GB1594136A - Methods of construction of central heating radiators - Google Patents

Methods of construction of central heating radiators Download PDF

Info

Publication number
GB1594136A
GB1594136A GB49847/77A GB4984777A GB1594136A GB 1594136 A GB1594136 A GB 1594136A GB 49847/77 A GB49847/77 A GB 49847/77A GB 4984777 A GB4984777 A GB 4984777A GB 1594136 A GB1594136 A GB 1594136A
Authority
GB
United Kingdom
Prior art keywords
radiator
header
heat
section
panels
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB49847/77A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Simpson V J
Original Assignee
Simpson V J
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Simpson V J filed Critical Simpson V J
Priority to GB49847/77A priority Critical patent/GB1594136A/en
Publication of GB1594136A publication Critical patent/GB1594136A/en
Expired legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F9/00—Casings; Header boxes; Auxiliary supports for elements; Auxiliary members within casings
    • F28F9/26—Arrangements for connecting different sections of heat-exchange elements, e.g. of radiators
    • F28F9/262—Arrangements for connecting different sections of heat-exchange elements, e.g. of radiators for radiators
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D1/00—Heat-exchange apparatus having stationary conduit assemblies for one heat-exchange medium only, the media being in contact with different sides of the conduit wall, in which the other heat-exchange medium is a large body of fluid, e.g. domestic or motor car radiators
    • F28D1/02—Heat-exchange apparatus having stationary conduit assemblies for one heat-exchange medium only, the media being in contact with different sides of the conduit wall, in which the other heat-exchange medium is a large body of fluid, e.g. domestic or motor car radiators with heat-exchange conduits immersed in the body of fluid
    • F28D1/04—Heat-exchange apparatus having stationary conduit assemblies for one heat-exchange medium only, the media being in contact with different sides of the conduit wall, in which the other heat-exchange medium is a large body of fluid, e.g. domestic or motor car radiators with heat-exchange conduits immersed in the body of fluid with tubular conduits
    • F28D1/053—Heat-exchange apparatus having stationary conduit assemblies for one heat-exchange medium only, the media being in contact with different sides of the conduit wall, in which the other heat-exchange medium is a large body of fluid, e.g. domestic or motor car radiators with heat-exchange conduits immersed in the body of fluid with tubular conduits the conduits being straight
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F1/00—Tubular elements; Assemblies of tubular elements
    • F28F1/10—Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses
    • F28F1/12—Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses the means being only outside the tubular element
    • F28F1/14—Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses the means being only outside the tubular element and extending longitudinally
    • F28F1/16—Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses the means being only outside the tubular element and extending longitudinally the means being integral with the element, e.g. formed by extrusion
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D21/00—Heat-exchange apparatus not covered by any of the groups F28D1/00 - F28D20/00
    • F28D2021/0019—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for
    • F28D2021/0035—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for for domestic or space heating, e.g. heating radiators
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Geometry (AREA)
  • Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)

Description

(54) IMPROVEMENTS IN THE METHODS OF CONSTRUCTION OF CENTRAL HEATING RADIATORS (71) I, VICTOR JOHN SIMPSON, a British subject, of Tally Ho, Onslow Road, Burwood Park, Walton-on-Thames, Surrey, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following state ment This invention relates to a method of construction and manufacture of hot water radiators used generally for the purpose of central heating. The system of construction allows radiators of any desired length or height to be produced from a common extrusion die thus eliminating the need for moulds or dies for each height of radiator.A further advantage of this invention lies in the improved heat output which is in excess of three times that of a flat panel radiator of the same dimensions.
The main feature of this invention is the method by which two sections of extruded metal are interlocked to provide a fluid- and pressure- tight passage for the fluid within.
The sections of extruded metal are arranged so that one section forms the headers and the other section forms the heat exchanger.
The header sections interlock with the desired number of heat exchanger sections. The heat exchanger sections are located to link together the flow and return headers which complete the integral water circuit.
The heat exchanger section is so arranged to take full advantage of the differing thermal characteristics between the water to heat exchanger heat transfer coefficient and the air to heat exchanger film coefficient. The construdtion allows for this to be achieved by arranging longitudinal fins running parallel to the waterway through the heat exchanger. The fins are formed simultaneously with the water tube in the heat exchanger. In a preferred arrangement the surface area of the air-heating surface may be twenty times greater than the surface area inside the tube through which the water passes. Since the longitudinal fins are formed in the same metal as the water tube there is no mechanical or other bond to form a barrier to conducted heat flow within the structure of the heat exchanger.Unlike a conventional panel hot water radiator or cast iron or cast aluminium radiator where the internal internal surface area in contact with the heating fluid is roughly proportional to the external surface in contact with the air, which latter surface area determines the quantity of heat emission, in the case of this invention both sides of the metal forming the heat exchanger constructed around the fluid path are exposed to dissipate heat to the air. It therefore follows that for a given thickness or weight of material the utilization of both sides greatly reduces the overall weight of basic material required in the heat exchanger to achieve the same unit of heat emission.
The fluid or water headers are constructed from a metal extrusion in the same manner as the heat exchanger section. The header sections consist of a tubular core from which extends the capping profile, the edges of which have a longitudinal lip running parallel to the central tube. The ends of the header may conveniently be internally screwed to form a pipe connection.
The internal face of the tubular header is thickened in section to conveniently abut against the end of the heat exchanger profile.
A pressure tight connection between the waterway in the header and the waterway in the heat exchanger is achieved by the use of multiple chamfered barrel nipples one end of which presses as an interference fit into the tube formed in the heat exchanger section whilst the other end of the barrel nipple is pressed into suitable holes bored into the header section at right angles to the header tube. The holes bored into the header tube are also an interference fit to the chamfered nipples.
Any desired number of heat exchanger sections of any desired equal length may thus be laid side by side and headers of suitable length placed so that the chamfered barrel nipples engage both the holes bored in the header and the tube formed in the heat exchanger section. The headers may then be pressed together until the nipples are fully engaged and the inner face of the header is in abutment with the end of the heat exchanger profile.
In order that the assembled sections should be retained in the assembled position a slot may be cut across the fins of the heat exchanger section adjacent to each end of the section.
This slot may be on either or both sides of the heat exchanger section. It may be formed simultaneously with the operation where the heat exchanger section is cut to required lengths. It now follows that the taper lip on the edge of the capping profile which is an integral part of the header previously described is adjacent to the slots formed into the ends of the heat exchanger section. The lip is then pressed into the slots which are intersected at right angles. The lip thus forms a detent in the slots in the ends of the heat exchanger sections thus permanently locking the assembly together in such a manner that the load of any hydrostatic pressure within the waterway is carried by the detent engaged in the slots of the heat exchanger section. This feature removes any axial load acting on the taper nipples.
Assembly as described can be carried out at high speed with the minimum of skill.
An embodiment of the invention will now be described by way of example, with reference to the accompanying drawings in which: Figure 1 is a partial transverse vertical section through a hot-water radiator constructed in accordance with the invention; Figure 2 is a partial side elevation of the radiator of Figure 1; and, Figure 3 is a section on the line III-III of Figure 2.
As shown in the drawings a hot water radiator 10 constructed in accordance with the invention comprises a series of heatexchange panels 11 extruded from aluminium and having a central circular waterway 12 from diametrically opposed sides of which extend two webs; the web 13 having a root portion 14 which is thicker than an outer portion 15 and terminating in an off-set extremity 16 and the other web 17 having corresponding portion 18 and 19 but terminating in a plain extremity 20 which is slightly shorter than the extremity 16.
From each side of each of the webs 13 and 17 project three identical fins 21 which each terminate in a transverse flange 22. A slot 23 is formed near each end of each flange 22 and of each fin 21 to define channels running parallel to the end faces of the panels 11.
The heat-exchange panels 11 are capped at each end by identical headers, only the upper header 24 being shown in the drawings. As shown in Figure 1, the header 24 comprises a generally circular core 25 having a thickened base portion 26 with a flat face 27 which is drilled at intervals to form a series of holes, one of which, indicated by the reference 28, is shown in Figure 1. The upper, outer surface of the wall of the core 25 is formed with a series of decorative serrations 29 and from the core 25, at a point near one end of the serrated portion, there extends a capping flange 30 terminating in a tapered internal lip 31.A similar flange 32 extends from near the other end of the serrated portion and terminates in a lip 33, the flanges 30 and 32 together having generally an outwardly divergent channel section within which lies the core 25, the distance between the lips being, before assembly, slightly less than the thickness of the panels 11.
A chamfered barrel nipple 34 is inserted in an interference fit into each of each waterway 12.
To form the radiator 10 as many panels 11 of any desired length and as are necessary to form the desired width are laid said by side so that the flange 16 of one panel 11 overlies the terminal portion 20 of an adjacent panel 11.
The slots 23 may be formed at the same time as the panels 11 are cut to length.
Two corresponding lengths of header extrusion are then cut to form the upper header 24 and the lower header, the core 25 of each header being tapped at each end to receive convention flow and return connections, plugs or bleeder valves. "Loctite" (Registered Trade Mark) or similar jointing compound is then applied to the exposed portions of the chamfered nipples 34 and a header placed against each end of the juxtaposed panels 11, with the nipples 34 being received in the holes 28, the previously mentioned intervals between which correspond to the intervals between the nipples 34 projecting from the assembled panels 11.
The headers are then pressed together so that the nipples 34 are fully received, also in an interference fit, in the holes 28 and then the flanges 30 and 32 are clamped together so that the lips 31 and 33 are received in the respective channels defined by the slots 23. The consequent detent formed by the engagement of the flat inner face of the lips 31 and 32 with the outer side wall of the respective slots 23 ensures that the headers are positively interlocked and strongly resist any force tending to prise them away from the panels 11 and any axial load on the nipples 34 is relieved.
The above described construction allows a radiator of high thermal efficiency to be formed of aluminium extrusions which have a characteristic of requiring only about half the weight of metal required for a die cast aluminium radiator of the same heat output or approximately one fifth the weight of a conventional steel panel radiator of the same heat emission.
The resultant reduction in material required for a given heat minimum results in considerable cost advantage.
Each panel 11 could if desired have two or more waterways each pair being joined by an integral web.
WHAT I CLAIM IS: 1. A radiator for use in hot water central heating systems and constructed from extruded aluminium of aluminium alloy sections, one configuration of section having at least one tubular duct extending therethrough being used as the heat exchanger which interconnects other configurations of section which form the fluid flow and return headers and which each incorporate a locking flange which interlocks with a respective external slot pre
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. heat exchanger section. It may be formed simultaneously with the operation where the heat exchanger section is cut to required lengths. It now follows that the taper lip on the edge of the capping profile which is an integral part of the header previously described is adjacent to the slots formed into the ends of the heat exchanger section. The lip is then pressed into the slots which are intersected at right angles. The lip thus forms a detent in the slots in the ends of the heat exchanger sections thus permanently locking the assembly together in such a manner that the load of any hydrostatic pressure within the waterway is carried by the detent engaged in the slots of the heat exchanger section. This feature removes any axial load acting on the taper nipples. Assembly as described can be carried out at high speed with the minimum of skill. An embodiment of the invention will now be described by way of example, with reference to the accompanying drawings in which: Figure 1 is a partial transverse vertical section through a hot-water radiator constructed in accordance with the invention; Figure 2 is a partial side elevation of the radiator of Figure 1; and, Figure 3 is a section on the line III-III of Figure 2. As shown in the drawings a hot water radiator 10 constructed in accordance with the invention comprises a series of heatexchange panels 11 extruded from aluminium and having a central circular waterway 12 from diametrically opposed sides of which extend two webs; the web 13 having a root portion 14 which is thicker than an outer portion 15 and terminating in an off-set extremity 16 and the other web 17 having corresponding portion 18 and 19 but terminating in a plain extremity 20 which is slightly shorter than the extremity 16. From each side of each of the webs 13 and 17 project three identical fins 21 which each terminate in a transverse flange 22. A slot 23 is formed near each end of each flange 22 and of each fin 21 to define channels running parallel to the end faces of the panels 11. The heat-exchange panels 11 are capped at each end by identical headers, only the upper header 24 being shown in the drawings. As shown in Figure 1, the header 24 comprises a generally circular core 25 having a thickened base portion 26 with a flat face 27 which is drilled at intervals to form a series of holes, one of which, indicated by the reference 28, is shown in Figure 1. The upper, outer surface of the wall of the core 25 is formed with a series of decorative serrations 29 and from the core 25, at a point near one end of the serrated portion, there extends a capping flange 30 terminating in a tapered internal lip 31.A similar flange 32 extends from near the other end of the serrated portion and terminates in a lip 33, the flanges 30 and 32 together having generally an outwardly divergent channel section within which lies the core 25, the distance between the lips being, before assembly, slightly less than the thickness of the panels 11. A chamfered barrel nipple 34 is inserted in an interference fit into each of each waterway 12. To form the radiator 10 as many panels 11 of any desired length and as are necessary to form the desired width are laid said by side so that the flange 16 of one panel 11 overlies the terminal portion 20 of an adjacent panel 11. The slots 23 may be formed at the same time as the panels 11 are cut to length. Two corresponding lengths of header extrusion are then cut to form the upper header 24 and the lower header, the core 25 of each header being tapped at each end to receive convention flow and return connections, plugs or bleeder valves. "Loctite" (Registered Trade Mark) or similar jointing compound is then applied to the exposed portions of the chamfered nipples 34 and a header placed against each end of the juxtaposed panels 11, with the nipples 34 being received in the holes 28, the previously mentioned intervals between which correspond to the intervals between the nipples 34 projecting from the assembled panels 11. The headers are then pressed together so that the nipples 34 are fully received, also in an interference fit, in the holes 28 and then the flanges 30 and 32 are clamped together so that the lips 31 and 33 are received in the respective channels defined by the slots 23. The consequent detent formed by the engagement of the flat inner face of the lips 31 and 32 with the outer side wall of the respective slots 23 ensures that the headers are positively interlocked and strongly resist any force tending to prise them away from the panels 11 and any axial load on the nipples 34 is relieved. The above described construction allows a radiator of high thermal efficiency to be formed of aluminium extrusions which have a characteristic of requiring only about half the weight of metal required for a die cast aluminium radiator of the same heat output or approximately one fifth the weight of a conventional steel panel radiator of the same heat emission. The resultant reduction in material required for a given heat minimum results in considerable cost advantage. Each panel 11 could if desired have two or more waterways each pair being joined by an integral web. WHAT I CLAIM IS:
1. A radiator for use in hot water central heating systems and constructed from extruded aluminium of aluminium alloy sections, one configuration of section having at least one tubular duct extending therethrough being used as the heat exchanger which interconnects other configurations of section which form the fluid flow and return headers and which each incorporate a locking flange which interlocks with a respective external slot pre
formed in the side of each heat-exchanger section, the arrangement being such as to result in a rigid assembly with pressure tight fluid connection between the headers and the duct or ducts of each heat-exchanger section.
2. A radiator as claimed in Claim 1, in which the flow and return headers each incorporate two locking flanged which interlock with respective slots pre-formed in opposite sides of the heat-exchanger.
3. A radiator as claimed in Claim I or 2, in which fins projecting from at least one face of the heat-exchanger are provided at each end with a slot in which an end portion of a respective flange is engaged.
4. A radiator as claimed in Claim 3, in which said end portion is an internal lip which is arranged for positive engagement with a wall of the slot to resist any force urging the header away from the heat-exchanger.
5. A radiator as claimed in any preceding claim, in which the flow and return headers are drilled at intervals to coincide with the position of the tubular duct or ducts in each heatexchanger section and in which in respect of the or each said duct, one end of a doubleended chamfered barrel nipple is engaged with and pressed into the end of said duct and the other end of the chamfered nipple is pressed into the corresponding hole drilled into the header at right angles to the cored flow path, thus forming a fluid pressure tight connection at each joint between the heat-exchanger duct and the header.
6. A radiator as claimed in any preceding claim, in which a face of each header abuts the corresponding end face of the heat-exchanger.
7. A radiator as claimed in Claim 1 and substantially as herein described.
8. A radiator substantially as hereinbefore described with reference to the accompanying drawings.
GB49847/77A 1978-05-30 1978-05-30 Methods of construction of central heating radiators Expired GB1594136A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB49847/77A GB1594136A (en) 1978-05-30 1978-05-30 Methods of construction of central heating radiators

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB49847/77A GB1594136A (en) 1978-05-30 1978-05-30 Methods of construction of central heating radiators

Publications (1)

Publication Number Publication Date
GB1594136A true GB1594136A (en) 1981-07-30

Family

ID=10453763

Family Applications (1)

Application Number Title Priority Date Filing Date
GB49847/77A Expired GB1594136A (en) 1978-05-30 1978-05-30 Methods of construction of central heating radiators

Country Status (1)

Country Link
GB (1) GB1594136A (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2167549A (en) * 1984-11-24 1986-05-29 Holden William J Central heating radiator and method of construction thereof
EP0183211A2 (en) * 1984-11-23 1986-06-04 Norsk Hydro A/S Heat exchanger modules and method of manufacturing
GB2170000A (en) * 1985-01-17 1986-07-23 British Alcan Aluminium Ltd Space heating radiator
US4856581A (en) * 1986-08-08 1989-08-15 Gennaro Santoro Heat exchanger unit formed of a plurality of modular units including connection couplers
ITAN20080050A1 (en) * 2008-11-28 2010-05-29 Rag All Spa FINNED RADIATOR IN ALUMINUM PROFILES OF REDUCED WEIGHT AND HIGH THERMAL PERFORMANCE

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0183211A2 (en) * 1984-11-23 1986-06-04 Norsk Hydro A/S Heat exchanger modules and method of manufacturing
EP0183211A3 (en) * 1984-11-23 1986-10-29 Norsk Hydro A/S Heat exchanger modules and method of manufacturing
GB2167549A (en) * 1984-11-24 1986-05-29 Holden William J Central heating radiator and method of construction thereof
GB2170000A (en) * 1985-01-17 1986-07-23 British Alcan Aluminium Ltd Space heating radiator
US4703889A (en) * 1985-01-17 1987-11-03 British Alcan Aluminium Limited Space heating radiator
US4856581A (en) * 1986-08-08 1989-08-15 Gennaro Santoro Heat exchanger unit formed of a plurality of modular units including connection couplers
ITAN20080050A1 (en) * 2008-11-28 2010-05-29 Rag All Spa FINNED RADIATOR IN ALUMINUM PROFILES OF REDUCED WEIGHT AND HIGH THERMAL PERFORMANCE
WO2010061263A1 (en) * 2008-11-28 2010-06-03 Rag-All S.P.A. Fin radiator made of mechanically connected aluminium section bars

Similar Documents

Publication Publication Date Title
US3467180A (en) Method of making a composite heat-exchanger tube
US6173493B1 (en) Modular heat exchanger and method of making
US5311661A (en) Method of pointing and corrugating heat exchange tubing
US5190101A (en) Heat exchanger manifold
US4688311A (en) Method of making a heat exchanger
US4923002A (en) Heat exchanger rib
US4936379A (en) Condenser for use in a car cooling system
JP4099513B2 (en) Metal plate for flat tube manufacturing, flat tube and flat tube manufacturing method
US4341346A (en) Radiators for use in hot water central heating systems
US5704423A (en) Flat tube for heat exchanger
US5441105A (en) Folded parallel flow condenser tube
CZ261396A3 (en) Heat-exchanging pipe for heating boilers, particularly for gas heating boilers with high efficiency
EP0044365A1 (en) Radiators for use in hot water central heating systems
US4789027A (en) Ribbed heat exchanger
US4509672A (en) Method of constructing headers of heat exchangers
US3732921A (en) Heat exchanger
CN105121988A (en) Folded tube multiple bank heat exchange unit
GB1594136A (en) Methods of construction of central heating radiators
EP0461781B1 (en) Heat exchanger
US6354002B1 (en) Method of making a thick, low cost liquid heat transfer plate with vertically aligned fluid channels
AU747879B2 (en) Modular heat exchanger and method of making
CA1139301A (en) Radiators for use in hot water central heating systems
US4381033A (en) Header construction
JP2006336885A (en) Heat exchanger and its manufacturing method
US4274186A (en) Heat exchanger

Legal Events

Date Code Title Description
PS Patent sealed
429A Application made for amendment of specification (sect. 29/1949)
732 Registration of transactions, instruments or events in the register (sect. 32/1977)
429C Application to amend the specification withdrawn (sect. 29/1949)
429A Application made for amendment of specification (sect. 29/1949)
429H Application (made) for amendment of specification now open to opposition (sect. 29/1949)
429D Case decided by the comptroller ** specification amended (sect. 29/1949)
SP Amendment (slips) printed
PE20 Patent expired after termination of 20 years

Effective date: 19980529