Method for regulating boiling phase change behavior of liquid droplets on solid surfaces and spray cooling system

Abstract

The present application relates to the technical field of phase change heat transfer, in particular to a method for regulating boiling phase change behavior of liquid droplets on solid surface and a spray cooling system, which uses a solution containing surfactant as working liquid droplets, and regulates the boiling phase change behavior of the working liquid droplets by regulating the concentration of the surfactant and the structure of the substrate. The spray cooling system comprises an atomization module, a heat conduction medium module and a data control module, wherein the atomization module is used to construct atomized droplets; one side of the heat conduction medium module is used to receive the atomized droplets, and the other side is used to contact and set with a workpiece to be cooled, so as to cool the workpiece to be cooled. Based on the synergistic wall surface characteristics and the liquid droplet properties, the present application regulates the bubble growth and distribution of the solid-liquid interface, so as to effectively control the evolution of the liquid droplet boiling morphology, effectively enhance the heat transfer, improve the energy utilization rate and save resources.

Description

Technical Field

[0001] This invention relates to the field of phase change heat transfer technology, and in particular to a method for controlling the boiling phase change behavior of liquid droplets on a solid surface and a spray cooling system. Background Technology

[0002] Boiling phase transition characteristics are a crucial topic in heat transfer, and a key factor limiting heat transfer performance in energy and power engineering fields. At different temperatures on solid surfaces, droplets exhibit different boiling modes: nucleation boiling, transition boiling, and film boiling. These boiling modes reflect the rate of heat exchange between the droplet and the solid surface. During boiling heat transfer, the generation, coalescence, and breakup of bubbles within the droplet significantly impact the heat transfer efficiency. Therefore, by controlling the dynamics of bubbles at the solid-liquid interface, the boiling phase transition of droplets can be regulated, effectively improving boiling heat transfer performance. Especially when used in spray cooling, the cooling state of atomized droplets on the workpiece surface can be specifically controlled based on their boiling phase transition behavior, achieving more precise and intelligent regulation.

[0003] Surfactants, as key additives in the formulation of heat-enhancing composite working fluids, can alter interfacial properties during boiling, increase vaporization nucleus density, and reduce the critical size of boiling bubbles, thereby strengthening the boiling heat transfer phase transition process. Furthermore, the microstructure of the solid surface and its wettability and foaming properties also significantly influence the boiling phase transition of surfactants. The impact of surfactant droplets on a high-temperature substrate is a physical process involving the interaction of fluid dynamics (droplet flow) and thermodynamics. It involves the coupling of multiple physical fields, including solid-liquid-gas three-phase flow, heat transfer, and phase transition. It is also necessary to consider the influence of substrate microstructure, wettability, and surfactant adsorption on the bubble growth process inside the droplet and the gas-liquid-solid three-phase contact line. Therefore, the boiling phase transition process of surfactant droplets impacting a heated wall surface more closely resembles real-world operating conditions, making the droplet boiling phase transition process more complex and challenging to control. Current technologies lack research on controlling droplet composition and substrate surface structure to regulate boiling phase transition behavior for related applications. Summary of the Invention

[0004] The purpose of this invention is to address the problems existing in the prior art by providing a method for regulating the boiling phase transition behavior of droplets on a solid surface and applying it to a spray cooling system. By coordinating wall properties and droplet properties, the growth and distribution of bubbles at the solid-liquid interface are regulated, thereby achieving effective control over the evolution of droplet boiling morphology. This can effectively enhance heat transfer, improve energy utilization, and save resources.

[0005] To achieve the above objectives, this invention provides a method for regulating the boiling phase transition behavior of droplets on a solid surface. Using a solution containing a surfactant as the working droplet and a silicon surface with a different structure as the substrate, the boiling phase transition behavior of the working droplet is regulated by controlling its physical properties (concentration, type) and the structure of the substrate. Effective construction of the microstructure and modification of the chemical composition can achieve regulation of the bubble behavior inside the boiling droplet. Surfactants can alter the interfacial properties during boiling, increase the vaporization nucleus density, and reduce the critical size of the boiling vaporization bubble, thereby enhancing the boiling heat transfer phase transition process. Therefore, by synergistically controlling the bubble behavior within the surfactant droplet through the microstructure and chemical composition of the solid surface, the evolution of the droplet's boiling phase transition is regulated, effectively enhancing heat transfer and providing scientific guidance for related applications such as spray cooling, facilitating more accurate and intelligent applications.

[0006] Optionally, the surfactant is anionic, cationic, or amphoteric, and its concentration is 0-12 / 9 CMC (critical micelle concentration). Studies have found that in the system designed in this invention, the surfactant concentration has a significant impact on the droplet boiling phase transition behavior. A suitable surfactant concentration can greatly improve heat transfer efficiency, promoting bubble nucleation and foaming, thus contributing to improved spray cooling effects. This invention allows for precise control of the cooling rate at a given temperature by adjusting the surfactant concentration according to the workpiece surface temperature and actual cooling rate requirements.

[0007] Furthermore, the surfactant is an anionic surfactant, preferably sodium dodecyl sulfonate; preferably, the concentration of the sodium dodecyl sulfonate is (0-12)×10⁻⁶. -3 The CMC of sodium dodecyl sulfate (mol / L) is 9 × 10⁻⁶. - 3 mol / L. When the concentration of sodium dodecyl sulfonate is 9 × 10⁻⁶ mol / L. -3 At concentrations of mol / L and above, droplets exhibit a transitional boiling state between 170-200℃. For optimal cooling, nucleation boiling is the most favorable state for increasing the cooling rate. Film boiling, on the other hand, generates a vapor film that impairs heat exchange, leading to a decrease in the heat transfer rate. Transitional boiling lies between nucleation boiling and film boiling; therefore, this invention allows for the regulation of heat transfer effects by controlling the boiling state at the corresponding temperature.

[0008] Furthermore, the temperature of the substrate is 50–300°C, preferably 150–250°C. At different substrate temperatures, the droplets exhibit different boiling phase transition behaviors.

[0009] Furthermore, the substrate structure comprises smooth silicon, silicon nanowires, silicon micropillars (height: 5 μm, width: 5 μm, spacing: 10 μm), silicon micropillars (height: 5 μm, width: 10 μm, spacing: 10 μm), silicon micropillars (height: 5 μm, width: 15 μm, spacing: 10 μm), and silicon nanowires. By constructing nanowire or micropillar structures on the surface of a smooth silicon wafer, its surface roughness can be adjusted, thereby regulating the wettability of droplets on its surface.

[0010] Furthermore, the substrate is heated to 50–300°C, and then the solution containing the surfactant is injected as working droplets. A high-speed camera is used to record the boiling phase transition behavior of the working droplets containing the surfactant as they impact the substrate surface. By observing the changes in droplet morphology, the boiling phase transition behavior is determined, and the substrate temperature and surfactant concentration can be adjusted to change the droplet boiling phase transition behavior.

[0011] Preferably, the falling height of the working droplet is 3-4 mm, more preferably 3.5 mm. The injection rate is 0.01 mL / min.

[0012] In a preferred embodiment, a silicon micropillar with a height of 5 μm, a width of 5 μm, and a spacing of 10 μm is used as the substrate, and a silicon concentration of 9 × 10⁻⁶ is used. -3 Using sodium dodecyl sulfonate at mol / L as the working droplet, the substrate temperature is controlled between 100-210℃, preferably between 150-205℃, to achieve controllable regulation of nucleation boiling and transition boiling, so as to ensure the optimal heat transfer effect at this temperature and facilitate subsequent spray cooling applications.

[0013] The present invention also provides a spray cooling system, comprising: an atomization module, a heat-conducting medium module, and a data control module.

[0014] The atomization module is used to construct atomized droplets;

[0015] A heat-conducting medium module has one side for receiving the atomized droplets and the other side for contacting the workpiece to be cooled, thereby cooling the workpiece. This configuration, with a layer of heat-conducting medium module on the surface of the workpiece, aims to prevent droplets from directly contacting the workpiece and adversely affecting its surface. It is particularly suitable for precision workpieces or those that cannot easily come into direct contact with water. This invention protects the workpiece and facilitates the control of the cooling effect by utilizing the boiling phase change behavior of the atomized droplets on the surface of the heat-conducting medium module. The boiling phase change behavior of the droplets is not affected by changes in the workpiece being treated, thus broadening its applicability.

[0016] The data control module is used to determine the composition of the atomized droplets based on the droplet boiling phase change behavior control module. Based on the required cooling rate, the composition of the atomized droplets can be controlled according to the known boiling phase change behavior of the atomized droplets at different temperatures, thereby achieving the required cooling rate with superior accuracy and intelligence.

[0017] Preferably, the cooling effect can be controlled by adjusting the composition of the atomized droplets and the structure of the heat-conducting medium module.

[0018] Preferably, it further includes a droplet boiling phase change behavior control module, used to control the surface cooling state of the workpiece to be cooled based on the droplet boiling phase change behavior of the atomized droplets.

[0019] Based on the spray cooling system of the present invention, it is only necessary to understand the boiling phase change behavior of droplets on the surface of the heat-conducting medium module before use, so that the cooling effect of the workpiece can be specifically controlled during use.

[0020] Preferably, the droplet boiling phase transition behavior control module employs any of the above-described methods for controlling the boiling phase transition behavior of solid surface droplets to determine the boiling phase transition behavior of the atomized droplets, thereby determining the composition of the atomized droplets. In this case, the thermally conductive medium module of the present invention corresponds to the aforementioned silicon micron-pillar substrate, and the atomized droplets correspond to the working droplets. Based on the boiling phase transition behavior of different surfactant concentrations at different substrate temperatures, the concentration of surfactant corresponding to the target cooling rate is determined.

[0021] In use, the workpiece to be cooled is placed in contact with the heat transfer medium module, and its temperature is transferred to the heat transfer medium module. By monitoring the temperature of the heat transfer medium module, the temperature of the workpiece to be cooled can be obtained indirectly (a temperature sensor can also be placed on the surface of the workpiece to be cooled at the same time). Based on the current temperature, the target cooling rate is input to determine the corresponding droplet boiling phase change behavior. Then, based on the known droplet boiling phase change behavior and the composition of the atomized droplets, the required composition of the atomized droplets is determined.

[0022] Furthermore, the heat-conducting medium module is made of a material with a thermal conductivity ≥50W / (m·K); its thickness is 0.1-5mm, preferably 0.2-2mm. Using a heat-conducting medium module with superior thermal conductivity facilitates rapid cooling of the workpiece and reduces energy waste.

[0023] Preferably, the heat-conducting medium module is selected from the silicon micron column described in any of the above-described control methods. However, this is not a limitation. The key feature of the spray system of the present invention is that the composition of the atomized droplets can be controlled according to the boiling phase change behavior of the droplets, thereby controlling the cooling effect. In practical use, the heat-conducting medium module can be selected according to actual needs to achieve different cooling effects required at the same temperature.

[0024] Preferably, the atomized droplets contain a surfactant, more preferably sodium dodecyl sulfonate. The cooling effect at different temperatures can be controlled by adjusting the concentration of sodium dodecyl sulfonate.

[0025] In particular, the heat transfer medium module can be structurally designed according to the surface shape of the workpiece to be cooled, so that the heat transfer medium module is set in close contact with the surface of the workpiece to be cooled, so as to achieve better heat transfer effect.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. The method for regulating the boiling phase change behavior of liquid droplets on solid surfaces provided by the present invention regulates the growth and distribution of bubbles at the solid-liquid interface by coordinating wall characteristics and droplet properties, thereby achieving effective control of the evolution of droplet boiling morphology, which can effectively enhance heat transfer, improve energy utilization, and save resources.

[0028] 2. The spray cooling system provided by the present invention has a heat-conducting medium module on the surface of the workpiece to be cooled. On the one hand, the cooling effect can be purposefully controlled according to the boiling phase change behavior of the atomized droplets on the surface of the heat-conducting medium module. On the other hand, it can prevent the droplets from having an adverse effect on the surface of the workpiece due to direct contact with the workpiece to be cooled, thereby protecting the workpiece. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 (a) is an electron microscope image of smooth silicon, and (b) is an electron microscope image of a silicon micropillar.

[0031] Figure 2 Boiling behavior of SDS droplets with different concentrations impacting silicon micropillars (pillar height:pillar width:pillar spacing = 5 μm: 5 μm: 10 μm); (a) Droplet concentration: 1.0 × 10⁻⁶ -3 (a) mol / L; (b) Droplet concentration: 4.0 × 10⁻⁶-3 (c) Droplet concentration 1.0 × 10⁻⁶ mol / L; -2 mol / L.

[0032] Figure 3 9.0×10 -3 Boiling morphology of mol / L surfactant SDS droplets impacting different substrates; (a) smooth silicon wafer; (b) silicon micropillar.

[0033] Figure 4 This is a schematic diagram of the spray cooling system. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0035] This invention provides a method for controlling the boiling phase transition behavior of droplets on solid surfaces. Using a silicon micropillar as a substrate and a solution containing a surfactant as the working droplet, the boiling phase transition behavior of the working droplet is controlled by adjusting the concentration of the surfactant and the temperature of the substrate. During the investigation, a high-speed camera was used to record the phase transition behavior of the surfactant droplets impacting different surface structures, thereby obtaining the control results. This invention, through the combined use of a silicon micropillar substrate and a surfactant-containing working droplet, achieves boiling phase transition behavior control results different from existing technologies, providing important guidance for the optimized application of spray cooling.

[0036] Based on the method for controlling the boiling phase transition behavior of liquid droplets on solid surfaces, this invention also provides a spray cooling system, such as... Figure 4 As shown, the system includes a spray cooling system comprising an atomization module, a heat-conducting medium module, and a data control module. The atomization module is used to construct atomized surfactant working droplets; one side of the heat-conducting medium module receives the working droplets, and the other side is used to contact the workpiece to be cooled, thereby cooling the workpiece; the data control module can adjust the composition of the working droplets according to the temperature of the heat-conducting medium module and the target cooling rate, thus controlling the cooling rate.

[0037] For example, using the silicon micropillar in Experiment 1 below as the heat-conducting medium module and SDS (sodium dodecyl sulfonate) solution as the working droplet, the concentration of the working droplet is adjusted according to the temperature of the workpiece to be cooled and the target cooling rate to achieve the corresponding cooling purpose.

[0038] This design, by placing a layer of heat-conducting medium module on the surface of the workpiece to be cooled, aims to prevent liquid droplets from directly contacting the workpiece and adversely affecting its surface. It is particularly suitable for precision workpieces or those that cannot be directly exposed to water. This invention protects the workpiece and facilitates the control of the cooling effect by utilizing the boiling phase change behavior of atomized droplets on the surface of the heat-conducting medium module. The boiling phase change behavior of the droplets is not affected by changes in the workpiece being treated, thus broadening its applicability.

[0039] Experimental Example 1

[0040] In this embodiment, the working droplet is a surfactant SDS (sodium dodecyl sulfonate) solution, and the substrate material is a silicon micropillar with a column height: column width: column spacing of 5μm: 5μm: 10μm, and its structure is as follows. Figure 1 As shown in (b), compared to (a), it can be seen that the silicon wafer surface has micron-sized protrusions.

[0041] Step 1, Selection of working droplets: An SDS solution was selected as the working droplet, and a 1.0 × 10⁻⁶ solution was prepared. - 3 mol / L 4.0×10 -3 mol / L and 10.0×10 -3 A mol / L aqueous solution.

[0042] The second step is cleaning the silicon wafers:

[0043] The second step further involves immersing the substrate silicon micropillar sequentially in acetone, anhydrous ethanol, and deionized water for ultrasonic cleaning for 10 minutes, immersing it in a piranha solution (VH2SO4:VH2O2 = 7:3), heating it in a water bath at 80°C for 0.5 hours, and then removing it, rinsing it, and drying it for later use.

[0044] The third step involves using a high-speed camera to record the phase transition behavior of droplets of different surfactants impacting the same structural surface:

[0045] Set up the experimental setup. Before starting the experiment, adjust the positions of the light source, high-speed camera, and substrate to ensure they are all aligned in a straight line. The side view of the substrate should also be clearly displayed on the camera control monitor. After adjusting the optical path, heat the substrate using a hot stage. Once the temperature reaches the specified level, inject droplets using a precision syringe pump at a rate of 0.01 mL / min, with a droplet drop height of 3.5 mm. Record the entire droplet descent process using a high-speed camera. The experimental temperature range is 50–300 °C.

[0046] like Figure 2 As shown, from Figure 2As can be seen in (a), when the concentration of SDS is 1.0 × 10⁻⁶, -3 At a concentration of 4.0 × 10⁻⁶ mol / L, nucleation boiling occurs at 180 °C, film boiling at 190 °C, and droplets bounce. -3 At a concentration of 10.0 × 10⁻⁶ mol / L, nucleation boiling occurs at 160 °C, film boiling at 170 °C, and droplets bounce. - 3 At a concentration of mol / L, SDS exhibits nucleation boiling at 150℃, transition boiling at 170℃ (where droplets bounce but no vapor film forms), and film boiling at 180℃. This demonstrates that different SDS concentrations result in different boiling states at the same temperature, leading to variations in heat conduction and cooling effects. Based on this phenomenon, the concentration of atomized droplets can be adjusted according to the current workpiece temperature and the target cooling rate to achieve the desired cooling effect.

[0047] Experimental Example 2

[0048] In this embodiment, the working droplet uses a surfactant SDS (sodium dodecyl sulfonate) solution to compare the boiling phase transition behavior of smooth silicon wafers and silicon micropillars as substrate materials.

[0049] The first step is the selection of the working droplet:

[0050] The first step involves selecting a surfactant SDS solution as the working droplet and preparing 9.0 × 10⁻⁶ droplets. -3 A mol / L aqueous solution.

[0051] The second step is cleaning the silicon wafers:

[0052] The second step further involves immersing the substrate (smooth silicon wafer, silicon micropillar) in acetone, anhydrous ethanol, and deionized water respectively for ultrasonic cleaning for 10 minutes, immersing it in piranha solution (VH2SO4:VH2O2 = 7:3), heating it in a water bath at 80°C for 0.5 hours, and then taking it out, rinsing it, and drying it for later use.

[0053] The third step involves using a high-speed camera to record the phase transition behavior of surfactant droplets of the same concentration impacting different surface structures:

[0054] Set up the experimental setup. Before starting the experiment, adjust the positions of the light source, high-speed camera, and substrate to ensure they are all aligned in a straight line. The side view of the substrate should also be clearly displayed on the camera control monitor. After adjusting the optical path, heat the substrate using a hot stage. Once the temperature reaches the specified level, inject droplets using a precision syringe pump at a rate of 0.01 mL / min, with a droplet drop height of 3.5 mm. Record the entire droplet descent process using a high-speed camera. The experimental temperature range is 50–300 °C.

[0055] from Figure 3 It can be seen that when the substrate is a smooth silicon wafer, nucleation boiling occurs at 100℃, and film boiling occurs at 150℃. When the substrate is a silicon micropillar, at 9.0 × 10⁻⁶... -3 At a SDS concentration of mol / L, nucleation boiling occurs at 150°C, transition boiling at 200°C (droplets bounce but no vapor film forms), and a thin vapor film appears at 210°C, gradually transitioning to film boiling. Therefore, the system of this invention achieves higher temperatures for modal boiling at the same surfactant concentration, which is more conducive to heat conduction.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for cooling a workpiece using the boiling phase change behavior of liquid droplets, characterized in that, The method is carried out through a spray cooling system, including: an atomization module, a heat-conducting medium module, and a data control module; The atomizing module is used to construct atomized surfactant working droplets; one side of the heat-conducting medium module is used to receive the working droplets, and the other side is used to contact the workpiece to be cooled, thereby cooling the workpiece; the data control module can adjust the composition of the working droplets according to the temperature of the heat-conducting medium module and the target cooling rate, thereby controlling the cooling rate. The working droplet is a solution containing a surfactant. The cooling effect can be controlled by adjusting the composition of the atomized droplet and the structure of the heat-conducting medium module. The thermally conductive medium module is a silicon micropillar substrate obtained by etching a smooth silicon wafer, silicon nanowires, and a mask to etch the smooth silicon wafer. The boiling phase transition behavior includes nucleation boiling which is conducive to cooling, film boiling which is not conducive to cooling, and transitional boiling with a cooling effect between the two.

2. The method according to claim 1, characterized in that, The surfactant is anionic surfactant, cationic surfactant, or amphoteric surfactant, and the concentration of the surfactant is 0-12 / 9 CMC.

3. The method according to claim 2, characterized in that, The anionic surfactant is sodium dodecyl sulfonate.

4. The method according to any one of claims 1 to 3, characterized in that, The injection rate of the working droplet is 0.01 mL / min, the droplet falls at a height of 3.5 mm, and the temperature of the substrate is 50~300℃.

5. A spray cooling system for exercising the method of claim 1, characterized in that, include: The spray cooling system includes an atomization module, a heat transfer medium module, and a data control module; The atomization module is used to construct atomized surfactant working droplets; One side of the heat-conducting medium module is used to receive the working liquid droplets, and the other side is used to contact the workpiece to be cooled, so as to cool the workpiece. The data control module can adjust the composition of the working liquid droplets according to the temperature of the heat-conducting medium module and the target cooling rate, so as to control the cooling rate. The working droplet is a solution containing a surfactant. The cooling effect can be controlled by adjusting the composition of the atomized droplet and the structure of the heat-conducting medium module. The thermally conductive medium module is a silicon micropillar substrate obtained by etching a smooth silicon wafer, silicon nanowires, and a mask to etch the smooth silicon wafer. The boiling phase transition behavior includes nucleation boiling which is conducive to cooling, film boiling which is not conducive to cooling, and transitional boiling with a cooling effect between the two.

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