Abstract:
The present invention relates to an insulating layer for use in thermal insulation, including a radiation shield for reflecting thermal radiation and a spacer material which is attached to the radiation shield by means of a fastening material, from which insulating layer the air has been evacuated. The radiation shield of the insulating layer includes a plurality of through holes. The present invention also relates to an insulation for thermal insulation of an object as well as a method of manufacturing such an insulation.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an insulation layer for use in thermal insulation. The present invention also relates to an insulation for thermal insulation of an object and a method of manufacturing such an insulation. 
       TECHNICAL BACKGROUND 
       [0002]    Heat transfer from an arbitrary object to its surroundings is caused by convection, heat conduction and heat radiation. In order to avoid such heat transfer, there is a general need for thermal insulations. Insulations of simple constructions adapted to reduce the heat transfer are used in e.g. heat or cold preserving beverage containers such as Thermos®. In such a container, the content is insulated from the surroundings by an enclosing space of vacuum. Since vacuum reduces the heat transfer to radiation only, no heat transfer is caused by convection or conduction. Thus, an insulating effect is obtained which allows the beverage content inside the container to preserve its temperature. 
         [0003]    There are higher demands put on the thermal insulation when the applications are more sophisticated. Some gases, e.g. nitrogen and oxygen, are preferred to be kept in liquid phase when they are transported and stored in order to enclose a higher amount of gas in the same container volume. In many cases, this requires either extremely low temperatures or extremely high pressures. High pressures are preferably avoided for safety reasons, which is why the gas container needs to be thermally insulated in order for the gas to preserve its low temperature. 
         [0004]    The increase in heat transfer by radiation is according to Stefan-Boltzmann&#39;s law proportional to the fourth power of the difference in temperature between the object and the surroundings. It is thus necessary to reduce the heat transferred by radiation in cases where the difference in temperature between the object and the surroundings is large, e.g. as in the case of transporting and storing gas. 
         [0005]    One method of reducing the heat radiation is to introduce several radiation shields in an enclosing space of vacuum. The radiation shields, which may be in the form of thin aluminium foil sheets, increase the total reflection of heat radiation. An intermediate layer may be arranged between the radiation shields to prevent the radiation shields from being in contact with each other, in which case they are allowing for heat conduction between the radiation shields. The intermediate layer is made of a material having a low heat conductivity. By attaching each radiation shield to the intermediate layer, the mounting of such insulation (also known as a Multi Layer Insulation) is simplified and the multi layer insulation is formed by winding the intermediate layer and the attached radiation shield in several layers around the gas container. 
         [0006]    A schematic cross section of an insulating layer  10  according to prior art is shown in  FIG. 1 . The insulating layer is formed of a radiation shield  16  and an intermediate layer  12 . The radiation shield  16  is attached to the intermediate layer  12  by means of a fastening material  14 . 
         [0007]    The multi layer insulation according to prior art causes long production times when the surrounding vacuum space is to be evacuated. The dense layers of aluminium foil also affect the production time, i.e. the time required for pumping vacuum in a negative manner,. Moreover, the efficiency of the insulation is reduced due to the fact that water which is bonded to the glass fibre may contribute to heat transfer caused by convection. 
       SUMMARY OF THE INVENTION 
       [0008]    One object of the present invention is to provide an improvement of the prior art as described above. 
         [0009]    A particular object of the present invention is to provide an insulating layer and an insulation which reduce the production time and which have an improved efficiency. 
         [0010]    According to the present invention, the above objects are achieved by an insulating layer for use in thermal insulation comprising a radiation shield for reflecting thermal radiation and a spacer material which is attached to the radiation shield by means of a fastening material, from which insulating layer the air has been evacuated. The insulating layer is characterised in that said radiation shield comprises a plurality of through holes. 
         [0011]    This is advantageous in that the space that surrounds the insulating layer is evacuated faster. 
         [0012]    The spacer material may be sewn to said radiation shield by means of a thread acting as fastening material, which is advantageous in that the radiation shield is attached to the spacer material in a simple and production-friendly manner. 
         [0013]    The fastening material may be oxygen compatible, which is advantageous in that the insulation can be used for transporting and storing oxygen. 
         [0014]    The fastening material may be inorganic, which is advantageous in that it is oxygen compatible. 
         [0015]    The spacer material may comprise fibre, which is advantageous in that the spacer material thus can have a lower density, and consequently lower heat conductivity. 
         [0016]    The spacer material may comprise glass fibre, which is advantageous in that easily accessible and cheap material can be used. 
         [0017]    The fibre of the spacer material may comprise a surface that reflects thermal radiation. The heat radiation is thereby further reduced. 
         [0018]    The cross section of the fibre of the spacer material may be oval, which allows alternative and cheaper methods of production. 
         [0019]    The fibre of the spacer material may be spiral-shaped, which results in lower fibre density and consequently lower heat conductivity. 
         [0020]    According to a second aspect of the present invention, an insulation for thermal insulation of an object is provided. The insulation comprises at least a first and a second insulating layer according to the first aspect of the invention, said first and second insulating layer being arranged adjacent to each other. Such insulation is advantageous in that it provides a more efficient insulation. 
         [0021]    The insulating layers may be arranged such that the spacer material of the first insulating layer separates the radiation shield of the first insulating layer from the radiation shield of the second insulating layer. This is advantageous in that the spacer material prevents heat conduction between the radiation shields. 
         [0022]    The number of insulating layers may be greater than 5, which allows for an even more efficient insulation. 
         [0023]    The number of insulating layers may be lower than 50, which is advantageous in that a relatively thin and cheap insulation is provided. 
         [0024]    According to a third aspect of the invention, a method of manufacturing an insulation for use in thermal insulation comprising at least one insulating layer having a radiation shield for reflecting thermal radiation and a spacer material is provided. The method is characterised by providing a plurality of through holes in the radiation shield, attaching the spacer material to the radiation shield, and evacuating air from the insulation. 
         [0025]    The spacer material may be attached to the radiation shield by means of sewing, which is advantageous in that the radiation shield is attached to the spacer material in a simple and production-friendly manner. 
         [0026]    The holes of the radiation shield may be formed by means of sewing, which reduces the number of production steps since attaching the layers and making the holes can be performed in a single step. 
         [0027]    The spacer material may be coated with a surface that reflects thermal radiation, which is advantageous in that a product having an improved insulating property is obtained. 
         [0028]    Further, at least a first and a second insulating layer may be arranged adjacent to each other such that the spacer material of the first insulating layer separates the radiation shield of the first insulating layer from the radiation shield of the second insulating layer. In this way, heat conduction from one radiation shield to another is avoided. 
         [0029]    The advantages of the first and second aspects of the invention are also applicable for the third aspect of the invention. 
         [0030]    The expression “oxygen compatible” indicates that a material is applicable in an environment with an increased oxygen rate without any risk of fire or explosion. 
         [0031]    The advantages and features of the present invention described above are further disclosed in the detailed description as well as in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    Further objects, advantages, features and embodiments of the invention will be apparent from the following description of a number of embodiments, in which reference is made to the appended drawings. 
           [0033]      FIG. 1  shows schematically an insulation according to prior art. 
           [0034]      FIG. 2  is a cross-sectional view of an insulating layer according to the present invention. 
           [0035]      FIG. 3  is a cross-sectional view of an insulation according to the present invention. 
           [0036]      FIG. 4  is a cross-sectional view of a gas container comprising an insulation according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0037]      FIG. 2  shows an embodiment of an insulating layer  100  according to the present invention. The insulating layer  100  comprises a radiation shield  160  for reflecting thermal radiation and a spacer material  120 . The radiation shield  160  is attached to the spacer material  120  by means of a fastening material  140 . A plurality of holes  180  are provided in the radiation shield  160 . The spacer material  120  consists of a fibre material comprising a quantity of fibres  130 . The fastening material  140  consists of a thread, which runs right through the porous spacer material  120  and the holes  180  provided in the radiation shield  160 . Thus, the spacer material  120  is sewn to the radiation shield  160 . The insulating layer  100  is arranged in vacuum. 
         [0038]    In  FIG. 3 , five insulating layers  100  according to  FIG. 2  are shown which form an insulation  300 , also known as a multi layer insulation. The insulating layers  100  are arranged such that the spacer material  120  of a first insulating layer  100  separates the radiation shield  160  of the first insulating layer  100  from the radiation shield  160  of a second insulating layer. Heat conduction from one radiation shield to another is thereby prevented. 
         [0039]      FIG. 4  shows a gas container  400  having an insulation  300  according to the present invention. For example, the container  400  encloses a certain amount of liquid gas  420 . The container  400  is further equipped with an inner wall  440  and an outer wall  440 , which together define a space  480 . The insulation  300 , comprising a plurality of insulating layers  100 , is provided in the space  480 . The air of the space  480  is evacuated, thus providing vacuum. The insulating layers  100  are formed by one insulating layer  100  that is winded in several turns around the container  400 . The number of turns may be more than 10, and fewer than 40. 
         [0040]    The spacer material  120  is made of fibre material, e.g. glass fibre. The thermal conductivity of glass is approximately 1 W.m −1 .K −1 , that is to be compared with the thermal conductivity of aluminium which is approximately 235 W.m −1 .K −1 . Due to the fact that the glass is provided as fibre, thus allowing for a porous material, the thermal conductivity of the spacer material  120  is further reduced down to approximately 0.03 W.m −1 .K −1 . Of course, other materials having a low thermal conductivity, as for example plastics, can be used as spacer material as long as considerations are made due to possible demands for oxygen compatibility. 
         [0041]    The fibre density of the spacer material  120  is low in order to minimize the heat conduction. When several insulating layers  100  are arranged adjacent to each other the spacer material  120  is compressed, which is why the fibre density must be high enough to separate the radiation shields  160  from each other. 
         [0042]    The single fibres  130  can be formed in different ways in order to minimize the fibre density. When compressing the spacer material  120 , the deformation of every single fibre  130  is reduced if the modulus of elasticity of the fibres is increased. The spacer material  120  can thereby have a lower density without causing the radiation shields  160  to engage with each other. The fibres  130  can further be provided with an optional shape. Such a shape can for example comprise a spiral shape, or any part of a spiral shape, such as a curved shape. A lower fibre density can thereby support a higher force of compression without the risk of the radiation shields  160  to engaging with each other. One way to achieve such a shape may be to provide the fibres  130  with an oval cross-section, for example by injecting the fibres through an oval mouthpiece during manufacturing. An inherent “curl” is thereby created in each fibre  130 . Other methods known per se of manufacturing fibres can of course also be used. It should be noted that the adaptation of the spacer material  120  described above can be used as such to improve insulations, without being dependent on other features described herein. 
         [0043]    An insulating layer  100  and an insulation  300  according to the invention can preferably be used for insulating a number of different objects. Some gases are subject to rigorous safety regulations. In particular, this is the case for explosive gases like oxygen and hydrogen. In order for the insulation to be applicable also together with such gases, all materials must be compatible with the gases that are contained inside the insulation. The radiation shield  160 , the spacer material  120  and the fastening material  140  should thus be formed of specific materials. When insulating oxygen, the radiation shield  160  could be made of any metal such as aluminium, and the spacer material  120  could be made of glass fibre. A thread acting as fastening material  140  could also be made of glass fibre. In this case, the radiation shield  160  is sewn to the spacer material by means of the glass fibre thread. Other inorganic alloys can also be suitable for use in an insulating layer  100 . In case of a more easily handled gas, like nitrogen, other materials such as plastics can be used. Thus, the material cost of the insulating layer  100  can be reduced. 
         [0044]    In a further embodiment, the efficiency of the insulating layer  100  is improved by further reducing the heat transfer caused by radiation. Preferably, this is done by providing the spacer material  120  with a surface that reflects thermal radiation. Every single fibre  130  can, for example, be subject to metallization by any suitable process such as thermal evaporation, sputtering, etc. Moreover, the fastening material  140  can also be provided with such a reflective surface. By providing the spacer material  120  and/or the fastening material  140  with such a surface, the heat transfer between the radiation shields  160  is reduced. It should be noted that the adaptation of the spacer material  120  and the fastening material  140  described above can be used as such to improve insulations  300 , without being dependent on other features described herein. 
         [0045]    It will be appreciated that a number of modifications of the embodiments described herein can be made without departing from the scope of the invention as defined by the subsequent claims.