RU2841719C1 - Device for measuring low liquid flow rates - Google Patents

Abstract

FIELD: measuring.

SUBSTANCE: invention relates to measurement equipment, namely to measurement of volumetric flow rates of liquid and can be used in production processes of nuclear and chemical industry. Device for measuring low flow rates has a capillary tube made from stainless steel, the middle part of which is made in form of a spiral and is placed in a sealed casing. Inlet and outlet of the capillary tube are connected by pipelines through the first and second T-bends and through the first and second shut-off valves to corresponding outlets of the chambers of the differential pressure sensor. Differential pressure transducer chamber inlets are connected via pipelines via first, second solenoid valves and third T-bend with tank filled with parting fluid. Pump, first and second solenoid valves and differential pressure sensor are connected to a controller which is connected to a computer. Distilled water or nitric acid is used as parting fluid.

EFFECT: wider range of measurement equipment.

2 cl, 2 dwg, 1 tbl

Description

The invention relates to the field of measurement technology, namely to the field of measuring volumetric flow rates of liquids and can be used in production processes in the nuclear and chemical industries.

A device for measuring small liquid flow rates is known [JP 4825254 B2, IPC G01 F1/48, published 30.11.2011], selected as a prototype, containing a stainless steel capillary tube, a differential pressure sensor and a controller. This device is divided into 3 blocks by functional significance: the main block, which is mounted in the measuring pipeline; the pressure measuring block, in which the differential pressure sensors are located, measuring the pressure drop at the ends of the capillary tube; the capillary block, in which the capillary tube is located. When the controlled liquid flows through the main block along the capillary tube, a pressure drop occurs at its ends, which is measured by the pressure measuring block. The measured drop is transmitted to the controller and the volumetric flow rate is calculated according to Poiseuille's law.

When measuring with this device, there is direct contact between the measured liquid and the sensitive elements (strain gauges, piezoresistors, capacitive cells) of the differential pressure sensor, which significantly reduces the service life of both the sensor itself and the entire device in cases where the measured liquid is radio and/or chemically active.

The technical result that the present invention is aimed at achieving is the expansion of the arsenal of technical means for measuring small liquid flow rates.

The proposed device for measuring small flows, as in the prototype, contains a stainless steel capillary tube and a differential pressure sensor, which is connected to a controller.

According to the invention, the middle part of the capillary tube is made in the form of a spiral and is placed in a sealed casing. The input and output of the capillary tube are connected by pipelines through the first and second tees and through the first and second shut-off valves with the corresponding outputs of the differential pressure sensor chambers. The inputs of the differential pressure sensor chambers through the first, second electromagnetic valves and the third tee are connected by pipelines to a tank filled with a separating liquid. The pump, the first and second electromagnetic valves are connected to a controller, which is connected to a computer.

Distilled water or nitric acid was used as a separating liquid.

Compared with the prototype, the proposed device eliminates contact between the controlled liquid and the sensitive elements of the differential pressure sensor.

Fig. 1 shows a diagram of the proposed device for measuring small liquid flow rates.

Fig. 2 shows a graph of the dependence of the volumetric flow rate of liquid on the pressure drop at the ends of the capillary tube.

Table 1 (see in the graphic section) shows the flow rates of the controlled liquid measured using the Bronkhorst CORI-FLOW M13 flow meter and measured using the proposed device.

The device for measuring small liquid flow rates comprises a control cabinet 1 (CC) in the lower part of which a peristaltic pump 2 is located, connected by pipelines through a third tee 3 with the first 4 and second 5 electromagnetic valves, each of which is connected to the input of the corresponding chamber of the differential pressure sensor 6 and to a programmable logic controller 7 (PLC). The differential pressure sensor 6 and the peristaltic pump 2 are connected to the programmable logic controller 7 (PLC), which is connected to a personal computer 8 (PC). The outputs of the chambers of the differential pressure sensor 6 are connected by pipelines 9 with the first 10 and second 11 shut-off valves mounted in the lower wall of the control cabinet 1 (CC).

Peristaltic pump 2 is connected by a pipeline to tank 12 (B) filled with separating liquid, which can be either distilled water or a solvent suitable for a specific process (e.g. nitric acid). Tank 12 (B) filled with separating liquid is installed next to control cabinet 1 (CC).

The first 10 shut-off valve is connected via the first tee 13 by a pipeline to the input of the capillary tube 14, the middle part of which is made in the form of a spiral and is placed in a sealed casing 15. The capillary tube 14 is made of stainless steel.

The capillary tube input is intended for connection through the first tee 13 with the measuring pipeline 16.

The second 11 shut-off valve is connected via the second tee 17 to the outlet of the capillary tube 14. The outlet of the capillary tube is intended for connection via the second tee 17 to the measuring pipeline 16.

Before measuring the liquid flow rate using a personal computer 8 (PC), numerical values are entered into the corresponding registers of the programmable logic controller 7 (PLC) memory, determining the flushing time of the connecting pipelines 9, the chambers of the differential pressure sensor 6, the time between these flushes, as well as the values of the internal diameter d , the length L of the capillary tube 14 and the dynamic viscosity of the liquid η.

Then, on command from the programmable logic controller 7 (PLC), the peristaltic pump 2 is turned on and the first 4 and second 5 electromagnetic valves are opened for a time specified by the operator, as a result of which the separating liquid from the tank 12 (B) fills the chambers of the differential pressure sensor 6 and the pipelines 9 connecting the differential pressure sensor 6 and the capillary tube 14.

After this, on command from the programmable logic controller 7 (PLC), the first 4 and second 5 electromagnetic valves are closed, and the peristaltic pump 2 is turned off.

When the controlled liquid flows through the measuring pipeline 16 through the first tee 13 along the capillary tube 14 and through the second tee 17 between the input and output of the capillary tube 14, a pressure differential arises, which is transmitted through the pipelines 9 through the first 10 and second 11 shut-off valves to the chambers of the differential pressure sensor 6, which transmits the measured pressure differential to the programmable logic controller 7 (PLC). The programmable logic controller 7 (PLC) recalculates the pressure differential value into the flow rate of the controlled liquid.

The value of the volumetric flow rate of the controlled liquid Q is determined from the following expression:

where Δ P is the pressure difference measured by the differential pressure sensor 6;

L - length of capillary tube 14 (from the first tee 13 to the second tee 17, including the middle part in the expanded form);

d - internal diameter of capillary tube 14;

η - dynamic viscosity of the controlled liquid;

a, b - coefficients obtained as a result of approximation by a second-order polynomial using the least squares method of the experimental data of the obtained dependence of the flow rate on the pressure drop, for a capillary tube 14, a given internal diameter d , length L and a given winding diameter.

The flow rate of the controlled liquid determined in this way is transmitted to the personal computer 8 (PC).

A capillary tube 6 m long and 2 mm in internal diameter was used in laboratory tests. Distilled water with a dynamic viscosity coefficient of 8.9⋅10 ^-4 Pa⋅s was used as the controlled liquid. A Bronkhorst CORI-FLOW M13 flow meter was used to compare the measured flow rate with the proposed device. The liquid flow rate was measured with the Bronkhorst CORI-FLOW M13 flow meter, the pressure drop was measured with the proposed device, and the dependence of the flow rate on the pressure drop at the ends of the capillary tube 14 was obtained. As a result of the approximation of the experimental data in Fig. 2 by a second-order polynomial using the least squares method, the following coefficient values were obtained:

.

Table 1 shows the flow rates of the controlled liquid measured using the Bronkhorst CORI-FLOW M13 flow meter and measured by the proposed device.

The average value of the relative error of the flow rate of the controlled liquid measured using the proposed device was 7.57%.

Claims (2)

1. A device for measuring small liquid flow rates, comprising a stainless steel capillary tube, a differential pressure sensor and a controller, characterized in that the middle part of the capillary tube is made in the form of a spiral and is placed in a sealed casing, wherein the inlet and outlet of the capillary tube are connected by pipelines through the first and second tees and through the first and second shut-off valves with the corresponding outlets of the chambers of the differential pressure sensor, the inlets of the chambers of which are connected by pipelines through the first and second electromagnetic valves and the third tee to a tank filled with a separating liquid, wherein the pump, the first and second electromagnetic valves are connected to a controller, which is connected to a computer. 2. The device according to item 1, characterized in that distilled water or nitric acid is used as the separating liquid.