US3195624A

US3195624A - Heat exchangers

Info

Publication number: US3195624A
Application number: US229364A
Authority: US
Inventors: Richards William Gwynfab; Burton Robin Sydney
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1961-11-16
Filing date: 1962-10-09
Publication date: 1965-07-20
Anticipated expiration: 1982-07-20
Also published as: DE1401658A1; GB944772A

Description

y 1965 w. G. RICHARDS ETAL 3,

HEAT- EXCHANGERS Filed Oct. 9', 1962 4 Sheets-Sheet 1 lllll INVENTORS WILLIAM GWYNFAB RiCHARDS ROBIN SYDNEY BURTON BY MORGAN, FINNEGAN, DURHAM a PINE ATTORNEYS 1965 w. G. RICHARDS ETAL 3,

HEAT EXGHANGERS Filed Oct. 9, 1962 4 Sheets-Sheet 2 FIG-IA INVENTORS WILLIAM GWYNFAB RICHARDS ROBIN SYDNEY BURTON BY MORGAN, FINNEGAN, DURHAM a PINE ATTORNEYS July 20, 1965 w. s. RICHARDS ETAL 3,195,624

HEAT xcmmms Filed Oct. 9, 1962 4 Sheets-Sheet 5 INVENTORS WILLIAM GWYNFAB RICHARDS BY ROBIN SYDNEY BURTON MORGAN,F!NNEGAN,DURHAM 8 PINE ATTORNEYS July 20, 19 65 w. e. RICHARDS ETAL HEAT EXGHANGERS Filed Oct. 9, 1962 4 Sheets-Sheet 4 Pia-4c v v INVENTOR5 WILLUXM GWYNFAB RICHARDS ROBIN SYDNEY BURTON BY MORGAN, FINNEGAN, DURHAM 8 PINE ATTORNEYS Patented July 2Q, 1%55 tine 3,l5,624 HEAT EXfll-EANGERS William Gwyniah Richards and Robin Sydney Burton, Sunhury-on-Thames, Middlesex, England, assignors to The Eritish Eetroleurn Company Limited, London, England, a British joint-stock corporation Filed Got. 9, 1962, Ser. No. 229,36 Claims priority, application Great Britain, Nov. 16, N61, 41,034/61 9 tllaims. (QR. 165-153) This invention relates to an improved heat exchanger, more particularly to an improved head cover for a heat exchanger oi the return pass tube and shell type. The term heat exchanger includes condensers within its scope.

Tube and sheh heat exchangers are Well known and generally comprise a cylindrical shell encasing a tube bundle. The tube bundle comprises a number of tubes, set in rows known as banks, the tubes being kept in position by header plates into which the ends of the tubes are expanded. Recessed head covers are set over the header plates. inlets and outlets to the shell and head covers are provided in such manner that, in use, one fluid passes through the tubes of the bundle and a second fluid passes through the shell and over the tubes of the bundle.

A common type of tube and shell heat exchanger is the return pass type in which the fluid flowing through the tubes passes along a first bank of tubes, known as a forward bank, in one direction, emerges from the tubes, has its direction of flow reversed by contact with a head cover, known as the return head cover, is deflected into a second bank of tubes, known as a return bank, and returns along the second bank in the opposite direction to its direction of passage through the first bank. Before entering the second bank of tubes the fluid must necessarily impinge on the header plate into which the inlet ends of the tubes forming the second bank are set. This plate is referred to as the return header plate. Several forward and return banks are usually present.

When the difference in temperature between the tubes and the shell is likely to be appreciable, it is necessary to make provision for the expansion of the one relative to the other. This is generally allowed for by employing a floating head cover. In heat exchangers of the floating head cover type, one of the cover plates is rigidly fixed in position with respect to the shell, the other, known as the floating head cover, is free to move longitudinally within the shell and is usually encased by a further cover.

In general, heat exchangers are constructed with tubes, head covers, header plates and shells of mild steel. For certain duties, e.g. for heat transfer between oil and sea water, with sea Water passing through the tubes, mild teel is unsatisfactory since it tends to corrode badly. For

such duties, tubes, header plates and head covers are constructed from non-ferrous materials such as admiralty or naval brass.

Heat exchangers of the return pass type with tubes, header plates and head covers fabricated from non-ferrous materials are generally employed at the present date when it is desired to cool a liquid or condense a gas using sea Water as a cooling medium. Such heat exchangers, While less prone to extensive corrosion from the action of sea water than heat exchangers constructed entirely from mild steel, are still unsatisfactory in service since they tend to sufier from impingement attack.

impingement attack takes the form of pitting and cavitation of the return header plate at or near the entrances to the return banks of the heat exchanger and also of pitting and cavitation of the ends of the tubes of the return banks at or near their entrances.

Such corrosion, although local in its action is obviously undesirable and may lead to contamination and/or loss of valuable products, and will almost certainly result in expensive equipment frequently lying idle for a considerable time until repairs can be eliccted.

In order to reduce such corrosion it is common practice to connect a sacrificial anode to the inside of the cover. The anode comprises a block of a metal which is more electronegative than the metals of the heat exchanger and in consequence the block corrodes in preference to the heat exchanger. Magnesium and zinc are suitable materials from which to construct sacrificial anodes for use with heat exchangers constructed from iron or iron and brass.

Sacrificial anodes reduce impingement attack but are wasteful to a limited extent in that small quantities of expensive materials are irretrievably lost. They suffer from the more important defect that heat exchangers in which they are employed must periodically be taken out of service and opened up so that a fresh anode may be inserted.

it is our opinion that impingement attack is due, in part, to the velocity pattern of the Water impinging on the return header plate being non-uniform.

We have discovered that by altering the shape of the return head cover it is possible to alter the velocity pattern of water flowing through the return banks and hence of Water impinging on the return header plate of the heat exchanger.

According to one aspect of the present invention there is provided a return head cover for a heat exchanger comprising an internal surface, a section of which is a concave surface and a section of which is a convex surface.

Preferably the concave surface is hemispherical or paraboloidal.

Suitably the convex surface includes two hemispherical surfaces, the hemispherical surfaces being symmetrically situated in the convex surface.

Alternatively the convex surface may include a cylin drical surface extending across the convex surface.

According to another aspect of the present invention there is provided a heat exchanger comprising (1) an outer shell encasing an inner tube bundle comprising (a) at least one forward bank containing at least one tube (b) a return header plate and (c) a plurality of return banks of tubes, and (2) a return head cover, the return head cover being set over the return header plate, the return head cover being shaped in such manner, that, in use, liquid emerges from the forward bank or banks, impinges on the return head cover, is deflected on to the return header plate and passed into the return banks, the liquid impinging on the return head cover in such manner that the velocity pattern of liquid flowing through the return banks of the tube bundle is rendered more uniform than would be the case if a conventionally shaped return head cover were employed.

The term conventionally shaped return head cover is used herein with rerere'nce to a cover in the form of a minor segment of a sphere of considerably greater radius than the radius of the return header plate.

Preferably the surface of the return head cover which faces the inner tube bundle is concave except in the region of the return banks; in this region the surface is convex. i reterably the concave surface is hemispherical or paraboloidal.

Suitably the con ex surface includes two hemispherical surfaces, the hemispherical surfaces being symmetrically ituated in the convex surface.

Alternatively the convex surface may include a cylindrical surface extending across the region of the return banks.

Suitably the return head cover is a Hosting head cover.

Suitably the return head cover, the return header plate sunr ses and the tubes of the return banks are constructed of nonferrous metal.

Preferably the non-ferrous metal is rniralty brass or naval brass.

The invention is illustrated by, but not limited with reference to FIGURES 1-4C of the drawings accompanying the specification, wherein:

FIGURE 1 is a side elevation, partly broken away, partly sectional, illustrating a heat exchanger having a return head cover mounted thereon embodying the invent-ion.

FIGURE. 1A is a view taken along lines llA-TA of FTGURE 1, with the ends of the tubes shown in dotted lines to illustrate the relationship between the forward and return banks of tubes and the concave and convex surfaces of the return head cover illustrated in ETGURE 1.

FIGURE 2 is an end elevation of the heat exchanger.

FIGURES 3A, 3B and 3C are three perspective views of the return head cover illustrated in FIGURE 1, and

FIGURES 4A, 4B and 4C are three perspective views of a modified return head cover in accordance with the invention.

With reference to FIGURES l and 2.

A heat exchanger comprises a shell I mounted on legs 2 enclosing a tube bundle containing a plurality of tubes '5 arranged in five forward banks :1, Z2, a", and e and five return banks a, b, c, d, and e. The tube ends are expanded into a forward header plate 4 and a return header plate 5. A return head cover is set over the return header plate 5, as more fully described hereinbelow. An inlet '7 is provided through which liquid may be supplied to the forward banks. The return banks a, b, c, d and e are uncovered at their exits and discharge to atmosphere.

With reference to FIGURES 3A, 3B, and 3C.

A head cover 8 is shown which was constructed in accordance with the invention by producing one cylindrical depression 9 in a hollow non-ferrous hemisphere.

.From an examination of FIGURES 1, 1A and FIG- URES 3A, 3B and 3C, it will be understood that the return head cover is mountw over the return header plate in a manner such that the concave portion extends generally over the outlets of the forward banks of tubes and the convex portion 9 extends generally over the inlets to the return banks of tubes.

With reference to FIGURES 4A, 4B and 4C.

A modified return head cover it) is shown which was constructed in accordance with the invention by producing two spherical depressions Ill and 12 in a hollow nonferrous hemisphere. it will be understood that modified cover 1% is mounted over the return header plate in a manner similar to that illustrated for return head cover 8, as previously described.

It will be appreciated that a heat exchanger in accordance with our present invention may be constructed from the experimental heat exchanger, (a) by replacing a conventional return head cover by either of the return head covers 8 or 11 and (b) by removing the experimental inlet 7 and replacing it by a conventional heat exchanger inlet head cover having provision for the outlet of liquid passing through the tube banks a, b, c, d and e.

The invention is further illustrated by but not limited with reference to the following examples.

EXAMPLE 1 The velocity pattern of the tubes in the return banks of the heat exchanger described with reference to IGS. l and 2 of the accompanying drawings was studied. Water was delivered to the exchanger at a rate which was exbrass, suitably ad- Table 1 Bank No a b c m d 0 Water Velocity, ft./sec 7. 4 7. 7 8. 3 6. 6 9. l a 10. 9

*First tube in bank 0.

The results set out in Table 1 show that an overall difference in water velocity of 4.3 feet per second was obtained, but the results also show that the first tube in bank 0 carried water at 1.7 feet per second lower than its neighbours. Ignoring this tube, the overall difierence was 3.5 feet per second.

EXAMPLE 2 The conventional return head cover was then replaced by a paraboloidal head cover and the results set out in Table 2 were obtained.

' TableZ Bank No r a 12 b c d e Water Velocity, ft./sec

*Two outer tubes of bank a.

The results set out in Table 2 show that the overall difference in water velocity was reduced to 2.6 feet per seconds, 2.4 feet per second if the irregular velocity of the two outer tubes of bank a is neglected.

EXAMPLE 3 A hemispherical return head cover was employed and the results set out in Table 3 were obtained.

Table 3 BankNo a b c d e Water velocity, fir/sec 6.7 7.6 5.4 8.6 8.0

The results set out in Table 3 show that the over-all difierence in water velocity was reduced to 1.9 feet per second.

EXAMPLE 4 The head cover described with reference to PIG-S. 4A, 4B, 4C was then employed and the results set out in Table 4 were obtained.

Table 4 Bank No rl a 41 b c d a Water velocity, tin/sec 7. 9 7. 7 7. 9 7. 9 8. 2 8. 2

*Two outer tubes of bank a.

The results set out in Table 4 show that the overall difference in water velocity was reduced to 0.5 foot per second, 0.3 foot per second if the irregular velocity of the two outer tubes of bank a is neglected.

' EXAMPLE 5 in Table 5 were obtained.

*Jet from first tube in bank a oscillated slowly.

The results set out in Table 5 show that the overall difference in water velocity in this case was 0.8 foot per second, 0.3 foot per second if the irregular velocity of the first tube in bank a is neglected.

It will be seen that by employing unconventionally shaped head covers of the type hereinbefore described, the velocity pattern of water passing through the banks of the return pass of the heat exchanger Was rendered more uniform.

We claim:

1. In a heat exchanger including forward and return banks of tubes, a return header plate, means securing said tubes to said header plate, and means to supply liquid to said forward tubes, a return head cover having an internal surface, said surface comprising a first portion having a concave surface and a second portion having a convex surface, said concave surface intersecting said convex surface to form an interface therebetween, means mounting said return head cover over said return header plate so that said concave portion extends generally over the outlets of said forward tubes and said convex portion extends generally over the inlets to said return tubes, whereby liquid emerging from said forward tubes gen erally impinges on said concave surface of said return head cover and is deflected onto said convex surface of said return head cover from where the liquid is deflected into said return tubes to flow in said return tubes at a substantially uniform velocity.

2. A heat exchange according to claim 1 wherein said concave portion of said return head cover asymmetrically intersects said convex portion thereof to form an interface therebetween.

3. A heat exchanger according to claim 1 wherein said concave portion of said return head cove meets said con vex portion at a sharply defined interface.

4. A heat exchanger according to claim 1 wherein said concave surface is hemispherical.

5. A heat exchanger according to claim 1 wherein said concave surface is paraboloidal.

(a. A heat exchanger according to claim 1, wherein said convex surface comprises two hemispherical surfaces, said hemispherical surfaces being symmetrically situated in said convex surface.

'7. A heat exchanger according to claim 1 wherein said convex surface comprises a cylindrical surface extending thereacross.

e. A heat exchanger according to claim 1 wherein said return head cover is a floating head cover.

9. A heat exchanger according to claim 1 wherein said return head cover, said return header plate and said return bank tubes are constructed of non-ferrous metal.

References Cited by the Examiner UNITED STATES PATENTS 4/52 Fletcher et al. 174 8/59 Iiclzford 165158 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3,195,624 July 20, 1965 William Gwynfab Richards etal.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 55, for "our" read the line 56, for "the" read an Signed and sealed this 19th day of April 1966.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer Commissioner of Patents EDWARD J. BRENNER

Claims

1. IN A HEAT EXCHANGER INCLUDING FORWARD AND RETURN BANKS OF TUBES, A RETURN HEADER PLATE, MEANS SECURING SAID TUBES TO SAID HEADER PLATE, AND MEANS TO SUPPLY LIQUID TO SAID FORWARD TUBES, A RETURN HEAD COVER HAVING AN INTERNAL SURFACE, SAID SURFACE COMPRISING A FIRST PORTION HAVING A CONCAVE SURFACE AND A SECOND PORTION HAVING A CONVEX SURFACE, SAID CONCAVE SURFACE INTERSECTING SAID CONVEX SURFACE TO FORM AN INTERFACE THEEBETWEEN, MEANS MOUNTING SAID RETURN HEAD COVER OVER SAID RETURN HEADER PLATE SO THAT SAID CONCAVE PORTIONS EXTEND GENERALLY OVER THE OUTLETS OF SAID FORWARD TUBES AND SAID CONVEX PORTION EXTENDS GENERALLY OVER THE INLETS TO SAID RETURN TUBES, WHEREBY LIQUID EMERGING FROM SAID FORWARD TUBES GENERALLY IMPINGES ON SAID CONCAVE SURFACE OF SAID RETURN HEAD COVER AND IS DEFLECTED ONTO SAID CONVEX SURFACE OF SAID RETURN HEAD COVER FROM WHERE THE LIQUID IS DEFLECTED INTO SAID RETURN TUBES TO FLOW IN SAID RETURN TUBES AT A SUBSTANTIALLY UNIFORM VELOCITY.