JP4081639B2 - Thermal mass flow meter for liquids - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermal mass flow meter for liquids, and more specifically, a pipe that allows the liquid to be measured to pass through is formed of a synthetic resin member, and has a structure that can withstand corrosion, etc., and is suitable for measuring a wide range of liquids. The present invention relates to a thermal mass flow meter for liquid.
[0002]
[Prior art]
In a typical thermal mass flowmeter for liquids in the prior art, a heater and a plurality of temperature sensors are attached to a sensor tube for measurement provided outside the pipe as in the case of gas, and the temperature distribution of the liquid in the vicinity of the heater It is well known that the flow rate is measured by detecting the change in.
[0003]
Here, an element that performs heating or cooling is referred to as a heat transfer element. Of the temperature sensors, a temperature sensor that monitors the initial liquid temperature in order to maintain a heating temperature at which the liquid does not vaporize is particularly called a liquid temperature sensor.
[0004]
As shown in FIG. 2, the specific configuration includes a first temperature sensor 2 installed on the upstream side of the sensor tube 1 that is a capillary (capillary tube), and a heater 3 that heats the liquid to be measured in the sensor tube 1. And a second temperature measuring sensor 4 installed on the downstream side of the sensor tube 1, and an arithmetic unit for measuring the flow rate of the fluid to be measured based on the temperatures from the first and second temperature measuring sensors 2 and 4, It is composed of
[0005]
A calculation unit (not shown) calculates the flow rate of the liquid to be measured based on the temperature difference (ΔT = T2−T1) measured by the first and second temperature measuring sensors 2 and 4 with the heater 3 interposed therebetween.
[0006]
Here, if the temperature of the heater 3 is too high, it may be vaporized, and some of them are cooled not by a heating element but by a Peltier element or the like, but these principles are also the same.
[0007]
In addition to this method, there are a method for detecting a temperature change only on the upstream side or the downstream side of the heater 3 and a method for detecting the amount of heat consumed by different heaters according to the flow velocity.
[0008]
[Problems to be solved by the invention]
However, in the case of the above-described prior art thermal mass flow meter for liquids, the heat transfer element and the temperature sensor have a signal indicating the amount of heat transmitted to the liquid, and therefore the signal of the amount of heat transmitted to the pipe becomes an error. There is a problem that it is impossible to accurately measure the amount of heat conducted.
[0009]
In addition, the thermal conductivity can be increased by using a sensor tube, which is a thin metal tube, and the heat capacity of the sensor tube itself for flowing the fluid to be measured can be extremely reduced, so the amount of heat transferred to the sensor tube is reduced. It is possible to reduce heat transfer errors. On the other hand, there is also a problem that it cannot be used for measuring the flow rate of a chemical solution that corrodes the metal used or a liquid that dislikes elution of metal ions.
[0010]
Therefore, there is a problem that must be solved in the structure of a thermal mass flow meter for liquid that can be widely used for chemicals that corrode metals.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems, the thermal mass flow meter for liquid according to the present invention is configured as follows.
[0012]
(1) Temperature measuring means for measuring the temperature of the liquid to be measured flowing in the pipe formed of the synthetic resin member, and the temperature measured by the temperature measuring means so as to be a constant temperature based on the initial temperature. A heat transfer means that conducts heat to the liquid to be measured; a pipe temperature measurement means that is disposed near the heat transfer means and that measures heat conducted to the pipe out of the heat conducted by the heat transfer means; and A flow rate measuring unit that corrects the amount of heat conducted to the liquid to be measured by the heat unit by the amount of heat to the pipe measured by the pipe temperature measuring unit and measures the flow rate of the liquid to be measured from the amount of heat conducted to the liquid to be measured. And a thermal mass flowmeter for liquids.
(2) The liquid temperature sensor of the temperature measuring means and the heat transfer element of the heat transfer means are arranged in contact with the liquid to be measured, and the pipe temperature measurement sensor of the pipe temperature measuring means is in the vicinity of the heat transfer element. The thermal mass flowmeter for liquid according to (1), wherein the thermal mass flowmeter for liquid according to (1) is disposed at a position and not in contact with the liquid to be measured.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a thermal mass flow meter for liquid according to the present invention will be described with reference to the drawings.
[0014]
A thermal mass flow meter for liquid uses a heat transfer element and measures the flow rate from the amount of heat consumed. Unlike conventional models, it does not use a sensor tube, which is a metal thin tube, A synthetic resin member measuring pipe having the same diameter as that of the pipe is used.
[0015]
As shown in FIG. 1, the configuration is in contact with the measurement pipe 5 installed between the pipes (not shown) and formed of a synthetic resin member, and the liquid to be measured that is upstream of the measurement pipe 5 and flows in. And a liquid temperature sensor 6 for detecting the temperature of the liquid to be measured, and a heat transfer element 7 which is disposed downstream of the measurement pipe 5 and in contact with the liquid to be measured and conducts heat to the liquid to be measured. And the heat transfer element 7 is controlled so as to conduct heat to the liquid to be measured so as to reach a constant temperature increased by several degrees with respect to the initial temperature (liquid temperature) of the liquid to be measured measured by the liquid temperature sensor 6. Measured by a first temperature calculating unit 9, a pipe temperature measuring sensor 8 that is installed near the heat transfer element 7 and in a non-wetted state and measures the temperature of the measuring pipe 5, and the pipe temperature measuring sensor 8. The temperature of the measured pipe 5 is added to the measured pipe 5 by the heat transfer element 7. It calculates the amount of heat, and a second arithmetic unit 10 for calculating the flow rate of the liquid to be measured by calculating the amount of heat consumed by the heat transfer element 7 by using this heat to the correction.
Here, the liquid temperature sensor 6 and the first calculation unit 9 serve as temperature measurement means, the heat transfer element 7 and the first calculation unit 9 serve as heat transfer means, and the heat transfer element 7 and the pipe temperature measurement sensor 8. And the second calculation unit 10 constitute a flow rate measuring means.
[0016]
In such a configuration, the amount of heat consumed by the heat transfer element 7 detected as a signal includes the amount of heat transferred to the liquid to be measured and the amount of heat transferred to the measurement pipe 5. Unlike the case where a sensor tube made of a metal thin tube (capillary tube) is used as in the conventional case, when a synthetic resin member having the same diameter as the pipe is used, the thermal conductivity is small, and the thickness of the measurement pipe 5 is high because of pressure resistance. Since the heat capacity is large because the thickness is thick, the amount of heat transferred to the measurement pipe 5 cannot be ignored.
[0017]
Therefore, the amount of heat conducted to the measurement pipe 5 is calculated using the temperature measured by the pipe temperature measuring sensor 8 disposed in the vicinity of the heat transfer element 7 and corrected by the amount of heat conducted to the measurement pipe 5. If the amount of heat conducted to the liquid to be measured is calculated, the amount of heat conducted to the liquid to be measured can be accurately measured, and a highly accurate flow rate can be measured.
[0018]
Theoretically, the amount of heat conducted to the measurement pipe 5 is proportional to the difference between the temperature of the heat transfer element 7 and the temperature of the measurement pipe 5, so that the measurement pipe is corrected by correcting it with the temperature obtained from the pipe temperature measuring sensor 8. The influence of the amount of heat on 5 can be removed.
[0019]
As a result, the signal becomes the amount of heat transferred to the liquid to be measured, and when the temperature difference between the liquid temperature and the heat transfer element 7 is controlled to be constant, the signal depends only on the flow rate of the liquid to be measured. In the case of laminar flow, the signal is proportional to the square root of the flow velocity.
[0020]
Although the constant temperature control is used in the above embodiment, the same measurement can be performed even at a constant current. Moreover, you may use what cools instead of heating as a heat-transfer element.
[0021]
Thus, by measuring the temperature of the measurement pipe 5 in the vicinity of the heat transfer element 7, the influence of heat conduction on the measurement pipe 5 can be eliminated, and even if the measurement pipe 5 made of a synthetic resin member is used, it is highly accurate. It is possible to measure the flow rate.
[0022]
【The invention's effect】
As described above, the thermal mass flowmeter for liquid according to the present invention includes a temperature sensor that measures the temperature of the pipe in the vicinity of the heat transfer element that conducts heat to the liquid to be measured, and the amount of heat conducted to the pipe. Since the flow rate is calculated from the amount of heat conducted to the liquid under measurement in a form where the pipe is removed, the amount of heat conducted to the liquid is accurately measured even if the pipe is thick, such as a synthetic resin member, and has a large heat capacity. Therefore, there is an effect that the flow rate can be measured with high accuracy.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a thermal mass flow meter for liquid according to the present invention.
FIG. 2 is an explanatory diagram showing the principle of liquid flow rate measurement using a bypassed sensor tube (narrow tube) in the prior art.
[Explanation of symbols]
5 Measurement Piping 6 Liquid Temperature Sensor 7 Heat Transfer Element 8 Piping Temperature Temperature Sensor 9 First Computing Unit 10 Second Computing Unit

Claims (2)

Temperature measuring means for measuring the temperature of the liquid to be measured flowing in the pipe formed of the synthetic resin member;
A heat transfer means for conducting heat to the liquid to be measured so as to be a constant temperature based on the initial temperature among the temperatures measured by the temperature measuring means;
A pipe temperature measuring means that is arranged in the vicinity of the heat transfer means and measures heat conducted to the pipe among heat conducted by the heat transfer means;
The amount of heat conducted to the liquid to be measured and the pipe by the heat transfer means is corrected by the amount of heat to the pipe measured by the pipe temperature measuring means, and the flow rate of the liquid to be measured is measured from the amount of heat conducted to the liquid to be measured. Flow rate measuring means,
A thermal mass flow meter for liquids, comprising: The liquid temperature sensor of the temperature measurement means and the heat transfer element of the heat transfer means are arranged in contact with the liquid to be measured, and the pipe temperature measurement sensor of the pipe temperature measurement means is located near the heat transfer element. 2. The thermal mass flow meter for liquid according to claim 1, wherein the thermal mass flow meter for liquid is arranged in a non-wetted state on the liquid to be measured.

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