CN103292847A - Short-capillary flow sensor - Google Patents

Abstract

The present invention is a short capillary flow sensor for measuring the mass flow rate of refrigerant fluid under high pressure, comprising a short capillary throttling device and a pressure detection device, the short capillary throttling device includes a short capillary inner tube and an outer tube; The pressure detection device is located at both ends of the capillary throttling device, and is used to measure the high pressure P ₁ and the low pressure P ₂ respectively. The short capillary flow sensor described is a throttling or differential pressure flow sensor, and the volume flow and pressure difference

Relevant; the relationship between the mass flow coefficient κ changing with the pressure P ₁ is measured experimentally

, capable of measuring mass flow . The present invention is mainly used for dosing control in the process of container fumigation and disinfection, specifically, the liquid sulfuryl fluoride in the high-pressure steel cylinder is exported, simultaneously measured and controlled, and the gaseous sulfuryl fluoride is injected into the container; the present invention The invention can also be used in the measurement and control of the refrigerant flow in the refrigeration process.

Description

A Short Capillary Flow Sensor

technical field

The invention relates to a short capillary flow sensor, in particular to a measuring device which uses a short capillary as a throttling element to measure the mass flow rate of a refrigerant fluid medium, and belongs to the technical field of throttling or differential pressure flow measurement.

Background technique

In the container fumigation and disinfection operation, it is necessary to send the liquid sulfuryl fluoride in the high-pressure steel cylinder into the container through the connecting pipeline according to the specified method and quality. When liquid sulfuryl fluoride in a high-pressure state passes through the transmission pipeline, the pressure decreases, the volume expands, and the temperature decreases. Under the condition of absorbing enough heat, it can all turn into a gas. According to the requirements of the National Entry-Exit Inspection and Quarantine Bureau, the dosage must be strictly controlled. The purpose is to ensure the requirements of killing and disinfection, and to minimize the harm of sulfuryl fluoride gas to the human body and the environment, and to control fumigation. Disinfection costs.

There are three forms of matter, solid, liquid and gas, and as the external conditions change, the three forms can be transformed into each other. For example, under standard conditions, sulfuryl fluoride is in a gaseous state. When the temperature drops below -55.2°C, it becomes a liquid state, and when the temperature continues to drop below -136.7°C, it becomes a solid state; when the pressure changes within a certain range, sulfuryl fluoride It will switch between gaseous state and liquid state, and the temperature will also change at this time, which can produce heat exchange. This situation is the same as the physical phenomenon that occurs in the refrigeration process of the cold medium.

The quantitative measurement of sulfuryl fluoride can adopt a variety of schemes, one scheme is the weighing measurement method, and the other scheme is the mass flow meter method. The weighing measurement method is to put the dosing device together with the sulfuryl fluoride high-pressure steel cylinder on the weighing device, and weigh the reduction of sulfuryl fluoride to obtain the dosing amount. Since the total weight of the dosing device and the sulfuryl fluoride steel cylinder is 30-40 kg, and the dosage is 0.4-0.8 kg each time, such a weighing method is difficult to ensure sufficient measurement accuracy. If the effects of dew condensation and moisture absorption of the dosing device and the vibration of the pipeline are taken into account, the weight measurement method is actually unfeasible in the quantitative measurement of sulfuryl fluoride due to too large errors. Although technologies and devices related to weighing and measuring methods have appeared in the sulfuryl fluoride fumigation of containers, they have not yet reached the measurement accuracy requirements that can be accepted by the market.

The flow meter used in the mass flow meter method can be a gas mass flow meter. Gas mass flowmeters generally use thermal gas mass flowmeters. Although the technology is relatively mature, the main problem is that there is no thermal gas mass flowmeter suitable for measuring sulfuryl fluoride gas. The development of this thermal gas mass flowmeter is difficult and costly, and it is necessary to overcome the influence of the ultra-low temperature of sulfuryl fluoride gas and the rapid change of pressure on the fluid characteristics.

The flowmeter involved in the mass flowmeter method can also be a liquid mass flowmeter. This liquid sulfuryl fluoride flowmeter used under high-pressure conditions can directly measure the mass flow of sulfuryl fluoride, has high measurement accuracy, and can also meet other requirements related to the fumigation and disinfection of sulfuryl fluoride in containers. It is a relatively good Sulfuryl fluoride dosage method.

Contents of the invention

The invention proposes a short capillary flow sensor, which is mainly used to measure the mass flow of liquid sulfuryl fluoride under relatively high pressure conditions, and can also be used to measure the flow of refrigerant in the refrigeration process.

The medium measured by the liquid mass flow sensor proposed by the present invention is a fluid that is liquefied due to a relatively high pressure. When the fluid pressure decreases, accompanied by a decrease in temperature, a part of the liquefied fluid will be vaporized, forming a A medium in a gas-liquid coexistence state; if the gas-liquid coexistence medium absorbs heat again, the liquid state will all become gaseous.

In order to be able to measure the flow of the medium, the flow sensor proposed by the present invention includes a short capillary and two sets of pressure detection devices, the short capillary includes a short capillary inner tube and an outer tube, and the two sets of pressure detection devices are located in the short capillary The two ends are used to measure the inlet pressure P ₁ and the outlet pressure P ₂ respectively.

The pressure detection device includes a tee and a pressure sensor installed at the vertical outlet of the tee.

。 According to the theory of fluid mechanics and the working principle of throttling or differential pressure flow sensors, in order to measure the mass flow, the volume flow Q must be measured first, and then the mass flow can be obtained by multiplying the density ρ of the fluid with the volume flow Q:

.

。 The flow sensor involved in the present invention is a throttling or differential pressure flow sensor. The throttling element is a short capillary, which is characterized in that there is a large pressure difference between the inlet and outlet of the short capillary:

.

和体积流量系数α的关系为：

。 The throttling or differential pressure flow sensor can measure the volume flow of the fluid. The size of the volume flow is proportional to the result of the square root of the pressure difference ΔP. The proportional coefficient is called the volume flow coefficient α; the volume flow coefficient α is related to the capillary The shape, length and diameter are related to the characteristics of the fluid, which can be determined through experiments; volume flow Q, pressure difference

The relationship with the volume flow coefficient α is:

.

代入所述质量流量

，求得质量流量表示式：

，其中

，称κ为质量流量系数；质量流量系数κ也与毛细管的形状、长度和直径以及流体的特性有关，能通过实验确定。 The volume flow

Substitute into the mass flow

, get the mass flow expression:

,in

, called κ as the mass flow coefficient; the mass flow coefficient κ is also related to the shape, length and diameter of the capillary and the characteristics of the fluid, and can be determined through experiments.

After the short capillary is selected, its shape, length and diameter are completely determined. At this time, the mass flow coefficient κ is only related to the fluid characteristics. Under certain conditions, the factor that can affect the fluid characteristics is the inlet pressure P ₁ ; the mass flow rate The coefficient κ varies with the pressure P ₁ as follows: , where κ ₀ , β ₀ and β ₁ are constants that can be determined experimentally.

和

，即可求得流入短毛细管的流体的质量流量：

。 Send the two pressure signals P ₁ and P ₂ obtained by a short capillary flow sensor according to the present invention to the intelligent signal processing device, in which the parameters κ ₀ , β ₀ and β ₁ have been pre-installed, according to the formula :

and

, the mass flow rate of the fluid flowing into the short capillary can be obtained:

.

Description of drawings

Fig. 1 is a schematic diagram of the external structure and assembly of a short capillary flow sensor of the present invention; Fig. 2 is a schematic diagram of the internal structure of a short capillary flow sensor of the present invention.

Detailed ways

The short capillary flow sensor proposed by the present invention is a conversion device that converts flow signals into pressure signals. Figure 1 is a schematic diagram of the external structure and assembly of this embodiment, and Figure 2 is a schematic diagram of the internal structure of this embodiment.

The short capillary flow sensor is a throttling or differential pressure flow sensor, wherein the throttling element is a short capillary 1; the short capillary 1 is composed of a short capillary inner tube 8 and an outer tube 9; the throttling type Or the pressure difference in the differential pressure flow sensor is actually generated when the fluid flows through the short capillary inner tube 8, and the effect of the outer tube 9 is to fix the short capillary inner tube 8 and connect with the front and rear pipelines.

The flow that flows through the short capillary inner tube 8 is also the flow that flows through the pipeline. The size of the flow is related to the pressure difference before and after the short capillary inner tube 8. Specifically, the flow is proportional to the square root of the pressure difference, and the proportional coefficient can be determined through experiments. .

Tee 2 and tee 3 are pipe fittings connecting the inlet and outlet of short capillary 1 respectively. Pressure sensor 4 and pressure sensor 5 are respectively installed on the vertical interface of tee 2 and tee 3. The two pressure sensors are used to measure the short capillary respectively. Inlet pressure P ₁ and outlet pressure P ₂ of capillary 1.

The external structure and assembly schematic diagram of FIG. 1 also includes a gasket 6 between the tee 2 and the short capillary 1 and a gasket 7 between the tee 3 and the short capillary 1 .

2 shows the fluid inlet 10 and the fluid outlet 11 of a short capillary flow sensor in this embodiment, as well as the connection port 12 of the pressure sensor 4 and the connection port 13 of the pressure sensor 5 in the schematic diagram of the internal structure of FIG. 2 .

In the schematic diagram of the internal structure of Fig. 2, the fluid at both ends of the short capillary inner tube 8 in a short capillary flow sensor of this embodiment, the inlet end fluid 14 and the outlet end fluid 15 are also marked; it should be noted that although the fluid is a high pressure liquid But it may contain air bubbles. In order to make the two pressure sensors work normally, the installation position of the pressure sensors should be lower than the fluid level, that is, during actual installation, the connection port 12 and the connection port 13 of the two tees should be installed downward.

Claims (7)

1. a short capillary flow sensor comprises short capillary restriction device and pressure-detecting device, and described short capillary restriction device comprises pipe and outer tube in the short capillary; Described pressure-detecting device comprises threeway and is installed in pressure transducer on the vertical joint of threeway, and two cover pressure-detecting devices are respectively applied to measure the inlet pressure P of short capillary ₁With top hole pressure P ₂

2. a kind of short capillary flow sensor according to claim 1 is characterized in that pipe is the kapillary of taper shape closing in the described short capillary, and described outer tube is for managing in fixing and being connected for pipeline.

3. a kind of short capillary flow sensor according to claim 2 is characterized in that the entrance and exit of pipe in the described short capillary is symmetrical structure.

4. a kind of short capillary flow sensor according to claim 2, the outer tube that it is characterized in that described short capillary comprise with the connected mode of described threeway be threaded, cutting ferrule is connected and be welded to connect.

5. a kind of short capillary flow sensor according to claim 1 is characterized in that described pressure transducer and the connected mode of described threeway comprise that external thread is connected with internal thread and be connected.

6. a kind of short capillary flow sensor according to claim 1, what it is characterized in that described pressure transducer adopts is refrigerant or refrigerant pressure sensor.

7. according to the described a kind of short capillary flow sensor of claim 1-6, the input signal that it is characterized in that described flow sensor is the flow of fluid media (medium), and output signal is two pressure signals relevant with measured flux; If require the delivery rate signal, also to dispose corresponding signal processing apparatus.

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