CN103048186A - Pipeline steel drop hammer tearing specimen gas medium cooling method - Google Patents

Abstract

The invention relates to a pipeline steel drop hammer tearing specimen gas medium cooling method. Heating and cooling are carried out in a sealed container, and measures are taken in the container to ensure that the difference between each effective space temperature in the container and the test target temperature does not exceed +/-1 DEG C; a specimen, the temperature of which is same as the room temperature, is placed in the sealed container, and the shortest heat insulation time is set according to a table 1; the shortest retention time of the specimen in the table 1 in a gas medium can be used for guiding the normality of a pipeline steel drop hammer test and has a certain significance for ensuring the accuracy and the reliability of the test data; and the pipeline steel drop hammer tearing specimen gas medium cooling method provides a basis for formalizing the drop hammer test standard.

Description

Pipeline steel block hammer is torn sample air medium cooling means

Technical field

The present invention relates to a kind of pipeline steel block hammer and tear the temperature retention time that sample heats, cools off under the gas medium condition.

Background technology

When carrying out the pipeline steel block hammer test, specimen temperature is an important control parameter.Only under appropriate test temperature condition, test, just can obtain reliable test figure.

The cooling system of sample in liquid medium, in the existing standard regulation is arranged, but owing to reasons such as test conditions, sample often need to be under the gas medium condition cools off in such as refrigerator, and the specific requirement under the gas medium condition does not all relate in ASTM, API and domestic relevant criterion.For enlarging the range of choice of heat eliminating medium, on the basis of computational analysis, the temperature retention time under the gas medium condition is carried out clear and definite requirement and regulation has important practical significance.

Summary of the invention

The objective of the invention is to provide heating, the cooling temperature retention time of sample in gas medium that original state is in the different wall of (25 ℃) under the room temperature condition.

In order to guarantee that sample reaches heating, cooling target temperature under the gas medium condition, the technical solution used in the present invention is as follows:

Heating, cooler environment should be airtight container, and container the planted agent take measures, and the temperature of all useful spaces in the container and test objective temperature differed be no more than ± 1 ℃.Be that the sample of room temperature (25 ℃) is put into this airtight container with temperature, the shortest temperature retention time should be according to the regulation of table 1.

Table 1 sample the shortest retention time in gas medium

Beneficial effect of the present invention is as follows:

The sample of guaranteeing the pipeline steel block hammer test reaches the required target temperature of sample, has guaranteed the accurate and reliable of test figure; In addition, provide theoretical foundation for establishment drop-weight test standard.

Description of drawings

Fig. 1 sample cooling insulating process synoptic diagram

Fig. 2 sample cooling keeping temprature curve synoptic diagram

Fig. 3 specimen geometry and size synoptic diagram

Fig. 4 3D grid is divided synoptic diagram

Figure 51 2.7mm sample forced convertion core temperature change curve

Figure 62 5.4mm sample forced convertion core temperature change curve

Figure 73 8.1mm sample forced convertion core temperature change curve

Figure 81 2.7mm sample natural convection core temperature change curve

Figure 92 5.4mm sample natural convection core temperature change curve

Figure 103 8.1mm sample natural convection core temperature change curve

Embodiment

1, physical problem is described and mathematical model

1.1 physical problem is described

Sample cooling insulating process as shown in Figure 1.In order to carry out the pipeline steel block hammer tear test, to be in the refrigerator that 25 ℃ of different wall samples under the room temperature condition are put into respectively-20 ℃, be furnished with stirring apparatus in the refrigerator, change forced convertion with the heat exchange mode with specimen surface and surrounding medium into by natural convection, increase coefficient of heat transfer h, accelerate sample cooling and insulation speed.Simultaneously so that the interior medium temperature field of refrigerator is tending towards even.

In refrigerator, be furnished with thermocouple temperature measuring apparatus.When sample was put into, because specimen temperature is higher than ambient temperature, sample was emitted heat, so that medium temperature raises.When the medium temperature that records when thermopair was higher than setting value, refrigerating plant was started working, and by evaporator the medium heat was taken away, to reduce the temperature of air.Meanwhile, owing to there is the temperature difference, proceed heat exchange between sample and the medium.When the temperature of gas medium was stabilized to again-20 ± 1 ℃, this process was called cooling procedure; Reach in the of-20 ± 1 ℃ from medium, sample continues cold and hot exchange, until core temperature reaches-20 ± 1 ℃ and when remaining unchanged, this process is called medium to warm insulating process.Cooling and medium are called total temperature retention time to the used time sum of warm insulating process, as shown in Figure 2.This moment, the specimen temperature parameter can be thought the requirement that has reached drop-weight test.Total be exactly the temperature retention time of the at present test operation of reality control, but, even the ability of heating and cooling equipment is very large, because sample quantities affects the time that the circulation of putting into this process heat and medium come back to target temperature to a certain extent, so control medium should be more accurate, more reasonable to the temperature retention time of temperature, so this patent not only provides total temperature retention time, also provide medium to warm temperature retention time.Table 2 is the thermophysical property parameter of air.

Table 2 air thermophysical property

1.2 mathematical model

Because actual pipe line steel sample cooling insulating process is very complicated, not only closely related with the performance of refrigerating plant, and with quantity and performance and the environment temperature etc. of stirring apparatus very large relation is arranged.In order to simplify practical problems, so that calculate feasiblely, when setting up the three-dimensional transient temperature mathematical model of sample cooling insulating process, do following hypothesis:

(1) is furnished with fan in the refrigerator, thinks that medium temperature wherein equates everywhere.

(2) suppose that refrigerator has enough refrigerating capacitys, do not consider that refrigeration system is on the impact of sample cooling insulating process.

(3) suppose that each surface of sample has the identical coefficient of heat transfer.

It is rectangular parallelepiped that pipeline steel block hammer is torn sample, and specimen length l is 305mm, and height h is 76mm, and thickness b is respectively 12.7mm, 25.4mm, 38.1mm, and Fig. 3 is specimen geometry and size synoptic diagram.

Among Fig. 3, T _cBe the temperature of sample core that is sample central spot, T _wBe the temperature of sample wall surface (ABCD face) center, T _sTemperature for sample cusp that is A point place.

Described as can be known by physical problem, sample is put into and is one behind the refrigerator and because its temperature variation is little, can thinks that coefficient of heat conductivity is constant without the Three dimensional transient Heat Conduction Problems of endogenous pyrogen, and this moment, temperature governing equation was:

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

In the formula:

A---thermal diffusivity, m ²/ s;

τ---the time, s;

T---temperature, ℃;

X, y, z---coordinate, m.

1.2.1 boundary condition

(1) convection heat transfer

Main heat exchange mode between specimen surface and the surrounding medium is forced-convection heat transfer, and this is third boundary condition.The coefficient of heat transfer calculates by formula (2):

$h_{\mathrm{cv}}=\frac{\mathrm{Nu\λ}}{l}---\left(2\right)$

In the formula:

Nu---Nusselt number;

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

L---characteristic length is taken as 0.076m.

The Nu number calculates by formula (3):

Nu＝0.102Re ^0.675Pr ^1/3 (3)

In the formula:

Re---Reynolds number;

Pr---Prandtl number.

The Re calculating formula is:

$\mathrm{Re}=\frac{\mathrm{ul}}{v}---\left(4\right)$

In constant temperature refrigerator, think u=7m/s, as shown in Table 1, T _fIn the time of=-20 ℃, v=11.61 * 10 ^-6m ²/ s, λ=0.0228W/ (m K), Pr=0.716, l=0.076m.

Can be got by formula (4): Re=4.58 * 10 ⁴

Can be got by formula (3): Nu=127.74

Can be got by formula (2) at last: h _Cv=38.3W/ (m ²K)

(2) radiation heat transfer

When sample had just been put into refrigerator, the temperature difference of specimen surface and refrigerator wall was maximum, and Radiant exothermicity is also maximum, and this moment, radiation heat transfer coefficient calculated by formula (5):

$h_{\mathrm{rad}}=\frac{{\mathrm{\&epsiv;}}_1\mathrm{\&sigma;}({\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HDA0000099389560000013.png"\; state="\{\{state\}\}">T</figure-callout>}}_1^4-T_2^4)}{T_1-T_2}={\mathrm{\&epsiv;}}_1\mathrm{\&sigma;}({\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HDA0000099389560000013.png"\; state="\{\{state\}\}">T</figure-callout>}}_1^2+T_2^2)({\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HDA0000099389560000013.png"\; state="\{\{state\}\}">T</figure-callout>}}_1+T_2)---\left(5\right)$

In the formula:

ε ₁---the specimen surface emissivity;

σ---this fence-Boltzmann constant of making a mistake, 5.67 * 10 ^-8W/ (m ²K ⁴);

T ₁---specimen surface temperature, K;

T ₂---refrigerator wall surface temperature, K.

Can be got by known conditions: T ₁=298.15K, T ₂=253.15K.

Look into as can be known ε of metal material handbook ₁=0.3.

Bring above-mentioned parameter into formula (5), can get h _Rad=1.4W/ (m ²K).

(3) compound boundary condition

The heat exchange of sample and surrounding medium had both comprised forced-convection heat transfer, also comprised the radiation heat transfer mode.By above-mentioned calculating as can be known, the radiation heat transfer proportion is less, and along with leveling off to of cooling insulating process is zero.The boundary condition of considering forced convertion and radiation heat transfer is:

h＝h _cv+h _rad (6)

To constant temperature refrigerator:

h＝38.3+1.4＝39.7W/(m ²K)

(7)

1.2.2 starting condition

When sample had just been put into refrigerator and begun to cool off insulating process, its temperature was 25 ℃ of room temperatures, so starting condition is suc as formula shown in (8):

T| _x，y，z＝25℃ (8)

2, grid is divided and method of value solving

Adopt at present in the world general large-scale flowing with Calculation of Heat Transfer business software FLUENT sample to be carried out grid and divide (seeing Fig. 4) and solving equation (1), (2), (5) and (8), after can obtaining thus the pipe line steel sample and putting into refrigerator, cool off the Temperature Distribution in arbitrary moment of insulating process.

3, cooling insulating process result of calculation and analysis

3.1 specimen temperature change curve

Fig. 5,6,7 and Fig. 8,9,10 be respectively under forced convertion and the Natural Convection Conditions, the initial temperature that calculates is that core temperature Tc is curve over time after 25 ℃ different wall sample was put into-20 ℃ of refrigerators.After sample had just been put into refrigerator, because the temperature difference of sample and surrounding medium is larger, specimen temperature descended very fast, and along with the carrying out of cooling procedure, the cooling velocity of sample reduces gradually.

3.2 temperature retention time is calculated

When sample was cooled to-19 ℃ from-18 ℃, the sample thermal discharge was suc as formula shown in (9):

Q＝cmVT＝cm[-18-(-19)] (9)

In the formula:

Q---thermal discharge, J;

C---sample specific heat capacity, J/ (kg K);

M---sample mass, kg.

The specimen surface heat flow density is determined by formula (10):

$q=\frac{Q}{\mathrm{F\&Delta;\&tau;}}---\left(10\right)$

In the formula:

Q---heat flow density, W/m ²

F---specimen surface is long-pending, m ²

Δ τ---sample is cooled to-19 ℃ of required times, s by-18 ℃.

Medium temperature reaches-20 ℃, when namely beginning to enter insulating process, wall surface temperature calculates by formula (11):

$T_w=\frac{q}{h}-T_f---\left(11\right)$

In the formula: T _f---medium temperature, ℃.

For the sample of different wall, can determine T by formula (9), (10), (11) _fThe surface temperature of each sample in the time of=-20 ℃, and then can obtain core temperature T _cThis for the zero point of insulation beginning, works as T constantly _cDrop to below-19 ℃ and when remaining unchanged, think that insulating process finishes, and can calculate temperature retention time thus.

(1) 12.7mm wall thickness sample

A) forced convertion: according to calculating as can be known Q=1073.21J, q=51.76W/m ², Δ τ=370s.Can get T by formula (10) _fIn the time of=-20 ℃, T _w=-18.65 ℃.And then can get T _c=-18.648 ℃.As seen from Figure 5, T behind the cooling insulation 72.5min _cReach-19.9 ℃, rounding is to 75min, and therefore cooling is incubated T.T. τ _z=75min, its medium is to the temperature retention time τ of temperature _Kt=48.3min, rounding is to 50min.

B) natural convection: according to calculating as can be known Q=1073.21J, q=9.55W/m ², Δ τ=2006s.Can get T by formula (10) _fIn the time of=-20 ℃, T _w=-19.045 ℃.And then can get T _c=-19.045 ℃.As seen from Figure 8, T behind the cooling insulation 140.2min _cReach-19 ℃, rounding is to 140min, and therefore cooling is incubated T.T. τ _z=140min, its medium is to the temperature retention time τ of temperature _Kt=33.3min, rounding is to 35min.

(2) 25.4mm wall thickness sample

A) forced convertion: according to calculating as can be known Q=2146.43J, q=52.68W/m ², Δ τ=620s.Can get T by formula (10) _fIn the time of=-20 ℃, T _w=-18.626 ℃.And then can get T _c=-18.621 ℃.As seen from Figure 6, T behind the cooling insulation 100.6min _cReach-19.9 ℃, rounding is to 100min, and therefore cooling is incubated T.T. τ _z=100min, its medium is to the temperature retention time τ of temperature _Kt=54.6min, rounding is to 55min.

B) natural convection: according to calculating as can be known Q=2146.43J, q=12.22W/m ², Δ τ=2672s.Can get T by formula (10) _fIn the time of=-20 ℃, T _w=-18.78 ℃.And then can get T _c=-18.776 ℃.As seen from Figure 9, T behind the cooling insulation 223.1min _cReach-19 ℃, rounding is to 225min, and therefore cooling is incubated T.T. τ _z=225min, its medium is to the temperature retention time τ of temperature _Kt=46.5min, rounding is to 47min.

(3) 38.1mm wall thickness sample

A) forced convertion: according to calculating as can be known Q=3219.64J, q=50.36W/m ², Δ τ=848s.Can get T by formula (10) _fIn the time of=-20 ℃, T _w=-18.686 ℃.And then can get T _c=-18.678 ℃.As seen from Figure 7, T behind the cooling insulation 148.2min _cReach-19.9 ℃, rounding is to 150min, and therefore cooling is incubated T.T. τ _z=150min, its medium is to the temperature retention time τ of temperature _Kt=90.1min, rounding is to 90min.

B) natural convection: according to calculating as can be known Q=3219.64J, q=10.78W/m ², Δ τ=3960s.Can get T by formula (10) _fIn the time of=-20 ℃, T _w=-18.92 ℃.And then can get T _c=-18.92 ℃.As seen from Figure 10, T behind the cooling insulation 308.5min _cReach-19 ℃, rounding is to 310min, and therefore cooling is incubated T.T. τ _z=310min, its medium is to the temperature retention time τ of temperature _Kt=67.5min, rounding is to 68min.

Claims (1)

1. a pipeline steel block hammer is torn sample air medium cooling means, it is characterized in that: heating, cooler environment should be airtight container, and container the planted agent take measures, and the temperature of all useful spaces in the container and test objective temperature differed be no more than ± 1 ℃; Be that the sample of room temperature is put into this airtight container with temperature, the shortest temperature retention time should be according to the regulation of table 1;

Table 1 sample the shortest retention time in gas medium

Described forced convertion refers to medium circulating under the fan effect;

Described natural convection refers to the condition that the fan-free measure impels medium circulation to flow;

Described total temperature retention time is to point to put into sample in the medium be in target temperature and finish and begin timing that time, until the sample core temperature reaches the used time of target temperature;

Described to warm temperature retention time, after referring to put into sample, when medium temperature comes back to target temperature that time as timing zero point, the sample core temperature reaches the used time of target temperature.

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