阅读说明：本技术 包含润滑剂浸渍的表面的传热和传质部件 (Heat and mass transfer component comprising lubricant impregnated surface ) 是由 N·米利科维奇 S·赛特 G·巴拉克 L·W·博尔顿 于 2020-04-21 设计创作，主要内容包括：一种传热和传质部件,该不见包含润滑剂浸渍的表面,该表面包含疏水性表面结构,该结构包含其上连接有疏水性物质的纳米结构化表面凸起。该疏水性表面结构用粘度为约400mPa·s至约6000mPa·s的氟化润滑剂浸渍。一种在传热和传质部件上制造润滑剂浸渍的表面的方法,该方法包括：清洁导热基底来形成清洁的基底；将该清洁的基底暴露于热水或热碱溶液来形成具有纳米结构化表面凸起的导热基底；将疏水性物质沉积在该纳米结构化表面凸起上来形成疏水性表面结构；和用粘度为400mPa·s至6000mPa·s的氟化润滑剂涂覆该疏水性表面结构。该传热和传质部件在烃凝结过程中会表现出传热系数显著增加。(A heat and mass transfer component comprising a lubricant impregnated surface comprising a hydrophobic surface structure comprising nanostructured surface protrusions having a hydrophobic substance attached thereto. The hydrophobic surface structure is impregnated with a fluorinated lubricant having a viscosity of from about 400 mPa-s to about 6000 mPa-s. A method of making a lubricant-impregnated surface on a heat and mass transfer component, the method comprising: cleaning the thermally conductive substrate to form a cleaned substrate; exposing the cleaned substrate to hot water or a hot alkaline solution to form a thermally conductive substrate having nanostructured surface protrusions; depositing a hydrophobic substance on the nanostructured surface projections to form a hydrophobic surface structure; and coating the hydrophobic surface structure with a fluorinated lubricant having a viscosity of 400 to 6000 mPa-s. The heat and mass transfer components exhibit a significant increase in heat transfer coefficient during hydrocarbon condensation.)

1. A heat and mass transfer section comprising:

a lubricant-impregnated surface, the surface comprising:

a hydrophobic surface structure comprising nanostructured surface protrusions having a hydrophobic substance attached thereto; and

a fluorinated lubricant having a viscosity of about 400mPa · s to about 6000mPa · s impregnating the hydrophobic surface structure.

2. The heat and mass transfer means of claim 1 which is part or all of a heat exchanger.

3. The heat and mass transfer means of claim 1 which is part or all of a distillation column.

4. The heat and mass transfer component according to any one of claims 1-3, wherein when a working fluid having a surface tension of from about 15mN/m to about 30mN/m contacts the lubricant-impregnated surface, the working fluid undergoes droplet-like condensation, thereby promoting heat transfer from the component.

5. The heat and mass transfer component according to claim 4, wherein the droplets condense for a period of at least about 1000 hours, whereby the lubricant-impregnated surface exhibits long-term durability.

6. The heat and mass transfer element according to any of claims 1-5, wherein when a working fluid comprising dissolved, suspended, entrained, crystallized and/or precipitated solids contacts the lubricant-impregnated surface, deposition of solids on the lubricant-impregnated surface is inhibited, whereby the element is resistant to fouling.

7. The heat and mass transfer component of claim 6, wherein deposition of solids is inhibited for at least about 1000 hours, whereby the lubricant-impregnated surface exhibits long-term durability.

8. The heat and mass transfer component of any of claims 1-7, wherein the thermally conductive substrate comprises a metal selected from the group consisting of Cu, Al, Fe, and Ti, and

wherein the nanostructured surface projections comprise an oxidized metal selected from the group consisting of copper oxide, aluminum oxide, iron oxide, and titanium dioxide.

9. The heat and mass transfer component according to any one of claims 1-8, wherein the nanostructured surface projections exhibit a roughness factor r of about 5 to 50.

10. The heat and mass transfer component according to any one of claims 1-9, wherein the height of the nanostructured surface projections is from about 300nm to about 3 microns.

11. The heat and mass transfer component according to any one of claims 1-10, wherein the nanostructured surface projections comprise a paddle-like shape.

12. The heat and mass transfer component according to any one of claims 1-11, wherein the nanostructured surface projections are irregular in size, shape, and/or location.

13. The heat and mass transfer component of any of claims 1-12, wherein the hydrophobic substance comprises a silane.

14. The heat and mass transfer component of claim 13 wherein the silane is selected from the group consisting of: methyl silanes, linear alkyl silanes, branched alkyl silanes, aromatic silanes, fluorinated alkyl silanes, and dialkyl silanes.

15. The heat and mass transfer component of any of claims 1-14, wherein the fluorinated lubricant comprises a perfluoropolyether (PFPE) oil.

16. The heat and mass transfer component of claim 15, wherein the fluorinated lubricant is selected from the group consisting of Krytox^TM-VPF 1525、Krytox^TMVPF 16256 and-Y25/6。

17. the heat and mass transfer component of any of claims 1-16, wherein the fluorinated lubricant comprises:

the liquid density p is about 1800kg/m³To about 2000kg/m³；

A low surface tension γ is about 10mN/m to about 30 mlM/m; and

vapor pressure P_vapNot greater than about 1X10^-7kPa。

18. A process for using a heat and mass transfer means according to any one of claims 1 to 17, the process comprising:

exposing the lubricant-impregnated surface to a working fluid having a surface tension of about 15mN/m to about 30 mN/m; and

during exposure, the working fluid effects a droplet-like condensation on the lubricant-impregnated surface,

wherein the heat and mass transfer components exhibit at least about 6kW/m as a result of the droplet-shaped condensation²K steady state condensation heat transfer coefficient.

19. The method of claim 18, wherein the steady state condensation heat transfer coefficient is at least about 9kW/m²K。

20. The method of claim 18 or 19, wherein the exposing of the working fluid is performed for a period of at least about 10 hours.

21. The method of claim 20, wherein the period is hundreds or thousands of hours.

22. The method according to any one of claims 18-21, wherein the working fluid further comprises dissolved, suspended, entrained, crystallized and/or precipitated solids, and

wherein during exposure, deposition of solids on the lubricant-impregnated surface is inhibited, whereby the heat and mass transfer component is resistant to fouling.

23. The method of any one of claims 18-22, wherein the working fluid comprises an alcohol and/or a hydrocarbon.

24. The method of claim 23, wherein the working fluid comprises a hydrocarbon or a mixture of purified hydrocarbons.

25. The method of claim 23 or 24, wherein the working fluid is selected from the group consisting of: ethanol, isopropanol, pentane, hexane, xylene, and toluene.

26. A method of making a lubricant-impregnated surface on a heat and mass transfer component, the method comprising:

cleaning the thermally conductive substrate to form a cleaned substrate;

exposing the cleaned substrate to hot water or a hot alkaline solution to form a thermally conductive substrate having nanostructured surface protrusions;

depositing a hydrophobic substance onto the nanostructured surface projections to form a hydrophobic surface structure; and

the hydrophobic surface structure is coated with a fluorinated lubricant having a viscosity of 400 to 6000 mPa-s, thereby forming a lubricant-impregnated surface on the heat and mass transfer components.

27. The method of claim 26, wherein the cleaning comprises: the thermally conductive substrate is immersed in one or more of acetone, alcohol, deionized water, and subsequently rinsed in deionized water.

28. The method of claim 26 or 27, further comprising exposing the thermally conductive substrate to an acid solution after the cleaning.

29. The method according to any one of claims 26-28, wherein the temperature of the hot water or hot base solution is about 85 ℃ to about 95 ℃.

30. The method of any one of claims 26-29, wherein depositing the hydrophobic substance comprises atmospheric pressure chemical vapor deposition of silane.

31. The method according to any one of claims 26-30, wherein coating with the fluorinated lubricant comprises dip coating.

32. The method of any of claims 26-31, further comprising draining excess fluorinated lubricant from the hydrophobic surface structure after coating the hydrophobic surface structure with the fluorinated lubricant, and then drying in a gas stream.

Technical Field

The present invention relates generally to heat and mass transfer technology, and more particularly to surface structures for enhanced heat transfer and reduced fouling.

Background

Vapor condensation, which is widely used in industrial processes to transfer heat and separate fluids, is critical to the success of many industrial processes, including power generation, distillation, air conditioning and refrigeration systems, and natural gas processing.

In the last century, low surface energies have been developed<10mJ/m²) The hydrophobic surface promotes droplet-like condensation of water vapor to enhance heat transfer. However, low surface tension fluids such as alcohols and hydrocarbons have their equivalent surface energies (10 mJ/m)²<γ<25mJ/m²) While presenting unique challenges to hydrophobic surfaces. On hydrophobic substrates, hydrocarbon liquids exhibit low advancing contact angles and high contact angle hysteresis, resulting in film-like condensation. The challenge of creating non-wetting droplet condensation surfaces for low surface tension fluids has raised concerns about vapor condensation heat transfer with little progress for other fluids.

Given that recent paradigms have turned to alternative energy sources and biofuels, the need for efficient coagulation and separation of low surface tension fluids has grown dramatically. For example, the global production of fuel ethanol from corn has increased from 65 billion gallons in 2000 to 267 billion gallons in 2017, and a wide range of aliphatic and aromatic hydrocarbons are continuously produced in the petrochemical industry as pure materials and in refineries as blends. Furthermore, the use of low global warming potential (low GWP) refrigerants, many of which are aliphatic hydrocarbons, has been required to replace existing non-flammable options, and several industrial applications including Organic Rankine Cycle (ORC) power generation and building energy technologies rely on efficient low surface tension refrigerant condensation to perform efficiently.

Despite advances in developing low surface energy hydrophobic and superhydrophobic coatings to enhance water vapor condensation, stable droplet-like condensation of low surface tension fluids has not been achieved.

Disclosure of Invention

A heat and mass transfer component comprises a lubricant-impregnated surface comprising a hydrophobic surface structure comprising nanostructured surface projections having a hydrophobic substance attached thereto. The hydrophobic surface structure is impregnated with a fluorinated lubricant having a viscosity of about 400 mPa-s to about 6000 mPa-s.

A method of making a lubricant-impregnated surface on a heat and mass transfer component, the method comprising: cleaning the thermally conductive substrate to form a cleaned substrate; exposing the cleaned substrate to hot water or a hot alkaline solution to form a thermally conductive substrate having nanostructured surface protrusions; depositing a hydrophobic substance on the nanostructured surface projections to form a hydrophobic surface structure; and coating the hydrophobic surface structure with a fluorinated lubricant having a viscosity of 400 to 6000 mPa-s, thereby forming a lubricant-impregnated surface on the heat and mass transfer component.

Drawings

FIG. 1A is a perspective view of a portion of an exemplary heat and mass transfer component, and FIG. 1B is a cross-sectional view of a lubricant-impregnated surface on the heat and mass transfer component.

Fig. 2A and 2B are Scanning Electron Microscope (SEM) and Focused Ion Beam (FIB) images of nanostructured surface protrusions comprising copper oxide.

Fig. 3 shows water, ethanol and hexane droplets in an apparent advancing state on a smooth hydrophobic copper surface (top panel) and a lubricant-impregnated copper oxide surface (LIS K1525) (bottom panel).

Fig. 4A-4C show the condensation of water, ethanol and hexane, respectively, on smooth hydrophobic copper tubing, and fig. 4D-4F show the condensation of water, ethanol and hexane, respectively, on copper tubing processed to have a lubricant impregnated surface (LIS K1525). Vapor pressure of the chamber is P_v＝4.5kPa(4A，4D)，P_v7kPa (4B, 4E), and P_v＝12kPa(4C，4F)。

FIGS. 5A and 5B show the experimental steady state log mean water to gas temperature difference (Δ T ") as a function of the overall surface heat flux (q") for the condensation of (5A) ethanol and (5B) hexane on smooth hydrophobic copper surfaces (HP Cu, film) and lubricant impregnated surfaces (LIS, drop-shaped)_LMTD). Rapid droplet removal due to droplet-like condensation achieves the highest thermal flux for the LIS sample for the overall surface thermal flux (q "), which is the saturated vapor pressure (P)_v) As a function of (c). Error bars represent the propagation of errors associated with fluid inlet and outlet temperatures (+ -0.25K), pressure measurements (+ -1%), and flow rates (+ -1%).

FIGS. 5C-5E show the as saturated vapor pressure (P) for (5C) ethanol, (5D) hexane and (5E) xylene condensation on HP Cu (film) and LIS (drop) surfaces_v) Experimental and theoretical steady state coagulation coefficients (h) of the function of (c)_c). Error bars represent the propagation of errors associated with fluid inlet and outlet temperatures (+ -0.25K), pressure measurements (+ -1%), and flow rates (+ -1%). Theoretical predictions (dashed lines) are obtained from the classical Nusselt (Nusselt) film-like condensation pattern on tubes.

Fig. 6 shows a time-lapse image sequence of both ethanol (top panel) and hexane (bottom panel) coagulation on LIS K1525 for 7 hours. And (3) coagulation conditions: Δ T for ethanol_LMTD＝16℃，q”＝80kW/m²And Δ T for hexane_LMTD＝9℃，q”＝65kW/m²For ethanol P_v8kPa and for hexane P_v＝14kPa。

FIGS. 7A-7D show the coagulation pattern (drop or film) over a time of 2805 hours in sequential ethanol coagulation experiments on LIS K1525, LIS K16256, LIS Y25/6 and superhydrophobic CuO, respectively.

Detailed Description

Fig. 1A is a schematic illustration of a portion of an exemplary heat and mass transfer component 100 that includes a durable lubricant-impregnated surface 102 to improve heat transfer performance and/or fouling resistance of the component 100. In this schematic, the heat and mass transfer section 100 has a tubular shape, but the section 100 is not limited to this geometry and may alternatively have any size or shape suitable for the intended application. The heat and mass transfer section 100 can be used for power generation, distillation, air conditioning or refrigeration, natural gas processing, and/or the production of purified or mixed aliphatic and/or aromatic hydrocarbons. The component 100 may form part or all of a heat exchanger or a fractionation column, for example.

Referring to fig. 1B, lubricant-impregnated surface 102 comprises a hydrophobic surface structure 110 impregnated with a fluorinated lubricant 112 (which preferably has a viscosity of 400 to 6000 mPa-s), as described below. The hydrophobic surface structure 110 comprises nanostructured surface protrusions 106 to which a hydrophobic substance 108 is attached. The areas between adjacent surface protrusions 106 define surface crevices 106a that allow the fluorinated lubricant 112 to become impregnated by capillary forces. The heat and mass transfer component 100 further comprises a thermally conductive substrate 104 that supports a lubricant-impregnated surface 102.

Advantageously, when the working fluid contacts the lubricant-impregnated surface 102, droplet-like condensation of the working fluid occurs, thereby promoting heat transfer from the component 100. This result is obtained even when using low surface tension working fluids (e.g. working fluids of ethanol, having a surface energy of about 15-30 mN/m) which are generally prone to film-like condensation. In addition, the droplet coagulation may occur stably over a period of 10 hours or more, and possibly hundreds or thousands of hours, due to the stability of the lubricant 112 within the hydrophobic surface structure 110 during exposure to the working fluid. Experiments have shown that drop coagulation can be achieved over a period of more than 1000 hours, even more than 2880 hours (>120 days).

Similarly, when a working fluid containing dissolved, suspended, entrained, crystallized, and/or precipitated solids contacts the lubricant-impregnated surface 102, deposition of the solids on the lubricant-impregnated surface may be inhibited. In addition, crystallization and/or precipitation of the solid may be inhibited. Thus, the component 100 may be resistant to fouling. Also, due to the stability of the lubricant 112 within the hydrophobic surface structure 110, this anti-fouling performance may be maintained during exposure to the working fluid for periods of 10 hours or more, possibly up to hundreds or thousands of hours (e.g., greater than 1000 hours, or greater than 2880 hours).

The thermally conductive substrate 104 may include a metal selected from Cu, Al, Fe, and Ti. For example, the thermally conductive substrate 104 may include copper or a copper alloy such as brass, aluminum or an aluminum alloy, iron or an iron alloy such as stainless steel, and/or titanium or a titanium alloy. The nanostructured surface protrusions 106 may comprise an oxidized metal selected from the group consisting of copper oxide, aluminum oxide, iron oxide, and titanium dioxide. As described below, the nanostructured surface protrusions 106 can be formed in a process that oxidizes the surface of the thermally conductive substrate 104 and nanostructured the surface. Typically, the nanostructured/surface oxidation extends into the thermally conductive substrate 104 to a depth of about 2 microns or less, or about 1 micron or less.

The nanostructured surface protrusions 106 may exhibit a roughness factor r of about 5 to about 50. The roughness factor r may be defined as the ratio of the total surface area to the convex area (e.g., the area of a smooth surface of the same size and geometry). The size, shape and location of the nanostructured surface projections may be uniform, or the size, shape and/or location of the surface projections may be non-uniform (irregular), as shown in fig. 1B. Depending on the fabrication method, the surface protrusions may be described as having a knife-like or blade-like shape, as seen in the SEM and FIB images of fig. 2A and 2B, where the length of each protrusion is greater than its width, and the width is much greater than the thickness. In other examples, the surface protrusions may be conical, cylindrical, and/or rod-shaped. Typically, the height of the nanostructured surface protrusions can be from about 300nm to about 3 microns, or more typically from about 500nm to about 1 micron. The width or diameter of the surface protrusions may be from about 50nm to about 1 micron, or more typically from about 100nm to about 500 nm. In the case of a knife-like protrusion, the thickness may be about 10nm to about 200nm, or about 10nm to about 100 nm.

Hydrophobicity is imparted to the nanostructured surface projections by surface modification (or functionalization) with hydrophobic substances. The Chemical Vapor Deposition (CVD) method described below or another suitable method may be used for surface functionalization. In a CVD process, the desired hydrophobic substance is deposited onto the surface protrusions. Thus, a so-called conformal coating or monolayer comprising a hydrophobic substance may be formed on/attached to the surface protrusions. Hydrophobic substances are understood to be hydrophobic molecules or compounds. Typically, the hydrophobic material comprises a silane, such as methylsilane, linear alkylsilane, branched alkylsilane, aromatic silane, fluorinated alkylsilane and/or dialkylsilane. A suitable silane may be Heptadecafluorodecyltrimethoxysilane (HTMS).

As described above, the regions between adjacent surface protrusions 106 define surface crevices 106a that allow the fluorinated lubricant 112 to be impregnated by capillary forces. The critical contact angle for immersion can be defined as follows:whereinIs the fraction of the raised area occupied by the solid, and r is the ratio of the total surface area to the raised area. In the following examples using silane-functionalized copper oxide surface protrusions, θ_C≈85°，And r 10. For successful impregnation, the inherent contact angle of the lubricant 112 on a smooth metal surface may be less than the critical angle.

When the surface tension of the working fluid and fluorinated lubricant are comparable, the lower viscosity lubricant is more prone to droplet drop, which results in better heat transfer from the lubricant impregnated surface. However, if the viscosity of the lubricant is too low, the lubricant-impregnated surface may degrade rapidly due to lubricant drainage. Thus, viscosities of 400 to 6000mPa · s are believed to be suitable for fluorinated lubricants; when the viscosity is less than 400 mPas, the lubricant is easily discharged, and when the viscosity is more than 6000 mPas, the lubricant is hardly dropped. Due to this reasonThus, lower viscosities, for example from about 400 to about 4000 mPas, or from about 400 to about 1000 mPas, may be preferred. Also, it would be advantageous for fluorinated lubricants to have low surface energy and vapor pressure. For example, a suitable fluorinated lubricant may have about 1800kg/m³To about 2000kg/m³A low surface tension gamma of about 10 to about 30mN/m, and/or not more than about 1x10^-7Vapor pressure P of kPa_vap。

The fluorinated lubricant may include a perfluoropolyether (PFPE) oil that may have a branched or linear chemical structure. The PFPE oil may be commercially available Krytox^TMOrPFPE oil. The PFPE oil may comprise a low molecular weight fluoro-terminated homopolymer of hexafluoropropylene epoxide having the chemical structure shown below:

wherein n is 10-60, e.g. Krytox^TMPFPE oil. The polymer chain may be fully saturated and contain only elements C, O and F; preferably, hydrogen (H) is absent. The PFPE oil may comprise, on a weight basis, about 22% carbon, about 9% oxygen, and about 69% fluorine. Alternatively, the PFPE oil may have the following chemical structure:

such asY PFPE oil. Krytox^TMIs 60164-51-4 and the CA index name is poly [ trifluoro (trifluoromethyl) oxirane]；CAS registry number for Y is 69991-67-9, and linear formula is CF₃O[-CF(CF₃)CF₂O-]_x(-CF₂O-)_yCF₃. Exemplary Krytox that may be suitable for use as a fluorinated lubricant^TMAndPFPE oils include Krytox^TMVPF 1525 (average molecular weight 3470), Krytox^TMVPF 16256 (whose average molecular weight is 9400) andy25/6 (its average molecular weight is 3300).

The impregnated fluorinated lubricant can create a chemically homologous and atomically smooth interface to both the deposited and condensed droplets of the working fluid, which promotes droplet drop. Advantageously, the fluorinated lubricant is immiscible with the working fluid. The fluorinated lubricant comprises a spreading factor S with respect to the working fluid_oiLess than 0 is also advantageous, as discussed in more detail below.

The working fluid may be an aqueous fluid or an organic fluid. For example, the working fluid may comprise water, alcohols, aliphatic and aromatic hydrocarbons, or mixtures thereof. Specific examples include ethanol, isopropanol, pentane, hexane, xylene, and/or toluene. The working fluid may be a low surface tension working fluid (e.g., surface tension as low as about 15 mN/m). The working fluid may comprise dissolved, suspended or entrained organic and/or inorganic solids. The image of fig. 3 shows the behaviour of droplets comprising water, ethanol and hexane on a smooth hydrophobic surface (upper panel) and with droplets comprising water, ethanol and hexane, respectively, on a fluorinated lubricant, in particularThe behaviour on lubricant-impregnated surfaces of VPF 1525 (lower panel) was compared.

As seen in the experiments described below, when a lubricant-impregnated surface is contacted with a working fluid having a surface tension of about 15mN/m to about 30mN/m, heat transfer from a heat and mass transfer component can be improved by at least about 100%, or at least about 150%, as compared to heat transfer from a conventional component that does not include the lubricant-impregnated surface. More particularly, when the lubricant is impregnatedCan achieve at least about 6kW/m in a range of vapor pressures when contacted with a working fluid, such as ethanol, xylene or hexane²Steady state condensation heat transfer coefficient h of K_c。

Similarly, it is expected that the onset of fouling of heat and mass transfer elements can be significantly delayed when a lubricant-impregnated surface is contacted with a working fluid containing dissolved solids, such that fouling is reduced by up to 97% over the same duration as compared to conventional elements that do not contain the lubricant-impregnated surface.

The invention also describes a method of making the above lubricant impregnated surface. Simple and cost effective, the method can be easily scaled up for large size parts and/or large scale manufacturing. The method includes cleaning a thermally conductive substrate to form a cleaned substrate as described below, and then exposing the cleaned substrate to hot water or a hot alkaline solution to form a thermally conductive substrate having nanostructured surface protrusions. A hydrophobic substance is deposited on the nanostructured surface projections to form a hydrophobic surface structure, which is then impregnated with a fluorinated lubricant. In other words, the fluorinated lubricant is applied to or coated on the hydrophobic surface structure and impregnated by capillary forces. Preferably, the viscosity of the lubricant is 400 to 6000mPa · s. Thus, a lubricant-impregnated surface may be formed on the heat and mass transfer components.

Cleaning may include exposing the thermally conductive substrate to the following fluids: one or more of acetone, alcohol, deionized (Dl) water. The exposure may immerse (e.g., immerse) the thermally conductive substrate in the fluid for a suitable period of time, e.g., at least 1 minute, and typically tens of minutes (e.g., about 1 minute to about 60 minutes). For example, the thermally conductive substrate may be continuously exposed to acetone, ethanol, isopropanol, and deionized water, typically for at least about 1 minute each. A typical time period for each exposure is 5-15 minutes. After cleaning, the thermally conductive substrate may optionally be exposed to an acid solution, such as hydrochloric acid, to remove any native oxides on the surface. Cleaning and/or acid exposure is typically followed by rinsing in deionized water, and may optionally include drying in a clean nitrogen atmosphere.

Nano-junctionFormation of structured surface projections (or "nanostructures") may require exposure to (e.g., immersion in) hot water or a hot alkaline solution at a temperature of about 85 ℃ to about 95 ℃. Hot water would be suitable for aluminum substrates, while hot alkaline solutions may be used for copper substrates. An exemplary hot alkali solution includes NaClO₂、NaOH、Na₃PO₄·12H₂O and deionized (Dl) water, wherein the weight ratio of the components can be 3.75:5:10:100, respectively.

Deposition of the hydrophobic substance, which may comprise a silane as described above, on the nanostructured surface protrusions may be performed by atmospheric pressure Chemical Vapor Deposition (CVD) of the hydrophobic substance. Atmospheric pressure CVD can be performed in a closed chamber containing a precursor solution of a hydrophobic substance and a clean substrate with nanostructured surface protrusions. By heating to a suitable temperature (e.g., 70-90 ℃), the precursor solution will evaporate and the hydrophobic substance will deposit on and attach to the nanostructured surface projections, forming a hydrophobic surface structure. An exemplary atmospheric pressure CVD method is described below.

Once the hydrophobic surface structures are formed, they may be coated with a fluorinated lubricant, by, for example, dip coating or using another coating technique known in the art. As described above, the impregnation of the fluorinated lubricant into the surface cracks may be driven by capillary forces. After coating the hydrophobic surface structure with the fluorinated lubricant, the method may further comprise draining excess fluorinated lubricant from the hydrophobic surface structure, optionally followed by a gas flow (e.g., N)₂) And (4) drying.

As demonstrated in the examples below, stable drop-like coagulation of ethanol, hexane and xylene can be achieved on hydrophobic surface structures comprising surface-modified nanostructured protrusions impregnated with fluorinated lubricants, in particular PFPE oil. Ethanol, n-hexane, and xylene were chosen as working fluids for the examples because they provide a good display of general alcohol and hydrocarbon behavior, and their condensation properties serve as benchmarks for such molecules.

Rigorous heat transfer measurements revealed that the heat transfer coefficient and thus the condensation heat transfer flux of lubricant-impregnated surfaces was significantly improved by 100% -150% compared to smooth hydrophobic surfaces. It has also been demonstrated that careful selection of the lubricant may enable long-term continuous droplet condensation with negligible variation in heat transfer properties. Furthermore, it is believed that the chemical oxidation-based nanostructured process for fabricating surfaces provides a simple, scalable and cost-effective method to produce heat and mass transfer components that are resistant to fouling and capable of maintaining drop-like condensation of low surface tension fluids.

Lubricant selection

The primary criterion for lubricant impregnated surface stability is that the lubricant and working fluid, or coagulum, are immiscible. The strong intramolecular interactions (hydrogen bonding) of water molecules in the liquid phase make it immiscible with a wide variety of lubricants, most of which are non-polar in nature. However, many low surface tension fluids do not have strong intramolecular forces and are non-polar in nature, which can limit the rational choice of lubricant. To select suitable lubricants for ethanol and hexane, low surface tension alcohols and hydrocarbons (γ 12-30mN/m) with a wide range of interfacial parameters, vapor pressure (5 × 10) were investigated^-8To 0.7kPa) and viscosity (4-5300mPa · s). Although they are immiscible with water, most of the lubricants tested, particularly silicone oils, are miscible with ethanol and hexane. Fluorinated oils have been found to be immiscible with both ethanol and hexane.

In addition to the immiscibility criterion, it is desirable to avoid lubricant "cloaking" droplets. The lubricant on the surface may encapsulate the coagulum droplet, forming a mask around it; during the condensation process, such covered droplets are inhibited, stopping droplet growth and falling. The presence of masking can be determined by calculating the spreading factor of the lubricant on the condensate droplet, which is given by S_ol＝γ_l-γ_o+γ_olIs given by_l，γ_oAnd gamma_olThe liquid-gas surface tension of the working fluid (condensate), the liquid-gas surface tension of the lubricant, and the interfacial tension between the lubricant and the condensate, respectively. For S_ol>0, the lubricant will mask the condensate droplets. Two kinds of calculationFluorinated lubricants (i.e.VPF 1525 ("K1525", μ 496mPa · s) andVPF 16256 ("K16256", μ ═ 5216mPa · s) has expansion coefficients of-4.11 and-4.83, respectively, on ethanol and-2.54 and-2.45, respectively, on hexane. Thus, for these fluorinated lubricants with ethanol and hexane, S is achieved_ol<A desired non-masking condition of 0. Indeed, fluorinated lubricants are the only suitable alternative for designing stable lubricant impregnated surfaces using ethanol and hexane, in view of both miscibility and hiding. Perfluorinated lubricants were also used in the experiments (Y25/6; "Y25/6"), which is also immiscible with ethanol and hexane and non-hiding. In chemical composition, viscosity and surface tension with Krytox^TMLubricants like Krytox^TMIn contrast to the branched molecules present in the lubricant,the lubricant has linear perfluorinated molecules. See table 1 for a summary.

TABLE 1 physical properties of working fluids at 10 ℃ and of reasonably selected lubricants at 20 ℃.

For the working fluid on the surface, the lubricant properties determine both the apparent advancing contact angle and the contact angle hysteresis, which are necessary to prevent working fluid film formation and promote tight droplet-like coagulation. The following drop coagulation results for ethanol and hexane show that the heat transfer performance is independent of lubricant viscosity for working fluids with higher surface tension than the lubricant in the lubricant-impregnated surface. However, when the surface tensions of the working fluid and the lubricant become comparable, the lower viscosity of the lubricant makes droplet drop easier, resulting in better heat transfer from the lubricant-impregnated surface. However, if the viscosity of the lubricant is too low, the lubricant-impregnated surface may be rapidly degraded by the lubricant discharge. Generally, lubricants having a dynamic viscosity μ of at least about 400 mPas, or at least about 450 mPas, are preferred. Lubricants having a dynamic viscosity μ of about 6000 mPa-s or less, about 1000 mPa-s or less, or about 700 mPa-s or less may also be advantageous. For optimal heat transfer results, lubricants having dynamic viscosities μ of 450 to 600 mPa-s (e.g., about 500 mPa-s) may be used for heat and mass transfer components having stable and durable lubricant-impregnated surfaces. The terms "dynamic viscosity" and "viscosity" are used interchangeably throughout this disclosure, and the value of viscosity and/or other physical property may be determined at ambient temperature (e.g., 20 ℃) and/or ambient pressure (e.g., 1 atm).

Heat transfer performance

To determine the overall condensation heat transfer performance, smooth hydrophobic (silane-functionalized) copper surfaces ("HP Cu") and lubricant-impregnated surfaces as formed in the fabrication details section below were tested in a test chamber with a controlled environment. Prior to the condensation experiments, a separate steam generator filled with test liquid was vigorously boiled. After chamber isolation, the test chamber was evacuated to a pressure P <4 + -2 Pa with a leak rate of 0.1 Pa/min. The chamber evacuation is first performed to eliminate non-condensable gases (which would cause additional diffusional resistance to condensation heat transfer). During the condensation experiments, the chamber pressure and the steam generator temperature were continuously monitored to ensure saturation conditions. The bulk heat flux was determined by independently controlling the surface temperature of the tube sample with an external water cooling loop and continuously measuring the inlet and outlet temperatures using a class a Resistance Temperature Detector (RTD). Typical inlet to outlet tube temperature differences are 0.5-7.5 ℃, depending on the tube sample, working fluid and vapor pressure. For all experiments, the cooling water inlet temperature was kept constant at 6 ± 1 ℃ and the flow rate was 11 ± 0.3L/min, which produced complete turbulence and reynolds number Re 36000.

Therefore, the condensation heat transfer performance is 3.5kPa for ethanol<P_v<10kPa and 11kPa for hexane<P_v<A vapor pressure range of 15kPa, which is a common condition for condensers used in industrial separation and distillation applications.

Fig. 4A-4C show condensation of water, ethanol and hexane, respectively, on smooth hydrophobic copper tubing, and fig. 4D-4F show condensation of water, ethanol and hexane, respectively, on copper tubing treated to have a lubricant impregnated surface. Table 2 below shows the wetting characteristics of ethanol and hexane on smooth hydrophobic copper ("HP Cu") and lubricant impregnated surfaces containing different fluorinated lubricants ("LIS K1525", "LIS K16256" and "LIS Y25/6"), including the inherent advancing contact angle (θ) of_a) Receding contact Angle (θ)_r) And contact angle hysteresis (Δ θ ═ θ)_a-θ_r). Due to the inherent hydrophobicity of the tube surface, the water vapor condensate forms discrete droplets on the outer tube surface, which grow over time and are then removed by gravity, which maintains a continuous droplet-like condensation (fig. 4A). However, the solid-gas interface of the smooth HP Cu tube does not have a low enough surface energy to prevent wetting by low surface tension fluids, as demonstrated in fig. 4B and 4C. It was expected from the high contact angle hysteresis on the smooth HP Cu surface that ethanol (fig. 4B) and hexane (fig. 4C) experienced film-like condensation, which limits heat transfer due to the increased thermal resistance of the thin condensate film. In contrast, as shown in fig. 4D-4F, condensation on a lubricant-impregnated surface made with K1525 oil ("LIS K1525") provides a liquid-liquid interface between the condensate droplet and the immiscible lubricant, which results in negligible droplet pinning, low contact angle hysteresis, and easy droplet removal.

Table 2 sample wetting characteristics.

For all condensation heat transfer experiments, the rate of condensation is dependent on P_vIs increased. Heat transfer measurements were done by steaming prior to using ethanol and hexaneSteam is used as the reference of the working fluid. For both the drop and film modes of condensation on the horizontal tube, the measurements were highly consistent with previous steam condensation results.

FIGS. 5A and 5B show the steady state bulk condensation heat flux (q ") as a function of the log mean gas to liquid temperature difference (Δ T) measured for ethanol and hexane, respectively_LMTD＝[(T_v-T_in)-(T_v-T_out)]/ln[(T_v-T_in)/(T_v-T_out)]Wherein T is_v，T_inAnd T_outSteam, cooling water inlet and cooling water outlet temperatures, respectively). To maximize the heat transfer coefficient inside the tubes, the cooling water mass flow rate was kept constant at 11. + -. 0.3L/min (1.02) for all experiments<S≤1.7，7<T_s<25 ℃ wherein S is supersaturated, and T_sIs the temperature of the surface of the tube being pushed out. The overall Heat Transfer Coefficient (HTC),from the measured value (q') of the condensation heat flux and the calculated Delta T_LMTDA value is calculated. Knowing the thermal resistance of the single-phase forced convection of the inner tube and the radial conduction through the copper tube wall, the steady-state condensation heat transfer coefficient h at the outer surface of the tube can be calculated_c. To verify the results, the classical Nusselt (Nusselt) theory for tube coagulation was used to simulate film coagulation. The film-like condensation results (square symbols in fig. 5A-5D) of ethanol and hexane on smooth hydrophobic copper (HP Cu) surfaces are highly consistent with nussel's theory (dashed lines).

As expected, the HP Cu tube showed membranous behavior with the lowest overall and condensed HTC for ethanol and hexane (for ethanol,h_{c, film shape}≈3.38±1.3kW/m²K, and for hexane,h_{c, film shape}≈3.93±1.07kW/m²K) This is because the thin condensate film acts asThe primary thermal resistance to heat transfer. Steady state film-like condensation HTC (h)_{c, film shape}) With P_vIs decreased (fig. 5C and 5D) because the build-up of condensate on the tube outer surface increases the overall thermal resistance.

In contrast, both ethanol and hexane exhibited steady state drop-like coagulation behavior on tubes with Lubricant Impregnated Surfaces (LIS). The heat transfer performance during the dropwise condensation of ethanol and hexane on the LIS tube significantly exceeded that of the film-like condensation (for ethanol,h_{c, drop shape}≈6.23±0.7kW/m²K, and for hexane,h_{c, drop shape}＝9.4±1.6kW/m²K) As shown in fig. 5C and 5D, respectively. Three different lubricant impregnated surfaces with three respective lubricants (LIS K1525, LIS K16256 and LIS Y25/6) gave similar enhanced heat transfer performance for condensation of ethanol and hexaneWith a difference of + -11% and + -30%, respectively, and h for ethanol and hexane_{c, drop shape}With a variation of + -13% and + -40%, respectively. At a higher P_vThe drop-shaped condensation heat transfer improvement is more pronounced, with film-shaped HTC decreasing due to the increase in condensate film thickness, and drop-shaped HTC increasing due to activation at higher supersaturation nucleation sites.

The enhanced heat transfer performance of the dropwise condensation of hexane on all three LIS tubes was more pronounced when observed with ethanol than the film-like condensation on smooth, hydrophobic Cu tubes. Referring to fig. 5D, K1525 impregnated LIS tube (LIS K1525) exhibited the best performance. H of LIS K1525_{c, drop shape}Ratio of h to_{c, film shape}150% higher, 100% higher with LIS Y25/6 and 50% higher with LIS K16256. Interestingly, although all three LIS tubes are aligned to the h of ethanol_{c, drop shape}With a variation of. + -. 13%, but h was observed for hexane_{c, drop shape}Is statistically significant.

To explain this difference, both lubricant and hexane thermophysical properties (table 1) and contact angle hysteresis of the condensate droplets on the lubricant-impregnated surface (table 2) were examined. Intrinsic advancing contact angle (θ) on three lubricant impregnated surfaces for ethanol_a) Is 62.4 °<θ_a<71.1 DEG, has maximum contact angle hysteresis, Delta theta is theta_a-θ_r2.7 ° (Table 2). Low delta theta<2.7 deg. and medium theta_aThe 65 deg. ensures stable droplet condensation of all three lubricant impregnated surfaces with minimal expected heat transfer results. However, for hexane, θ on three lubricant impregnated surfaces_aIs 37.4 °<θ_a<45.7 deg., with a maximum of delta theta 3.6 deg. (table 2), produces condensation close to the drop-to-film transition. The droplet coagulation stability depends on the Δ θ regulated drop (slip) length scale of the droplet. For a signal having a relatively low Δ θ: (<For a 50 deg. droplet, as observed for hexane (table 1), the droplet drop length scale would be larger than needed to be in the capillary control regime. For a signal having an increased Δ θ and a relatively low θ_aThe drop length dimension of the droplet becomes so large that capillary action ceases to control droplet dynamics, which gives way to the gravity control regime (Bo 1, where Bo is dependent on θ)_aB (Bond number), Bo ═ Δ ρ gD²,/γ), formation of puddles on the surface, and film-like condensation.

In these experiments, although hexane experienced a dropwise condensation on all three LIS tubes, K1525 had a favorable performance with a maximum of θ_aTo ensure drop stability due to its low surface tension (γ ≈ 19mN/m), with a correspondingly low lubricant viscosity (μ, table 1) to ensure easy drop of the droplets and contact line movement during coalescence. The good drop-shaped condensation stability makes it the most stable lubricant in these experiments for the heat transfer of hexane drop-shaped condensation, realizes g_{Drop shape}≈6.9±0.9kW/m²K and h_{c, drop shape}≈9.6±1.5kW/m²K。

Although it is not limited toHexane droplets deposited on LIS Y25/6 showed the lowest θ due to high lubricant surface tension (γ ≈ 25mN/m, Table 1)_aHowever, these droplets have the lowest Δ θ due to the high chemical homology of the linear fluorinated Fomblin vacuum oil. Although a low Δ θ ensures good drop coagulation stability, the coagulation of hexane on LIS Y25/6 is closer to the drop-to-film transition than LIS K1525. Accordingly, slightly lower heat transfer performance due to the presence of instantaneous quasi-droplet condensation (temporary liquid film formation) on the surface is observed, and≈5.7±0.4kW/m²k and h_{c, drop shape}≈7.5±0.7kW/m²K。

Finally, LIS K16256, although having a hexane wetting behavior similar to LIS K1525 (table 2), had a viscosity that was an order of magnitude higher than the two LIS options (table 1). The increased viscosity shows an alternative mechanism for the heat transfer barrier, resulting in slow droplet coalescence and temporary film formation during hexane condensate droplet coalescence. The high viscosity of the K16256 lubricant may be used to inhibit movement of the coalesced droplet contact line, produce a larger droplet exit radius, and have an irregularly shaped transient film. Furthermore, additional shear stress between the lubricant layer and the condensate droplet can hinder droplet removal, increasing the residence time on the LIS tube before the condensate droplet is removed by gravity compared to lower viscosity K1525 and Y25/6 lubricants. Slower droplet removal from the tube reduces the re-nucleation rate, which reduces the condensation rate and heat transfer performance, resulting in And h_{c, drop shape}≈6.8±1.8kW/m²K. Despite the lowest heat transfer performance among the three LISs, K16256 LIS promoted continuous dropwise condensation of hexane and exhibited 50% higher h than conventional film-like condensation_{c, drop shape}See fig. 5D.

The heat transfer performance of hexane during the droplet coagulation on all three tubes with lubricant impregnated surfaces was higher than that of ethanol coagulation. For LIS K1525, h of hexane_{c, drop shape}H of particular alcohol_{c, drop shape}45% higher, 35% higher for LIS Y25/6, and 15% higher for LIS K16256. On three lubricant-impregnated surfaces, with ethanol (62.4 °)<θ_a<71.1 deg.) the higher coagulation HTC of hexane may be attributed to the lower intrinsic advancing contact angle (theta) compared to_a)(37.4°<θ_a<45.7 °). The lower contact angle results in a larger contact area between the hexane condensate droplet and the lubricant impregnated surface, thereby reducing droplet conduction resistance and increasing heat transfer.

Durability and long term performance

The durability and long-term performance of functionalized coatings are of paramount importance to their acceptance in industrial applications. For lubricant impregnated surfaces, there is concern about the removal of lubricant from within the surface nanostructures. To test the durability over time and heat transfer performance of the lubricant impregnated surfaces, in an initial experiment, continuous condensation of ethanol and hexane was performed within 7 hours based on the capacity of the steam generator.

Fig. 6 shows a time-lapse image sequence of coagulation of both ethanol (top panel) and hexane (bottom panel) on LIS K1525, showing drop-like coagulation over the entire period of 420 minutes. Similar effects were observed with LIS K16256 and LIS Y25/6, which showed that lubricant drainage from the lubricant-impregnated surface was negligible over a time scale of at least 7 hours, so that the trickle-like heat transfer performance could be maintained for a long period of time. The results show that shear drainage and lubricant depletion do not interfere with the coagulation performance of lubricant impregnated surfaces on a reasonable time scale (at least 10 hours). It is believed that the use of a sufficiently high viscosity fluorinated lubricant (400-6000 mPas) ensures extended droplet coagulation of ethanol and hexane. In summary, the three lubricants used herein have the following properties:VPF 1525(μ＝496mPa·s，v＝250cSt)，VPF 16256(μ 5216mPa · s, v 2560cSt), andy25/6(μ ═ 524mPa · s, v ═ 276 cSt). It should be noted that the optimum lubricant viscosity range for optimum heat transfer performance of the lubricant-impregnated surface may also depend on the working fluid and its properties.

In additional experiments, the durability of the lubricant-impregnated surfaces was evaluated at a significantly longer time scale (>120 days) during continuous ethanol coagulation. The lubricant impregnated surface showed no visible degradation and remained coagulated in drops during the experiment (over 2880 hours).

The long-term durability test is conducted in a vacuum chamber (e.g., a tube with a lubricant-impregnated surface) designed to simultaneously test the durability of multiple samples, under conditions similar to those encountered in an industrial condenser, for a period of up to several months. The chamber was initially filled with liquid ethanol (one third of the total volume) and the liquid was boiled with a wrapped band heater. The tubes are placed near the top of the chamber and cooling water from the chiller pump flows through them from the inside. Vapor (ethanol in these experiments) was generated inside the chamber and condensed upon contact with the cold outer tube surface. A camera is installed to observe the coagulation on the tube inside the chamber and determine if and when the coagulation pattern changes from drop to film. A data acquisition system was installed to record thermocouple readings, vapor pressure and cooling liquid flow rate. The coolant (water) flow rate and heater settings are adjusted so that the cumulative condensation rate from all surfaces matches the liquid (ethanol) boiling rate, thereby maintaining steady state saturation conditions (vapor pressure) inside the chamber. For ethanol coagulation, the condition used is T_{Cooling device}＝5℃，T_{Saturation of}18 ℃ and P_{Saturation of}＝5.15kPa。

FIGS. 7A-7D show sequential CuO for LIS K1525, LIS K16256, LIS Y25/6 and superhydrophobic, respectivelyThe coagulation pattern at 2805 hours (approximately 117 days) during the ethanol coagulation experiment. Each lubricant impregnated surface (LIS K1525, LIS K16256 and LIS Y25/6) exhibited a droplet-like coagulation behavior throughout the long-term experiment, whereas the superhydrophobic CuO surface exhibited film-like coagulation from the beginning. It is to be noted that Krytox is contained^TMLubricant-impregnated surfaces of GPL 101 (a general-purpose PFPE oil with a dynamic viscosity (μ ═ 33mPa · s) much lower than the other lubricants) showed a transition from a drop-like to a film-like setting behavior over 10 days during the course of successive ethanol setting experiments.

INDUSTRIAL APPLICABILITY

The findings reported herein are of great significance for the potential development of durable, scalable and robust surfaces for the dropwise condensation of low surface tension fluids. In particular, refrigerant condensation is a widely used industrial process, wherein surfaces with higher heat transfer coefficients substantially reduce energy consumption. Demonstration of stable droplet-like condensation of ethanol and hexane suggests that lubricant-impregnated surfaces may be a potential solution for creating surfaces that repel refrigerants. Furthermore, the presence of 1-5% oil content (which results from compressor lubricant entrainment) in commercial refrigeration systems provides a unique opportunity for developing closed cycle lubricant impregnated condenser surfaces that can be replenished with compressor lubricant at steady state. In essence, at the condenser inlet of an air conditioning system, the refrigerant enters as a superheated vapor entrained with low vapor pressure compressor oil droplets that may deposit on the condenser surfaces, which provides an opportunity to translate system losses (oil entrainment) into benefits.

In addition to refrigeration, systems such as chemical plants, natural gas production facilities, biomass combustion units, and the food industry that use non-refrigerant low surface tension processing fluids would clearly benefit from droplet condensation in terms of reduced condenser size and energy cost savings. This effort shows for the first time that strict sustainable drop-like condensation can be achieved for low surface tension fluids on lubricant impregnated surfaces, achieving a heat transfer coefficient of 150% higher than film-like condensation on conventional smooth hydrophobic surfaces.

In addition to improving the heat transfer by condensation, lubricant impregnated surfaces can also inhibit fouling and scale build-up in industrial scale processes, which is an important concern in many industrial heat transfer applications. The synergistic effect provided by anti-fouling and enhanced heat transfer has significant potential for significantly enhancing both the performance and life of heat and mass transfer components.

Details of manufacture

Tube cleaning procedure: the copper tubing used in these experiments was systematically cleaned prior to testing. All tubes were joined at each end with a female 1/4 "stainless steel union coupling and terminated with 1/4" stainless steel union coupling nuts. The end-capping of the tube ensures that no oxidation or functionalization occurs on the inner surface to maintain the same cooling water flow conditions. Once capped, the tubes were cleaned by subsequently immersing them in acetone, ethanol, Isopropanol (IPA), and deionized (Dl) water, each for about 10 minutes, at room temperature in separate custom made polyvinyl chloride (PVC) tanks. After rinsing the tube in deionized water and drying in a stream of clean nitrogen, the tube was immersed in a 2.0M hydrochloric acid solution for 10 minutes to remove the native oxide film on the surface. Finally, the tube was flushed three times with deionized water and dried with a stream of clean nitrogen.

Manufacturing a CuO nano structure: by dipping the tube into a solution containing NaClO₂、NaOH、Na₃PO₄·12H₂O and deionized water (3.75:5:10:100 wt%) in a hot (90 ± 3 ℃) alkaline solution to form nanostructured copper oxide (CuO) surface protrusions on the cleaned copper samples. This oxidation process forms thin (. apprxeq.300 nm) Cu₂O layer reoxidized to form sharp, knife-like CuO bumps (h ≈ 1 μm, fraction of solids)And a roughness factor r ≈ 10).

And (3) silane deposition: nanostructured CuO and smooth Cu tubes were functionalized using atmospheric pressure chemical vapor deposition of fluorinated silane (heptadecafluorodecyltrimethoxysilane, abbreviated as HTMS, Sigma-Aldrich). The sample tube was placed in a 24 "diameter, 36" height cylinder surrounded on the outside by a band heater to maintain a stable temperature. Along the tube sample, 10mL of HTMS-toluene solution (5% v/v) was placed in a glass vial inside the barrel. The cartridge was sealed with a lid and heated to 80 ℃ under normal pressure. The canister is insulated covered and appropriately sealed to prevent escape of vapor. The tube sample was oriented obliquely in the vertical direction on the wall of the tube and left in the tube for 3 hours to add a monolayer of silane molecules to the smooth and structured surface.

Lubricant impregnated surface: samples of functionalized nanostructured CuO tubes were dip coated to impregnate the surface with the selected lubricant. The tube samples were immersed in the lubricant for 10min using the above-described PVC tank. The tube sample was then removed and left in a vertical position for 24 hours at ambient conditions to allow excess lubricant to drain under gravity. The LIS sample tubes were then dried in a stream of clean nitrogen and tested.

To study the morphology of the fabricated tube surface using SEM and Focused Ion Beam (FIB) imaging, and to measure the contact angle using a micro-goniometer, additional flat small samples (1 "× 1") were fabricated using the same procedure as described above.

Heat transfer calculation

Overall heat transfer coefficientThe energy balance on the cooling water flowing inside the tube sample was used to calculate the overall condensation heat transfer rate as shown in equation 1:

where Q is the overall condensation heat transfer rate,is the cooling water mass flow rate, cp is the liquid water specific heat, and T_outAnd T_inOutlet and inlet temperatures, respectively. Thus, the overall heat transfer rate (Q) is the overall heat transfer coefficientTo balance, such as:

wherein A is_oIs the external surface area of the tube (A)_o＝πd_ODL, wherein d_OD6.35mm, L76.2 cm) and Δ T_LMTDIs a logarithmic mean temperature difference defined as:

where Tv is the temperature of the ambient saturated vapor inside the chamber (T)_v＝T_sat(P_v)). Thus, the overall heat transfer coefficient (which is a function of the only experimentally obtained parameter) can be calculated as follows:

coefficient of heat transfer by condensation (h)_c): calculatedIs a measure of the overall heat transfer performance from the steam to the cooling water. It includes convective resistance on the inner and outer walls and conductive resistance through the copper wall. Further calculations were performed to separate the thermal resistances on the outer walls to quantify the condensation heat transfer coefficient h_cMeasured from the vapor to the tube exterior surface.

To select h_cThe conduction resistance is calculated using the thermal conductivity, and the internal resistance is calculated by estimating the internal heat transfer coefficient. Estimation of the Water side Heat transfer coefficient (h) by the Petukhov correlation (equation 5-7)_i) It is related to coolant flow conditions and has an accuracy of about 6%.

f＝[0.79ln(Re)-1.64]^-2 (7)

In the above equation, f is the pipe wall friction coefficient, Re is the Reynolds number (Reynolds number) of the cooling water, Pr is the Planndtl number (Prandtl number) of the cooling water, ρ is the density of the cooling water, and k is_iIs the cooling water thermal conductivity, and_band mu_sThe dynamic viscosity of the cooling water at the body and wall temperatures, respectively.

Know h_iBy combining all the relevant thermal resistances (internal convection and radial conduction through the tube wall), one can obtain a solution for h_cClosed solutions of (2):

wherein A is_oIs the external surface area of the tube (A)_o＝πd_oDL，A_iIs the inner tube surface area (A)_i＝πd_IDL), L is the length of the tube sample, and k_tIs the thermal conductivity (k) of the wall_Cu＝401W/m·K)。

Tube surface temperature (T)_s) (ii) a Using the temperature T of the external surface of the tube_sThe supersaturation for each test condition was calculated. The total heat transfer rate and conduction and water side convective resistance were used to calculate the outer wall temperature as shown in equation 9:

wherein T is_avg＝(T_out+T_in)/2. Recombinant formula 9, the tube surface temperature can be calculated as follows:

finally, supersaturation S (defined as the ratio of vapor pressure to saturation pressure, which corresponds to the tube sample surface temperature) is shown below:

a membranous coagulation model; to simulate the film-like condensation of steam, ethanol and hexane on the tube samples, a classical nussel model was used, as follows:

h_fg′＝h_fg+0.68c_p，lΔT (13)

wherein g is the acceleration due to gravity (g-9.81 m/s)²)，ρ_vIs the vapor density, ρ₁Is the coagulum liquid density, μ₁Is the dynamic viscosity of the coagulum liquid, h_fg' is the latent heat of evaporation adjusted after taking into account the change in specific heat of the condensate, and c_p,lIs the specific heat of the condensate liquid.

And (3) error analysis: calculating the overall heat transfer coefficient by transmitting the instrumental uncertainty of each measured variableUncertainty of (table 3), as shown in equation 14:

as the heat transfer coefficient of condensation, h_cIs the product of powers and is taken as h_cDetermining an error as a function of the first partial derivative of its component:

wherein R is_tIs the thermal resistance of the tube, as follows:

table 3. uncertainty corresponding to experimental measurements.

Although the present invention has been described in considerable detail with reference to certain embodiments, other embodiments are possible without departing from the invention. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained therein. All embodiments that come within the meaning of the claims are intended to be embraced therein either literally or equivalently.

Moreover, the advantages described above need not be the only advantages of the present invention, and it is contemplated that all of the advantages need not be realized in every embodiment of the present invention.