Pulsed electric field enhanced flow boiling device and visual measurement method

Abstract

The invention provides a pulsed electric field enhanced flow boiling device and a visual measurement method. The device comprises a high-precision visual heating system, a transparent electrode pulse electric field generation system and a stable flow control system, wherein the high-precision visual heating system comprises a nickel metal sheet, a transparent polytetrafluoroethylene rectangular microchannel, a Joule direct current measurement system and a high-speed camera. The nickel metal sheet can accurately measure heat flow and wall temperature through the Joule direct current measurement system; the transparent electrode pulsed electric field generating system comprises a single-layer titanium coating transparent electrode with a scale, a double-layer titanium coating transparent electrode, a high-voltage electrostatic generator and an electric travel switch. The single-layer titanium coating transparent electrode with the scale realizes flow boiling visual measurement; the stable flow control system comprises a double-layer heat preservation water tank, a peristaltic pump, a water storage tank, an inlet valve, an outlet valve, a drainage pipeline, an inlet pipeline and a backflow pipeline. The double-layer heat preservation water tank provides stable liquid level height.

Description

Technical Field

[0001] The invention belongs to the field of engineering thermophysics multiphase flow, and specifically relates to a pulse electric field enhanced flow boiling device and a visual measurement method. Background Art

[0002] The flow pattern and bubble dynamics in flow boiling are key factors affecting the heat transfer and flow of the working fluid. The electric field exerts a dielectric electrophoretic force on the bubble motion in flow boiling, and the heat transfer and flow characteristics of flow boiling can be enhanced by applying an electric field. However, conventional electric field application methods such as copper plate electrodes hinder the visualization of bubble motion in flow boiling. In their patent "A microchannel heat exchanger with electric field enhanced boiling heat transfer", Zhuang Xiaoru and others from the Southern University of Science and Technology proposed a solution of indium tin oxide (ITO) transparent electrode to solve the visualization problem of electric field enhanced boiling heat transfer. The ultra-thin transparent indium tin oxide (ITO) coating has high transmittance and strong conductivity, and can be used as a transparent electrode to realize the visualization of electric field enhanced flow boiling heat transfer. In addition, a thermocouple in the temperature measuring hole is used to measure the wall temperature, and the heating tube in the heating hole heats the microchannel heat exchanger. However, this solution still has the following problems that need to be solved, which are also common in other patents for electric field enhanced flow boiling heat transfer. First, the electric field regulation is completely dependent on the high-voltage electrostatic generator, which has high performance requirements. For example, programming functions are required to realize the pulsed electric field, which is not conducive to expanding applications. Secondly, there is a certain distance between the temperature measuring hole and the heating surface, which affects the measurement of the wall temperature by the thermocouple. The heating tube in the heating hole is locally heated, and the basic experimental requirement of uniform heat flow on the heating surface cannot be achieved. Thirdly, there is no description of flow control, and precise flow control is crucial to the measurement of flow boiling heat transfer performance. Finally, the visualization device for electric field enhanced flow boiling heat transfer does not have the function of visual measurement of bubble size.

[0003] Therefore, it is necessary to design a pulsed electric field enhanced flow boiling device and a visual measurement method with high-precision visual heating and precise flow control. Summary of the invention

[0004] The purpose of the present invention is to realize the visualized measurement in the field of engineering thermophysics multiphase flow, and to provide a pulse electric field enhanced flow boiling device and a visualized measurement method. The pulse electric field is generated by a double-layer titanium (Ti) plated transparent electrode with a changeable electrode spacing, and the change of the electrode spacing is achieved by an electric travel switch. The double-layer titanium (Ti) plated transparent electrode and the electric travel switch are combined to generate a pulse electric field at a low cost, avoiding the use of a high-voltage electrostatic generator that requires programming functions.

[0005] First, the single-layer Ti-coated transparent electrode with a ruler has high transmittance, and combined with a high-speed camera, it can realize the visualized measurement of electric field enhanced flow boiling heat transfer; secondly, the double-layer Ti-coated transparent electrode has an electrode spacing, which can be automatically replaced at a fixed frequency to realize a pulsed electric field; thirdly, the nickel (Ni) metal sheet has a linear relationship between resistance and temperature, and the Joule DC measurement system can be used to accurately measure the heat flow and wall temperature; finally, the liquid level method based on the double-layer insulated water tank has the advantage of weak inlet pressure fluctuations, and can realize a pulsed electric field enhanced flow boiling device and a visualized measurement method with high-precision visualized heating for precise flow control, which improves the experimental efficiency and accuracy.

[0006] The technical solution adopted by the pulse electric field enhanced flow boiling device and the visualization measurement method described in the present invention is: a pulse electric field enhanced flow boiling visualization device, including a high-precision visualization heating system, a transparent electrode pulse electric field generating system and a stable flow control system.

[0007] The high-precision visual heating system includes a Ni metal sheet, a transparent PTFE rectangular microchannel, a Joule DC measurement system, and a high-speed camera. The Ni metal sheet has a linear relationship between resistance and temperature, and can accurately measure heat flow and wall temperature through the Joule DC measurement system. The bubble generation, bubble detachment, and bubble deformation process in flow boiling can be dynamically recorded through the transparent PTFE rectangular microchannel and the high-speed camera. The transparent PTFE rectangular microchannel has poor thermal conductivity and strong thermal stability, which effectively prevents the heat of the Ni metal sheet from being lost to the surrounding air.

[0008] The transparent electrode pulse electric field generating system comprises a single-layer titanium (Ti) plated transparent electrode, a double-layer titanium (Ti) plated transparent electrode, a high-voltage electrostatic generator, and an electric travel switch. The double-layer Ti plated transparent electrode and the electric travel switch are combined to generate a pulse electric field by dynamically adjusting the electrode spacing. The single-layer Ti plated transparent electrode with a scale has the dual characteristics of light transmission and conductivity. The high-voltage electrostatic generator is connected through a wire to achieve a uniform pulse electric field while ensuring the visualization of the flow pattern and bubble generation process in flow boiling. The uniform pulse electric field intensity and frequency are adjusted by the electric travel switch (14) and the high-voltage electrostatic generator (15).

[0009] The stable flow control system includes a double-layer insulated water tank, a peristaltic pump, a water storage tank, an inlet valve, an outlet valve, a discharge pipeline, an inlet pipeline, and a return pipeline. The double-layer insulated water tank mainly provides stable fluid temperature and liquid level height, reduces pressure fluctuations caused by the peristaltic pump, and realizes stable control of the flow. The peristaltic pump realizes the reflux of the experimental working fluid from the water storage tank to the double-layer insulated water tank through the return pipeline. The inlet valve and the outlet valve respectively fine-tune the inlet flow and the outlet pressure.

[0010] In the above scheme, the high-precision visualization heating system mainly realizes high-precision measurement of heating power and wall temperature through the Ni metal sheet and the Joule DC measurement system, and realizes visualization and heat preservation of gas-liquid two-phase flow through the transparent PTFE rectangular microchannel. The size and position of the Ni metal sheet and the transparent PTFE rectangular microchannel are determined according to actual needs.

[0011] In the above scheme, the transparent electrode pulse electric field generating system mainly provides a uniform pulse electric field, and the uniform pulse electric field strength and frequency are adjusted by the double-layer Ti-coated transparent electrode, the electric travel switch and the high-voltage electrostatic generator, and the visual measurement of pulse electric field enhanced flow boiling is realized by the single-layer Ti-coated transparent electrode with a ruler. The size and position of the single-layer Ti-coated transparent electrode with a ruler and the double-layer Ti-coated transparent electrode are determined according to actual needs.

[0012] In the above scheme, the stable flow control system mainly reduces the pressure fluctuation caused by the peristaltic pump through the double-layer insulated water tank to achieve stable flow control, and achieves fine adjustment of the inlet flow and outlet pressure through the inlet valve and outlet valve. The size and position of the double-layer insulated water tank, the inlet valve and the outlet valve are determined according to actual needs.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. The transparent electrode pulse electric field generating system of the present invention realizes the visualization of pulse electric field enhanced flow boiling by combining the single-layer Ti-plated transparent electrode with a scale, the double-layer Ti-plated transparent electrode and the electric travel switch. On the one hand, it solves the problem that conventional electric field application methods such as copper plate electrodes hinder the visualization of bubble movement in flow boiling; on the other hand, it generates a pulse electric field by dynamically adjusting the electrode spacing.

[0015] 2. The high-precision visual heating system of the present invention can measure the heat flux and wall temperature efficiently, quickly and accurately through the Ni metal sheet and the Joule DC measurement system, timely reflect the flow, boiling and heat transfer characteristics of the working fluid, and realize comparative analysis of the heat flux and wall temperature data with the bubble generation, detachment and deformation images recorded by the high-speed camera.

[0016] 3. The stable flow control system of the present invention can effectively reduce the inlet pressure fluctuation and can achieve stable control of the flow according to experimental requirements.

[0017] 4. The electric travel switch of the present invention is controlled by a uniform speed motor with adjustable speed, and suitable motor parameters can be selected according to the frequency required by the pulse electric field.

[0018] 5. The present invention can enhance the flow boiling process and realize different flow boiling phenomena by changing the electric field form.

[0019] 6. The electric field applied by the present invention is a direct current electric field, and an alternating current electric field can also be used to achieve convenient conversion between alternating current and direct current.

[0020] 7. The single-layer Ti-plated transparent electrode used in the present invention has a ruler to achieve visual measurement of bubble size. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a 3D schematic diagram of a pulse electric field enhanced flow boiling device and a visualized measurement method according to an embodiment of the present invention.

[0022] Figure 2 It is a structural schematic diagram of a transparent electrode pulse electric field generating system in a pulse electric field enhanced flow boiling device and a visualization measurement method according to an embodiment of the present invention.

[0023] Figure 3 It is a bubble merging timing diagram in a pulse electric field enhanced flow boiling device and a visualization measurement method according to an embodiment of the present invention.

[0024] In the figure, 1, double-layer insulated water tank, 2, peristaltic pump, 3, Ni metal sheet, 4, transparent PTFE rectangular microchannel, 5, water storage tank, 6, Joule DC measurement system, 7, inlet valve, 8, outlet valve, 9, discharge pipeline, 10, inlet pipeline, 11, return pipeline, 12, double-layer Ti-coated transparent electrode, 13, single-layer Ti-coated transparent electrode with scale, 14, electric travel switch, 15, high-voltage electrostatic generator, 16, high-speed camera, 17, sealing gasket, 18, bolts and nuts. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below with reference to the specific implementation modes of the accompanying drawings, but the protection scope of the present invention is not limited thereto.

[0026] Figure 1The figure shows an implementation of a pulse electric field enhanced flow boiling device and a visualization measurement method of the present invention, which includes a high-precision visualization heating system, a transparent electrode pulse electric field generation system and a stable flow control system. The transparent electrode pulse electric field generation system includes a double-layer Ti-plated transparent electrode 12, a single-layer Ti-plated transparent electrode 13 with a scale, an electric travel switch 14, and a high-voltage electrostatic generator 15. The double-layer Ti-plated transparent electrode and the electric travel switch are combined to generate a pulse electric field by dynamically adjusting the electrode spacing. The single-layer Ti-plated transparent electrode 13 with a scale has the dual characteristics of light transmission and conductivity. The high-voltage electrostatic generator 15 is connected by a wire to achieve a uniform pulse electric field while ensuring the visualization of the flow type and bubble generation process in the flow boiling. On the one hand, it solves the technical problem that the conventional electric field generation method cannot realize the visualization of the bubble movement in the flow boiling. On the other hand, the pulse electric field is generated by dynamically adjusting the electrode spacing.

[0027] The high-precision visualization heating system includes a Ni metal sheet 3, a transparent PTFE rectangular microchannel 4, a Joule DC measurement system 6, and a high-speed camera 16; the Ni metal sheet 3 has a linear relationship between resistance and temperature, and can accurately measure heat flow and wall temperature through the Joule DC measurement system 6; the transparent PTFE rectangular microchannel 4 can be used to prevent the Ni metal sheet 3 from dissipating heat to the surrounding air while realizing the visualization of circulation boiling, which helps to achieve high-precision heat flow measurement.

[0028] The stable flow control system includes a double-layer insulated water tank 1, a peristaltic pump 2, a water storage tank 5, an inlet valve 7, an outlet valve 8, a discharge pipeline 9, an inlet pipeline 10, and a return pipeline 11. The double-layer insulated water tank 1 mainly provides stable fluid temperature and liquid level height, reduces pressure fluctuations caused by the peristaltic pump 2, and realizes stable flow control. The discharge pipeline 9 directly discharges the working fluid that exceeds the inner cylinder height of the double-layer insulated water tank 1 to the water storage tank 5. The peristaltic pump 2 and the return pipeline 11 realize the return of the working fluid to the double-layer insulated water tank 1.

[0029] When used specifically, for example, when performing a pulse electric field enhanced flow boiling visualization experiment, the water storage tank 5 is filled with the experimental working fluid, and the stable flow control system, the high-precision visualization heating system, and the transparent electrode pulse electric field generating system are turned on in sequence. The inlet flow and outlet pressure are adjusted by the inlet valve 7 and the outlet valve 8. The uniform pulse electric field intensity and frequency are adjusted by the electric travel switch 14 and the high-voltage electrostatic generator 15. The heat flow and wall temperature of the Ni metal sheet 3 are measured by the Joule DC measurement system 6. The bubble movement characteristics during flow boiling are recorded by the high-speed camera 16. When the device is stopped, the transparent electrode pulse electric field generating system, the high-precision visualization heating system, and the stable flow control system are turned off in sequence, and the experimental working fluid in the water storage tank 5 is emptied, and the operation is terminated. According to the above-mentioned usage, the transparent electrode pulse electric field enhanced flow boiling device and the visualization measurement method can also be used in teaching and popular science demonstrations, with a wide range of applications and safe and easy operation.

[0030] The examples are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Without departing from the essential content of the present invention, obvious improvements, substitutions or modifications that can be made by those skilled in the art all fall within the protection scope of the present invention.

Claims

1. A pulse electric field enhanced flow boiling device and a visual measurement method, characterized in that: include: A double-layer insulated water tank (1), a peristaltic pump (2), a nickel (Ni) metal sheet (3), a transparent polytetrafluoroethylene (PTFE) rectangular microchannel (4), a water storage tank (5), a Joule direct current measurement system (6), an inlet valve (7), an outlet valve (8), a discharge pipeline (9), an inlet pipeline (10), a return pipeline (11), a double-layer titanium (Ti)-plated transparent electrode (12), a single-layer titanium (Ti)-plated transparent electrode with a scale (13), an electric travel switch (14), a high-voltage electrostatic generator (15), a high-speed camera (16), a sealing gasket (17), bolts and nuts (18), etc.

2. A pulse electric field enhanced flow boiling device and a visual measurement method according to claim 1, characterized in that: The high-precision visual heating system comprises a Ni metal sheet (3), a transparent PTFE rectangular microchannel (4), a Joule DC measurement system (6), and a high-speed camera (16). The Ni metal sheet (3) has a linear relationship between resistance and temperature, and can accurately measure heat flow and wall temperature through the Joule DC measurement system (6). The transparent PTFE rectangular microchannel (4) and the high-speed camera (16) can dynamically record the bubble generation, bubble detachment, and bubble deformation process in flow boiling. The transparent PTFE rectangular microchannel (4) has poor thermal conductivity and strong thermal stability, which effectively prevents the heat of the Ni metal sheet (3) from being lost to the surrounding air.

3. The pulse electric field enhanced flow boiling device and the visual measurement method according to claim 1 are characterized in that: The transparent electrode electric field generating system comprises a double-layer Ti-plated transparent electrode (12), a single-layer Ti-plated transparent electrode (13) with a scale, an electric travel switch (14), and a high-voltage electrostatic generator (15). The double-layer Ti-plated transparent electrode (12) and the electric travel switch (14) are combined to generate a pulse electric field by dynamically adjusting the electrode spacing. The single-layer Ti-plated transparent electrode (13) with a scale has the dual characteristics of light transmission and conductivity, and is connected to the high-voltage electrostatic generator (15) through a wire, so that while achieving a uniform electric field, visual measurement of the flow pattern and bubble generation process in flow boiling is ensured. The uniform pulse electric field intensity and frequency are adjusted by the electric travel switch (14) and the high-voltage electrostatic generator (15).

4. The pulse electric field enhanced flow boiling device and the visual measurement method according to claim 1, characterized in that: The stable flow control system comprises a double-layer insulated water tank (1), a peristaltic pump (2), a water storage tank (5), an inlet valve (7), an outlet valve (8), a discharge pipeline (9), an inlet pipeline (10), and a return pipeline (11). The double-layer insulated water tank (1) mainly provides stable fluid temperature and liquid level height, reduces pressure fluctuations caused by the peristaltic pump, and realizes stable flow control. The discharge pipeline (9) directly discharges the working fluid that exceeds the inner cylinder height of the double-layer insulated water tank (1) to the water storage tank (5). The peristaltic pump (2) realizes the reflux of the experimental working fluid from the water storage tank (5) to the double-layer insulated water tank (1) through the return pipeline (11). The inlet valve (7) and the outlet valve (8) respectively fine-tune the inlet flow and the outlet pressure.

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