GB2113201A - The manufacture of evacuated containers - Google Patents

Abstract

A process for the manufacture of a thermal solar collector of the type comprising a heat pipe (5) partially enclosed within a glass vacuum jacket from an open tube, one end of which is sealed into the neck (6) of a glass envelope (7), comprises the steps of providing a region of reduced bore (10) at the enveloped end of the tube, locating fusible sealing means in the tube adjacent the region of reduced bore, evacuating the envelope via the tube, and melting the fusible means so that it seals the tube on solidifying. The fusible means may be a metal ball (9) coated with silver solder. The process avoids the creation of a seal in the glass envelope. <IMAGE>

Description

SPECIFICATION The manufacture of evacuated containers This invention relates to the manufacture of assemblies of the kind comprising an evacuated container enclosing an end of a sealed evacuated pipe. More especially it relates to the manufacture of evacuated tube heat pipe thermal solar collectors, that is to say solar collectors of the type comprising a directly or indirectly heated solarheated heat pipe partially enclosed within a transparent vacuum jacket. In such collectors (subsequently referred to simply as heat pipe solar collectors) the heat pipe, which consists of an evacuated sealed metal tube partially filled with a volatile liquid, serves to transfer heat from the collector to an external heat exchanger.The collector end of the heat pipe is held lower than the heat exchanger, so that in use, the volatile liquid collects at the heated end of the heat pipe, boils, condenses at the far end of the heat pipe and transfcrs heat to the heat exchanger, and trickles back to the heated end of the pipe (preferab!y aided by a suitable capillary network) in a continuous process. Not only does the heat pipe act as an efficient thermodynamic heat conductor, but it aiso acts as a thermal diode, preventing loss of heat from the collector via the heat exchanger, as would tend to occur during the night For example. The heat pipe is therefore largely responsible for the success of such collectors, and any improvement in the manufacture or incorporation of a heat pipe into a solar thermal collector is highly desirable.

Hitherto, heat pipe solar collectors have been made from preformed heat pipes and open tubular glass vacuum jackets. In this method, the heat pipe is inserted into one end of the vacuum jacket so that it projects therefrom, and the vacuum jacket is evacuated through an axial tubular extension at the opposite end of the jacket. The tubular extension is then sealed off.

This process suffers from the disadvantage that two pump stems are required -- one for the evacuation of the heat pipe and one for the evacuation of the vacuum jacket. Furthermore, since the metal seal is somewhat fragile, the vacuum jacket must be handled carefully when it is being evacuated and sealed off. The resulting glass seal creates a further point of weakness.

According to the present invention, a process for the manufacture of an assembly of the kind referred to comprises the steps of providing a region of reduced bore at one end of the tube, locating fusible scaling means comprising a quantity of fusible material within or closely adjacent to said region in such a manner as to permit gas to pass into the tube through said reduced bore, sealing the metal tube through the wall of the otherwise closed container with said end of the tube lying within the container, evacuating the container through the tube, sealing said reduced bore by heating the fusible sealing means to a temperature sufficient to melt the fusible material and then permitting it to solidify, and subsequently sealing the exterior end of the tube.

Where the pipe is required to contain a quantity of liquid, for example the volatile liquid in the case of a heat pipe solar collector the liquid will, of course, be introduced into the pipe before the final sealing step. Preferably the liquid in such a case is introduced through the vacuum system and where the tube is formed of a suitable metal the exterior end of the tube is conveniently sealed by a cold welding technique, air being excluded from the inside of the metal tube by the vacuum system throughout these steps of the process. Preferably a getter is mounted on the outside of the tube adjacent the region of reduced bore, and is melted inductively immediately before the interior end of the tube is sealed. Any dissolved gases released when the getter is melted may be continuously pumped off by the vacuum system prior to sealing the tube.

The tube is preferably wholly of metal and in the casc of a heat pipe solar collector is preferably of a metal having a high thermal conductivity such as copper. The fusible sealing means may comprise a metal spheroid supported by fusible material, said sealing means in turn being supported at said reduced bore portion of said tube, for example at a frustoconical surface thereof. The frusto-conical surface is preferably providecl by a tubular metal plug inserted into the tube. The fusible material may be applied as a coating to the spheroid or to said frusto-conical surface, in which case a gas flow path may be provided by one or more flutes or other passages formed in the fusible material.Alternatively the fusible material may be in the form of a cage which at least partially encloses the metal spheroid and is engaged by the frusto-conical surface. The cage may be formed from a strip of fusible material of length approximately equal to the circumference of the spheroid divided along its length by transverse slots. The strip is then wrapped around the equator of the spheroid and the sides of the strip bent inwards to form a spheroidal cage. In this case the slots in the strip constitute a gas flow path between the metal spheroid and the frustoconical surface.

In yet another method of carrying out the invention the sealing means may simply consist of a quantity of fusible material, supported above a surface pierced by a plurality of holes forming said region of reduced bore the holes being of sufficiently small cross-section to retain the molten material following the heating thereof by virtue of its surface tension.

In a further method of carrying out the invention, the said reduced bore is formed by a curved tubular extension from the said tube, the sealing means consists of a length of fusible material, which is inserted into the tubular extension so as to lie above and adjacent to a Ubend in the tubular extension, and, on melting flows into at least said bend and thereby blocks the tubular extension.

In the case where a heat pipe solar collector is made by a method according to the invention, the fusible material is preferably silver solder, owing to the high temperatures reached by the heat pipe in use (up to 3000 C). The heat pipe is preferably made of copper, since this metal may easily be cold welded. The volatile liquid is preferably water.

The invention will now be described more specifically, with reference to the accompanying drawings, of which: Figure 1 shows a method of manufacturing a heat pipe solar collector according to the invention; and Figures 2, 3 and 4 illustrate alternative methods of providing silver solder for the embodiment shown at insert 1A.

Referring to Figure 1, a vacuum system 1 is shown, consisting of a diffusion vacuum pump 2 and a vacuum line provided with valves 3 and 4.

The vacuum system is connected to a copper tube 5 which is sealed at 6 to a glass jacket 7. The lower-end of the copper tube may take either of the alternative forms shown in section at 1A and 1 B respectively. Insert 1A shows a tubular brass plug inserted into the tube 5 supporting a metal ball 9 on a frusto-conical part 10 of its bore. The tube 5 carries a barium getter 11. The ball 9 is slightly separated from the part 10 of the bore by silver solder (not shown) so that a free flow path exists throughout the tube 5. This will be described in more detail subsequently.

Insert 1 B shows a tubular extension 12 carried by a brass plug 13 inserted into the tube 5. A stick of silver solder inserted into the tube 12 lies immediately above a U-bend in said tube but does not close the tube.

In either case the jacket 7 is evacuated, via the tube 5 by opening the valve 3 and actuating the diffusion pump. The lower end of the tube 5 is heated by the RF induction coil 15, with the result that the barium getter 11 melts and emits gases which are continuously pumped off by the vacuum system. The lower end of the tube 5 is then sealed off by increasing the power input to the induction coil 1 5 and thereby melting the silver solder, which either seals the joint at 10 (insert 1 A) or flows into the base of the U-bend at 12 (insert 1 B).

The vacuum in the jacket 7 is preferably about 10-s Torr. The flF heating coil 1 5 is then switched off, the lower end of the tube 5 allowed to cool, and the valve 3 is closed. Valve 4 is then opened, allowing a predetermined quantity of water to flow into the tube 5 from a reservoir 1 6. Valve 4 is then closed and the exterior end of the tube 5 is sealed off by a cold welding tool 17.

Figure 2 is a plan view traken in the direction A2 from the insert 1 A, and shows one method of applying solder to the metal ball. A tubular brass plug 8 inserted into the tube 5 supports the metal ball 9 on a frusto-conical region 10 of its bore.

This region is tinned with silver solder, and a free flow path between the wide-bore section 1 8 and the narrow-bore section 1 9 of the tube 5 is provided by a longitudinal flute 20 in the tinned surface 10.

Figure 3 shows an alternative arrangement, similar to that shown in insert 1 A, but in more detail. The ball 9 is tinned with 3 blobs of silver solder 21 equally spaced around its equation.

These support the ball on a frusto-conical region 10 of the bore of the plug 8 as shown at 22, and form passages such as 23 between the narrowbore section 19 and the wide-bore section 1 8 of the plug. The equatorially spaced solder blobs ensure that the ball is supported by solder irrespective of the way it hits the surface 10 when it is dropped into the plug.

Figure 4, schematically shows three stages A, B and C in forming a cage of silver solder which may be used to surround the metal ball in an alternative embodiment of the arrangement shown in insert 1 A. A slotted strip of silver solder is bent into a short tube as shown in B, and the ends of the tube are pinched in towards the axis of the tube around the metal ball (not shown) so as to enclose it within a three-ribbed cage shown in C. The caged ball is dropped into the tubular plug 8 shown in insert 1 A, and the gaps 24 form a free flow path irrespective of the orientation of ball.

Claims (10)

1. A process for the manufacture of an assembly comprising an evacuated container enclosing an end of a sealed evacuated tube; comprising the steps of providing a region of reduced bore at one end of the tube, locating fusible sealing means comprising a quantity of fusible material within or closely adjacent to said region in such a manner as to permit gas to pass into the tube through said reduced bore, sealing the metal tube through the wall of the otherwise closed container with said end of the tube lying within the container, evacuating the container through the tube, sealing said reduced bore by melting and then solidifying the fusible material and subsequently sealing the exterior of the tube.

2. The process of Claim 1 further including the step of introducing a volatile liquid into and exhausting air from said tube before it is sealed.

3. A process according to Claim 1 or Claim 2 wherein said fusible sealing means comprises a metal spheroid supported by fusible material and is initially supported at said reduced bore portion of said tube.

4. A process according to Claim 3 wherein said fusible material is in the form of a cage round said spheroid and is supported by a frusto-conical surface of said reduced bore portion.

5. A process according to Claim 1 or Claim 2 wherein said fusible means is initially supported immediately above a U-bend in said reduced bore portion.

6. A process according to Claim 1 or Claim 2 wherein said fusible means is initially supported above a surface pierced by a plurality of holes forming said region of reduced bore, the holes being of sufficiently small cross-section to retain said sealing means when it is molten.

7. An evacuated tube heat pipe thermal solar collector produced by the process of any preceding Claim.

8. A process for producing an evacuated tube heat pipe thermal solar collector substantially as described hereinabove with reference to Figure 1A or 1 B in the accompanying drawings.

9. A process for producing an evacuated tube heat pipe solar thermal collector substantially as described hereinabove with reference to Figure 2 of the accompanying drawings.

10. A process for producing an evacuated tube heat pipe solar thermal collector substantially as described hereinabove with reference to Figure 3 of the accompanying drawings.

1 A process for producing an evacuated tube heat pipe solar thermal collector substantially as described hereinabove with reference to Figure 4 of the accompanying drawings.