CN203981621U - A kind of solid material thermal diffusion coefficient test macro - Google Patents

Abstract

The utility model relates to material thermal physical property parameter technical field of measurement and test, discloses a kind of solid material thermal diffusion coefficient test macro, comprising: water circulation system produces a circulating water flow, and circulating water flow contacts with the one side of tabular sample, carries out convection heat transfer; Convection transfer rate between described circulating water flow and specimen surface is large enough to make finish wet several Bi and is tending towards infinitely great; The temperature of temperature control system controlled circulation current, makes it keep constant temperature; Temperature acquisition and analytic system gather the adiabatic side surface temperature variation of described tabular sample, by calculated with mathematical model, obtain tested sample thermal diffusion coefficient value.The utility model utilizes the mobile water of high temperature circulation as thermal source, and between tested sample, does not have thermal contact resistance, is conducive to guarantee enough measuring accuracies.By controlling, finish wet several Bi, make to meet the heat transfer process under First Boundary Condition between water and specimen surface, reach the target of directly resolving thermal diffusion coefficient.

Description

A kind of solid material thermal diffusion coefficient test macro

Technical field

The utility model belongs to material thermal physical property parameter technical field of measurement and test, is specifically related to a kind of solid material, particularly has the thermal diffusion coefficient test macro of impervious solid material.

Background technology

Thermal diffusion coefficient, as the important parameter of solid material, has characterized heat transfer property and the temperature equalization performance of material, is the important indicator of conduction process in analysis of material; And in fields such as material, the energy, building, national defence, chemical industry, Refrigeration Engineerings, there is important purposes, along with its method of testing of development of modern industry is also one of study hotspot always.Existing method of testing is mainly divided into steady state method and unstable state method, steady state method is based on Fourier Heat Conduction law, mainly comprise pipe method, heat flow meter method, protective heat plate method etc., but steady state method is often because experimental period has thermal contact resistance compared with length simultaneously, application occasion is restricted.Unstable state method, because test period is short, often can be obtained coefficient of heat conductivity simultaneously, and be widely adopted, and mainly comprises flicker method, radial heat flows method, movable heat resource method, Forbes rod method, Periodic Heat Flux Method etc.But in practical application, still there are some problems, for example flicker method can only be applied to light-proof material, radial heat flows method is not still better solved at aspects such as thermal source uniformity coefficient, power swing, the losses of side direction hot-fluid, and great majority adopt the method for solid thermal source still to have difficulties for the thermal contact resistance problem representation between thermal source and testee simultaneously.

Utility model content

The deficiency existing for existing survey solid material thermal diffusion coefficient method of testing, the utility model proposes a kind of new solid material thermal diffusion coefficient test macro.

For achieving the above object, the utility model proposes a kind of above-mentioned solid material thermal diffusion coefficient test macro, comprise water circulation system, temperature control system, temperature acquisition and analytic system;

Described water circulation system, for generation of circulating water flow, described circulating water flow contacts with the one side of tabular sample, carries out convection heat transfer; Convection transfer rate between described circulating water flow and specimen surface is large enough to make finish wet several Bi and is tending towards infinitely great;

Described temperature control system, for the temperature of controlled circulation current, makes it keep constant temperature;

Described temperature acquisition and analytic system, for gathering the adiabatic side surface temperature variation of sample, and utilize calculated with mathematical model to obtain tested sample thermal diffusion coefficient value.

Preferably, described water circulation system comprises outer case, internal box, bottom cylindrical passageway, helical blade device, shaft coupling and motor; Described internal box is placed in described outer case, and the top of described outer case, internal box is open respectively, and tabular sample is placed on top, the internal box over top of outer case, between described internal box wall and outer container body wall, forms water circulation channel; Described bottom cylindrical passageway is at the bottom of described internal box and between outer case bottom, described helical blade is positioned at described bottom cylindrical passageway, by shaft coupling, be connected with motor, utilize driven by motor rotation, water in the cylindrical passageway of extruding bottom, produce circulating water flow, simultaneously contact generation convection heat transfer with tabular sample.Described helical blade device is snail sheet endless screw apparatus.

Preferably, described temperature control system comprises temperature controller and heating rod, and described temperature controller, according to the temperature setting in advance, is controlled the temperature of water and made its constant temperature by heating rod;

Preferably, described temperature acquisition and analytic system comprise temperature point, temperature acquisition and transmitting device, data processing equipment; Described temperature point gathers the adiabatic side surface temperature variation of sample and is converted into current signal, is transferred to temperature acquisition and transmitting device; Described temperature acquisition and transmitting device are transferred to described data processing equipment by collection signal, and data processing equipment utilizes calculated with mathematical model to obtain tested sample thermal diffusion coefficient value.

Preferred, the length of width≤bottom cylindrical passageway of tabular sample, with eliminate fluid in the inhomogeneous impact bringing of flow section boundary speed.

The utility model is mainly applicable to have the solid of impervious as the thermal diffusion coefficient measurement of the materials such as metal, glass, has following beneficial effect:

1, utilize the mobile water of high temperature circulation as thermal source, temperature homogeneity is good, and and tested sample between there is not thermal contact resistance, be conducive to guarantee enough measuring accuracies.

2, by the rotation of Electric Machine Control snail sheet endless screw apparatus, water circulation is flowed, adjust the water velocity contacting with sample and change convection transfer rate, and then control and finish wet several Bi, make to meet the heat transfer process under First Boundary Condition between water and specimen surface, reach the target of directly resolving thermal diffusion coefficient.

Accompanying drawing explanation

Fig. 1 is principle sketch of the present utility model.

Fig. 2 is the one-piece construction figure of the utility model embodiment.

Average heat transfer coefficient h when Fig. 3 is different water circulation flowing velocity u0 (m/s) _mvariation relation figure.

Fig. 4 is the part vertical view of Fig. 2.

Fig. 5 is the part left view of Fig. 2.

In figure, tabular sample 1, heating rod 2, motor 3, shaft coupling 4, snail sheet endless screw apparatus 5, bottom cylindrical passageway 6, outer case 7, internal box 8, water circulation channel 9.

Embodiment

Below in conjunction with the drawings and specific embodiments, the utility model is described in more detail.

As shown in Figure 1, tabular sample 1, initial temperature is t ₀, one pleurapophysis so and temperature be t _∞fluid contact, an other side is adiabatic, establishes and does not consider its lateral heat conduction, between fluid and solid surface, conducts heat, and can be considered the one-dimensional and unsteady state diabatic process under third boundary condition, its analytic solution are as follows:

$\frac{\mathrm{\θ}(x,\mathrm{\τ})}{{\mathrm{\θ}}_0}={\mathrm{\Σ}}_{n=1}^{\∞}\frac{2\sin {\mathrm{\β}}_n}{{\mathrm{\β}}_n+\sin {\mathrm{\β}}_n\cos {\mathrm{\β}}_n}\cos \left({\mathrm{\β}}_n\frac{x}{\mathrm{\δ}}\right)e^{-{{\mathrm{\β}}_n}^2\mathrm{Fo}}---\left(1\right)$

θ-excess enthalpy temperature in formula, θ=t-t _∞.

β _n-transcendental equation series solution.

be called and finish wet number, represent the ratio of dull and stereotyped thermal conduction resistance and its surperficial convection heat transfer thermal resistance.

be called Fourier number, represent the dimensionless time of Unsteady Heat Transfer process.

Formula based on third boundary condition (1) contains infinite progression, cannot direct solution, research show and when Fo >=0.2 first of desirable formula (1) replacement whole infinite series, the error of its result of calculation, in 1%, is enough to meet engineering calculation accuracy requirement:

$\frac{\mathrm{\θ}(x,\mathrm{\τ})}{{\mathrm{\θ}}_0}=\frac{2\sin {\mathrm{\β}}_1}{{\mathrm{\β}}_1+\sin {\mathrm{\β}}_1\cos {\mathrm{\β}}_1}\cos \left({\mathrm{\β}}_1\frac{x}{\mathrm{\δ}}\right)e^{-{{\mathrm{\β}}_1}^2\mathrm{Fo}}---\left(2\right)$

Taken the logarithm in formula (2) both sides,

$\ln \mathrm{\θ}=-{{-\mathrm{\β}}_1}^2\frac{\mathrm{a\ι}}{{\mathrm{\δ}}^2}+\ln \left[{\mathrm{\θ}}_0\frac{2\sin {\mathrm{\β}}_1}{{\mathrm{\β}}_1+\sin {\mathrm{\β}}_1\cos {\mathrm{\β}}_1}\cos \left({\mathrm{\β}}_1\frac{x}{\mathrm{\δ}}\right)\right]---\left(3\right)$

Formula (3), although carried out significantly simplifying compared with formula (1), but still comprises two unknown number β ₁and Fo, and cannot directly calculate thermal diffusion coefficient a by measuring temperature θ.

Research shows, during Bi → ∞, and β ₁be constantly equal to 1.5708, thereby will only have a unknown number a in formula (3), the not excess enthalpy temperature change value θ of τ in the same time by measuring that sample contacts with water that adiabatic face (x=0) afterwards locates, can directly calculate a.And in fact Bi can not be infinitely great, but show by calculating, work as B _inumber is 30 o'clock, β ₁value is 1.5202, the β while being ∞ with Bi number ₁value 1.5708, relative error =3.2%, thereby Bi is only greater than 30, it (gets β for infinitely great with hypothesis ₁=1.5708) error of bringing is in tolerance interval.

Based on above-mentioned principle, the utility model proposes a kind of solid material thermal diffusion coefficient test macro, as shown in Figure 2, internal box 8 is placed in outer case 7, the top of described outer case, internal box is open respectively, tabular sample 1 is placed on top, internal box 8 over top of outer case 7, between internal box wall and outer container body wall, forms water circulation channel 9; Bottom cylindrical passageway 6 is at the bottom of internal box and between outer case bottom, and snail sheet endless screw apparatus 5 is positioned at bottom cylindrical passageway 6, and snail sheet endless screw apparatus 5 is connected with motor 3 by shaft coupling 4.At the bottom of heating rod 2 inserts in internal box and in outer case, temperature controller is controlled heating and the insulation that heating rod 2 is realized water, to obtain the water of design temperature.Motor 3 drives helical blades 5 to rotate by shaft coupling 4, and the water in the cylindrical passageway 6 of compression bottom circulates it in water circulation channel 7 with certain speed, so with tabular sample 1 convection heat transfer.Temperature point in temperature acquisition and analytic system gathers the variation of tabular sample 1 adiabatic side surface temperature, be transferred to temperature acquisition and transmitting device simultaneously, temperature acquisition and transmitting device are converted to Temperature numerical by signal and send microcomputer to, and then substitution (3) formula is calculated thermal diffusion coefficient a.Different water velocities can directly calculate corresponding convection transfer rate h, and from fluid mechanics knowledge, water flow has Laminar Flow or two kinds of forms of turbulent flow, and its flow boundary layer is distinct, and convection transfer rate h computing formula is different.

When current flow through tabular sample 1 wall convection heat transfer' heat-transfer by convection with laminar condition:

$h_m=0.664\frac{k}{L}R{e}_L^{1/2}P{r}^{1/3}---\left(4\right)$

When current flow through tabular sample 1 wall convection heat transfer' heat-transfer by convection with turbulence state

$h_m=0.0365\frac{k}{L}P{r}^{\frac{1}{3}}({\mathrm{Re}}_L^{0.8}-A)---\left(5\right)$

$A={\mathrm{Re}}_{\mathrm{xc}}^{0.8}-18.19R{e}_{\mathrm{xc}}^{0.5}---\left(6\right)$

In all formulas, the physical properties of fluids parameter in dimensionless group is by medial temperature value, above

$t_m=\frac{t_s+t_0}{2}$

T in formula _s, t ₀be respectively the surperficial initial temperature of tabular sample 1 and water initial temperature; If sheet material solid material initial temperature is 20 ℃ of water initial temperatures is 100 ℃.

K in formula-at t _mthe coefficient of heat conductivity of water at temperature, at 60 ℃ of temperature, the coefficient of heat conductivity of water is 0.659W/ (mk)

L-characteristic length, refers to that water flows through the length of direction tabular sample 1 herein.Characteristic length L=100 (mm) herein.

Re _lreynolds number under-characteristic length L is that inertial force is measured with a kind of of ratio of viscous force.Kinematic viscosity ν=the 4.78*10 of water at 60 ℃ of temperature ^-7(m ²/ s).

Pr-at t _mthe Prandtl number of water at temperature is that momentum diffusivity and a kind of of heat diffusion ability measure.The Pr=2.99 of water at 60 ℃ of temperature.

Re _xc---critical thunder Lip river number, when current dropped down tabular sample 1 surface, tabular sample 1 leading edge to the boundary layer of laminar flow of take is converted into the thunder Lip river number that turbulent boundary layer place is characteristic length.

H _m---represent average heat transfer coefficient.

If tabular sample 1 is of a size of 100*100*5 (mm), its initial temperature is t ₀=20 ℃.T _∞the water of=100 ℃ is with average velocity u ₀(m/s) flow through tabular sample 1 surface, if Fig. 3 is different water circulation flowing velocity u ₀(m/s) average heat transfer coefficient h time _m.

Water velocity u0, when 4.5m/s left and right, can make convection transfer rate reach more than 12000 as seen from Figure 3, establishes tabular sample thickness δ=5mm, and coefficient of heat conductivity λ=1W/ (mk) now finishes wet several Bi=60, and be regarded as infinity, directly gets β ₁=1.5708, obviously can not bring obvious errors, thereby technical scheme is feasible.

As shown in Figure 4 and Figure 5, for eliminate fluid is in the inhomogeneous impact bringing of flow section boundary speed, the size b (mm) of the dimension width a of tabular sample 1 (mm)≤bottom cylindrical passageway 6, gets a=0.8b in this device.

The parameter that above example is supposed and size are all to help to understand method of the present utility model and core concept, should look into relevant handbook determine its parameter and measure its size according to actual conditions for different solid materials.In sum; this instructions parameter and size should not be construed as restriction of the present utility model; do not departing from spirit and scope situation of the present utility model; can also make a variety of changes; therefore all technical schemes that are equal to also belong to category of the present utility model, and rights protection scope of the present utility model should be defined by the claims.

Claims (4)

1. a solid material thermal diffusion coefficient test macro, is characterized in that, comprises water circulation system, temperature control system, temperature acquisition and analytic system;

Described water circulation system, comprises outer case, internal box, bottom cylindrical passageway, helical blade device, shaft coupling and motor; Described internal box is placed in described outer case, and the top of described outer case, internal box is open respectively, and tabular sample is placed on top, the internal box over top of outer case, between described internal box wall and outer container body wall, forms water circulation channel; Described bottom cylindrical passageway is at the bottom of described internal box and between outer case bottom, described helical blade is positioned at described bottom cylindrical passageway, by shaft coupling, be connected with motor, utilize driven by motor rotation, water in the cylindrical passageway of extruding bottom, produce circulating water flow, simultaneously contact generation convection heat transfer with tabular sample; Convection transfer rate between described circulating water flow and specimen surface is large enough to make finish wet several Bi and is tending towards infinitely great;

Described temperature control system, for the temperature of controlled circulation current, makes it keep constant temperature;

Described temperature acquisition and analytic system, comprise temperature point, temperature acquisition and transmitting device, data processing equipment; Described temperature point gathers the adiabatic side surface temperature variation of sample and is converted into current signal, is transferred to temperature acquisition and transmitting device; Described temperature acquisition and transmitting device are transferred to described data processing equipment by collection signal, and data processing equipment utilizes calculated with mathematical model to obtain tested sample thermal diffusion coefficient value.

2. solid material thermal diffusion coefficient test macro according to claim 1, it is characterized in that, described temperature control system comprises temperature controller and heating rod, and described temperature controller, according to the temperature setting in advance, is controlled the temperature of water and made its constant temperature by heating rod.

3. solid material thermal diffusion coefficient test macro according to claim 1, is characterized in that, the length of width≤bottom cylindrical passageway of tabular sample.

4. according to the solid material thermal diffusion coefficient test macro described in claim 1,2 or 3, it is characterized in that, described helical blade device is snail sheet endless screw apparatus.