channels positioned around primary channel <NUM>. At the lower end of the heat exchange portion of heat exchanger <NUM> each secondary channel <NUM> transitions from second portion <NUM> to a third portion <NUM> that extends from near primary channel <NUM> to outlet header <NUM>. In the example shown in <FIG>, second portions <NUM> of secondary channels <NUM> are positioned generally vertically along longitudinal axis A while first and third portions <NUM> and <NUM> of secondary channels <NUM> are positioned generally normal (i.e., generally at <NUM>°) to axis A, however, it is to be appreciated that first and third portions <NUM> and <NUM> of secondary channels <NUM> may be oriented at any non-zero angle with respect to second portions <NUM> without varying from the scope of the present invention.

Continuing to refer to <FIG>, circumferential inlet and outlet headers <NUM> and <NUM> may extend completely around heat exchanger <NUM>, such as illustrated by the outlet header <NUM> in <FIG>, or may extend only partially around the heat exchanger <NUM>, as illustrated by the inlet header <NUM> in <FIG>. Circumferential headers <NUM> and <NUM> may be formed as separate components and attached to the heat exchanger <NUM> via any suitable means (e.g., without limitation, mechanically or by welding) or may be formed integrally with heat exchanger <NUM> via any suitable means.

<FIG> illustrates another heat exchanger <NUM> in accordance with a second embodiment of the present invention that includes integral inlet and outlet headers <NUM> and <NUM> instead of the circumferential inlet and outlet headers <NUM> and <NUM> shown in <FIG>. In all other respects, heat exchanger <NUM>, illustrated in <FIG>, is the same as the heat exchanger <NUM> illustrated in <FIG>.

<FIG> shows a partially exploded view of a portion of outlet header <NUM> of heat exchanger <NUM> of <FIG>, showing third portions <NUM> of secondary channels <NUM> that extend from adjacent primary channels <NUM> to the outlet header <NUM> with second portions <NUM> of secondary channels <NUM> traversing multiple layers of the block segments <NUM>, which are also referred to herein as shims or plates. Though the upper segment <NUM> and the lower segment <NUM> of <FIG> are shown as thick portions of the heat exchange portion, each of the segments <NUM> and <NUM> may be, and preferably are, made up of multiple layers of plates <NUM> that are bonded together. Each of the secondary channels <NUM> may 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 portions <NUM> of each secondary channel <NUM> consist of a plurality of small conduits or sub-channels circumferentially spaced around the respective primary channel <NUM>.

<FIG> shows a similar arrangement as <FIG> except the arrangement of <FIG> can interface with circumferential headers <NUM> and <NUM> such as those illustrated in <FIG>, rather than the integrated headers <NUM> and <NUM> such as illustrated in <FIG> and <FIG>.

<FIG> and <FIG> show a similar arrangement to that shown in <FIG> and <FIG> except third portions <NUM> of secondary channels <NUM> are only defined in, and extend in one layer of the plates <NUM>, rather than through the tiered layers such as shown in the arrangement of <FIG>. Note that in such example the layer <NUM> housing third portions <NUM> of secondary channels <NUM> is much thicker than the other layers of plates <NUM> in 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 sCO<NUM> secondary cycle, it is to be appreciated that the arrangements are applicable to other applications where the primary fluid would transverse the primary channels <NUM> and the secondary fluid would traverse the secondary channels <NUM>. 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.

Claim 1:
An integrated block style heat exchanger (<NUM>) for use with a heat pipe reactor (<NUM>) having a plurality of heat pipes (<NUM>) extending from a reactor core (<NUM>), the heat exchanger comprising:
a plurality of primary channels (<NUM>) each for receiving heat transferred from the core (<NUM>) via a corresponding one of the plurality of heat pipes (<NUM>), the plurality of primary channels (<NUM>) defined within a block of one or more materials, each primary channel extending in a first direction along a longitudinal axis (A) of the heat exchanger (<NUM>) from a first end of the heat exchanger to a second end of the heat exchanger; and
a plurality of secondary channels (<NUM>) defined within the block, each secondary channel (<NUM>) being structured to transmit a flow of the secondary heat transfer medium through the heat exchanger from an inlet (<NUM>) to an outlet (<NUM>) of the heat exchanger (<NUM>), each secondary channel (<NUM>) comprising:
a first portion (<NUM>) extending from the inlet (<NUM>) to adjacent at least one of the primary channels (<NUM>);
a second portion (<NUM>) extending along, being situated in heat exchanger (<NUM>) proximity to, and separated from, at the at least one of the primary channels (<NUM>); and
a third portion (<NUM>) extending from the second portion (<NUM>) to the outlet (<NUM>),
wherein each of the first portion (<NUM>) and the third portion (<NUM>) is disposed at a non-zero angle with respect to the second portion (<NUM>); and
wherein the block comprises one or both of:
a plurality of plates (<NUM>) bonded together, with each plate defining at least a portion of one or more of the plurality of primary channels (<NUM>) and/or the plurality of secondary channels (<NUM>), and/or
a unitary piece of material formed from an additive manufacturing process;
said heat exchanger (<NUM>) being characterized in that the second portion (<NUM>) of each secondary channel (<NUM>) comprises a plurality of separate sub channels spaced around the at least one of the primary channels (<NUM>) and extending between the first portion (<NUM>) and the third portion (<NUM>) of the secondary channel (<NUM>).