WO2014011372A2 - Surfaces repoussant un réfrigérant - Google Patents

Surfaces repoussant un réfrigérant Download PDF

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Publication number
WO2014011372A2
WO2014011372A2 PCT/US2013/046646 US2013046646W WO2014011372A2 WO 2014011372 A2 WO2014011372 A2 WO 2014011372A2 US 2013046646 W US2013046646 W US 2013046646W WO 2014011372 A2 WO2014011372 A2 WO 2014011372A2
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WO
WIPO (PCT)
Prior art keywords
refrigerant
contact angle
vapor
surface features
water
Prior art date
Application number
PCT/US2013/046646
Other languages
English (en)
Other versions
WO2014011372A3 (fr
Inventor
William P. King
Original Assignee
The Board Of Trustees Of The University Of Illinois, A Body Corporate And Politic Of The State Of Illinois
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Application filed by The Board Of Trustees Of The University Of Illinois, A Body Corporate And Politic Of The State Of Illinois filed Critical The Board Of Trustees Of The University Of Illinois, A Body Corporate And Politic Of The State Of Illinois
Publication of WO2014011372A2 publication Critical patent/WO2014011372A2/fr
Publication of WO2014011372A3 publication Critical patent/WO2014011372A3/fr

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B39/00—Evaporators; Condensers
    • F25B39/04—Condensers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
    • F28F13/04—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by preventing the formation of continuous films of condensate on heat-exchange surfaces, e.g. by promoting droplet formation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
    • F28F13/18—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by applying coatings, e.g. radiation-absorbing, radiation-reflecting; by surface treatment, e.g. polishing
    • F28F13/185—Heat-exchange surfaces provided with microstructures or with porous coatings
    • F28F13/187—Heat-exchange surfaces provided with microstructures or with porous coatings especially adapted for evaporator surfaces or condenser surfaces, e.g. with nucleation sites
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
    • F25B2400/12—Inflammable refrigerants
    • F25B2400/121—Inflammable refrigerants using R1234

Definitions

  • the contact angle may be defined as the interior angle formed by the substrate and the tangent to the interface between the liquid and gas or vapor at the apparent intersection of the substrate, liquid and gas or vapor phases (see Fig. 1 a).
  • the dimension of the droplet is often comparable to or smaller than the capillary length of the liquid.
  • the contact angle may be measured or calculated from images of the droplet on the substrate.
  • the substrate is characterized as being wetted if the contact angle between the droplet and the substrate is less than 90°; or non-wetted if the contact angle between the droplet and the substrate is greater than 90°.
  • the surface is considered hydrophobic when the contact angle between the water droplet and the substrate is greater than 90°.
  • the surface is considered oleophobic when the contact angle between the refrigerant droplet and the substrate is greater than 90°.
  • Condensation of a liquid phase from a vapor phase occurs in condenser heat transfer devices used in power generation and refrigeration systems.
  • the latent heat of vaporization is released during condensation on a surface, heat is transferred to the surface.
  • the condensing liquid may form a film over the entire surface in a process termed filmwise condensation.
  • the condensed liquid may form as drops on the surface in a process termed dropwise condensation.
  • dropwise condensation Higher heat transfer coefficients have been reported for dropwise condensation of steam than filmwise condensation at atmospheric pressure (Rose 2002, Dropwise condensation theory and experiment: a review, Proc Instn Mech Engrs, 216(Part 4): 1 15-128).
  • the surface and various aspects of the system are configured to ensure the surface is refrigerant repelling.
  • the refrigerant repelling surface is configured so that a refrigerant that may normally wet a surface is instead repelled
  • the surface and various aspects of the system may also be configured to enhance droplet mobility, condensation rate and/or the heat transfer coefficient.
  • the systems and devices of the invention are configured so as to increase the contact angle between a condensed droplet and a surface. For example, the contact angle may be increased as compared to the contact angle on a droplet of the same liquid on a flat smooth surface of the same material. Relevant aspects that facilitate an increase in contact angle include surface
  • any of the methods and devices provided herein can relate to selection of any one or more of these aspects so as to ensure a maximal or acceptable increase in contact angle.
  • Whether or not a surface is considered a repelling surface may be influenced by contact angle between a condensed droplet and the contact surface.
  • a refrigerant-repelling surface may be textured to provide a nonwetting surface even for surface-refrigerant systems that may normally be considered as wetting systems.
  • Examples of relevant physical process characteristics affecting the refrigerant-repellency of a surface include pressure, temperature and composition of the atmosphere. Another process characteristic that may affect the refrigerant-repellency of the surface is the condensation rate within the heat transfer device.
  • Provided herein are methods and devices for accurately operating at atmospheric pressure or at non- atmospheric pressures, including below atmospheric pressure, above atmospheric pressure and substantially above atmospheric pressure.
  • many conventional systems suffer from the limitation of having air present in the atmosphere of the heat transfer system.
  • the vapor pressure of refrigerant in the atmosphere can affect the contact angle of a droplet on a surface; in some cases the characteristic or apparent contact angle may be lower in a vapor saturated atmosphere as compared to an air atmosphere (see Example 2 and Figure 17).
  • increasing the contact angle of a liquid droplet on a surface when the atmosphere is substantially vapor of the refrigerant may be more difficult than for a droplet exposed to an atmosphere which is essentially air.
  • precise control over operating parameters are achieved, providing the ability tailor the process and device to particular refrigerant/substrate systems to achieve maximum possible increase in contact angle, thereby increasing the repellency of the surface to condensed droplets of refrigerant vapor.
  • the invention provides methods for condensation heat transfer which lead to dropwise condensation of refrigerant or working fluid.
  • the dropwise condensation heat transfer methods of the invention can lead to heat transfer exceeding 1 kW / cm 2 .
  • the condensation heat transfer processes of the invention take place under saturation conditions, under near saturation conditions, under conditions where the vapor is superheated, under conditions where the surface is undercooled or combinations thereof.
  • condensation heat transfer processes of the invention take place under saturation conditions.
  • the invention provides a method for condensation heat transfer comprising condensing a refrigerant vapor on a textured portion of an interior surface of a chamber to form a plurality of refrigerant droplets at a user selected pressure, thereby transferring heat from the refrigerant vapor to the interior surface wherein the user selected pressure is not atmospheric pressure, the textured portion of the interior surface comprises surface features, the surface features comprising a surface material and the apparent contact angle of the refrigerant droplets on the surface features is non-zero and greater than the characteristic contact angle of the refrigerant droplets on the surface material of the surface features.
  • the apparent contact angle may be greater than the characteristic contact angle by at least 20 degrees or by at least 45 degrees.
  • the methods of the invention may comprise condensing a refrigerant vapor on a textured surface to form a plurality of refrigerant droplets having an apparent contact angle greater than 90 °.
  • the apparent contact angle of the droplets may be greater than 90 ° to less than or equal to 180 ° , 160 ° 150 ° 140 ° 130 ° 120 ° or 1 10 °.
  • the refrigerant may comprise a halocarbon or hydrocarbon refrigerant and a lubricant such as a polyol ester or polyalkylene glycol lubricant.
  • the composition of the refrigerant vapor may vary with position in the heat exchanger.
  • the refrigerant vapor may contain up to 5 %, 10%, 15%, 20%, 25%, 30%, 40%, 45% or 50% by mass lubricant.
  • the textured surface may comprise elevated or relief surface features.
  • the surface features may form a "waffle" pattern as schematically illustrated in Figures 3A and 3B, Other surface features may have a reentrant geometry and may take the general form of "micromushrooms" schematically illustrated in cross-section in Figure 19.
  • the textured surface comprises a surface material.
  • the surface material may be a material with relatively low surface energy such as a fluorosilane or a polymer formed as a coating on the interior of the chamber.
  • Suitable type of surface coating materials is a mixture comprising a polymer such as polydimethylsiloxane (PDMS) and a filler material, such as zinc oxide or silica.
  • PDMS polydimethylsiloxane
  • a filler material such as zinc oxide or silica.
  • nonwetting refrigerant droplets can be achieved on the textured surface even though droplets of the refrigerant wet nontextured surface material.
  • the characteristic contact angle of the refrigerant on the surface materials is less than 75 ° less than 60°, less than 50°, less than 40 °, less than 30 °, less than 20°, less than 10° or less than 5°.
  • a plurality of refrigerant droplets on the textured surface have an apparent contact angle of 90 ° or less than 90 °, but the apparent contact angle is greater than the characteristic contact angle of the refrigerant on the surface material.
  • the temperature of the interior surface of the chamber where condensation occurs may be in a preselected temperature range and the surface tension of the refrigerant in the preselected temperature range may be from 5 mN/m to 25 mN/m, 5 mN/m to 20 mN/m, 5 mN/m to 15 mN/m or 5 mN/m to 10 mN/m.
  • the textured surface may be located inside a chamber such as a pressure vessel or vacuum chamber.
  • the condensation process can take place under saturation conditions or near saturation conditions.
  • the vapor may also be superheated and/or the surface may be supercooled in at least a portion of the chamber.
  • the pressure in the vessel may be from 5 kPa to 5 MPa, including specific subranges thereof such as above atmospheric pressure, below atmospheric pressure, or a pressure that is not atmospheric, including substantially not atmospheric.
  • standard atmospheric pressure may be taken as approximately 101 .3 kPa.
  • the pressure in the vessel may be greater than atmospheric pressure and less than 5 MPa.
  • “Substantially not atmospheric” refers to a pressure range that is at least 20% different from atmospheric.
  • the temperature of the interior surface of the chamber where condensation occurs may be in a preselected range; the preselected range may be the saturation temperature of the refrigerant vapor +/- 20%, 15%, 10% or 5%
  • the methods of the invention may also comprise condensing a refrigerant vapor on a textured surface comprising a surface material to form a plurality of refrigerant droplets, wherein the mobility of the droplets is higher on the textured surface than the mobility of droplets formed on an "untextured” or “smooth” surface of the surface material, the condensation rate is higher on the textured surface than the condensation rate of an "untextured” or “smooth” surface of the surface material, and/or the heat transfer coefficient is higher for the textured surface than the heat transfer coefficient on an "untextured” or “smooth” surface of the surface material.
  • the invention provides a heat exchanger system which is a closed system containing both liquid and vapor phases.
  • at least a portion of the heat exchanger system comprises a textured portion, the textured portion of the system facilitating dropwise condensation of refrigerant vapor.
  • the surface features of the texture may vary within the heat exchanger system in
  • FIG. 35 schematically illustrates a heat exchanger system comprising a condenser (100), evaporator (200) and compressor (300).
  • the invention provides a heat exchanger system for condensation heat transfer through condensation of a refrigerant vapor into droplets of the refrigerant, the heat exchanger system comprising: a chamber comprising an interior hollow portion and an interior surface, the interior surface comprising a textured portion , the textured portion of the surface comprising surface features, the surface features comprising a surface material wherein the apparent contact angle of the refrigerant droplets on the surface features is greater than the characteristic contact angle of the refrigerant droplets on the surface material of the surface features.
  • the invention provides a heat exchanger system for condensation heat transfer, the heat exchanger system comprising: a) a chamber comprising an interior hollow portion and an interior surface, the interior surface comprising a textured portion , the textured portion of the surface comprising surface features, the surface features comprising a surface material; and
  • a refrigerant positioned in the hollow portion of the chamber, the refrigerant being selected from the group consisting of halocarbon, hydrofluorocarbon (HFC), hydrofluoroolefin (HFO) and hydrocarbon (HC)
  • the characteristic contact angle of a refrigerant droplet on the surface material in an atmosphere substantially comprising refrigerant vapor is less than 50° under saturation conditions.
  • the invention provides a heat exchanger system for condensation heat transfer, the heat exchanger system comprising: a) a chamber comprising an interior hollow portion and an interior surface, the interior surface comprising a textured portion , the textured portion of the surface comprising surface features, the surface features a surface material; and
  • a refrigerant positioned in the hollow portion of the chamber, the refrigerant being selected from the group consisting of halocarbon, hydrofluorocarbon (HFC), hydrofluoroolefin (HFO) and hydrocarbon (HC)
  • the mobility of the droplets is higher on the textured surface than the mobility of droplets formed on an smooth surface of the surface material
  • the condensation rate is higher on the textured surface than the condensation rate of a smooth surface of the surface material
  • the heat transfer coefficient is higher for the textured surface than the heat transfer coefficient on a smooth surface of the surface material
  • the refrigerant may be any suitable refrigerant known to the art.
  • the refrigerant may comprise a component selected from the group consisting of halocarbon , hydrofluorocarbon (HFC), hydrofluoroolefin (HFO), hydrocarbon (HC) and water or may be selected from the group consisting of halocarbon, hydrofluorocarbon (HFC), hydrofluoroolefin (HFO) and hydrocarbon (HC).
  • the surface characteristics are selected to contribute to refrigerant repellency, increased droplet mobility, increased condensation rate and/or higher heat transfer coefficient.
  • the surface features on the interior surface of the pressure vessel comprise nanoparticles.
  • the average diameter of the nanoparticles is 2-300 nm and the average spacing between nanoparticles is 10-1000 nm.
  • the elevated features form a network of "walls" surrounding features of lower elevation (relative depressions) to form a "waffle" pattern.
  • the elevated “wall” features may have an average width between 5 nm and 10 microns and an average spacing or pitch between 50 nm and 250 micron or from 5 micron to 100 micron, 10 to 50 microns or from 15 microns to 30 microns.
  • the depth of the depressions may be from 50 nm to 250 microns, from 5 micron to 100 micron, 5 to 50 microns or from 15 microns to 30 microns.
  • the pitch may be greater than the depth of the depressions.
  • the surface features comprise elevated features shaped like "micromushrooms" with a "cap” typically wider than the "stem".
  • Figure 19 illustrates several parameters which can be used to characterize such "micromushroom” structures.
  • a refrigerant repelling surface may have any surface texture capable of contributing to refrigerant repellency and may be such that the surface features of the textured surface provide a re-entrant geometry or such that surface features form a "waffle" or grid pattern.
  • the surface material composing the refrigerant repelling material may have a relatively low surface energy and may comprise a polymer or a surface treatment material such as a silane coating.
  • the surface material comprises a fluoropolymer or a fluorosilane.
  • Other materials proposed for use as relatively low surface energy coatings include diamond-like carbon and fluorinated diamond-like coatings.
  • the atmosphere in the pressure vessel substantially comprises refrigerant vapor.
  • the amount of air present in the atmosphere of the pressure vessel may be less than 50%, less than 25%, less than 10%, less than 5%, or about zero.
  • Figures 1 a-1 c Standard conceptual models for a liquid droplet on a flat surface (1 a), on a wetted rough surface (1 b), and on a partially wetted surface (1 c).
  • the wetting state in the middle (1 b) is the Wenzel mode
  • the wetting state on the right (1 c) is the Cassie-Baxter mode.
  • Figures 3A-B Schematic top view of a hexagonal waffle structure (Fig. 3A) and a grid-like waffle structure (Fig. 3B).
  • Figures 4A-4C Schematic top view of different configurations of pillar elements: hexagonal arrangement (Fig. 4A), square arrangement (Fig. 4B), and honeycomb arrangement (Fig. 4C).
  • Figure 6 Contact angles plotted at the saturation pressure of water for a given temperature between 25 and 250 °C.
  • Figure 7 Image of a droplet of distilled water on a waffle patterned Si wafer coated in PTFE inside of pressure vessel. Image taken at 35.8°C and 62.0 kPa. Vapor is water.
  • Figure 8 Image sequence of a droplet of water evaporating on a flat Si wafer coated in PTFE inside of the pressure vessel. Images taken at labeled
  • Figures 10a-10b Image sequence of water droplet on waffle patterned Si wafer coated in PTFE. Droplet heated from 31 .7 °C to 54.1 °C . Droplet triple line expands outward due to expansion of trapped pockets of water vapor between droplet and surface until reaching a maximum at 46.4 °C. Vapor is water.
  • Figure 10a shows 31 .7 °C to 43.2 °C.
  • Figure 10b shows 46.4 °C to 54.1 °C.
  • Figure 10c magnified image of vapor expansion inside of water droplet, (from Fig. 10b) Vapor is water.
  • Figure 1 1 Image sequence of water droplet on waffle textured (25 ⁇ squares 50 ⁇ pitch) Si wafer coated with PTFE inside pressure vessel. As triple line expands, ⁇ * decreases from -90° to -32° after the trapped water vapor completes expansion inside droplet. Vapor is water.
  • Figure 12 Droplet of water on a glass slide with micro textured surfaces coated in silane inside of pressure vessel. Image taken at 22 °C and 100. 3 kPa. Vapor is water. Apparent contact angle 1 13°.
  • Figure 13 droplet of water on a glass slide with micro textured surfaces without silane coating inside of pressure vessel. Image taken at 22 °C and 100. 3 kPa. Vapor is water. Apparent contact angle 60°.
  • Figure 14 Scanning Electron Microscope (SEM) image of microtextures on glass slide.
  • Figure 15 Water droplet on zinc-oxide nano particle coated glass slide. Image taken at 22 °C and 100. 3 kPa. Apparent contact angle 170 degrees. Vapor is water.
  • Figures 16a and b SEM images of a PDMS:ZnO coating at two different magnfications
  • Figure 17 Water droplets on a flat PTFE coated surface and various micro textured surfaces as indicated. All images taken at 22° C.
  • Figure 18a Apparent contact angle of water droplets on flat and square pillar textured surfaces in saturated water vapor. Model predictions also shown.
  • Figure 18b Apparent contact angle of water droplets on flat and square waffle textured surfaces in saturated water vapor. Model predictions also shown.
  • Figure 19 Schematic cross-sectional view of "micromushroom” features. Partial micromushroom shown at right and left edges.
  • Figures 20a-f SEM images of micro mushrooms of various dimensions
  • Figure 21 a water on uncoated surface.
  • Figure 21 b oleic acid on uncoated surface.
  • Figure 21 c water on surface coated with Teflon® AF.
  • Figure 21 d oleic acid on surface coated with Teflon® AF.
  • Figure 22a water on uncoated surface.
  • Figure 22b oleic acid on uncoated surface.
  • Figure 22c water on surface coated with Teflon® AF.
  • Figure 22d oleic acid on surface coated with Teflon® AF.
  • Figure 23a water on uncoated surface.
  • Figure 23b oleic acid on uncoated surface.
  • Figure 23c water on surface coated with Teflon® AF.
  • Figure 23d oleic acid on surface coated with Teflon® AF.
  • Figure 24a water on uncoated surface.
  • Figure 24b oleic acid on uncoated surface.
  • Figure 24c water on surface coated with Teflon® AF.
  • Figure 24d oleic acid on surface coated with Teflon® AF.
  • Figure 25a water on uncoated surface.
  • Figure 25b oleic acid on uncoated surface.
  • Figure 25c water on surface coated with Teflon® AF.
  • Figure 25d oleic acid on surface coated with Teflon® AF.
  • Figure 26a water on uncoated surface.
  • Figure 26b oleic acid on uncoated surface.
  • Figure 26c water on surface coated with Teflon® AF.
  • Figure 26d oleic acid on surface coated with Teflon® AF.
  • Figure 27 Images of halocarbon 200 oil on ZnO particle coated slide. Image taken at 22 °C and 100. 3 kPa.
  • Figure 28a Image of RL 68H oil droplet on ZnO particle coated surface (5% ZnO, 2:1 fPDMS). The apparent contact angle was measured as 25.4°.
  • Figure 28b Image of contact angle obtained for a PDMS:ZnO 2:1 coating at standard temperature and pressure (STP). The apparent contact angle obtained was 138.6 °.
  • Figure 28c Image of RL 68H oil droplet on micropillar textured surface
  • Fig. 29a 0% R-134a;
  • Fig 29b 25% R-134a.
  • Fig. 29c 33% R-134a.
  • Fig. 29d 50%R-134a.
  • Fig. 29e 60% R-134a.
  • Fig. 29f 80% R-134a.
  • Fig. 30a 0% R-134a;
  • Fig 30b 25% R-134a.
  • Fig. 30c 33% R-134a.
  • Fig. 30d 50%R-134a.
  • Fig. 30e 60% R-134a.
  • Fig. 30f 80% R-134a.
  • Fig. 31 a 0% R-134a;
  • Fig 31 b 25% R-134a.
  • Fig. 31 c 33% R-134a.
  • Fig. 31 d 50%R-134a.
  • Fig. 31 e 60% R-134a.
  • Fig. 31 f 80% R-134a.
  • Fig. 32a 0% R-134a;
  • Fig 32b 25% R-134a.
  • Fig. 32c 33% R-134a.
  • Fig. 32d 50%R-134a.
  • Fig. 32e 60% R-134a.
  • Fig. 32f 80% R-134a.
  • Fig. 33a 0% R-134a;
  • Fig 33b 25% R-134a.
  • Fig. 33c 33% R-134a.
  • Fig. 33d 50%R-134a.
  • Fig. 33e 60% R-134a.
  • Fig. 33f 80% R-134a.
  • Figure 34 Image of R-134a droplet with a relatively high apparent contact angle on PTFE coated waffle pattern Si wafer in pressure vessel. Image taken at 24° C and 645.8 kPa. Vapor is R134a.
  • Figure 35 Schematic of heat exchanger system including a condenser, evaporator and compressor.
  • a refrigerant is a substance used in a heat cycle that undergoes a phase change between gas and liquid. Accordingly, a refrigerant vapor is the gas phase of a refrigerant. If the refrigerant is a mixture of components, the composition of the vapor phase may differ from that of the liquid. For example if the refrigerant is a mixture of a halocarbon refrigerant and a lubricant, the vapor of the mixture may be mostly halocarbon refrigerant vapor.
  • Refrigerants include inorganic refrigerants, halocarbon refrigerants, and hydrocarbon refrigerants. Refrigerants also include mixtures of inorganic refrigerants, halocarbon refrigerants and hydrocarbon refrigerants with additional components in the system such as lubricants.
  • the methods and devices provided herein are compatible with a wide range of refrigerants, so long as the vapor is capable of condensing into liquid droplets on a surface, including onto a surface that is refrigerant repelling.
  • refrigerants of interest include: R-1 1 Trichlorofluoromethane, R-12 Dichlorodifluoromethane, R-13 B1 Bromotrifluoromethane, R-22 Chlorodifluoromethane, R-32 Difluoromethane R-1 13, Trichlorotrifluoroethane, R-1 14 Dichlorotetrafluoroethane, R-123
  • Inorganic refrigerants known to the art include air, ammonia, carbon dioxide sulfur dioxide and water.
  • water may be used as a refrigerant in the methods of the invention under selected process conditions (e.g. under saturation or near saturation conditions and the pressure is less than atmospheric pressure).
  • the surface tension of water is 72.8 mN/m @ 20 °C.
  • halocarbon refers to a chemical compound including carbon and one or more of the halogens (bromine, chlorine, fluorine, iodine). In an embodiment, the halocarbon may also include hydrogen.
  • Exemplary halocarbon refrigerants include R-1 1 Trichlorofluoromethane, R-12 Dichlorodifluoromethane, R-13 B1 Bromotrifluoromethane, R-22 Chlorodifluoromethane, R-32 Difluoromethane R-1 13, Trichlorotrifluoroethane, R-1 14 Dichlorotetrafluoroethane, R-123 Dichlorotrifluoroethane, R-124 Chlorotetrafluoroethane, R-125 Pentafluoroethane, R-134a Tetrafluoroethane, R- 143a Trifluoroethane, R-152a Difluoroethane and R-245a Pentafluoropropane.
  • the halocarbon refrigerant is a hydrofluorocarbon (HFC) or hydrofluoroolefin (HFO).
  • HFC refrigerants include, but are not limited to, R-125 Pentafluoroethane, R-134a Tetrafluoroethane, R-143a Trifluoroethane, R-152a Difluoroethane and R-245a Pentafluoropropane.
  • hydrofluorolefin refrigerants include but are not limited to 2,3,3,3- tetrafluoroprop-1 -ene (HFO 1234yf) and rans-1 ,3,3-tetrafluoroprop-1 -ene (HFO 1234zeE).
  • Surface tension of R-134a is 14.6 mN/m @ -20 °C; surface tension of HFO-1234yf is 2.0 @ 55 °C, 9.5 @ 0 °C.
  • hydrocarbon refers to a chemical compound consisting of carbon and hydrogen.
  • Hydrocarbon refrigerants include, but are not limited to R290 propane, R600 n-butane, R600a isobutene (2-methyl propane), R1 150 ethylene and R1270 propylene.
  • Refrigerant mixtures are also possible.
  • the mixture may be an
  • azeotropic mixture whose vapor and liquid phases retain identical compositions over a wide range of temperatures.
  • the mixture may also be a zeotropic mixture whose composition in liquid phase differs from that in vapor phase. Zeotropic refrigerants therefore do not boil at constant temperatures unlike azeotropic refrigerants.
  • Exemplary refrigerant mixtures are R-401 A (53% R-22, 34% R-124, 13% R-152a), R-401 B (61 % R- 22, 28% R-124, 1 1 % R-152a), R-402A (38% R-22, 60% R-125, 2% R-290), R-404A (44% R-125, 52% R-143a, R-134a), R-407A (20% R-32, 40% R-125, 40% R-134a) , R- 407C (23% R-32, 25% R-125, 52% R-134a), R-502 (48.8% R-22, 51 .2% R-1 15) 0.283 4.1 R-507 (45% R-125, 55% R-143).
  • the lubricant may be a polyol ester (POE) or a polyalkylene glycol (PAG).
  • PEO polyol ester
  • PAG polyalkylene glycol
  • Polyol esters include, but are not limited to neopentyl glycols, trimethylolpropanes, pentaerythritols and dipentaerytrhitols.
  • Specific polyol esters include, but are not limited to RL68H.
  • the viscosity of the lubricant may be described by an ISO viscosity grade number such as ISO 68, ISO 46 or ISO 100.
  • the temperature and pressure of the vapor is generally less than the critical temperature and pressure of the refrigerant.
  • the temperature and pressure of the vapor may vary within the heat exchanger apparatus.
  • the vapor may be superheated after exiting a compressor and be at a lower temperature, such as at or near its saturation temperature, adjacent to a surface of surface of the condenser.
  • the refrigerant can exist in both liquid and vapor form.
  • the saturation temperature is the temperature where a substance changes between its liquid and its vapor phase (at a given pressure).
  • the saturation vapor pressure is the vapor pressure where a substance changes between its liquid and its vapor phase (at a given temperature).
  • near saturation conditions where the pressure and temperature are close to but not at the steady state values, can also support evaporation and condensation.
  • near saturation conditions capable of supporting evaporation and condensation may involve pressures and temperatures which are within 20%, 15%, 10% or 5% of their saturation values.
  • the condensation heat transfer processes of the invention take place in an enclosure such as a pressure vessel under saturation or near saturation conditions.
  • characteristic contact angle refers to the static contact angle of a droplet of refrigerant on an essentially flat or smooth solid surface of a given material, including under standard conditions.
  • the characteristic contact angle may be taken as the mean or median of several measurements of contact angle.
  • the characteristic contact angle of the refrigerant on a surface material is less than 50°, less than 40 °, less than 30 °, less than 20°, less than 10° or less than 5°.
  • the characteristic contact angle may be a static contact angle, an advancing contact angle or a receding contact angle.
  • apparent contact angle refers to the contact angle of a droplet of refrigerant on a textured surface and may also be referred to as ⁇ * .
  • the size of the droplet is greater than or equal to the size of the features creating the surface texture. For example, if the surface texture is created by particles on the surface, the droplet size may be greater than the particle size.
  • the apparent contact angle of a droplet of refrigerant on a textured surface of a given material is greater than the characteristic contact angle of the refrigerant on the same material (without texture) when the droplet size is greater than the size of the features creating the surface texture, the surrounding atmosphere, temperature and pressure being the same in both cases.
  • the apparent contact angle may be greater than the characteristic contact angle by greater than 45°.
  • the apparent contact angle of at least some of the droplets is greater than 90°.
  • the apparent contact angle on a given surface texture is assessed in the temperature or pressure range of interest under saturation conditions.
  • the contact angle of a droplet may also depend on whether the measurement is a static measurement or a dynamic measurement.
  • the contact angle of a droplet with a surface may change during droplet formation.
  • any of the methods and devices provided herein may measure contact angle at a user-defined times or stages, thereby providing the ability to better characterize and compare different systems.
  • the time point may be at specified time after droplet condensation begins, or may be at a specific stage of the process, such as immediately prior to exit of the moving droplet from the system or any stage between formation to exit, such as at a half-way point.
  • Other relevant parameters may include rates or speed at which maximum contact angle is achieved as certain fluids may initially condense with a rather flat contact angle and then increased in contact angle as the droplet further forms.
  • any of the devices and methods provided herein may be characterized in terms of a surface repellency ratio defined as ⁇ ⁇ for a given system, such as a surface repellency ratio that is greater than or equal 2, including selected from a range that is greater than or equal to 2 and less than or equal 150, greater than or equal to 5 and less than or equal 100 ratio, or greater than or equal to 5 and less than or equal 15, or about 10 or more, with ⁇ * > 90° and ⁇ ⁇ 90°.
  • the surface may comprise a fluoropolymer or fluorosilane.
  • Suitable fluoropolymers include, but are not limited to, Polytetrafluoroethylene (PTFE and amorphous PTFE (e.g. Teflon® AF).
  • PTFE and amorphous PTFE e.g. Teflon® AF.
  • C ommercially available fluorosilanes such as Dow Corning 2604, 2624, and 2634; DK Optool DSXTM; Shintesu OPTRONTM;
  • heptadecafluoro silane manufactured, for example, by Gelest
  • FLUOROSYLTM FLUOROSYLTM
  • textured surfaces useful for the invention have surface textures which facilitate droplet mobility along the surface. In this manner, as droplets form on a surface, the droplets move along the surface thereby avoiding film formation.
  • the refrigerant repelling surfaces of the invention facilitate droplet movement along the surface.
  • One way to measure the ease of roll-off is to determine the angle of tilt from the horizontal needed before a drop will roll off a surface. The lower the tilt angle, the more easily the drop rolls off the surface.
  • surface texture can refer to three-dimensional features on a surface that intrudes into an interior volume that contains the refrigerant.
  • surface texture may comprise relief and recess features.
  • an elevated surface feature is considered a relief feature, and the corresponding non- elevated portion may be considered, relative to the relief feature, a recess feature.
  • the "micromushroom” features shown in Figure 19 may be considered to be relief features.
  • Refrigerant behavior on textured surfaces may be compared to that on smooth surfaces.
  • a "smooth" surface has a surface roughness significantly less than (e.g.
  • the surface texture of the interior of the pressure vessel includes topographically complex, three-dimensional microstructures or nanostructures with reentrant
  • Surfaces having a reentrant geometry typically include a protruding portion configured to protrude toward a liquid and a reentrant portion opposite the protruding portion.
  • Such reentrant structures can be formed by particles or fibers, whose curvature provides the reentrant feature.
  • the reentrant structures can also be made with etching techniques.
  • Nonwoven or woven fabrics, including fabrics woven of metal fibers, can also provide reentrant geometry.
  • the surface features on the interior surface of the pressure vessel comprise nanoparticles.
  • the average diameter of the nanoparticles is 2-300 nm and the average spacing between nanoparticles 10-1000 nm.
  • the nanoparticles may be selected from the group consisting of ZnO and other metal oxides as well as silica and silicon dioxide.
  • the surface of the nanoparticle may also be treated to adjust the wettability of the nanoparticle.
  • the nanoparticles can be halogenated, perhalogenated, perfluorinated, or fluorinated nanoparticles, for example, perfluorinated or fluorinated silsesquioxanes.
  • FIG. 3A schematically illustrates a top view of features forming a "waffle” pattern of interconnected elevated “wall” or “ridge” features (indicated by double lines in the figure) surrounding hexagonal depressions.
  • Figure 3B
  • FIG. 1 schematically illustrates a top view of features forming a "waffle” pattern interconnected elevated grid-like "wall” or “ridge” features (indicated by double lines in the figure) surrounding square depressions.
  • Such features may be characterized by the dimension of the depression (e.g. w or w), the pitch or microstructure period (dimension of depression +dimension of wall, e.g. p or p) and the depth of the depression (e.g. d or d) or height of the wall (e.g. h or h).
  • the elevated wall features in the "waffle” have an average width between 5 nm and 1 0 microns and an average spacing between 50 nm and 250 microns.
  • the depth of the depressions/height of the elevated features may be on the order of the width of the depressions (spacing between the elevated features. In different embodiments, the depth of the depressions may be from 5 nm to 250 microns or 50 nm to 250 microns.
  • the dimensions of the surface features are selected in accordance with operating conditions and refrigerant
  • the surface texture is selected so that the surface is considered refrigerant repelling, even though refrigerant may wet a flat surface of the surface material.
  • the features of the textured surface resemble mushrooms, with a top cap portion that is wider than its stem.
  • this type of structure can be characterized by its cap width (2W), the height between the bottom of the cap and the surface (H), the cap radius (R) and the spacing between neighboring caps (2D).
  • Equations 1 and 2 give relationships between the flat surface contact angle and the relevant surface free energies and the variation in the surface free energy with temperature.
  • Figure 1 a illustrates the contact angle on a flat surface; in Figure 1 a ⁇ is equivalent to 9 C in equation 1 .
  • FIG. 2 shows water surface tension as a function of temperature.
  • Equation 2 to solve Equations 3 - 5 simultaneously. This determines Tc YSL , y SL @25°, and c ysL .Once these values are known, Equation 1 can be solved at any temperature. Tables 1 and 2 show initial conditions and unknowns related to interfacial energy related parameters and contact angle parameters respectively.
  • Figures 3A-B and 4A-C schematically illustrate some of the waffle and pillar surface textures fabricated for testing.
  • Figure 3 is a schematic top view of a hexagonal waffle structure (Fig. 3A) and a grid-like waffle structure (Fig. 3B).
  • Figure 4 is a schematic top view of different configurations of pillar elements: hexagonal arrangement (Fig. 4A), square arrangement (Fig. 4B), and honeycomb arrangement (Fig. 4C).
  • Tables 3 and 4 respectively provide additional information about waffle and pillar surface textures.
  • h is element height
  • p is pitch
  • w is width of square or hexagonal depression.
  • A is elements per area p 2
  • d is diameter of the pillar
  • p is pitch
  • h is element height.
  • Figure 5 shows an experimental setup used for contact angle
  • the apparatus includes a pressure chamber 10, a pump 20, which may be an infusion pump, a camera 30, a light source 40 and data acquisition unit 50.
  • Table 5 shows the contact angle (CA) measured for water and oleic acid oil on smooth and microtextured surfaces.
  • the surfaces are either smooth, textured with a waffle pattern of Fig. 3 as either hexagons or squares, or textured with a standard lotus leaf type pattern consisting of dense pillar structures (Fig. 4).
  • w is feature width
  • d is diameter
  • p is microstructure period
  • h is feature height (or depth of waffles).
  • Figure 6 shows a graph for ⁇ values between 25 and 250 °C. Contact angles plotted at the saturation pressure of water for a given temperature for different surface textures (values from model).
  • Figure 7 shows an image of a droplet of distilled water on a waffle patterned Si wafer coated in PTFE inside of pressure vessel. Image taken at 35.8°C and 62.0 kPa. Vapor is water.
  • Figure 8 shows an image sequence of a droplet of water evaporating on a flat Si wafer coated in PTFE inside of the pressure vessel. Images taken at labeled temperatures and corresponding saturation pressures.
  • Figures 10a-10b show an image sequence of water droplet on waffle patterned Si wafer coated in PTFE. Droplet heated from 31 .7 °C to 54.1 °C. Droplet triple line expands outward due to expansion of trapped pockets of water vapor between droplet and surface until reaching a maximum at 46.4 °C. Vapor is water.
  • Figure 10c shows a magnified image of vapor expansion inside of water droplet, (see Fig. 10b) Vapor is water. Waffle pattern 10 micrometer squares, 20 micrometer pitch.
  • Figure 1 1 shows an image sequence of water droplet on waffle textured (25 ⁇ squares 50 ⁇ pitch). Si wafer coated with PTFE inside pressure vessel. As triple line expands, ⁇ * decreases from -90° to -32° after the trapped water vapor completes expansion inside droplet. Vapor is water.
  • Figure 12 shows a droplet of water on a glass slide with micro textured surfaces coated in silane inside of pressure vessel. Image taken at 22 °C and 100. 3 kPa. Vapor is water. Apparent contact angle 1 13°.
  • Figure 13 shows a droplet of water on a glass slide with micro textured surfaces without silane coating inside of pressure vessel. Image taken at 22 °C and 100. 3 kPa. Vapor is water. Apparent contact angle 60°.
  • Figure 14 shows an SEM image of microtextures on glass slide (see Figs. 12 and 13).
  • Figure 15 shows a water droplet on zinc-oxide nano particle coated glass slide. Image taken at 22 °C and 100. 3 kPa. Vapor is water
  • Figures 16a-b show SEM images of a 2PDMS:1 ZnO coating at two different magnfications.
  • Figure 17 shows water droplets on flat and microtextured PTFE coated surfaces, when the surrounding environment is air, low pressure air, or water vapor.
  • the apparent contact angle of the droplets decreased for both the square pillar and square waffle textured surfaces when the vapor phase was changed from air to water vapor.
  • Figure 19 illustrates relevant dimensions for surface features having a "mushroom” or “micro mushroom” geometry.
  • W is width from the center of the stem to the edge of the cap.
  • R is the radius of the cap.
  • H is the distance between the lower portion of the surface and the bottom of the cap.
  • 2D is the spacing between the edges of the caps.
  • ⁇ is the characteristic contact angle
  • ⁇ is the local geometry angle
  • hi is a sagging height
  • h2 is a pore depth (Tuteja et al., 2008, PNAS, 107(47), 18200- 19205).
  • Table 6 lists relevant dimensions for several micromushroom surface textures.
  • Figure 20a shows a SEM image of micromushroom sample texture 1 (see Table 6)
  • Figure 20b shows an SEM image of micromushroom sample texture 2
  • Figure 20c shows a SEM image of micromushroom sample texture 3
  • Figure 20d shows an SEM image of micromushroom sample texture 4
  • Figure 20e shows a SEM image of micromushroom sample texture 5
  • Figure 20f shows a SEM image of
  • micromushroom sample texture 6 samples 1 -6 as given in Table 6)
  • Table 7 lists apparent contact angles measured and calculated for water and oleic acid for the coated and uncoated micromushroom geometries of Table 6.
  • Figures 21 a-d show sessile drops on micromushroom texture 1 .
  • Figures 21 a-b respectively show a drop of water and a drop of oleic acid on the uncoated texture while
  • Figures 21 c-d respectively show a drop of water and a drop of oleic acid on the texture as coated with Teflon® AF.
  • Figures 22a-d show sessile drops on micromushroom texture 2.
  • Figures 22a-b respectively show a drop of water and a drop of oleic acid on the uncoated texture while
  • Figures 22c-d respectively show a drop of water and a drop of oleic acid on the texture as coated with Teflon® AF.
  • Figures 23a-d show sessile drops on micromushroom texture 3.
  • Figures 23a-b respectively show a drop of water and a drop of oleic acid on the uncoated texture while Figures 23c-d respectively show a drop of water and a drop of oleic acid on the texture as coated with Teflon® AF.
  • Figures 24a-d show sessile drops on micromushroom texture 4.
  • Figures 24a-b respectively show a drop of water and a drop of oleic acid on the uncoated texture while
  • Figures 24c-d respectively show a drop of water and a drop of oleic acid on the texture as coated with Teflon® AF.
  • Figures 25a-d show sessile drops on micromushroom texture 5.
  • Figures 25a-b respectively show a drop of water and a drop of oleic acid on the uncoated texture while
  • Figures 25c-d respectively show a drop of water and a drop of oleic acid on the texture as coated with Teflon® AF.
  • Figures 26a-d show sessile drops on micromushroom texture 6.
  • Figures 26a-b respectively show a drop of water and a drop of oleic acid on the uncoated texture while
  • Figures 26c-d respectively show a drop of water and a drop of oleic acid on the texture as coated with Teflon® AF.
  • Advancing and receding contact angles were measured using the sliding angle method.
  • a droplet was deposited on a tilted surface.
  • a camera captures the droplet movement as it slides down the inclined surface.
  • T 20 °C
  • P T 40 °C
  • T 60 °C
  • T 100 °c
  • Pillar h 20
  • HC-200 is a liquid polymer oil with the chemical name chlorotrifluoroethylene.
  • HC-200 has a surface tension about 0.025 N/m, which is lower than the surface tension for oleic acid.
  • Table 9 shows the results, where the square waffle patterns are oleophobic, while a smooth surface of the same material is oleophillic.
  • w is feature width
  • p is microstructure period
  • d is feature depth.
  • Figure 27 shows images of halocarbon 200 oil on ZnO particle coated slides; these images illustrate the change in contact angle over 20 seconds. Image taken at 22 °C and 100. 3 kPa.
  • PDMS Polydimethylsiloxane
  • PTFE polytetrafluoroethylene
  • Figures 29a, 30a, and 31 a illustrate drops obtained on micromushroom structures and
  • Figures 32a and 33a illustrate drops obtained on waffle structures.
  • R-134a and RL 68H were as follows. A quantity of RL 68H was measured to +/- 0.5 g. The RL 68H was then added to the pressure vessel. The pressure vessel was then evacuated to 0.15 psi at 22 c to remove air and water vapor. The pressure vessel was then cooled to 10 C. A quantity of R-134a was then measured to within +/- 0.5 g and added to the pressure vessel. The mixture was then recovered into a sampling vessel.
  • Figure 34 shows an image of R-134a droplet with a relatively high apparent contact angle on PTFE coated textured Si wafer in pressure vessel. Image taken at 24° C and 645.8 kPa. Vapor is R134a. The surface texture was a waffle pattern, 25 ⁇ squares, 50 ⁇ pitch. The contact angle for R-134a on a flat surface coated with PTFE was less than 10 degrees Surface tension of R-134a is 14.6 mN/m @ -20 °C.

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Abstract

L'invention concerne des procédés et des dispositifs permettant la condensation sous forme de gouttes d'une vapeur de réfrigérant sur une surface. La surface et différents aspects du système sont configurés pour faire en sorte que la surface repousse le réfrigérant et augmente la mobilité des gouttes pour élever le taux de condensation et/ou élever le taux de transfert de chaleur. La surface repoussant le réfrigérant peut être configurée de telle manière qu'un réfrigérant qui pourrait normalement mouiller une surface plate non structurée soit effectivement repoussé.
PCT/US2013/046646 2012-06-19 2013-06-19 Surfaces repoussant un réfrigérant WO2014011372A2 (fr)

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