Air specific heat capacity measuring device and measuring method

Abstract

The invention discloses an air specific heat ratio measuring device and a measuring method, particularly relates to the technical field of air specific heat ratio measurement, and solves the technical problem that in an air specific heat ratio measuring experiment in the prior art, a large error of test data is easily caused by closing a deflation valve by listening to sound. According to the technical scheme, a gas flow sensor is used, pulses are applied to a stepping motor according to the change of gas flow, the stepping motor is made to automatically close a valve, and accidental errors caused by subjective judgment of students are reduced; the experimental device is improved, so that the experimental result is more accurate.

Description

Technical Field

[0001] The invention relates to the technical field of air specific heat ratio measurement, and in particular to an air specific heat ratio measurement device and a measurement method. Background Art

[0002] In the experiment of measuring the specific heat ratio of air, the FD-NCD-II type air specific heat ratio measuring instrument is used more frequently. The FD-NCD-II type air specific heat ratio measuring instrument has the following problems in the experiment: ① The data is displayed as a voltage value, which needs to be converted into the actual pressure difference and temperature value by a certain relationship. ② The sensitivity of the sensor used in the experimental device is relatively low, and there is a delay in reading the data. ③ The data displayed by the instrument is only the gas pressure difference and temperature value in the device at a certain moment, which is not convenient for observing the real-time changes in the state of the device. According to the manufacturer, the differential pressure sensor has a lag in response. When the differential pressure sensor shows zero, the deflation process has ended in advance, and the moment when the deflation sound ends is closer to the end of the adiabatic deflation process. Therefore, the textbooks all advocate or require students to close the deflation valve by listening to the sound. However, in fact, the size of the deflation sound is determined by the internal and external pressure difference. When the deflation process is nearing the end, the internal and external pressure difference is relatively small, and the deflation sound formed becomes difficult for the human ear to distinguish. In addition, in the classroom, students are using experimental instruments for the first time, and they are lacking in experience and judgment. Therefore, the method of listening to the sound will inevitably have systematic errors and accidental errors. The traditional experimental device requires students to manually pump air, but the manual pumping speed is slow, which will cause heat exchange between the gas in the bottle and the atmosphere, and cannot meet the requirements of a near-adiabatic process. Summary of the invention

[0003] Therefore, the present invention solves the technical problem that in the prior art, in the measurement experiment of the specific heat ratio of air, due to the hysteresis of the response of the differential pressure sensor, when the differential pressure sensor indicates zero, the deflation process has ended in advance, and the moment when the deflation sound ends is closer to the end of the adiabatic deflation process. Therefore, the textbooks all advocate or require students to close the deflation valve by listening to the sound, but in fact, the size of the deflation sound is determined by the internal and external pressure difference. When the deflation process is nearing the end, the internal and external pressure difference is relatively small, and the deflation sound formed becomes difficult for the human ear to distinguish. The present invention provides an air specific heat capacity measurement device and measurement method. Through comprehensive consideration and experiments on different sensors, it is finally determined to use a gas flow sensor. By changing the gas flow, pulses are applied to the stepper motor to automatically close the valve, thereby reducing accidental errors caused by students' subjective judgment.

[0004] The present invention provides an air specific heat capacity measuring device, including a gas storage bottle, the top of which is sealed, and the interior of which is connected to an electric air pump through an air pipe, and an air charging valve is arranged between the electric air pump and the gas storage bottle; a gas flow meter is arranged on the top of the gas storage bottle, and the gas flow meter is connected to the interior of the gas storage bottle, and an air release valve is arranged between the gas flow meter and the gas storage bottle. There is a certain randomness in closing the air release valve by listening to the sound. When the air release process is nearing the end, the internal and external pressure difference is relatively small, and the air release sound formed becomes difficult for the human ear to distinguish. In order to reduce such errors, we have comprehensively considered and experimented with different sensors, and finally determined to use a gas flow meter. By changing the gas flow, pulses are applied to the stepper motor to automatically close the valve, reducing accidental errors caused by students' subjective judgment.

[0005] Furthermore, a heating rod is provided in the gas storage bottle, and the electric control end of the heating rod is connected to the control end of the temperature controller outside the gas storage bottle. By installing the heating rod device in the bottle, the temperature in the bottle can be dynamically regulated, so that it is not limited to room temperature, and students can measure the changes in the specific heat ratio of air at different temperatures.

[0006] Furthermore, a BMP388 sensor is provided in the gas cylinder, and its output end is connected to the control end of the Arduino control board outside the gas cylinder. The BMP388 sensor is a 24-bit high-precision pressure and temperature sensor that can achieve accurate height tracking, detect atmospheric pressure and temperature, and has small size, low power consumption, low noise, and high precision. It is particularly suitable for application scenarios such as environmental monitoring and the Internet of Things. We incorporate BMP388 into this experiment, so that the pressure and temperature in the bottle can be measured in real time, making the measurement more accurate.

[0007] Furthermore, the exhaust valve switch is connected to the output shaft of the stepper motor, the electronically controlled driving end of the stepper motor is connected to the input end of the motor driver, and a power supply module is provided at the bottom of the motor driver.

[0008] Furthermore, a bracket is arranged at the bottom of the stepping motor.

[0009] Furthermore, a drying tube is provided between the electric air pump and the air charging valve.

[0010] The present invention also provides a measurement method based on the above-mentioned air specific heat ratio measurement device,

[0011] S1: When measuring the specific heat ratio of air at room temperature, the following steps are included:

[0012] S11: close the charging valve and open the venting valve to connect the gas storage bottle to the atmosphere; then close the venting valve and open the charging valve, and use the electric charging pump to pressurize the air originally at the ambient atmospheric pressure P0 and room temperature T0 into the gas storage bottle through the electric charging pump. After about 2 to 3 seconds, close the charging valve to stop charging, and observe the changes in the gas pressure and temperature in the bottle during this process;

[0013] S12: Let it stand for a while, and wait until the temperature in the bottle drops to room temperature T1, and then record the pressure P1;

[0014] S13: Open and close the air release valve once through the stepper motor;

[0015] S14: Let it stand for a while until the temperature in the bottle drops to room temperature T2, and record the pressure P2 at this time;

[0016] S15: Calculate the specific heat ratio of air at room temperature;

[0017] S16: Repeat steps S11 to S15, measure and record five sets of data, and calculate relative error and uncertainty;

[0018] S2: When measuring the specific heat ratio of air at different temperatures, the following steps are included:

[0019] S21: Open the vent valve to connect the gas storage bottle to the atmosphere, close the vent valve, turn on the temperature controller, control the heating rod to the required temperature, observe the data transmitted by the bmp388 sensor, and when the temperature in the bottle remains unchanged for 5 minutes, record the temperature T0 and pressure P0 in the bottle at this time;

[0020] S22: Open the inflation valve, and use the electric inflation pump to pressurize the air originally at the ambient atmospheric pressure P0 and room temperature T0 into the gas storage bottle through the inflation pump, and the duration is about 2 to 3 seconds. Close the inflation valve and stop inflation, and observe the changes in the gas pressure and temperature in the bottle during this process;

[0021] S23: When the temperature in the bottle returns to T1 after a period of time, the pressure P1 in the bottle is recorded;

[0022] S24: Open and close the air release valve once through the stepper motor;

[0023] S25: After the temperature in the bottle is left to stand for a period of time and drops to temperature T2, the pressure P2 at this time is recorded;

[0024] S26: Calculate the specific heat ratio of air at this temperature;

[0025] S27: Repeat steps S21 to S26, change the temperature controlled by the heating rod in step S21, measure and record 10 sets of data, and calculate the relative error and uncertainty.

[0026] Furthermore, the step S15 and step S26 may be calculated using a computer, and the formula used to calculate the specific heat ratio is as follows:

[0027]

[0028] Furthermore, the formula used to calculate the specific heat ratio is obtained as follows: suppose the room temperature before inflation is T, after inflation, the room temperature when the gas in the bottle is balanced is T', and the gas state is I (P1, V1, T1); after deflation, adiabatic expansion occurs, and the gas state is II (P0, V2, T0); the room temperature when the gas in the isochoric endothermic bottle is balanced is T", and the gas state changes to III (P2, V2, T2), where V is the volume of the gas storage bottle, and V1 is the volume of the gas retained in the bottle in state I (P1, T1); the state of the gas in the bottle changes to:

[0029] I(P1,V1,T1)---------II(P0,V2,T0)--------III(P2,V2,T2)

[0030] I→II is an adiabatic process, and from the adiabatic process equation we get:

[0031] P1(V1) γ =P0(V2) γ

[0032] For the two states I and III, the ideal gas state equation gives:

[0033] P1V1=nRT1

[0034] P2V2=nRT2

[0035] Combining the above three equations and eliminating V1 and V2, we get:

[0036]

[0037] Therefore, at this time we only need to measure P1, P0, P2, T1, and T2 to calculate the accurate air specific heat ratio γ.

[0038] Furthermore, the steps S5 and S12 use Python code to calculate the formula by computer. Finally, in order to analyze the data and study the effect of temperature on the specific heat ratio of air, we designed a Python program to help us calculate and analyze the data faster and more accurately, and present the results of multiple measurements in a table.

[0039] In the above technical solution, the technical effects and advantages provided by the present invention are:

[0040] 1. The present invention provides an air specific heat capacity measuring device and a measuring method, which uses a BMP388 pressure sensor to measure changes in air pressure and temperature in a bottle. The sensor has high sensitivity, good linearity and stability, and can display data in real time by connecting to a computer; by optimizing the sensor design and signal processing algorithm, the measuring device can respond to changes in air temperature and pressure more quickly.

[0041] 2. The present invention provides an air specific heat capacity measurement device and method, which utilizes a stepper motor to control the opening and closing of an air release valve to reduce human-caused errors; and by changing the temperature, it is possible to explore changes in the air specific heat ratio at different temperatures.

[0042] 3. The present invention provides an air specific heat capacity measuring device and method. Compared with the original experimental device, the device adopts more cost-effective materials and technologies to reduce the cost of the entire measurement system. At the same time, it improves on the basis of the original experimental calculation formula to make the calculation result more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0044] Figure 1 It is a schematic diagram of the overall structure of the air specific heat capacity measuring device of the present invention;

[0045] Figure 2 It is a connection diagram of the air specific heat capacity measuring device of the present invention;

[0046] Figure 3 This is an operation flow chart of the air specific heat capacity measuring device of the present invention;

[0047] Figure 4 This is a test actual picture of the air specific heat capacity measuring device of the present invention.

[0048] Description of reference numerals:

[0049] 1. Power module; 2. Motor driver; 3. Bracket; 4. Gas storage bottle; 5. Heating rod; 6. Temperature controller; 7. Electric air pump; 8. Drying tube; 9. Inflation valve; 10. Gas flow meter; 11. Deflation valve; 12. Stepper motor; 13. Arduino control board; 14. BMP388 sensor. DETAILED DESCRIPTION

[0050] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0051] Embodiment 1:

[0052] The present embodiment provides an air specific heat capacity measuring device, including a gas cylinder 4, the top of which is sealed, and the inside of which is connected to an electric air pump 7 through an air pipe, and an air charging valve 9 is arranged between the electric air pump 7 and the gas cylinder 4; a gas flow meter 10 is arranged on the top of the gas cylinder 4, and the gas flow meter 10 is connected to the inside of the gas cylinder 4, and a deflation valve 11 is arranged between the gas flow meter 10 and the gas cylinder 4. A heating rod 5 is arranged in the gas cylinder 4, and the electric control end of the heating rod 5 is connected to the control end of the temperature controller 6 outside the gas cylinder 4. A BMP388 sensor 14 is arranged in the gas cylinder 4, and its output end is connected to the control end of the Arduino control board 13 outside the gas cylinder 4. The valve switch of the deflation valve 11 is connected to the output shaft of the stepper motor 12, and the electric control drive end of the stepper motor 12 is connected to the input end of the motor driver 2, and a power supply module 1 is arranged at the bottom of the motor driver 2.

[0053] By connecting the Arduino control board 13 to the host computer, the user can operate the measuring device on the host computer interface and directly obtain the measurement data and results; there is a certain randomness in closing the deflation valve 11 by listening to the sound. When the deflation process is nearing the end, the internal and external pressure difference is relatively small, and the deflation sound formed becomes difficult for the human ear to distinguish. In order to reduce such errors, we have comprehensively considered and experimented with different sensors and finally determined to use a gas flow sensor. By applying pulses to the stepper motor 12 according to the change of gas flow, it automatically closes the valve and reduces the accidental errors caused by students' subjective judgment. By installing a heating rod 5 device in the bottle, the temperature in the bottle can be dynamically adjusted, so that it is not limited to room temperature, and students can measure the changes in the specific heat ratio of air at different temperatures.

[0054] In this embodiment, a bracket 3 is disposed at the bottom of the stepping motor 12 .

[0055] The stepper motor 12 can be raised by the bracket 3 to facilitate the control of the air release valve 11;

[0056] In this embodiment, a drying tube 8 is provided between the electric air pump 7 and the air charging valve 9. The drying tube 8 can dry the air.

[0057] Embodiment 2:

[0058] This embodiment provides a measurement method based on the above-mentioned air specific heat ratio measurement device,

[0059] S1: When measuring the specific heat ratio of air at room temperature, the following steps are included:

[0060] S:1: Close the charging valve 9 and open the venting valve 11 to connect the gas storage bottle 4 to the atmosphere; then close the venting valve 11 and open the charging valve 9, and use the electric charging pump 7 to press the air originally at the ambient atmospheric pressure P0 and room temperature T0 into the gas storage bottle 4 through the electric charging pump 7. After about 2 to 3 seconds, close the charging valve 9 to stop charging, and observe the changes in the gas pressure and temperature in the bottle during this process;

[0061] S12: Let it stand for a while, and wait until the temperature in the bottle drops to room temperature T1, and then record the pressure P1;

[0062] S13: Open and close the air release valve 11 once through the stepper motor 12;

[0063] S14: Let it stand for a while until the temperature in the bottle drops to room temperature T2, and record the pressure P2 at this time;

[0064] S15: Calculate the specific heat ratio of air at room temperature;

[0065] S16: Repeat steps S11 to S15, measure and record five sets of data, and calculate relative error and uncertainty;

[0066] S2: When measuring the specific heat ratio of air at different temperatures, the following steps are included:

[0067] S:21: Open the vent valve 11 to connect the gas storage bottle 4 to the atmosphere, close the vent valve 11, turn on the temperature controller 6, control the heating rod 5 to adjust to the required temperature, observe the data transmitted by the bmp388 sensor, and when the temperature in the bottle remains unchanged for 5 minutes, record the temperature T0 and pressure P0 in the bottle at this time;

[0068] S22: Open the inflation valve 9, and use the electric inflation pump 7 to pressurize the air originally at the ambient atmospheric pressure P0 and the room temperature T0 into the gas storage bottle 4 through the inflation pump, and the duration is about 2 to 3 seconds. Then, close the inflation valve 9 and stop inflation, and observe the changes in the gas pressure and temperature in the bottle during this process;

[0069] S23: When the temperature in the bottle returns to T1 after a period of time, the pressure P1 in the bottle is recorded;

[0070] S24: Open and close the air release valve 11 once through the stepper motor 12;

[0071] S25: After the temperature in the bottle is left to stand for a period of time and drops to temperature T2, the pressure P2 at this time is recorded;

[0072] S26: Calculate the specific heat ratio of air at this temperature;

[0073] S27: Repeat steps S21 to S26, change the temperature controlled by the heating rod 5 in step S21, measure and record 10 sets of data, and calculate the relative error and uncertainty.

[0074] In this embodiment, the formula used in step S15 and step S26 to calculate the specific heat ratio is as follows:

[0075]

[0076] The measurement data of this device is compared with the measurement data of the original experimental equipment through the above measurement method as follows;

[0077] Data measured by the original experimental equipment before improvement:

[0078]

[0079]

[0080]

[0081]

[0082] The data measured by the improved present invention are as follows:

[0083]

[0084]

[0085]

[0086]

[0087] After comparison, it can be found that the measurement result of the present invention is 4 percentage points more accurate than the measurement result of the original equipment.

[0088] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. An air specific heat ratio measuring device, characterized in that: The invention comprises a gas storage bottle (4), the top of which is sealed and the interior of which is connected to an electric air pump (7) via an air pipe, and an air charging valve (9) is arranged between the electric air pump (7) and the gas storage bottle (4); a gas flow meter (10) is arranged on the top of the gas storage bottle (4), the gas flow meter (10) is connected to the interior of the gas storage bottle (4), and an air release valve (11) is arranged between the gas flow meter (10) and the gas storage bottle (4).

2. The air specific heat ratio measuring device according to claim 1, characterized in that: A heating rod (5) is arranged inside the gas storage bottle (4), and an electric control end of the heating rod (5) is connected to a control end of a temperature controller (6) outside the gas storage bottle (4).

3. The air specific heat ratio measuring device according to claim 2, characterized in that: The gas storage bottle (4) is provided with a BMP388 sensor (14), the output end of which is connected to the control end of an Arduino control board (13) outside the gas storage bottle (4).

4. The air specific heat ratio measuring device according to claim 3, characterized in that: The valve switch of the air release valve (11) is connected to the output shaft of the stepping motor (12), the electric control drive end of the stepping motor (12) is connected to the input end of the motor driver (2), and a power supply module (1) is arranged at the bottom of the motor driver (2).

5. The air specific heat ratio measuring device according to claim 4, characterized in that: A bracket (3) is arranged at the bottom of the stepping motor (12).

6. The air specific heat ratio measuring device according to claim 5, characterized in that: A drying pipe (8) is provided between the electric air pump (7) and the air charging valve (9).

7. A measurement method based on the air specific heat ratio measurement device according to any one of claims 1 to 6, characterized in that: S1: When measuring the specific heat ratio of air at room temperature, the following steps are included: S11: close the charging valve (9) and open the venting valve (11) to allow the gas storage bottle (4) to communicate with the atmosphere; then close the venting valve (11) and open the charging valve (9), and use the electric charging pump (7) to press the air originally at the ambient atmospheric pressure P0 and the room temperature T0 into the gas storage bottle (4), and after a certain period of time, close the charging valve (9) to stop charging, and observe the changes in the gas pressure and temperature in the bottle during this process; S12: Let it stand for a while, and wait until the temperature in the bottle drops to room temperature T1, and then record the pressure P1; S13: opening and closing the air release valve (11) once via the stepping motor (12); S14: Let it stand for a while until the temperature in the bottle drops to room temperature T2, and record the pressure P2 at this time; S15: Use the following formula to let the computer calculate by itself: S16: Repeat steps S11 to S15, measure and record multiple sets of data, and calculate relative errors and uncertainties at the same time; S2: When measuring the specific heat ratio of air at different temperatures, the following steps are included: S21: Open the vent valve (11) to allow the gas storage bottle (4) to communicate with the atmosphere, close the vent valve (11), turn on the temperature controller (6), control the heating rod (5) to adjust to the required temperature, observe the data transmitted by the bmp388 sensor, and when the temperature in the bottle remains unchanged for 5 minutes, record the temperature T0 and pressure P0 in the bottle at this time; S22: opening the inflation valve (9), and using the electric inflation pump (7) to pressurize the air originally at the ambient atmospheric pressure P0 and the room temperature T0 into the gas storage bottle (4) through the inflation pump, and after a certain period of time, closing the inflation valve (9) and stopping the inflation, and observing the changes in the gas pressure and temperature in the bottle during this process; S23: When the temperature in the bottle returns to T1 after a period of time, the pressure P1 in the bottle is recorded; S24: opening and closing the air release valve (11) once via the stepping motor (12); S25: After the temperature in the bottle is left to stand for a period of time and drops to temperature T2, the pressure P2 at this time is recorded; S26: Use Python code to let the computer calculate the following formula: S27: Repeat steps S21 to S26, change the temperature regulated by the heating rod (5) in step S21, measure and record multiple sets of data, and calculate relative errors and uncertainties at the same time.

8. The measuring method according to claim 7, characterized in that: The formula used in step S5 and step S12 to calculate the specific heat ratio is as follows: The formula used to calculate the specific heat ratio is as follows: suppose the room temperature before inflation is T, after inflation, the room temperature when the gas in the bottle is balanced is T', and the gas state is I (P1, V1, T1). After deflation, adiabatic expansion occurs, and the gas state is II (P0, V2, T0). The room temperature when the gas in the isochoric endothermic bottle is balanced is T", and the gas state changes to III (P2, V2, T2), where V is the volume of the gas storage bottle, and V1 is the volume of the gas retained in the bottle in state I (P1, T1); the state of the gas in the bottle changes to: I(P1,V1,T1)---------II(P0,V2,T0)--------III(P2,V2,T2) I→II is an adiabatic process, and from the adiabatic process equation we get: <h2 style=";text-align:left;direction:ltr">P1(V1)<h2 style=";text-align:left;direction:ltr"> γ <h2 style=";text-align:left;direction:ltr"> =P0(V2)<h2 style=";text-align:left;direction:ltr"> γ For the two states I and III, the ideal gas state equation gives: P1V1=nRT1 P2V2=nRT2 Combining the above three equations and eliminating V1 and V2, we get: Measure P1, P0, P2, T1, T2, and calculate the accurate specific heat ratio γ of air.

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