Spacer for a long substrate

A spacer for a long substrate in the interior of a long tube, with a superinsulation material being disposed between the substrate and the tube. The spacer includes two rings (3, 4) seated on the substrate (1) and spaced apart from each other at a longitudinal axial distance, a tube section (5) supported on the rings (3, 4) and a second ring (6) disposed on the tube section (5). The first rings (3, 4), the tube section (5) and the second ring (6) are made of a material with poor thermal conductivity and high mechanical strength.

This application is based on and claims the benefit of German Patent Application No. 103 10 960.9 filed Mar. 13, 2003.

BACKGROUND OF THE INVENTION

The invention relates to a spacer for a long substrate in the interior of a long tube, of the type wherein a superinsulation material is arranged between the substrate and the tube, and to a coaxial tube system with such a spacer.

The invention is based on the following considerations:

Optimal thermal insulation in refrigeration technology is achieved by multi-layer foil insulation in a high vacuum (superinsulation). The total heat flow is brought to what is currently the lowest technically possible value by minimizing the components Qgas, QFKand Qrad.

The heat loss flows Qgasare reduced by evacuating the insulation space.

The solid heat bridges, e.g., spacers, which are responsible for QFK, are structurally reduced by minimizing the solid-state contact flows.

The radiation losses Qradare reduced by metallizing the interior walls or by installing highly reflective foils.

QFKplays a decisive role, especially in flexible, vacuum-insulated cryogenic conduits. To prevent direct contact at any point along the course of the conduit between the cold interior tube and the exterior tube, which is at room temperature, spacers of various designs have heretofore been used. These spacers must be capable of transmitting the largest possible force component but must likewise have the property of low thermal conductivity. The spacers of the prior art have the drawback that they do not implement these two necessary goals equally well. If low thermal conductivity was achieved, the mechanical loading capacity was low; if high mechanical loading capacity was achieved, very high thermal conductivity had to be accepted.

German publication DE-C2-2 136 176 discloses a tube system consisting of two concentric tubes, e.g., an electrical cable operated at low temperatures or a conduit for transporting liquid or gaseous heated or cooled media, whose interior tube is held in position inside the surrounding exterior tube by spacers, which are made of little material. The spacers are seated at intervals on the interior tube and are supported against the inner surface of the exterior tube. The spacer consists of a plurality of slotted rings, whose slot width corresponds to the diameter of the interior tube. On each ring, a thread element is fastened in the slot area. The rings are interconnected in such a way that they can be pivoted about a common axis of rotation. When the spacer is placed onto the interior tube, the thread elements partially wrap around the interior tube. The exterior tube is supported against the outer circumference of the spacer formed by the rings. This design requires very little material but a relatively large amount of space within the insulation area. Since it is furthermore difficult to fix the thread elements permanently to the rings and the fixation can be loosened under tensile loads, this spacer is less suitable for flexible tube systems where tensile or compression loads of more than 10,000 N may occur during bending.

U.S. Pat. No. 2,914,090 discloses a spacer for a coaxial tube system. The spacers are seated on the interior tube spaced apart from each other at a longitudinal axial distance. They hold the interior tube at a distance from the exterior tube. Each spacer consists of an interior metal tube section enclosing the interior tube and an exterior tube section, which is likewise made of metal and contacts the interior wall of the exterior tube. Between the interior and the exterior tube sections, three spoke-like struts spaced equidistantly across the circumference are provided and welded to both the interior and the exterior tube section. The interior tube section is made of two coaxial tubes between which thermal insulation, e.g., made of asbestos, is inserted.

Although this spacer has great mechanical strength it lacks the necessary insulating properties.

SUMMARY OF THE INVENTION

Thus, an object of the invention is to provide a spacer which is made with little material and consequently has good heat insulating properties and which can withstand high mechanical loads.

This object is attained by a spacer wherein a superinsulation material is arranged between the substrate and the tube, characterized by two first rings (3,4) seated on the substrate (1) and spaced apart at a longitudinal axial distance from one another, a tube section (5) supported on the rings (3,4) and a second ring (6) located on the tube section (5), wherein the first rings (3,4), the tube section (5) and the second ring (6) are made of a material that has poor thermal conductivity but high mechanical strength.

Additional advantageous embodiments of the spacer are set forth in the remaining claims and are described in detail below.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a tube system comprising two conduits arranged concentrically to each other. The tube system is intended, for example, for transporting cryogenic media.

The tube system includes a corrugated interior metal tube1, which is preferably made of stainless steel, and a likewise corrugated exterior metal tube2, which is preferably also made of stainless steel. Because of the corrugation of the interior tube1and the exterior tube2, the tube system is flexible and can be wound onto transport reels and thus can be transported to the place of use. If the tubes1and2are produced by shaping a nearly endless metal strip into a tube with a longitudinal slit, welding the longitudinal slit and subsequently corrugating the tube, it is possible to obtain tubes of nearly endless lengths.

Between the interior tube1and the exterior tube2, spacers are provided at specific intervals in the longitudinal axial direction. These spacers comprise rings3and4seated on the interior tube1, a tube section5and a ring6located between the tube section5and the exterior tube2. The rings3and4of the tube section5and the ring6are made of fiber-reinforced plastic, e.g., glass fiber-reinforced epoxy resin.

The spacer can be assembled from parts3,4,5and6and pushed onto the interior tube1as a unit.

As an alternative thereto, the spacer produced as a unit can be separated into two parts, such that it can be laterally placed onto the interior tube.

A so-called superinsulation7formed of a plurality of layers of metallized plastic foils is placed between the interior tube1and the exterior tube2.

This superinsulation7is also provided in the area of the spacer. In an embodiment where the spacer is made of two parts that are laterally placed onto the interior tube1, the superinsulation is fixed to the interior wall of the tube section5.

In the embodiment shown inFIG. 2, the superinsulation7is first wrapped around the entire length of the interior tube1. Thereafter, the spacers are placed onto the superinsulation, which is thereby compressed in the area of the rings3and4.

This process is suitable if large tube system lengths are to be produced.

Here, the interior tube1is produced first and is wound onto a supply reel. During production of the interior tube1, the superinsulation7can be wound up in the same operation.

In the next working step, the insulated interior tube1is pulled off the supply reel and the spacers are placed onto the superinsulation.

A metal strip is pulled from a supply reel and in a continuous operation is shaped into a slit tube around the interior tube1, the longitudinal seam is welded and the tube is corrugated. A plastic jacket can further be extruded onto the exterior tube2thus formed.

At the installation site, the gap between the interior tube and the exterior tube is evacuated.