A temperature control system for the additional volume in a pVTt method gas flow standard device

Abstract

The present invention relates to a temperature control system suitable for an additional volume of a pVTt method gas flow standard device, which can realize temperature compensation at the additional volume after passing through a critical flow venturi nozzle (CFVN) to be measured, realize temperature control at the additional volume, reduce the thermal equilibrium time of the pVTt method gas standard device, and improve the measurement efficiency of the pVTt method gas flow standard device.

Description

Technical Field

[0001] The invention relates to a temperature control system, in particular to a temperature control system at an additional volume in a pVTt method gas flow standard device. Background Art

[0002] Gas flow measurement is widely used in flow monitoring in the fields of energy, environment or medical treatment. Specifically, in gas measurement, it is especially used for the detection of household gas meters; in environmental gas measurement, it is used to monitor exhaust gas; in the gas measurement of the medical field, it is used to monitor the gas materials used; it can also be used for process control in industrial manufacturing such as pharmaceuticals, semiconductors, steel, petrochemicals, etc. Therefore, the accuracy of gas flow measurement plays a major role in the development of my country's economy.

[0003] The internal geometric parameters of the critical flow venturi nozzle (CFVN) are differential pressure flow meters of the gradually converging and expanding type. The smallest cross-section is called the throat. It gradually converges from the inlet to the throat, and then gradually expands from the throat to the outlet, including the contraction section, throat and diffusion section. CFVN is used as a transfer standard for value transfer of other types of gas flow meters due to its simple structure, no moving parts, high accuracy, and good repeatability. At the same time, CFVN can be directly traced back to the national gas flow primary standard device. Therefore, the sonic nozzle occupies an important position in the gas flow value traceability system and is a key link to ensure accurate and reliable gas flow measurement and unified value.

[0004] The pVTt method gas flow device is a commonly used gas flow reference device and the source of the unified gas flow value. The pVTt gas flow device mainly includes CFVN, a switch valve (with an additional timer), a standard container of known volume, a valve, a vacuum pump, a pressure and temperature measurement, and a control system for data acquisition and storage. When the pVTt method gas flow device is used to detect CFVN, due to the special geometric structure of the nozzle, the reduction in the nozzle cross-sectional area during the gas flow from the inlet to the throat brings about a sharp increase in gas flow rate, a decrease in pressure, and a decrease in temperature; when the gas flows from the throat to the outlet, the increase in cross-sectional area brings about a recovery of pressure and temperature, but the temperature cannot be completely restored to the stagnation temperature of the inlet. In addition, when a gas with a certain speed flows into a standard container through an additional volume, the drastic change in the speed of the gas itself will lead to an increase in the gas temperature.

[0005] Therefore, when the gas enters the standard container from a stagnant state, its temperature will change dramatically, resulting in a longer thermal equilibrium time for the pVTt method gas flow standard device and lower experimental efficiency. Summary of the invention

[0006] The purpose of the present invention is to implement a temperature control system at the additional volume to reduce the thermal equilibrium time of the pVTt method gas flow standard device and improve the detection efficiency of the pVTt method gas flow standard device.

[0007] The present invention provides a temperature control system at an additional volume in a pVTt method gas flow standard device, the pVTt method gas flow standard device comprises a critical flow Venturi nozzle, a switch valve, a standard container and a control system; an additional volume is provided between the critical flow Venturi nozzle and the switch valve; one end of the additional volume is connected to the critical flow Venturi nozzle, and the other end of the additional volume is connected to the switch valve; a temperature control system is provided at the additional volume, and the temperature control system regulates the temperature at the additional volume.

[0008] The switch valve is connected with a timer to control the start of measurement of the pVTt method gas standard device and record the air intake time.

[0009] The control system of the standard device measures the upstream stagnation temperature and stagnation pressure of the critical flow Venturi nozzle, and records the air intake time recorded by the timer, and the initial and final temperature and pressure in the standard container.

[0010] Wherein, the temperature control system regulates the temperature according to the flow rate of the critical flow Venturi nozzle to be measured.

[0011] The present invention also provides a method for controlling the temperature of an additional volume in a pVTt method gas flow standard device, comprising:

[0012] Start the vacuum pump, open the downstream valve of the standard container, and evacuate the pressure in the standard container to a starting pressure lower than 200Pa, i.e., p i <200Pa, ensure that the critical flow Venturi nozzle is in the critical flow state, and record the temperature and pressure in the standard container after the temperature and pressure in the standard container are stable;

[0013] Determine the temperature control at the additional volume based on the throat diameter, stagnation temperature and stagnation pressure of the critical flow Venturi nozzle;

[0014] Open the switch valve, trigger the timer, and collect the stagnation temperature and stagnation pressure of the Venturi nozzle corresponding to the critical flow to be measured during the intake process. Ensure the critical flow, close the switch valve, record the intake time, and record the temperature and pressure in the standard container after the temperature and pressure in the standard container reach stability.

[0015] The present invention also provides an additional volume temperature control system for a pVTt method gas flow standard device, which comprises:

[0016] A heating part, one end of which is directly connected to the nozzle outlet, and the other end of which is extended to the cooling part; the amount of heating is controlled by the heating power of the electric heating wire;

[0017] One end of the refrigeration part is connected to the heating part, and the other end is connected to the standard container of the pVTt method gas standard device. The refrigeration capacity is controlled by the flow rate of the cooling circulating water.

[0018] The control system of the device controls and records the stagnation parameters of the sonic nozzle, the air intake switch valve and the air intake time, the temperature control system at the additional volume and the thermodynamic parameters in the standard container.

[0019] The present invention also provides a method for controlling the temperature at the additional volume of a pVTt method gas flow standard device, the steps of which are:

[0020] Start the vacuum pump to pump the pressure in the standard container of the pVTt method gas flow standard device to 200 Pa;

[0021] The control system measures the temperature and pressure in the standard container in real time. After the temperature and pressure parameters are balanced, the temperature and pressure in the standard container are recorded, which are the starting temperature and pressure, i.e., T i , p i ;

[0022] Open the on-off valve and start recording the air intake time and the stagnation parameters upstream of the nozzle;

[0023] The heating part of the temperature control system at the additional volume is started, and when the pressure in the standard container reaches a certain pressure value, the cooling part is started;

[0024] When the pressure in the standard container reaches a predetermined value, the switch valve is closed and the time recording is stopped to obtain the intake time of the standard device, t; and the average value of the stagnation parameter during the intake time is calculated to obtain T0, p0;

[0025] The control system measures the temperature and pressure in the standard container in real time. After the temperature and pressure parameters are balanced, the temperature and pressure in the standard container are recorded, which are the end temperature and pressure, i.e. T f , p f ;

[0026] Based on the throat diameter of the nozzle to be tested, the nozzle discharge coefficient, C d Right now

[0027]

[0028] The present invention establishes a temperature control system for the additional volume in the pVTt method gas flow standard device. Through the temperature control system, the temperature entering the standard container is controlled, thereby reducing the thermal equilibrium time of the temperature in the standard container after the intake of air, and effectively improving the detection efficiency of the standard device. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of the pVTt method gas flow standard device system of the present invention;

[0030] Figure 2 It is a schematic diagram of a temperature control system at an additional volume of a pVTt method gas flow standard device of the present invention;

[0031] Figure 3 This is the temperature control method at the additional volume of the present invention. DETAILED DESCRIPTION

[0032] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0033] It will be understood by those skilled in the art that, unless otherwise stated, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we say "connected" or "coupled", it can be directly connected or coupled to other components, or there may be intermediate components.

[0034] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0035] To facilitate understanding of the embodiments of the present invention, further explanation will be given below using specific embodiments as examples in conjunction with the accompanying drawings.

[0036] Figure 1 FIG. 1 is a schematic diagram of the structure of the pVTt method gas flow standard device of the present invention. Figure 1 As shown, the pVTt method gas flow standard device includes a critical flow Venturi nozzle (CFVN) and a switch valve, the switch valve is connected with a timer, which is used to control the measurement start of the pVTt method gas standard device and record the intake time, and there is an additional volume between the critical flow Venturi nozzle (CFVN) and the switch valve, one end of the additional volume is connected to the critical flow Venturi nozzle (CFVN), and the other end of the additional volume is connected to the switch valve; the upstream of the critical flow Venturi nozzle (CFVN) is the atmosphere, the stagnation temperature is T0, and the stagnation pressure is p0; the downstream is connected to the standard container through the additional volume, the temperature in the standard container is T, and the pressure is p; the standard container is connected to a vacuum pump, and a valve is provided between the standard container and the vacuum pump.

[0037] Considering that the additional volume is connected to the standard container, at the beginning of the air intake, due to the low pressure at the additional volume, the temperature at the additional volume is dominated by the decrease factor; with the increase of the air intake time, the pressure at the additional volume and in the standard container gradually increases, and the temperature at the additional volume is dominated by the increase factor. Therefore, in order to reduce the thermal equilibrium time of the pVTt method gas flow standard device and improve its detection efficiency, during the air intake process, when the pressure in the standard container is low, the heating part of the temperature control system at the additional volume needs to be turned on; when the pressure in the standard container reaches a certain critical value, the cooling part of the temperature control system at the additional volume needs to be turned on. The determination of this critical value is closely related to the flow rate of the sonic nozzle and the structural parameters of the additional volume.

[0038] A temperature control system is provided at the additional volume, and the temperature control system regulates the temperature at the additional volume; the temperature control system comprises a heating part and a cooling part, the heating part preferably adopts an electric heating wire with adjustable heating power, and the cooling part preferably adopts a refrigerating liquid for circulating cooling, and further preferably adopts circulating water for cooling; the control system of the standard device automatically measures and records the upstream stagnation temperature and pressure of the critical flow Venturi nozzle (CFVN), and the temperature, pressure and other parameters in the standard container; the throat diameter of the critical flow Venturi nozzle under test is input into the control system, and based on the parameters of the control system of the standard device, the control system automatically calculates the amount of heat exchange, compensates for the temperature change at the additional volume, and effectively reduces the thermal equilibrium time of the standard container.

[0039] Figure 2 This is a schematic diagram of the structure of the temperature control system of the additional volume of the pVTt method gas flow standard device of the present invention. Figure 2As shown, the temperature control system includes: a heating part (a), one end of which is directly connected to the nozzle outlet, and the other end extends close to the cooling part (b), the amount of heat in the heating part is controlled by the heating power of the electric heating wire, the heating wire is wound on the additional volume, and the additional volume is preferably a pipeline; one end of the cooling part is adjacent to the heating part, and the other end is close to the standard container of the pVTt method gas standard device, the amount of cooling in the cooling part is controlled by the flow rate of the cooling circulating water; the cooling part includes a water pump, a cooling water tank and a cooling water pipe, the cooling water pipe is wound on the additional volume, and the additional volume is cooled by the cooling water pipe. The control system of the standard device controls and records the stagnation parameters of the sonic nozzle, the air intake switch valve and the air intake time, the temperature control system at the additional volume, and the thermodynamic parameters in the standard container.

[0040] The temperature control method at the additional volume of the pVTt method gas flow standard device of the present invention is introduced below. The steps of the control method include:

[0041] First, start the vacuum pump to draw vacuum from the standard container;

[0042] The control system of the standard device measures the temperature and pressure in the standard container in real time. After the temperature and pressure parameters are balanced, the temperature and pressure in the standard container are recorded and expressed as the starting temperature and pressure, i.e., T i , p i Preferably, the pressure in the standard container of the pVTt method gas flow standard device is pumped to 200Pa, that is, p i <200Pa;

[0043] Open the on-off valve and start recording the air intake time and the stagnation parameters upstream of the nozzle;

[0044] Start the heating part of the temperature control system at the additional volume, and the amount of heating can be roughly determined by the following formula, ΔH

[0045]

[0046] The amount of heating is related to the flow rate of the nozzle to be tested (m), the specific heat of the gas in the system to be tested (C p ) and the heat transfer coefficient (k h ) and the difference between the temperature at the additional volume and the stagnation temperature (ΔT).

[0047] When the pressure in the standard container reaches a certain value, usually not exceeding 15kPa, the refrigeration part is started and the heating part is turned off. The cooling capacity, ΔC, can be estimated by the following formula:

[0048] ΔC=kc ·m·C p ΔT (2)

[0049] The cooling capacity is related to the flow rate of the nozzle under test (m), the specific heat of the gas in the system under test (C p ) and the heat transfer coefficient (k c ) and the difference between the temperature at the additional volume and the stagnation temperature (ΔT).

[0050] The heating and cooling capacity in a standard container varies with pressure. Figure 3 As shown, when the pressure in the standard container reaches a first predetermined value, the heating part is turned off and the cooling part is started, and the heat exchange control changes with the increase of pressure.

[0051] When the pressure in the standard container reaches a predetermined value, the final pressure in the standard container reaches about 50 kPa, i.e., p f <50kPa; close the switch valve and stop recording time to obtain the intake time t of the standard device; and calculate the average value of the stagnation parameters during the intake time to obtain T0, p0;

[0052] The control system of the standard device measures the temperature and pressure in the standard container in real time. After the temperature and pressure parameters are balanced, the temperature and pressure in the standard container are recorded, which are the end temperature and pressure, i.e. T f , p f ;

[0053] Based on the throat diameter of the nozzle to be tested, the nozzle discharge coefficient, C d Right now

[0054]

[0055] Among them, q m is the actual mass flow rate through the nozzle measured by the pVTt device; q mi is the ideal mass flow rate through the nozzle; R u is the universal gas constant; M is the molecular weight; C * is the critical flow function; d is the throat diameter of the nozzle; V is the standard volume of the pVTt method gas flow standard device; p0 is the stagnation pressure; T0 is the stagnation temperature; p i 、p f is the starting and ending pressure of the gas in the standard container; T i , T f is the starting and ending temperature of the gas in the standard container; Z i , Z f are the starting and ending compression factors of the gas in the standard container.

[0056] Outflow coefficient Cd As one of the important parameters of the outflow characteristics of a sonic nozzle, it is an important parameter that correlates the actual mass flow rate and the ideal mass flow rate flowing through the sonic nozzle, and is also a key parameter to ensure accurate and reliable gas flow measurement and uniform value. The pVTt method gas flow standard device is the main standard device for detecting the outflow coefficient of a sonic nozzle, and its calculation formula is shown in formula (3). The present invention can reduce the thermal equilibrium time of the pVTt method gas flow standard device through the temperature control system at the additional volume, thereby improving the detection efficiency. Based on the measurement capability of the pVTt method gas flow standard device, the initial parameters of the temperature control system can be prefabricated in the control system of the standard device, and through typical experiments, the optimized control parameters can be finally determined, thereby reducing the detection efficiency of the pVTt method gas flow standard device from the traditional hour level to a value within 10 minutes, greatly improving its detection efficiency.

[0057] Although the present invention has been disclosed as above with preferred embodiments, the above embodiments are not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A temperature control system at an additional volume in a pVTt method gas flow standard device, characterized in that: The pVTt method gas flow standard device comprises a critical flow venturi nozzle, a switch valve, a standard container and a control system; an additional volume is provided between the critical flow venturi nozzle and the switch valve; One end of the additional volume is connected to the critical flow venturi nozzle, and the other end of the additional volume is connected to the switch valve; A temperature control system is provided at the additional volume, and the temperature control system comprises: a heating part, one end of which is directly connected to the nozzle outlet, and the other end of which extends close to the cooling part, the amount of heat in the heating part is controlled by the heating power of the electric heating wire, the heating wire is wound around the additional volume, and the additional volume is a pipeline; one end of the cooling part is adjacent to the heating part, and the other end is close to the standard container of the pVTt method gas flow standard device, the amount of cooling of the cooling part is controlled by the flow of cooling circulating water; the cooling part comprises a water pump, a cooling water tank and a cooling water pipe, the cooling water pipe is wound around the additional volume, and the additional volume is cooled by the cooling water pipe; The temperature control system regulates the temperature at the additional volume, starts the vacuum pump, and draws vacuum from the standard container; the control system of the standard device measures the temperature and pressure in the standard container in real time, and after the temperature and pressure parameters are balanced, records the temperature and pressure in the standard container, which are expressed as the starting temperature and pressure, i.e. T i , p i ; Pump the pressure in the standard container of the pVTt method gas flow standard device to a starting pressure lower than 200 Pa, that is p i <200 Pa; Open the on-off valve and start recording the air intake time and the stagnation parameters upstream of the nozzle; Start the heating part of the temperature control system at the additional volume and determine the amount of heating by the following formula, ΔH The amount of heating and the flow rate of the nozzle being tested m , gas specific heat of the system to be measured C p and heat transfer coefficients depending on standard device geometry and material properties k h and the difference between the temperature at the additional volume and the stagnation temperature Δ T Related; When the pressure in the standard container reaches a certain value, usually no more than 15kPa, the refrigeration part is started and the heating part is turned off. The cooling capacity, Δ C By estimating it through the following formula, The cooling capacity and the flow rate of the nozzle being tested m , gas specific heat of the system to be measured C p and heat transfer coefficients depending on standard device geometry and material properties k c and the difference between the temperature at the additional volume and the stagnation temperature Δ T Related; collect the stagnation temperature and stagnation pressure of the critical flow Venturi nozzle to be tested during the intake process; Ensure critical flow, close the switch valve, record the air intake time, and after the temperature and pressure in the standard container become stable, record the temperature and pressure in the standard container.

2. The temperature control system at the additional volume in the pVTt method gas flow standard device according to claim 1, characterized in that: The switch valve is connected with a timer, which is used to control the measurement start of the pVTt method gas standard device and record the air intake time.

3. The temperature control system at the additional volume in the pVTt method gas flow standard device according to claim 1, characterized in that: The control system of the standard device measures the upstream stagnation temperature and stagnation pressure of the critical flow Venturi nozzle, and records the air intake time recorded by the timer, and the initial and final temperature and pressure in the standard container.

4. The temperature control system at the additional volume in the pVTt method gas flow standard device according to claim 1, characterized in that: The temperature control system regulates the temperature according to the flow rate of the critical flow Venturi nozzle to be measured.

5. A temperature control method for a temperature control system at an additional volume in a pVTt method gas flow standard device according to any one of claims 1 to 4, comprising: Start the vacuum pump, open the downstream valve of the standard container, and evacuate the pressure in the standard container until the initial pressure is lower than 200Pa. p i <200 Pa, ensure that the critical flow Venturi nozzle is in the critical flow state, and record the temperature and pressure in the standard container after the temperature and pressure in the standard container are stable; Determine the temperature control at the additional volume based on the throat diameter, stagnation temperature and stagnation pressure of the critical flow Venturi nozzle; Open the switch valve, trigger the timer, and start recording the air intake time and the stagnation parameters upstream of the nozzle; Start the heating part of the temperature control system at the additional volume and determine the amount of heating by the following formula, Δ H The amount of heating and the flow rate of the nozzle being tested m , gas specific heat of the system to be measured C p and heat transfer coefficients depending on standard device geometry and material properties k h and the difference between the temperature at the additional volume and the stagnation temperature Δ T Related; When the pressure in the standard container reaches a certain value, not exceeding 15kPa, the refrigeration part is started and the heating part is closed. The cooling capacity, Δ C By estimating it through the following formula, The cooling capacity and the flow rate of the nozzle being tested m , gas specific heat of the system to be measured C p and heat transfer coefficients depending on standard device geometry and material properties k c and the difference between the temperature at the additional volume and the stagnation temperature Δ T Related; collect the stagnation temperature and stagnation pressure of the critical flow Venturi nozzle to be tested during the intake process; Ensure critical flow, close the switch valve, record the air intake time, and after the temperature and pressure in the standard container become stable, record the temperature and pressure in the standard container.

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