Experimental device and method for measuring constant-pressure specific heat capacity of fluid in near-critical zone

Abstract

The invention relates to an experimental device and method for measuring the constant-pressure specific heat capacity of fluid in a near-critical zone. The device comprises a measuring body, a direct-current power source, a measured fluid bottle, a flow adjusting pump, a fluid recycling bottle, a data collecting system, an inlet pressure sensor, an inlet temperature sensor, a measuring cavity temperature sensor, a measuring cavity pressure sensor and a heat insulation assembly. The measuring body and the internal heat insulation assembly are used for heating a measured fluid and insulating heat; the temperature sensor and the pressure sensor are used for measuring the fluid state; the direct-current power supply and the flowmeter are used for indirectly obtaining fluid enthalpy difference changes. The heat insulation capacity is enhanced by measuring the multi-layer spherical shell structure in the body, the heat leakage error is reduced, meanwhile, the constant-pressure specific heat capacity of the fluid in the near-critical zone is calculated by measuring the change rule of the enthalpy value of the fluid in the cavity relative to the enthalpy value at the inlet under the steady-state condition, and therefore the necessary temperature difference needed by conventional measurement is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of measuring the thermophysical properties of fluids, and in particular to an experimental device and method for measuring the constant-pressure specific heat capacity of a near-critical region fluid. Background Art

[0002] As an important thermophysical parameter of fluid, constant pressure specific heat capacity is the basic data in design engineering of chemical industry, energy industry, etc. Therefore, accurate measurement of fluid specific heat capacity data is very important.

[0003] However, the near-critical point is a second-order phase transition point, and the violent fluctuations have a strange effect on the thermophysical properties of the fluid. In the near-critical region, the specific heat capacity of the fluid changes dramatically and tends to infinity at the critical point, making it difficult to measure: the specific heat capacity is extremely sensitive to state changes, and the standard uncertainty of temperature and pressure sensors will cause huge measurement errors; in the near-critical region, the fluctuations are violent, and the thermophysical properties are not uniformly distributed in space and change with time; the critical point temperature is usually high, and it is difficult to suppress heat leakage errors.

[0004] In summary, the conventional temperature difference method that requires a necessary temperature difference is not suitable for the constant pressure specific heat measurement of the near critical region; the quasi-static measurement method will be affected by the measurement process. Therefore, it is still difficult to achieve high-precision measurement of the isobaric specific heat of near-critical fluids. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide an experimental device and method for measuring the constant-pressure specific heat capacity of near-critical fluids, which can effectively solve the problem of the difficulty in accurately measuring the constant-pressure specific heat capacity of near-critical fluids.

[0006] The technical solution adopted by the present invention is as follows:

[0007] The present invention proposes an experimental device for measuring the constant-pressure specific heat capacity of near-critical fluid, comprising a measuring body, a direct current power supply, a measured fluid bottle, a flow regulating pump, a fluid recovery bottle, a data acquisition system, an inlet pressure sensor, an inlet temperature sensor, a measuring cavity temperature sensor, a measuring cavity pressure sensor and a thermal insulation component; an inlet channel and an outlet channel are respectively arranged on both axial sides inside the measuring body; a measuring cavity is coaxially arranged at the inner end of the outlet channel; the thermal insulation component is coaxially connected between the inner end of the inlet channel and the measuring cavity; the inlet pressure sensor and the inlet temperature sensor are respectively arranged on both sides of the inlet channel of the measuring body and connected to the data acquisition system; the measuring cavity temperature sensor and the measuring cavity pressure sensor are respectively arranged on both sides of the measuring cavity and connected to the data acquisition system; the direct current power supply is connected to the thermal insulation component; the measured fluid bottle is connected to the outer end of the inlet channel of the measuring body through a stop valve, a flow regulating pump and a flowmeter in turn, and the flowmeter is connected to the data acquisition system; the outer end of the outlet channel of the measuring body is connected to the fluid recovery bottle through a back pressure valve.

[0008] Furthermore, the thermal insulation assembly includes a spherical heating plate and a spherical insulation plate; the spherical heating plate and the spherical insulation plate are alternately and evenly distributed along the axial direction of the measuring body; a closed conical cavity structure is formed between the front ends of the spherical heating plate and the spherical insulation plate and the inner end of the measuring cavity, the spherical insulation heating plate located in the innermost layer is coaxially connected to the inner end of the measuring cavity, and the spherical insulation plate located in the outermost layer is coaxially connected to the inlet channel of the measuring body; small holes are opened on the spherical heating plate and the spherical insulation plate, and the small holes are staggered; the spherical heating plate is connected to a DC power supply.

[0009] Furthermore, an integrally formed thermal insulation sleeve I is provided between the inner end of the measuring cavity, the front end of the spherical heating plate and the spherical insulation plate and the outside of the inlet channel of the measuring body; and a thermal insulation sleeve II is provided on the outside of the measuring cavity and the outlet channel of the measuring body.

[0010] Furthermore, the curvature of the spherical heating plate and the spherical insulation plate is ≥π, thereby reducing the heat leakage surface.

[0011] Furthermore, the thermal insulation sleeve I, the spherical insulation plate and the thermal insulation sleeve II are all made of thermal insulation ceramic materials.

[0012] Furthermore, the diameter of the measuring cavity is larger than the diameter of the inlet channel of the measuring body.

[0013] An experimental method for measuring the constant-pressure specific heat capacity of a near-critical fluid, the method comprising the following steps:

[0014] S1, open the stop valve and back pressure valve, turn on the flow regulating pump to adjust the flow Pump the measured fluid into the measuring body, expel the remaining gas and possible impurities in the pipeline and the measuring body 1, and collect the fluid through the fluid recovery bottle;

[0015] S2. After the pipeline is cleaned, adjust the back pressure valve to make the pressure at the pressure sensor of the measuring chamber reach p 1 , turn on the DC power supply and adjust the heating power Q of the spherical heating plate;

[0016] S3. When the measuring body reaches stability, the pressure p at the inlet is measured by the inlet pressure sensor and the inlet temperature sensor. 0 , Temperature T 0 The pressure p of the measuring chamber is measured by the measuring chamber pressure sensor and the measuring chamber temperature sensor. 1 , Temperature T 1 And the DC power Q 1 , complete a measurement;

[0017] S4. After completing step S3, start the next measurement and keep the pressure and temperature of the inlet pressure sensor and the inlet temperature sensor stable at p 0 , T 0 , keep the pressure of the measuring chamber pressure sensor of the measuring chamber stable at P 1 , the heating power Q of the spherical heating plate is adjusted by a DC power supply 2 ; When the measuring body reaches thermal equilibrium again, record the temperature T of the test cavity temperature sensor 2 ;

[0018] S5. Repeat step S4 several times and record the flow rate of the flow meter Measuring cavity temperature sensor temperature T i , DC power supply power Q i ;

[0019] S6. Before stopping the measurement, first turn off the DC power supply and continue to keep the flow regulating pump turned on to cool the measuring body with the measured fluid to prevent damage to the spherical heating plate;

[0020] S7. Calculate the molar specific heat capacity of the fluid.

[0021] Further, the step S7 specifically includes: adjusting the flow rate of the pump according to the flow rate set in step S1 And step S2 sets the power Q of the DC power supply 1 Get the measured fluid in state (T 1 , p 1 ) relative to the reference state (T 0 , p 0 )'s molar enthalpy change Δh 1 ; Similarly, obtain the measured fluid in state (T 2 , p 1 ) relative to (T 0 , p 0 )'s molar enthalpy change Δh 2 ; The state (T, p) is obtained by fitting the experimental data 1 ) The relative molar enthalpy change Δh(T, p) of the fluid compared to the reference state 1 ); the constant pressure specific heat under different states is obtained according to the fitting function.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] In the present invention, the flow meter and the DC power supply are used to jointly control the enthalpy difference of the measured fluid in the measuring cavity relative to the inlet of the measuring body. Improve its measurement accuracy; the spherical heating plate and the spherical insulation orifice plate are used to reduce the heat dissipation in the incoming flow direction based on the fluid flow, thereby reducing the high-temperature heat leakage of the near-critical fluid. The present invention uses the change law of the enthalpy value of the measured fluid in the measuring cavity compared to the inlet to infer the constant-pressure specific heat capacity of the near-critical fluid, overcomes the accuracy limitation of the sensor, and realizes high-precision measurement of the constant-pressure specific heat capacity of the near-critical fluid under steady-state conditions.

[0024] The invention is not only applicable to the measurement of the constant-pressure specific heat of pure fluid in the near-critical region, but also applicable to the near-critical region solution and fluids in any region with drastic changes in the constant-pressure specific heat. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the structure of an experimental device for measuring the constant-pressure specific heat capacity of near-critical fluids proposed by the present invention;

[0026] Figure 2 for Figure 1 Schematic diagram of the structure of the measurement body part.

[0027] Figure 3 for Figure 3 A schematic diagram of a side cross-sectional structure;

[0028] Figure 4 Schematic diagram of experimental data and fitting function.

[0029] Among them, the figure markings are: 1. measuring body; 2. DC power supply; 3. measured fluid bottle; 4. stop valve; 5. flow regulating pump; 6. back pressure valve; 7. fluid recovery bottle; 8. data acquisition system; 9. inlet pressure sensor; 10. inlet temperature sensor; 11. measuring cavity temperature sensor; 12. measuring cavity pressure sensor; 13. spherical heating plate; 14. insulation sleeve I; 15. spherical insulation plate; 17. insulation sleeve II; 16. measuring cavity; 18. flow meter. DETAILED DESCRIPTION

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] See attached Figure 1-3The experimental device for measuring the constant-pressure specific heat capacity of near-critical fluid proposed in this embodiment includes a measuring body 1, a DC power supply 2, a measured fluid bottle 3, a flow regulating pump 5, a fluid recovery bottle 7, a data acquisition system 8, an inlet pressure sensor 9, an inlet temperature sensor 10, a measuring cavity temperature sensor 11, a measuring cavity pressure sensor 12 and a thermal insulation component.

[0032] Among them, the measuring body 1 is cut on a metal cylinder, and an inlet channel and an outlet channel are coaxially arranged on both sides of the inner axial direction; a measuring cavity 16 is coaxially arranged at the inner end of the outlet channel; the insulation component is coaxially connected between the inner end of the inlet channel and the measuring cavity 16; the inlet pressure sensor 9 and the inlet temperature sensor 10 are respectively arranged on both sides of the inlet channel of the measuring body 1 and connected to the data acquisition system 8; the measuring cavity temperature sensor 11 and the measuring cavity pressure sensor 12 are respectively arranged on both sides of the measuring cavity 16 and connected to the data acquisition system 8; the DC power supply 2 is connected to the insulation component; the measured fluid bottle 3 is connected to the outer end of the inlet channel of the measuring body 1 through the stop valve 4, the flow regulating pump 5 and the flowmeter 18 in sequence, and the flowmeter 18 is connected to the data acquisition system 8; the outer end of the outlet channel of the measuring body 1 is connected to the fluid recovery bottle 7 through the back pressure valve 6.

[0033] In this embodiment, the thermal insulation assembly includes two spherical heating plates 13 and two spherical insulation plates 15; the spherical heating plates 13 and the spherical insulation plates 15 are axially and alternately distributed in sequence along the outlet to the inlet direction of the measuring body 1; a closed conical cavity structure is formed between the front ends of the spherical heating plates 13 and the spherical insulation plates 15 and the inner end of the measuring cavity 16, the spherical insulation heating plate 13 located in the innermost layer is coaxially connected to the inner end of the measuring cavity 16, and the spherical insulation plate 15 located in the outermost layer is coaxially connected to the inlet channel of the measuring body 1; the spherical heating plates 13 and the spherical insulation plates 15 are both provided with small holes, and the small holes are staggeredly distributed to ensure that all fluids flow without stagnation points; the spherical heating plate 13 is connected to a DC power supply 2, powered by the DC power supply 2, and the power of the DC power supply 2 is adjustable.

[0034] An integrally formed heat-insulating sleeve I14 is arranged on both sides of the inner end of the measuring cavity 16, between the front ends of each spherical heating plate 13 and the spherical insulation plate 15 and the outside of the inlet channel of the measuring body 1; a heat-insulating sleeve II17 is arranged on the outside of the outlet channel of the measuring cavity 16 and the measuring body 1.

[0035] The radian of the spherical heating plate 13 and the spherical insulation plate 15 is ≥π, that is, it exceeds a hemisphere, so as to reduce the heat leakage angle as much as possible, so as to minimize the heat leakage in the incoming flow direction.

[0036] The heat-insulating sleeve I14, the spherical heat-insulating plate 15 and the heat-insulating sleeve II17 are all made of heat-insulating ceramic materials.

[0037] The diameter of the measuring cavity 16 is larger than the diameter of the inlet channel of the measuring body 1, so as to suppress the pressure drop error caused by the flow.

[0038] The spherical heating plate 13 is driven by a DC power supply 2 to heat the fluid, and the heating power of the spherical heating plate 13 can be adjusted by the DC power supply 2; the back pressure valve 6 is connected to the measuring body 1 and the fluid recovery bottle 7, and can adjust and stabilize the pressure in the measuring cavity 13; the flow meter 18 is located between the flow regulating pump 5 and the measuring body 1, measures the fluid flow and intersects with the data acquisition system 8; the inlet temperature sensor 10 and the measuring cavity temperature sensor 11 are connected to the data acquisition system 8; the inlet pressure sensor 9 and the measuring cavity pressure sensor 12 communicate with the data acquisition system 8; the data acquisition system 8 collects and saves data from the inlet temperature sensor 10, the measuring cavity temperature sensor 11, the inlet pressure sensor 9, the measuring cavity pressure sensor 12 and the flow meter 18.

[0039] After the pressure of the measured fluid in the measuring chamber 16 is stabilized by the back pressure valve 6, the flow rate of the flow regulating pump 5 is controlled in coordination. and the power Q of the DC power supply 2, to measure and regulate the molar enthalpy of the measured fluid in the measuring chamber 16 (M: molar mass of the fluid being measured), improves the accuracy of calculating the molar enthalpy of the fluid being measured within the measurement intensity 16.

[0040] By measuring the enthalpy change law of the measured fluid in the measuring cavity 16 at different temperatures compared with the inlet, the constant pressure specific heat capacity of the fluid is calculated, thereby avoiding the necessary temperature difference limitation;

[0041] The convection effect of the measured fluid is used to reduce the heat leakage from the measuring body to the flow direction of the measured fluid. An experimental method for measuring the constant pressure specific heat capacity of near-critical fluids, the specific implementation steps are as follows:

[0042] S1, open the stop valve 4 and the back pressure valve 6, and then turn on the flow regulating pump 5 to adjust the flow The measured fluid is pumped into the measuring body 1 , the gas and possible impurities remaining in the pipeline and the measuring body 1 are expelled, and the fluid is collected by the fluid recovery bottle 7 .

[0043] S2. After the system is cleaned, adjust the back pressure valve 6 so that the pressure at the pressure sensor 12 reaches p 1 , turn on the DC power supply 2 and adjust the heating power Q of the spherical heating plate 13.

[0044] S3. When the measuring body 1 reaches stability, the pressure p at the inlet is measured by the inlet pressure sensor 9 and the inlet temperature sensor 10. 0 , Temperature T 0 The pressure p of the measuring chamber 16 is measured by the measuring chamber pressure sensor 12 and the measuring chamber temperature sensor 11.1 , Temperature T 1 And the DC power Q 1 , complete a measurement.

[0045] S4. After completing step S3, start the next measurement, and keep the pressure and temperature of the inlet pressure sensor 9 and the inlet temperature sensor 10 stable at p respectively. 0 , T 0 , keep the pressure of the measuring chamber pressure sensor 12 stable at P 1 , adjust the heating power of the spherical heating plate 13 to Q through the DC power supply 2 2 When the measuring body 1 reaches thermal equilibrium again, the temperature T of the measuring cavity temperature sensor 11 is recorded. 2 .

[0046] S5, repeat step S4 several times and record the flow rate of flow meter 18 The temperature T of the measuring cavity temperature sensor 11 i , DC power supply power Q i .

[0047] S6. Before stopping the measurement, first turn off the DC power supply 2 and continue to keep the flow regulating pump 5 turned on to cool the measuring body 1 with the measured fluid to prevent damage to the spherical heating plate 13.

[0048] S7. Calculate the molar specific heat capacity of the fluid;

[0049] Adjust the pump flow rate according to the flow rate set in step S1 And step S2 sets the power Q of DC power supply 2 1 Get the measured fluid in state (T 1 , p 1 ) relative to the reference state (T 0 , p 0 )'s molar enthalpy change Δh 1 ; Similarly, obtain the measured fluid in state (T 2 , p 1 ) relative to (T 0 , p 0 )'s molar enthalpy change Δh 2 ; The state (T, p) is obtained by fitting the experimental data 1 ) of the fluid compared to the reference state. 1 ); the constant pressure specific heat under different states is obtained according to the fitting function.

[0050] Experimental data processing method:

[0051] Since the direct measurement results of the above-mentioned device for measuring the specific heat capacity of the fluid are temperature, pressure, flow rate and heating power, it is necessary to process the directly measured data and calculate the specific heat capacity of the fluid.

[0052] First, adjust the pump flow according to the flow Fluid molar mass M, DC power supply power Q 1 Calculate the fluid in the measuring chamber in the state (T 1 , p 1 ) relative to the reference state (at the inlet of the measuring body) Δh 1 :

[0053]

[0054] Then the method is repeatedly used to obtain the i , p 1 ) Fluid relative enthalpy change Δh i , based on the experimental data set Δh i (T i , p 1 ) fitting to obtain the empirical correlation h(T, p 1 ),like Figure 4 As shown. Finally, the empirical correlation is derived to obtain the constant pressure specific heat cp of the fluid under different states:

[0055]

[0056] Matters not described in detail in the present invention are all known technologies.

[0057] The embodiments described above are merely descriptions of preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. An experimental device for measuring the constant pressure specific heat capacity of near-critical fluid, characterized by: The device includes a measuring body, a direct current power supply, a measured fluid bottle, a flow regulating pump, a fluid recovery bottle, a data acquisition system, an inlet pressure sensor, an inlet temperature sensor, a measuring cavity temperature sensor, a measuring cavity pressure sensor and a heat insulation component; an inlet channel and an outlet channel are respectively arranged on both axial sides inside the measuring body; a measuring cavity is coaxially arranged at the inner end of the outlet channel; the heat insulation component is coaxially connected between the inner end of the inlet channel and the measuring cavity; the inlet pressure sensor and the inlet temperature sensor are respectively arranged on both sides of the inlet channel of the measuring body and connected to the data acquisition system; the measuring cavity temperature sensor and the measuring cavity pressure sensor are respectively arranged on both sides of the measuring cavity and connected to the data acquisition system; the direct current power supply is connected to the heat insulation component; the measured fluid bottle is connected to the outer end of the inlet channel of the measuring body through a stop valve, a flow regulating pump and a flowmeter in turn, and the flowmeter is connected to the data acquisition system; the outer end of the outlet channel of the measuring body is connected to the fluid recovery bottle through a back pressure valve.

2. The experimental device for measuring the constant pressure specific heat capacity of near-critical fluid according to claim 1, characterized in that: The thermal insulation component includes a spherical heating plate and a spherical insulation plate; the spherical heating plate and the spherical insulation plate are alternately and evenly distributed along the axial direction of the measuring body; a closed conical cavity structure is formed between the front ends of the spherical heating plate and the spherical insulation plate and the inner end of the measuring cavity, the spherical insulation heating plate located in the innermost layer is coaxially connected to the inner end of the measuring cavity, and the spherical insulation plate located in the outermost layer is coaxially connected to the inlet channel of the measuring body; small holes are opened on the spherical heating plate and the spherical insulation plate, and the small holes are staggered; the spherical heating plate is connected to a DC power supply.

3. The experimental device for measuring the constant pressure specific heat capacity of near-critical fluid according to claim 2, characterized in that: An integrally formed heat-insulating sleeve I is arranged between the inner end of the measuring cavity, the front end of the spherical heating plate and the spherical insulation plate and the outer side of the inlet channel of the measuring body; a heat-insulating sleeve II is arranged on the outer side of the measuring cavity and the outlet channel of the measuring body.

4. The experimental device for measuring the constant pressure specific heat capacity of near-critical fluid according to claim 2, characterized in that: The radian of the spherical heating plate and the spherical insulation plate is ≥π, which reduces the heat leakage surface.

5. The experimental device for measuring the constant pressure specific heat capacity of near-critical fluid according to claim 3, characterized in that: The heat-insulating sleeve I, the spherical heat-insulating plate and the heat-insulating sleeve II are all made of heat-insulating ceramic materials.

6. The experimental device for measuring the constant pressure specific heat capacity of near-critical fluid according to claim 1, characterized in that: The diameter of the measuring cavity is greater than the diameter of the inlet channel of the measuring body.

7. The experimental method of the experimental device for measuring the constant pressure specific heat capacity of near-critical fluid according to claim 2, characterized in that: The method comprises the following steps: S1, open the stop valve and back pressure valve, turn on the flow regulating pump to adjust the flow Pump the measured fluid into the measuring body, expel the remaining gas and possible impurities in the pipeline and the measuring body 1, and collect the fluid through the fluid recovery bottle; S2. After the pipeline is cleaned, adjust the back pressure valve to make the pressure at the pressure sensor of the measuring chamber reach p1, turn on the DC power supply, and adjust the heating power Q of the spherical heating plate; S3. When the measuring body reaches stability, the pressure p0 and temperature T0 at the inlet are measured by the inlet pressure sensor and the inlet temperature sensor, and the pressure p1 and temperature T1 of the measuring cavity and the DC power supply Q1 are measured by the measuring cavity pressure sensor and the measuring cavity temperature sensor, thus completing one measurement; S4. After completing step S3, start the next measurement, keep the pressure and temperature of the inlet pressure sensor and the inlet temperature sensor stable at p0 and T0 respectively, keep the pressure of the measuring cavity pressure sensor of the measuring cavity stable at P1, and adjust the heating power Q2 of the spherical heating plate through the DC power supply; when the measuring body reaches thermal equilibrium again, record the temperature T2 of the test cavity temperature sensor; S5. Repeat step S4 several times and record the flow rate of the flow meter Measuring cavity temperature sensor temperature T i , DC power supply power Q i ; S6. Before stopping the measurement, first turn off the DC power supply and continue to keep the flow regulating pump turned on to cool the measuring body with the measured fluid to prevent damage to the spherical heating plate; S7. Calculate the molar specific heat capacity of the fluid.

8. The experimental method for measuring the constant pressure specific heat capacity of near-critical fluid according to claim 7, characterized in that: The step S7 specifically includes: adjusting the flow rate of the pump according to the flow rate set in step S1 And in step S2, the power Q1 of the DC power supply is set to obtain the molar enthalpy change Δh1 of the measured fluid in the state (T1, p1) relative to the reference state (T0, p0); similarly, the molar enthalpy change Δh2 of the measured fluid in the state (T2, p1) relative to (T0, p0) is obtained; the relative molar enthalpy change Δh(T, p1) of the fluid in the state (T, p1) compared to the reference state is obtained by fitting the experimental data; the constant-pressure specific heat under different states is obtained according to the fitting function.

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