US 3612175 A
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O United States Patent [111 3,6 12,175
 Inventors James A. Ford 249,547 11/1881 Reed 138/38 North Haven; 770,599 9/1904 Monteagle. 138/38 Wade Wol1e,,]r., Mount Carmel, both of 1,777,782 10/1930 Bundy 138/38 Conn. 2,913,009 11/1959 Kuthe 138/38  p 838l72 Primary Examiner-Charles Sukalo  Filed July 1, 1969 A R b H B h G d G M h d  Patented Oct. 12, 1971 tt0rne vso ert ac man, or on 6I1Z1eS, 1c ar  Assignee Olin Corporation S. Strlckler, Donald R. Motsko and Thomas P. 0 Day  CORRUGATED METAL TUBING 6 Claims, 2 Drawing Figs.
ABSTRACT: The instant disclosure teaches an improved cor- U-S. mgated meta] tubing having an improved heabtransfer coefi'i- 138/38 cient and having a plurality of lands and grooves extending  lnt.Cl F281 l/42 along the circumference th f The grooves comprise at  Field of Search 138/38; least we independent continuous grooves extending helically 165/177 156 along the circumference of the tube, with each groove being in  References Cited spaced relationship to each other. Improved heat transfer is obtained by providing that the land width, the groove width UNITED STATES PATENTS and the angle of advance of the helically extending grooves are related in a particular defined manner.
SHEEIIUFZ "I Q 1 E 0 r R t q 4 Q t O 7 b CL 1 8 a Q 9 co 0 N INVENTORS.
0 JAMES A. FORD 001 x n WADE WOLFE JR.
PATENIEnncnzmn 3612175 I SHEET 2 (1F 2 JAMES A. FORD WADE WOLFE JR.
ay 1552M T RNEY CORRUGATED METAL TUBING The production of potable water from saline water requires extensive quantities of v heat-transfer surface in the form of condenser tubing. Estimates have variously placed the capital investment involved with the heat exchange surface in desalting plants at as much as 50 percent of the total.
Accordingly, it becomes extremely pertinent in the continuing efforts to reduce the cost of potable water that the cost of the heat-transfer surface be reduced. it is known in the art that corrugated tubing or surface enhancement provides an improved heat-transfer coefficient as compared to a plain cylindrical tube.
It is further well known that large amounts of cooling water, sea water in the case of desalting apparatus, must be pumped through condenser tubing. Surface enhancement always leads to increased pumping requirements because the pressure drop, AP, on the inside of the condenser tubes is increased by the surface enhancement. Thus it becomes highly desirable to provide for improved condenser tubing in which the heat transfer is maximized but the increase in the pressure drop kept as low as practical.
It is highly desirable, however, to provide still further improvement in this art. 7
Accordingly, it is a principal object of the present invention to provide an improved metal tubing.
A further object of the present invention is toprovide a large increase in heat transfer with a minimum increase in pressure drop.
It is a still further object of the present invention to provide an improved tubing as aforesaid which achieves a surprisingly high heat-transfer coefficient at a reasonable cost.
Still further objects and advantages of the present invention will appear from the ensuing specification, especially when taken into consideration with the accompanying drawings,
FIG. 1 graphically represents heat-transfer data from the examples which form a part of the present specification; and
FIG. 2 shows a side view of a portion of representative tubing of the present invention.
in accordance with the present invention it has now been found that the foregoing objects and advantages may be readily achieved and a metal tubing with improved heat transfer provided. The tubing of the present invention comprises a hollow corrugated tube having a plurality of lands and grooves extending along the circumference thereof, said grooves comprising at least two independent, continuous grooves extending helically along the circumference of the tube, with each groove being in spaced relationship to each other, with said tubing satisfying the following formula:
(L.W./G.\V.)+(X0.03) From 0.5 to 2.25 wherein LW. land width, G.W. groove width, and 0 angle of advance of the helically extending grooves. in the preferred embodiment of the present invention the grooves comprise three independent, continuous grooves extending helically along the circumference of the tube, with each groove being in spaced relationship to each other.
In accordance with the present invention it has been found that the foregoing corrugated metal tubing achieves a surprising high heat-transfer coefficient. This surprising heat-transfer coefficient could not be anticipated even in view of the improved heat-transfer coefficient obtained by corrugated tubing in general.
A further advantage of the improved heat-transfer coefficient is the resultant equipment savings and many other cost savings in heat exchange machinery. This is especially important in cases where large capital investment is required.
In accordance with the present invention the metal tubing may be corrugated by any method known in the art. A particularly preferred method and apparatus is shown in copending application Ser. No. 679,459, now abandoned, by Joseph Winter for "Apparatus For Forming Corrugated Tubing." ln accordance with the teaching of the foregoing patent application, corrugated tubing is produced by an apparatus characterized by having an inner frame movably mounted on an outer frame, with a die rotatably mounted on the inner frame. The die has an annular opening through which passes the tube to be corrugated and shaped die members projecting into the annular opening. The pitch and depth of the spirals or corrugations can be adjusted and controlled over a wide range of configurations. The resultant corrugated tubing is characterized by having a plurality of lands and grooves extending helically along the circumference thereof. In cross section, the tube has a plurality of uniform, symmetrical, wavelike in, dentations, with the wall thickness of the tube being approxi mately uniform throughout. The grooves comprise a plurality of independent, continuous grooves extending helically along the circumference of the tube, with each groove being in spaced relationship to each other.
The tubing of the present invention may be made of a wide variety of metals and their alloys. For example, copper and its alloys, aluminum and its alloys, titanium and its'alloys, iron and its alloys and so forth. Corrugated tubing made from welded seam tubemay be readily used. 7
The corrugated tubing of the present invention should preferably have a wall thickness from 0.010 inch to 0.50 inch and an outside diameter of from 0.25 inch to 10.5 inch.
in use, when tubing is corrugated normally a section of the tubing is left uncorrugated to provide a plain undistorted tube wall at each end of the corrugated tubing for a locus for sealing into a tube sheet. A multitude of tubes are conventionally attached to tube sheets which separate the heat-transfer media on the outside from the heat-transfer media on the insideof the tubes. The tubes are normally sealed at the point between the heat exchange tubes and the tube sheet by rolling in the tubes or by welding or by brazing.
As pointed out hereinabove, it is a finding of the present invention that improved overall heat-transfer coefficient, U is obtained when the tubing satisfies the following formula:
(L.W./G.W.)-H 0x0.03) From 0.5 to 2.25 The term L.W. refers to the land width in inches, with the land being measured at right angles instead of along the tube axis. The term G.W. refers to the groove width measured in the same manner. The term 0 refers to the angle of advance of the helically extending grooves from a right angle to the tube axis. ln general, it can be stated that the lower the value of (L.W.IG.W.'), the better the heat-transfer coefficient. It may be hypothesized that the lower values of L.W./G.W. are caused by larger groove widths in relation to smaller land widths which enhance liquid film thinning at the peaks of the lands and decreases film thickening at the valleys of the grooves. The relatively larger groove width in relation to relatively smaller land width is clearly shown in FIG. 2, wherein reference numeral 1 shows the plain uncorrugated end'and reference numeral 2 shows the corrugated portion. This is particularly apparent with respect to the heat-transfer coefficient on the steam side.
The value for (L.W./G.\V.)+(0X0.03) may for convenience be termed the heat transfer efiiciency number, P.
Furthermore, the overall heat-transfer coefficient for corrugated tubes may be expressed in terms of the above geometric parameters by the following formula:
U,,=l245-l-48.3P62.2P'-+8.34P wherein P is the heat-transfer efficiency number defined above and U, is the overall heat-transfer coefficient. in accordance with this equation for the enhancement of the present invention, the value of P may vary from 0.5 to 2.25.
in addition to the foregoing, the pressure drop, AP, should be kept at a reasonable value, preferably between 0.6 and 4.5 at 6 feet per second of water.
The present invention will be morereadily apparent from a consideration of the following illustrative examples.
EXAMPLE I This example utilizes a copper base alloy having the following'composition: iron, 2.3 percent; phosphorus, 0.025 percent; copper essentially balance. Several pieces of seamwelded tubing were prepared from the foregoing alloy having a tube length of 42 inches. The tubing had a 1-inch OD. and a wall thickness of 0.049 inch. Some of the tubing was formed characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive. the scope of the invention being indicated by the appended claims, and all changes which come within the meaninto corrugated tubing havinga plurality of lands and grooves 5 ing and range of equivalency are intended to be embraced extending along the circumference thereof with the grooves therein. comprising at least two independent, helically extending con- We claim: tinuous grooves. The characteristics of the corrugated tubings 1. Improved metal tubing having improved heat-transfer are shown in table 1 below. The corrugated tubing of the characteristics comprising: a hollow corrugated metal tube present invention generally exhibited no change in weight per l havin a plurality of lands and grooves extending along the cir- Unlt g the corrugated tubing had 110 greater Surface cumference thereof, wherein there is relatively larger groove area in one part. The convoluted section of the tube was about id h i l i n to relatively smaller land widths, said 33 inches long. The corrugated tubing had about a 4 to inch ooves comprising at least two independent, continuous plain section on either end. grooves extending helically along the circumference of the In the following table: Tube A represents plain, uncorru- 1 tube with each groove being in spaced relationship to each gated tubings; tubes B-I represent the tubing of the present inother, said tubing exhibiting substantially no change in weight vention; and tubes represent mp r i ing. per unit length, with said tubing satisfying the following for- TABLE 1 Bore Weight Angle Groove Width, inches dlarnper of ad- Number Pitch, depth, eter, foot, Vance, Tube of leads inch inches Land Groove inches 1b. degrees 40 TABLE 11 Overall EXAMPLE u heat Pressure t Hti at A 8 01' The plain tubing and the corrugated tubing were both tested oe f fii l e y ft l 3. 5mi. efli cl eitcy in the same manner. A single-tube, horizontal calorimeter was U0 it. 1150 Noi used operating on filmwise condensation of steam at approxi- 4 mately 240 F. using water as cooling water on the interior of 760 0.6 m o 1, 235 3. 6 1. 48 the tube. The inlet temperature of the tap water was about 40 1 210 8 L F. The heat transfer and pressure drop characteristics of the 1,170 2.1 2% tubes were determined over a range of water velocity. The 33g 51 values in table II set out below are for a velocity of 6 feet per 1,215 1 1. 02 second. The heat-transfer coefficient was determined by mea- 3:: ,22 suring cooling waterflow in mass rate and measuring inlet and 1', 090 5. 5 3. 04 1 215 6.7 2.81 outlet temperature of cooling water to determine heat flux. 1'035 3 8 284 This was related to overall heat-transfer coefficient, U using 55 2, 7 2. 58 the equation 1, 1 Q=U AAT wherein 975 2. 70 3. 88 Q: heat flux in B.t.u. per hour; 950 o6 915 1.80 3. 58 A heat transfer area of the outside surface of the tube; and 800 1, 00 32 AT log mean temperature difference for condensing 22( 1 3g i. gt; steam-cooling water system. 875 1: 30 4: 17 The results are shown in table II below. The heat transfer coef- 22g 2 i. Z; ficients are expressed in the following units: B.t.u./hour square foot F. mula:
The pressure drop was measured directly in feet of water w w g o o3 =p 5 to 2 25 using appropriate indicating gauges at the calorimeter inlet wherein w id and outlet. The results are shown in table II. w groove width and In addltlon, able [1 below Shows the Value for 0 angle of advance of the helically extending grooves. l- -H' expressed as the heat transfer 2. Tubing according to claim 1 made of a copper base alloy. "umber, 3. Improved tubing according to claim 1 having a wall The heat-transfer data are shown more graphically in the drawing which forms a part of the present specification From the foregoing data it can be clearly seen that the tubing of the present invention achieves a surprisingly high heattransfer coefficient while the accompanying increased pressure drop may be kept at a reasonable level.
This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential thickness of from 0.010 to 0.50 inch.
4. Improved tubing according to claim 1 having an outside diameter of from 0.25 to 10.5 inches.
5. Improved tubing according to claim 1 wherein the pressure drop is from 0.6 to 4.5 feet of water at 6 feet per second of water.
6. Improved tubing according to claim 1 having three independent, continuous grooves.