CN203350206U - Optical fiber grating measurement system for thermal diffusion rate of cylinder structure - Google Patents

Abstract

The utility model relates to an optical fiber grating measurement system for a thermal diffusion rate of a cylinder structure, and belongs to the technical filed of measurement. The system comprises a heating water tank (1), a water pump (2), a to-be-measured cylinder (5), a control valve (10), an inner wall thermoelectric couple (3), an outer wall thermoelectric couple (4), an inner wall optical fiber grating sensor (7) and an outer wall optical fiber grating sensor (8). A measurement method comprises the steps as follows: firstly, a condition that a central wavelength of an optical fiber grating attached to the surface of the structure changes with the temperature is required to be measured firstly, and calculation is performed, so that a function relationship between the temperature and the grating central wavelength is acquired; secondly, by means of a flowing hot water heating cylinder structure, the condition that the optical fiber grating central wavelength changes with the time is measured, so that a function relationship between the time and the optical fiber grating central wavelength is acquired; then according to the Fourier's second law and boundary conditions, a temperature and time function is acquired; and finally according to a Fourier's one-dimensional heat conduction equation, the thermal diffusion rate of the material is calculated.

Description

The fiber grating measuring system of cylindrical structure thermal diffusivity

Technical field

The utility model relates to material thermophysical parameter field of measuring technique, comprises a kind of fiber grating measuring system of cylindrical structure thermal diffusivity, particularly relates to a kind of fiber grating that utilizes and measures the cylindrical structure thermal diffusivity.

Background technology

Heat transfer is a kind of modal spontaneous phenomenon, nearly all engineering field all can run into some heat transfer problems under given conditions, now science and technology is advanced by leaps and bounds, and the deep development of nuclear maximization, space technology etc. require the detailed-oriented and Calculation of Heat Transfer precision of analysis of Heat Transfer.

Cylindrical structure has higher specific strength, specific stiffness and low expansion character, therefore be widely used in the structure of high-performance, low weight requirement, these application mainly comprise movable bridge girder construction, the supporting member of helicopter and pull bar and other similar aircraft structural components.In structure is heated the Unsteady Heat Transfer process of intensification (cooling), the heat that enters object constantly is absorbed and makes local temperature to raise on the way, in this process, lasts till that interior of articles each point temperature all is tending towards balanced and stable.The thermograde that the heat transfer of this ad hoc fashion of heat conduction relies on interior of articles, from high-temperature area to the low-temperature region transferring energy, is used for the speed degree of exosyndrome material transferring heat usually by thermal diffusivity.In the modern project design, often run into relevant heating, cooling, evaporate, condense, melt, solidify, the various practical problemss such as heat-insulation and heat-preservation, so the height of material thermal diffusivity has the important computations meaning for thermal stability and the thermodynamic property under hot environment of structure.

In the various method of testings of having set up, roughly can be summarized as two large classes according to its characteristics of heat transfer: steady state method and unstable state method.

Steady state method is based on Fourier's 1st law.When heat transfer reaches while stablizing, measure the temperature variation of heat and the heated medium of heating medium simultaneously, try to achieve the thermophysical parameter of measured material by energy equilibrium.Common method of testing has: linear hot flow type method of testing and heated filament method of testing.The mensuration of steady state method need to, by the long-time preheating of testee under stationary temperature, often obtain an experimental data and approximately need a few hours.For making up the thermal loss of test process, system is done to obtain more complicated, but measuring accuracy is higher, can directly measure the coefficient of heat conductivity of material.

The unstable state method is based on Fourier's 2nd law.The temperature of utilization tested material in astable diabatic process is relation over time, measures its thermophysical parameter.The unstable state method often adopts the transient test technology of surface heat flux; Two kinds of basic implementation methods having developed for this technology are: diaphragm type surface temperature measurement method and thick-film type calorimetric method.

Existing result of study shows, no matter is steady state method or unstable state method, all has certain complicacy, needs special experimental system, very high to experimental situation and conditional request; And rarely seen have fiber grating is measured for thermal diffusivity.

The utility model content

The purpose of this utility model is to provide that a kind of simple possible, favorable repeatability, accuracy are high, the fiber grating measuring system of the cylindrical structure thermal diffusivity of strong interference immunity.

For achieving the above object, the technical solution of the utility model comprises measuring system and measuring method two parts.

A kind of fiber grating measuring system of cylindrical structure thermal diffusivity, for measuring the thermal diffusivity that axial length is greater than the cylindrical structure of 5 times of external diameters, this measuring system comprises heating water tank, water pump, cylinder to be measured, operation valve, inner surface heat galvanic couple, outer wall thermopair, inwall fiber-optic grating sensor, outer wall fiber-optic grating sensor;

One end of above-mentioned cylinder to be measured seals by the second heat insulation encapsulant by the first heat insulation encapsulant sealing, the other end; The outlet of above-mentioned heating water tank is connected with the import of water pump, and the outlet of water pump is divided into two-way, and a road is connected with cylinder interior to be measured through the first heat insulation encapsulant, and another road is through the venting valve connection water channel; The pipeline of the inflow point of heating water tank is connected with cylinder interior to be measured through the second heat insulation encapsulant after operation valve;

Above-mentioned inwall optical light sensor and the corresponding inner and outer wall that is separately fixed at cylinder to be measured in outer wall fiber-optic grating sensor position; The above-mentioned inner surface heat galvanic couple inner and outer wall that lay respectively to be measured cylinder corresponding with the outer wall thermocouple location; The grating part of above-mentioned inwall fiber-optic grating sensor, outer wall fiber-optic grating sensor, the probe segment of inner surface heat galvanic couple and outer wall thermopair all is positioned at cylinder axial length to be measured 1/2 place;

The lead-in wire of above-mentioned inwall fiber-optic grating sensor and outer wall fiber-optic grating sensor is connected with fiber Bragg grating (FBG) demodulator.

The measuring method of the fiber grating measuring system of cylindrical structure thermal diffusivity, mainly comprise that centre wavelength and temperature fitting function calculate, the original state monitoring, and course of work monitoring, computer data is processed four processes;

Step 1, demarcate the funtcional relationship that fiber grating sticks on temperature and centre wavelength behind the cylindrical structure surface, obtain the temperature characterisitic function of fiber grating;

Step 2, make operation valve in open state, open water pump, make to fill with water in cylinder to be measured;

The Temperature numerical of observation inner surface heat galvanic couple, outer wall thermopair, record is as initial temperature;

By inwall fiber grating, outer wall fiber grating incoming fiber optic grating demodulation instrument, gather wherein heart wavelength signals as initial wavelength;

Step 3, keep water pump in running order, fiber Bragg grating (FBG) demodulator keeps the data acquisition state, opens the heating water tank heater switch, sets the heating maximum temperature, with constant speed heating;

In heating process, heating water tank, water pump, water pipe make detected materials inside in dynamic full state, the internal hot-water temperature raises gradually, heat is propagated from the inside to the outside, the inwall fiber grating is experienced the inside configuration thermal strain, the outer wall FBG monitoring structure outer wall heat situation of being heated, the instantaneous transmission of fiber bragg grating center wavelength data also is stored to computing machine;

Heating water tanks enters temperature constant state to design temperature, until inner surface heat galvanic couple, outer wall electric thermo-couple temperature, shows that when consistent, fiber Bragg grating (FBG) demodulator stops data collection, and closes heater switch and water pump;

Step 4, the centre wavelength data of fiber Bragg grating (FBG) demodulator collection in above-mentioned steps 3 and time are carried out to the data fitting processing, obtain respectively inner structural wall fiber bragg grating center wavelength and time function relation expression formula f ₁(t), structure outer wall fiber bragg grating center wavelength and time function relation expression formula f ₂(t);

In heating process, the cylindrical structure two ends are when adiabatic condition, and heat can only radially transmit, the cylindrical structure that is r for internal diameter, and heat transmission radially meets one-dimensional and unsteady state heat conduction, according to Fourier's 2nd law, obtains following one dimension diffusivity equation:

$\frac{\∂T}{\∂t}=\mathrm{\α}(\frac{{\∂}^{2}T}{{\∂r}^2}+\frac{1}{r}\frac{\∂T}{\∂r})$

Wherein r is radial distance, and t is the time, the function that T is temperature and time, radial distance, and referred to as the Temperature Distribution function, the thermal diffusivity that α is material;

From thermodynamics, if known the medium of investigating at borderline temperature regime (or exchange heat situation) and medium in the temperature of initial time, just can determine medium each temperature constantly afterwards.So the most basic one of heat-conduction equation to determine the solution problem be exactly to ask the solution of problem under to starting condition and boundary condition;

As the initial temperature of fruit structure is evenly distributed, establish starting condition and boundary condition is respectively:

Starting condition: t=0, T=T ₀

Boundary condition: r=0,

r=r ₀, T=T _b

In formula, T ₀for structure initial temperature, T _bfor structure reaches the temperature after thermal equilibrium state, r representative structure radius, r ₀for the structural outer radius distance value.

Therefore, can, according to the Temperature Distribution function, obtain following result:

$\frac{\∂T}{\∂t}={f_1}^{\′}\left(t\right)-\ln \frac{r}{r_1}\frac{{f_1}^{\′}\left(t\right)-{f_2}^{\′}\left(t\right)}{\ln \frac{r_2}{r_1}}$

$\frac{{\∂}^{2}T}{{\∂r}^2}=\frac{f_1\left(t\right)-f_2\left(t\right)}{r^2\ln \frac{r_2}{r_1}}$

Thus can be in the hope of thermal diffusivity α, wherein, r ₁the representative structure inside radius, r ₂the structure external radius.

The beneficial effects of the utility model are that the employing fiber grating is measured the cylindrical structure thermal diffusivity, has advantages of highly versatile; Architectural feature is not had to specific (special) requirements, can reach the requirement of Site Detection; It is highly sensitive that fiber-optic grating sensor is measured, and can reuse after making encapsulation, reduces costs; Sensor performance is stable, not affected by electromagnetic interference (EMI) and rugged surroundings, and functional reliability is good; The method is easily operation in fulfillment process, and system forms relatively simple, can reduce the introducing measuring error, improves result precision; In addition, can extract as required temperature required segment data and be analyzed, realize the multiple temperature sections measurement.

The accompanying drawing explanation

Accompanying drawing 1 is fiber grating and thermopair fixed position;

Accompanying drawing 2 is experimental system structural drawing.

Number in the figure title: 1----heating water tank; The 2---water pump; 3---inner surface heat galvanic couple; 4---outer wall thermopair; 5---cylinder to be measured; 6-1---the first heat insulation encapsulant; 6-2---the second heat insulation encapsulant; 7---inwall fiber-optic grating sensor; 8---outer wall fiber-optic grating sensor; The 9---venting valve; The 10----operation valve.

Embodiment

The utility model measuring system consists of heating water tank, water pump, thermopair, cylindrical structure to be measured, heat insulation encapsulant and fiber-optic grating sensor, fiber Bragg grating (FBG) demodulator, operation valve.

Wherein between heating water tank, water pump, cylinder to be measured, water pipe is connected, and operation valve is between cylinder to be measured and heating water tank, for controlling the speed of current; Water pump is between heating water tank and cylinder to be measured, and its function is that the water in heating water tank is injected to cylindrical structure, and keeps dynamic circulation; Water pipe combines with the heat insulation encapsulant, with cylindrical structure to be measured, is communicated with; Fiber grating is separately fixed on inner structural wall and outer wall, and wherein the fiber grating tail optical fiber in structure partly is connected with fiber Bragg grating (FBG) demodulator through adiabatic encapsulant, and the fiber grating be fixed on outer wall directly is connected with (FBG) demodulator; In the fiber grating relevant position, arrange two thermopairs, measure the inside and outside wall temperature, probe positions and fiber grating are adjacent; Wherein fiber grating is relative in the inside and outside wall fixed position, and inside and outside wall thermocouple probe fixed position is relative, is distributed in inside and outside wall axial length 1/2 place.

Whole experimental implementation comprises following process: at first will demarcate fiber grating and stick on temperature and function of wavelength relation behind the cylindrical structure surface, obtain the temperature characterisitic function of fiber grating, and show by the form of funtcional relationship; Next is opened operation valve and is communicated with heating water tank, water pipe, cylindrical structure, opens water pump, makes to fill with water in cylinder to be measured; At room temperature, the Temperature numerical of observation thermopair, the numerical value of inner surface heat galvanic couple collection is the cylinder inner wall temperature, and the outer wall thermopair gathers the cylinder outer wall temperature, and when experiment starts, both numerical value should be identical or close;

By incoming fiber optic grating demodulation instrument after fiber grating tail optical fiber part and wire jumper welding, gather wherein cardiac wave personal attendant time-varying signal and store; Keep water pump in running order, heating water tank, pipeline, cylindrical structure to be measured form the circulation system, open the water tank heater switch, and with constant speed heating, hot-fluid enters cylinder with constant speed, reaches the purpose of stable state heating; In heating process, water temperature inside raises gradually, and heat is propagated from the inside to the outside, and the inwall fiber grating is experienced the inside configuration thermal strain, outer wall FBG monitoring structure outer wall-heated situation; In this process, fiber Bragg grating (FBG) demodulator gathers centre wavelength temporal evolution signal, until two thermocouple readings and Temperature numerical reach unanimity and stablize, stops afterwards heating and data acquisition, and in whole experimentation, it is stable that ambient temperature need to keep,

In heat transfer process, hot-fluid is measuring of transferring energy size, can not adopt direct method to measure, but because it and observable temperature scalar interrelate, therefore, can be from the angle research hot-fluid of macroscopical temperature and the basic law of thermograde.Determine Temperature Distribution function in object, determine the distribution situation of object temperature in time and locus.According to Fourier's heat-conduction equation, determine that one conducts heat and meets following form (referring to " engineering Heat Transfer " chapter 2, the king mends a surname's work) without the endogenous pyrogen object:

$\frac{{\∂}^{2}T}{{\∂x}^2}+\frac{{\∂}^{2}T}{{\∂y}^2}+\frac{{\∂}^{2}T}{{\∂z}^2}=\frac{1}{\mathrm{\α}}\frac{\∂T}{\∂t}---\left(1\right)$

Wherein, T is the Temperature Distribution function, and t is time variable, and x, y, z is the structure three-dimensional coordinate, and α represents the thermal diffusivity of material, and dimensional unit is m ²/ s.

For cylindrical structure common in engineering, under cylindrical coordinates, Fourier's heat-conduction equation can turn to following form:

$\frac{1}{r}\frac{\∂}{\∂r}\left(r\frac{\∂T}{\∂r}\right)+\frac{1}{r^2}\frac{\∂}{\∂\mathrm{\φ}}\left(r\frac{\∂T}{\∂\mathrm{\φ}}\right)+\frac{\∂}{\∂z}\left(\frac{\∂T}{\∂z}\right)=\frac{1}{\mathrm{\α}}\frac{\∂T}{\∂t}---\left(2\right)$

Wherein, r, φ, z are the structure three-dimensional cylindrical coordinates.

Cylindrical structure is modal structure in engineering, supposes that the inside and outside radius of cylindrical structure is respectively r ₁, r ₂, axial length l is greater than 10r ₂, work as so inside and outside wall surface temperature and respectively be maintained isothermal T ₁, T ₂, for cylindrical wall, each isothermal surface will be all the face of cylinder concentrically with respect to one another, and face of cylinder radius is r, and its surface area is 2 π rl, and along with radius r increases and strengthens.Putting before this, thinking in the wall of this long cylinder that Temperature Distribution is axisymmetric one-dimension temperature field, hot-fluid is towards radially, and do not having under the steady working condition of endogenous pyrogen, and hot-fluid is constant on the way.

The cylindrical wall that is 2 π rl for the face of cylinder, according to the heat conduction philosophy:

$Q=-2\mathrm{\πrl\λ}\frac{\mathrm{dT}}{\mathrm{dr}}---\left(3\right)$

λ is material thermal conductivity.According to hypothesis,

without endogenous pyrogen, and be one dimension radially, above formula can be reduced to:

$\frac{d}{\mathrm{dr}}\left(\mathrm{r\λ}\frac{\mathrm{dT}}{\mathrm{dr}}\right)=0---\left(4\right)$

That is

$\mathrm{r\λ}\frac{\mathrm{dT}}{\mathrm{dr}}=C_1---\left(5\right)$

Above (3) (5) two formulas of contrast: known

variables separation, to the cylindrical wall integration:

$\frac{Q}{2\mathrm{\πl}}{\∫}_{r_1}^{r_2}\frac{\mathrm{dr}}{r}=-{\∫}_{T_1}^{T_2}\mathrm{\λdt}\≡{\mathrm{\λ}}_m(T_1-T_2)---\left(6\right)$

$Q=\frac{2\mathrm{\πrl}{\mathrm{\λ}}_m(T_1-T_2)}{\ln \frac{r_2}{r_1}}---\left(7\right)$

When λ is constant, maximum coefficient of heat conductivity λ in formula _m=λ, if formula (6) changes by r ₁be integrated to r, corresponding temperature is by T ₁be integrated to T, when λ is constant,

$T=T_1-\frac{Q}{2\mathrm{\πl}}1n\frac{r}{r_1}---\left(8\right)$

With (7) formula simultaneous cancellation Q, obtain:

$T=T_1-\frac{T_1-T_2}{\ln \frac{r_2}{r_1}}\ln \frac{r}{r_1}---\left(9\right)$

This is the Temperature Distribution function, when it in dynamic process, T ₁, T ₂can replace with the optical fiber grating temperature function of wavelength.In heating process, the cylindrical structure two ends are when adiabatic condition, and heat can only radially transmit, and therefore can utilize (9) formula to carry out the thermal diffusivity of Calculating material.

From thermodynamics, if known the medium of investigating at borderline temperature regime (or exchange heat situation) and medium in the temperature of initial time, just can determine medium each temperature constantly afterwards.So the most natural while of heat-conduction equation also the most basic one determine the solution problem be exactly to starting condition and boundary condition under ask the solution of problem.The cylindrical structure that is r for internal diameter, heat transmission radially meets one-dimensional and unsteady state heat conduction, according to Fourier's 2nd law, obtains following one dimension diffusivity equation:

$\frac{\∂T}{\∂t}=\mathrm{\α}(\frac{{\∂}^{2}T}{{\∂r}^2}+\frac{1}{r}\frac{\∂T}{\∂r})---\left(10\right)$

As the initial temperature of fruit structure is evenly distributed, starting condition and boundary condition are respectively:

Starting condition: t=0, T=T ₀

Boundary condition: r=0,

r=r ₀, T=T _b

In formula, T representation temperature distribution function, T ₀for structure initial temperature, T _bfor structure reaches the temperature after thermal equilibrium, r representative structure radius, r ₀for the structure external radius.

Therefore, can, according to the Temperature Distribution function, obtain following result:

$\frac{\∂T}{\∂t}={f_1}^{\′}\left(t\right)-\ln \frac{r}{r_1}\frac{{f_1}^{\′}\left(t\right)-{f_2}^{\′}\left(t\right)}{\ln \frac{r_2}{r_1}}---\left(11\right)$

$\frac{{\∂}^{2}T}{{\∂r}^2}=\frac{f_1\left(t\right)-f_2\left(t\right)}{r^2\ln \frac{r_2}{r_1}}---\left(12\right)$

Thus can be in the hope of thermal diffusivity α.

Accompanying drawing 1 is the design of fiber grating distributing position, at cylinder axial length 1/2 place, at surfaces externally and internally, pastes fiber grating, known according to thermodynamics and Elasticity, can avoid like this impact of cylindrical structure edge effect.Keep two gratings on same bus, radially can be more accurate on bang path at hot-fluid; Inner surface heat galvanic couple 3 is measured the temperature of inwall fiber-optic grating sensor 7 positions, and outer wall thermopair 4 is measured the temperature of outer wall fiber-optic grating sensor 8.

Accompanying drawing 2 is measuring system structural drawing, wherein heating water tank 1, water pump 2, cylinder to be measured 5 are connected by water pipe, operation valve 10 is on water pipe, between cylinder 5 to be measured and heating water tank 1, water pump 2 is between heating water tank 1 and cylinder to be measured, water pipe combines with the first heat insulation encapsulant 6-1, with cylinder 5 to be measured, is communicated with; Inwall fiber-optic grating sensor 7 is fixed on inner structural wall, draws tail optical fiber and is connected with fiber Bragg grating (FBG) demodulator by the first heat insulation encapsulant, and outer wall fiber-optic grating sensor 8 is fixed on the structure outer wall, and its extension is connected with (FBG) demodulator; Inner surface heat galvanic couple 3 is positioned at inner structural wall, measures inner wall temperature, and outer wall thermopair 4 is positioned at the cylindrical structure outer wall, measures outside wall temperature.Probe positions and inwall fiber-optic grating sensor 7, outer wall fiber-optic grating sensor 8 are adjacent.Wherein inwall fiber-optic grating sensor 7, outer wall fiber-optic grating sensor 8 fixed positions are relative, and thermopair 3,4 fixed positions are relative, are distributed in axial length 1/2 place.

By on cylindrical structure to be measured surface, pasting fiber grating, obtain the funtcional relationship between structure temperature, time, fiber bragg grating center wavelength, calculate the thermal diffusivity of material.Alleviated the complexity of optics in the past or electronic measurement system, test macro and the method for foundation be simple and convenient, reproducible, good stability, reliability are higher.

Claims (1)

1. the fiber grating measuring system of a cylindrical structure thermal diffusivity, be greater than the thermal diffusivity of the cylindrical structure of 5 times of external diameters for measuring axial length, it is characterized in that:

This measuring system comprises heating water tank (1), water pump (2), cylinder to be measured (5), operation valve (10), inner surface heat galvanic couple (3), outer wall thermopair (4), inwall fiber-optic grating sensor (7), outer wall fiber-optic grating sensor (8);

One end of above-mentioned cylinder to be measured (5) seals by the second heat insulation encapsulant (6-2) by the first heat insulation encapsulant (6-1) sealing, the other end; The outlet of above-mentioned heating water tank (1) is connected with the import of water pump (2), and the outlet of water pump (2) is divided into two-way, and a road is connected with cylinder to be measured (5) inside through the first heat insulation encapsulant (6-1), and another road is through venting valve (9) connection water channel; The pipeline of the inflow point of heating water tank (1) is connected with cylinder to be measured (5) inside through the second heat insulation encapsulant (6-2) after operation valve (10);

Above-mentioned inwall fiber-optic grating sensor (7) and the corresponding inner and outer wall that is separately fixed at cylinder to be measured (5) in outer wall fiber-optic grating sensor (8) position; Above-mentioned inner surface heat galvanic couple (3) and the corresponding inner and outer wall that lays respectively at cylinder to be measured (5) in outer wall thermopair (4) position; The grating part of above-mentioned inwall fiber-optic grating sensor (7), outer wall fiber-optic grating sensor (8), the probe segment of inner surface heat galvanic couple (3) and outer wall thermopair (4) all is positioned at cylinder to be measured (5) axial length 1/2 place;

Above-mentioned inwall fiber-optic grating sensor (7) is connected with fiber Bragg grating (FBG) demodulator with the lead-in wire of outer wall fiber-optic grating sensor (8).

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