RU2066850C1 - Method of measurement of mass flow of gas - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: measured flow is passed through constrictor, part of flow is taken away through two parallel by-pass tubes. laminar throttle is placed into one tube and turbulent throttle and heat flowmeter - into the other one. Taken part of flow is returned downstream from construction. Mass flow is measured in by-pass tube by heat flowmeter and mass flow across constrictor is determined. EFFECT: enhanced authenticity of method. 1 dwg

Description

 The invention relates to measuring equipment for measuring the mass flow of gas and can be used to create flowmeters used in any sectors of the economy.

 A known method of measuring gas flow, based on the creation and measurement of the pressure drop on the narrowing device installed in the measuring pipe (1).

 When flowing through this device, the differential pressure is used to judge the volumetric flow rate. To obtain information about the mass flow rate, either a gas densitometer or additional instruments for measuring gas pressure and temperature are required. In both cases, a computing device is also needed to introduce continuous correction into the diphnometer readings.

 Flowmeters with a narrowing device based on this method are widely used in industry, mainly because exemplary flowmeter installations are not required for their calibration and calibration.

 The disadvantages of the known measurement method are the quadratic dependence between the flow rate and the pressure drop and, as a result, a very small measurement range (not more than 1: 3).

 A known method of measuring gas flow, based on measuring the flow-dependent effect of thermal effects on the stream (2).

 If at the same time the entire mass of the flow is heated, then the flow meter changes the mass flow. The implementation of this method for high costs, and, accordingly, for pipes of large diameter is not economically feasible, since it requires the use of a high-power heater. To solve the problem of measuring flow in large diameter pipes, a method is used in which heating extends only to a limited part of the total flow. This eliminates the need for high power consumption.

 A known method of measuring the mass flow rate of gas, in which the gas stream is passed through a constriction device, and part of the gas stream is taken to the constriction device and fed into the stream behind it through a bypass tube in which the hydraulic resistance is installed to create a turbulent flow regime and a heat flow sensor, which measure the flow rate in the bypass tube, proportional to the flow rate through the restriction device (3).

 The advantages of this method are the ability to directly measure the mass flow rate of gas passing through the constriction device, and the use of a low power heater.

 However, the flow meter that implements the known method of measuring the mass flow of gas, has a low operational reliability due to the presence of a turbulent throttle. In order to be able to use the linear portion of the calibration characteristic of the heat flow meter sensor, the operating range of the flow rates in the bypass tube should be located at the beginning of the calibration characteristic, i.e. not exceed units nl / h. On the other hand, in order for the turbulent throttle to operate in turbulent mode at such costs, its flow area must be tenths or even hundredths of a millimeter.

 Such holes are difficult to manufacture with sufficient accuracy and it is practically impossible to control their mechanical wear during operation.

 The known method can only be used to measure the consumption of highly pure gases.

 The technical result from the use of the invention is the task of creating methods that directly measure the mass flow of gas using flowmeters with narrowing devices and achieve their operational reliability.

 This is achieved in a method of measuring mass flow, in which the gas stream is passed through a normal constriction device, part of the flow is taken to the constriction device and fed into the stream behind it through a bypass tube in which the flow resistance is established to create a turbulent flow regime and a heat flow sensor, which measure the flow rate in the bypass tube, proportional to the flow rate through the restriction device, and part of the already branched flow is taken to the sensor of the heat flow meter and diverted to the flow behind it through an additional bypass pipe, in which using the hydraulic resistance create a laminar regime of gas flow, as in the sensor of the heat flow meter.

 The drawing shows a flow meter for implementing the proposed method.

 The flow meter comprises a constriction device 1, a bypass tube 2 and an additional bypass tube 2 ′, a turbulent throttle 3, a heat meter sensor 4 and a laminar throttle 5.

 The method is as follows.

 The measured flow is fed to the flow meter, where the gas flow is redistributed and passes through the constriction device 1, the bypass tube 2. The sensor of the flow meter 4 heats the part of the gas flow passing through the bypass tube 2, and at the same time measure the change in the flow temperature (temperature sensors perform a double function to measure the flow temperature and due to the supply energy they heat the flow).

Наличие турбулентного дросселя позволяет вычислить расход M в основном трубопроводе по расходу в байпасной трубке M_δ′ по формуле
M=(K₂+1)M_δ′, (2)
где

Используя формулы (1) и (2), получим выражение для расчета искомого расхода M через измеряемый расход M_δ
M=(K₁+1)(K₂+1)M_δ (3)
Для известного способа расчетная формула имеет вид
M=(K₃+1)M_δ, (4)
где

Как видно из формул (3) и (4), двойное байпасирование сужающего устройства позволяет снизить кратность деления потока и увеличить сечение турбулентного дросселя 3, что и обеспечивает повышение эксплуатационной надежности расходомера.Temperature sensors are included in the bridge measuring circuit of a standard measuring bridge, according to the testimony of which they judge the measured flow. The parallel inclusion of two sections with laminar flow regimes of the flows M _δ and M _{δ ″} allows us to measure the total flow through them M _{δ ′} = M _δ + M _{δ ″} using the sensor of the heat flow meter according to the formula
M _{δ ′} = (K ₁ +1) M _δ , (1)
Where

The presence of a turbulent throttle allows you to calculate the flow rate M in the main pipeline by the flow rate in the bypass pipe M _{δ ′} according to the formula
M = (K ₂ +1) M _{δ ′} , (2)
Where

Using formulas (1) and (2), we obtain the expression for calculating the desired flow rate M through the measured flow rate M _δ
M = (K ₁ +1) (K ₂ +1) M _δ (3)
For the known method, the calculation formula has the form
M = (K ₃ +1) M _δ , (4)
Where

As can be seen from formulas (3) and (4), double bypassing of the constriction device allows to reduce the frequency division of the flow and increase the cross section of the turbulent throttle 3, which ensures an increase in the operational reliability of the flow meter.

Claims (1)

 The method of measuring the mass flow rate of gas, which consists in the fact that the gas stream is passed through a constriction device, part of the flow is taken to the constriction device and fed into the stream behind it through a bypass tube, in which the first hydraulic resistance is installed in series to create a turbulent flow mode and a thermal sensor a flowmeter with a laminar mode of movement, measure the mass flow of gas in the bypass tube, proportional to the mass flow through the constriction device, characterized in that already branched flow is taken to the sensor of the heat flow meter and diverted into the stream behind it through an additional bypass pipe, in which using the second hydraulic resistance create a laminar flow regime.