Horizontal Tube External Falling Film Evaporation Liquid Film Thickness Measuring Device and Measuring System Composed Thereof

Abstract

The present invention discloses a device for measuring the thickness of a falling film outside a horizontal tube and a measurement system composed thereof, aiming to provide a device and a system that can distribute liquid evenly and stably and measure the three-dimensional distribution of the falling film thickness. The device includes a falling film evaporation film-forming unit and a falling film thickness measurement unit. The falling film evaporation film-forming unit includes a falling film flow main body bracket and a liquid distribution pipe, a diversion pipe, a diversion plate and an experimental pipe installed on the falling film flow main body bracket. The falling film thickness measurement unit includes a measurement main bracket, a circumferential positioning bracket, a measurement instrument bracket and a non-contact falling film thickness measurement instrument. The circumferential positioning bracket is slidably installed on the measurement main bracket through an axial moving shaft; the circumferential measurement of the falling film thickness is realized by the movement of the measurement instrument bracket along the arc-shaped guiding groove and the arc-shaped positioning groove, and the measurement of the falling film thickness along the axial direction of the experimental pipe is realized by the axial movement of the circumferential positioning bracket along the axial moving shaft. The present invention realizes uniform and stable liquid distribution and three-dimensional measurement of the falling film thickness.

Description

Technical Field

[0001] The present invention relates to the field of measurement technology, and more particularly to a device and a system for measuring the thickness of a falling film evaporation liquid film outside a horizontal tube. Background Art

[0002] In falling-film evaporation technology, the thickness and uniformity of the liquid film are crucial fluid properties and key factors in the efficient and effective operation of horizontal tube falling-film evaporators. Accurately predicting liquid film thickness and studying its flow characteristics during heating can effectively prevent localized wall drying outside the heat exchange tubes, which can reduce heat transfer efficiency. Therefore, studying liquid film thickness is crucial for further understanding the heat transfer mechanism of falling-film evaporation outside the tubes and improving its efficiency.

[0003] During liquid film flow, the film thickness is typically very small, thus presenting significant challenges in experimental observation. To address this challenge, researchers have intensively investigated and proposed numerous methods for measuring film thickness, which can be broadly categorized into two main categories: contact and non-contact. Contact methods can interfere with the flow field, leading to inaccurate measurements. Among non-contact measurement methods, currently employed by researchers include laser-induced fluorescence (LIF) and digital image processing. LIF is expensive, complex, and difficult to operate. It is also suitable for applications involving relatively gentle interphase fluctuations. However, if the surface fluctuations are intense or the wave fronts are steep, the light may be misrepresented by multiple refractions, resulting in poor detection at the receiver and low measurement accuracy. Furthermore, LIF cannot provide convenient and fast point-by-point measurement of the three-dimensional distribution of liquid film thickness. Digital image processing, implemented using high-speed cameras, can only capture cross-sections of liquid films with a hypothetical uniform circumferential distribution, such as sheet-like flows. It cannot provide three-dimensional, point-by-point observation of columnar flows with three-dimensionally uneven distributions, thus failing to accurately observe the flow of liquid films. In practical applications of falling-film evaporation in horizontal tubes, the liquid film flow pattern is primarily columnar. However, the distribution of this columnar film exhibits significant non-uniformity both circumferentially and axially. Using existing methods to measure the film thickness along the tube circumference and to interpret the film thickness and heat transfer characteristics of the falling-film evaporator based on the measured film thickness distribution would significantly impact the design of the falling-film evaporator.

[0004] In addition, for the convenience of measurement, scholars have carried out research on cold-state liquid film flow on the premise of ignoring evaporation heat transfer. That is, a heat exchange tube is used for falling film evaporation of the liquid film, and the pure working fluid is measured by scholars. In the field of seawater desalination, the working fluid in the falling film evaporation equipment is seawater. In the chemical industry, the working fluid in the falling film evaporation equipment is a mixed raw material. In the refrigeration field, as a refrigerant alternative option, non-azeotropic mixed working fluids have begun to be used in falling film evaporation equipment. In actual situations, the thickness of the evaporating liquid film is thinner. Especially for mixed working fluids, the Marangoni effect and mass transfer resistance caused by liquid film evaporation make the distribution of the liquid film outside the tube more inconsistent with the cold-state situation. Therefore, it is necessary to measure the thickness of the falling film evaporation liquid film at a specific temperature for the design of falling film evaporation equipment.

[0005] In addition, the heat transfer performance of horizontal tube falling film evaporation is mainly affected by liquid distribution and flow pattern. Uneven liquid distribution will cause disordered fluctuations of the liquid film in the tube length direction, which makes the measurement error of the liquid film fluctuation characteristics very large or even incorrect data appear, and will also cause a very large error in the measured value of the liquid film thickness. In the existing technology, the liquid is directly taken out of the constant temperature liquid bath and flows into the shunt tube, and the liquid flow has large fluctuations, which is bound to cause uneven spraying of the liquid by the liquid distribution tube, and the liquid film distribution on the heat exchange tube is chaotic and disordered. Therefore, it is necessary to design a measuring device and system for the thickness of the falling film evaporation liquid film outside the tube that can distribute the liquid evenly and stably and can accurately measure the three-dimensional distribution of the liquid film thickness in a certain temperature environment in real time. Summary of the Invention

[0006] The purpose of the present invention is to provide a measuring device for the thickness of the falling film evaporation liquid film outside the horizontal tube that can distribute the liquid evenly and stably and can measure the three-dimensional distribution of the liquid film thickness in real time in a non-cold-state environment in view of the technical defects existing in the prior art.

[0007] Another purpose of the present invention is to provide a measuring system for the thickness of the falling film evaporation liquid film outside the horizontal tube that can distribute the liquid evenly and stably and can measure the three-dimensional distribution of the liquid film thickness in real time.

[0008] The technical solutions adopted to achieve the purpose of the present invention are as follows:

[0009] A device for measuring the thickness of a falling film outside a horizontal tube, comprising a falling film evaporation film-forming unit and a liquid film thickness measuring unit. The falling film evaporation film-forming unit includes a falling film flow main body bracket and a liquid distribution pipe, a diversion pipe, a diversion plate and an experimental pipe installed on the falling film flow main body bracket. The liquid distribution pipe, the diversion pipe, the diversion plate and the experimental pipe are arranged horizontally and successively in the vertical direction. The liquid distribution pipe is a casing structure composed of an inner pipe and an outer pipe. Liquid inlets are respectively arranged at both ends of the inner pipe. A notch for liquid to flow into the space between the inner pipe and the outer pipe is arranged at the top of the inner pipe. A plurality of spray holes are arranged at the bottom of the outer pipe. An electric heater is installed in the experimental pipe. The liquid film thickness measuring unit includes a measuring main bracket, a circumferential positioning bracket, a measuring instrument bracket and a non-contact liquid film thickness measuring instrument. The circumferential positioning bracket is slidably installed on the measuring main bracket through an axial moving shaft. An arc-shaped guiding groove and an arc-shaped positioning groove concentric with the experimental pipe are arranged on the circumferential positioning bracket. The measuring instrument bracket is detachably connected to the circumferential positioning bracket at the arc-shaped guiding groove and the arc-shaped positioning groove. The non-contact liquid film thickness measuring instrument is fixedly installed on the measuring instrument bracket. The circumferential liquid film thickness is measured by moving the measuring instrument bracket along the arc-shaped guiding groove and the arc-shaped positioning groove. The liquid film thickness along the axial direction of the experimental pipe is measured by axially moving the circumferential positioning bracket along the axial moving shaft.

[0010] Positioning marks are arranged on the falling film flow main body bracket. The diversion pipe is installed on the falling film flow main body bracket through diversion pipe positioning plates at both ends. The diversion plate is installed on the falling film flow main body bracket through diversion plate positioning plates at both ends. The experimental pipe is installed on the falling film flow main body bracket through experimental pipe positioning plates at both ends. Positioning identifiers corresponding to the positioning marks on the falling film flow main body bracket are respectively arranged on the diversion pipe positioning plates, the diversion plate positioning plates and the experimental pipe positioning plates.

[0011] The measuring main bracket includes support plates on both sides, a bottom plate connecting the support plates on both sides, a plurality of connecting rib plates connecting the support plates on both sides, and an adjusting rib plate in the height direction located between the support plates on both sides. Long adjusting holes arranged in the height direction are respectively arranged on the support plates and the adjusting rib plate in the height direction. Threads are respectively arranged at both ends of the axial moving shaft. The axial moving shaft passes through the corresponding long adjusting holes and is installed on the measuring main bracket through nuts screwed to the threads at both ends. The adjusting rib plate is fixed to the bottom plate through a rib plate fixing plate. The falling film flow main body bracket is connected to the support plate through a connection fixing plate.

[0012] The falling film flow main bracket is composed of support plates at both ends and a plurality of rib plates connecting the support plates at both ends. A first chute is provided in the middle of each support plate. Second chutes are respectively provided on both sides of the first chute. A groove is provided at the top of the support plate. Both ends of the liquid distribution pipe are respectively placed in the grooves of the two support plates. The diversion pipe is installed on the support plate through a diversion pipe positioning plate detachably connected to the second chute; the diversion plate is installed on the support plate through a diversion plate positioning plate detachably connected to the first chute, and the experimental pipe is installed on the support plate through an experimental pipe positioning plate detachably connected to the first chute. The positions of the diversion pipe, the diversion plate and the experimental pipe are adjusted by fixing the diversion pipe positioning plate and the experimental pipe positioning plate at different positions in the first chute and fixing the diversion plate positioning plate at different positions in the second chute.

[0013] There are three axial movement shafts arranged in a triangle; the distance between the diversion pipe and the liquid distribution pipe is 1 mm - 2 mm.

[0014] The non-contact liquid film thickness measuring instrument is a confocal scanning displacement meter, and the focus of the confocal scanning displacement meter is located on the center line of the experimental pipe.

[0015] Guide holes corresponding to the arc-shaped guide grooves and positioning holes corresponding to the arc-shaped positioning grooves are provided on the measuring instrument bracket. The measuring instrument bracket is connected to the circumferential positioning bracket through guide bolts and nuts passing through the corresponding arc-shaped guide grooves and guide holes and positioning bolts and nuts passing through the corresponding arc-shaped positioning grooves and positioning holes.

[0016] A measurement system containing the measuring device for the liquid film thickness of the falling film evaporation outside the horizontal tube, comprising a liquid supply device and the measuring device for the liquid film thickness of the falling film evaporation outside the horizontal tube; the measuring device for the liquid film thickness of the falling film evaporation outside the horizontal tube is placed on an experimental table with adjustable levelness; the electric heater is connected to the power supply through a power meter and a voltage regulator; the liquid supply device includes a constant temperature liquid tank, a filter, a circulation pump, a high-level liquid storage tank, a small-range flowmeter and a large-range flowmeter; the high-level liquid storage tank is divided into a pressure stabilizing chamber, a constant pressure chamber and an overflow chamber which are communicated with each other in the upper part; the outlet of the constant temperature liquid tank is connected to the inlet of the corresponding pressure stabilizing chamber of the high-level liquid storage tank through the filter, the circulation pump and a first valve; a bypass branch is arranged between the constant temperature liquid tank and the water outlet end of the circulation pump, and a bypass valve is installed on the bypass branch; the outlet of the high-level liquid storage tank corresponding to the constant pressure chamber is divided into two paths, one path is connected to the inlet of a second valve, and the other path is respectively connected to the inlets of a fourth valve and a fifth valve; the outlet of the high-level liquid storage tank corresponding to the overflow chamber is connected to the inlet of a third valve; the outlets of the second valve and the third valve are connected to the water return port of the constant temperature liquid tank; the fourth valve and the fifth valve are respectively connected to the inlets of the small-range flowmeter and the large-range flowmeter, and the outlets of the small-range flowmeter and the large-range flowmeter are connected in parallel and then divided into two paths, which are respectively connected to the inlets at both ends of the inner tube of the liquid distribution pipe; a liquid storage tank is arranged at the bottom of the falling film main body bracket, and the liquid storage tank is connected to the constant temperature liquid tank; a refrigeration device and an electric auxiliary heating device for maintaining constant temperature are arranged in the constant temperature liquid tank.

[0017] Temperature detectors are respectively installed at both ends of the inner tube of the liquid distribution pipe.

[0018] The first valve, the second valve, the third valve, the fourth valve and the fifth valve all adopt globe valves.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1. The measuring device and system of the present invention adopt a liquid distribution pipe with a sleeve structure composed of an inner tube and an outer tube, and the working medium enters from both ends of the inner tube of the liquid distribution pipe, effectively solving the problem of uneven pressure in the axial direction, uneven incoming flow distribution and poor stability, resulting in uneven flow. The liquid distribution is more uniform and stable. At the same time, through the structural design, real-time three-dimensional measurement of the liquid film thickness is realized, which is beneficial to the research on the heat transfer mechanism of falling film evaporation outside the tube and provides a basis for the design of falling film evaporation equipment.

[0021] 2. In the measuring device and measuring system of the present invention, the working medium enters from both ends of the inner tube of the liquid distribution pipe, flows out from the notch at the top of the inner tube to the gap between the inner tube and the outer tube, and then flows out from the bottom of the outer tube through a row of spray holes, and finally a uniform and stable thin film is naturally formed on the experimental tube, effectively weakening the influence of the spraying method on the liquid flow, and improving the uniformity and stability of liquid distribution.

[0022] 3. In the measuring device and measuring system of the present invention, an electric heater is arranged in the experimental tube, and the heating temperature of the electric heater can be adjusted according to different evaporation temperatures, so as to realize the measurement in a non-cold state environment, which is closer to the actual operation situation, ensure the accuracy of the measurement data, accurately predict the liquid film thickness, and is beneficial to the study of the falling film evaporation heat transfer mechanism outside the tube and the improvement of its heat transfer efficiency.

[0023] 4. The measuring device and measuring system of the present invention realize the measurement of the circumferential liquid film thickness by the movement of the measuring instrument support along the arc-shaped guide groove, and realize the measurement of the liquid film thickness along the axial direction of the experimental tube by the axial movement of the circumferential positioning support along the axial movement shaft, so as to obtain comprehensive data on the three-dimensional distribution of the liquid film thickness, which is beneficial to the study of the falling film evaporation heat transfer mechanism outside the tube and the improvement of its heat transfer efficiency.

[0024] 5. The measuring device and system of the present invention adopt a non-contact measurement method. The confocal scanning displacement meter measurement will not disturb the liquid film flow field, can realize real-time liquid film thickness measurement, is sensitive and has high precision, and is not affected by the material and color of the test tube.

[0025] 6. In the measuring system of the present invention, flow meters with two ranges are included for measuring the working fluid flow rate, ensuring that the monitored flow rate range can cover the flow rate designed in the experiment, and guaranteeing the reliability and accuracy of the measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The front view of the measuring device for the liquid film thickness of falling film evaporation outside the horizontal tube of the present invention is shown;

[0027] Figure 2 The rear view of the measuring device for the liquid film thickness of falling film evaporation outside the horizontal tube of the present invention is shown;

[0028] Figure 3 The schematic diagram of the circumferential positioning support is shown;

[0029] Figure 4 The schematic diagram of the measuring instrument support is shown;

[0030] Figure 5 The schematic diagram of the support plate is shown;

[0031] Figure 6 The schematic diagram of the measuring system of the present invention is shown;

[0032] Figure 7 The schematic diagram of the high-level liquid storage tank is shown. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] The schematic diagram of a device for measuring the liquid film thickness of falling film evaporation outside a horizontal tube according to the present invention is as follows Figures 1 - 5 shown, which includes a falling film evaporation film-forming unit and a liquid film thickness measuring unit. The falling film evaporation film-forming unit includes a falling film flow main body bracket 10 and a liquid distribution pipe 1, a diversion pipe 2, a diversion plate 4 and an experimental tube 6 installed on the falling film flow main body bracket 10. The liquid distribution pipe 1, the diversion pipe 2, the diversion plate 4 and the experimental tube 6 are arranged horizontally and sequentially in the vertical direction. The liquid distribution pipe 1 is a sleeve structure composed of an inner pipe and an outer pipe. Liquid inlets are respectively arranged at both ends of the inner pipe. A notch for liquid to flow into the space between the inner pipe and the outer pipe is arranged at the top of the inner pipe. A plurality of spray holes are arranged at the bottom of the outer pipe. An electric heater 26 is installed in the experimental tube 6. The liquid film thickness measuring unit includes a measuring main bracket, a circumferential positioning bracket 13, a measuring instrument bracket 17 and a non-contact liquid film thickness measuring instrument 18. The circumferential positioning bracket 13 is slidably installed on the measuring main bracket through an axial moving shaft passing through an axial sliding hole 13c. An arc-shaped guiding groove 13a and an arc-shaped positioning groove 13b concentric with the experimental tube 6 are arranged on the circumferential positioning bracket 13. The measuring instrument bracket 17 is detachably connected to the circumferential positioning bracket 13 at the arc-shaped guiding groove 13a and the arc-shaped positioning groove 13b. The non-contact liquid film thickness measuring instrument 18 is fixedly installed on the measuring instrument bracket 17 through a stud passing through a fixing hole 17c. In this embodiment, the arc-shaped guiding groove 13a and the arc-shaped positioning groove 13b are detachably connected to the circumferential positioning bracket 13 by butterfly-shaped split bolts and nuts. When the liquid film thickness at a certain angle is measured, the butterfly-shaped split bolts and nuts are unscrewed, and the measuring instrument bracket is moved to the next measuring angle along the arc-shaped guiding groove and the arc-shaped positioning groove, and then the butterfly-shaped split bolts and nuts are tightened. The circumferential liquid film thickness measurement is realized by the movement of the measuring instrument bracket 17 along the arc-shaped guiding groove 13a and the arc-shaped positioning groove 13b. The measurement of the liquid film thickness along the axial direction of the experimental tube is realized by the axial movement of the circumferential positioning bracket 13 along the axial moving shaft. In this embodiment, there are three axial moving shafts, namely a first axial moving shaft 14, a second axial moving shaft 15 and a third axial moving shaft 16, and the three axial moving shafts are arranged in a triangle. The first axial moving shaft 14, the second axial moving shaft 15 and the third axial moving shaft 16 penetrate into the axial sliding hole 13c on the circumferential positioning bracket 13 to achieve the effects of fixation and axial sliding, so as to perform axial liquid film measurement.

[0035] In this embodiment, the non-contact liquid film thickness measuring instrument 18 is a confocal scanning displacement meter, and the focus of the confocal scanning displacement meter is located on the center line of the experimental tube 6.

[0036] In this embodiment, for the convenience of installation, positioning marks are provided on the falling film flow main bracket 10. In this embodiment, the scale engraved on the falling film flow main bracket is used as the positioning mark. The diversion pipe 2 is installed on the falling film flow main bracket 10 through the diversion pipe positioning plates 3 at both ends, the diversion plate 4 is installed on the falling film flow main bracket 10 through the diversion plate positioning plates 5 at both ends, and the experimental pipe 6 is installed on the falling film flow main bracket 10 through the experimental pipe positioning plates 7 at both ends. Positioning identifiers corresponding to the positioning marks on the falling film flow main bracket are respectively provided on the diversion pipe positioning plate 3, the diversion plate positioning plate 5, and the experimental pipe positioning plate 7. In this embodiment, a scratch is provided at the center of each of the diversion pipe positioning plate 3, the diversion plate positioning plate 5, and the experimental pipe positioning plate 7 as the positioning identifier, which is flush with the scale on the falling film flow main bracket and is used for positioning and adjusting to a specified height.

[0037] In this embodiment, the measurement main bracket includes support plates 20 on both sides, a bottom plate 23 connecting the support plates on both sides, a plurality of connecting rib plates connecting the support plates on both sides, and an adjusting rib plate 21 in the height direction located between the support plates on both sides. In this embodiment, there are two connecting rib plates, namely a first connecting rib plate 25 and a second connecting rib plate 24. Long adjusting holes are respectively provided on the support plate 20 and the adjusting rib plate 21 in the height direction. Threads are provided at both ends of the axial movement shaft. The axial movement shaft passes through the corresponding long adjusting holes and is installed on the measurement main bracket through nuts screwed to the threads at both ends, so as to adjust the height of the circumferential positioning bracket 13 and ensure that the focus of the confocal scanning displacement meter can be located on the center line of the experimental pipe 6 under different spray pipe diameters and different spray heights. The adjusting rib plate 21 is fixed to the bottom plate 23 through a rib plate fixing plate 22, and the falling film flow main bracket 10 is connected to the support plate 20 through a connection fixing plate 12, thereby connecting the falling film flow main bracket and the measurement main bracket into an integrated body.

[0038] The falling film flow main body bracket 10 is composed of support plates 9 at both ends and a plurality of rib plates 8 connecting the support plates at both ends. A first chute 9b is provided in the middle of each support plate. Second chutes 9a are respectively provided on both sides of the first chute 9b. A groove 9c is provided at the top of the support plate. Both ends of the liquid distribution pipe 1 are respectively placed in the grooves of the two support plates. The diversion pipe 2 is installed on the support plate through a diversion pipe positioning plate 3 detachably connected to the second chute 9a. The diversion plate 4 is installed on the support plate through a diversion plate positioning plate 5 detachably connected to the first chute 9b. The experimental pipe 6 is installed on the support plate through an experimental pipe positioning plate 7 detachably connected to the second chute 9a. The positions of the diversion pipe 2, the diversion plate 4 and the experimental pipe 6 are adjusted by fixing the diversion pipe positioning plate 3 and the experimental pipe positioning plate 7 at different positions in the first chute and fixing the diversion plate positioning plate 5 at different positions in the second chute. In this embodiment, the above detachable connection method preferably uses a butterfly-shaped split bolt and a nut.

[0039] In this embodiment, the distance between the diversion pipe 2 and the liquid distribution pipe 1 is preferably 1 mm - 2 mm to reduce the impact of the liquid outlet holes and make the film flow smoothly.

[0040] In this embodiment, a guide hole 17a corresponding to the arc-shaped guide groove and a positioning hole 17b corresponding to the arc-shaped positioning groove are provided on the measuring instrument bracket 17. The measuring instrument bracket 17 and the circumferential positioning bracket 13 are connected by a guide bolt and nut passing through the corresponding arc-shaped guide groove and arc-shaped guide hole and a positioning bolt and nut passing through the corresponding arc-shaped positioning groove and positioning hole.

[0041] The diversion pipe positioning plate 3, the diversion plate positioning plate 5, and the experimental pipe positioning plate 7 can all change the sizes of the respective positioning holes according to the diameter of the diversion pipe 2, the height of the diversion plate 4, and the pipe diameter of the experimental pipe 6, so as to realize the replacement of experimental pipes with different pipe diameters, diversion pipes with different pipe diameters, and diversion plates with different heights, thereby realizing the change of the spraying height and the pipe diameter of the experimental pipe.

[0042] The schematic diagram of the measuring system of the present invention is as Figures 6 - 7 shown, including a liquid supply device and as Figures 1 - 5The measuring device 101 for the thickness of the falling film outside the horizontal tube shown. The measuring device 101 for the thickness of the falling film outside the horizontal tube is placed on the experimental bench 28 with adjustable level. In this embodiment, the experimental bench can adopt an optical bench to facilitate the adjustment of the level and ensure that the falling direction of the liquid working medium at a given temperature sprayed down by the liquid distribution pipe 1 is vertical. The electric heater 26 inside the experimental tube 6 is connected to the power supply through the power meter 42 and the voltage regulator 27. In this embodiment, the electric heater 26 adopts an electric heating rod. The liquid supply device includes a constant temperature liquid tank 29, a filter 30, a circulation pump 31, a high-level liquid storage tank 32, a small-range flowmeter 33 and a large-range flowmeter 34. The high-level liquid storage tank is divided into a pressure stabilizing chamber 32c, a constant pressure chamber 32b and an overflow chamber 32a that are connected at the upper part. The structure of the high-level liquid storage tank 32 can ensure that the water level height of the working medium is always flush with the height of the overflow plate, thereby stabilizing the working medium pressure. The outlet 29d of the constant temperature liquid tank is connected to the inlet 32d of the corresponding pressure stabilizing chamber of the high-level liquid storage tank through the filter 30, the circulation pump 31 and the first valve 37; a bypass branch is provided between the inlet 29c of the constant temperature liquid tank and the water outlet end of the circulation pump 31, and a bypass valve 36 is installed on the bypass branch. The outlet 32e of the high-level liquid storage tank corresponding to the constant pressure chamber is divided into two paths, one path is connected to the inlet of the second valve 38, and the other path is respectively connected to the inlets of the fourth valve 40 and the fifth valve 41. The outlet 32f of the high-level liquid storage tank corresponding to the overflow chamber is connected to the inlet of the third valve 39; the outlets of the second valve 38 and the third valve 39 are connected to the water return port 29b of the constant temperature liquid tank; the fourth valve 40 and the fifth valve 41 are respectively connected to the inlets of the small-range flowmeter 33 and the large-range flowmeter 34, and the outlets of the small-range flowmeter and the large-range flowmeter are connected in parallel and then divided into two paths, which are respectively connected to the inlets at both ends of the inner tube of the liquid distribution pipe 1. A liquid storage tank 11 is provided at the bottom of the falling film main body bracket, and the liquid storage tank 11 is connected to the inlet 29a of the constant temperature liquid tank. In this embodiment, a drain pipe 19 is installed at the bottom of the liquid storage tank, and the liquid working medium in the liquid storage tank flows into the constant temperature liquid tank 29 through the drain pipe 19. A refrigeration device and an electric auxiliary heating device for maintaining constant temperature are provided in the constant temperature liquid tank to adjust the temperature of the working medium (i.e., the inlet spraying temperature).

[0043] Further, temperature detectors 35 are respectively installed at both ends of the inner tube of the liquid distribution pipe 1. In this embodiment, the temperature detectors preferably adopt armored thermocouples (T-type or K-type armored thermocouples) or platinum resistors.

[0044] In this embodiment, the first valve, the second valve, the third valve, the fourth valve and the fifth valve adopt globe valves.

[0045] The voltage regulator 27 is connected to the power meter 42 and the electric heating rod. The voltage regulator adjusts the input voltage of the electric heating rod to provide stable heat. Armored thermocouples are provided at the two ends of the liquid distribution pipe 1 to ensure that the temperature of the working medium entering the liquid distribution pipe 1 remains constant and meets the experimental requirements.

[0046] The measuring device 101 for the thickness of the falling film evaporation outside the horizontal tube of the present invention needs to be placed in an enthalpy difference laboratory to ensure that the ambient temperature and humidity are constant during the falling film evaporation of the liquid film.

[0047] The change range of the working medium flow rate in the tube is relatively large, and it is difficult to accurately measure it with a single flow meter. In this application, two ranges of flow meters are arranged to measure the working medium flow rate to ensure that the monitored flow range can cover the flow designed in the experiment and ensure the reliability and accuracy of the measurement. When the flow rate is small, the fifth valve 41 is closed and the fourth stop valve 40 is opened, and the small-range flow meter 33 is used to monitor the flow rate of the sprayed liquid. When the flow rate is large, the fifth valve 41 is opened and the fourth valve 40 is closed, and the large-range flow meter 34 is used to monitor the flow rate of the sprayed liquid.

[0048] Further, the electric heating rod is inserted into the experimental tube 6, and both ends are filled with asbestos rope, which plays a role in support and heat insulation and temperature resistance. The gap between the electric heating rod and the experimental tube 6 is filled with thermal conductive silicone grease.

[0049] During the experiment, the circulating working medium first flows into the pressure stabilizing chamber to slow down the fluctuation of the water pressure caused by the fluctuation of the liquid flow. When the height of the working medium in the pressure stabilizing chamber is higher than the height of the partition between the pressure stabilizing chamber and the constant pressure chamber, the working medium flows into the constant pressure chamber. When the height of the working medium is higher than the overflow plate between the constant pressure chamber and the overflow chamber, the excess water enters the overflow chamber and flows back to the constant temperature liquid tank 29 through the outlet of the overflow chamber.

[0050] Further, the circulating working medium is an atmospheric pressure working medium, and according to the needs of the test fluid, it can be pure working media such as water, brine, ethylene glycol, ethanol, or mixed working media.

[0051] Further, all pipelines need to be wrapped with heat insulation cotton for heat insulation.

[0052] During the experiment, the working fluid enters the inner tube from both ends of the liquid distribution pipe, flows out from the notch at the top of the inner tube to the gap between the inner tube and the outer tube, and then uniformly sprays the liquid working fluid at a certain temperature through a row of spray nozzles of the liquid distribution pipe. The liquid working fluid, under the flow stabilizing effect of the flow guiding pipe 2 and the flow guiding plate 4, flows towards the experimental pipe 6, and a uniform and stable thin film is naturally formed on the experimental pipe. The liquid working fluid evaporates under the heat of the electric heating rod. The unevaporated liquid working fluid flows into the liquid storage tank 11. The drain pipe 19 at the bottom of the liquid storage tank 11 returns the liquid working fluid to the constant temperature liquid tank 29. Thus, a cycle is formed in the system. The circumferential liquid film thickness is measured by the movement of the measuring instrument support along the arc-shaped guiding groove, and the axial liquid film thickness along the experimental pipe is measured by the axial movement of the circumferential positioning support along the axial movement shaft, so as to obtain comprehensive data on the three-dimensional distribution of the liquid film thickness.

[0053] The measuring device and measuring system of the present invention can distribute liquid uniformly and stably, and accurately measure the liquid film thickness of the falling film evaporation outside the tube in the three-dimensional distribution of the liquid film thickness in real time, providing a basis for the research on the heat transfer mechanism of falling film evaporation outside the tube and the design of falling film evaporation equipment.

[0054] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A measuring device for the thickness of a falling film outside a horizontal tube, characterized in that, It includes a falling film evaporation film-forming unit and a liquid film thickness measurement unit. The falling film evaporation film-forming unit includes a falling film flow main body bracket and a liquid distribution pipe, a diversion pipe, a diversion plate and an experimental pipe installed on the falling film flow main body bracket. The liquid distribution pipe, the diversion pipe, the diversion plate and the experimental pipe are arranged horizontally and arranged in sequence vertically. The liquid distribution pipe is a casing structure composed of an inner pipe and an outer pipe. Liquid inlets are respectively arranged at both ends of the inner pipe. A notch for liquid to flow into the gap between the inner pipe and the outer pipe is arranged at the top of the inner pipe. A plurality of spray holes are arranged at the bottom of the outer pipe. An electric heater is installed in the experimental pipe. The liquid film thickness measurement unit includes a measurement main bracket, a circumferential positioning bracket, a measuring instrument bracket and a non-contact liquid film thickness measuring instrument. The circumferential positioning bracket is slidably installed on the measurement main bracket through an axial moving shaft. An arc-shaped guiding groove and an arc-shaped positioning groove concentric with the experimental pipe are arranged on the circumferential positioning bracket. The measuring instrument bracket is detachably connected to the circumferential positioning bracket at the arc-shaped guiding groove and the arc-shaped positioning groove. The non-contact liquid film thickness measuring instrument is fixedly installed on the measuring instrument bracket. The circumferential liquid film thickness is measured by the movement of the measuring instrument bracket along the arc-shaped guiding groove and the arc-shaped positioning groove. The liquid film thickness along the axial direction of the experimental pipe is measured by the axial movement of the circumferential positioning bracket along the axial moving shaft. The working medium enters the inner pipe from both ends of the liquid distribution pipe, flows out from the notch at the top of the inner pipe to the gap between the inner pipe and the outer pipe, and then the liquid working medium is evenly sprayed down through a row of spray openings of the liquid distribution pipe. The liquid working medium flows to the experimental pipe through the flow stabilizing action of the diversion pipe and the diversion plate, and a uniform and stable thin film is naturally formed on the experimental pipe. The liquid working medium evaporates under the heat of the electric heater.

2. The measuring device for the thickness of the falling film outside the horizontal tube according to claim 1, characterized in that, Positioning marks are arranged on the falling film flow main body bracket. The diversion pipe is installed on the falling film flow main body bracket through diversion pipe positioning plates at both ends. The diversion plate is installed on the falling film flow main body bracket through diversion plate positioning plates at both ends. The experimental pipe is installed on the falling film flow main body bracket through experimental pipe positioning plates at both ends. Positioning identifiers corresponding to the positioning marks on the falling film flow main body bracket are respectively arranged on the diversion pipe positioning plates, the diversion plate positioning plates and the experimental pipe positioning plates.

3. The measuring device for the thickness of the falling film outside the horizontal tube according to claim 1 or 2, characterized in that, The measurement main bracket includes support plates on both sides, a bottom plate connecting the support plates on both sides, a plurality of connecting rib plates connecting the support plates on both sides and an adjusting rib plate in the height direction located between the support plates on both sides. Long adjusting holes arranged in the height direction are respectively arranged on the support plates and the adjusting rib plate in the height direction. Threads are respectively arranged at both ends of the axial moving shaft. The axial moving shaft passes through the corresponding long adjusting holes and is installed on the measurement main bracket through nuts connected to the threads at both ends. The adjusting rib plate is fixed to the bottom plate through a rib plate fixing plate. The falling film flow main body bracket is connected to the support plate through a connection fixing plate.

4. The device for measuring the thickness of the falling liquid film outside the horizontal tube according to claim 3, characterized in that, The falling film flow main bracket is composed of support plates at both ends and a plurality of rib plates connecting the support plates at both ends. A first chute is provided in the middle of each support plate. Second chutes are respectively provided on both sides of the first chute. A groove is provided at the top of the support plate. Both ends of the liquid distribution pipe are respectively placed in the grooves of the two support plates. The diversion pipe is installed on the support plate through a diversion pipe positioning plate detachably connected to the second chute; the diversion plate is installed on the support plate through a diversion plate positioning plate detachably connected to the first chute, and the experimental pipe is installed on the support plate through an experimental pipe positioning plate detachably connected to the first chute. The positions of the diversion pipe, the diversion plate and the experimental pipe are adjusted by fixing the diversion pipe positioning plate and the experimental pipe positioning plate at different positions in the first chute and fixing the diversion plate positioning plate at different positions in the second chute.

5. The measuring device for the thickness of the falling film outside the horizontal tube according to claim 3, wherein There are three axial movement shafts arranged in a triangle; the distance between the diversion pipe and the liquid distribution pipe is 1 mm - 2 mm.

6. The measuring device for the thickness of the falling film outside the horizontal tube according to claim 3, characterized in that The non-contact liquid film thickness measuring instrument is a confocal scanning displacement meter, and the focus of the confocal scanning displacement meter is located on the center line of the experimental pipe.

7. The measuring device for the thickness of the falling film outside the horizontal tube according to claim 3, characterized in that, Guide holes corresponding to the arc-shaped guide grooves and positioning holes corresponding to the arc-shaped positioning grooves are provided on the measuring instrument bracket. The measuring instrument bracket is connected to the circumferential positioning bracket through guide bolts and nuts passing through the corresponding arc-shaped guide grooves and guide holes and positioning bolts and nuts passing through the corresponding arc-shaped positioning grooves and positioning holes.

8. A measurement system comprising the measurement device for measuring the thickness of the falling film outside the horizontal tube according to any one of claims 1-7, characterized in that, It includes a liquid supply device and the horizontal tube external falling film evaporation liquid film thickness measuring device; the horizontal tube external falling film evaporation liquid film thickness measuring device is placed on an experimental table with adjustable level; the electric heater is connected to the power supply through a power meter and a voltage regulator; the liquid supply device includes a constant temperature liquid tank, a filter, a circulation pump, a high-level liquid storage tank, a small-range flowmeter and a large-range flowmeter; the high-level liquid storage tank is divided into a voltage stabilizing chamber, a constant pressure chamber and an overflow chamber that are connected in the upper part; the outlet of the constant temperature liquid tank is connected to the inlet of the corresponding voltage stabilizing chamber of the high-level liquid storage tank through the filter, the circulation pump and the first valve; a bypass branch is provided between the constant temperature liquid tank and the water outlet end of the circulation pump, and a bypass valve is installed on the bypass branch; the outlet of the high-level liquid storage tank corresponding to the constant pressure chamber is divided into two paths, one path is connected to the inlet of the second valve, and the other path is respectively connected to the inlets of the fourth valve and the fifth valve; the outlet of the high-level liquid storage tank corresponding to the overflow chamber is connected to the inlet of the third valve; the outlets of the second valve and the third valve are connected to the water return port of the constant temperature liquid tank; the fourth valve and the fifth valve are respectively connected to the inlets of the small-range flowmeter and the large-range flowmeter, and the outlets of the small-range flowmeter and the large-range flowmeter are connected in parallel and then divided into two paths, which are respectively connected to the two ends of the inner pipe inlet of the liquid distribution pipe; a liquid storage tank is provided at the bottom of the falling film main bracket, and the liquid storage tank is connected to the constant temperature liquid tank; a refrigeration device and an electric auxiliary heating device for maintaining constant temperature are provided in the constant temperature liquid tank.

9. The measurement system according to claim 8, wherein Temperature detectors are respectively installed at both ends of the inner pipe of the liquid distribution pipe.

10. The measurement system according to claim 8, characterized in that, The first valve, the second valve, the third valve, the fourth valve and the fifth valve all adopt globe valves.

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