GB2326210A

GB2326210A - Tube assembly for process fluids using vacuum as thermal insulation

Info

Publication number: GB2326210A
Application number: GB9716386A
Authority: GB
Inventors: Ramesh Rajagopal; Jyothsna Ramesh; Pathepur Subramani Shankar Sha
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-06-13
Filing date: 1997-08-04
Publication date: 1998-12-16
Also published as: GB9716386D0

Abstract

The process fluid requiring thermal insulation flows through an inner tube 2, surrounded by an outer tube 1, located concentrically with respect to the inner tube, by means of spacers 5 and the annular ends sealed and vacuum applied, measured and sealed to act as the necessary thermal insulation. End caps 4 are sealed to the tubes 1, 2, optionally via a bellows 12 for accommodating expansion, or the end caps may be of bellows form. Inner tubes 2 may be coupled, with an external sleeve slidable over the outer tubes 1 and sealed thereto with vacuum applied within.

Description

AN ROVED TfflRMAL INSULATION METUOD FOR PROCESS FLUIDS USING VAC This invention relates to providing Thermal Insulation for process fluids using VACUUM instead of conventional insulating materials.

In order to facilitate better understanding of the present invention prior art methods are described here below.

DESCRIPTION OF TnE PRIOR ART Process fluids requiring Thermal Insulation flowing through tubular members such as pipes or tubes are normally insulated with conventional materials, which can be classified into five major types, -Flake, Fibrous, Granular, Cellular and Reflective.

In order to protect the insulating material from the environment and meet mechanical and safety requirements, necessary protective covers are provided at the site. All these operations are carried out by skilled personnel, at site conditions.

Insulation to cryogenic liquids are done using double walled vessels, filled with insulation, provided with reflective foil and vacuum applied in the space in-between.

To obtain maximun efficiency to retard heat flow by the combined action of all heat transfer mechanisms (Radiation, Conduction, Convection) cryogenic insulations are of two types -one composed of powders in partial vacuum, -the other composed of multilayered reflective sheets in partial vacuum.

Reference :- Thermal insulation by John.F.Malloy 1969 by VAN NOSTRAND REINIIOLD CO. 1969. Though vaccum insulation was superior to all existing types of insulation it was mainly confined to cryogenic and other specialised applications.

The purpose of this invention is to provide a method of providing thermal insulation for process fluids using vacuum instead of conventional thermal insulating materials. This method comprises of an inner tube for flow of process fluid and an outer tube, surrounding the inner one. The concentricity between the two tubes maintained by providing several spacer members fixed rigidly at regular intervals by bonding or fusing on the outside of the inner tube, then the outer tube is slid over the spacer members. The inner diameter of the spacer members must be slightly greater than the outer diameter of the inner tube, and the outer diameter of the spacers must be slightly lower than the inner diameter of the outer tube, for easy sliding, of outer tube. These spacers act as mechanical supports, preventing collapse of the outer tube under vacuum, and help in reducing the wall thickness of outer tube member.

The spacer members are made of rigid, good thermal insulating materials such as engineering plastics, elastomers, compressed asbestos and metals, etc. The spacer members are designed to have minimum area of contact with the inner and outer tube surfaces to reduce direct thermal conductivity, and with holes or gaps to enable vacuum to pass through the entire annular area between the two tubes. The spacer members can be machined out of the above materials in the form of a disc with suitable thickness or can be moulded out of engineering polymer materials to have consistent dimensions, and minimum contact points. The inner tube is made sufficiently long at either ends than the outer tube to receive end connections. After ensuring proper alignment between the two tubes, the annular space between the outer and inner tube at either ends, is sealed using suitable sealing means, which comprises of end cap members welded/fused, or bonded at the contact points of the inner and outer tube. The end cap members are made of plastics or metals as required.

Standard adaptors are screwed on or fused on holes provided earlier on either the outer tube or the end cap members. The adaptors are connected to a vacuum source, to obtain the necessary vacuum level in the annular space and sealed using standard methods.

The outer and inner tubes can be of metal, plastics or either and of required lengths and wall thickness as process requirements need. The ratio of the inner diameter of the outer tube to the outer diameter of the inner tube is greater than one, and can be up to 5 times as required to meet process requirements of fluid flow and desired insulation levels.

The end caps can either be fitted in-between the outer diameter of the inner tube and the inner diameter of the outer tube, comprising an annular ring, made of metal or plastics, welded/fused or bonded, at all the contact points, or can be in the form of a end cap, sliding on to the outer diameters of the inner and outer tubes, and welded/fused or bonded at all the contact points.

The end caps can also be of thin strong flexible metallic members fused to the two tubes and capable of permitting expansion & contraction of inner tube and of sufficient length to dissipate direct thermal conductivity to the atmosphere. Alternatively the end caps can be made with a bellows type seal at one or both ends to provide for expansion and contraction of the inner tube.

The bellows can be of plastics or metals. Also sealing rings can be provided in the grooves of the end cap members to provide additional sealing. The bonding or fusing of the end caps is done only on the contact points on the inner tube, and the other end fixed by means of bellows and sealing rings. The bellows and sealing rings are made of metal or elastomeric materials. Such assembly can be made at desired lengths and erected at site, with vacuum provided earlier or at site after erection. Only the area at the end connections or at the bends need to be insulated by conventional methods.

These junctions at end connections can be also sealed using vacuum. After leak check at end connections, which are connected with suitable standard coupling, a third tubular member whose inner diameter is greater than the outer diameter of the outer tube and of sufficent length and thickness previously positioned over one of the outer tube is slid to cover the end connection junction and sealed to the outer tubes on either side of the end connection by means of bellows type seals or other standard available methods of sealing. Adaptors provided on the third tube member are used to apply read & seal the annular space in the end connection junction with vacuum.

Similarly at the bends such methods of sealing can be adopted to give complete vaccum insulation.

Alternatively instead of sealing individual lenghts for vaccum insulation the inner & outer tube assembly without end cap members are joined at end connecton to desired lengths. After leak check at end connections, a third tube member slid and sealed at each end connection junction, and end cap members provided only at the extreeme two ends of process fluid flow.

Vaccum can be applied at one point and sealed over the entire annular space area between the two tube member including the end connection junctions and bends1 this will also enable to read vaccum level in the complete system which can be of several hundred meters.

This improved method of insulation provides a higher level of insulation with good degree of protection against environment, and lower cost since skilled labour is not required, and requires no expensive insulation materials and protective covers.

This improved method of insulation provides a high degree of effiency against thermal conductivity. Since vacuum is the medium, the only place where direct thermal conductivity takes place are at the either ends, through the end caps, and only a minimum amount through the contact points of the spacer members, as the spacer members are good thermal insulators.

The total thermal loss will be a small factor compared to the overall efficency.

The effect of convection can be made minimal with a higher degree of vacuum, and the effects or radiation can be minimised by providing suitable reflective paints or films on the outside of the outer tube, or by using reflective films, foils or paints on the outer side of the inner tube before joining the two tube members, depending on the temperature of process fluid, as per existing materials and methods.

This improved method of insulation is suitable for, insulating a wide range of process fluids, requiring thermal insulation in the range of -58 to +5880C, by suitable selection of tubes. levels of vacuum1 and sutiable spacer members, and end cap members.

The innovative features of this invention is the use of vacuum as a thermal insulation for process fluids, use of spacer members which are themselves good thermal insulators, with few contact points to minimise direct thermal conductivity to provide concentricity between the two tubes and use of end caps with provision for thermal expansion and use of third tubular member to provide vacuum insulation at junctions of the end connections and a total vaccum insulation from one end to the other.

For the purpose of illustration, an embodiment of this invention is described1 with reference to the accompanying drawing.

DETAILED DESCRIPTION OF THE DRAWINGS.

FIGURE 1: is a isometric view ot the embodiment.

FIGURE 2:is a section of one end of the embodiment wherein 1. Represents the outer tube member 2. Represents the inner tube member 3. Represents the end connections of the inner tube.

4. Represents the end cap member 5. Represents the spacer member 6. Represents the adaptor member used for vacuum application, reading and sealing.

7. Represents the places of fusion or bonding between the members.

8. Represents the annular space between tube members 1 and 2 and and enclosed by end cap member 4.

FIGURE 3:represents the plan of the spacer member 5, wherein 10.

the dotted line represents the outer diameter of the spacer member, the dotted circle 9. represents the inner diameter of the spacer member1 the holes in the spacer member are representated by 11.

FIGURE 4: is the sectional elevation at-AA of figure 3.

FIGURE 5:is an alternate spacer member 5. with minimal contact points 12.

FIGURE 6: is an alternate section of figure 2. wherein 4.

represents a different end cap member arrangement. 13. represents the bellows member.

14. represents the circular clamping members which clamp the bellows 13. with outer tube 1. and end cap member 4.

15. represents sealing ring located in a groove in the end cap member 4.

FIGURE 7: Represents an alternative section of fig.2 wherein 4. represents a thin flexible end cap member, fused/bonded to the outer and inner tubes 1 and 2 all around at 7.

FIGURE 8:Represents a section at a junction of two end connections of two inner tubes 2. wherein 16. represents the third tubular member 17. represents the coupling to connect both the end connections 3.

of the two inner tube members 2.

18. represents the annular space at the end connection junction which is applied with vacuum and sealed using adaptor member 6.

fused/bonded on to the third tube member 16.

13. represents the two bellow members clamped rigidly with clamping members 14. on either end of third tube member 16. and the respective outer tube memebers 1.

FIGURE 9: represents an alternate section of a junction of two end connections, wherein 19. represents flanged type coupling joining the end connections, 3. of the inner tubes. 8.represents the annular space between the two tube memebers, under vacuum.

The invention has been described and illustrated herein above with references to a particular embodiment. It is to be understood that obvious equivalents and variations known to persons skilled in the art are possible within the scope and ambit of the appended claims.

Claims

WE CLAIM

1. An improved thermal insulation method for process fluids using vacuum as the medium of insulation, comprising of an inner tubular member1 with several spacer members spaced and rigidly located over its outer surface and having an outer tubular member positioned over the inner tubular member, over the spacer memebers1 such that the inner tubular member projects out sufficiently at both ends with end connection means1 the annular gap between the inside of the outer member and the outside of the inner member, is sealed with suitable sealing means at both ends and with the adaptor means1 provided earlier on the outer tubular member or on the said sealing means, Vacuum is applied, read and sealed, in the annular space between the outer surface of the inner tubular member and the inner surface of the outer tubular member enclosed by the said sealing means.

2. The improved method as claimed in 1, wherein the outer and inner tubular members are both made of plastics, metals, or either.

3. The improved method as claimed in 1 and 2, wherein the length, diameter and thickness of the said tubular members are as necessary to suit the process requirements.

4. The improved method as claimed in any of the above claims wherein the spacer members are made out of high strength thermally non-conductive materials1 like engineering polymers, synthetic materials, and metals, etc..

5. The improved method as claimed in any of the above claims, wherein the spacer members are made to have minimum contact points with the respective tubular members.

6. The improved method as claimed in any of the above claims, wherein the sealing means comprise of end cap members in the form of an annular ring, with it's inner and outer diameter greater than the outer diameter of the inner tube member and less than the inner diameter of the outer tube member respectively and fused all round at the points of contact with the respective tubular member.

7. The improved method as claimed in any of the above claims, wherein the sealing means comprise of end cap members in the form of a cap which are sealed by fusing or bonding at the circular area of contact over the inner tube and the other end of cap members is sealed to the outer tube member with bellows type sealing.

8. The improved method as claimed in and of the above claims, wherein the sealing means comprise of end cap members, which are thin bellows type members directly bounded/fused on to the respective inner and outer tubular member all around the points of contact with the respective tubular member.

9. The improved method as claimed in 7, wherein the said end cap members has grooves to receive elastomeric sealing rings, to seal the end cap with the outer diameter of the outer tubular, members.

l.The improved method as claimed in any of the above claims, wherein the adaptor means comprise of standard end fittings capable of being applied, read and sealed with vaccum and the said adaptor means either screwed on or fused to the outer tubular member or the said end cap members.

11.The improved method as claimed in any of the above claims wherein the said end connections means of the said inner tube member is connected to another end connection means with coupling means and a third tubular member slid over the junction of the end connection and both ends of the third tube member sealed with the said sealing means to the respective outer tube member1 and vacuum applied, read and sealed in the annular space of the end connection junction with adaptor means provided on the said third tubular member.

12. The improved method as claimed in any of the above claims wherein the said end connection means of the said inner tube member is connected to another end connection means with coupling means and wherein the said sealing means at these end junctions are not provided with end cap members and several such end connections junctions provided and a third tube member slid over each end connection junction and sealed at either ends and sealing means with end cap members provided only at the extreme ends and vaccum applied, read and sealed for the entire assembly at one point through the adaptor means provided.

13.The improved method as claimed in any of the above claims, is described herein with particular reference to the accompanying drawings.

14.An improved method for VACUUM THERMAL INSULATION as claimed in any of the above claims.