CA1036804A - Method for forming a serrated-fin tube - Google Patents

Method for forming a serrated-fin tube

Info

Publication number
CA1036804A
CA1036804A CA258,270A CA258270A CA1036804A CA 1036804 A CA1036804 A CA 1036804A CA 258270 A CA258270 A CA 258270A CA 1036804 A CA1036804 A CA 1036804A
Authority
CA
Canada
Prior art keywords
tube
fins
fin
serrated
heat transfer
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
CA258,270A
Other languages
French (fr)
Inventor
D. Luis Miletti
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.)
Noranda Inc
Original Assignee
Noranda Inc
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 Noranda Inc filed Critical Noranda Inc
Priority to CA258,270A priority Critical patent/CA1036804A/en
Application granted granted Critical
Publication of CA1036804A publication Critical patent/CA1036804A/en
Expired legal-status Critical Current

Links

Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B21MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21CMANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C37/00Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
    • B21C37/06Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape of tubes or metal hoses; Combined procedures for making tubes, e.g. for making multi-wall tubes
    • B21C37/15Making tubes of special shape; Making tube fittings
    • B21C37/20Making helical or similar guides in or on tubes without removing material, e.g. by drawing same over mandrels, by pushing same through dies ; Making tubes with angled walls, ribbed tubes and tubes with decorated walls
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B21MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21CMANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C37/00Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
    • B21C37/06Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape of tubes or metal hoses; Combined procedures for making tubes, e.g. for making multi-wall tubes
    • B21C37/15Making tubes of special shape; Making tube fittings
    • B21C37/20Making helical or similar guides in or on tubes without removing material, e.g. by drawing same over mandrels, by pushing same through dies ; Making tubes with angled walls, ribbed tubes and tubes with decorated walls
    • B21C37/207Making helical or similar guides in or on tubes without removing material, e.g. by drawing same over mandrels, by pushing same through dies ; Making tubes with angled walls, ribbed tubes and tubes with decorated walls with helical guides
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28HEAT EXCHANGE IN GENERAL
    • F28FDETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F1/00Tubular elements; Assemblies of tubular elements
    • F28F1/10Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses
    • F28F1/40Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses the means being only inside the tubular element

Abstract

ABSTRACT OF THE DISCLOSURE:

A method of forming serrated-fin tubing to improve heat transfer performance is disclosed. The method comprises providing a round metal tube having an annular peripheral wall and integral inner metal fins projecting from such wall parallel to each other, and inserting a tool into said tube for interrupting the continui-ty of such fins so as to promote turbulence in the boundary layer of the flow in the tube thus improving heat transfer performance.

Description

1036~0~
This invention relates to finned tubing generally used in heat exchangers and more particularly to a method of serrating the internal fins of a tubing to improve heat transfer.
A method of providing indentations, interruptions or serrations in finned tubing has been disclosed and claimed in Ca-nadian Patent No. 958,408 which has issued to the same interest as the present application. However, the patented method invol-ves a number of manufacturing steps including annealing, flatte-ning, reannealing, pressurization to round the tube, possibly a draw bench operation to truly round out the tube, and a final anneal. In addition, the above method can only be used with spi-ral finned tubes since the serrations are made by interpressing of opposed fins at their crossing during the flattening opera-tion. Furthermore, the fins have to be relatively high to obtain serrations without over flattening the tube and cracking the wall at the crease. Also, the depth of the indentations is limited to about 50% of the fin height. Finally, the tubing wall cannot be too thin or too thick for flattening considerations.
It is therefore the object of the present invention to provide a new method of serrating the internal fins of a tube which is not subject to the above constraints and will be suita-ble for any given finned tube, be it spiral or straight, high or low fin, thin or thick wall, and wherein the serrated configura-tion is infinitely variable to suit any possible application, that is the number of serrations per unit length, the depth of the serrations and their shape.
The method of forming serrated finned tubing, in accor-dance with the invention, comprises the steps of providing a round metal tube having an annular peripheral wall and integral inner metal fins projecting from such wall parallel to each other, and inserting a tool into said tube for interrupting the continuity of such fins so as to promote turbulence of the flow in the tube - 1 - , q~

thus improving heat transfer performance. The serrated-fin tube may be annealed after the serrations are put in if required.
Serrations of the fins may be done in any conventio-nal manner such as by using a suitablY machined tap operated by any conventional tooling. Any serration configuration can be put in such as "U" or "V" shaped serrations. The pitch of the serra-tions may be varied depending on the application and is preferably between 1 and 20 serrations per inch.
The serration depth is preferably about equal to the height of the fins although it could possibly be less.
~he invention will now be disclosed, by way of examples, with reference to the accompanying drawings in which:
Figures 1 and 2 illustrate a cross-sectional view and a sectional longitudinal view, respectively, of a finned tube prior to putting in the serrations;
Figure 3 illustrates schematically a method of serra-ting the fins inside a finned tubing;
Figure 4 illustrat0s a longitudinal section view of a tube having the serrations therein, Figure 5 illustrates a comparison of heat transfer data for serrated-fin and unserrated-fin tubes in laminar oil flow as compared to the Kern and Othmer smooth tube correlation;
Figure 6 illustrates a comparison of heat transfer for serrated-fin and unserrated-fin tubes in turbulent water flow as compared to the Sieder-Tate smooth tube correlation;
Figure 7 illustrates the ratio of the heat transfer coefficient of the finned tube over the heat transfer coefficient of the smooth tube at constant pumping power for serrated-fin and unserrated-fin tubes in turbulent water flow; and Figure 8 illustrates the heat transfer performance of a transmission oil cooler versus oil flow rate for serrated-fin and unserrated-fin tubes.

Referring to Figures 1 and 2, there is shown a tubing 10 provided with internal fins 12. Such fins may be spiral as shown in Figure 2 or straight Cnot shown). Figure 3 illustrates one method of interrupting the fins. The tube 10 is held in a chuck 14 and the interrupting is being done by a tap 16 secured to the end of an extension rod 18 provided with interruptors 19 at one end and rotated by any conventional tooling in the direc-tion of arrow 20. Suitable tooling apparatus are drilling machi-ne5, horizontal lathe-type machines or broaching machines. It is to be understood that either the tube or the tool can be rotated.
Figure 4 illustrates the serrations 22 made in tubing 10 at the end of the interrupting operation. It will be understood that the shape of the serrations will depend on the configuration of the tap. The number of serrations per inch will also depend on the pitch on the tap. Thus, the configuration and frequency of the serrations in the tubing can easily be varied by simply selecting a tap to 9uit a particular application. Similarly, the depth of the serrations can be varied at will by selecting a tap of suita-ble configuration. It is also to be understood that the serra-tions need not be spirals and could possibly follow any path de-pending on the tool used for making them as long as such path in-tersect the path of the fins.
Tests have been carried out to determine the effect of fin serration on the heat transfer of a finned tube having the dimensions of the following Table I. Both the serrated-fin and unserrated-fin tubes were tested in laminar oil flow and turbulent water flow.

1036~4 TABLE I
DIMENSIONS OF FINNED TUBE

Outside tube diameter, in. 1.000 Inside tube diameter, in. 0.930 Type of fins High spiral Number of fins 22 Fin height, in. 0.060 Fin pitch, in. 5.0 Inter-fin spacing, in. 0.095 Hydraulic diameter, in. 0.460 Laminar Oil Flow In this test, oil was pumped from a storage tank through the tube under test where it was heated by steam condensing on the outside of the tube. Steam was supplied by a steam boiler wherein the tube under test was placed.
Heat transfer data for the serrated and unserrated-fin tubes in laminar oil flow are compared in Figure 5 with the smooth tube Kern and Othmer empirical correlation based on inside diame-ter and nominal area. This correlation is given by:
119 l~g l~g 0'1~
NNU - 1- 86 NRe NPr (Di/ ~ w) where ~ = [2.25 (1 + 0.01 NG )/log NR ]

NNu = Nusselt number NRe = Reynolds number i NPr = Prandtl number N = Grashof number Gri L = length of the finned tube -l036~a4 ., Di = inner diameter of the finned tube ~ = bulk viscosity of the oil based on the average temperature between the inlet and outlet temperature of the oil entering the finned tube ~w = wall viscosity of the oil based on wall temperature of the finned tube.
The above equation is well known in the art and referen-ce is made to the article entitled "Heat Transfer and Pressure Drop of Internally Finned Tubes in Laminar Oil Flow" presented by A.P. Watkinson, D.L. Miletti and G.R. Kubanek at the ALChE-ASME
Heat Transfer Conference, San Francisco, California, August 11-13, 1975; ASME Paper 75-HT-41.
While the data obtained was scattered and tended to a cyclic behavior, the performance of both the serrated-fin and un-serrated-fin tubes was significantly better than that of the smooth tube Kern and Othmer correlation. More importantly, the effect of fin serration was to increase the Nusselt modulus by 60 to 100%.
Turbulent Water Flo~
A comparison of heat transfer data for serrated-fin and unserrated-fin tubes in turbulent water flow with the Sieder-Tate smooth tube correlation based on inside diameter and nominal area is shown in Figure 6. Such emperical correlation is similar in some respect to the Kern and Othmer correlation and is as follows:
0.3g 0- ~4 NNU = 0-023 NRei Npr ~/~w) where the definition of the symbols is as given above for the Kern and Othmer correlation.
The ~usselt modulus for the serrated-fin tube was 250-300~ higher than that for the smooth tube, and 45-65% higher than that for the unserrated-fin tube. The friction factor based on inside diameter and nominal area (well defined in the above arti-103~04 cle) for the serrated-fin tube was higher than for the unserra-ted-fin tube as would be expected because of the fin serrations.
However, the ratio of the heat transfer coefficient of the finned tube over the heat transfer coefficient of the smooth tube at constant pumping power remained essentially constant when plotted against the Reynolds num~er as shown in Figure 7 of the drawings.
In addition, the performance ratio or the serrated-fin tube was 10% higher than for the unserrated-fin tube.
Tests were also carried out to determine the effect of fin serration on the heat transfer and pressure drops performance of finned tubes used in transmission oil coolers. The dimensions of a duplex transmission oil cooler using an outer finned tube and an inner smooth tube are shown in the following Table II:

~ - ~

10;16~04 ~ a) ~ . o o ~ ,~ ,~
H :1 ~1 ~I

. ~ O
1 U~ U~
o E~

U~ ~ ~ ~d .
~ ~ _~ ~
O :¢ 13 a~ a~
~ .

~-I O ~U ~ O
Z ~ rl H ~U
H
~
H Z ,a ~ O CO
~ ~ o _l ~ ~ Ie~ O O .' P ~ `~D O
a~ ~ . . u~
J~ ~ ~ C a~ a~
~4 ~
O O E~O O
U~ .
o ~O O
H ~ .a ~ ~: O O
U~ ~ 1 . . S~
~ O E~ O_~ ~1 J~
H ~ ~t`l 1`
~ . .r' 1-1`
~ 1 . . I.q ~rl H E-' O O ~r1 $~ ~ o o a~ ,~
) ~ . ~ r- r E~
s~.
~1 0 ~1 ~

. _, ~036~4 In the transmission oil cooler test, oil was circulated in between the two concentric tubes whereas cooling water was circulated inside the inner tube and outside of the outer tube.
The heat transfer performance of the transmission coo-ler usin~ a serrated-fin outer tube is far superior to the one using an outer fin tube with no serrations as shown in Figure 8 of the drawings. The pressure drop performance using a serrated-fin outer tube was higher as would be expected but that can be compensated for by machining the inner tube to increase the dia-metral fin clearance without substantially effecting the heattransfer performance.
Although the invention has been disclosed with respect to a preferred method of interrupting the fins of internally fin-ned tubing, it is to be understood that other methods of internal-ly serrating are also envisaged and that the invention is to be limited by the scope of the claims only.

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. Method of forming a serrated-fin tubing comprising:
a) providing a round metal tube having an annular peri-pheral wall and integral inner metal fins projecting inwardly from said wall parallel to each other; and b) inserting a tool into said tube for interrupting the continuity of said fins so as to promote turbulence of the flow in the tube, thus improving heat transfer performance.
2. A method as defined in claim 1, wherein interrupting is done by means of a tap forming a desired serration configuration in a spiral path.
3. A method as defined in claim 2, wherein the pitch of the serrations is between 1 and 20 serrations per inch.
4. A method as defined in claim 2, wherein the serration depth is about equal to the height of the fins.
5. A method as defined in claim 2, wherein the serration depth is less than the height of the fins.
CA258,270A 1976-08-02 1976-08-02 Method for forming a serrated-fin tube Expired CA1036804A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CA258,270A CA1036804A (en) 1976-08-02 1976-08-02 Method for forming a serrated-fin tube

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CA258,270A CA1036804A (en) 1976-08-02 1976-08-02 Method for forming a serrated-fin tube

Publications (1)

Publication Number Publication Date
CA1036804A true CA1036804A (en) 1978-08-22

Family

ID=4106558

Family Applications (1)

Application Number Title Priority Date Filing Date
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Country Status (1)

Country Link
CA (1) CA1036804A (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2410238A1 (en) * 1977-11-25 1979-06-22 Tokyo Shibaura Electric Co Heat exchanger tube design - incorporates longitudinal grooving and equally spaced circumferential grooves
US4541261A (en) * 1982-09-22 1985-09-17 Hitachi, Ltd. Method of producing heat pipe
WO1995009324A1 (en) * 1993-09-30 1995-04-06 Siemens Aktiengesellschaft Internally ribbed tube for a steam generator, and a steam generator using such tubes
CN106391913A (en) * 2016-11-10 2017-02-15 华南理工大学 Device and method for forming three-dimensional internal finned tubes based on multi-blade ploughing-extrusion
CN106391914A (en) * 2016-11-10 2017-02-15 华南理工大学 Rolling and ploughing-extrusion device and method for manufacturing three-dimensional internal and external finned tubes

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2410238A1 (en) * 1977-11-25 1979-06-22 Tokyo Shibaura Electric Co Heat exchanger tube design - incorporates longitudinal grooving and equally spaced circumferential grooves
US4541261A (en) * 1982-09-22 1985-09-17 Hitachi, Ltd. Method of producing heat pipe
WO1995009324A1 (en) * 1993-09-30 1995-04-06 Siemens Aktiengesellschaft Internally ribbed tube for a steam generator, and a steam generator using such tubes
CN106391913A (en) * 2016-11-10 2017-02-15 华南理工大学 Device and method for forming three-dimensional internal finned tubes based on multi-blade ploughing-extrusion
CN106391914A (en) * 2016-11-10 2017-02-15 华南理工大学 Rolling and ploughing-extrusion device and method for manufacturing three-dimensional internal and external finned tubes
CN106391914B (en) * 2016-11-10 2018-07-20 华南理工大学 Three-dimensional internal and external finned tubes manufacturing equipment and method are cut-squeezed to a kind of roll with plough
US10807145B2 (en) 2016-11-10 2020-10-20 South China University Of Technology Device and method for forming inside three-dimensional finned tube by multi-edge ploughing and extruding

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