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1 vacuum powder insulation work in low-temperature vacuum tank
Vacuum powder insulation vacuum a low vacuum, vacuum requirements
In more than 67Pa. Despite remaining in the work of the average molecular gas
Free path greater than the powder gap, thermal conductivity coefficient and the residual gas pressure as
Proportional to, but because of the characteristics of powder insulation: pearl white sand stars
Tablets, tortuous path of solid thermal conductivity and local contacts, which constitute so many
Anti-radiation screen, reducing the radiation heat transfer. Vacuum powder insulation is a solid
Body thermal conductivity, convective heat transfer elements as well as to maintain the sum of radiative heat transfer in the
Level, the impact of a wide range of factors. As long as the vacuum
A certain degree of control over the scope of the layers of pressure on the overall thermal conductivity video
Small ring. Drawn through the experimental thermal conductivity with the apparent average interlayer
The relationship between the pressure curve in Figure 1, 2, 3 shown.
Figure 1 vacuum powder insulation materials apparent average thermal conductivity K and the pressure of the relationship between P
1 - High Voltage aerogels, Bulk Density 124kg / m3 2 - Atmospheric aerogels, Bulk Density
120kg / m3 3 - Gas plastic, packing density of 290kg / m3 4 - pearlescent sand, the accumulation of dense
Degree of 130kg / m3 5 - vermiculite, packing density of 300kg / m3
Figure 2 The apparent vacuum powder insulation materials珚average thermal conductivity K and the pressure of the relationship between P
1 - airgel 2 - phenolic resin ball 3 - black 4 - Diatomite
5 - Pearl Sand (temperature: 76K ~ 300K, filled with gas: nitrogen)
6 - airgel (temperature: 20K ~ 76K, filled with gas: Helium)
As can be seen from Figure 1: When the vacuum has risen to more than 1313Pa
, The apparent thermal conductivity curve of the average level of close to a straight line;
Figure 3 Apparent Pearl Sand average thermal conductivity K and the pressure of the relationship between P
1 - packing density for the 73 ~ 77kg / m3 2 - accumulation density of 60 ~ 70kg / m3
3 - accumulation of density 130kg / m3
Figure 2 shows that the vacuum has risen to more than 113Pa greatly reduced slope,
0113Pa vacuum that has been completely above the level of close to a straight
Line; Figure 3 reflects the three kinds of filling the average apparent density of sand Pearl I.
Vacuum heat transfer coefficient and the relationship between the curve, although the thermal conductivity with the filling
Pearlescent sand of different densities are small, but when the vacuum up to
13Pa above, all three curves tend to level the continued vacuum
Increase the impact of the thermal conductivity is very small.
China and Japan pearlescent sand under vacuum in different grades of thermal conductivity
Number shown in Table 1.
Table 1 pearlescent sand in different vacuum units under the thermal conductivity: 11163W / (m K)
Bulk Density
/ (Kg / m3)
Size / head temperature / K
Vacuum / Pa
Atmospheric pressure 133 × 102 133 × 101 133 × 100 133 × 10 - 1 133 × 10 - 2 133 × 10 - 3
73 ~ 77 20 ~ 40
130 40 ~ 80
60 ~ 70 (Japan) granular
77 ~ 310
--
01024 010232 010191 010147 0100153 0100148 0100144
010254 010228 0100354 0100138 0100104 01000885 --
010215 010195 0100626 0100174 0100149 0100138 --
Seen from Table 1, when the vacuum in more than 13Pa, really
Increase in porosity to reduce the role of thermal conductivity have been obvious.
Large amounts of data and the actual use have proven that low-vacuum powder insulation
The work of the liquid temperature vacuum tank in the scope of 1 ~ 67Pa have
Good insulation properties on the basis of 1Pa continue to enhance its work
For vacuum, thermal insulation material to reduce the average of the apparent thermal conductivity has been
No practical significance.
2 leakage rate is to ensure that the key to life vacuum
No matter what technology, what technology capacity of the vacuum
, And must be omitted from the external environment into the fluid medium, the vacuum to drop
Low, the longer the lower the vacuum. Vacuum container to ensure that
Vacuum life, it is necessary to the provisions of the leakage rate is based on true leakage rate
Determined by space life.
Just making a good low-temperature liquid tank, there are two reasons lead to
Its lower vacuum laminated vacuum: ① the inner and outer shell tube leakage;
② laminated material is deflated. Laminated material gas is temporary, and filling
Cryogenic liquid gas will be accelerated and stopped very quickly deflated. And
As long as the sandwich in a vacuum leak phenomenon has been the existence of leakage
Vacuum gas on the impact of a long-term, therefore, should pay special attention to.
Vacuum sealed end (the end of time to balance the vacuum pressure laminated
The room temperature pressure) is a cryogenic liquid tank to the rigid assessment indicators,
The level of the indicators related to the cryogenic liquid tank manufacturing costs.
Is to 10m3, 100m3 cryogenic liquid tank as an example to show closed end
Vacuum tank of cryogenic liquid vacuum life. Vacuum life
t usually by formula (1) calculated as follows:
t =
(P2 - p1) V n
3115 × 107 q
(1)
Where: p1 --- the initial work of vacuum (in vacuum sealed knot
Reduction of one order of magnitude), Pa;
p2 --- vacuum vacuum powder insulation failure, check 67Pa;
V --- vacuum laminated volume, L;
q --- the leak rate requirements, Pa L / s;
laminated sand n --- Pearl share volume from 017.
According to type (1) calculation of 10m3, 100m3 Cryogenic Liquid Tank
Life of the vacuum table 2. Of which: 10m3 tank: V =
11000L, q = 310 × 10 - 3 Pa L / s; 100m3 tank: V
= 60000L, q = 116 × 10 - 3Pa L / s.
Table 2 knot vacuum tank of cryogenic liquid vacuum Life of
Leakage rate of dissection of the cryogenic liquid tank vacuum life table
3, 4. Calculation conditions: vacuum sealed knot 40Pa, the initial work
Vacuum for 4 Pa.
Table 3 leakage rate on the mezzanine 10m3 vacuum cryogenic liquid tank life
The total leakage rate of dissection / (Pa L / s) Vacuum life / a
310 × 10 - 3 511
218 × 10 - 3 5147
216 × 10 - 3 5189
214 × 10 - 3 6139
210 × 10 - 3 7166
118 × 10 - 3 815
116 × 10 - 3 916
From Table 2, we can see that closure by the end 40Pa vacuum up to 4Pa,
Vacuum sealed junction increased by 10 times, but the cryogenic liquid tank 10m3
Life of the vacuum is only an increase of 013 years, 100m3 Cryogenic Liquid Tank
Table 4 leakage rate on the mezzanine 100m3 vacuum cryogenic liquid tank life
The total leakage rate of dissection / (Pa L / s) Vacuum life / a
118 × 10 - 2 4164
116 × 10 - 2 5123
114 × 10 - 2 5197
112 × 10 - 2 6197
111 × 10 - 2 7160
110 × 10 - 2 8136
019 × 10 - 2 9129
The vacuum is only an increase of life expectancy in 0133. From Table 3, we can see, 10m3
Cryogenic liquid tank leakage rate from 310 × 10 - 3 Pa L / s down to
214 × 10 - 3Pa L / s, leakage rates increased only 016Pa L / s,
The vacuum has increased life expectancy in 1129; from Table 4, we can see that
100m3 Cryogenic Liquid tank leakage rate from 116 × 10 - 2Pa L / s to reduce
To 112 × 10 - 2Pa L / s, leakage rates increased only 014Pa L / s,
And life expectancy has increased by a vacuum in 1174. It can be seen to improve the seal
End vacuum tank of cryogenic liquid to increase the level of vacuum life
Limited to reduce the leakage rate of vacuum to increase its life expectancy is an effective measure.
3 National Institute of Standards vacuum end of the closure are more
Between 1981 and developed the first "fixed vacuum powder
Tank insulation "(JB / TQ 260 -81) the industry standard, up to now
The "low-temperature thermal insulation of pressure vessels" (GB 18442) National Institute of Standards,
A total of four versions, each version of the standard vacuum end of the closure requirements see
Table 5.
Table 5 for the four versions of the standard cryogenic liquid vacuum tank end closure are more
JB / TQ 260 -81 standard is China's low-temperature vacuum powder insulation
Liquid tank section of an enterprise standard, low-temperature liquid at the time in our country
Tank just by the manufacturer into the production trial, without regard to his
Effective volume size, vacuum sealed knot for all 2167Pa; "fixed
Vacuum powder insulation cryogenic liquid tank "(ZBJ 76003 -88,
JB / T 9072 -1999) is a standard low-temperature liquid tank Secondly,
Third Edition, closed end of the vacuum tank by the volume done a sub-file, and
2167Pa break through the boundaries, to not less than the relaxation 4Pa; low-temperature
The fourth edition of the standard liquid tank, that is, the national GB 18442 -2001
Standards, to further relax the end of the vacuum sealing requirements.
However, in general, standards require that knot closure or partial vacuum
High, can significantly reduce the need for vacuum powder insulation with suitable properties
Should be, which is to reduce energy consumption, lower costs should be taken into account.
4, adjusted vacuum sealed end of the feasibility and significance of indicators
Node is vacuum sealed at room temperature measured value, when the tank is filled in the low-temperature
After the liquid, on the one hand, as a result of shrinkage gas dissection, on the other hand, by
Sand in the Pearl with adsorption layers of vacuum will rise 1 to 2
Of magnitude, that is, when the closure knot 40Pa vacuum, the filling into the low-temperature
After the laminated vacuum liquid can rise to more than 4Pa.
China's low-temperature liquid tank manufacturing industry for more than 30 years after the fat
Fair and effective capacity development from a few hundred up to several hundred cubic meters, storage of low-level
Temperature of liquid medium from oxygen, nitrogen, argon expanded to cover almost all the low-temperature
Liquids, the manufacturer has also been extended to dozens of design and manufacture of low -
Temperature liquid tank technology has been basically mature. However, due to the excessive
Important to improve the vacuum seal on the end of the role of deflation, an increase of unnecessary
Time of the time. For example, a cryogenic liquid containers of 600L
(Tank), 10Pa vacuum laminated letters for taking the time to end, a life expectancy of the vacuum
619 years; 1Pa taking the time to end closures, vacuum lifetime of 7 years, vacuum
Life expectancy increased by just over 1 month. However, in order to achieve closed-end 1Pa
Objectives, to spend the winter at least more than 10 days time to time, summer
Days need to spend more than 20 days to a month's time, that is, the use of a
Time to time on the extension of a life on the vacuum. As early as 20
Century 80's, Iron and Steel from abroad cryogenic liquid tank, the
Vacuum sealed for colorectal 40Pa, the initial vacuum for the work of 617Pa.
Comparison of domestic and foreign similar products cryogenic liquid tank, for
Effective volume in more than 5m3 of cryogenic liquid tank, closure of domestic
Vacuum knot abroad requirement is 4 to 8 times. Unnecessarily increase the
Vacuum sealed end, the extended time period, resulting in time and energy
Waste, an increase of manufacturing cost.
5 Conclusion
Regular low-temperature liquid tank manufacturers of products
Carried out strictly in accordance with the standard assessment. Standards are controlled and the impact of
A wide range, it is proposed to lower the standard of end closures to the vacuum
Demand for standard GB 18442 -2001 end closure means of vacuum
Standard, based on the existing 2 ~ 8 times lower (effective volume is less than
5m3 of the tank should be reduced by 2-fold). This will not only satisfy the vacuum powder
At the end of the insulation properties and can lower production costs, on the low-temperature liquid
Body tank manufacturing energy-saving benefit of energy, significant economic benefits
Forward.
References:
[1] and chemical industries and design editor of the fourth. Cryogenic Manual [M]. Beijing:
Chemical Industry Press, 1979.
[2] GB 18442 -2001 adiabatic low-temperature pressure vessels [S].
[3] JB / T 9072 -1999 fixed vacuum powder insulation cryogenic liquid tank
[S].
[4] ZBJ 76003 -88 fixed vacuum powder insulation cryogenic liquid tank
[S].
[5] JB / TQ 260 -81 powder tank stationary vacuum [S].