US3400757A

US3400757A - Tubular heat exchanger with elastomeric outer sleeve

Info

Publication number: US3400757A
Application number: US606294A
Authority: US
Inventors: Campbell David Neil
Original assignee: Hymatic Engineering Co Ltd
Current assignee: Hymatic Engineering Co Ltd
Priority date: 1966-01-07
Filing date: 1966-12-30
Publication date: 1968-09-10
Anticipated expiration: 1985-09-10
Also published as: DE1551459A1; NL6700193A; GB1166941A

Description

Sept. 10, 1968 D. N. CAMPBELL ,7

TUBULAR HEAT EXCHANGER WITH ELASTOMERIC OUTER SLEEVE Filed Dec. 30,- 1966 INVENTOR wan, wflww M ATTORNEYS United States Patent 3,400,757 TUBULAR HEAT EXCHANGER WITH ELASTOMERIC OUTER SLEEVE David Neil Campbell, Redditch, England, assignor to The Hymatic Engineering Company Limited, Redditch, Worcestershire, England, a company of Great Britain Filed Dec. 30, 1966, Ser. No. 606,294 Claims priority, application Great Britain, Jan. 7, 1966,

854/66 5 Claims. (Cl. 165-134) ABSTRACT OF THE DISCLOSURE A heat exchanger comprising a finned t-ube helically wound round an inner tube which has an elastomeric sleeve shrunk round the finned helical tube and bulging inwards between its convolutions.

inner body comprising an inner tube in the form of a helix extending substantially co-axially within the outer tube and provided with annular disc-like heat-exchanging fine lying generally in planes containing the axis, in which the outer body includes an elastomeric sleeve shrunk round and embracing the exposed edges of the fins and bulging inwards between successive convolutions of the helix so as to constrain fluid passing between the fins at their outermost points to remain in contact with them for an appreciable distance.

Preferably one or each end of the elastomeric sleeve is sealed to a rigid tubular header. Thus the header at each end may conveniently be secured to a single rigid outer protective tube enclosing and protecting the elastorneric sleeve and sealed to it adjacent one or each of its ends. The sleeve may afford one or more annular ribs engaging the inner surface of the outer protective tube to form the seal or seals. It may be desirable that the part, or each part, of the sleeve forming the seal with the outer tube should be spaced longitudinally from the part which is shrunk round the inner body.

The invention may be put into practice in various ways. A specific embodiment will be briefly described by way of example with reference to the accompanying drawing, which is a fragmentary longitudinal section through the wall of a heat exchanger embodying the invention.

In the example the invention is applied to a heat exchanger of the type described in the present applieants United States of America patent application Ser. No. 570,062, now abandoned. The heat exchanger is embodied in a cryogenic cooler, working on the principle of the Joule-Thomson effect, to effect heat exchange between fluid travelling from the atmospheric end to the cold end of the apparatus and fluid returning in the opposite direction.

The heat exchanger is generally in the form of a straight tube and, in the drawing the inner portion, in the region of the axis 9, is occupied by other parts of the apparatus. The heat exchanger comprises an inner tube 10 in the form of a helix coaxial with the apparatus. The helical tube is provided with disc-like cooling fins 11 which accordingly lie generally in planes containing the axis of the helix. The finned helical tube is wound round a central axial tube 12 which is either provided with a grooved former having a helical groove to receive and. locate the innermost portions of the fins or (as shown) is provided with a helical single start or two start winding of thread 13 for the same purpose.

In such an arrangement it has hitherto been customary to provide a similar winding or windings of thread round the outer portion of the finned helical tube, and fit a rigid metal outer tube round the outer thread winding, the outer thread winding serving both to eifect a seal with the outer containing wall and to force the gas into more intimate contact with the heat exchange area. In practice it is necessary to exercise close dimensional control over the effective outside diameter of the wound assembly to ensure a good fit with the outer wall.

In the arrangement in accordance with the present invention the outer winding of thread is omitted, and instead a sleeve 15 of synthetic elastorneric material is placed over the finned helical tube and is shrunk in position. The sleeve is of a material such as irradiated polyvinyl chloride or irradiated polytetrafluoroethylene, which has the property that upon gentle heating it shrinks to conform closely to the surface to which it is applied.

The elastomeric sleeve is in turn contained within an outer rigid metal tube 16 which protects it, .and, at its ends, carries headers 18 for the inlet and outlet of fluid. Headers 18 may be rigid circular rings channel-shaped in cross-section with its flanges respectively secured to outer tube 16 and central tube 12. The headers are provided with apertures 19 to permit both insertion of coil 10 through the heat exchanger unit and, as may be located along the circumference of headers 18, to permit fluid to flow past the fins 11. The elastomeric sleeve is provided at its 'ends with external annular ribs 17 which form a seal with the outer rigid tube 16. These ribs may if desired be spaced longitudinally from the portion of the sleeve that is shrunk round the finned helical inner tube.

The outer rigid tube 16 may be afforded by the inner wall of an outer containing vessel such as a dewar vessel in which the assembly is removably mounted. The arrangement allows the assembly to be readily removed from the container with its header and pipe connections.

It will be appreciated that the elastomeric sleeve bulges inwards between successive convolutions of the helical finned tube, so as not only to locate the: tube but also to constrain the fluid flowing past the outermost points of the fins to remain in contact with them for an appreciable distance. This eliminates the possibility that certain portions of the gas may flow from end to end of the heat exchanger while hardly coming into contact with the fins of the inner tube.

What I claim as my invention and desire to secure by Letters Patent is:

1. A heat exchanger in a cryogenic cooler working on the principle of the Joule Thomson eifect including a generally tubular outer body and an elongated inner body comprising an inner tube in the form of a helix extending substantially co-axially within the outer tube and provided with annular disclike heat-exchanging fins lying generally in planes containing the axis, in which the outer body ineludes an elastomeric sleeve shrunk round and embracing the exposed edges of the fins and bulging inwards between successive convolutions of the helix so as to constrain fluid passing between the fins at their outermost points to remain in contact with them for an appreciable distance.

2. A heat exchanger as claimed in claim 1 in which at least one end of the elastomeric sleeve is sealed to a rigid header.

3. A heat exchanger as claimed in claim 2 in which 3 '4 headers at each end are, secured to a single rigid outer References Cited protective tube enclosing and protecting the elastomeric UNITED STATES PATENTS sleeve and sealed to it adjacent at least one of its ends. 2,643,863 6/1953 Buschow 165 180 X 4. A heat exchanger as claimed in claim 3 in which the 3,326,015 6/1967 Webster 62 514 sleeve affords at least one annular rib engaging the inner 5 FOREIGN PATENTS surface of the outer protective tube to form the seal. 861 2/1961 Great Britain I 5. A heat exchanger as claimed in claim 2 in which at 938372 10/1963 Great Britain:

least one part of the sleeve forming the seal with the outer rigid tube is spaced longitudinally from the part 10 ROBERT Examinerwhich is shrunk round the inner body. A. W. DAVIS, Assistant Examiner.