Fluid pVT tester

Abstract

The utility model discloses a fluid pVT tester, and aims to overcome the defect that the conventional pVT tester is inconvenient to observe supercritical carbon dioxide. A transparent compression cylinder body and a temperature control cylinder body are installed outside the machine box, the temperature control cylinder body is sleeved outside the compression cylinder body, the compression cylinder body is connected with a telescopic rod with a piston in a matched mode, the compression cylinder body is communicated with an air inlet pipe, a pressure detector is installed on the machine box, and the pressure detector detects the internal pressure of the compression cylinder body. According to the fluid pVT tester, observation of the testing process is facilitated, and the whole device is good in sealing performance, safe and environmentally friendly.

Description

TECHNICAL FIELD

[0001] The utility model relates to fluid determination technology, more particularly, it relates to a kind of fluid pVT determination instrument. BACKGROUND

[0002] The supercritical state of carbon dioxide refers to the state when the pressure and temperature of carbon dioxide exceed its critical point simultaneously. When carbon dioxide enters the supercritical state, it is neither gas nor liquid, but has some characteristics of both gas and liquid. To obtain supercritical carbon dioxide, a pVT determination instrument is needed. Due to the structure limitation, the existing pVT determination instrument is inconvenient to observe supercritical carbon dioxide, and the tidal phenomenon under the critical state is not obvious. During the operation process, the sealing element is easily damaged, leading to oil leakage. Moreover, a large amount of mercury is used to compress the gas carbon dioxide, which requires a large amount of liquid mercury to be loaded in advance on the device. Mercury is toxic and volatile, which poses a safety risk during the daily storage of the device. SUMMARY

[0003] To overcome the above-mentioned shortcomings, the utility model provides a kind of fluid pVT determination instrument, which facilitates the observation of the determination process, and the entire device has good sealing performance and is safe and environmentally friendly.

[0004] To solve the above technical problems, the utility model adopts the following technical scheme: a kind of fluid pVT determination instrument, comprising a case, a transparent compression cylinder and a temperature control cylinder are installed outside the case, the temperature control cylinder is sleeved outside the compression cylinder, the compression cylinder is connected with a telescopic rod with a piston, the compression cylinder is connected with an air inlet pipe, a pressure detector is installed on the case, and the pressure detector detects the pressure inside the compression cylinder.

[0005] When the fluid pVT determination instrument is working, the gas source is delivered to the compression cylinder through the air inlet pipe, the pressure detector detects the pressure inside the compression cylinder, and the temperature control cylinder is sleeved outside the compression cylinder to provide a constant temperature environment for the gas source in the compression cylinder. The telescopic rod moves to compress the gas source in the compression cylinder with the piston, and when the pressure and temperature in the compression cylinder reach the supercritical pressure and supercritical temperature of the gas source, the supercritical state of the gas source in the compression cylinder can be observed directly through the transparent side wall of the compression cylinder and the temperature control cylinder. The compression cylinder and the temperature control cylinder are sleeved together and are transparent, which facilitates the observation of the determination process.

[0006] Preferably, the compression cylinder is a quartz glass tube.

[0007] The quartz glass tube is used as the compression cylinder, which facilitates the direct observation of the state change of the gas source in the compression cylinder.

[0008] Preferably, a temperature detector is installed in the temperature control cylinder.

[0009] The temperature detector detects the temperature in the temperature control cylinder, so as to accurately control the temperature.

[0010] Preferably, the temperature control cylinder is connected to the water inlet pipe and the water outlet pipe.

[0011] The temperature control water flow is delivered from the water inlet pipe to the temperature control cylinder and discharged from the water outlet pipe, so as to adjust the temperature in the temperature control cylinder and further adjust the temperature of the gas source in the compression cylinder, so that the temperature of the gas source reaches the critical temperature.

[0012] Preferably, the compression cylinder is connected to the drainage pipe at the top, and the pressure detector is installed on the drainage pipe.

[0013] The drainage pipe facilitates the installation of the pressure detector.

[0014] Preferably, the drainage pipe is connected to the exhaust pipe and the pressure relief pipe in parallel, the exhaust pipe is installed with an exhaust valve, and the pressure relief pipe is installed with a safety valve.

[0015] The safety valve installed on the pressure relief pipe plays a safety protection role for the compression cylinder, avoiding safety hazards caused by excessive pressure in the compression cylinder. The exhaust pipe facilitates the complete discharge of the gas in the compression cylinder, preventing the mixing of other gases into the gas source. At present, many compressed cylinders on the market store fluids in a closed manner, which cannot be replaced and can only measure a single fluid. However, in the present application, the gas inlet pipe and the exhaust pipe are provided, which can measure different fluids. When switching fluids, the exhaust valve is opened, the fluid enters the compression cylinder from the gas inlet pipe, and the residual fluid in the compression cylinder is discharged from the exhaust pipe. After a period of time, the exhaust valve is closed, and the new fluid is filled into the compression cylinder.

[0016] Preferably, an electric cylinder is installed in the machine box, and the telescopic rod is connected to the electric cylinder, and the electric cylinder drives the telescopic rod to move.

[0017] The electric cylinder is used as a power source, which avoids oil leakage compared with the oil cylinder. Moreover, the electric cylinder is relatively simple to arrange, and the hydraulic system required by the oil cylinder is omitted.

[0018] Preferably, a gas source tank is installed in the machine box, a gas delivery pipe is connected between the gas inlet pipe and the gas source tank, and an air valve and a gas pressure gauge are installed on the gas delivery pipe.

[0019] When delivering gas, the air valve is opened, the gas pressure is observed through the gas pressure gauge, and the air valve is closed after the gas delivery is completed.

[0020] Preferably, a loading platform is arranged on the machine box, the compression cylinder and the temperature control cylinder are installed on the loading platform, the compression cylinder and the temperature control cylinder are open at the upper end, and the compression cylinder and the temperature control cylinder are sealingly connected to the cover plate at the upper end.

[0021] The compression cylinder body and the temperature control cylinder body are installed between the loading table and the cover plate, and the cover plate seals the upper openings of the compression cylinder body and the temperature control cylinder body, and the sealing performance is good.

[0022] As preferred, a controller is installed in the case, the controller is electrically connected with the display, and the display is installed on the outer wall of the case.

[0023] The controller can realize data collection and processing, and the display can visually display data, so that the user can control at any time.

[0024] Compared with the prior art, the fluid pVT measuring instrument has the advantages that (1) the fluid pVT measuring instrument facilitates observation of the measuring process, and the whole device has good sealing performance, safety and environmental protection; and (2) the fluid pVT measuring instrument can realize switching measurement of different fluids and has good versatility. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a side view of the utility model.

[0026] Figure 2 is a structural schematic view of the utility model without the case.

[0027] Figure 3 is a side view of the utility model without the case.

[0028] Figure 4 is a compression cylinder body connection schematic view of embodiment 1 of the utility model.

[0029] Figure 5 is a compression cylinder body connection schematic view of embodiment 2 of the utility model.

[0030] Figure 6 is a carbon dioxide phase diagram of the utility model.

[0031] In the figure: 1, case, 2, compression cylinder body, 3, temperature control cylinder body, 4, piston, 5, telescopic rod, 6, ring groove, 7, sealing ring, 8, air inlet pipe, 9, pressure detector, 10, drainage pipe, 11, exhaust pipe, 12, pressure relief pipe, 13, exhaust valve, 14, safety valve, 15, temperature detector, 16, water inlet pipe, 17, water outlet pipe, 18, loading table, 19, cover plate, 20, connecting rod, 21, air inlet nozzle, 22, drainage nozzle, 23, electric cylinder, 24, gas source storage tank, 25, air valve, 26, air pressure gauge, 27, controller, 28, display, 29, electric heating wire. DETAILED DESCRIPTION

[0032] The technical scheme of the utility model will be further specifically described below by means of specific embodiments and in combination with the drawings:

[0033] Embodiment 1: a fluid pVT measuring instrument (see the attachedFigure 1 To the attached Figure 4 ), is a test device for observing the pVT (p is pressure, V is volume, and T is temperature) relationship of a fluid, exhibiting the different forms of the fluid, and the fluid pVT tester comprises a cabinet 1, a transparent compression cylinder body 2 and a temperature control cylinder body 3 are installed outside the cabinet 1, the compression cylinder body 2 and the temperature control cylinder body 3 are both installed above the cabinet 1, and the temperature control cylinder body 3 is sleeved outside the compression cylinder body 2. The compression cylinder body 2 is adaptively connected with an extension rod 5 with a piston 4, a plurality of ring grooves 6 are arranged on the outer wall of the piston 4, so that a plurality of sealing rings 7 are formed on the outer wall of the piston 4. The compression cylinder body 2 is communicated with an air inlet pipe 8, a pressure detector 9 is installed on the cabinet 1, and the pressure detector 9 detects the internal pressure of the compression cylinder body 2. The extension rod 5 extends out of the lower end of the compression cylinder body 2, and the air inlet pipe 8 is communicated with the upper end of the compression cylinder body 2.

[0034] The compression cylinder body 2 is a quartz glass tube, which has a larger volume than a glass capillary tube, and is convenient for directly observing the internal airflow state transformation. The compression cylinder body 2 is communicated with a drainage pipe 10 at the top, and the pressure detector 9 is installed on the drainage pipe 10. The drainage pipe 10 is connected in parallel with an exhaust pipe 11 and a pressure relief pipe 12, the exhaust pipe 11 is provided with an exhaust valve 13, and the pressure relief pipe 12 is provided with a safety valve 14. The drainage pipe 10 facilitates the installation of the pressure detector 9.

[0035] The safety valve 14 installed on the pressure relief pipe 12 plays a safety protection role for the compression cylinder body 2, avoiding safety hazards caused by excessive internal pressure of the compression cylinder body 2. The exhaust pipe 11 facilitates the exhaust of the gas in the compression cylinder body 2, preventing other gases from mixing into the gas source. At present, many compression cylinders on the market store fluids in a closed manner, which cannot be replaced and can only realize the measurement of a single fluid. However, through the arrangement of the air inlet pipe 8 and the exhaust pipe 11 in the present application, the measurement of different fluids can be realized. When switching the fluid, the exhaust valve 13 is opened, the fluid enters the compression cylinder body 2 from the air inlet pipe 8, and the residual fluid in the compression cylinder body 2 is discharged from the exhaust pipe 11, and after a period of time, the exhaust is completely completed, and then the exhaust valve 13 is closed, so that the new fluid is filled into the compression cylinder body 2.

[0036] A temperature detector 15 is installed in the temperature control cylinder body 3, which is convenient for controlling the temperature in the temperature control cylinder body 3. The temperature control cylinder body 3 is connected with an inlet water pipe 16 and an outlet water pipe 17. The inlet water pipe 16 extends to the bottom of the temperature control cylinder body 3, and the outlet water pipe 17 extends to the top of the temperature control cylinder body 3.

[0037] A loading platform 18 is provided on the chassis 1. The compression cylinder 2 and the temperature control cylinder 3 are both mounted on the loading platform 18. The compression cylinder 2 and the temperature control cylinder 3 are an integral structure, with open upper ends and closed lower ends. A cover plate 19 is sealingly connected to the upper ends of the compression cylinder 2 and the temperature control cylinder 3. The cover plate 19 and the loading platform 18 are fixedly connected by a connecting rod 20. An air inlet 21 is provided on the cover plate 19 corresponding to the air inlet pipe 8, and the air inlet pipe 8 is connected to the air inlet 21. A drainage nozzle 22 is provided on the cover plate 19 corresponding to the drainage pipe 10, and the drainage pipe 10 is connected to the drainage nozzle 22. Both the air inlet 21 and the drainage nozzle 22 are connected to the upper end of the compression cylinder 2. A water inlet pipe 16 and a water outlet pipe 17 pass through the cover plate 19.

[0038] An electric cylinder 23 is installed inside the casing 1. The electric cylinder 23 is vertically arranged, and the telescopic rod 5 is connected to the electric cylinder 23. The electric cylinder 23 drives the telescopic rod 5 to extend and retract. Using the electric cylinder 23 as a power source avoids oil leakage compared to a hydraulic cylinder. Moreover, the electric cylinder 23 is relatively simple to install, eliminating the need for a hydraulic system required by a hydraulic cylinder.

[0039] An air source storage tank 24 is installed inside the chassis 1. An air supply pipeline connects the air inlet pipe 8 to the air source storage tank 24, and an air supply valve 25 and a pressure gauge 26 are installed on the air supply pipeline. When supplying air, the air supply valve 25 is opened, and the air pressure is observed through the pressure gauge 26. After supplying air, the air supply valve 25 is closed. A controller 27 is installed inside the chassis 1, and the controller 27 is electrically connected to a display 28, which is mounted on the outer wall of the chassis 1. The controller 27 can realize data acquisition and processing, and the display 28 displays the data intuitively, making it convenient for users to control at any time.

[0040] When the fluid pVT analyzer is working, the gas source is delivered to the compression cylinder 2 through the air inlet pipe 8. The pressure detector 9 detects the internal pressure of the compression cylinder 2. The temperature control cylinder 3, fitted outside the compression cylinder 2, provides a constant temperature environment for the gas source inside the compression cylinder 2. The electric cylinder 23 operates, driving the telescopic rod 5 to move, causing the piston 4 to compress the gas source inside the compression cylinder 2. When the pressure and temperature inside the compression cylinder 2 reach the supercritical pressure and supercritical temperature of the gas source, the supercritical state of the gas source inside the compression cylinder 2 can be directly observed through the transparent side walls of the compression cylinder 2 and the temperature control cylinder 3. The compression cylinder 2 and the temperature control cylinder 3, fitted together, are transparent, facilitating observation of the measurement process. Taking carbon dioxide as an example, the critical temperature of carbon dioxide is 31.10℃, and the critical pressure is 7.38 MPa. The temperature outside the compression cylinder 2 is controlled at 31.10℃, and the electric cylinder 23 pushes the telescopic rod 5 upward to compress the carbon dioxide gas. At the same temperature, when the pressure inside the compression cylinder 2 reaches the liquid state range of the carbon dioxide phase diagram, carbon dioxide changes from a gaseous state to a liquid state. This state can be directly observed through the transparent compression cylinder 2 and the temperature control cylinder 3. Figure 6 As shown, when the temperature and pressure reach their critical values, the following critical phenomena of carbon dioxide can be observed:

[0041] Critical milk light phenomenon: keep the critical temperature unchanged, adjust the compression cylinder 2 pressure to reach about 7.38 MPa, and then suddenly reduce the pressure, at this time, the internal appearance of the conical milk white flash phenomenon can be observed, which is the critical milk light phenomenon.

[0042] Overall phase transition phenomenon: at the critical point, the saturation gas line and the saturation liquid line are combined at a point, and the heat of vaporization is 0, at this time, the mutual transformation of gas and liquid is not accumulated gradually as below the critical temperature, but needs a certain time, which is a gradual process, and when the pressure changes slightly, the gas and liquid phases are transformed into each other in a sudden form.

[0043] Gas and liquid two-phase ambiguity phenomenon: carbon dioxide at the critical point cannot be distinguished as gaseous or liquid. According to the adiabatic process, the compression cylinder 2 pressure is suddenly reduced to about 7.64 MPa, and the carbon dioxide state point is lowered along the adiabatic line to the liquid phase region, and the cylinder carbon dioxide appears obvious liquid surface. That is to say, if the internal carbon dioxide is gas at this time, the gas is close to the liquid phase region, and can be said to be a gas close to liquid. When the carbon dioxide is suddenly compressed after expansion, the liquid surface will immediately disappear. This shows that the carbon dioxide liquid is also very close to the gas phase region, and can be considered as a liquid close to gas. This is the saturation gas and liquid phase ambiguity phenomenon near the critical point.

[0044] Since the mass of CO2 filled into the compression cylinder 2 and the cross-sectional area of the compression cylinder 2 are not easy to measure, an indirect method is used to determine the specific volume of CO2 in the experiment. It is assumed that the specific volume v of CO2 is linearly related to its height. The specific volume v of CO2 liquid (20℃, 9.8MPa) = 0.00117 cubic meters per kilogram is known, and if the actual measured CO2 liquid column height △h0(m) at 20℃, 9.8MPa is known, then:

[0045] v(20℃, 9.8MPa) = △h0A / m = 0.00117(m 3 ·kg -1 );

[0046] K = m / A = △h0 / 0.00117; K is the mass area constant of CO2 in the compression cylinder, kg·m -2 。 The specific volume of CO2 at the experimental temperature and pressure is: v = △h0 / (m / A) = △h0 / K; from the formula, only the CO2 liquid column height △h0 is known, the specific volume of CO2 liquid can be indirectly calculated.

[0047] The traditional pVT curve measuring experimental device adopts a glass capillary as a compression cavity, adopts mercury sealing and compressed carbon dioxide gas, and uses oil as a hydraulic pressure transmission component to push liquid mercury to compress the gas. The glass capillary has a small volume, is inconvenient to observe, and the tidal phenomenon at the critical state is not obvious. Meanwhile, in the operation, the toxic mercury as the sealing and pressure transmission component has a greater safety hazard, and the existing device often causes oil leakage due to aging of the rubber component of the oil seal under high pressure. In the present application, the quartz glass tube is used as the compression cylinder 2, and the temperature control cylinder 3 is used as the constant temperature device, which can achieve good demonstration effect under the premise of safety and environmental protection. The risk factors of the experimental device can be effectively reduced, and at the same time, the teaching personnel and researchers can understand and explore the critical point, critical pressure and critical temperature of various fluid pure substances, understand the thermodynamic state of pure substances, master the pVT relationship of fluid, and draw the isotherm and phase diagram of fluid. It is a powerful tool for thermodynamics teaching and research.

[0048] Embodiment 2: a fluid pVT measuring instrument (see attached Figure 1 to the attached Figure 3 , attached Figure 5 ), is an experimental measuring device for observing the pVT (p is pressure, V is volume, T is temperature) relationship of fluid, showing the different morphological processes of fluid. The fluid pVT measuring instrument comprises a case 1, a transparent compression cylinder 2 and a temperature control cylinder 3 are installed outside the case 1, the compression cylinder 2 and the temperature control cylinder 3 are both installed above the case 1, and the temperature control cylinder 3 is sleeved outside the compression cylinder 2. The compression cylinder 2 is adaptively connected with an extension rod 5 with a piston 4, a plurality of ring grooves 6 are arranged on the outer wall of the piston 4, so that a plurality of sealing rings 7 are formed on the outer wall of the piston 4. The compression cylinder 2 is communicated with an air inlet pipe 8, a pressure detector 9 is installed on the case 1, and the pressure detector 9 detects the internal pressure of the compression cylinder 2. The extension rod 5 extends out of the lower end of the compression cylinder 2, and the air inlet pipe 8 is communicated with the upper end of the compression cylinder 2.

[0049] The compression cylinder 2 is a quartz glass tube, which has a larger volume than the glass capillary, and is convenient for direct observation of the internal gas flow state change. The top of the compression cylinder 2 is communicated with a drainage pipe 10, and the pressure detector 9 is installed on the drainage pipe 10. The drainage pipe 10 is connected in parallel with an exhaust pipe 11 and a pressure relief pipe 12, the exhaust pipe 11 is provided with an exhaust valve 13, and the pressure relief pipe 12 is provided with a safety valve 14. The setting of the drainage pipe 10 facilitates the installation of the pressure detector 9.

[0050] A safety valve 14 is arranged on the pressure relief pipe 12, which plays a safety protection role for the compression cylinder body 2, avoiding the safety hazard caused by the excessive pressure in the compression cylinder body 2. The exhaust pipe 11 facilitates the exhaust of the gas in the compression cylinder body 2, preventing other gases from mixing into the gas source. At present, many compression cylinders on the market store the fluid in a closed manner, which cannot be replaced and can only measure a single fluid. However, in the present application, the arrangement of the air inlet pipe 8 and the exhaust pipe 11 can realize the measurement of different fluids. When switching the fluid, the exhaust valve 13 is opened, the fluid enters the compression cylinder body 2 from the air inlet pipe 8, and the residual fluid in the compression cylinder body 2 is exhausted from the exhaust pipe 11, and after a period of time, the exhaust is completely completed, and then the exhaust valve 13 is closed, so that the new fluid is filled into the compression cylinder body 2.

[0051] A temperature detector 15 is arranged in the temperature control cylinder body 3, which facilitates the control of the temperature in the temperature control cylinder body 3. The temperature control cylinder body 3 is provided with a heating fluid and an electric heating wire 29, and the electric heating wire 29 is powered to heat the heating fluid, so that the temperature in the temperature control cylinder body 3 is increased to the required temperature. In this way, it is no longer necessary to separately arrange a water flow circulation system for heating, and the structure is simplified.

[0052] A loading table 18 is arranged on the case 1, and the compression cylinder body 2 and the temperature control cylinder body 3 are arranged on the loading table 18. The compression cylinder body 2 and the temperature control cylinder body 3 are integrated, the upper ends of the compression cylinder body 2 and the temperature control cylinder body 3 are open, the lower end of the temperature control cylinder body 3 is closed, and the upper ends of the compression cylinder body 2 and the temperature control cylinder body 3 are sealingly connected with a cover plate 19. The cover plate 19 and the loading table 18 are fixedly connected through a connecting rod 20, an air inlet nozzle 21 corresponding to the air inlet pipe 8 is arranged on the cover plate 19, the air inlet pipe 8 is connected with the air inlet nozzle 21, a drainage nozzle 22 corresponding to the drainage pipe 10 is arranged on the cover plate 19, and the drainage pipe 10 is connected with the drainage nozzle 22. The air inlet nozzle 21 and the drainage nozzle 22 are both in communication with the upper end of the compression cylinder body 2.

[0053] An electric cylinder 23 is arranged in the case 1, the electric cylinder 23 is arranged vertically, the telescopic rod 5 is connected with the electric cylinder 23, and the electric cylinder 23 drives the telescopic rod 5 to move up and down. The electric cylinder 23 is used as a power source, which avoids the oil leakage phenomenon compared with the oil cylinder. Moreover, the electric cylinder 23 is relatively simple to arrange, and the hydraulic system required by the oil cylinder is omitted.

[0054] A gas source storage tank 24 is arranged in the case 1, a gas conveying pipeline is connected between the air inlet pipe 8 and the gas source storage tank 24, and an air valve 25 and a gas pressure gauge 26 are arranged on the gas conveying pipeline. When the gas is conveyed, the air valve 25 is opened, the gas pressure is observed through the gas pressure gauge 26, and the air valve 25 is closed after the gas conveying is completed. A controller 27 is arranged in the case 1, the controller 27 is electrically connected with a display 28, and the display 28 is arranged on the outer wall of the case 1. The controller 27 can realize the collection and processing of data, and the display 28 can visually display the data, which is convenient for the user to control at any time.

[0055] When the fluid pVT tester is in operation, the gas source is delivered into the compression cylinder 2 through the gas inlet pipe 8, the pressure detector 9 detects the pressure inside the compression cylinder 2, and the temperature control cylinder 3 is sleeved outside the compression cylinder 2 to provide a constant temperature environment for the gas source in the compression cylinder 2. When the electric cylinder 23 is in operation, the telescopic rod 5 is driven to move to compress the gas source in the compression cylinder 2 by the piston 4. When the pressure and temperature in the compression cylinder 2 reach the supercritical pressure and supercritical temperature of the gas source, the supercritical state of the gas source in the compression cylinder 2 can be directly observed through the transparent side walls of the compression cylinder 2 and the temperature control cylinder 3. The compression cylinder 2 and the temperature control cylinder 3 are transparent and are sleeved together, which facilitates the observation of the determination process. Taking carbon dioxide as an example, the critical temperature of carbon dioxide is 31.10℃, and the critical pressure is 7.38 MPa. The temperature outside the compression cylinder 2 is controlled at 31.10℃, and the telescopic rod 5 is driven upward by the electric cylinder 23 to compress the carbon dioxide gas. At the same temperature, when the pressure in the compression cylinder 2 reaches the liquid region range of the carbon dioxide phase diagram, the carbon dioxide changes from gas to liquid. At this time, the state can be directly observed through the transparent compression cylinder 2 and the temperature control cylinder 3. As shown in FIG. 13, when the temperature and pressure reach the critical values, the critical phenomenon of carbon dioxide can be observed as follows: Figure 6

[0056] Critical opalescence phenomenon: keep the critical temperature unchanged, adjust the pressure of the compression cylinder 2 to about 7.38 MPa, and then suddenly reduce the pressure. At this time, a conical milky white flash phenomenon appears inside, which is the critical opalescence phenomenon.

[0057] Overall phase transition phenomenon: at the critical point, the saturated gas line and the saturated liquid line meet at a point, and the heat of vaporization is 0. At this time, the mutual transformation of gas and liquid is not a gradual accumulation as below the critical temperature, but a sudden change when the pressure changes slightly.

[0058] Gas-liquid two-phase ambiguity phenomenon: carbon dioxide at the critical point cannot be distinguished as gas or liquid. According to the adiabatic process, first, the pressure in the compression cylinder 2 is adjusted to about 7.64 MPa and then suddenly reduced. The state point of carbon dioxide is lowered from the isotherm line to the liquid phase region along the adiabatic line, and the cylinder inside carbon dioxide appears obvious liquid surface. This means that if the carbon dioxide inside is gas, it is very close to the liquid phase region and can be regarded as a gas close to liquid. When the carbon dioxide is suddenly compressed after expansion, the liquid surface will immediately disappear. This shows that the carbon dioxide liquid is also very close to the gas phase region and can be regarded as a liquid close to gas. This is the saturation gas-liquid phase ambiguity phenomenon near the critical point.

[0059] ​Because the mass of CO2 filled in the compression cylinder 2 and the cross-sectional area of the compression cylinder 2 are not easy to measure, the specific volume of CO2 is determined by an indirect method in the experiment. It is assumed that the specific volume v of CO2 is linearly related to the height of CO2. The specific volume v of CO2 liquid (20 DEG C, 9.8 MPa) is known as 0.00117 cubic meters per kilogram. If the actual measured height of CO2 liquid column △h0 (m) at 20 DEG C and 9.8 MPa is known, then there is:

[0060] v (20 DEG C, 9.8 MPa) = △h0A / m = 0.00117 (m 3 ·kg -1 );

[0061] K = m / A = △h0 / 0.00117; K is the mass area constant of CO2 in the compression cylinder, kg·m -2 。 The specific volume of CO2 at the experimental temperature and pressure is v = △h0 / (m / A) = △h0 / K. From the formula, only the height of CO2 liquid column △h0 is known, the specific volume of CO2 liquid can be indirectly calculated.

[0062] The traditional pVT curve determination experimental device adopts a glass capillary as a compression cavity, adopts mercury sealing and compresses carbon dioxide gas, and uses oil as a hydraulic pressure transmission component to push liquid mercury to compress the gas. The glass capillary has a small volume, is inconvenient to observe, and the tidal phenomenon at the critical state is not obvious. Meanwhile, in the operation, the toxic mercury as the sealing and pressure transmission component has a greater safety hazard, and the existing device often leaks oil due to aging of the rubber component of the oil seal under high pressure. In the present application, the quartz glass tube is used as the compression cylinder 2, and the temperature control cylinder 3 is used as the constant temperature device, which can achieve good demonstration effect under the premise of safety and environmental protection. The dangerous factors of the experimental device can be effectively reduced, and the teaching personnel and researchers can understand and explore the critical point, critical pressure and critical temperature of various fluid pure substances, understand the thermodynamic state of pure substances, master the pVT relationship of the fluid, and draw the isotherm and phase diagram of the fluid. It is a powerful tool for thermodynamics teaching and research.

[0063] The above-described embodiments are only the preferred schemes of the present application, and do not limit the present application in any form. Other variants and modifications can be made without exceeding the technical schemes recited in the claims.

Claims

1. A fluid pVT meter comprising a cabinet, characterized in that, The transparent compression cylinder and the temperature control cylinder are installed outside the case, the temperature control cylinder is sleeved outside the compression cylinder, the compression cylinder is connected with the telescopic rod with piston, the compression cylinder is communicated with the air inlet pipe, the pressure detector is installed on the case, and the pressure detector detects the internal pressure of the compression cylinder.

2. A fluid pVT apparatus according to claim 1, wherein, The compression cylinder is a quartz glass tube.

3. A fluid pVT apparatus according to claim 1, wherein, The temperature detector is installed in the temperature control cylinder.

4. A fluid pVT apparatus according to claim 1, wherein, The temperature control cylinder is connected with the water inlet pipe and the water outlet pipe.

5. A fluid pVT apparatus according to claim 1, wherein, The compression cylinder is communicated with the drainage pipe at the top, and the pressure detector is installed on the drainage pipe.

6. A fluid pVT apparatus according to claim 5, wherein, The drainage pipe is connected with the exhaust pipe and the pressure relief pipe in parallel, the exhaust pipe is provided with an exhaust valve, and the pressure relief pipe is provided with a safety valve.

7. A fluid pVT apparatus according to claim 1, wherein, The electric cylinder is installed in the case, the telescopic rod is connected with the electric cylinder, and the electric cylinder drives the telescopic rod to move up and down.

8. A fluid pVT apparatus according to claim 1, wherein, The gas source storage tank is installed in the case, the air inlet pipe is connected with the gas source storage tank, the air supply pipeline is provided with an air valve and an air pressure gauge.

9. A fluid pVT apparatus according to any one of claims 1 to 8, wherein, The loading table is arranged on the case, the compression cylinder and the temperature control cylinder are installed on the loading table, the upper ends of the compression cylinder and the temperature control cylinder are opened, and the upper ends of the compression cylinder and the temperature control cylinder are sealingly connected with the cover plate.

10. A fluid pVT apparatus according to any one of claims 1 to 8, wherein, The controller is electrically connected with the display, and the display is installed on the outer wall of the case.

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