US3183970A

US3183970A - Finned tubes and heat exchangers formed of such tubes

Info

Publication number: US3183970A
Application number: US153991A
Authority: US
Inventors: Norman G Worley
Original assignee: Babcock and Wilcox Ltd
Current assignee: Babcock International Ltd
Priority date: 1960-11-24
Filing date: 1961-11-21
Publication date: 1965-05-18
Anticipated expiration: 1982-05-18
Also published as: GB944108A

Description

May 18, 1965 N. e. WORLEY FINNED TUBES AND HEAT EXCHA NGERS FORMED OF SUCH TUBES Filed Nov. 21, 1961 2 Sheets-Sheet 1 Fig.4.

ATTORNEY y 1965 N. e. WORLEY 3,183,970

FINNED TUBES AND HEAT EXCHANGERS FORMED OF SUCH TUBES Filed Nov. 21, 1961 2 Sheets-Sheet 2 A77UPNEY 3,183,970 FINNED TUBES AND HEAT EXCHANGERS FORMED OF SUCH TUBES Norman G. Worley, London, England, assignor to Babcock & Wilcox Limited, London, England, a British company Filed Nov. 21, 1961, Ser. No. 153,991 Claims priority, application Great Britain, Nov. 24, 1960, 40,429/ 60 7 Claims. (Cl. 165-181) This invention relates to finned tubes of the kind provided with a fin or fins affording longitudinally spaced, transversely extending, heat exchange surfaces and to heat exchangers formed of such tubes.

In heat utilising plant in which a fluid heat carrier is forcibly circulated in series through a heat source and a heat exchanger wherein the fluid is cooled through a limited temperature range, conflicting requirements arise. On the one hand the power required to effect circulation of the fluid flowing over the extended surfaces must be maintained at a 'value as low as possible and on the other hand and effective heat exchange must be achieved with a heat exchanger of compact form.

An object of the invention is the provision of finned tubes of improved form as regards heat transfer.

In the specification of U.S. Patent No. 3,073,385 there is described a finned tube with longitudinally spaced, transversely extending surfaces provided by a fin or fins in which the fins or each fin includes a main part extending from the tube and formed with parallel or substantially parallel sides and a border tapering from the main part towards an edge in a manner adapted to reduce eddying during its passage over the faces of the fin of fluid which flows transversely of the tube and directly towards gaps between opposed fin surfaces.

In the complete specification of U.S. Patent No. 3,014,- 120 there is described a machine for welding a succession of studs to a surface which includes means for moving a stud holder to and fro between a stud loading station and a stud welding station, stud feeding means capable of supplying a succession of studs from a reservoir, and stud dispensing means adapted to receive studs from the stud feeding means and to supply a stud to the stud holder each time the stud holder moves to the stud loading station.

United States Patent Another form of fin and a method of ataching such Q to a tube is disclosed in U.S. Patent No. 3,020,027.

The present invention includes a finned tube having extended heat exchange surfaces extending from the tube transversely to the tube, wherein the heat exchange surfaces include fin surface's formed with means adapted to create turbulence and consequent disturbance between edges of the fins of fluid boundary layer flows in fluid flowing transversely of the tube.

The invention also includes a finnned tube with a multiplicity lof longitudinally spaced plate-like fins the faces of which extend transversely of the tube, wherein fin surfaces are formed with means adapted to create at locations intermediate opposite fin edges turbulence and consequent disturbance of the fluid boundary layer flow at the said surfaces of fluid flowing transversely of the tube and between the said fin edges.

The invention further includes a finned tube with longitudinally spaced, transversely extending heat exchange surfaces provided by a helical fin, wherein the fin surfaces are formed with means adapted to create turbulence and consequent disturbance of the fluid boundary layer flows at the said fin surfaces in fluid flowing transversely of the tube.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a cross-sectional end elevation of a heat exchanger tube provided with a multiplicity of rectangular fins;

FIGURE 2 is a side elevation of a length of the finned tube of FIGURE 1;

FIGURE 3 is an end elevation of part of a heat exchanger tube bank in section on a plane at right angles to the tube axes.

FIGURE 4 is an end elevation of an alternative form of rectangular fin;

FIGURE 5 is a plan view of the fin of FIGURE 3;

FIGURE 6 is a plan view of a further alternative form of rectangular fin;

FIGURE 7 is a plan view of another alternative form of rectangular fin;

FIGURE 8 is a plan view of another further alternative form of rectangular fin;

FIGURE 9 is a cross-sectional end elevation of a heat exchanger tube provided with a helical fin; and

FIGURE 10 is a side elevation of a length of the finned tube of FIGURE 9 with its upper half shown in section on a plane through its axis.

If the width of rectangular fins such as described in conjunction with the complete specification of the aforesaid U.S. Patent No. 3,073,385 is reduced so that the number of fins that may be disposed around the circumference of a tube is increased, there is an improvement in the heat transfer coefiicient without significantly increasing the pumping power, even when the number of fins is doubled. However, increasing the number of fins has the disadvantage that the cost of welding the fins to the tube is also increased. By promoting turbulence in the fluid by means of centrally disposed, radially extending grooves in the fin surfaces an improved rate of heat exchange may be obtained over the rate obtained with fins without such a surface discontinuity without increasing the number of fins.

Referring to FIGURES 1, 2 and 3 of the drawings, a heat exchanger tube 2 which is adapted for the transfer of heat from a gaseous fluid flowing past the exterior of the tube generally perpendicularly to the tube axis to a fluid flowing through the tube is provided with a multiplicity of fins 4 adapted to increase the rate of heat removed from the gaseous fluid. The fins 4- are each provided on the faces thereof with central grooves 6 and are arranged on the tube 2 in circumferential rows or sets. Each fin set consists of six fins arranged in a plane perpendicular to the tube axis and disposed equi-angularly around the tube, the fin sets are uniformly spaced along the tube and the fins of alternate sets are staggered with respect to the fins of the remaining sets. All the fins have similar dimensions and are welded to the tube surface.

A number of such finned tubes are arranged parallel to one another to form a bank with the tubes of adjacent rows in staggered relationship, the tubes extending in a direction normal to the general direction of fluid flow through the bank. FEGURE 3 indicates such an arrangement of

rows

18, 19, 2t), 21 of parallel tubes 2 in a tube bank, Where each tube extends in a direction normal to the general direction, indicated by the arrows 22, of gas flow through the bank, and each row of tubes extends in a plane normal to the general direction of gas flow.

By way of example, in one embodiment of the invention, the fins provided on a tube of 2 inches outside diameter and 1% inches internal diameter, are of rectangular form 1 inch in Width, of an inch in height and of an inch in thickness having converging border parts extending inwardly of an inch from each edge with an angle of bevel of 10 to the central plane of the fin. The centrally disposed grooves 6 are of arcuate cross-section having a width of A; of an inch and a depth of of an inch. The fins are applied to the tube by electric resistance welding with a pitching of /4 of an inch between circumferential rows by the automatic machine described in U.S. Patent No. 3,041,120. By this machine two diametrically opposite fins are simultaneously -weldedinto position while held by respective reciprocable Welding heads, the tube is turned through 60, a

secondpairof fins is attached to the tube by the same welding heads, the tube is turned through a further 60, a third pair of fins is attached to the tube to complete a circumferential row of six co-planar fins, the tube is turned through 30 and moved axially of an inch and the procedure is repeated.

Since the grooves 6 are centrally positioned it is not necessary to provide means on the machine to orientate the fins with regard to which edge is presented to the fluid flow.

Alternatively the fins may have a lenticular, elliptical or other streamline cross-section. Thus FIGURES 4 and illustrate a rectangular fin 8 of similar overall dimensions as the fins shown in FIGURES 1 and 2 but having an elliptical outline in plan view.

In the alternative arrangement shown in FIGURE 6, the central grooves 9, instead of being of arcuate crosssection are of V-shape.

Alternatively, in the arrangement shown in FIGURE 7,

grooves 6A are ofiset to either side of the centre line of a fin 4A. in order to maintain the mechanical strength of .the fin; whilst still obtaining the promotion of turbulence from the grooves.

In another, further alternative arrangement, shown in FIGURE 8, two grooves 10 are provided on each side of a fin 11 disposed symmetrically about the axis and adjacent the edges of the fin.

Referring to FIGURES 9 and 10 a single helical fin 12 adapted to increase the rate of heat transfer from a gaseous fluid to a heat exchanger tube 13 is Welded along its inner edge to the tube surface. Radial grooves 14 of arcuate cross-section are spaced at 30 intervals arourd the fin and are adapted to create turbulence and consequent disturbance of the fiuid boundary layer flows at the said fin surfaces in the iiuid flowing transversely of the tube.

By way of example, in one embodiment, the helical fin provided on a tube of 2 inches outside diameter, 1 /8 inches internal diameter, is of an inch in height and A of an inch in thickness having symmetrically bevelled outer border parts 15 extending inwardly of an inch and each making an angle of 10 with the axis of the the main part of each of said fins being formed by a pair or" substantially parallel fiat sides extending from and rigidly secured to the tube, all of the sides of the main parts of said fins being in parallel relationship with each other, the border part of each fin extending along at least a portion of the edge of the corresponding main part in the same plane as the main part and tapering outwardly from the main part to'an edge of the fin in a manner adapted to reduce eddying of the fluid during its flow into and beyond the spaces between the sides of the main parts of the fins, the flow of fluid being such as to pass transversely of the tube in a direction generally parallel to the sides of the main parts of said fins, each of said fins having a groove formed in at least one of the sides of its corresponding main part and extending completely across the main part of the fin to create turbulence and consequent disturbance of the fiuid boundary layer flow at the sides of the main parts of the fins as the fluid passes through the spaces between the sides of the main parts of the fins.

groove has'a shallow V-shape cross-section.

6. A finned tube having a multiplicity of longitudinally spaced transversely extending fins positioned on its exterior surface to form gas flow spaces therebetween with the fins extending parallel to the general direction of gas flow, each of said fins comprising a main part and a border part, the main part of each of said fins being formed by a pair of substantially parallel fiat sides extending from and rigidly secured to the tube, all of the sides of the main parts of said fins being in parallel relationship with each other, the border part of each fin extending along at least a portion of the edge of the corresponding main part in the same plane as the main part and tapering. outwardly from the main part to an edge of the fin in a manner adapted to reduce eddying of the fluid during its flow into and beyond the spaces between the sides of the main parts of the fins, each of said fins having a groove formed in at least one of the sides of its corresponding main part and in the border part corresponding to the main part and extending completely across the main part of the fin and its corresponding border part to create turbulence and consequent disturbance of the fluid boundary layer flow at the sides of the main parts of the fins as the fluid passes through the spaces between the sides of the main parts of the fins.

7. A finned tube having a multiplicity of longitudinally spaced transversely extending fins positioned on its exterior surface and arranged for the flow of'a heat transfer fluid passing over said tube and between said fins, each of said fins comprising a main part and a border part, the main part of each of said fins being formed by a pair of substantially parallel fiat sides extending from and rigidly secured to the tube, all of the sides of the main parts of said fins being in parallel relationship with each other, the border part of each fin extending along opposite edges of the main part in the same plane as the main part and tapering outwardly from the main part to the adjacent edge of the fin in a manner adapted to reduce eddying of the fluid during its fiow into and beyond the spaces between the sides of themain parts of the fins, the

flow of fluid being such as to pass transversely of the tube References Cited by the Examiner in a direction generally parallel to the sides of the main UNITED STATES PATENTS parts of said fins, each of said fins having a groove formed in at least one of the sides of its corresponding 1354278 4/32 Smlth 165' 182 main part and in the border part corresponding to the 5 2667337 1/54 Chapman 165-184 main part and extending radially of the tube and com- 1 I I a l plete y across the main part of the fin and 1ts correspond 3073385 1/63 Peters 165 181 ing border part to create turbulence and consequent disturbance of the fluid boundary layer flow at the sides of the main parts of the fins as the fluid passes through 10 CHARLES SUKALO Exammer' the spaces between the sides of the main parts of the fins.

Claims

1. A FINNED TUBE HAVING A MULTIPLICITY OF LONGITUDINALLY SPACED TRANSVERSELY EXTENDING FINS POSITIONED ON ITS EXTERIOR SURFACE AND ARRANGED FOR THE FLOW OF A HEAT TRANSFER FLUID PASSING OVER SAID TUBE AND BETWEEN SAID FINS, EACH OF SAID FINS COMPRISING A MAIN PART AND A BORDER PART, THE MAIN PART OF EACH OF SAID FINS BEING FORMED BY A PAIR OF SUBSTANTIALLY PARALLEL FLAT SIDES EXTENDING FROM AND RIGIDLY SECURED TO THE TUBE, ALL OF THE SIDES OF THE MAIN PARTS OF SAID FINS BEING IN PARALLEL RELATIONSHIP WITH EACH OTHER, THE BORDER PART OF EACH FIN EXTENDING ALONG AT LEAST A PORTION OF THE EDGE OF THE MAIN PART AND TAPERING OUTPART IN THE SAME PLANE AS THE MAIN PART AND TAPERING OUTWARDLY FROM THE MAIN PART TO AN EDGE OF THE FIN IN A MANNER ADAPTED TO REDUCE EDDYING OF THE FLUID DURING ITS