JP6378388B2 - Vacuum insulated container for low temperature - Google Patents

Description

The present invention relates to a low-temperature vacuum heat insulating container that can be applied to a container for low-temperature liquefied gas, a container for cryogenic equipment, and the like.

  As an example of a low-temperature vacuum insulation container, a cryogenic tank for liquefied gas is used in many industries. The low temperature tank for liquefied gas stores a so-called low temperature liquefied gas obtained by liquefying an inorganic gas such as nitrogen, argon, oxygen or carbon dioxide, a natural gas, or an organic gas such as ethylene. These low-temperature liquefied gases can be taken out in the form of liquid or vaporized gas.

  Such a liquefied gas cryogenic tank includes a large stationary low-temperature liquefied gas storage tank disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2007-24057) and a comparison disclosed in Patent Document 2 (Actual Publication No. 4-17906). There is a small portable low-temperature liquefied gas container. There is also a mobile type mounted on a tank truck disclosed in Patent Document 3 (Japanese Patent Laid-Open No. 2007-40386).

Such a cryogenic tank for liquefied gas is provided with a vacuum heat insulating layer surrounding the internal space like a thermos. This vacuum heat insulating layer is configured by evacuating the space between the inner tank and the outer tank to reduce convection to the minimum and filling the heat insulating material to reduce heat conduction. As this heat insulating material, parlarite powder is generally used. Glass wool may be used.

JP 2007-24057 A Japanese Utility Model Publication No. 4-17906 JP 2007-40386 A

  Glass wool uses an organic adhesive as a binder to prevent the bulk (bulge) from returning every time the vacuum insulation layer is decompressed and decompressed during maintenance of the liquefied gas cryostat.

  Although the liquefied gas to be stored has no particular problem with nitrogen or argon, glass wool using a binder when storing oxygen is considered inappropriate. This is because, in the unlikely event that leakage occurs in the stored oxygen, it cannot be denied that there is a possibility of causing a dangerous state by contacting the vaporized binder with oxygen under vacuum. For this reason, even if there is no legal regulation, in the high-pressure gas industry, it is reluctant to apply glass wool using a binder to a storage tank for liquefied oxygen, so to speak, it is in a state where it is voluntarily regulated.

  Therefore, glass wool products (trade name such as cryolite) and pearlite powder using a binder that is difficult to melt are used for storing liquefied oxygen.

  However, glass wool using a binder may cause the binder to vaporize in a vacuum and reduce the degree of vacuum of the vacuum heat insulating layer, and sufficient cold insulation may not be obtained. In addition, the pearlite powder is vibrated during use to compress the powder, and a space without a heat insulating material is formed in the upper portion, resulting in a decrease in cold insulation. Therefore, it is necessary to additionally fill the powder for maintenance, and there is a great problem in maintainability.

  The present invention has been made in order to solve the above-described problems, and has an object to provide a low-temperature vacuum heat insulating container that can obtain sufficient cold insulation, is excellent in maintainability, and does not select a cold insulation object. And

In order to achieve the above object, the low-temperature vacuum heat insulation container of the present invention is a low-temperature vacuum heat insulation container in which a vacuum insulation layer is formed by vacuum-reducing the space between the inner container and the outer container,
The vacuum heat insulating layer is configured by being filled with a heat insulating mat made of glass wool not containing a binder formed by short glass fibers in a cotton shape ,
A plurality of the heat insulating mats are stacked on the inner container side, and a plurality of the heat insulating mats are stacked on the outer container side.
The gist is that a single radiation layer made of metal foil exists between the heat insulating mats stacked on the inner container side and the heat insulating mats stacked on the outer container side. To do.

The vacuum heat insulating container for low temperature of the present invention is configured such that the vacuum heat insulating layer is filled with a heat insulating mat made of glass wool not containing a binder in which short glass fibers are formed into a cotton shape.
For this reason, sufficient cold insulation with glass wool is ensured. Further, there is no need to perform additional filling of powder unlike powder pearlite, and there is no problem of maintainability. Further, since no binder is used in the heat insulating mat constituting the vacuum heat insulating layer, there is no possibility of melting by oxygen, and there is no need to select an object to be kept cold.

In addition, since a plurality of the heat insulating mats are stacked on the inner container side and a plurality of the heat insulating mats are stacked on the outer container side, the heat insulating mat may be stacked and filled when forming the vacuum heat insulating layer. The space between the inner container and the outer container can be easily filled with a heat insulating mat without any gaps, and the workability is excellent.
In addition, since the heat insulating mat laminated on the inner container side and the heat insulating mat laminated on the outer container side, a single radiation layer made of metal foil is present, and therefore, In addition to the heat conduction cut by the heat insulating mat and the reduction of the convection by the vacuum, the heat conduction is cut by radiation between the layers of the heat insulating mat, so that further excellent cold insulation can be secured.

In the present invention, when the vacuum heat insulating layer is configured by forming a radiation layer with a metal foil on the outermost side of the heat insulating material layer filled with the heat insulating mat,
In addition to the heat conduction cut by the heat insulating mat and the reduction of convection due to the vacuum, the heat conduction is cut by radiation on the outside of the heat insulating mat, so that further excellent cold insulation can be secured.

In the present invention , the heat insulating material layer in which a plurality of the heat insulating mats are laminated is preferably filled so as to have a density of about 16 kg / m ³ or more and 50 kg / m ³ or less.
This is because if the density of the heat insulating material layer is less than 16 kg / m ³ , a sufficient cooling effect cannot be obtained, and if it exceeds 50 kg / m ³ , a further cooling effect cannot be obtained and the cost increases.

It is sectional drawing which shows the vacuum heat insulation container for low temperature of 1st Embodiment of this invention. It is sectional drawing explaining the vacuum heat insulation layer in the said 1st Embodiment. It is sectional drawing explaining the support part in the said 1st Embodiment, (A) is an upper support part, (B) is a lower support part. It is CC sectional drawing which shows the vacuum heat insulation container for low temperature of 2nd Embodiment of this invention. It is a figure which shows the vacuum heat insulation container for low temperatures of the said 2nd Embodiment, (A) is AA sectional drawing, (B) is BB sectional drawing. It is sectional drawing explaining the support part in the said 2nd Embodiment, (A) is a front upper support part, (B) is a rear upper support part, (C) is a lower support part.

  Next, an embodiment for carrying out the present invention will be described.

  FIG. 1 is a cross-sectional view showing a low-temperature vacuum insulation container according to a first embodiment to which the present invention is applied.

  In this example, the low-temperature vacuum insulation container of the present invention is applied to a container for storing a low-temperature liquefied gas. The application range of the low-temperature vacuum heat insulating container of the present invention is not limited to the low-temperature liquefied gas storage container exemplified here. If it is a container for maintaining an internal low temperature, it is the meaning which makes various uses applicable. For example, the present invention can also be applied to a storage container that stores cryogenic equipment such as a cryopump and a refrigerator.

  The low-temperature vacuum heat insulating container has a vertically long capsule shape as a whole. A double structure comprising an inner container 3 and an outer container 5, comprising an inner container 3 in which a low-temperature liquefied gas 2 is stored in an inner space 1, and an outer container 5 that forms a predetermined space 4 between the inner container 3. It has become. Further, in the space 4 sandwiched between the inner container 3 and the outer container 5, an upper support member 6 and a lower support member 7 are provided to support the relative position of the inner container 3 with respect to the outer container 5 without shifting. An installation leg portion 8 is provided at the lower portion of the outer container 5.

  In this low-temperature vacuum heat insulating container, the space 4 sandwiched between the inner container 3 and the outer container 5 is vacuum depressurized to form a vacuum heat insulating layer 10. Thereby, the heat | fever which is going to penetrate | invade from the outer side of the outer container 5 is interrupted | blocked by the vacuum heat insulation layer 10, and the internal space of the inner container 3 can be maintained at low temperature.

  FIG. 2 is a diagram showing an example of the structure of the vacuum heat insulating layer 10.

  The vacuum heat insulating layer 10 is configured by filling the space 4 with a heat insulating mat 11 made of glass wool formed without using a binder.

  The vacuum heat insulating layer 10 is configured by a plurality of heat insulating mats 11 stacked and filled. In this example, six heat insulating mats 11 are stacked in a direction along the walls of the inner container 3 and the outer container 5 in the space 4 between the inner container 3 and the outer container 5.

  The vacuum heat insulating layer 10 is configured by forming a radiation layer of an aluminum foil 12 that is a metal foil while a plurality of the heat insulating mats 11 are stacked. In this example, the radiation layer made of the aluminum foil 12 is an example in which only one layer is disposed between a plurality of heat insulating mats 11 stacked. A radiation layer made of aluminum foil 12 is formed between the three heat insulating mats 11 stacked on the inner container 3 side and the three heat insulating mats stacked on the outer container 5 side.

  Further, the vacuum heat insulating layer 10 may be configured by forming a radiation layer made of a metal foil such as an aluminum foil 12 on the outermost side of the heat insulating material layer filled with the heat insulating mat 11. By enclosing the outermost layer of the heat insulating material layer with a metal foil such as the aluminum foil 12, in addition to performing radiation heat insulation, it is possible to prevent the heat insulating mat 11 from collapsing during construction. The outermost radiation layer of such a heat insulating material layer can be used in combination with the radiation layer provided between the heat insulating mats 11 described above. Without providing a radiation layer between the heat insulating mats 11, the outermost radiation layer can be disposed alone.

  The metal foil for forming the radiation layer described above is not limited to the aluminum foil 12, and various metal foils can be used.

  In the illustrated example, the vacuum heat insulating layer 10 is configured by disposing a metal mesh 13 on the outermost side of the heat insulating material layer filled with the heat insulating mat 11. The heat insulating mat 11 can be prevented from collapsing during construction by surrounding the heat insulating material layer from the outside with the metal mesh 13.

Glass wool molded without using the binder that forms the heat insulating mat 11 is also called white wool, and is a material that does not contain a binder in which short glass fibers are formed into a cotton shape. As said heat insulation mat 11, what was shape | molded by the fabric weight of 800 g / m < ² >, width 1000mm, length 20000mm, and thickness about 50mm can be used, for example. The glass wool fiber used for the heat insulating mat 11 may be, for example, one having a wire diameter of 5 μm.

The heat insulating material layer in which a plurality of heat insulating mats 11 as described above are laminated is preferably filled so as to have a density of about 16 kg / m ³ or more and 50 kg / m ³ or less. This is because if the density of the heat insulating material layer is less than 16 kg / m ³ , a sufficient cooling effect cannot be obtained, and if it exceeds 50 kg / m ³ , a further cooling effect cannot be obtained and the cost increases.

  The vacuum heat insulating container for low temperature according to the present invention supports the vacuum heat insulating layer 10 by supporting the inner container 3 with respect to the outer container 5 without shifting the relative position in the space 4 sandwiched between the inner container 3 and the outer container 5. A support member for maintaining the layer size is provided.

  In the first embodiment, as the support member, the upper support member 6 disposed at the upper vertex of the inner container 3 and the outer container 5 and supporting the inner container 3, and the lower vertex of the inner container 3 and the outer container 5 And a lower support member 7 that is disposed and supports the inner container 3.

  The upper support member 6 and the lower support member 7, which are the support members, are each cylindrical in this example. One end surface is brought into contact with the outside of the inner container 3, and the other end surface is placed inside the outer container 5. By the contact, the layer size of the vacuum heat insulating layer 10, that is, the gap size of the space 4 is maintained.

  The upper support member 6 and the lower support member 7 that are the support members are made of a resin material. Specifically, for example, FRP having a small thermal conductivity can be used. The resin material constituting the support member is not limited to this as long as the strength when supporting the inner container 3 relative to the outer container 5 without shifting the relative position can be secured, and various resin materials can be used. Can be used.

  FIG. 3A is a cross-sectional view illustrating the peripheral structure of the upper support member 6.

  One end of the upper support member 6 is inserted into an inner sleeve 14 attached to the inner container 3, and the other end is inserted into an outer sleeve 15 attached to the outer container 5. In the inner sleeve 14, a cylinder 14 </ b> B is erected on a substrate 14 </ b> A that is fixed to the outer wall surface of the inner container 3. The outer sleeve 15 has a cylinder 15B passing through a flange 15A fixed to the outer wall surface of the outer container 5, and the outer opening of the cylinder 15B is closed by a lid 15C. The inner sleeve 14 and the outer sleeve 15 are arranged so that the respective cylinders 14B and 15B are located at the upper apexes of the inner container 3 and the outer container 5.

  The upper support member 6 is inserted into the inner sleeve 14 and the outer sleeve 15 and is not fixed. Therefore, when the inner container 3 is cooled by filling with the low-temperature liquefied gas and the length dimension contracts, the upper support member 6 slides in the outer sleeve 15 accordingly. The same applies when the low-temperature liquefied gas in the inner container 3 is emptied and returns to room temperature, and the length is restored. In this way, dimensional changes associated with temperature changes are absorbed to prevent distortion.

  FIG. 3B is a cross-sectional view illustrating the peripheral structure of the lower support member 7.

  One end of the lower support member 7 is inserted into the inner sleeve 16 attached to the inner container 3, and the other end is inserted into the outer sleeve 17 attached to the outer container 5. In the inner sleeve 16, a cylinder 16 </ b> B is erected on a substrate 16 </ b> A that is fixed to the wall surface of the inner container 3. In the outer sleeve 17, a cylinder 17 </ b> B is erected on a substrate 17 </ b> A that is fixed to the wall surface of the outer container 5. The inner sleeve 16 and the outer sleeve 17 are arranged so that the respective cylinders 16B and 17B are positioned at the lower apexes of the inner container 3 and the outer container 5.

  4 and 5 are views showing a vacuum insulation container for low temperature according to a second embodiment of the present invention. 4 is a cross-sectional view taken along the line CC, FIG. 5A is a cross-sectional view taken along the line AA, and FIG. 5B is a cross-sectional view taken along the line BB.

  In this example, the inner container 3 and the outer container 4 are placed horizontally. Such a horizontally placed low-temperature vacuum insulation container for low temperature can be installed on the ground or floor, and can also be used for in-vehicle use such as a tank truck.

  In this example, the support member is provided with a pair of left and right lower support members 21 at the front and rear, and supports the lower side of the inner container 3 with the four lower support members 21. A pair of front upper support members 22 are disposed on the front side of the upper part, and a pair of rear upper support members 23 are disposed on the rear side of the upper part.

  FIG. 6 is a cross-sectional view for explaining the peripheral structure of each of the above support members. (A) is the front upper support member 22, (B) is the rear upper support member 23, and (C) is the lower support member 21.

  One end of the front upper support member 22 is inserted into a sleeve 22 </ b> A fixed inside the outer container 5. The other end of the front upper support member 22 is in contact with the outer wall surface of the inner container 3.

  One end of the rear upper support member 23 is inserted into the inner sleeve 23 </ b> A fixed outside the inner container 3, and the other end is inserted into the outer sleeve 23 </ b> B fixed inside the outer container 5.

  One end side of the lower support member 21 is inserted into a sleeve 21 </ b> A fixed inside the outer container 5. The other end of the lower support member 21 is in contact with the outer wall surface of the inner container 3.

By inserting the rear upper support member 23 into the inner sleeve 23A fixed to the inner container 3 and the outer sleeve 23B fixed to the outer container 5, the relative positions of the inner container 3 and the outer container 5 are determined. The front upper support member 22 and the lower support member 21 do not have a sleeve on the inner container 3 side. Thus, when the inner container 3 expands and contracts due to a temperature change, sliding between the outer wall surface of the inner container 3 and the end surfaces of the front upper support member 22 and the lower support member 21 in contact with the outer wall surface is allowed. In this way, dimensional changes associated with temperature changes are absorbed to prevent distortion.

  Next, examples will be described.

First, a low-temperature liquefied gas container having the configuration shown in FIGS. 1 to 3 was manufactured as a low-temperature vacuum heat insulating container, and an evaporation test of liquid nitrogen was performed to evaluate the heat insulating performance. The specifications of the low temperature liquefied gas container used for the test are as follows.
Inner container outer diameter 457.2mm, inner volume 120L
Outer container inner diameter 603.6mm
Vacuum insulation layer thickness 73.2mm

The test was conducted as follows.
Place container on load cell. The degree of vacuum of the vacuum insulation layer is detected by a vacuum sensor. A temperature sensor detects the temperature and the outside temperature at a plurality of locations on the outer peripheral surface of the inner container. The inner container is filled with about 1/2 of liquid nitrogen. Liquid nitrogen evaporates due to the heat that has entered the container, and is released from the open valve at the top of the container. The weight change at this time is measured with a load cell. Thereby, the amount of intrusion heat can be measured.
Q = (W · q) / (H · ΔT · V)
Q: Intrusion heat (J / h ° C L)
W: Vaporized gas volume (kg)
q: latent heat of vaporization of liquid nitrogen (J / kg): adopting a value of 200000 J / kg H: measurement time (Hr)
ΔT: Difference between boiling point of liquid nitrogen and outside air temperature (℃)
V: Internal volume (L): 120.95L

The heat insulating materials used for the test are as follows.
1 Glass wool (with aluminum foil) 16kg / m ³ Thickness 50mm
2 Cryolite (with aluminum foil) 16kg / m ³ Thickness 25mm
3 White wool

The white wool heat insulating mat 11 is formed such that the glass wool fiber has a wire diameter of 5 μm, a basis weight of 800 g / m ² , a width of 1000 mm, a length of 20000 mm, and a thickness of about 50 mm. The heat insulating material layer obtained by laminating a plurality of the heat insulating mats 11 has a filling thickness of 73 mm and a filling density of about 16 kg / m ³ . The aluminum foil which comprises a radiation layer used the thing of thickness 50micrometer.

  Table 1 below shows the degree of vacuum of the vacuum heat insulating layer 10 using each heat insulating material and the number of days until all 44 L of liquid nitrogen evaporates.

  As can be seen from Table 1, it can be seen that the vacuum heat insulation layer using white wool can secure a sufficient number of evaporation days.

  Next, simulation was performed assuming a low-temperature liquefied gas container having the configuration shown in FIGS.

The configuration of the vacuum heat insulating layer 10 is described from the inside as follows.
Inner container: SUS304, thickness 6mm
Insulation: thickness 50mm
Radiation layer: Aluminum foil thickness 0.05mm
Insulation: thickness 50mm
Wire mesh outer container: SS400 Thickness 9mm

  The upper support member 6 and the lower support member 7 were each having an outer diameter of 149 mm, an inner diameter of 125 mm, a thickness of 12 mm, and a total length of 268 mm.

  When the upper support member 6 and the lower support member 7 were made of stainless steel (SUS304) and the heat insulating material was made of pearlite, glass wool, cryolite, or white wool, the amounts of intrusion heat and heat leak values were calculated. The amount of intrusion heat was calculated from the heat of the atmospheric temperature entering from the vacuum heat insulating layer 10, the upper support member 6, the lower support member 7, and the piping.

The conditions used as the basis for the calculation are as follows.
[Tank specification]
Inner container inner diameter 1250mm
Wall thickness 6mm
Length 3609mm
Mirror shape 2: 1 half ellipse
Outer surface area 17.76m ²
Outer container inner diameter 1650mm
Length 4211mm
Mirror shape 10% dish type
Inner surface area 27.22m ²
Film heat transfer coefficient 30 kcal / m · h · ° C

〔Environmental condition〕
Atmospheric temperature 20 ℃

[Storage solution] Liquid nitrogen Saturation temperature -196 ° C
Saturated liquid density 0.809kg / L
Evaporation latent heat 47.61 kcal / kg
Standard state gas density 1.251 kg / m ³
Storage amount 4940.2L (100%)

[Upper support member / Lower support member]
Thermal conductivity 10.790 kcal / m · h · ° C

〔Plumbing〕
Material SUS304
Thermal conductivity 10.790 kcal / m · h · ° C

[Thermal conductivity of thermal insulation]
Perlite: 1.745 × 10 ⁻³
Glass wool (16 kg / m ³ ): 2.484 × 10 ⁻³
Cryolite (16 kg / m ³ ): 1.359 × 10 ⁻³
White wool: 1.67 × 10 ^-3
White wool + aluminum foil: 1.12 × 10 ⁻³

* Perlite is made by Mitsui Mining & Smelting Co., Ltd.
* Cryolite is manufactured by Rydoll in the United States.
* White wool is manufactured by Asahi Fiber Glass Co., Ltd.
Other manufacturers of white wool include Mag Co., Ltd. and Paramount Glass Industry Co., Ltd.

  The results are shown in Table 2 below. The heat leak value is a percentage of liquid nitrogen that evaporates per day.

Next, the intrusion heat amount and the heat leak value were calculated when the upper support member 6 and the lower support member were FRP and the heat insulating material was white wool.
Intrusion heat amount: 30.4 (W)
Heat leak value: 0.329 (% / day)

In the case of pearlite heat insulation using a conventional stainless steel support member, the heat leak value was 0.626 (% / day), but this was a white wool heat insulation example using the FRP support member of the example. The heat leak value was 0.329 (% / day), and the amount of gas loss was half that of the conventional one.
Further, in the case of white wool insulation without a radiation layer made of aluminum foil, the heat leak value was 0.475 (% / day).

  As described above, in this embodiment, it is possible to suppress the intrusion heat amount to about half of the conventional pearlite heat insulation. In this embodiment, the evaporation loss amount can be reduced to about half that of pearlite insulation.

  As described above, according to the vacuum heat insulating container for low temperature of the present embodiment, the following operational effects can be obtained.

That is, the said vacuum heat insulation layer is filled with the heat insulation mat which consists of glass wool shape | molded without using a binder.
For this reason, sufficient cold insulation with glass wool is ensured. Further, there is no need to perform additional filling of powder unlike powder pearlite, and there is no problem of maintainability. Further, since no binder is used in the heat insulating mat constituting the vacuum heat insulating layer, there is no possibility of melting by oxygen, and there is no need to select an object to be kept cold.

Moreover, since the vacuum heat insulating layer is configured by being stacked and filled with a plurality of the heat insulating mats,
When the vacuum heat insulating layer is formed, the heat insulating mat may be stacked and filled, so that the space between the inner container and the outer container can be easily filled without any gap, and the workability is excellent.

In addition, when the vacuum heat insulating layer is configured by forming a radiation layer with a metal foil on the outermost side of the heat insulating material layer filled with the heat insulating mat,
In addition to the heat conduction cut by the heat insulating mat and the reduction of convection due to the vacuum, the heat conduction is cut by radiation on the outside of the heat insulating mat, so that further excellent cold insulation can be secured.

In addition, the vacuum heat insulating layer is formed by forming one or more radiation layers of metal foil while a plurality of the heat insulating mats are stacked.
In addition to the heat conduction cut by the heat insulating mat and the reduction of the convection by the vacuum, the heat conduction is cut by radiation between the layers of the heat insulating mat, so that further excellent cold insulation can be secured.

And a support member for maintaining a layer size of the vacuum heat insulating layer by supporting the relative position of the inner container with respect to the outer container so as not to shift in a space between the inner container and the outer container. Because it consists of
By configuring the support member from a resin material having a low thermal conductivity, heat transfer from the outer container to the inner container via the support member is reduced, and further excellent cold insulation can be secured.

DESCRIPTION OF SYMBOLS 1 Internal space 2 Low temperature liquefied gas 3 Inner container 4 Space 5 Outer container 6 Upper support member 7 Lower support member 8 Leg 10 Vacuum heat insulation layer 11 Heat insulation mat 12 Aluminum foil 13 Metal mesh 14 Inner sleeve 14A Substrate 14B Tube 15 Outer sleeve 15A Flange 15B Cylinder 15C Lid 16 Inner sleeve 16A Substrate 16B Cylinder 17 Outer sleeve 17A Substrate 17B Cylinder 21 Lower support member 21A Sleeve 22 Front upper support member 22A Sleeve 23 Rear upper support member 23A Inner sleeve 23B Outer sleeve

Claims (3)

A vacuum heat insulating container for low temperature in which a space between the inner container and the outer container is vacuum depressurized to form a vacuum heat insulating layer,
The vacuum heat insulating layer is configured by being filled with a heat insulating mat made of glass wool not containing a binder formed by short glass fibers in a cotton shape ,
A plurality of the heat insulating mats are stacked on the inner container side, and a plurality of the heat insulating mats are stacked on the outer container side.
Between the heat insulating mats stacked on the inner container side and the heat insulating mats stacked on the outer container side, a single radiation layer made of metal foil is present and configured. Vacuum insulated container for low temperature. The vacuum insulation layer, the outermost of the insulating mat is filled with heat insulating material layer, the low-temperature vacuum heat insulating container according to claim 1 Symbol placement radiation layer of a metal foil is formed is formed. The vacuum heat insulating container for low temperature according to claim 1 or 2 , wherein the heat insulating material layer obtained by laminating a plurality of the heat insulating mats is filled so as to have a density of about 16 kg / m ³ or more and 50 kg / m ³ or less.

Images