A hierarchical carbon nanomaterial thin film coating for enhanced boiling heat transfer and its preparation method

Abstract

The application discloses a hierarchical carbon nanomaterial film coating for enhancing boiling heat transfer and a preparation method thereof, and relates to the technical field of nanocoating enhanced phase change heat transfer. The film coating is completely coated on the surface of a target substrate and is composed of two different carbon nanomaterial film coatings A and B. The carbon nanomaterial film coating A is a graphene oxide laminated structure film coating which uniformly and continuously covers the surface of the target substrate. The carbon nanomaterial film coating B is a hydrophilic carbon nanotube nanoporous network structure film coating which covers the surface of the graphene oxide film coating in a discontinuous layout mode to form a plurality of uniformly distributed carbon nanotube film coating stripes, and a microscale channel structure is formed between the carbon nanotube film coating stripes. The hierarchical carbon nanomaterial film coating organically combines a plurality of micro-nanoscale characteristic structures and excellent properties, can produce a synergistic enhancement effect, greatly and synchronously improves CHF and HTC, and realizes a breakthrough in boiling heat transfer performance.

Description

Technical Field

[0001] This invention relates to the field of nano-coating enhanced phase change heat transfer technology, specifically to a hierarchical carbon nanomaterial thin film coating for enhancing boiling heat transfer and its preparation method. Background Technology

[0002] Boiling heat transfer utilizes the enormous latent heat of the liquid-gas phase transition to achieve efficient heat transport and dissipation, and is widely used in industrial fields such as power generation, refrigeration, cooling of high-power-density electronic devices, and thermal management of high-power lasers. The heat transfer coefficient (HTC) and critical heat flux (CHF) are two important parameters characterizing boiling heat transfer performance, describing the heat transfer efficiency and maximum safe heat transfer capacity of the boiling process, respectively. Developing advanced boiling heat transfer technologies and improving HTC and CHF is of great significance for solving the heat dissipation challenges of high-power-density electronic devices and improving the energy efficiency, economic benefits, and safety of thermal systems.

[0003] Constructing micro / nano structures on traditional metal heat transfer surfaces can significantly enhance the boiling heat transfer performance of liquid working fluids, showing great promise for applications. Among these, carbon nanomaterials such as carbon nanotubes and graphene possess excellent mechanical and thermal properties, good stability, and highly tunable wettability, offering significant advantages over metal nanomaterials and demonstrating great potential for enhancing boiling heat transfer. In recent years, researchers have developed various carbon nanomaterial thin film coatings for this purpose. However, existing technologies almost exclusively focus on designing and developing single carbon nanomaterial thin film coatings. Boiling heat transfer characteristics are closely related to multiple factors, including surface wettability, roughness, porosity, capillary properties, thermal conductivity, and mechanical strength. A single nanofilm coating can hardly simultaneously address all these factors, making it difficult for existing carbon nanomaterial thin film coatings to achieve comprehensive enhancement of boiling heat transfer performance (simultaneously improving HTC and CHF) and further improvement.

[0004] Compared to single nanocoatings, hierarchical carbon nanomaterial thin film coatings, formed by the rational design and construction of multiple high-performance carbon nanomaterial thin film coatings on a substrate, can combine the characteristic structures and properties at different scales, potentially producing a synergistic enhancement effect and significantly improving CHF and HTC simultaneously, leading to breakthroughs in boiling heat transfer performance. However, hierarchical carbon nanomaterial thin film coatings are currently lacking. On the other hand, current methods for preparing carbon nanomaterial thin film coatings are generally complex, require sophisticated equipment, have long processing times, and lack scalability. Therefore, achieving the preparation of hierarchical carbon nanomaterial thin film coatings with multiple characteristic structures and properties remains a significant challenge. Summary of the Invention

[0005] The purpose of this invention is to propose a hierarchical carbon nanomaterial thin film coating for enhanced boiling heat transfer and its preparation method. The proposed hierarchical carbon nanomaterial thin film coating organically combines structures such as high thermal conductivity nanochannels, nanoporous networks, and microchannels. It also possesses advantages such as superhydrophilic wettability, high in-plane thermal conductivity, high surface bubble nucleation density, and excellent micron- and nano-scale capillary effects. This effectively prevents the formation and expansion of local hot spots under high heat flux densities, promotes bubble nucleation, growth, and detachment, and rapidly replenishes the heat transfer surface with additional liquid under high heat flux densities, significantly improving both HTC and CHF simultaneously. Furthermore, the preparation method of the proposed hierarchical carbon nanomaterial thin film coating has advantages such as simplicity, low cost, strong scalability, and easy controllability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A hierarchical carbon nanomaterial thin film coating for enhancing boiling heat transfer is completely coated on the surface of a target substrate and consists of two different carbon nanomaterial thin film coatings, A and B. The carbon nanomaterial thin film coatings A and B are arranged in a tightly stacked configuration from bottom to top in a direction perpendicular to the substrate. Carbon nanomaterial thin film coating A is a graphene oxide laminated structure thin film coating that uniformly and continuously covers the surface of the target substrate. Carbon nanomaterial thin film coating B is a hydrophilic carbon nanotube nanoporous network structure thin film coating that covers the surface of the graphene oxide thin film coating in a discontinuous configuration, forming multiple uniformly distributed carbon nanotube thin film coating stripes. The discontinuous configuration includes discontinuity in the x-direction within the substrate plane (e.g., forming stripes), discontinuity in the y-direction within the substrate plane (e.g., forming stripes), or discontinuity in both the x and y directions within the substrate plane (e.g., forming an array). The multiple carbon nanotube thin film coating stripes have the same length, width, and thickness, and micrometer-scale channel structures are formed between the carbon nanotube thin film coating stripes. The microchannels, with the carbon nanotube thin film coating stripes acting as ribs, have the same width.

[0008] The graphene oxide laminated film coating contains 1-9 layers of graphene oxide nanosheets with a thickness of 0.5-5 nm, a lateral dimension of 0.5-70 μm, and an oxygen content >30 wt%. Numerous nanochannels with a width of 0.6-3.0 nm are formed between the graphene oxide nanosheets. The hydrophilic carbon nanotube nanoporous network film coating is composed of at least one of carboxylated, hydroxylated, or aminated carbon nanotubes. The carbon nanotubes have an outer diameter of 1-80 nm, a length of 0.5-100 μm, and an oxygen content >1 wt%. Carbon nanomaterial film coatings A and B have a thickness of 0.2-100 μm. The carbon nanotube film coating stripes uniformly distributed on the surface of the graphene oxide film coating have a length and width of 10-500 μm, and the width of the microchannels formed between these stripes is 10-500 μm.

[0009] This invention also provides a method for preparing a hierarchical carbon nanomaterial thin film coating to enhance boiling heat transfer, comprising the following steps:

[0010] Step A: Perform ultrasonic cleaning on the target substrate using a cleaning solution;

[0011] Step B: Coat a uniform and continuous graphene oxide laminate thin film coating on the surface of the target substrate using at least one of the following methods: dip coating, spin coating, spray coating, electrodeposition, or self-assembly.

[0012] Step C: A mask with a specific hollow pattern is tightly attached to the surface of a graphene oxide film coating. A discontinuous carbon nanotube film coating is further deposited on the surface of the graphene oxide film coating by spraying to prepare a hierarchical carbon nanomaterial film coating, wherein microchannel structures are formed between the stripes of the carbon nanotube film coating.

[0013] Step D: The prepared hierarchical carbon nanomaterial thin film coating is thermally cured.

[0014] In step C of the above preparation method, the mask with a specific hollow pattern has a hollow pattern size and spacing of 10-500 μm, and can be prepared by photolithography or laser etching. The mask material is one of stainless steel, polytetrafluoroethylene, polyetheretherketone, and polyimide.

[0015] In step D of the above preparation method, the thermosetting temperature is 80-200 °C and the time is 10-180 min.

[0016] The beneficial effects of this invention are as follows:

[0017] The hierarchical carbon nanomaterial thin film coating proposed in this invention has a uniform and continuous graphene oxide thin film coating at the bottom, which has ultra-high in-plane thermal conductivity. This effectively prevents the formation and expansion of local hot spots during high heat flux density in boiling heat transfer. Furthermore, the graphene oxide nanosheets within the graphene oxide laminate film form a large number of nanochannels, the width of which can be controlled by surface modification. Liquid molecules exhibit ultra-fast transport and permeation properties within this nanochannel network, demonstrating a unique nanocapillary effect that promotes liquid replenishment on the heat transfer surface. Discontinuous carbon nanotube thin film coating stripes are uniformly distributed on the surface of the graphene oxide thin film coating. These stripes have a nanoporous network structure, which can increase the density of vaporization nuclei during boiling, improve the nucleation, growth, and detachment behavior of bubbles, and thus enhance the phase change heat transfer efficiency of the surface liquid. The nanopores can induce large capillary pressure, which can also promote liquid replenishment on the heat transfer surface. In addition, micron-scale channel structures are formed between the discontinuous carbon nanotube thin film coating stripes, which can serve as micron-scale capillary replenishment channels with advantages such as high permeability and high capillary flow velocity. Due to its abundant hydrophilic groups and porous structure, the hierarchical carbon nanomaterial thin film coating exhibits superhydrophilicity. Therefore, the hierarchical carbon nanomaterial thin film coating proposed in this invention organically combines multiple micro- and nano-scale characteristic structures and excellent properties, generating a synergistic enhancement effect and significantly improving CHF and HTC simultaneously, achieving a breakthrough in boiling heat transfer performance. Furthermore, the preparation method of the hierarchical carbon nanomaterial thin film coating provided by this invention has advantages such as simplicity, ease of implementation, independence from large-scale equipment, low cost, strong scalability, and easy controllability. In summary, the hierarchical carbon nanomaterial thin film coating and its preparation method for enhancing boiling heat transfer proposed in this invention have significant application prospects in the fields of thermal energy conversion, utilization, and management. Attached Figure Description

[0018] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0019] Figure 1 is a schematic diagram of the structure of the hierarchical carbon nanomaterial thin film coating in Example 1 of the present invention. The enlarged schematic diagram on the right is a SEM image of the microstructure of different carbon nanomaterial thin film coatings.

[0020] Figure 2 The figure shows a comparison of the boiling heat transfer performance of four different boiling surfaces using deionized water as the working fluid in a saturated pool under normal pressure in Example 1 of the present invention. (a) is the boiling curve, and (b) is the heat transfer coefficient curve.

[0021] Figure 3 This is a schematic diagram of the structure of the hierarchical carbon nanomaterial thin film coating in Embodiment 2 of the present invention. Detailed Implementation

[0022] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the invention. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0023] Example 1

[0024] like Figure 1 As shown, a hierarchical carbon nanomaterial thin film coating for enhancing boiling heat transfer is composed of a graphene oxide laminated structure thin film coating 2 and a carboxylated multi-walled carbon nanotube nanoporous network structure thin film coating 3. The graphene oxide laminated structure thin film coating 2 uniformly and continuously covers the surface of a target substrate 1, which is copper, with dimensions of 2.2 mm and 5 mm in the x and y directions, respectively. The carboxylated multi-walled carbon nanotube nanoporous network structure thin film coating 3 covers the surface of the graphene oxide thin film coating 2 in a discontinuous layout. The discontinuous layout means that it is discontinuous in the x direction within the plane of the substrate 1, forming multiple uniformly distributed carbon nanotube thin film coating stripes, and microchannel structures are formed between these carbon nanotube thin film coating stripes.

[0025] The graphene oxide laminated film coating has a thickness of 500 nm and consists of a single layer of graphene oxide nanosheets with a thickness of 0.6–1.0 nm, a lateral dimension of 0.5–5.0 μm, and an oxygen content of approximately 50 wt%. The nanochannels between the graphene oxide nanosheets have a width of approximately 2 nm. The carboxylated multi-walled carbon nanotubes have an outer diameter of 5–15 nm, a length of 10–30 μm, and an oxygen content of approximately 4 wt%. The carbon nanotube film coating has a thickness of 500 nm. Discontinuous carbon nanotube film coating stripes, 5 mm in length and 200 μm in width, are uniformly distributed on the surface of the graphene oxide film coating. The microchannels formed between these stripes have a width of 200 μm.

[0026] The method for preparing the above-mentioned hierarchical carbon nanomaterial thin film coating for enhancing boiling heat transfer includes the following steps:

[0027] Step A: Chemically polish the target copper substrate using a cleaning solution, followed by ultrasonic cleaning for 10 min; prepare four copper substrates under the same conditions, one as a smooth copper surface for boiling test, and the other three for preparing a single graphene oxide thin film coating, a single carbon nanotube thin film coating, and a hierarchical carbon nanomaterial thin film coating.

[0028] Step B: A uniform and continuous graphene oxide laminated thin film coating with a thickness of 500 nm was formed on the surface of a copper substrate by spin coating. Two graphene oxide thin film coating samples were prepared under the same conditions. One was used for subsequent preparation of hierarchical carbon nanomaterial thin film coatings, and the other was used as a comparison sample of a single graphene oxide thin film coating for boiling performance testing.

[0029] Step C: A polytetrafluoroethylene mask with a long striped perforated pattern is tightly bonded to the surface of a graphene oxide film coating. The long striped perforated pattern has a length of 5 mm, a width of 200 μm, and a spacing of 200 μm. A discontinuous carboxylated multi-walled carbon nanotube film coating is further deposited on the surface of the graphene oxide film coating using a spraying method to prepare a hierarchical carbon nanomaterial film coating, wherein microchannel structures are formed between the stripes of the carbon nanotube film coating. At the same time, a continuous carbon nanotube film coating with a completely coated surface is prepared on a copper substrate using the same spraying process parameters. This is used as a comparison sample of a single carbon nanotube film coating for boiling performance testing to verify the beneficial effect of the hierarchical carbon nanomaterial film coating in enhancing boiling heat transfer.

[0030] Step D: Place the prepared hierarchical carbon nanomaterial thin film coating on a hot plate for air curing at a temperature of 150 °C for 30 min.

[0031] Saturated pool boiling heat transfer tests were conducted on the four different boiling surfaces under the same conditions. The working fluid was deionized water, and the test pressure was atmospheric pressure. Figure 2 This is a comparison chart of the boiling performance of saturated tanks. Figure 2 (a) is the boiling curve. Figure 2 Figure (b) shows the heat transfer coefficient curves. As can be seen from the figure, the boiling performance of the three carbon nanomaterial thin film coatings is significantly better than that of the traditional copper surface. Compared with the single graphene oxide thin film coating and the single carbon nanotube thin film coating, the hierarchical carbon nanomaterial thin film coating has a higher critical heat flux density and heat transfer coefficient. This indicates that it can effectively combine the characteristic structures and excellent properties of multiple micro-nano scales, resulting in a synergistic enhancement effect. This leads to a further significant improvement in CHF and HTC, confirming its beneficial effects and demonstrating important application prospects in the fields of thermal energy conversion, utilization and management.

[0032] Example 2

[0033] like Figure 3As shown, a hierarchical carbon nanomaterial thin film coating for enhancing boiling heat transfer is composed of a graphene oxide laminated structure thin film coating 2 and a hydroxylated single-walled carbon nanotube nanoporous network structure thin film coating 3. The graphene oxide laminated structure thin film coating 2 is uniformly and continuously covered on the surface of a target substrate 1, which is an aluminum alloy with dimensions of 5.5 mm × 5.5 mm. The hydroxylated single-walled carbon nanotube nanoporous network structure thin film coating 3 is covered on the surface of the graphene oxide thin film coating 2 in a discontinuous layout. The discontinuous layout means that it is discontinuous in both the x and y directions within the plane of the substrate 1, forming multiple uniformly distributed square stripes of carbon nanotube thin film coating. Microchannel structures are formed between these square stripes of carbon nanotube thin film coating.

[0034] The graphene oxide laminated film coating is 10 μm thick and consists of approximately 7 layers of few-layer graphene oxide nanosheets. The nanosheets are 0.55–1.2 nm thick, have a lateral dimension >50 μm, and an oxygen content of approximately 40 wt%. The nanochannels between the graphene oxide nanosheets have a width of approximately 3 nm. The hydroxylated single-walled carbon nanotubes have an outer diameter <2 nm, a length of 5–30 μm, and an oxygen content >2 wt%. The carbon nanotube film coating is 10 μm thick. Discontinuous square stripes of carbon nanotube film coating are uniformly distributed on the surface of the graphene oxide film coating, with a length and width of 500 μm. The microchannels formed between these stripes have a width of 500 μm.

[0035] The method for preparing the above-mentioned hierarchical carbon nanomaterial thin film coating for enhancing boiling heat transfer includes the following steps:

[0036] Step A: Physically polish the target aluminum alloy substrate using a cleaning solution, followed by ultrasonic cleaning for 20 minutes;

[0037] Step B: A uniform and continuous graphene oxide laminate thin film coating with a thickness of 10 μm is formed on the surface of a copper substrate using the nucleus boiling self-assembly method.

[0038] Step C: A stainless steel mask with a square perforated pattern is tightly bonded to the surface of a graphene oxide film coating. The square perforated pattern has a length and width of 500 μm and a spacing of 500 μm. A discontinuous hydroxylated single-walled carbon nanotube film coating is further deposited on the surface of the graphene oxide film coating using a spraying method to prepare a hierarchical carbon nanomaterial film coating, wherein microchannel structures are formed between the square stripes of the carbon nanotube film coating.

[0039] Step D: The prepared hierarchical carbon nanomaterial thin film coating is placed in a vacuum drying oven for thermal curing at a temperature of 80 °C for 60 min.

[0040] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A hierarchical carbon nanomaterial thin film coating that enhances boiling heat transfer, characterized by, The hierarchical carbon nanomaterials film coating is entirely coated on the surface of the target substrate and is composed of two different carbon nanomaterials film coatings A and B; the carbon nanomaterials film coatings A and B are in a close stack layout from bottom to top in the direction perpendicular to the substrate; the carbon nanomaterials film coating A is a graphene oxide laminated structure film coating which is uniformly and continuously coated on the surface of the target substrate; the carbon nanomaterials film coating B is a hydrophilic carbon nanotube nanoporous network structure film coating which is in a discontinuous layout mode and is coated on the surface of the graphene oxide laminated structure film coating to form a plurality of uniformly distributed carbon nanotube film coating stripes, the discontinuous layout mode including discontinuity in the x direction in the substrate plane, discontinuity in the y direction in the substrate plane, or discontinuity in both the x and y directions in the substrate plane; a microscale channel structure is formed between the carbon nanotube film coating stripes; The hydrophilic carbon nanotube nanoporous network structure film coating is composed of at least one of carboxylated carbon nanotubes, hydroxylated carbon nanotubes and aminated carbon nanotubes, the carbon nanotubes having an outer diameter of 1-80 nm, a length of 0.5-100 μm and an oxygen atom content of >1 wt%; The plurality of carbon nanotube film coating stripes are of the same length, the same width and the same thickness, and the microchannels with the carbon nanotube film coating stripes as ribs have the same width; The graphene oxide nanoplatelets in the graphene oxide laminated structure film coating have a layer number of 1-9, a thickness of 0.5-5 nm and a lateral dimension of 0.5-70 μm, and have an oxygen atom content of >30 wt%, a large number of nanochannels being formed between the graphene oxide nanoplatelets, the nanochannels having a width of 0.6-3.0 nm.

2. The thin film coating of hierarchical carbon nanomaterials for enhanced boiling heat transfer according to claim 1, wherein, The carbon nanomaterials film coatings A and B have a thickness of 0.2-100 μm.

3. The thin film coating of hierarchical carbon nanomaterials for enhanced boiling heat transfer according to claim 1, wherein, The carbon nanotube film coating stripes uniformly distributed on the surface of the graphene oxide laminated structure film coating have a length and a width of 10-500 μm, and the microchannels formed between the stripes have a width of 10-500 μm.

4. The method of claim 1-3 for the preparation of the thin film coating of hierarchical carbon nanomaterials for enhanced boiling heat transfer, characterized in that, The method comprises the following steps: Step A: ultrasonic cleaning of the target substrate with a cleaning solution; Step B: coating of the target substrate surface with at least one of dip coating, spin coating, spray coating, electrodeposition or self-assembly to form a uniform and continuous graphene oxide laminated structure film coating; Step C: close adhesion of a mask with a specific hollow pattern on the surface of the graphene oxide laminated structure film coating, and further deposition of a discontinuous hydrophilic carbon nanotube nanoporous network structure film coating on the surface of the graphene oxide laminated structure film coating by spray coating to prepare a hierarchical carbon nanomaterials film coating, wherein a microchannel structure is formed between the carbon nanotube film coating stripes; Step D: heat curing of the prepared hierarchical carbon nanomaterials film coating.

5. The method of claim 4, wherein the method further comprises the step of: In the step C, the mask with the specific hollow pattern has a size and a pitch of 10-500 μm, and is prepared by a photolithography method or a laser etching method, and the mask material is one of stainless steel, polytetrafluoroethylene, polyether ether ketone and polyimide.

6. The method of claim 4, wherein the method further comprises the step of: In the step D, the heat curing temperature is 80-200 ℃, and the time is 10-180 min.

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