Device for measuring thickness of falling film evaporation liquid film outside horizontal pipe and measuring system formed by same

Abstract

The invention discloses a horizontal pipe external falling film evaporation liquid film thickness measuring device and a measuring system formed by the same, and aims to provide a device and a system which can uniformly and stably distribute liquid and can measure three-dimensional distribution of liquid film thickness. The device comprises a falling film evaporation film forming unit and a liquid film thickness measuring unit. The falling film evaporation film-forming unit comprises a falling film flow main body bracket, and a liquid distribution pipe, a flow guide pipe, a flow guide plate and an experiment pipe which are arranged on the falling film flow main body bracket. The liquid film thickness measuring unit comprises a measuring main support, a circumferential positioning support, a measuring instrument support and a non-contact type liquid film thickness measuring instrument. The circumferential positioning support is installed on the measuring main support in a sliding mode through an axial moving shaft. The measuring instrument support moves along the arc-shaped guide groove and the arc-shaped positioning groove to measure the thickness of the liquid film in the circumferential direction, and the circumferential positioning support moves in the axial direction of the axial moving shaft to measure the thickness of the liquid film in the axial direction of the experimental tube. According to the invention, uniform and stable liquid distribution and liquid film thickness three-dimensional measurement are realized.

Description

Technical Field

[0001] The invention relates to the field of measurement technology, and more specifically 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 important fluid properties and key factors for the normal and efficient operation of the horizontal tube falling film evaporator. Accurate prediction of the thickness of the liquid film and research on the flow characteristics of the liquid film during the heating process can also effectively prevent the local wall drying caused by external factors of the heat exchange tube, which leads to a decrease in heat transfer efficiency. Therefore, studying the thickness of the liquid film is of great significance for further revealing the heat transfer mechanism of falling film evaporation outside the tube and improving its heat transfer efficiency.

[0003] During the flow of liquid film, the thickness of the liquid film is usually very small, so there are many difficulties in experimentally observing the thickness of the liquid film. Based on this problem, researchers have made a lot of efforts and proposed many methods for measuring the thickness of the liquid film, which can be roughly divided into two categories: contact measurement method and non-contact measurement method. The contact measurement method is inaccurate due to interference with the flow field of the liquid film. Among the non-contact measurement methods, the methods currently used by scholars are laser-induced fluorescence optics and digital image processing. The laser-induced fluorescence optics method has high cost, complex equipment, and difficult operation. It is also suitable for the case where the two-phase interface fluctuation is relatively gentle. If the surface fluctuation is violent or the front of the surface wave is relatively steep, the light may be refracted multiple times, resulting in the receiving end not being able to detect the light or the measurement accuracy is low. In addition, the laser-induced fluorescence optics method cannot perform convenient and fast fixed-point measurement of the three-dimensional distribution of the liquid film thickness. The digital image processing method is realized by a high-speed camera, which can only shoot the cross-sectional liquid film of the assumed circumferentially uniformly distributed sheet flow, and cannot perform three-dimensional fixed-point observation of the three-dimensionally unevenly distributed columnar flow, so it cannot accurately observe the flow of the liquid film. In the actual application of horizontal tube falling film evaporation, the flow pattern of the liquid film is mainly columnar flow. The distribution of the columnar flow liquid film in the circumferential direction and axial direction of the tube shows obvious unevenness. If the existing measurement method is used to measure the liquid film thickness in the circumferential direction of the tube, and the measured liquid film thickness distribution is used to reflect the falling film evaporation liquid film thickness and heat transfer characteristics, it will cause great deviations in the falling film evaporation design.

[0004] In addition, for the convenience of measurement, scholars have carried out cold liquid film flow research under the premise of ignoring evaporation heat transfer, that is, using heat exchange tubes for liquid film falling film evaporation, and scholars have measured pure working fluids. 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 field of refrigeration, non-azeotropic mixed working fluids have begun to be used in falling film evaporation equipment as a refrigerant alternative. In actual situations, the thickness of the evaporated 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. Therefore, the measurement of the thickness of the falling film evaporation liquid film at a specific temperature is necessary for the design of falling film evaporation equipment.

[0005] In addition, the heat transfer performance of the horizontal tube falling film evaporation is mainly affected by the liquid distribution and flow form. Uneven liquid distribution will cause disordered fluctuations in the liquid film in the tube length direction, which makes the measurement error of the liquid film fluctuation characteristics very large and even produces erroneous data, and also causes a very large error in the measurement value of the liquid film thickness. In the prior art, the liquid is directly taken out of the constant temperature liquid tank and flows into the diversion pipe. The liquid flow is highly volatile, which is bound to cause uneven liquid spraying in the liquid distribution pipe and disordered distribution of the liquid film in the heat exchange tube. Therefore, it is necessary to design a liquid film thickness measurement device and system for falling film evaporation outside the tube that can evenly and stably distribute liquid and can accurately measure the three-dimensional distribution of liquid film thickness in real time under a certain temperature environment. Summary of the invention

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

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

[0008] The technical solution adopted to achieve the purpose of the present invention is: A device for measuring the thickness of a falling film evaporation liquid film outside a horizontal tube, comprising a falling film evaporation film forming unit and a liquid film thickness measuring unit, wherein the falling film evaporation film forming unit comprises a falling film flow main body support and a liquid distribution pipe, a guide pipe, a guide plate and an experimental tube installed on the falling film flow main body support, wherein the liquid distribution pipe, the guide pipe, the guide plate and the experimental tube are arranged in the horizontal direction and arranged in sequence in the vertical direction; the liquid distribution pipe is a sleeve structure composed of an inner tube and an outer tube, wherein both ends of the inner tube are respectively provided with liquid inlets, a notch for liquid to flow into the inner tube and the outer tube is provided at the top of the inner tube, and a plurality of spray holes are provided at the bottom of the outer tube; an electric heater is installed in the experimental tube; the liquid film thickness measuring unit The 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; the circumferential positioning bracket is provided with an arc guide groove and an arc positioning groove concentric with the experimental tube, the measuring instrument bracket is detachably connected to the circumferential positioning bracket at the arc guide groove and the arc positioning groove, and 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 guide groove and the arc positioning groove, and the liquid film thickness along the axial direction of the experimental tube is measured by axially moving the circumferential positioning bracket along the axial moving shaft.

[0009] Positioning marks are provided on the falling film flow main body support; the guide tube is installed on the falling film flow main body support through the guide tube positioning plates at both ends, the guide plate is installed on the falling film flow main body support through the guide plate positioning plates at both ends, and the experimental tube is installed on the falling film flow main body support through the experimental tube positioning plates at both ends, and the guide tube positioning plate, the guide plate positioning plate and the experimental tube positioning plate are respectively provided with positioning marks corresponding to the positioning marks on the falling film flow main body support.

[0010] The measuring main bracket includes support plates on both sides, a bottom plate connecting the support plates on both sides, a plurality of connecting ribs connecting the support plates on both sides and an adjusting rib along the height direction located between the support plates on both sides, the support plates and the adjusting ribs in the height direction are respectively provided with corresponding long adjusting holes arranged in the height direction, both ends of the axial movable shaft are respectively provided with threads, the axial movable shaft passes through the corresponding long adjusting holes and is installed on the measuring main bracket through nuts threadedly connected to both ends; the adjusting ribs are fixed to the bottom plate through a rib fixing plate, and the falling film flow main bracket is connected to the support plate through a connecting fixing plate.

[0011] The falling film flow main body support is composed of support plates at both ends and a plurality of ribs connecting the support plates at both ends, a first slide groove is arranged in the middle of each support plate, second slide grooves are arranged on both sides of the first slide groove, a groove is arranged on the top of the support plate, the two ends of the liquid distribution pipe are respectively placed in the grooves of the two support plates, the guide tube is installed on the support plate through a guide tube positioning plate detachably connected to the second slide groove; the guide plate is installed on the support plate through a guide plate positioning plate detachably connected to the first slide groove, and the experimental tube is installed on the support plate through an experimental tube positioning plate detachably connected to the first slide groove, and the positions of the guide tube, the guide plate and the experimental tube are adjusted by fixing the guide tube positioning plate and the experimental tube positioning plate at different positions in the first slide groove and fixing the guide plate positioning plate at different positions in the second slide groove.

[0012] There are three axial moving shafts arranged in a triangle; the distance between the guide pipe and the liquid distribution pipe is 1mm-2mm.

[0013] 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 tube.

[0014] The measuring instrument bracket is provided with a guide hole corresponding to the arc-shaped guide groove and a positioning hole corresponding to the arc-shaped positioning groove. The measuring instrument bracket is connected to the circumferential positioning bracket by a guide bolt and a nut passing through the corresponding arc-shaped guide groove and guide hole, and a positioning bolt and a nut passing through the corresponding arc-shaped positioning groove and positioning hole.

[0015] A measuring system containing the device for measuring the thickness of a liquid film of a falling film evaporation outside a horizontal tube, comprising a liquid supply device and the device for measuring the thickness of a liquid film of a falling film evaporation outside a horizontal tube; the device for measuring the thickness of a liquid film of a falling film evaporation outside a horizontal tube is placed on a laboratory table with adjustable horizontality; the electric heater is connected to a power source through a power meter and a voltage regulator; the liquid supply device comprises 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 bin, a constant pressure bin and an overflow bin which are connected at the top; the outlet of the constant temperature liquid tank is connected to the inlet of the corresponding pressure-stabilizing bin 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 of the circulation pump, and the bypass branch A bypass valve is installed; the outlet of the high-level liquid storage tank corresponding to the constant pressure bin is divided into two paths, one path is connected to the inlet of the second valve, and the other path is connected to the inlet of the fourth valve and the fifth valve respectively; the outlet of the overflow bin corresponding to the high-level liquid storage tank is connected to the inlet of the third valve; the outlets of the second valve and the third valve are connected to the return water port of the constant temperature liquid tank; the fourth valve and the fifth valve are respectively connected to the inlet 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 divided into two paths, which are respectively connected to the inlet at both ends of the inner tube of the liquid distribution pipe; a liquid storage tank is provided 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 a constant temperature are provided in the constant temperature liquid tank.

[0016] Temperature measuring devices are respectively installed at both ends of the inner tube of the liquid distribution pipe.

[0017] The first valve, the second valve, the third valve, the fourth valve and the fifth valve are all stop valves.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The measuring device and system of the present invention adopts a liquid distribution pipe of a sleeve structure composed of an inner pipe and an outer pipe, and the working fluid enters from both ends of the inner pipe of the liquid distribution pipe, which effectively solves the problem of biased flow caused by uneven pressure in the axial direction, uneven flow distribution and poor stability, and the liquid distribution is more uniform and stable. At the same time, the real-time three-dimensional measurement of liquid film thickness is realized through structural design, which is conducive to the study of the heat transfer mechanism of falling film evaporation outside the tube and provides a basis for the design of falling film evaporation equipment.

[0019] 2. The measuring device and measuring system of the present invention allow the working fluid to enter from both ends of the inner tube of the liquid distribution tube, flow out from the notch on the top of the inner tube to the gap between the inner tube and the outer tube, and then flow out from the bottom of the outer tube through a row of spray holes, eventually forming a uniform and stable film naturally on the experimental tube, effectively reducing the impact of the spraying method on the liquid flow and improving the uniformity and stability of the liquid distribution.

[0020] 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 to achieve measurement in a non-cold environment, which is closer to the actual operation situation, ensures the accuracy of the measurement data, and can accurately predict the liquid film thickness, which is conducive to studying the heat transfer mechanism of falling film evaporation outside the tube and improving its heat transfer efficiency.

[0021] 4. The measuring device and measuring system of the present invention realize the measurement of the circumferential liquid film thickness by moving the measuring instrument bracket along the arc guide groove, and realize the measurement of the liquid film thickness along the axial direction of the experimental tube by axial movement of the circumferential positioning bracket along the axial moving axis, thereby obtaining comprehensive data on the three-dimensional distribution of the liquid film thickness, which is beneficial to the study of the heat transfer mechanism of falling film evaporation outside the tube and improving its heat transfer efficiency.

[0022] 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, and can realize real-time liquid film thickness measurement. The measurement is sensitive and accurate, and is not affected by the material and color of the test tube.

[0023] 6. The measurement system of the present invention includes a flow meter with two measuring ranges for measuring the working fluid flow rate, ensuring that the monitored flow range can cover the flow rate designed for the experiment, thereby ensuring the reliability and accuracy of the measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The figure shows a front view of the device for measuring the thickness of the falling film evaporation liquid film outside the horizontal tube of the present invention; Figure 2 The figure shows a rear view of the device for measuring the thickness of the falling film evaporation liquid film outside the horizontal tube of the present invention; Figure 3 Shown is a schematic diagram of a circumferential positioning bracket; Figure 4 Shown is a schematic diagram of a measuring instrument bracket; Figure 5 Shown is a schematic diagram of the support plate; Figure 6 Shown is a schematic diagram of a measurement system of the present invention; Figure 7 Shown is a schematic diagram of the high-level fluid storage tank. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] A schematic diagram of a device for measuring the thickness of a falling film evaporation liquid film outside a horizontal tube according to the present invention is shown in FIG. Figure 1-Figure 5As shown, it 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 support 10 and a liquid distribution pipe 1, a guide pipe 2, a guide plate 4 and an experimental tube 6 installed on the falling film flow main body support 10. The liquid distribution pipe 1, the guide pipe 2, the guide plate 4 and the experimental tube 6 are arranged in the horizontal direction and arranged in sequence in the vertical direction. The liquid distribution pipe 1 is a sleeve structure composed of an inner tube and an outer tube. The two ends of the inner tube are respectively provided with liquid inlets. The top of the inner tube is provided with a notch for liquid to flow into the inner tube and the outer tube, and the bottom of the outer tube is provided with a plurality of spray holes. An electric heater 26 is installed in the experimental tube 6. The liquid film thickness measuring unit includes a measuring main support, a circumferential positioning support 13, a measuring instrument support 17 and a non-contact liquid film thickness measuring instrument 18. The circumferential positioning support 13 is slidably installed on the measuring main support through an axial moving shaft passing through the axial sliding hole 13c. The circumferential positioning bracket 13 is provided with an arc guide groove 13a and an arc positioning groove 13b which are concentric with the experimental tube 6. The measuring instrument bracket 17 is detachably connected to the circumferential positioning bracket 13 at the arc guide groove 13a and the arc positioning groove 13b. The non-contact liquid film thickness measuring instrument 18 is fixedly installed on the measuring instrument bracket 17 by a stud passing through the fixing hole 17c. In this embodiment, the arc guide groove 13a and the arc positioning groove 13b are detachably connected to the circumferential positioning bracket 13 by butterfly-shaped clevis bolts and nuts. After the liquid film thickness measurement at a certain angle is completed, the butterfly-shaped clevis bolts and nuts are unscrewed, the measuring instrument bracket is moved along the arc guide groove and the arc positioning groove to the next measuring angle, and then the butterfly-shaped clevis bolts and nuts are tightened. The circumferential liquid film thickness is measured by the movement of the measuring instrument bracket 17 along the arc guide groove 13a and the arc positioning groove 13b. The axial movement of the circumferential positioning bracket 13 along the axial moving shaft realizes the measurement of the liquid film thickness along the axial direction of the test tube. 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 the axial sliding hole 13c on the circumferential positioning bracket 13 to achieve the effect of fixing and axial sliding, thereby performing axial liquid film measurement.

[0027] 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.

[0028] In this embodiment, in order to facilitate installation, a positioning mark is provided on the falling film flow main body support 10. In this embodiment, the scale engraved on the falling film flow main body support is used as a positioning mark. The guide tube 2 is installed on the falling film flow main body support 10 through the guide tube positioning plates 3 at both ends, the guide plate 4 is installed on the falling film flow main body support 10 through the guide plate positioning plates 5 at both ends, and the experimental tube 6 is installed on the falling film flow main body support 10 through the experimental tube positioning plates 7 at both ends. The guide tube positioning plates 3, the guide plate positioning plates 5 and the experimental tube positioning plates 7 are respectively provided with positioning marks corresponding to the positioning marks on the falling film flow main body support. In this embodiment, there is a scratch at the center of the guide tube positioning plates 3, the guide plate positioning plates 5 and the experimental tube positioning plates 7 as a positioning mark, which is flush with the scale on the falling film flow main body support and is used for positioning and adjusting the specified height.

[0029] In this embodiment, the measurement main support includes support plates 20 on both sides, a bottom plate 23 connecting the support plates on both sides, a plurality of connecting ribs connecting the support plates on both sides, and an adjustment rib 21 along the height direction located between the support plates on both sides. In this embodiment, there are two connecting ribs, namely, a first connecting rib 25 and a second connecting rib 24. The support plate 20 and the adjustment rib 21 in the height direction are respectively provided with corresponding long adjustment holes arranged in the height direction, and threads are respectively provided at both ends of the axial movable shaft. The axial movable shaft passes through the corresponding long adjustment holes and is installed on the measurement main support through nuts connected to the threads at both ends, and the height of the circumferential positioning support 13 can be adjusted to ensure that the focus of the confocal scanning displacement meter can be located on the center line of the experimental tube 6 under different spray pipe diameters and different spray heights. The adjustment rib 21 is fixed to the bottom plate 23 through a rib fixing plate 22, and the falling film flow main support 10 is connected to the support plate 20 through a connecting fixing plate 12, so that the falling film flow main support and the measurement main support are connected into one.

[0030] The falling film flow main body support 10 is composed of support plates 9 at both ends and a plurality of ribs 8 connecting the support plates at both ends. A first chute 9b is provided in the middle of each support plate, and second chute 9a is provided on both sides of the first chute 9b, and a groove 9c is provided on the top of the support plate. The two ends of the liquid distribution pipe 1 are respectively placed in the grooves of the two support plates, and the guide tube 2 is installed on the support plate through the guide tube positioning plate 3 detachably connected to the second chute 9a. The guide plate 4 is installed on the support plate through the guide plate positioning plate 5 detachably connected to the first chute 9b. The experimental tube 6 is installed on the support plate through the experimental tube positioning plate 7 detachably connected to the second chute 9a. The positions of the guide tube 2, the guide plate 4 and the experimental tube 6 are adjusted by fixing the guide tube positioning plate 3 and the experimental tube positioning plate 7 at different positions in the first chute and fixing the guide plate positioning plate 5 at different positions in the second chute. In this embodiment, the above-mentioned detachable connection method preferably adopts butterfly-type clevis bolts and nuts.

[0031] In this embodiment, the distance between the guide tube 2 and the liquid distribution tube 1 is preferably 1 mm-2 mm, so as to reduce the impact of the liquid outlet hole and make the film flow smoothly.

[0032] In this embodiment, the measuring instrument bracket 17 is provided with a guide hole 17a corresponding to the arc-shaped guide groove and a positioning hole 17b corresponding to the arc-shaped positioning groove. The measuring instrument bracket 17 is connected to the circumferential positioning bracket 13 by means of guide bolts and nuts passing through the corresponding arc-shaped guide grooves and arc-shaped guide holes, and positioning bolts and nuts passing through the corresponding arc-shaped positioning grooves and positioning holes.

[0033] The guide tube positioning plate 3, the guide plate positioning plate 5, and the experimental tube positioning plate 7 can change the size of each positioning hole according to the diameter of the guide tube 2, the height of the guide plate 4, and the diameter of the experimental tube 6, so as to realize the replacement of experimental tubes of different diameters, guide tubes of different diameters, and guide plates of different heights, thereby realizing the change of the spray height and the diameter of the experimental tube.

[0034] The schematic diagram of the measurement system of the present invention is as follows Figure 6-Figure 7 As shown, including a liquid supply device and Figure 1-Figure 5The device 101 for measuring the thickness of the liquid film of the falling film evaporation outside the horizontal tube is shown. The device 101 for measuring the thickness of the liquid film of the falling film evaporation outside the horizontal tube is placed on a test bench 28 with adjustable level. The test bench in this embodiment can adopt an optical platform to adjust the level and ensure that the liquid working medium of a given temperature sprayed from the liquid distribution pipe 1 falls vertically. The electric heater 26 inside the test 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 tank 32c, a constant pressure tank 32b and an overflow tank 32a connected to each other at the upper part. The structure of the high-level liquid storage tank 32 can ensure that the water level 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 pressure stabilizing tank corresponding to the high-level liquid storage tank through the filter 30, the circulating 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 of the circulating pump 31, and a bypass valve 36 is installed on the bypass branch. The outlet 32e of the constant pressure tank corresponding to the high-level liquid storage tank is divided into two paths, one of which is connected to the inlet of the second valve 38, and the other is connected to the inlet of the fourth valve 40 and the fifth valve 41 respectively. The outlet 32f of the overflow tank corresponding to the high-level liquid storage tank 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 return water port 29b of the constant temperature liquid tank; the fourth valve 40 and the fifth valve 41 are connected to the inlet of the small-range flowmeter 33 and the large-range flowmeter 34 respectively, and the outlets of the small-range flowmeter and the large-range flowmeter are connected in parallel and divided into two paths, which are respectively connected to the inlet of the inner tube of the liquid distribution pipe 1 at both ends. A liquid storage tank 11 is provided at the bottom of the falling film main support, 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. The constant temperature liquid tank is provided with a refrigeration device for maintaining a constant temperature and an electric auxiliary heating device for adjusting the working medium temperature (i.e., the inlet spray temperature).

[0035] Furthermore, temperature detectors 35 are installed at both ends of the inner tube of the liquid distribution pipe 1. In this embodiment, the temperature detector is preferably an armored thermocouple (T-type or K-type armored thermocouple) or a platinum resistor.

[0036] In this embodiment, the first valve, the second valve, the third valve, the fourth valve and the fifth valve are stop valves.

[0037] 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 set at the inlets at both ends of the liquid distribution pipe 1 to ensure that the temperature of the working fluid entering the liquid distribution pipe 1 is always kept constant and meets the experimental requirements.

[0038] The device 101 for measuring the thickness of the liquid film during falling film evaporation outside a 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 falling film evaporation of the liquid film.

[0039] The flow rate of the working fluid in the pipe varies greatly, and it is difficult to measure accurately with one flow meter. This application arranges two flow meters with different ranges to measure the flow rate of the working fluid, ensuring that the monitored flow range can cover the flow rate designed for the experiment, and ensuring the reliability and accuracy of the measurement. When the flow rate is small, close the fifth valve 41, open the fourth stop valve 40, and use the small-range flow meter 33 to monitor the flow rate of the spray liquid. When the flow rate is large, open the fifth valve 41, close the fourth valve 40, and use the large-range flow meter 34 to monitor the flow rate of the spray liquid.

[0040] Furthermore, the electric heating rod is inserted into the experimental tube 6, and both ends are filled with asbestos ropes, which play a supporting and heat-insulating role. The gap between the electric heating rod and the experimental tube 6 is filled with thermal conductive silicone grease.

[0041] During the experiment, the circulating working fluid first flows into the pressure stabilizing bin to mitigate the fluctuation of water pressure caused by the fluctuation of liquid flow. When the height of the working fluid in the pressure stabilizing bin is higher than the height of the partition between the pressure stabilizing bin and the constant pressure bin, the working fluid flows into the constant pressure bin. When the height of the working fluid is higher than the overflow plate between the constant pressure bin and the overflow bin, excess water enters the overflow bin and flows back to the constant temperature liquid tank 29 through the outlet of the overflow bin.

[0042] Furthermore, the circulating working fluid is a normal pressure working fluid, and can be a pure working fluid or a mixed working fluid such as water, salt water, ethylene glycol, ethanol, etc. according to the needs of the test fluid.

[0043] Furthermore, all pipelines need to be wrapped with thermal insulation cotton for heat insulation.

[0044] During the experiment, the working medium 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 evenly sprays the liquid working medium of a certain temperature through a row of spray ports of the liquid distribution pipe. The liquid working medium flows to the experimental tube 6 through the stabilizing effect of the guide tube 2 and the guide plate 4, and naturally forms a uniform and stable film on the experimental tube. The liquid working medium evaporates under the heat of the electric heating rod. The liquid working medium that has not been completely evaporated flows into the liquid storage tank 11. The drain pipe 19 at the bottom of the liquid storage tank 11 returns the liquid working medium to the constant temperature liquid tank 29. At this point, the system forms a cycle. The circumferential liquid film thickness is measured by moving the measuring instrument bracket along the arc guide groove, and the axial liquid film thickness along the axial direction of the experimental tube is measured by the axial movement of the circumferential positioning bracket along the axial moving axis, thereby obtaining comprehensive data on the three-dimensional distribution of the liquid film thickness.

[0045] The measuring device and measuring system of the present invention can distribute liquid evenly and stably, and measure the three-dimensional distribution of liquid film thickness of the outer tube falling film evaporation liquid film thickness in real time and accurately, providing a basis for the study of the heat transfer mechanism of the outer tube falling film evaporation and the design of the falling film evaporation equipment.

[0046] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A device for measuring the thickness of falling film evaporation liquid film outside a horizontal tube, characterized in that: It 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 support and a liquid distribution pipe, a guide pipe, a guide plate and an experimental tube installed on the falling film flow main body support. The liquid distribution pipe, the guide pipe, the guide plate and the experimental tube are arranged in the horizontal direction and arranged in sequence in the vertical direction. The liquid distribution pipe is a sleeve structure composed of an inner tube and an outer tube. Both ends of the inner tube are respectively provided with liquid inlets. The top of the inner tube is provided with a notch for liquid to flow into the inner tube and the outer tube, and the bottom of the outer tube is provided with a plurality of spray holes. An electric heater is installed in the experimental tube. The liquid film thickness measuring unit includes a measuring main support, A circumferential positioning bracket, a measuring instrument bracket and a non-contact liquid film thickness measuring instrument, wherein the circumferential positioning bracket is slidably mounted on the measuring main bracket via an axial moving shaft; the circumferential positioning bracket is provided with an arc guide groove and an arc positioning groove concentric with the experimental tube, the measuring instrument bracket is detachably connected to the circumferential positioning bracket at the arc guide groove and the arc positioning groove, and the non-contact liquid film thickness measuring instrument is fixedly mounted on the measuring instrument bracket; the circumferential liquid film thickness is measured by moving the measuring instrument bracket along the arc guide groove and the arc positioning groove, and the liquid film thickness along the axial direction of the experimental tube is measured by axially moving the circumferential positioning bracket along the axial moving shaft.

2. The device for measuring the thickness of falling film evaporation liquid film outside a horizontal tube according to claim 1 is characterized in that: Positioning marks are provided on the falling film flow main body support; the guide tube is installed on the falling film flow main body support through the guide tube positioning plates at both ends, the guide plate is installed on the falling film flow main body support through the guide plate positioning plates at both ends, and the experimental tube is installed on the falling film flow main body support through the experimental tube positioning plates at both ends, and the guide tube positioning plate, the guide plate positioning plate and the experimental tube positioning plate are respectively provided with positioning marks corresponding to the positioning marks on the falling film flow main body support.

3. The device for measuring the thickness of falling film evaporation liquid film outside a horizontal tube according to claim 1 or 2, characterized in that: The measuring main bracket includes support plates on both sides, a bottom plate connecting the support plates on both sides, a plurality of connecting ribs connecting the support plates on both sides and an adjusting rib along the height direction located between the support plates on both sides, the support plates and the adjusting ribs in the height direction are respectively provided with corresponding long adjusting holes arranged in the height direction, both ends of the axial movable shaft are respectively provided with threads, the axial movable shaft passes through the corresponding long adjusting holes and is installed on the measuring main bracket through nuts threadedly connected to both ends; the adjusting ribs are fixed to the bottom plate through a rib fixing plate, and the falling film flow main bracket is connected to the support plate through a connecting fixing plate.

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

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

6. The device for measuring the thickness of falling film evaporation liquid film outside a 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 tube.

7. The device for measuring the thickness of falling film evaporation liquid film outside a horizontal tube according to claim 3, characterized in that: The measuring instrument bracket is provided with a guide hole corresponding to the arc-shaped guide groove and a positioning hole corresponding to the arc-shaped positioning groove. The measuring instrument bracket is connected to the circumferential positioning bracket by a guide bolt and a nut passing through the corresponding arc-shaped guide groove and guide hole, and a positioning bolt and a nut passing through the corresponding arc-shaped positioning groove and positioning hole.

8. A measuring system comprising the device for measuring the thickness of a falling film evaporation liquid film outside a horizontal tube according to any one of claims 1 to 7, characterized in that: It comprises a liquid supply device and the aforementioned device for measuring the thickness of a liquid film of falling film evaporation outside a horizontal tube; the aforementioned device for measuring the thickness of a liquid film of falling film evaporation outside a horizontal tube is placed on a laboratory table with adjustable level; the aforementioned electric heater is connected to a power source via a power meter and a voltage regulator; the aforementioned liquid supply device comprises a constant temperature liquid tank, a filter, a circulation pump, a high-level liquid storage tank, a small-range flow meter and a large-range flow meter; the interior of the aforementioned high-level liquid storage tank is divided into a pressure stabilizing tank, a constant pressure tank and an overflow tank which are connected at the top; the outlet of the aforementioned constant temperature liquid tank is connected to the inlet of the corresponding pressure stabilizing tank of the aforementioned high-level liquid storage tank via the aforementioned filter, the circulation pump and the first valve; a bypass branch is provided between the aforementioned constant temperature liquid tank and the water outlet of the aforementioned circulation pump, and a bypass valve is installed on the aforementioned bypass branch; the aforementioned high-level liquid storage tank The outlet of the corresponding constant pressure bin is divided into two routes, one route is connected to the inlet of the second valve, and the other route is connected to the inlet of the fourth valve and the fifth valve respectively; the outlet of the overflow bin corresponding to the high-level liquid storage tank is connected to the inlet of the third valve; the outlets of the second valve and the third valve are connected to the return water port of the constant temperature liquid tank; the fourth valve and the fifth valve are respectively connected to the inlet 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 divided into two routes, which are respectively connected to the inlets at both ends of the inner tube of the liquid distribution pipe; a liquid storage tank is provided 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 a constant temperature are provided in the constant temperature liquid tank.

9. The measuring system according to claim 8, characterized in that Temperature measuring devices are respectively installed at both ends of the inner tube of the liquid distribution pipe.

10. The measuring system according to claim 8, characterized in that The first valve, the second valve, the third valve, the fourth valve and the fifth valve are all stop valves.

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