CN101639455A - Method and system for testing thermo-physical property of loose coals - Google Patents

Abstract

The invention discloses a method and a system for testing the thermo-physical property of loose coals, which are characterized in that three thermo-physical property parameters of heat conduction coefficients (gamma) of the loose coal, heat diffusivity rates (alpha) and specific heat capacity (cp) are simultaneously measured once based on a hot-wire method. The method comprises the concrete stepsas follows: placing a heating rod used as a heat source in the centre of a coal sample of the loose coals, arranged a temperature sensor on a temperature measuring point in the coal sample, and separating the coal sample between a temperature measuring point and the heating rod; placing the coal sample in a sample cylinder; measuring the density of the coal sample in the sample cylinder, setting the heating power of the heating rod, and recording the time when the heating rod underwent at the beginning of the heating; measuring the temperature of the coal sample at the corresponding moment; and firstly calculating the heat conduction coefficients (gamma) of the coal sample according to a principle of a parallel hot-wire method, and sequentially solving the heat diffusivity rates (alpha) ofthe coal sample and the specific heat capacity (cp) of the coal sample by the density, the heating power, the time and the temperature. The invention has simple method, high system testing accuracy and convenient experiment and operation.

Description

Thermo-physical property of loose coals method of testing and system

Technical field

The present invention relates to thermo-physical property of loose coals method of testing and system.Be applied to the thermo-physical property of loose coals parameter testing in the spontaneous combustion of coal burning things which may cause a fire disaster Study of location.

Background technology

The fire that the underground coal spontaneous combustion causes can cause heavy economic losses, in fact, breeding with evolution of spontaneous combustion of coal is slow, find to occur in the mine thing that spontaneous combustion burning things which may cause a fire disaster sign is not a difficulty, but find to position burning things which may cause a fire disaster accurately rapidly after the spontaneous combustion sign, causing and can not control and put out burning things which may cause a fire disaster timely and effectively, be one of major reason that causes spontaneous combustion of coal ignition heavy losses.

Technique for delineating for fire location and scope has infrared thermometer, temperature sensor, geophysical prospecting equipment, survey radon method and computer simulation method etc. at present, be the temperature probe method of representative wherein with infrared measurement of temperature method, direct temperature measurement method and computer simulation method etc. because have the efficient height, advantage such as easy and simple to handle has obtained certain application in engineering reality.These methods are based on heat transfer theory and flow field theory, set up the mathematic model of temperature field of goaf or coal column, utilize numerical solution to carry out computer simulation or in conjunction with observed temperature data, reach purpose to coal spontaneous combustion burning things which may cause a fire disaster high temperature dot location, and since the thermo-physical property of loose coals parameter in the mathematical model can't accurately obtain, be difficult to realize to the coal spontaneous combustion burning things which may cause a fire disaster carry out in time, accurate in locating.

More for the thermo-physical property of loose coals testing research at present, survey Coefficient of Heat Conductivity of Loose Coal Body, DSC method survey loose coal specific heat capacity etc. as heat-pole method or stable state cylinder method, and developed corresponding testing tool.But mostly be the method that single experiment only can be surveyed a parameter, must do repeatedly experiment if will obtain a plurality of parameters, this has prolonged experimentation and has increased experimental cost.

The heat-pole method that intersects on principle also can be realized measuring in coefficient of heat conductivity and the thermal diffusivity, but needs to consider the hot line radius in the formula of calorimetric diffusivity, and the heat-pole method test philosophy requires the hot line radius r ₀→ 0, the hot line radius is too for a short time, and to cause the diameter of thermopair pad on it to compare with hot line excessive, will use hot line effective radius r ₀' consider the error brought thus, nonetheless, because effective radius r ₀' be difficult to direct micrometric measurement, often cause the error at measurment of thermal diffusivity excessive (＞8%).And existing Coefficient of Heat Conductivity of Loose Coal Body testing tool is aspect hardware design, have that automaticity is not high, experimental implementation is inconvenient and shortcomings such as experiment condition and the on-the-spot actual degree difference that conforms to, cause measuring accuracy not high, can't satisfy the engineering application request well.Therefore, be necessary to study new method of testing and system, with realize the thermo-physical property of loose coals parameter efficient, accurately measure, for the accurate location of spontaneous combustion of coal burning things which may cause a fire disaster lays the foundation.

The applicant once published an article on " China Mining University's journal " (2009 the 3rd phases, the 38th volume) proposing to utilize combination of intersection heat-pole method and hot line spacing is r position τ temperature rise θ (r constantly, τ) survey the method for loose coefficient of heat conductivity and thermal diffusivity simultaneously, and designed test macro, dropped into actual use, and obtained good result, but because the loose coal thermal conductivity is relatively poor, temperature rise in the experimentation on the intersection hot line often differs bigger in parallel hot line temperature rise, there are some researches show that the Coefficient of Heat Conductivity of Loose Coal Body size is relevant with temperature, thereby the coefficient of heat conductivity that directly utilization intersection heat-pole method records bring considerable influence will inevitably for the thermal diffusivity estimation precision in conjunction with parallel hot line temperature rise data computation loose coal thermal diffusivity.In addition, the system hardware aspect, the heating rod in the original system is fixedly mounted on the test specimen tube base, and dismounting is inconvenient and break easily.Test specimen tube only has a movable end cover, takes down before the experiment with the filling coal sample, after experiment is finished, removes end cap and little by little takes out sample from test specimen tube, operates very inconvenient.

Summary of the invention

The present invention is for avoiding above-mentioned existing in prior technology weak point, a kind of thermo-physical property of loose coals method of testing and system are provided, directly utilize parallel heat-pole method to survey Coefficient of Heat Conductivity of Loose Coal Body and thermal diffusivity simultaneously, by existing temperature probe and system architecture are improved, with further raising system testing precision and enhancing convenient experimental operation.

Technical solution problem of the present invention adopts following technical scheme:

The characteristics of thermo-physical property of loose coals method of testing of the present invention are based on heat-pole method, disposable Coefficient of Heat Conductivity of Loose Coal Body λ, thermal diffusivity a and the specific heat capacity c of surveying simultaneously _pThree thermal physical property parameters, described method are to place heating rod as thermal source at the coal sample center of loose coal, temperature sensor is set on the point for measuring temperature in coal sample is used to detect the coal sample temperature, have coal sample to be separated by between described point for measuring temperature and the heating rod; Described coal sample is positioned in the test specimen tube; Measure the density p of coal sample in the described test specimen tube, the heating power (W/m) of the described heating rod of setting, the record heating rod is from beginning to heat the time of being experienced (s); The corresponding temperature of described coal sample constantly of measurement (℃); By described density, heating power, time and temperature, at first calculate the coefficient of heat conductivity λ of described coal sample according to parallel heat-pole method principle, formula calculates coal sample thermal diffusivity a below utilizing then:

$(\mathrm{\θ}(r,\mathrm{\τ})\·2\mathrm{\π\λ})/q=\frac{1}{2}(-\mathrm{\γ}-\ln p-\underset{n=!}{\overset{5}{\mathrm{\Σ}}}\frac{{(-1)}^n{p}^n}{\mathrm{nn}!})$

In the formula: p=r ²/ (4a τ),

R be in the coal sample certain a bit with the distance of hot line, m;

A is the thermal diffusivity of described coal sample, m ²/ s;

λ is described coal sample coefficient of heat conductivity, W/ (m.K);

τ is the time, s;

θ (r τ) is radial distance heating rod r position point τ temperature rise constantly in the coal sample, ℃;

γ=0.5772156 is an Euler's constant.

After trying to achieve thermal diffusion a, the specific heat capacity c of coal sample _pTry to achieve according to following formula: c _p=λ/(ρ α)

The characteristics of thermo-physical property of loose coals method of testing of the present invention are that also the coal sample amount that described test specimen tube is once surveyed is 25Kg～30Kg, the maximum 25mm of the granularity of described loose coal.

The characteristics of thermo-physical property of loose coals test macro of the present invention are to have:

One column test specimen tube is made of cover and cylindrical shell, and dodge gate is set on the cylindrical shell, and is provided with the salable hole that is used to insert thermopair and lead;

One is arranged on the heating rod on the described test specimen tube axial location, provides stable working power with stabilized voltage supply for described heating rod;

One data acquisition and transmission unit, be included in depart from the thermopair that is provided with on the described test specimen tube axial location and be arranged on the test specimen tube outside, as the PLC controller of slave computer, be connected with microsystem with described PLC controller by PPI programming cable as host computer; Carry out the collection of temperature data with described PC control PLC controller according to the sampling channel of appointment and the sampling period of setting.

The characteristics of thermo-physical property of loose coals test macro of the present invention also are:

Described cylindrical shell is a sandwich construction, and its skin is a stainless steel, and internal layer is the high temperature resistant silicon glue-line, and the middle part is to be interlayer with the nano heat insulating material.

Described thermopair is arranged in and the position of heating rod center at a distance of 15 ± 1mm, and described heating rod is that external diameter is the thin copper pipe of 2mm, built-in nickel chromium triangle heater strip in the thin copper pipe.

Compared with the prior art, beneficial effect of the present invention is embodied in:

1, the present invention utilizes parallel heat-pole method can record Coefficient of Heat Conductivity of Loose Coal Body and thermal diffusivity simultaneously, has realized once testing the purpose of a plurality of thermal physical property parameters such as surveying Coefficient of Heat Conductivity of Loose Coal Body, thermal diffusivity and specific heat capacity.

2, system of the present invention improves convenience, the system architecture compactedness that can further strengthen experimental implementation and improves the thermo-physical property of loose coals measuring accuracy.

3, the present invention is mainly used in the underlying parameter mensuration of spontaneous combustion of coal ignition prediction, coal spontaneous combustion burning things which may cause a fire disaster Study of location, and can be applicable to the hot physical property measurement of carbogel and other bulk solids material.

Description of drawings

Fig. 1 constitutes synoptic diagram for system of the present invention.

Number in the figure: 1 sample cover, 2 heating rods, 3 sample cylindrical shells, 4 thermal resistances, 5 handles, 6 are that PLC controller, 7 is PPI programming cable, 8 computing machines, 9 stabilized voltage supplys, 10 dodge gates, 11 salable holes, 12 heating rod pedestals.

Below pass through embodiment, and in conjunction with the accompanying drawings patent of the present invention is described further.

Embodiment

Test philosophy: the measuring system in the present embodiment as shown in Figure 1, system's setting comprises test specimen tube, data acquisition and transmission unit, control module and heating unit.

The setting of test specimen tube: in order to make sample particle packing situation and size-grade distribution and on-the-spot actual conditions more approaching, hold the high 670mm of test specimen tube external dimensions of coal sample, external diameter 420mm, the high 310mm of inner core, internal diameter 300mm, can hold coal sample amount 25～30Kg, it is maximum at present existing similar device that single can be surveyed the coal sample amount.Test specimen tube is made up of cover 4 and cylindrical shell 3, has dodge gate 10 on the cylindrical shell 3, and sample is taken out in the back in order to finish in experiment.

In order to eliminate the influence of external environment condition interference to measuring accuracy as far as possible, the test specimen tube skin is a stainless steel, and internal layer is the high temperature resistant silicon rubber cushion, and the middle part is interlayer with the nano heat insulating material, and this form has heat-insulating property preferably.Be reserved with the salable hole 11 that is used to insert thermopair 4 and lead on the sample cylindrical shell 3.

The setting of data acquisition and transmission unit:

The data acquisition transmission unit comprises thermopair 4, PLC controller 6 and PPI programming cable 7.

Thermopair 4 be arranged in heating rod 2 at a distance of 15 ± 1mm position, directly measure the temperature variation in the sample, temperature measuring data is gathered by PLC controller 6 and is conveyed into computing machine 8 by PPI programming cable 7.

The heating system unit:

Heating unit adopts heating rod 2, is set to the stabilized voltage supply 9 that heating rod 2 provides working power.

In the present embodiment, repack the heater strip in the traditional hot collimation method into heating rod 2, heating rod 2 is that external diameter is the built-in nickel chromium triangle heater strip of the thick thin copper pipe of 2mm, heating rod 2 is flexible connection with heating rod pedestal 12, before the experiment heating rod 2 is inserted heating rod pedestal 12 and be upright, connecting voltage of voltage regulation 9 can heat, and experiment finishes and can extract heating rod 2.

Control module:

System control unit carries out selection of temperature signal and transmission with PLC controller 6 as slave computer, microcomputer 8 is as host computer, human-computer interaction interface is provided, realize reception, demonstration and the computing of data, according to the sampling channel of appointment and the sampling period collecting temperature data of setting, programmed environment is Step7-Micro/Win32 with PC control PLC controller.

The every function that realizes with host computer comprises: 1, with the communicating to connect of PLC controller, the temperature data that PLC is collected is conveyed into computing machine; 2, for the monitoring and the demonstration of image data; 3, the formula with temperature data substitution sequencing carries out thermo-physical property of loose coals calculating; 4, real-time demonstration, output and the storage of result of calculation.

Concrete thermo-physical property of loose coals method of testing is as follows:

1, in coal sample, places heating rod and replace hot line, from a distance, heating rod center the thermopair measuring point is being set simultaneously as thermal source.

2, test specimen tube is cylindrical, and the lower end has movable wicket and is used for taking out coal sample after experiment finishes.Before the experiment heating rod is inserted, energized can heat, and experiment finishes and can extract heating rod and properly place.

3, test specimen tube once can be surveyed coal sample amount 25Kg～30Kg, can survey the maximum 25mm of loose coal particle size range, and is on-the-spot actual thereby coal sample size distribution and accumulation situation meet more.

4, heating rod is placed in the uniform coal sample of initial temperature, if the heating rod size satisfies infinite line thermal source condition, and heat energy will constitute an endless cylinder conduction model only in the radial direction conduction perpendicular to hot line.When heating rod continues heating with constant heat flux, known unit length thermal value q, W/m, order: $y=\frac{r}{2\sqrt{\mathrm{a\τ}}},$ Then the temperature-responsive in the coal sample can be expressed as:

$\mathrm{\θ}(r,\mathrm{\τ})=\frac{q}{2\mathrm{\π\λ}}{\∫}_y^{\∞}\frac{1}{y}{e}^{-y^2}\mathrm{dy}=\frac{q}{2\mathrm{\π\λ}}\mathrm{\Ω}\left(y\right)---\left(1\right)$

In the formula: θ (r, τ)-coal sample in radial distance heating rod r position point τ temperature rise constantly, ℃;

In the r-coal sample certain a bit with the spacing of hot line, m;

The a-thermal diffusivity, m ²/ s;

The coefficient of heat conductivity of λ-coal sample, W/ (mK);

τ-time, s;

Ω (y) is a special function, $\mathrm{\Ω}\left(y\right)={\∫}_y^{\∞}\frac{1}{u}\·e^{-u^2}\mathrm{du}.$

Survey the coefficient of heat conductivity principle according to parallel heat-pole method, utilize apart from the heating rod center radially the temperature rise θ of vertical range r position (r, τ), substitution formula (2) can be obtained Coefficient of Heat Conductivity of Loose Coal Body λ:

$\mathrm{\&lambda;}=\frac{\mathrm{<figure-callout\; id="4"\; label="UI"\; filenames="A2009101448080010H1.png"\; state="\{\{state\}\}">UI</figure-callout>}}{4\mathrm{\&pi;L}}\&times;\frac{-E_i\left(\frac{-r^2}{4\mathrm{a\&tau;}}\right)}{\mathrm{\&Delta;\&theta;}(r,\mathrm{\&tau;})}---\left(2\right)$

In the formula: I-electric current, A;

U-voltage, V;

L-hot line length, m;

-exponential integral, determined Δ θ (r, 2 τ)/Δ θ (r, τ) afterwards,

The acquisition of can tabling look-up.This test macro is inquired about table input computing machine automatically and is calculated by software programming in order to realize the real-time calculating of coefficient of heat conductivity.

To record Coefficient of Heat Conductivity of Loose Coal Body λ,, obtain formula (3) in conjunction with substitution (1) formula:

Ω(y)＝(θ(r，τ)·2πλ)/q (3)

In the formula, q=(UI)/L.

Make p=r ²/ (4 α τ) has again:

$\mathrm{\&Omega;}\left(y\right)=-\frac{1}{2}\mathrm{Ei}(-p)=-\mathrm{\&gamma;}-\ln p-\underset{n=1}{\overset{+\&infin;}{\mathrm{\&Sigma;}}}\frac{{(-1)}^n{p}^n}{\mathrm{nn}!}---\left(4\right)$

So have:

$\mathrm{\&Omega;}\left(y\right)=(\mathrm{\&theta;}(r,\mathrm{\&tau;})\&CenterDot;2\mathrm{\&pi;\&lambda;})/q=\frac{1}{2}\left(-\mathrm{\&gamma;}-\ln p-\underset{n=1}{\overset{5}{\mathrm{\&Sigma;}}}\frac{{(-1)}^n{p}^n}{\mathrm{nn}!}\right)---\left(5\right)$

In the formula, γ=0.5772156 is called Euler's constant.

A unknown number a is only arranged in the formula (5), and be transcendental equation, classic method can't be found the solution, can find the solution by programming as numerical approximation solutions such as bisection methods, all can try to achieve a corresponding thermal diffusivity a value for a certain particular moment τ, corresponding several constantly will calculate one group of a value, get the end value of weighted mean a as thermal diffusivity.

After trying to achieve thermal diffusion a, the specific heat capacity c of sample _pCalculate according to formula (6):

c _p＝λ/(ρα) (6)

5, according to measuring principle, the physical quantity that needs in the formula to measure has: sample density ρ, hot line heating power q, time τ and temperature θ, and concrete measuring method is:

(1) sample density

Utilize the high-precision electronic scale to adopt weight method to measure.

(2) hot line heating power

Utilize 6 half multimeters to measure the resistance R of heating load, measure heating voltage U then, utilize formula P=U ²/ R calculates heating power.

(3) time

Because temperature variation belongs to slow process in the test, utilize system clock writing time, show through actual measurement and can satisfy accuracy requirement.

(4) temperature

Utilize Programmable Logic Controller (PLC)+temperature sensor to carry out temperature signal collection in conjunction with software programming.PLC generally all has the self compensation function, promptly only needs temperature sensor is directly inserted temperature measurement module, configures sensor type, can realize the accurate collection of temperature signal, and need not to demarcate and provide cold junction compensation in advance to temperature sensor.

Claims (5)

1, a kind of thermo-physical property of loose coals method of testing is characterized in that based on heat-pole method, disposable Coefficient of Heat Conductivity of Loose Coal Body λ, thermal diffusivity a and the specific heat capacity c of surveying simultaneously _pThree thermal physical property parameters, described method are to place heating rod as thermal source at the coal sample center of loose coal, temperature sensor is set on the point for measuring temperature in coal sample is used to detect the coal sample temperature, have coal sample to be separated by between described point for measuring temperature and the heating rod; Described coal sample is positioned in the test specimen tube; Measure the density p of coal sample in the described test specimen tube, the heating power (W/m) of the described heating rod of setting, the record heating rod is from beginning to heat the time of being experienced (s); The corresponding temperature of described coal sample constantly of measurement (℃); By described density, heating power, time and temperature, at first calculate the coefficient of heat conductivity λ of described coal sample according to parallel heat-pole method principle, formula calculates coal sample thermal diffusivity a below utilizing then:

$(\mathrm{\&theta;}(r,\mathrm{\&tau;})\&CenterDot;2\mathrm{\&pi;\&lambda;})/q=\frac{1}{2}(-\mathrm{\&gamma;}-\ln p-\underset{n=1}{\overset{5}{\mathrm{\&Sigma;}}}\frac{{(-1)}^n{p}^n}{\mathrm{nn}!})$

In the formula: p=r ²/ (4a τ),

R be in the coal sample certain a bit with the distance of hot line, m;

A is the thermal diffusivity of described coal sample, m ²/ s;

λ is described coal sample coefficient of heat conductivity, W/ (mK);

τ is the time, s;

θ (r τ) is radial distance heating rod r position point τ temperature rise constantly in the coal sample, ℃;

γ=0.5772156 is an Euler's constant.

After trying to achieve thermal diffusion a, the specific heat capacity c of coal sample _pTry to achieve according to following formula:

c _p＝λ/(ρa)。

2, thermo-physical property of loose coals method of testing according to claim 1 is characterized in that the coal sample amount that described test specimen tube is once surveyed is 25Kg～30Kg, the maximum 25mm of the granularity of described loose coal.

3, a kind of thermo-physical property of loose coals test macro is characterized in that having:

One column test specimen tube is made of cover (1) and cylindrical shell (3), dodge gate (10) is set on the cylindrical shell (3), and is provided with the salable hole (11) that is used to insert thermopair (4) and lead;

One is arranged on the heating rod (2) on the described test specimen tube axial location, is that described heating rod (2) provides stable working power with stabilized voltage supply (9);

One data acquisition and transmission unit, be included in depart from the thermopair (4) that is provided with on the described test specimen tube axial location and be arranged on the test specimen tube outside, as the PLC controller (6) of slave computer, be connected with microsystem (8) with described PLC controller (6) by PPI programming cable (7) as host computer; Carry out the collection of temperature data with described PC control PLC controller (6) according to the sampling channel of appointment and the sampling period of setting.

4, thermo-physical property of loose coals test macro according to claim 3 is characterized in that described cylindrical shell (3) is sandwich construction, and its skin is a stainless steel, and internal layer is the high temperature resistant silicon glue-line, and the middle part is to be interlayer with the nano heat insulating material.

5, thermo-physical property of loose coals test macro according to claim 3, it is characterized in that described thermopair (4) is arranged in and the position of heating rod (2) center at a distance of 15 ± 1mm, described heating rod (2) is that external diameter is the thin copper pipe of 2mm, built-in nickel chromium triangle heater strip in the thin copper pipe.

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