US20250067521A1 - Wick and heat transport device - Google Patents

Wick and heat transport device Download PDF

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Publication number
US20250067521A1
US20250067521A1 US18/944,213 US202418944213A US2025067521A1 US 20250067521 A1 US20250067521 A1 US 20250067521A1 US 202418944213 A US202418944213 A US 202418944213A US 2025067521 A1 US2025067521 A1 US 2025067521A1
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Prior art keywords
wick
nanofiber
mqo
heat transport
transport device
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US18/944,213
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Inventor
Hiroyuki Morita
Akimaro YANAGIMACHI
Takayuki Kono
Takeshi Torita
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Murata Manufacturing Co Ltd
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Murata Manufacturing Co Ltd
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Assigned to MURATA MANUFACTURING CO., LTD. reassignment MURATA MANUFACTURING CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KONO, TAKAYUKI, TORITA, Takeshi, YANAGIMACHI, Akimaro, MORITA, HIROYUKI
Publication of US20250067521A1 publication Critical patent/US20250067521A1/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
    • F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
    • F28D15/04—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure
    • F28D15/046—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure characterised by the material or the construction of the capillary structure
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
    • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material

Definitions

  • the present disclosure relates to a wick and a heat transport device, and more particularly to a wick used for heat transport and a heat transport device utilizing a phase change of a working fluid.
  • a heat transport device utilizing a phase change (more particularly, evaporation and condensation) of a working fluid such as a heat pipe or a vapor chamber is known.
  • a wick that transfers a working fluid in a liquid state by a capillary force (suction force due to capillary phenomenon) is used.
  • Patent Document 1 describes that a sintered body of metal particles having an average particle diameter of not less than 20 ⁇ m and not more than 200 ⁇ m is used as a wick.
  • Patent Document 2 describes that a fiber-containing porous body in which a carbon porous body is filled in at least a part of a fiber structure containing carbon fibers and/or oxidized fibers, the fiber-containing porous body having at least one peak in a pore diameter region of 10 ⁇ m or less in the pore diameter distribution of the carbon porous body is used as the wick.
  • the heat transport device as described above uses a housing having at least partial thermal conductivity, and has a configuration in which the wick and a working fluid are disposed and sealed in the housing.
  • the working fluid evaporates in a relatively high temperature portion to which heat is supplied from the outside, the working fluid in a gaseous state moves in the housing and condenses in a relatively low temperature portion to release heat to the outside, and the working fluid in a liquid state is transferred (returned) to the relatively high temperature portion by the capillary force of the wick.
  • the heat transport device is required to further improve heat transport performance due to the downsizing and the like of an electronic device in which the heat transport device can be incorporated.
  • the speed at which the working fluid in the liquid state is transferred by the capillary force of the wick is lower than the speed at which the working fluid in the gaseous state moves in the housing, and the heat transport performance of the heat transport device can be limited by the speed at which the working fluid in the liquid state is transferred by the capillary force of the wick.
  • the transfer speed of the working fluid in the liquid state in the wick is desirably higher.
  • a wick used for heat transport comprising a material containing a nanofiber and/or a two-dimensional substance represented by the following formula:
  • a heat transport device utilizing a phase change of a working fluid
  • the heat transport device comprising: a housing having a space therein; the wick disposed in the housing; and the working fluid sealed in the housing in a contactable state with the wick.
  • a novel wick having a high transfer speed of a working fluid in a liquid state is provided. Furthermore, according to the present disclosure, a novel heat transport device using such a wick is provided.
  • FIG. 1 is a schematic cross-sectional view of a heat transport device according to one embodiment of the present disclosure.
  • FIG. 2 shows an XRD pattern of a material (TiCO) produced in Example 1.
  • FIG. 3 shows an FE-SEM image of a material (TiCO) produced in Example 1.
  • the present embodiment relates to a wick.
  • the “wick” means a member used for heat transport. More specifically, the “wick” means a member capable of transferring a working fluid in a liquid state by a capillary force.
  • the wick includes a material containing a nanofiber and/or a two-dimensional substance.
  • material means “a material containing a nanofiber and/or a two-dimensional substance” (in other words, a material containing at least one of a nanofiber and a two-dimensional substance).
  • the material containing a nanofiber and/or a two-dimensional substance typically means a material that is solid and does not contain a binder or the like (for example, a polymer).
  • the material contained in the wick of the present embodiment is a nanofiber (or nanofilament, etc.) of a predetermined material (substance) and/or a two-dimensional substance.
  • the predetermined material that can be used in the present embodiment is represented by the following Formula (1):
  • MQO predetermined material
  • MQO examples include materials represented by formulas such as TiO 2 , TiCO, TiCON, VO 2 , VCO, VCON, CrO 2 , CrCO, CrCON, MoO 2 , MoCO, MoCON, MnO 2 , MnCO, and MnCON.
  • M may be Ti
  • the Q may be C.
  • a may not be 0.
  • the predetermined material may have a peak in a range in which a diffraction angle 2 ⁇ is not less than 2° and not more than 100 in an X-ray diffraction (XRD) pattern.
  • XRD X-ray diffraction
  • MQO has a crystal structure different from that of a hexagonal system.
  • the present embodiment is not bound by any theory, it can be considered that the crystal structure of MQO is an anatase type, a lepidocrocite type, or a mixture thereof at present.
  • the crystal structure of MQO may be a lepidocrocite type.
  • MQO can be produced using a first raw material and a second raw material, for example, as follows.
  • the first raw material contains at least M
  • the second raw material contains at least Q
  • the first raw material and the second raw material can react in a protic solvent to generate MQO.
  • a material represented by the following Formula (2) can be used:
  • the material represented by Formula (2) needs to be different from MQO of the product.
  • the material represented by Formula (2) may not have a peak in a range in which a diffraction angle 2 ⁇ is not less than 2° and not more than 10° in an X-ray diffraction (XRD) pattern.
  • Examples of the first raw material represented by Formula (2) include TiB 2 , TiB, TiC, TiN, TiO 2 , Ti 5 Si 3 , Ti 2 SbP, VO 2 , V 2 O 4 , NbC, Nb 2 O 5 , MoO 2 , MoO 3 , MoS 2 , MnO 2 , Mn 3 O 4 , and MnCO 3 .
  • MAX phase a material represented by the following Formula (3) (hereinafter, also simply referred to as “MAX phase” or “MAX raw material”) can be used as the first raw material:
  • a 2 is at least one element selected from the group consisting of Groups 12, 13, 14, 15, or 16, is usually a Group A element, typically Group IIIA and Group IVA, and more particularly may contain at least one selected from the group consisting of Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, S, and Cd, and is preferably Al.
  • the MAX phase has a crystal structure in which a layer constituted by A 2 atoms is located between two layers represented by M m X n (each X may have a crystal lattice located in an octahedral array of M).
  • the MAX phase typically includes repeating units in which each one layer of X atoms is disposed in between adjacent layers of n+1 layers of M atoms (these are also collectively referred to as an “M m X n layer”), and a layer of A 2 atoms (“A 2 atom layer”) is disposed as a layer next to the (n+1)th layer of M atoms.
  • the MAX phase is not limited thereto.
  • Examples of the first raw material represented by Formula (3) include Ti 3 AlC 2 , Ti 3 GaC 2 , and Ti 3 SiC 2 .
  • the material represented by Formula (2) and the material represented by Formula (3) may be used together (for example, as a mixture).
  • an ion-binding substance having a carbon-containing group can be used as the second raw material.
  • the ion-binding substance having a carbon-containing group contains C.
  • Examples of the ion-binding substance include ammonium salts, phosphate salts, and sulfate salts.
  • a quaternary ammonium salt can be used as the second raw material.
  • the quaternary ammonium salt include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH or TBAOH), benzyltrimethylammonium hydroxide, tetrabutylammonium fluoride (TBAF), tetrabutylammonium chloride (TBACl), tetrabutylammonium bromide (TBAB), tetrabutylammonium iodide (TBAI), benzyltriethylammonium chloride (BTEAC), hexadecyltrimethylammonium bromide, cetyltrimethylammonium bromide (CTAB), benzetonium chloride, benzalkonium chloride,
  • ion-binding substances containing P and/or S etc. may be used as the second raw material.
  • the protic solvent may be any solvent that can at least partially dissolve the first raw material and the second raw material, and may be particularly an aqueous solvent.
  • aqueous solvent water, an alcohol (for example, ethanol, 1-propanol, isopropanol), or a carboxylic acid (for example, acetic acid, formic acid) or the like is used.
  • the aqueous solvent may be composed of water and optionally a liquid substance compatible with water (for example, a protic solvent other than water), and is preferably water.
  • the first raw material and the second raw material are reacted in the protic solvent.
  • the second raw material can be added to the protic solvent in advance.
  • the ratio of the second raw material to the total of the protic solvent and the second raw material may be, for example, 5% by mass or more, particularly 20% by mass or more, and/or may be, for example, 80% by mass or less, particularly 50% by mass or less.
  • the first raw material can be further added to and mixed with the protic solvent to which the second raw material has been added. In such a mixture, a reaction for producing MQO proceeds.
  • the temperature (reaction temperature) of the mixture (which may contain the reaction product) may be, for example, 15° C. or higher, particularly 40° C. or higher, and/or, for example, 100° C.
  • a mixing time may, for example, be 1 day or more, particularly 2 days or more, and/or may, for example, be 10 days or less, particularly 7 days or less.
  • the mixing can be performed, for example, by rotating and stirring a magnetic stirring bar charged into a container using a magnetic stirrer while the reaction temperature is maintained by a hot plate stirrer and a hot water bath.
  • the treatment operation and conditions (temperature and time and the like) under which the reaction can proceed are not limited to the above, and may be appropriately selected according to the first raw material, the second raw material, and the protic solvent and the like to be used.
  • the resulting nanofibers of the MQO may be in the form of nanoribbons extending at nanoscale widths.
  • a plurality of nanofibers (for example, nanoribbons) of MQO may be bonded and/or integrated with each other to grow into nanoflakes two-dimensionally extending.
  • a plurality of MQO nanoflakes may overlap each other (for example, by van der Waals force) to form a laminate.
  • MQO is a solid content.
  • MQO can be typically a particle (or powder).
  • the mixture after the reaction (also referred to as a reaction mixture) may be appropriately subjected to post-treatment.
  • post-treatment include washing, impact application (including shear force application), drying (for example, freeze dry, heat dry), and pulverization.
  • the washing may be performed using a protic solvent.
  • the protic solvent may be washed with, for example, water or an alcohol.
  • a separation operation centrifugation and/or decantation
  • the washing and separation operations may be repeated until the pH of a supernatant liquid after centrifugation is, for example, 8 or less.
  • washing may be performed using an aqueous solution of a metal salt instead of or in addition to the above washing.
  • the metal salt may be, for example, a halide (fluoride, chloride, bromide, or iodide) of an alkali metal (Li, Na, or K or the like), typically LiCl, NaCl, or KCl or the like.
  • washing may be performed using an aqueous solution of a metal salt having a molar concentration of 1 to 10.
  • a separation operation centrifugation and/or decantation
  • the washing and separation operations may be repeated as necessary until the pH of the supernatant liquid after centrifugation is, for example, 8 or less.
  • an impact such as vibration and/or ultrasound may be applied.
  • MQO particles for example, nanofibers/nanoflakes, and so on.
  • MQO particles When the MQO particles are aggregated, they can be crushed.
  • Such an effect is remarkably obtained when an impact is applied during washing using an aqueous solution of a metal salt (it is considered that metal cations derived from the metal salt can enter gaps of the aggregates and the aggregates can be crushed).
  • the impact can be imparted using, for example, any one or more of a handshake, an automatic shaker, a mechanical shaker, a vortex mixer, a homogenizer, and an ultrasonic bath and the like.
  • a separation operation may be performed at any suitable timing to remove unwanted liquid components if present.
  • a drying operation typically freeze drying or heat drying
  • the freeze-drying may be performed, for example, by freezing a mixture containing MQO particles and a liquid component at any suitable temperature (for example, ⁇ 40° C.), followed by drying under a reduced pressure atmosphere.
  • the heat drying can be performed, for example, by drying a mixture containing MQO particles and a liquid component at a temperature of 25° C. or higher (for example, 200° C. or lower) under a normal pressure or a reduced pressure atmosphere.
  • the pulverization is not particularly limited, but can be performed using, for example, a combination of a mortar and a pestle, or an IKA mill or the like. The pulverization may be performed after drying.
  • the MQO particles can be obtained as a material containing MQO.
  • MQO particles for example, nanofibers (and optionally, an aggregate of MQO nanofibers, for example, MQO nanoflakes, and these are also collectively referred to as “MQO nanofibers or the like”) can be obtained.
  • MQO is represented by Formula (1)
  • the material containing MQO does not need to be composed of only the constituent elements of Formula (1).
  • a material containing MQO may optionally contain protons and/or metal cations.
  • the present disclosure is not limited, the material containing MQO may optionally contain at least one selected from the group consisting of a hydroxyl group, a chlorine atom, an oxygen atom, a hydrogen atom, and a nitrogen atom as modification or termination T present on the surface.
  • the material containing MQO may have two or more layers, and at least one selected from the group consisting of ammonium ions (for example, quaternary ammonium cations) and metal cations (for example, alkali metal ions and alkaline earth metal ions) may be present between these layers.
  • ammonium ions for example, quaternary ammonium cations
  • metal cations for example, alkali metal ions and alkaline earth metal ions
  • the material containing MQO such as MQO nanofibers may contain unreacted first raw material and/or second raw material as impurities, and may contain a substance derived from the first raw material, the second raw material and/or the protic solvent.
  • N may be present (remain) in an arbitrary form in the material containing MQO such as MQO nanofibers.
  • the material containing MQO may contain ammonium ions and tetramethylammonium ions.
  • the material containing MQO may contain a relatively small amount of remaining A atoms, for example, 10% by mass or less with respect to the original A atoms.
  • the remaining amount of A atoms can be preferably 8% by mass or less, and more preferably 6% by mass or less.
  • the remaining amount of A atoms exceeds 10% by mass, there may be no problem depending on the use conditions or the like.
  • Such a supernatant liquid can be formed into a slurry containing MQO particles such as MQO nanofibers as it is, appropriately diluted with a liquid medium, or mixed with a liquid medium after drying.
  • the wick of the present embodiment can be produced by shaping (molding or cutting or the like) a material containing MQO such as MQO nanofibers into a desired shape and dimension by any appropriate method.
  • the wick of the present embodiment may be a fiber structure formed using MQO nanofibers or the like.
  • Such a fiber structure may be produced, for example, by applying a slurry containing MQO nanofibers onto a substrate by any suitable method (for example, filtering, spraying, bar coating, spin coating, and immersing and the like), drying, and then removing the substrate.
  • the liquid medium contained in the slurry can be appropriately selected, and for example, a protic solvent (the same description as described above can be applied), an aprotic solvent (for example, tetrahydrofuran, methylene chloride, acetonitrile, acetone, N,N-dimethylformamide, and dimethylsulfoxide and the like), a non-polar solvent (for example, hexane, benzene, toluene, diethyl ether, chloroform, and ethyl acetate) and the like can be used.
  • a protic solvent for example, tetrahydrofuran, methylene chloride, acetonitrile, acetone, N,N-dimethylformamide, and dimethylsulfoxide and the like
  • a non-polar solvent for example, hexane, benzene, toluene, diethyl ether, chloroform, and ethyl acetate
  • the wick of the present embodiment is obtained.
  • the shape and dimension of the wick of the present embodiment can be appropriately selected according to a desired application.
  • the material containing MQO may typically have a peak in a range in which a diffraction angle 2 ⁇ is not less than 2° and not more than 100 in an X-ray diffraction (XRD) pattern.
  • XRD X-ray diffraction
  • the peaks in the XRD pattern can be identified visually or using a software used with the XRD analyzer.
  • a c-axis oriented MQO membrane in an XRD analyzer (for example, as in Examples described later, a self-standing membrane obtained by removing a filter after suction filtration is disposed with a surface in contact with the filter on a lower side) to perform the measurement.
  • the material of the present embodiment may have a Raman shift with peaks at positions of at least 275 to 295 cm ⁇ 1 , 435 to 455 cm ⁇ 1 , and 665 to 745 cm ⁇ 1 in a Raman spectrum using a laser with a wavelength of 514 nm.
  • the material of the present embodiment may have a Raman shift with peaks at positions of 140 to 160 cm ⁇ 1 , 275 to 295 cm ⁇ 1 , 435 to 455 cm ⁇ 1 , and 665 to 745 cm ⁇ 1 in a Raman spectrum using a laser with a wavelength of 514 nm.
  • an anatase type peak is present at the position of 140 to 160 cm ⁇ 1 .
  • the material of the present embodiment (more specifically, MQO) has a crystal structure of an anatase type, a lepidocrocite type, or a mixture thereof. More preferably, the material has a lepidocrocite type crystal structure.
  • the material of the present embodiment may have an aspect in which a Raman shift has peaks at positions of at least 275 to 295 cm ⁇ 1 , 435 to 455 cm-1, and 665 to 745 cm ⁇ 1 in a Raman spectrum using a laser with a wavelength of 514 nm, and X is the largest when the intensity of each of the peaks is X, Y, and Z.
  • the material of the present embodiment may have an aspect in which in a Raman spectrum using a laser with a wavelength of 514 nm, a Raman shift has peaks at positions of at least 180 to 200 cm ⁇ 1 , 275 to 295 cm ⁇ 1 , 375 to 395 cm ⁇ 1 , 435 to 455 cm ⁇ 1 , and 665 to 745 cm ⁇ 1 , and X is the largest when the intensity of each of the peaks is V, X, Y, Z, and W.
  • the Raman spectrum is measured by a Raman spectrometer using a laser beam having a wavelength of 514 nm as an excitation light source (the vertical axis represents intensity, and the horizontal axis represents a Raman shift).
  • the peaks in the Raman spectrum can be identified visually or using a software used with the Raman spectrometer.
  • the particle diameter of the MQO particles may be, for example, 0.01 nm or more, particularly 0.1 nm or more, and 1 nm or more, and/or may be, for example, less than 1000 nm, particularly 100 nm or less, and 50 nm or less. Such particles may also be referred to as nanoparticles.
  • the form of the MQO particles is a nanofiber and/or a two-dimensional substance.
  • the two-dimensional substance includes one or more of nanoflake and a laminate of nanoflake.
  • the two-dimensional substance is not limited to only the nanoflake and the laminate of nanoflake.
  • a wick containing a material containing MQO typically MQO particles (for example, nanofibers/nanoflakes), for example, MQO nanofibers (and optionally an assembly of MQO nanofibers, for example MQO nanoflakes).
  • MQO particles for example, nanofibers/nanoflakes
  • MQO nanofibers and optionally an assembly of MQO nanofibers, for example MQO nanoflakes.
  • the MQO nanofibers have a hydrophilic surface and have a cross-sectional outer dimension on the order of nanometers.
  • the wick containing the MQO nanofibers has a large force (for example, a sucking force) for sucking the working fluid in the liquid state by capillary action, and thus can transfer (for example, suck) the working fluid in the liquid state at a large speed.
  • the reason is that the volume density of the nanofibers in the wick is high due to the nano-order cross-sectional outer dimension, a narrow space (flow path of the working fluid) is formed by the gap of the nanofibers, and the total surface area of the nanofibers that can be in contact with the working fluid in the liquid state increases, and the hydrophilic surface makes the working fluid in the liquid state (typically, but not limited to, water) easily wet spread with respect to the surface of the nanofibers of MQO.
  • the “nanofiber” of MQO means a solid object extending in a longitudinal direction, and an outer dimension (cross-sectional outer dimension) of a cross section perpendicular to the longitudinal direction is on the nano order (that is, not less than 1 nm and less than 1000 nm) or on the sub-nano order smaller than the nano order (less than 1 nm, for example, not less than 0.1 nm and less than 1 nm).
  • the longitudinal length of the nanofiber of MQO is not particularly limited.
  • the longitudinal length of the nanofiber is not limited to the nano order (that is, not less than 1 nm and less than 1000 nm), and may be in the micron order (not less than 1 ⁇ m and less than 1000 m).
  • the cross-sectional outer dimension of the nanofiber may be, for example, 0.1 nm or more, and particularly 1 nm or more, and may be, for example, 100 nm or less, particularly 50 nm or less, and preferably 15 nm or less.
  • the wick containing the MQO nanofibers and the like having such small cross-sectional outer dimensions can transfer the working fluid in the liquid state at a higher speed.
  • the present embodiment is not limited, according to the above-described producing method, it is possible to realize the MQO nanofibers having such small cross-sectional outer dimensions.
  • the cross-sectional outer dimension of the MQO nanofibers means the shortest distance passing through the center in the cross section crossing the longitudinal direction of the MQO nanofibers.
  • the shape of the cross section of the MQO nanofibers is not particularly limited, but can be approximated by, for example, a rectangle (rectangle and square and the like) or an ellipse (flat circle and true circle and the like).
  • the shape of the cross-section thereof can be approximated by the rectangle, and the cross-sectional outer dimension can correspond to the short side length of the rectangle.
  • the shape of the cross section thereof can be approximated by the flat circle, and the cross-sectional outer dimension can correspond to the short diameter length of the flat circle.
  • the BET specific surface area of the material containing MQO such as MQO nanofibers is not particularly limited, and may be, for example, not less than 10 m 2 /g and not more than 500 m 2 /g.
  • the BET specific surface area is calculated using a BET equation from the isothermal adsorption curve of nitrogen gas or other gases at a liquid nitrogen temperature (77 K) by an adsorption method with the nitrogen gas or the other suitable gases (such as krypton (Kr) gas).
  • a “two-dimensional substance” means a solid having a two-dimensionally extending surface (also referred to as a plane or a two-dimensional sheet surface) and having a thickness relatively small with respect to a maximum dimension of the surface (which may correspond to the “in-plane dimension” of a particle), the thickness being on the order of nanometers (that is, not less than 1 nm and less than 1000 nm) or sub-nanometers (less than 1 nm, for example, not less than 0.1 nm and less than 1 nm) smaller than that.
  • the in-plane dimension is not limited to the nano order (that is, not less than 1 nm and less than 1000 nm), and may be the micron order (not less than 1 ⁇ m and less than 1000 ⁇ m).
  • the two-dimensional substance includes one or more of nanoflake and a laminate of nanoflake as described above.
  • the nanoflake may also be referred to as a nanosheet or a two-dimensional (nano) sheet.
  • the thickness of one layer of the nanoflake may be, for example, 0.01 nm or more, particularly 0.8 nm or more and, for example, 20 nm or less, particularly 3 nm or less.
  • the in-plane dimension of the nanoflake may be, for example, 0.1 ⁇ m or more, particularly 1 ⁇ m or more, and may be, for example, 200 ⁇ m or less, particularly 40 ⁇ m or less.
  • the nanoflake can be constituted by the aggregation of nanofibers.
  • the stack of the nanoflakes may also be referred to as a multilayer MQO.
  • a distance (interlayer distance or void dimension) between two adjacent nanoflakes (or MQO of two adjacent layers) is not particularly limited.
  • Each dimension described above can be obtained as a number average dimension (number average of at least 40) based on a photograph observed with a scanning electron microscope (SEM), a transmission electron microscope (TEM), or an atomic force microscope (AFM) (if necessary, processing is performed by a method such as a focused ion beam (FIB)), or a distance in a real space calculated from a position on a reciprocal lattice space of a (002) plane measured by an X-ray diffraction (XRD) method.
  • SEM scanning electron microscope
  • TEM transmission electron microscope
  • AFM atomic force microscope
  • the cross-sectional outer dimensions of the MQO nanofibers are obtained by exposing the cross section of the wick containing the MQO nanofibers by a method such as a focused ion beam (FIB), photographing the exposed cross section with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), extracting at least 40 samples in which a cross section crossing the longitudinal direction of the MQO nanofibers appears in the obtained image, and calculating the number average of the cross-sectional outer dimensions.
  • FIB focused ion beam
  • SEM scanning electron microscope
  • TEM transmission electron microscope
  • MQO is not limited to the above-described form, and may have any suitable form.
  • the present embodiment relates to a heat transport device.
  • the “heat transport device” means a device that transports heat utilizing a phase change of a working fluid.
  • the phase change of the working fluid means evaporation and condensation.
  • a heat transport device 20 of the present embodiment includes: a housing 1 having a space therein; a wick 3 disposed in the housing 1 ; and a working fluid (not shown) sealed in the housing 1 in a state of being able to contact the wick 3 .
  • the wick 3 described above in the first embodiment is used.
  • FIG. 1 exemplarily shows a case where the heat transport device 20 is a loop heat pipe.
  • the housing 1 includes an evaporator 11 , a condenser 13 , and a gas flow path 15 and a liquid flow path 17 connecting the evaporator and the condenser.
  • the evaporator 11 , the condenser 13 , the gas flow path 15 , and the liquid flow path 17 integrally constitute the internal space of the housing 1 .
  • the wick 3 is disposed in the evaporator 11 .
  • a working fluid (not shown) is sealed in the internal space of the housing 1 .
  • the housing 1 is made of a material (for example, metal) having thermal conductivity at least in the evaporator 11 and the condenser 13 .
  • the working fluid evaporates in the evaporator 11 (relatively high temperature portion) to which heat is supplied from the outside (heat source), the working fluid in the gaseous state moves in the gas flow path 15 and condenses in the condenser 13 (relatively low temperature portion) to release heat to the outside, and the working fluid in the liquid state is transferred (returned) to the evaporator 11 through the liquid flow path 17 by the capillary force of the wick 3 .
  • the working fluid circulates in the housing 1 while changing in phase.
  • the flow of the working fluid is schematically shown by dotted arrows, and the supply of heat from the outside (heat input) and heat dissipation to the outside (heat output) are schematically shown by wavy arrows.
  • the working fluid in the liquid state can be transferred at a high speed, high heat transport performance is obtained, and the maximum heat transport amount of the heat transport device 20 is improved.
  • the heat transport device 20 is the loop heat pipe
  • the heat transport device of the present embodiment may employ the configuration of a known heat transport device (for example, a tubular heat pipe or a vapor chamber or the like) including a wick except that the wick 3 described above is used in the first embodiment.
  • a known heat transport device for example, a tubular heat pipe or a vapor chamber or the like
  • the wick and the heat transport device in an embodiment of the present disclosure have been described in detail above, the present disclosure can be modified in various ways. It should be noted that the wick of the present disclosure may be produced by a method different from the producing method in the above-described embodiment.
  • Example 1 relates to a wick of a first embodiment using TiCO nanofibers.
  • a container (100 mL I Boy) was charged with 1 g of titanium diboride (TiB 2 , manufactured by Alfa Aesar) and 30 mL of a 25 mass % aqueous tetramethylammonium hydroxide (TMAH) solution (manufactured by Tokyo Chemical Industry Co., Ltd.). Thereto was placed a stirrer chip having a length substantially equal to the inner diameter of the circular bottom surface of the container (35 mm). While the container was kept at 50° C. in a water bath, the mixture in the container was stirred with the stirrer chip and maintained for 120 hours, thereby allowing the reaction to proceed.
  • TiB 2 titanium diboride
  • TMAH tetramethylammonium hydroxide
  • the reaction mixture in the container was transferred to a 50 mL centrifuge tube with a stainless steel spatula (without the addition of a liquid medium such as ethanol or water). Centrifugation was performed using a centrifuge under conditions of 3500 G and 5 minutes to precipitate the solid content. (i) After centrifugation, the supernatant liquid was discarded, (ii) 40 mL of ethanol (manufactured by FUJIFILM Wako Pure Chemical Corporation) was added to the remaining precipitate in the centrifuge tube, and the mixture was subjected to handshake for 5 minutes (reslurry), and (iii) centrifugation was performed under the same conditions as described above.
  • a liquid medium such as ethanol or water
  • the sample slurry prepared above was filtered with suction overnight using a nutsche.
  • a membrane filter (Durapore, pore diameter 0.45 m, manufactured by Merck Corporation) was used.
  • a precursor membrane on the filter was dried overnight at 80° C. in a vacuum oven, and the filter was removed to obtain a free-standing membrane.
  • the obtained free-standing membrane was cut into a rectangle to obtain a wick sample having a width (W) of 1 cm, a length (L) of 2 cm, and a thickness (T) of 100 ⁇ m.
  • the wick sample prepared above was placed on a petri dish containing water in a state of being vertically erected so that a WT surface (1 cm ⁇ 100 ⁇ m) was an upper end surface and a lower end surface, and immersed in water at a depth of about 1 mm. Water was sucked up to the upper end surface at a speed of 4 mm/s. From this result, the volume of water sucked up by the wick sample per unit time unit area is 4 ⁇ 10 ⁇ 3 m 3 /(m 2 ⁇ s), and thus the mass of water sucked up per unit time unit area is 4 kg/(m 2 ⁇ s) (specific gravity of water: 1000 kg/m 3 ). Since the heat of evaporation of water per unit mass at 25° C.
  • the amount of heat that this wick sample can deprive by the evaporation of water at 25° C. is calculated to be 9768 kW/m 2 . That is, in the wick sample of Example 1, the transfer speed of water was 4 mm/s, and the heat transport performance of water at 25° C. was about 10 4 kW/m 2 .
  • the free-standing membrane obtained in the same manner as described above was analyzed by X-ray photoelectron spectroscopy (XPS). Peaks corresponding to Ti2p, C1s, O1s, and N1s were observed in the obtained XPS spectrum, and thus Ti, C, O, and N were detected. Since N is considered to be the residual content of TMAH of the raw material, the material of the free-standing membrane is considered to be composed of Ti, C, and O.
  • FIG. 3 shows an FE-SEM image. As understood from FIG. 3 , the material had a cross-sectional outside dimension of about 5 nm.
  • Comparative Example 1 relates to a wick using MXene particles as one type of two-dimensional material.
  • TiC powder, Ti powder, and Al powder (all manufactured by Kojundo Chemical Laboratory Co., Ltd.) were placed in a ball mill containing zirconia balls at a molar ratio of 2:1:1 and mixed for 24 hours.
  • the obtained mixed powder was calcined in an Ar atmosphere at 1350° C. for 2 hours.
  • the fired body (block) thus obtained was crushed with an end mill to a maximum size of 40 ⁇ m or less. Thereby, Ti 3 AlC 2 particles were obtained as MAX powder.
  • etching was performed under the following etching conditions to obtain a solid-liquid mixture (slurry) containing a solid component derived from the Ti 3 AlC 2 powder.
  • the slurry was divided into two portions, each of which was inserted into two 50 mL centrifuge tubes, centrifuged under the condition of 3500 G using a centrifuge. Then, the supernatant liquid was discarded. An operation of adding 40 mL of pure water to the remaining precipitate in each centrifuge tube, centrifuging again at 3500 G, and separating and removing the supernatant liquid was repeated 11 times. After final centrifugation, the supernatant liquid was discarded to obtain a Ti 3 C 2 T x -moisture medium clay.
  • the Ti 3 C 2 T x -moisture medium clay prepared by the above method was stirred at not lower than 20° C. and not higher than 25° C. for 12 hours using LiCl as a Li-containing compound to perform Li intercalation according to the following conditions.
  • this supernatant liquid was centrifuged under the conditions of 4300 G and 2 hours using a centrifuge, and then the supernatant liquid was discarded to obtain a single-layer/few-layer MXene-containing clay as a single-layer/few-layer MXene-containing sample.
  • the MXene-containing clay and pure water were mixed in appropriate amounts to prepare a sample slurry having a solid content concentration (MXene particle concentration) of 34 mg/mL.
  • the obtained sample slurry corresponds to a slurry containing MXene particles (MXene-water dispersion).
  • a wick sample having a width (W) of 1 cm, a length (L) of 2 cm, and a thickness (T) of 100 ⁇ m was obtained in the same manner as in Example 1 except that the sample slurry prepared above was used.
  • Comparative Example 2 relates to a wick using a sintered body (porous metal sintered body) of metal powder (copper powder).
  • Copper powder having an average particle diameter D50 of 50 ⁇ m was used as metal powder, and an acrylic resin (binder) and the copper powder were mixed at a volume ratio of 1:1.
  • the obtained mixture was subjected to a heat treatment at 400° C. for 1 hour to burn and remove the acrylic resin, thereby obtaining a porous metal sintered body.
  • the obtained porous metal sintered body was cut to obtain a wick sample having a width (W) of 1 cm, a length (L) of 2 cm, and a thickness (T) of 100 ⁇ m.
  • the wick sample prepared above was placed on a petri dish containing water in a state of being vertically erected so that a WT surface (1 cm ⁇ 100 m) was an upper end surface and a lower end surface, and immersed in water at a depth of about 1 mm. Water was sucked up to the upper end surface at a speed of 0.5 mm/s. From this result, in the wick sample of Comparative Example 2, the transfer speed of water was 0.5 mm/s, and the heat transport performance of water at 25° C. was about 10 3 kW/m 2 by the same calculation as in Example 1.
  • Comparative Example 3 relates to a wick using a sintered body (porous metal sintered body) of metal powder (titanium powder).
  • a wick sample having a width (W) of 1 cm, a length (L) of 2 cm, and a thickness (T) of 100 ⁇ m was obtained in the same manner as in Comparative Example 2 except that titanium powder having an average particle diameter D50 of 50 ⁇ m was used as the metal powder.
  • the wick sample prepared above was evaluated in the same manner as in Comparative Example 2, and water was sucked up to the upper end surface at a speed of 0.5 mm/s. From this result, in the wick sample of Comparative Example 3, the transfer speed of water was 0.5 mm/s, and the heat transport performance of water at 25° C. was about 10 3 kW/m 2 .
  • the wick of the present disclosure can be used to transfer a working fluid by capillary force in a heat transport device utilizing the phase change of the working fluid.
  • the heat transport device of the present disclosure may be incorporated into an electronic device and used to release (remove) heat from a heat source of the electronic device.
  • the wick and heat transport device of the present disclosure can be utilized for any suitable application, not only these.

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