Experimental system for measuring gas film interference at bottom of liquid drop under heating condition

Abstract

The invention discloses a liquid drop bottom gas film interference measurement experiment system under a heating condition, which comprises a liquid drop generation system and a surface temperature control system, and the surface temperature control system is controlled to be in a stable temperature heating range through a PID temperature controller. Liquid drops generated by the liquid drop generation system drop onto a sapphire substrate of the surface temperature control system; the liquid drop macroscopic shape image shooting system is arranged on the side surface of the liquid drop generated by the liquid drop generation system; the liquid drop bottom interference image shooting system is used for shooting an interference pattern of an air film formed by the liquid drop through an interference light path; and an image post-processing module. According to the system, interference measurement of the gas film at the bottom of the liquid drop under the heating condition is achieved, meanwhile, the synchronous control device is used for conducting synchronous triggering on the two high-speed cameras to be combined with a post-processing program, and synchronous measurement of liquid drop impact information and the contour of the gas film at the bottom can be achieved when the liquid drop impacts the heating surface.

Description

Technical Field

[0001] This invention relates to the field of research on the phenomenon of droplet impact on solid surfaces, and in particular to an experimental system for measuring the interferometry of the gas film at the bottom of a droplet under heating conditions. Background Technology

[0002] The phenomenon of droplets impacting solid surfaces is common in nature and industrial activities. Applications such as inkjet printing, droplet collection, and thermal management all involve droplet impact. However, the droplet impact process is not simply a direct solid-liquid contact. When a droplet impacts a solid surface, the gas pressure between the droplet bottom and the solid surface increases as it approaches the surface, causing a pit to form at the bottom of the droplet. Gas is trapped inside the pit, forming a micron-sized gas film that hinders direct solid-liquid contact.

[0003] The presence of a gas film significantly impacts the heat transfer process during the initial stage of droplet impact. From a solid-liquid heat transfer perspective, the gas film introduces an additional thermal resistance layer between the liquid and solid. Since the thermal conductivity of a gas is much lower than that of a liquid or solid material, this gas film effectively forms a high-thermal-resistance insulating layer at the interface, leading to a significant reduction in the effective heat flux density between the droplet and the surface during the initial stage of impact. The profile, spatial distribution, and evolution of the gas film directly determine the interfacial heat transfer coefficient and local heat flux distribution, thus affecting the droplet's evaporation rate, boiling mode, and cooling efficiency. When the solid surface temperature is extremely high, the Leidenfrost phenomenon occurs after droplet impact, and the gas film evolves into a continuous vapor layer, resulting in prolonged solid-liquid contact isolation and a sharp decrease in heat flux. Therefore, measuring the profile of the gas film at the bottom of the droplet under heating conditions is of great significance.

[0004] However, existing studies on droplet impacts on high-temperature solid surfaces mostly employ high-speed photography to capture the macroscopic morphology of droplets during the impact process from the side, recording the changes in the droplet profile and combining this with temperature detection techniques to analyze the droplet flow and heat transfer characteristics. The measurement of the micron-sized gas film profile at the bottom of the droplet has not received sufficient attention. Corresponding heat transfer models and mechanisms have not considered the formation of the gas film and its evolution over time, resulting in discrepancies between theoretical heat transfer models and reality. Therefore, the measurement of the droplet impact process and gas film profile under heating conditions is particularly important.

[0005] Therefore, based on the above-mentioned technical problems, those skilled in the art urgently need to develop an experimental system for measuring the gas film at the bottom of a droplet under heating conditions. Summary of the Invention

[0006] The purpose of this invention is to provide an experimental system for measuring the interferometric measurement of the gas film at the bottom of a droplet under heating conditions. This system can realize the interferometric measurement of the gas film at the bottom of a droplet under heating conditions. At the same time, by using a synchronous control device to synchronously trigger two high-speed cameras and combine them with a post-processing program, it can realize the synchronous measurement of droplet impact information and bottom gas film profile when the droplet impacts the heated surface.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The present invention provides an experimental system for measuring the gas film interferometry at the bottom of a droplet under heating conditions. The system comprises:

[0009] Droplet generation system;

[0010] A surface temperature control system that is coordinated with the droplet generation end position of the droplet generation system, wherein the surface temperature control system is controlled by a PID temperature controller to be in a stable temperature heating range, and the droplets generated by the droplet generation system fall onto the sapphire substrate of the surface temperature control system.

[0011] A macroscopic morphology imaging system for droplets is arranged on the side of the droplets generated by the droplet generation system.

[0012] A droplet bottom interferometric imaging system that captures the interference pattern of an air film formed by a droplet using an interference optical path; and

[0013] Image post-processing module.

[0014] Furthermore, the surface temperature control system includes:

[0015] An annular ceramic heating element is provided, and the annular ceramic heating element is fixed by a heating element support member. The annular ceramic heating element is fixed to the heating element support member by heat-resistant adhesive, and the central area of ​​the annular ceramic heating element is a central through hole.

[0016] A sapphire substrate is located on the upper surface of the annular ceramic heating element, and the sapphire substrate is fixed to the central region of the annular ceramic heating element by thermally conductive silicone.

[0017] The annular ceramic heating element is connected to a PID temperature controller, and the PID temperature controller maintains a constant heating temperature.

[0018] A K-type thermocouple thermometer is connected to the sapphire substrate to detect the actual temperature of the sapphire substrate.

[0019] Furthermore, the droplet generation system includes:

[0020] The needle is located directly above the sapphire substrate;

[0021] A syringe connected to the needle via a silicone tubing, wherein the syringe is a 1ml syringe, and the two ends of the silicone tubing are connected to the needle and the syringe end respectively via Luer connectors;

[0022] The syringe is placed on the injection pump, and the injection pump drives the piston movement of the syringe.

[0023] Furthermore, the droplet macroscopic morphology image capturing system includes an LED light source and a first high-speed camera respectively arranged on both sides of the formed droplet.

[0024] Furthermore, the light source of the interference optical path is a 532nm laser light source;

[0025] The interference optical path includes a beam splitter and a reflector. The beam emitted by the 532nm laser source is split by the beam splitter after passing through the laser beam expander. One of the optical paths is reflected by the beam splitter to the reflector, and then reflected by the reflector to the sapphire substrate. The area of ​​the beam reflected by the reflector on the sapphire substrate coincides with the area where the droplet contacts the sapphire substrate.

[0026] The light beam is reflected again by the sapphire substrate to the mirror, and then reflected by the mirror to the beam splitter before being transmitted to the droplet bottom interference image capturing system.

[0027] Furthermore, the droplet bottom interference image capturing system is a second high-speed camera that receives the light emitted from the beam splitter.

[0028] Furthermore, the image post-processing program receives image information from the droplet macroscopic morphology image capturing system and the droplet bottom interference image capturing system, which is then divided into side impact information extraction and bottom interference image calculation processing.

[0029] Furthermore, the side impact information extraction mainly involves calculating the droplet diameter and impact velocity, fitting the droplet profile into an ellipse, and calculating the horizontal diameter D of this ellipse. H and vertical diameter D V ;

[0030] The formula for calculating the droplet diameter D is:

[0031]

[0032] The impact velocity is calculated by fitting the centroid coordinates of the ellipse, and the average velocity of the droplet in the five frames before impact is taken as the impact velocity of the droplet.

[0033] Furthermore, the bottom interference image is a grayscale interference image obtained by taking a 532nm light source. The height difference between adjacent interference fringes is λ / 4, where λ is the wavelength of the light source. The increase or decrease in height is determined by the direction of movement of the interference fringes, thereby reconstructing the outline of the air film and its relative thickness.

[0034] The above technical solution provides an experimental system for measuring the gas film at the bottom of a droplet under heating conditions, which has the following beneficial effects:

[0035] The system of the present invention can realize the interference measurement of the gas film at the bottom of the droplet under heating conditions. At the same time, by using a synchronous control device to synchronously trigger and combine the post-processing program of two high-speed cameras, it can realize the synchronous measurement of droplet impact information and bottom gas film profile when the droplet impacts the heated surface. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0037] Figure 1 This is a system flowchart of the experimental system for measuring the gas film at the bottom of a droplet under heating conditions, as disclosed in an embodiment of the present invention.

[0038] Figure 2 This is a schematic diagram of the lens holder of the experimental system for measuring the gas film at the bottom of a droplet under heating conditions, as disclosed in an embodiment of the present invention.

[0039] Figure 3 The images are captured by the droplet macroscopic morphology image capturing system of the droplet bottom gas film interferometry measurement experimental system under heating conditions disclosed in the embodiments of the present invention.

[0040] Figure 4 The image is captured by the droplet bottom interference image capturing system of the experimental system for measuring the gas film at the bottom of a droplet under heating conditions, as disclosed in an embodiment of the present invention.

[0041] Explanation of reference numerals in the attached figures:

[0042] 1. K-type thermocouple thermometer; 2. LED light source; 3. PID temperature controller; 4. Reflector; 5. 532nm laser light source; 6. Laser beam expander; 701. First high-speed camera; 702. Second high-speed camera; 8. Injector pump; 9. Syringe; 10. Needle; 11. Droplet; 12. Sapphire substrate; 13. Ring-shaped ceramic heating element; 14. Heating element support; 15. Beam splitter. Detailed Implementation

[0043] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0044] See Figures 1 to 2 As shown;

[0045] The experimental system for measuring the gas film interferometry at the bottom of a droplet under heating conditions in this embodiment includes:

[0046] Droplet generation system;

[0047] The surface temperature control system is matched with the droplet generation end position of the droplet generation system. The surface temperature control system is controlled by the PID temperature controller 3 to keep it in a stable temperature heating range. The droplets 11 generated by the droplet generation system fall onto the sapphire substrate 12 of the surface temperature control system.

[0048] A macroscopic morphology imaging system for droplets is arranged on the side of the droplet 11 generated by the droplet generation system.

[0049] A droplet bottom interference image capturing system, which captures the interference pattern of the air film formed by the droplet 11 through an interference optical path; and an image post-processing module.

[0050] Specifically, this embodiment discloses an experimental system for measuring the gas film interferometry at the bottom of a droplet under heating conditions. This system mainly comprises five parts: a surface temperature control system, a droplet generation system, a droplet macroscopic morphology image capturing system, a droplet bottom interferometric image capturing system, and an image post-processing module. The image post-processing module, programmed in MATLAB, is responsible for extracting the droplet's velocity, impact velocity, and calculating the interferometric image.

[0051] Preferably, the surface temperature control system of this embodiment includes:

[0052] An annular ceramic heating element 13 is fixed by a heating element support 14. The annular ceramic heating element 13 is fixed to the heating element support 14 by heat-resistant adhesive, and the central area of ​​the annular ceramic heating element 13 is a central through hole.

[0053] A sapphire substrate 12 is located on the upper surface of the annular ceramic heating element 13, and the sapphire substrate 12 is fixed to the central area of ​​the annular ceramic heating element 13 by thermally conductive silicone.

[0054] The annular ceramic heating element 13 is connected to the PID temperature controller 3 and maintains a constant temperature through the PID temperature controller 3.

[0055] A K-type thermocouple thermometer 1 is connected to the sapphire substrate 12, and the actual temperature of the sapphire substrate 12 is detected by the K-type thermocouple thermometer 1.

[0056] Preferably, the droplet generation system of this embodiment includes a needle 10 located directly above the sapphire substrate 12; a syringe 9 connected to the needle 10 via a silicone tubing, wherein the syringe 9 is a 1ml syringe, and the two ends of the silicone tubing are connected to the ends of the needle 10 and the syringe 9 respectively via Luer connectors; the syringe 9 is placed on an injection pump 8, and the piston of the syringe 9 is driven by the injection pump 8.

[0057] In this embodiment, the needle 10 needs to be positioned directly above the sapphire substrate 12 and in the central region of the sapphire substrate 12, with the liquid dripping towards the central region. This ensures that the interference light path illuminates the dripping position. As an extended implementation, the needle 10 in this embodiment can be suspended above the sapphire substrate 12 using a height adjustment device. The droplet impact speed can be adjusted by changing the droplet release height, and different diameter needles 10 can produce droplets of different diameters. When droplets are generated, the feed speed of the syringe pump 8 is adjusted so that the syringe pump 8 slowly pushes the piston of the syringe 9 to move. The droplets gather at the syringe needle 10, and the droplets 11 drip naturally from the needle 10 under their own gravity.

[0058] Preferably, the droplet macroscopic morphology image capturing system of this embodiment includes LED light sources 2 and a first high-speed camera 701 respectively arranged on both sides of the formed droplet. Before each experiment, a scale needs to be placed on the focal plane of the first high-speed camera 701 to record the image scale.

[0059] Preferably, the light source for the interference optical path in this embodiment is a 532nm laser light source 5;

[0060] The interference optical path includes a beam splitter 15 and a reflector 4. The beam emitted by the 532nm laser source 5 passes through the laser beam expander 6 and is split by the beam splitter 15. One of the optical paths is reflected by the beam splitter 15 to the reflector 4, and then reflected by the reflector 4 to the sapphire substrate 12. The area of ​​the beam reflected by the reflector 4 that illuminates the sapphire substrate 12 coincides with the area where the droplet contacts the sapphire substrate 12.

[0061] The light beam is reflected again by the sapphire substrate 12 to the reflector 4, and then reflected by the reflector 4 to the beam splitter 15 before being transmitted to the interference image imaging system at the bottom of the droplet.

[0062] In this embodiment, the interference optical path of the droplet bottom interference image capturing system is constructed using a modular cage-like optical system. A laser beam is emitted from a 532nm laser source 5 and incident perpendicularly on a laser beam expander 6. The laser beam expander 6 broadens the light emitted from the 532nm laser source 5. The broadened light beam exits the laser beam expander 6 and illuminates a beam splitter 15 at a 45° incident angle. The beam splitter 15 divides the light beam into two parts: one part is reflected on the surface of the beam splitter 15, and the other part is transmitted through the beam splitter 15 along the crude oil direction. This latter part of the light is independent of the interference optical path. Subsequently, the light reflected by the beam splitter 15 is incident on the reflector 4 at 45°. The light is reflected on the reflector 4 and passes perpendicularly through the sapphire substrate 12 to the bottom of the droplet. The air film generated during the impact of the droplet 11 on the solid surface has the bottom of the droplet 11 and the surface of the sapphire substrate 12 as the interface. The light is reflected perpendicularly at the bottom of the droplet 11 and the surface of the sapphire substrate 12 and passes through the reflector 4 and the transmission beam splitter 15 along the same path, and finally enters the second high-speed camera 702, forming an interference pattern of the air film.

[0063] As an extended implementation, both the reflector 4 and the beam splitter 15 in this embodiment are installed in the lens holder 16. Based on the mature product structure of the existing technology, the lens holder 16 with lens angle adjustment function can be used to facilitate the adjustment of the tilt angle of the reflector 4 and the beam splitter 15 according to experimental requirements.

[0064] Preferably, the droplet bottom interference image capturing system in this embodiment is a second high-speed camera 702 that receives light emitted from the beam splitter 15.

[0065] Preferably, the image post-processing program in this embodiment is divided into side impact information extraction and bottom interference image calculation processing by receiving image information from the droplet macroscopic morphology image capturing system and the droplet bottom interference image capturing system.

[0066] In this embodiment, the side impact information extraction mainly involves calculating the droplet diameter and impact velocity, fitting the droplet profile into an ellipse, and calculating the horizontal diameter D of this ellipse. H and vertical diameter D V ;

[0067] The formula for calculating the droplet diameter D is:

[0068]

[0069] The impact velocity is calculated by fitting the centroid coordinates of the ellipse, and the average velocity of the droplet in the five frames before impact is taken as the impact velocity of the droplet.

[0070] In this embodiment, the bottom interference image is a grayscale interference image obtained by taking a 532nm light source. The height difference between adjacent interference fringes is λ / 4, where λ is the wavelength of the light source. The increase or decrease in height is determined by the direction of movement of the interference fringes, thereby reconstructing the outline of the air film and its relative thickness.

[0071] The above technical solution provides an experimental system for measuring the gas film at the bottom of a droplet under heating conditions, which has the following beneficial effects:

[0072] The system of the present invention can realize the interference measurement of the gas film at the bottom of the droplet under heating conditions. At the same time, by using a synchronous control device to synchronously trigger and combine the post-processing program of two high-speed cameras, it can realize the synchronous measurement of droplet impact information and bottom gas film profile when the droplet impacts the heated surface.

[0073] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A droplet bottom gas film interference measurement system under heating conditions, characterized in that, The system comprises: a droplet generation system; a surface temperature control system matched with the droplet generation end position of the droplet generation system, the surface temperature control system being controlled by a PID temperature controller (3) to be in a stable temperature heating range, and the droplets (11) generated by the droplet generation system falling on a sapphire substrate (12) of the surface temperature control system; a droplet macroscopic morphology image shooting system arranged at the side of the droplets (11) generated by the droplet generation system; a droplet bottom interference image shooting system for shooting the interference pattern of the air film formed by the droplets; and an image post-processing module.

2. The system of claim 1, wherein, The surface temperature control system comprises: a ring-shaped ceramic heating sheet (13) fixed by a heating sheet support (14), the ring-shaped ceramic heating sheet (13) being fixed on the heating sheet support (14) by heat-resistant glue, and the central region of the ring-shaped ceramic heating sheet (13) being a central through hole; a sapphire substrate (12) located on the upper surface of the ring-shaped ceramic heating sheet (13) and fixed on the central region of the ring-shaped ceramic heating sheet (13) by heat-conducting silicone glue; the ring-shaped ceramic heating sheet (13) being connected with the PID temperature controller (3) and kept at a constant temperature by the PID temperature controller (3); a K-type thermocouple thermometer (1) connected with the sapphire substrate (12) for detecting the actual temperature of the sapphire substrate (12).

3. The system of claim 2, wherein the system is configured to perform the experiment under heating conditions. The droplet generation system comprises: a needle (10) located directly above the sapphire substrate (12); a syringe (9) in communication with the needle (10) by a silicone hose, the syringe (9) being a 1ml syringe, and the two ends of the silicone hose being connected with the end of the needle (10) and the syringe (9) by Luer connectors respectively; the syringe (9) being placed on an injection pump (8) and driven by the injection pump (8) to move the piston of the syringe (9).

4. The system of claim 3, wherein the system is configured to perform the experiment under heating conditions. The droplet macroscopic morphology image shooting system comprises LED light sources (2) and a first high-speed camera (701) arranged respectively at the two sides of the formed droplets.

5. The system of claim 3, wherein the system is configured to perform the experiment under heating conditions. The light source of the interference optical path adopts a 532nm laser light source (5); the interference optical path comprising a beam splitter (15) and a mirror (4), the light beam emitted by the 532nm laser light source (5) being split by the beam splitter (15) after passing through a laser beam expander (6), one light path being reflected by the beam splitter (15) to the mirror (4) and then reflected by the mirror (4) to the sapphire substrate (12), and the light beam reflected by the mirror (4) being incident on the region of the sapphire substrate (12) and the region where the droplet (11) contacts the sapphire substrate (12); the light beam passing through the sapphire substrate (12) again, being reflected to the mirror (4), and being transmitted to the droplet bottom interference image shooting system after being reflected by the mirror (4) to the beam splitter (15).

6. The system of claim 5, wherein the system is configured to perform the experiment under heating conditions. The droplet bottom interference image shooting system is a second high-speed camera (702) receiving light emitted by the beam splitter (15).

7. The drop bottom gas film interferometry experiment system under heating conditions according to claim 1, wherein, The image post-processing program is divided into side impact information extraction and bottom interference picture calculation processing by receiving image information of the droplet macroscopic morphology image shooting system and the droplet bottom interference image shooting system.

8. The drop bottom gas film interferometry experiment system under heating conditions according to claim 7, characterized in that, The side impact information extraction mainly calculates the diameter and impact velocity of the liquid drop, and fits the drop profile as an ellipse to calculate the horizontal diameter D H and the vertical diameter D V of the ellipse. The calculation formula of the droplet diameter D is as follows: Wherein, the impact velocity is calculated by fitting the center coordinates of the ellipse, and the average velocity of the first five frames before the droplet impact is taken as the impact velocity of the droplet.

9. The drop bottom gas film interferometry experiment system under heating conditions according to claim 7, wherein, The bottom interference picture is a gray-scale interference picture obtained by shooting a 532nm light source, and the height difference corresponding to adjacent interference fringes is λ / 4, wherein λ is the wavelength of the light source; the increase and decrease of the height are determined by the moving direction of the interference fringes, so as to reconstruct the profile and relative thickness of the gas film.

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