CN115901866A - Method for measuring liquid water content - Google Patents
Method for measuring liquid water content Download PDFInfo
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- CN115901866A CN115901866A CN202211701405.9A CN202211701405A CN115901866A CN 115901866 A CN115901866 A CN 115901866A CN 202211701405 A CN202211701405 A CN 202211701405A CN 115901866 A CN115901866 A CN 115901866A
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
Abstract
The application relates to the field of aircraft icing detection, in particular to a method for measuring liquid water content. The liquid water content measuring method provided by the invention has the characteristics of high reliability, simple measurement, strong applicability and the like, the circuit schemes required by the method have mature and reliable multiple schemes, the platinum resistor is easy to select, and various devices are on-market devices and are easy to assemble. According to the invention, through reasonable layout of the two platinum resistors, the liquid water content of the current environment can be accurately measured in the flight process of the aircraft, in the field of icing detection, whether the current aircraft is in the icing environment can be comprehensively calculated by combining other atmospheric data such as temperature, pressure, attack angle and the like, and when the aircraft does not enter the icing area, an aircraft anti-icing system can be early warned in advance or automatically started, so that the working intensity of workers is reduced.
Description
Technical Field
The application relates to the field of aircraft icing detection, in particular to a method for measuring liquid water content.
Background
Compared with other traditional icing detection methods, the method can perform early warning before the airplane enters an icing area, and adopt corresponding measures to further improve the safety of the airplane.
The liquid water content is measured by two methods, one method is that the liquid water content is indirectly converted by measuring the icing rate and according to the corresponding relation between the icing rate and the liquid water content; another method is to directly measure the liquid water content in the air by a hot wire method. Since the latest icing detection requires early warning before the aircraft enters the icing area, hot-wire methods are used to measure the liquid water content.
A common hot-wire type instrument for measuring the liquid water content is a KING sensor of GOODRICH company, is used for measuring in an ice wind tunnel, measures the resistance of a thermistor through a Wheatstone bridge, the thermistor with a specific shape is exposed in air flow, the power of a heater is adjusted according to the thermistor value, the thermistor is kept at a constant temperature, then the power changes of the heater of dry air and air to be measured are respectively measured, and the liquid water content is obtained through calculation.
When the sensor is used in the icing wind tunnel, the icing wind tunnel is required to simulate the dry air condition to measure the liquid water content under the dry air condition, and then the sensor can work in the tested environment, but the airplane environment does not have the condition. This application refers to patent US6622556B1 total temperature sensor cavity and realizes dry air and liquid water separation, uses two platinum resistance to measure dry air data and humid air data respectively, provides a measurement circuit who measures liquid water content, can be used to the aircraft and freezes to survey and the liquid water content of icing wind tunnel surveys.
Disclosure of Invention
In order to solve the technical problems existing in the field at present, the invention provides a liquid water content measuring circuit.
Technical scheme
A method for measuring liquid water content comprises the following steps:
step one, measuring dry platinum resistance power: dry platinum resistor RD and resistor R 1 In series, applying controlled excitation across a dry platinum resistor and a resistorVoltage, adjusting the exciting voltage to make the temperature of the dry platinum resistor constant at T, and measuring the exciting voltage value U DE And the voltage U across the resistor 1 Calculating the power of the dry platinum resistor at this time
Step two, measuring the wet platinum resistance power: connecting a wet platinum resistor RW with a resistor R 2 Connecting in series, applying controllable excitation voltage across the wet platinum resistor and the resistor, adjusting the excitation voltage to maintain the wet platinum resistor at the same constant temperature T, and measuring the excitation voltage value U WE And the voltage U across the resistor 2 Calculating the power of the wet platinum resistor at that time
Step three, calculating the liquid water content, and calculating the P calculated in the step one D P calculated in step two W Substituting the obtained product into a liquid water content calculation formula to obtain the liquid water content LWC at the moment;
l is the platinum resistor length, d is the platinum resistor diameter, v is the incoming air velocity, l v Is latent heat of vaporization of water, T b Is the water evaporation temperature at the current atmospheric pressure, T a Is the outside atmospheric temperature and c is the specific heat capacity.
Further, said R 1 、R 2 The resistance value of the resistor is less influenced by temperature change for a precise resistor. The measurement precision is improved.
Further, the dry platinum resistor refers to a platinum resistor which is exposed to dry gas flow after being placed in gas separation; the wet platinum resistor refers to a platinum resistor exposed to a humid gas stream before being placed separate from the gas.
Further, the dry platinum resistor and the wet platinum resistor use the same platinum resistor to reduce measurement difference.
Further, the surfaces of the dry platinum resistor and the wet platinum resistor are made of stainless steel material shells. And the error caused by platinum resistance loss is reduced.
Further, the temperature T maintained by the heating dry platinum resistor and the heating wet platinum resistor is kept between 80 and 125 ℃ so as to completely evaporate the tiny water drops impacting on the wet platinum resistor.
Further, the dry platinum resistor and the wet platinum resistor are embodied in a cylindrical shape, and the LWC can be calculated by satisfying the above formula.
Furthermore, the external diameters of the dry platinum resistor and the wet platinum resistor are preferably 2.1mm, and the probes with the diameters can have better impact evaporation effect on liquid water drops of 10-40 um.
Furthermore, the dry platinum resistor and the wet platinum resistor are isolated from the installed metal shell by the same material, so that errors caused by different heat conduction amount of contact are reduced.
Further, the areas of the dry platinum resistor exposed to the air flow and the wet platinum resistor exposed to the air flow are kept the same, so that the calculation accuracy is improved.
Further, the resistor R 1 A resistor R 2 The aluminum shell resistor with high power and good heat dissipation is preferred.
The invention has at least the following advantages and beneficial effects:
the liquid water content measuring method provided by the invention has the characteristics of high reliability, simple measurement, strong applicability and the like, the circuit schemes required by the method have mature and reliable multiple schemes, the platinum resistor is easy to select types, and various devices are devices sold in the market and are easy to assemble.
According to the invention, through reasonable layout of the two platinum resistors, the liquid water content of the current environment can be accurately measured in the flight process of the aircraft, in the field of icing detection, whether the current aircraft is in the icing environment or not can be comprehensively solved by combining other atmospheric data such as temperature, pressure, attack angle and the like, and when the aircraft does not enter the icing area, an aircraft anti-icing system can be early warned in advance or automatically started, so that the working intensity of workers is reduced.
In addition, the method can also be used in ground facilities such as an icing wind tunnel and the like which need to measure the liquid water content, compared with other methods, the liquid water content detector manufactured according to the method can quickly measure the liquid water content in the icing wind tunnel in real time, and provides an effective measuring means for wind tunnel calibration and test state point calibration.
In addition, the method can be expanded to other scenes needing to measure the content of the suspended liquid drops in the gas, and the content of the suspended liquid drops in a static environment or a low-speed pipeline can be measured by adding the air entraining device into the detector.
Drawings
FIG. 1 is a circuit diagram of the acquisition of the present invention;
FIG. 2 is a control diagram of the excitation voltage of the present invention;
FIG. 3 is a diagram of a measurement method of the present invention.
Detailed Description
In order to make the implementation objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in more detail below with reference to the accompanying drawings of the present invention. The embodiments described below are exemplary and are intended to be illustrative of the present invention and should not be construed as limiting the present invention. Other similar embodiments, which can be derived by those skilled in the art from said embodiments of the invention without significant innovation, are within the scope of the invention. The following provides a detailed description of embodiments of the present invention.
A liquid water content measurement circuit, comprising: the device comprises an acquisition circuit, an excitation voltage control circuit and a signal processing circuit, wherein the excitation voltage control circuit outputs PRT _ EXC excitation voltage, the PRT _ EXC excitation voltage provides working voltage of two platinum resistors to enable the two platinum resistors to alternately keep constant temperature, the acquisition circuit respectively measures power voltage signals of the two platinum resistors at constant temperature and feeds the power voltage signals back to the signal processing circuit, and finally the liquid water content is calculated.
The RD refers to a dry platinum resistor indicating that the platinum resistor is located in the sensor in a position to be in contact with only dry air, and the RW refers to a wet platinum resistor indicating that the platinum resistor is located at the air flow inlet of the sensor and is in contact with the air to be measured, which includes dry air and a certain amount of liquid water.
The acquisition circuit comprises a Wheatstone bridge circuit consisting of two platinum resistors RD and RW and resistors R1 and R2, wherein the RD is connected with the R1 in series, and the RW is connected with the R2 in series.
And the RW voltage signal is led out from the middle of the resistors R2 and RW, connected with the filtering magnetic bead L1 and the low-pass filter and output to the positive input end of the instrumentation amplifier.
And the RD voltage signal is led out from the middle of the resistors R1 and RD, connected with the filtering magnetic bead L2 and the low-pass filter and output to the reverse input end of the instrument amplifier.
The excitation voltage monitoring circuit consists of a resistor R15 and a resistor R16 voltage division circuit, and an excitation voltage monitoring signal is output to the singlechip from between the resistor R15 and the resistor R16.
The wet voltage monitoring circuit consists of a resistor R3 and a resistor R4 voltage division circuit, and wet voltage monitoring signals are output to the single chip microcomputer from between the R3 and the R4.
The dry voltage monitoring circuit consists of a resistor R5 and a resistor R6 voltage dividing circuit, and a dry voltage monitoring signal is output to the singlechip from between the resistor R5 and the resistor R6.
The instrument amplifier amplifies the difference value of the RD voltage signal and the RW voltage signal, the difference value is divided by the resistor R9 and the resistor R10 and then output to the positive input end of the U2 operational amplifier, the reverse input end of the U2 is connected with the output end of the U2 through the zero-ohm resistor R11 to form a voltage follower, and voltage PRT _ DELTA is output to the single chip microcomputer.
The 5V reference voltage is divided by a resistor R13 and a resistor R14, and then is output to the forward input end of the U3 operational amplifier, the reverse input end of the U3 is directly connected with the forward input end to form a voltage follower, and the reference voltage VREF1 is output to pins U1-5.
And the U1, the U2 and the U3 are all supplied with power by +15V, and the negative end of the power supply is connected with the AGND.
The excitation voltage control circuit comprises an alternating voltage rectification part, a switching power supply chip U4 and peripheral circuit parts thereof and a voltage control signal part. Alternating current voltage is rectified by CR1, CR2, CR3 and CR4, filtered by capacitors C17, C18, C19, C20 and C21 and output to VIN pin of a switching power supply chip LM5116, and direct current voltage converted by LM5116 passes through L3 and is output as PRT _ EXC which is the excitation voltage of a platinum resistor and plays a role in heating.
The PRT _ ENABLE signal is output to an EN enabling pin of the U4 by the single chip microcomputer and is used for controlling the switch of the U4.
The single chip microcomputer outputs a PRT _ EXC _ CTRL signal through the digital-to-analog converter, is connected with the resistor R23, and controls PRT _ EXC excitation voltage output through the resistors R22, R23 and R24 and the voltage output by the digital-to-analog converter.
Aiming at the problem that the existing method for measuring the liquid water content of the airplane is converted according to the icing rate and is not suitable for the latest icing condition detection technology, a measuring circuit and a measuring method for measuring the liquid water content of the airplane are designed, and the technical problems mainly solved are as follows:
1) The problem of measuring the liquid water content in the icing condition detection technology is solved, and the liquid water content in the airflow can be accurately measured;
2) The cooperation prevents deicing system, when can realizing detecting the condition of freezing, opens automatically and prevents deicing system, improves the aircraft security, reduces staff's working strength.
The following describes the liquid water content measuring circuit and the measuring method of the present invention in further detail with reference to fig. 1, fig. 2, and fig. 3.
Example 1
In a first aspect, as shown in fig. 1 and fig. 2, the invention discloses a liquid water content measuring circuit and a measuring method, wherein the liquid water content measuring circuit is composed of an acquisition circuit and an excitation voltage control circuit.
The acquisition circuit comprises a platinum resistance bridge circuit, a monitoring circuit, an amplifying circuit and a reference voltage circuit.
In the platinum resistance bridge circuit, the RD platinum resistance and the RW platinum resistance both use PT50, and the R1 platinum resistance and the R2 platinum resistance both use high-power aluminum shell resistors with the resistance value of 20 ohms; the three voltage monitoring circuits are used for respectively measuring excitation voltage, dry platinum resistor voltage signals and wet platinum resistor voltage signals, voltage division circuits are adopted, meanwhile, in order to guarantee the accuracy of the measured voltage, the same type of resistors of the three voltage division circuits are kept consistent and high-precision circuits are used, namely R4, R5 and R15 use the same type of resistors, R3, R6 and R16 use the same type of resistors, and the precision of the resistors is 0.05%. The instrumentation amplifier amplifies the signal reflecting the dry and wet platinum resistance difference, the instrumentation amplifier has high precision and low noise characteristic, can restrain common mode interference, and the output voltage is:
V U_1 the output voltage is output as V after passing through the voltage division circuits of R9 and R10 PRT_DELTA And then output by a voltage follower to play roles of buffering and isolating.
The reference voltage is used to prevent V + Less than V - And the output is zero. The reference voltage circuit also takes the form of a voltage divider circuit plus a voltage follower.
In the excitation voltage control circuit, a switching power supply chip U4 converts the wide-range direct-current voltage after rectification and filtration into controllable and stable direct-current voltage and outputs the voltage as V PRT-EXC . V output by singlechip through digital-to-analog converter PRT_EXC_CTRL And R22, R23, R24 together control V PRT-EXC The formula is as follows:
the single chip microcomputer can calculate the resistance value of the platinum resistor by monitoring the voltage, calculate the current temperature of the platinum resistor by comparing with a platinum resistor resistance thermometer, and realize the purpose of constant temperature control of the platinum resistor by adjusting the excitation voltage.
It should also be noted that in practical use, the platinum resistor shape is usually a cylindrical probe with a diameter of 2.1mm, because this diameter is good for the impingement evaporation of 10-40um liquid water. In the determination of platinumWhen the resistance has a constant temperature value, the resistance can be measured by using a sensor when the airplane flies in dry air, and V under the conditions of different constant temperature values is recorded PRT_DELTA Since in the case of dry air, the ideal V is PRT_DELTA Should be 0, i.e. the wet and dry resistances should be kept at the same temperature, but there is often some deviation due to the influence of the process and the air flow, and V needs to be selected PRT_EELTA The minimum temperature value was used as the platinum resistance constant temperature value at the time of measurement.
In a second aspect, the invention also discloses a method for measuring the liquid water content, which comprises the following steps:
measuring the power of the dry platinum resistor, maintaining the dry platinum resistor at a constant temperature T by adjusting the excitation voltage, measuring the excitation voltage and the dry voltage monitoring voltage at the moment, and substituting the measured excitation voltage and the monitored dry voltage into a formula to calculate the power of the dry platinum resistor at the moment.
P D ＝U D ×I D
V D Indicating the measured dry platinum resistance voltage monitoring voltage, V EXC Represents a platinum resistance excitation voltage, U D 、I D 、P D The voltage, current and power of the dry platinum resistor are respectively shown.
And step two, measuring the power of the wet platinum resistor, maintaining the wet platinum resistor at a constant temperature T by adjusting the excitation voltage, measuring the excitation voltage and the wet voltage monitoring voltage at the moment, and substituting the measured excitation voltage and the measured wet voltage monitoring voltage into a formula to calculate the power of the wet platinum resistor at the moment.
P W ＝U W ×I W
V W Shows the measured wet platinum resistance voltage monitor voltage, V EXC Represents a platinum resistance excitation voltage, U W 、I W 、P W The voltage, current, and power of the wet platinum resistor are shown, respectively.
Step three, calculating the liquid water content, substituting the results obtained in the step one and the step two into a liquid water content calculation formula to obtain the liquid water content LWC at the moment;
l is the platinum resistor length, d is the platinum resistor diameter, v is the air velocity, l v Is latent heat of vaporization, T b Is the liquid evaporation temperature, T a Is the outside atmospheric temperature, and c is the specific heat capacity.
Example 2
In the embodiment, the overall dimension of the platinum resistor can be changed according to requirements to meet different measurement requirements, the cylindrical platinum resistor can be changed into two semi-cylindrical shapes, namely a concave surface and a convex surface, the two semi-cylindrical shapes are positioned in the same airflow state, all water drops and ice crystals impacted by the concave surface are evaporated under the ideal condition, all water drops are evaporated under the ideal condition of the convex surface, all ice crystals are splashed by collision, the ice crystal measurement is realized by the difference value of the two water drops and the ice crystals, but the calculation formula needs to be calibrated again or modified according to the theory.
Example 3
In the embodiment, the overall dimension of the platinum resistor can be changed according to requirements to meet different measurement requirements, one of two cylindrical platinum resistors can be changed into a cylindrical concave surface, the two platinum resistors are positioned in the same airflow state, all water drops impacted by the concave surface are evaporated under the ideal condition, only water drops with the diameter of 10-40um are evaporated under the ideal condition of the cylinder, the difference value of the two platinum resistors is used for realizing the measurement of the super-cooled large water drops, and the calculation formula needs to be calibrated again or modified according to the theory.
In conclusion, the invention relates to a measuring circuit and a measuring method for liquid water content, which use a hot-wire measuring method and a dry-wet separation structure as a reference, design and use two platinum resistors to complete power measurement of constant temperature maintenance of the dry and wet air platinum resistors, and use a formula to calculate the liquid water content.
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 commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only illustrative of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A method for measuring the water content in liquid state is characterized in that the method comprises the following steps:
step one, measuring dry platinum resistance power: the dry platinum resistor RD is connected with the resistor R 1 Connecting in series, applying controllable excitation voltage across the dry platinum resistor and the resistor, adjusting the excitation voltage to make the temperature of the dry platinum resistor constant at T, and measuring the excitation voltage value U DE And the voltage U across the resistor 1 Calculating the power of the dry platinum resistor at this time
Step two, measuring the wet platinum resistance power: connecting a wet platinum resistor RW with a resistor R 2 In series, in a wet platinum resistor andapplying controllable excitation voltage across the resistor, adjusting the excitation voltage to maintain the wet platinum resistor at the same constant temperature T, and measuring the excitation voltage value U WB And the voltage U across the resistor 2 Calculating the power of the wet platinum resistor at that time
Step three, calculating the liquid water content, and calculating the P calculated in the step one D P calculated in step two W Substituting the obtained product into a liquid water content calculation formula to obtain the liquid water content LWC at the moment;
l is the platinum resistor length, d is the platinum resistor diameter, v is the incoming air velocity, l v Is latent heat of vaporization of water, T b Is the water evaporation temperature at the current atmospheric pressure, T a Is the outside atmospheric temperature and c is the specific heat capacity.
2. The method of claim 1, wherein R is a measured moisture content of the liquid 1 、R 2 The resistance value of the resistor is less influenced by temperature change for a precise resistor.
3. The method of claim 1, wherein the dry platinum resistor is a platinum resistor exposed to a dry gas stream after gas separation; the wet platinum resistor refers to a platinum resistor exposed to a humid gas stream before being placed separate from the gas.
4. The method of claim 1, wherein the dry platinum resistor and the wet platinum resistor use the same platinum resistor to reduce measurement variation.
5. The method of claim 1, wherein the surfaces of the dry platinum resistor and the wet platinum resistor are coated with a stainless steel material.
6. A method of measuring liquid water content according to claim 1, wherein the temperature T maintained by heating the dry platinum resistor and the wet platinum resistor is maintained at 80-125 ℃ to enable complete evaporation of the minute water droplets impinging on the wet platinum resistor.
7. A method of measuring liquid water content according to claim 1, wherein said dry and wet platinum resistors are cylindrical in shape so as to satisfy the above formula for calculating LWC.
8. A method of measuring liquid water content according to claim 1, wherein the dry and wet platinum resistors are preferably 2.1mm in diameter.
9. The method of claim 1, wherein the dry and wet platinum resistors are isolated from the metal housing by the same material.
10. The method of claim 1, wherein the dry platinum resistor and the wet platinum resistor are exposed to the same area of the gas stream.
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| CN202211701405.9A CN115901866A (en) | 2022-12-29 | 2022-12-29 | Method for measuring liquid water content |
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