RU2417367C1 - Method and device to determine thermophysical properties of solid materials in field of centrifugal forces - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: heat-isolated wire or thin rod from solid material with electric heater fitted on one its ends is arranged on disk revolving at high speed. Said disk is placed in vacuum chamber at initial temperature, deep vacuum is generated and disk is loaded by two cycles of temperature and centrifugal forced effects. Intrinsic peripheral speed is set in each cycle. Preset peripheral speed reached, electric heater is switched on to record specimen temperature in time. Preset top temperature reached, electric heater and rotation drive are turned off, while, initial temperature reached, specimen is subjected to the next loading cycle. Obtained data allows determining experimental factor in rotation and static state to correct thermo physical characteristics of material static state, e.g. heat conductivity is the field of centrifugal forces. Proposed device comprises motor, vacuum acceleration chamber communicated with vacuum pump, disk fitted on motor shaft and placed in said vacuum chamber, electric heater secured on material specimen arranged on said disk, thermocouples arranged on, at least, both ends of specimen, temperature recorder connected via current collector to thermocouples and power supply, disk rpm control device connected to motor, rpm pickup arranged ahead of vacuum chamber and connected to control device. ^ EFFECT: higher validity of determination. ^ 6 cl, 4 dwg

Description

The invention relates to the field of experimental physics and testing equipment, namely to the creation of a method and apparatus for measuring the temperature characteristics of solid heat-conducting materials in the field of centrifugal forces.

The invention can be used to experimentally determine the thermal characteristics of solid heat-conducting materials that are part of parts and / or assemblies, heavily loaded with large centrifugal forces, for example, in engines, machines and other equipment.

A known method for determining the thermophysical characteristics of building materials of multilayer structures without violating their integrity (RF patent No. 2140070, IPC G01N 25/18, publ. 10/20/1999)

The thermal effect on the surface of the investigated material is carried out by a disk heater under the adiabatic conditions and the time dependence of the surface temperature of the studied material is recorded. Moreover, to determine the thermal diffusivity coefficients of the outer layers of the structure, the temperature versus time is recorded at four surface points, and to determine the thermophysical characteristics of the inner layers of the structure, one of the heaters is turned off and the surface temperature versus time is recorded at two of these points. To determine the thermal conductivity coefficients of the outer and inner layers of the structure, the experimental time dependences of temperature for surface points having a higher temperature are approximated by piecewise-step functions with a given time step, and the desired thermophysical characteristics are determined by the corresponding formulas.

A known installation for studying the thermal conductivity of heat-insulating materials (RF patent No. 2289126, IPC G01N 25/32, publ. 10.12.2006).

The installation contains a heat source, means for measuring the temperature on the hot and cold walls of the sample. The heat source is connected to a device for recording the power it develops and is located inside the axial channel of a cylindrical sample. Washers made of heat-insulating material with thermal resistance not lower than the thermal resistance of the arch of the test cylindrical sample are installed at the ends of the sample.

A known method and installation for measuring thermal conductivity of rocks at high pressures and temperatures (Vetrogradsky V.A., Popov Yu.A., Miklashevsky D.E. Method and installation for measuring thermal conductivity of rocks at high pressures and temperatures. News of higher educational institutions , series "Geology and exploration", 2003, No. 5, p. 47-51).

The installation contains a high-pressure and temperature chamber equipped with a temperature control system, a shutter, a power nut and rubber sealing rings, a container with a test sample and heat shields, a container electric heater with a thermocouple, a compressor with a discharge pipe, and a pressure sensor mounted on the chamber shutter. Current and potential taps from the sample and container pass through the tapered seal of the valve.

The method includes simultaneous exposure to a sample of high pressures and temperatures by a linear heat source of constant power, from which heat is supplied to the test medium. The power of the source is constant in time and evenly distributed along the length of the source. The change in time of the temperature of the sample in the area directly in contact with the source is recorded. The apparent thermal conductivity recorded during the experiment is determined by a certain ratio and the thermal conductivity is calculated using an analog-to-digital converter and a computer.

Known methods and devices allow the determination of the temperature characteristics of solid materials in the field of compression forces at high pressures.

Methods and devices for determining the temperature characteristics of solid heat-conducting materials in the field of action of centrifugal forces have not been identified.

The basis of the invention is the creation of a method and device for measuring the thermophysical characteristics of solid materials in the field of action of centrifugal forces, implemented on the installations of rotary machines. The technical result is to increase the reliability of thermophysical characteristics, in particular thermal diffusivity and thermal conductivity, solid materials at high peripheral speed of rotation, for example, turbine blades and disks.

The problem is solved in that in the method for determining the thermophysical characteristics of solid materials, a thermally insulated sample in the form of a wire or a thin rod of solid material with an electric heater placed at one of its ends is mounted on a disk configured for high-speed rotation, the disk is placed in a vacuum chamber at the initial temperature, create a deep vacuum and load with at least two cycles of the combined effect of temperature and the action field of the centrifugal force, at the volume in each cycle sets its own peripheral speed, when the peripheral speed reaches the set value, the electric heater is turned on and the change in temperature of the sample in time is recorded, when the specified upper temperature is reached, the electric heater and the rotation device are turned off, and when the initial temperature is reached, the next cycle is loaded, according to the received data, experimental coefficient c _i (υ _i ) in the form

c _i (υ _i ) = Vm _i (υ _i ) / Vm ₀ (υ ₀ ),

where Vm _i (υ _i ) and Vm ₀ (υ ₀ ) are the maximum values of the heating rate at the peripheral speed (υ _i ) and in the static state (υ ₀ ), respectively, and they correct the thermal properties of the static state of the material, for example, thermal diffusivity the field of action of centrifugal forces is determined by the formula:

a _i = a _0i c _i (υ _i ),

where a _i and a ₀ - thermal diffusivity of the material with and without the influence of centrifugal forces, respectively.

It is advisable that the diameter of the sample be approximately 0.5 mm.

It is also advisable that the depth of the vacuum would be approximately 0.03 atm.

In addition, it is advisable that the sample and the electric heater be insulated from the disk, and the end of the sample with the electric heater is located closer to the center of the disk than the other.

The problem is also solved by the fact that the installation for determining the temperature characteristics of solid heat-conducting materials in the field of action of centrifugal forces contains an electric motor, a vacuum booster chamber associated with a vacuum pump, a disk that is mounted on the motor shaft and placed in the booster chamber, an electric heater that is mounted on a sample of the material mounted on the disk, thermocouples placed at least at both ends of the sample, a temperature recording device connected through a stripper to thermocouples and a power source, a disk rotational speed control device connected to the electric motor, a rotational speed sensor mounted to the camera on the electric motor shaft and connected to the control device.

It is also advisable that additional control thermocouples along the radius of the main thermocouples connected to the temperature recording device would be installed on the disk.

The invention is further illustrated by the description and figures, in which figure 1 reflects a schematic diagram of a device for measuring the thermophysical characteristics of solid materials in the field of action of centrifugal forces according to the invention;

figure 2 is a front view along A of the surface of the disk of the device of figure 1;

figure 3 - curves illustrating the change in temperature and heating rate Vm _i (υ _i ) of a solid material in time for different rotational speeds;

figure 4 - curve of the experimental coefficients c _i (υ _i ) obtained according to the graph of figure 3, according to the invention.

The method is carried out using the installation (figure 1). The installation comprises an electric motor 4, a vacuum booster chamber 11 connected to a vacuum pump 12, a disk 6 mounted on the shaft 5 of the electric motor. The test sample 13 is fixed on the front surface of the disk 6 (Fig. 2), at the end of which is located near the shaft of the electric heater 1.

The electric motor 4 is selected in such a way that it provides the disk 6 with high-speed rotations, creating a corresponding field of action of centrifugal forces for the sample 13, such as, for example, in the blades and disks of turbines of aircraft engines and plants.

The installation contains (Fig.2) means for controlling the temperature of the sample in the form of thermocouples 3 located at both ends of the sample.

The installation may contain additional control thermocouples placed against the sample on the front surface of the disk 6 along the radius of the main thermocouples (centrally symmetrical to the main thermocouples).

Thermocouples 3 and 17 with wires 15, 16 and 18 (respectively) are connected to the temperature recording device 2 through a current collector 9 connected to a power source 10.

The installation also contains a speed sensor 8 mounted on the shaft 5. It is advisable to install the sensor 8 up to the camera 11.

In addition, the installation includes a device 7 for controlling the rotational speed of the disk, the input of which is connected to the electric motor 4, and the output to the sensor 8.

As a power source 10, it is advisable to use a stabilized DC source. As the device 2 registration temperature using a computer system.

The method according to the invention is carried out on the installation as follows.

A sample 13 is made of the test material in the form of a thin rod or wire of a certain diameter and length and is placed on the disk 6.

In this case, heat-insulated turns of electric heater 1 are wound around one end thereof and two main thermocouples 3 are connected from both ends, one of them being connected to sample 13 in front of electric heater 1. Sample 13 with thermocouples 3 and electric heater 1 by wires 15, 16 is insulated and placed on a disk .

The end of the sample 13 with electric heater 1 is located closer to the center of rotation of the disk 6 than the other end.

It is advisable to position the sample 13 at an angle, for example, 45 ° with respect to the tangent to the arc of a circle 19.

The disk 6 is installed in a vacuum accelerating chamber 11 and connected to the shaft 5 of the motor 4. Through the holes (not shown) of the shaft, wires 15, 16 and 18 from the thermocouples 3, the electric heater 1 and additional thermocouples 17 are connected and connected to the current collector 9. From the current collector 9 wires 15 and 17 (from thermocouples 3 and additional thermocouples 17) are connected to a temperature recording device 2, and wires 16 (from an electric heater 1) are connected to a power source 10. A speed sensor 8 is mounted on the shaft 5 of the electric drive 4 and connected to the control device 7 h rangefinders rotation, connected to the motor 4. By accelerating the vacuum chamber 11 is connected a vacuum pump 12.

Then carry out the determination of thermophysical characteristics, according to the invention, cyclically as follows.

Vacuum pump 12 create a deep vacuum and record the initial temperature of the sample with thermocouples 3.

The rotational speed of the shaft 5 is set by the device 7 and the disk 6 is driven into rotation by an electric motor 4. The rotational speed is monitored by a sensor 8. Upon reaching a predetermined speed, turn on the source 10 for power supply of the electric heater 4 and this load the sample with the combined effect of temperature and the action of the centrifugal force with a given peripheral speed. Sample 13 is heated to a certain upper temperature value and the device 2 registers a change in temperature over time.

When the specified temperature is reached, the electric heater 1 is turned off, the disk 6 is stopped.

When the sample reaches the initial temperature, a different rotational speed of the shaft 5 is set and the sample is loaded with the next cycle of the combined action of the temperature and the centrifugal force.

According to the data obtained, the experimental coefficient c _i (υ _i ) is calculated in the form c _i (υ _i ) = Vm _i (υ _i ) / Vm ₀ (υ ₀ ),

where Vm _i (υ _i ) and Vm ₀ (υ ₀ ) are the maximum values of the heating rate at the peripheral speed (υ _i ) and in the static state (υ ₀ ), respectively, and they correct the thermal properties of the static state of the material, for example, thermal diffusivity the field of action of centrifugal forces is determined by the formula:

a _i = a _0i c _i (υ _i ),

where a _i and a ₀ - thermal diffusivity of the material with and without the influence of centrifugal forces, respectively.

Thermal conductivity can be determined by the formula: k _i = k ₀ s _i (υ _i ), where k _i and k ₀ are the thermal conductivity of the material with and without centrifugal forces, respectively.

Using the device according to the method according to the invention, experimental studies of a sample of solid heat-conducting material in the field of action of centrifugal forces at specified rotational speeds from 2500 rpm to 5000 rpm were carried out.

In the device, chromel-alumel thermocouples with a diameter of 0.3 mm were used as thermocouples 3 and 17, 0.5 mm copel wires were used for wires 15, 16 and 18, disk 6 is made of heat-resistant nickel alloy, current collector 9 is made as a mercury current collector PTO- 32M. The temperature recording device 2 is designed as a computer system.

When implementing the method in a vacuum booster chamber, the pressure of the residual air was 0.03 atm, the initial temperature was about 24 ° C. The electric heater 1 was supplied with direct current from a stabilized power source 10 with a constant power of 24 watts.

The experiments were carried out by the method according to the invention, in a static state of the disk (without the action of centrifugal forces) at υ ₀ = 0 and at rotation frequencies of 2500 and 5000 rpm, which correspond to peripheral speeds υ ₁ = 25 m / s and υ ₂ = 50 m / from. The data obtained are presented in figure 3-4.

Curves 1-3 of Fig. 3 show the change in temperature and heating rate at a rotational speed: 1 - 0 rpm, 2 - 2500 rpm, 3 - 5000 rpm.

These curves in figure 3 have maximum values at points Vm _{, 0} = 0.026, Vm _{, 1} = 0.063 and Vm _{, 2} = 0.077 ° C / s, respectively.

Defined by the formula c _i (υ _i ) = Vm _{, i} (υ _i ) / Vm _{, 0} , the coefficient curve c _i (υ _i ) obtained according to the graph of Fig. 3, according to the invention, is presented in Fig. 4.

The thermal diffusivity of the material in the field of action of centrifugal forces, determined by the formula a _i = a _0i c _i (υ _i ), is: in a stationary state - a ₀ = 5.3 · 10 ^-6 m ² / s, at a rotation speed of 25 m ² / s - a ₁ = a ₀ · c _i = 5.3 · 10 ^-6 · 2.41 = 12.8 · 10 ^-6 m ² / s, at a rotation speed of 50 m / s ² - a ₂ = a ₀ C ₂ = 5.3 · 10 ^-6 · 2.87 = 15.1 · 10 ^-6 .

The thermal conductivity at k ₀ = 5.3 · 10 ^-6 W / (m · K) will accordingly be k ₁ = 24 · 2.42 = 58 W / (m · K), k ₂ = 24 · 2.96 = 71 W / ( m · K), respectively.

Analysis of the curves (figure 3) shows that centrifugal forces significantly affect the thermal diffusivity and, therefore, the thermal conductivity of the material. Therefore, the application of the proposed method and device increases the reliability of the thermophysical characteristics of the materials of parts operating in operating conditions at a high peripheral speed.

The proposed method and device can be used in aircraft engine manufacturing, energy and other engineering industries having rotor parts (discs, blades, coatings, etc.) operating in the field of high-speed centrifugal forces.

Claims (6)

1. The method of determining the thermophysical characteristics of solid materials in the field of centrifugal forces, in which a thermally insulated sample in the form of a wire or a thin rod of solid material with an electric heater placed at one of its ends is mounted on a disk configured for high-speed rotation, the disk is placed in a vacuum chamber at an initial temperature, create a deep vacuum and load with at least two cycles of the combined effect of temperature and centrifugal force in this case, each cycle sets its own peripheral speed, when the peripheral speed reaches the set value, the electric heater is turned on and the change in temperature of the sample over time is recorded, when the specified upper temperature is reached, the electric heater and the rotation device are turned off, and when the initial temperature is reached, the next cycle is loaded, according to the obtained data calculate the experimental coefficient c _i (υ _i ) in the form
c _i (υ _i ) = Vm _i (υ _i ) / Vm ₀ (υ ₀ ),
where Vm _i (υ _i ) and Vm ₀ (υ ₀ ) are the maximum values of the heating rate at the peripheral speed (υ _i ) and in the static state (υ ₀ ), respectively, and they correct the thermal properties of the static state of the material, for example, thermal diffusivity in the field the action of centrifugal forces is determined by the formula:
a _i = a _0i c _i (υ _i ),
where a _i and a ₀ - thermal diffusivity of the material with and without the influence of centrifugal forces, respectively. 2. The method according to claim 1, characterized in that the diameter of the wire is approximately 0.5 mm 3. The method according to claim 1, characterized in that the vacuum depth is approximately 0.03 atm. 4. The method according to claim 4, characterized in that the sample and the electric heater are insulated from the disk, the end of the sample with the electric heater is located closer to the center of the disk than the other. 5. Installation for determining the temperature characteristics of solid materials in the field of action of centrifugal forces according to claim 1, containing an electric motor, a vacuum booster chamber associated with a vacuum pump, a disk that is mounted on the shaft of the electric motor and placed in the booster chamber, an electric heater that is mounted on the sample material mounted on the disk, thermocouples located at least at both ends of the sample, a temperature recording device connected through a current collector to thermocouples and a power source, Disc speed control GUSTs connected to the motor, the speed sensor mounted to the camera on the motor shaft and connected to the control device. 6. Installation according to claim 5, characterized in that the additional control thermocouples are installed on the disk along the radius of the main thermocouples connected to the temperature registration device.

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