CN201662548U - Optic fiber Bragg grating sensor for measuring heat conduction coefficients of material - Google Patents

Abstract

The utility model relates to a sensor for measuring heat conduction coefficients of a material, in particular to an optic fiber Bragg grating sensor, belonging to the technical field of electronic measuring devices. In the sensor, the shell wall of radiating package of a positive temperature coefficient thermistor (PCT) is attached and arranged in a heat-conducting protecting tube; and the surface of radiating package is provided with a surface groove, the size of which is correspondingly same to that of a temperature-measuring optic fiber Bragg grating. The sensor has simple structure and accurate measurement, and can realize site online measurement of heat conduction coefficients and distributed measurement of measured medium.

Description

A kind of optical fiber Bragg grating sensor of measuring material thermal conductivity

Technical field

The utility model relates to a kind of sensor of measuring material thermal conductivity, particularly optical fiber Bragg grating sensor, belongs to photoelectron measuring element technical field.

Background technology

Coefficient of heat conductivity is the important physical amount of reflection material thermal behavior, characterizes the heat conducting ability of material.According to the variation relation of temperature and time, the method for thermal conductivity measurement can be divided into two big classes: steady state method and transient state method.With the immediate document of the utility model be: Liu Jianxiang, Liu Xianli, Peng Xiaoyong, Zhou Yaohui, " test of soil thermal property and applied analysis ", " University Of Nanhua's journal (natural science edition) ", the 21st the 1st phase of volume of March in 2007.This article uses pipe method heat conducting coefficient measuring, belong to steady state method, its test philosophy is: under heat transfer reaches stable case, heat flux by cylindrical inner wall equals the heat flux by cylindrical outer wall, this method needs from on-site sampling, this has brought a lot of uncertain factors to thermal Conductivity Determination, can not realize on-site on-line measurement.

Summary of the invention

The purpose of this utility model provides a kind of optical fiber Bragg grating sensor of measuring material thermal conductivity, and it is simple in structure, measures accurately, can realize the on-site on-line measurement and the distributed measurement of realizing measured medium of coefficient of heat conductivity.

The purpose of this utility model is achieved in that the shell wall of the heat radiation encapsulation of posistor PTC is fitted and packs in the protection tube of heat conduction; have and the corresponding identical surface groove of thermometric optical fiber Bragg raster size in the heat radiation package surface, the thermometric optical fiber Bragg raster is close in the surface groove.

Heat radiation encapsulation described in the utility model and protection tube adopt alumina based material, and the center of packing into, the two ends of protection tube has the aluminium matter trip bolt of through hole, and the lead-in wire of optical fiber and thermistor PTC passes from the center pit of aluminium matter trip bolt.

The measuring principle of this sensor: thermistor PTC connects with the mains and heats, and carries out heat interchange with measured medium on every side, and forms stable Temperature Distribution in measured medium.To in the different material of coefficient of heat conductivity, form different Temperature Distribution after the PTC heating.Temperature variation will cause the skew of the centre wavelength of thermometric optical fiber Bragg raster.Realize measurement by the different wavelength shift amount of thermometric optical fiber Bragg raster to the different materials coefficient of heat conductivity, and stick on thermometric optical fiber Bragg raster in the surface groove when being subjected to axial tension, make its wavelength produce additional offset, the thermometric optical fiber Bragg raster has been played the effect of thermal sensitization.

The mathematical model of this sensor measurement coefficient of heat conductivity:

The aluminium protection tube is close in the heat radiation of PTC encapsulation in the sensor, and aluminium heat radiation encapsulation and aluminium protection tube should be done thin when satisfying intensity as far as possible.Thin aluminium heat radiation encapsulation and protection tube are big because of temperature conductivity, can regard PTC as an integral body with the heat radiation encapsulation, and thermal source can be considered directly with measured medium and contacts.

Sensor is embedded in the measured medium, as same some pyrotoxin.Suppose that the pyrotoxin heating is constant, be embedded in isotropic medium that the coefficient of heat conductivity of measured medium is a constant.Only radially heat conduction of sensor so, then heat conduction equation is:

$\frac{2}{r}\frac{\mathrm{dT}}{\mathrm{dr}}+\frac{d^{2}T}{d{r}^2}+\frac{q_V}{\mathrm{\θ}}=0---\left(1\right)$

In the formula: θ is the coefficient of heat conductivity (unit: W/ (mK)) of measured medium; R is radius (unit: m) radially; q _vHeat generation rate (unit: W/m for unit volume ³); T is temperature (unit: ℃).

Boundary condition is:

During r=0, $\frac{\mathrm{dT}}{\mathrm{dr}}{|}_{r=0}=0;$

Coefficient of heat conductivity is θ ₁, r=r ₁The time, T=T ₁

Separating the differential equation gets:

$T=\frac{-{\mathrm{<figure-callout\; id="6"\; label="q\; V"\; filenames="HSA00000043836100011.png"\; state="\{\{state\}\}">q</figure-callout>}}_V}{6\mathrm{\&theta;}}{r}^2+C_1\frac{1}{r}+C_2---\left(2\right)$

In the formula: C ₁, C ₂Be constant coefficient.

According to boundary condition calculate constant coefficient:

C ₁＝0

$C_2=t_1+\frac{q_v}{6{\mathrm{\&theta;}}_1}{r}_1^2$

With calculate constant coefficient substitution (2) formula, obtain adding thermally-stabilised after, apart from the temperature T at thermal source r place:

$T=-\frac{{\mathrm{<figure-callout\; id="6"\; label="q\; v"\; filenames="HSA00000043836100011.png"\; state="\{\{state\}\}">q</figure-callout>}}_v}{6\mathrm{\&theta;}}{r}^2+\frac{q_v}{6{\mathrm{\&theta;}}_1}{r}_1^2+T_1---\left(3\right)$

Then from beginning to be heated to the thermally-stabilised process, be expressed as apart from the temperature variation Δ T at thermal source r place:

ΔT＝T-T ₀ (4)

In the formula: T ₀Initial temperature during for heating (unit: ℃).

(3) substitution (4) formula is got:

$\mathrm{\&Delta;T}=-\frac{{\mathrm{<figure-callout\; id="6"\; label="q\; v"\; filenames="HSA00000043836100011.png"\; state="\{\{state\}\}">q</figure-callout>}}_v}{6\mathrm{\&theta;}}{r}^2+\frac{q_v}{6{\mathrm{\&theta;}}_1}{r}_1^2+T_1-T_0---\left(5\right)$

The heat radiation encapsulation has the thermal sensitization effect to the thermometric optical fiber Bragg raster, and the centre wavelength of thermometric optical fiber Bragg raster and the pass between the temperature variation are:

$\frac{\mathrm{\&Delta;}{\mathrm{\&lambda;}}_B}{{\mathrm{\&lambda;}}_B}=[S_T+S_{\mathrm{\&epsiv;}}({\mathrm{\&alpha;}}_H-{\mathrm{\&alpha;}}_{\mathrm{\&Lambda;}})]\mathrm{\&Delta;T}---\left(6\right)$

In the formula: λ _B(unit: nm), Δ T is temperature variation (unit: ℃), α for optical fiber Bragg raster centre wavelength _HThe thermal expansivity that encapsulates for dispelling the heat (unit: ℃ ^-1), α _ΛFor the thermal expansivity of bare fibre (unit: ℃ ^-1), S _εBe bare fibre strain sensitive coefficient, S _TFor the temperature-sensitivity coefficient of bare fibre (unit: ℃ ^-1).

(5) formula substitution (6) formula is got:

$\mathrm{\&Delta;}{\mathrm{\&lambda;}}_B=-\frac{S_a{\mathrm{\&lambda;}}_{\mathrm{<figure-callout\; id="6"\; label="B\; q\; v"\; filenames="HSA00000043836100011.png"\; state="\{\{state\}\}">B</figure-callout>}}{q}_v{}_{}}{6\mathrm{\&theta;}}{r}^2+S_a{\mathrm{\&lambda;}}_B[(T_1-T_0)+\frac{q_v}{6{\mathrm{\&theta;}}_1}{r}_1^2]---\left(7\right)$

In the formula: S _a=S _T+ S _ε(α _H-α _Λ) be the apparent temperature sensitivity coefficient (unit: ℃ ^-1), θ is the coefficient of heat conductivity (unit: W/ (mK)) of measured medium, Δ λ _BBe optical fiber Bragg raster wavelength change amount (unit: nm).

The beneficial effects of the utility model are:

1, the on-line measurement of coefficient of heat conductivity steady state method: in different medium, produce different Temperature Distribution according to thermal source, directly imbed thermal source and Fiber Bragg Grating Temperature sensor in the measured medium, change by thermometric grating sense temperature, realize the on-site on-line measurement of coefficient of heat conductivity.

2, distributed dot is measured: imbed list in the measured medium and prop up sensor and can measure the local temperature at the place of imbedding, many sensors can connect into Measurement Network, realize the distributed measurement to measured medium.

3, the thermal sensitization of thermometric optical fiber Bragg raster: stick on the thermometric optical fiber Bragg raster in the aluminium matter heat radiation package surface groove of PTC, under the thermal expansion of heat radiation encapsulation, will produce an additional wavelength shift.This bonding method has played the effect of thermal sensitization to the thermometric optical fiber Bragg raster.

Description of drawings:

Fig. 1 is a structural representation front view of the present utility model,

Fig. 2 is a structural representation left view of the present utility model,

Fig. 3 is a structural representation vertical view of the present utility model.

Each label list is shown among the figure: heat radiation encapsulation 1, thermistor PTC 2, thermometric optical fiber Bragg raster 3, optical fiber 4, protection tube 5, PTC lead-in wire 6, trip bolt 7, surface groove 8.

Embodiment:

Referring to Fig. 1; the shell wall of the heat radiation of posistor PTC 2 encapsulation 1 is fitted and is packed in the protection tube 5 of heat conduction; have and the corresponding identical surface groove 8 of thermometric optical fiber Bragg raster 3 sizes on heat radiation encapsulation 1 surface, thermometric optical fiber Bragg raster 3 is close in the surface groove 8.Heat radiation encapsulation 1 and protection tube 5 all adopt alumina based material, and the center of packing into, the two ends of protection tube 5 has the aluminium matter trip bolt 7 of through hole, and the lead-in wire of optical fiber 4 and thermistor PTC 2 passes from the center pore of aluminium matter trip bolt 7.

The concrete enforcement parameter of this sensor is as follows:

1, the sensor protection pipe is of a size of: cylindrical wall overall diameter 12mm, long 30mm, thick 2mm;

2, an integral body is regarded in PTC and heat radiation encapsulation as, and the heat radiation package dimension is: circle wall overall diameter 10mm, long 10mm, thick 2mm;

3, sensor is imbedded in the measured medium, connected stabilized voltage supply, obtain the wavelength of optical fiber Bragg raster with the optical fiber Bragg raster (FBG) demodulator;

4, the terminal voltage of PTC is 100V, when temperature reaches constant, and operating resistance R _G=817 Ω calculate to such an extent that the thermal value of PTC is 12.24W according to the heat Calculation formula, and the volume of thermal source is 785mm ³, the thermal value q of unit volume then _v=0.0156W/mm ³

5, choose r ₁Be 15mm, its pairing temperature T ₁Be assumed to be 20 ℃, θ ₁Be 6W/ (mK).Initial temperature T ₀It is 20 ℃;

6, the Theoretical Calculation result shows: when the initial wavelength of optical fiber Bragg raster is 1550nm, and the strain sensitive coefficient S _ε=0.784, temperature-sensitivity coefficient S _T=6.00 * 10 ^-6℃ ^-1, the thermalexpansioncoefficient of heat radiation encapsulation _H=23.0 * 10 ^-6℃ ^-1, the thermalexpansioncoefficient of silica fibre _Λ=0.550 * 10 ^-6℃ ^-1, S _a=23.6 * 10 ^-6℃ ^-1Coefficient of heat conductivity θ=0.83W/ (mK) substitution (7) formula of earth is calculated: Δ λ _B=701pm.

Claims (2)

1. optical fiber Bragg grating sensor of measuring material thermal conductivity; it is characterized in that: the shell wall of the heat radiation of posistor PTC encapsulation is fitted and is packed in the protection tube of heat conduction; have and the corresponding identical surface groove of thermometric optical fiber Bragg raster size in the heat radiation package surface, the thermometric optical fiber Bragg raster is close in the surface groove.

2. the optical fiber Bragg grating sensor of measurement material thermal conductivity according to claim 1; it is characterized in that: heat radiation encapsulation and protection tube adopt alumina based material; the center of packing into, the two ends of protection tube has the aluminium matter trip bolt of through hole, and the lead-in wire of optical fiber and thermistor PTC passes from the center pit of aluminium matter trip bolt.

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