WO2007144899A2 - Conduit comportant des nervures hélicoïdales internes - Google Patents

Conduit comportant des nervures hélicoïdales internes Download PDF

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Publication number
WO2007144899A2
WO2007144899A2 PCT/IN2007/000228 IN2007000228W WO2007144899A2 WO 2007144899 A2 WO2007144899 A2 WO 2007144899A2 IN 2007000228 W IN2007000228 W IN 2007000228W WO 2007144899 A2 WO2007144899 A2 WO 2007144899A2
Authority
WO
WIPO (PCT)
Prior art keywords
duct
rib
cable
range
ribs
Prior art date
Application number
PCT/IN2007/000228
Other languages
English (en)
Other versions
WO2007144899A3 (fr
Inventor
Srinivas V. Veeravalli
Vijay Kiyawat
Original Assignee
Dura-Line India Pvt. Ltd.
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 Dura-Line India Pvt. Ltd. filed Critical Dura-Line India Pvt. Ltd.
Publication of WO2007144899A2 publication Critical patent/WO2007144899A2/fr
Publication of WO2007144899A3 publication Critical patent/WO2007144899A3/fr

Links

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
    • H02G3/00—Installations of electric cables or lines or protective tubing therefor in or on buildings, equivalent structures or vehicles
    • H02G3/02—Details
    • H02G3/04—Protective tubing or conduits, e.g. cable ladders or cable troughs
    • H02G3/0462—Tubings, i.e. having a closed section
    • H02G3/0487—Tubings, i.e. having a closed section with a non-circular cross-section

Definitions

  • Plastic ducts have long been used for installation of telecom or electrical cables. These ducts come with smooth inside surface or have multiple longitudinal ribs on the inside that are sometimes straight and sometimes helical. The number of such ribs in conventional ducts varies from 20-40 with varying helix angle in case of spiral ribs. Different manufacturers of such ducts also employ different rib heights with typical rib height in the range of 0.2 to 0.4 mm. However, the design of such ribs is not scientific and the efficiencies of cable installation shows only marginal, if any, improvement in a ribbed duct over the smooth wall duct. This has resulted in the industry often opting for a smooth wall duct over a ribbed duct.
  • cables were pulled through ducts by a winch line in which every time a bend or undulation in the duct was passed the pulling force is multiplied by a factor that depends on the friction. Higher the local pulling force, higher the friction that the cable is experiencing while being pulled against the internal duct wall resulting in an exponential force build-up with pull distance, producing generally high pulling forces. Tension in the cable on account of the pulling forces cannot exceed a certain safety margin of the cable or it may break.
  • Ducts with ribs, longitudinal or helical, are believed to reduce friction between the cable and duct.
  • Examples of ribbed duct are shown in U.S. Patent No. 4565351 and US 5087153 that are hereby incorporated by reference.
  • a smooth duct that is a duct having a smooth inner surface
  • the cable rests on one surface of the duct and the pulling force used to pull the cable through the duct has to overcome the frictional forces between the cable and the duct.
  • the use of ribbed ducts, as described in US Patent No. 5087153 attempts to overcome this drawback and experimental results disclosed therein indicate that for the same pulling force spiral ribs offer a reduction in frictional force.
  • Cable blowing involves the cable being installed through the duct using compressed air. This compressed air flows through the duct and along the cable at high speed. The friction of the cable is compensated locally by the distributed airflow and the large forces that would generate high friction are avoided. Special lubricants both solid as well as liquid have been developed for cable blowing that assist in the installation of cable by reducing friction.
  • Cable blowing has the advantage that longer installation distances can be reached and is less dependent on bends and undulations in duct. Forces exerted on the cable are also significantly lower. Cable blowing is especially popular for laying of fiber optical cables that are lightweight and flexible and require long lengths of uninterrupted cable. It is a requirement in the field of fiber optic cable blowing that greater length of cable be installed per day with the existing equipment and without a significant increase in the pressure of the compressed air. For the cable blowing method of installation a variety of factors assume importance. The factors that influence the design of a rib for a duct in which the cables are to be installed by pulling, as disclosed by US 5087153, are different from those that are relevant when the rib is used in a duct in which the cable is to be installed by blowing.
  • the axial force may be defined as the force acting on the cable by the flowing air, while the net force or net axial force on the cable is calculated by deducting the frictional and the other forces from the axial force.
  • the ribs be designed so that a reduction in friction force is achieved without a reduction in the net axial force.
  • the invention provides for a method of designing spiral ribs for a duct used in cable blowing comprising the steps of: a. selecting an apex angle of rib in the range of 80 to 120 degrees; b. determining the longitudinal spacing between the ribs from the cable thickness and mass; c. deriving a range of values for rib density and the helix angle from the longitudinal spacing, d. determining the optimum rib density and helix angle from the range of values by determining net axial force for the range of values; e. determining the optimum rib height for the optimum rib density and helix angle, such that a reduction in friction between the cable and the duct without a significant or no reduction in axial force is achieved.
  • the invention also provides for a duct with a forty-millimeter outer diameter for cables comprising an outer surface and an inner surface, wherein the inner surface is provided with 4 to 10 spiral ribs, each rib having apex angle in the range of 80 to 120 degrees; a helix angle in the range of 5 to 15 degrees and rib height in the range of 1 to 1.5 mm
  • Figure 1 illustrates the geometry of the rib in accordance with an embodiment of the invention.
  • the invention provides for a duct with ribs and more specifically to a duct with spiral ribs in which the ribs have been designed to optimize the net axial force. - ' •
  • the invention aims at optimizing the rib design so that a reduction in friction is achieved without compromising on the net axial force.
  • the invention also aims at providing a method of rib design for optimum ribs.
  • the design of the ribs in accordance with the invention is on the assumption that a lubricant will be used in the cable blowing process. Though various lubricants are available, a standard liquid lubricant is typically employed.
  • the friction force between the duct and the cable varies with contact area and the parameter controlling this is trie rib density and geometry.
  • the friction force is directly dependent on rib density.
  • the main parameter that is relevant to the blowing process is the net axial force on the cable at constant cable speed, that is the difference between the force exerted by the compressed air and the friction force between the cable and the duct.
  • the invention has been described with reference to a duct having an outer diameter of 40 mm, inner diameter of 34.2 m ⁇ i and for a cable having a 15 mm diameter.
  • the 40 mm outer diameter duct is the most commonly used duct in industry and the optimization of the rib parameters has therefore been done for this duct. It is, however, within the scope of the invention to apply the principles taught herein to other duct diameters without sacrificing the spirit of the invention.
  • results of experiment conducted on a smooth wall duct with a 15mm diameter cable are tabulated.
  • the cable was suspended with the gap below the cable varying from zero to a concentric configuration.
  • the average velocity in the duct is seen to reduce, however, the axial force on the cable increases since progressively larger regions of the cable are subjected to a large shear stress.
  • the cable is lifted off the bottom and it is therefore possible that lifting of cable compensate a reduction in the mean velocity due to ribs.
  • the aim of the rib is to move the cable towards the center of the duct without touching the duct inner surface so that the air force applied is all around the cable and greater net axial force may be achieved.
  • Experiments conducted by the applicant have shown that the conventional spiral-ribbed ducts result in a reduction in friction force while also resulting in a 15 to 20 per cent drop in the effective axial or pulling force. '
  • the mean hydraulic diameter of the duct has been defined as four times the cross sectional area of the duct divided by the wetted parameter of the duct (4 * cross sectional area/wetted perimeter).
  • the cross sectional area referred to is the inner cross sectional area of the duct with or without ribs and the wetted perimeter refers ko the inner perimeter of the duct with or without ribs.
  • the smaller the mean hydraulic diameter greater is the resistance to flow and thus resulting in lower axial force.
  • Conventionally available ducts tend to use a smaller rib height and a greater rib density.
  • an increase in the rib density results in the cross sectional area decreasing and the wetted perimeter increasing, thereby resulting in a decrease in the mean hydraulic diameter and a decrease in the net axial force, in spite of the reduction in frictional force.
  • the invention therefore provides for a method of optimum rib design applying the principle of mean hydraulic diameter.
  • the method provides for first selection of a apex angle and base angle of the rib irrespective of rib height.
  • On the basis of cable stiffness the longitudinal spacing between ribs is decided.
  • This longitudinal spacing may be achieved by using various combinations of rib density and helix angle.
  • This step is followed by the step of determining a range of helix angles for a range of rib densities and determining the optimum range of helix angles.
  • the range of rib density is determined.
  • the rib density range could be determined first followed by the computation of the range for helix angle.
  • the optimum helix angle and rib density are selected for the desired longitudinal spacing.
  • the optimum rib height is determined.
  • the apex angle of the rib should be at least 80 degrees and may be as large as 120 degrees. Furthermore, the larger of the two base angles of the rib results in the rib being inclined in a particular direction.
  • the duct having such ribs will have to be laid taking into consideration the direction of the inclination of the rib such that the net axial force is higher.
  • the base angle of the ribs be the same. In other words, it is preferred that the rib be an isosceles triangle with the apex angle of at least 80 degrees.
  • Such a rib configuration maximises the mean hydraulic diameter for a given rib density while at the same time, allowing the duct to be laid in any direction. Keeping the apex angle between 80-120 degrees maximizes the mean hydraulic diameter in all cases/configurations. From a manufacturing perspective, it is preferred that the angle be 90 degrees.
  • the longitudinal spacing between ribs is selected taking into account the stiffness of the cable to be blown and its mass per unit: length.
  • a suffer cable affords a larger distance between points of support and hence a lower rib density may be employed.
  • the longitudinal spacing between the ribs should lie between 10cm and 15cm. This spacing can be achieved using various combinations of rib density and helix angle.
  • the cable has been kept 1mm above the ribs.
  • the pitch of the ribs be not much greater than 10cm.
  • the pitch is 10.1 cm while with the 8 rib, 5° combination the pitch is 15.4cm.
  • the configuration with 6 ribs of helix angle 10° appears to be optimal.
  • the optimal rib height cannot be obtained with these calculations since the gap between the rib and the cable is comparable with the rib height.
  • a fourth set of calculations was done, wherein the gap between the cable and the rib was reduced to 0.25mm. ,•
  • the table below lists the findings of the computer simulations conducted by the applicant on a smooth duct, a conventional ribbed duct and the duct in accordance with the invention.
  • the smooth duct for a pressure drop of 4660 Pa/m provides a net axial force or pulling force of 1.16 N.
  • a duct having * thirty conventional spiral ribs with a rib height of 0.3 mm results in a drop in the effective axial force or pulling force.
  • the duct in accordance with the invention for a given rib density 6 to 8 and for a rib having an isosceles triangle with the apex angle between 80 degrees and 120 degrees, and a helical angle of 5 to 15 degrees the rib height was varied from 1 to 1.5 mm. As can be seen, for a rib height of 1.25 mm the effective axial force acting on the cable is nearly same as that in the case of smooth wall duct (1.17v/s 1.16 ). Experiments conducted at HT Delhi have also shown that a 15 to 20% reduction in friction was achieved with the conventional spiral duct over the smooth duct. The duct in accordance with the invention has much lower friction in comparison with the conventional spiral duct and hence is expected to yield a 35 to 40 % reduction in friction for the same axial force or blowing force.
  • rib density in the duct in accordance with the invention is much lower than that of the conventional ribbed duct.
  • Applying the method of rib design as taught by the invention ribs for different duct sizes may be determined. It is also to be noted that the optimum ribs as defined by the invention may be uni-direction or alternating.

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  • Engineering & Computer Science (AREA)
  • Architecture (AREA)
  • Civil Engineering (AREA)
  • Structural Engineering (AREA)
  • Details Of Indoor Wiring (AREA)
  • Light Guides In General And Applications Therefor (AREA)

Abstract

L'invention concerne un procédé de formation de nervures hélicoïdales pour un conduit utilisé dans le cadre d'un soufflage de câbles, comprenant les étapes consistant à sélectionner un angle de sommet de nervure compris dans la gamme de 80 à 120 degrés; déterminer l'espacement longitudinal entre les nervures par rapport à l'épaisseur et à la masse du câble; dériver une plage de valeurs pour la densité de nervures et l'angle d'hélice à partir de l'espacement longitudinal, déterminer la densité de nervures optimale et l'angle d'hélice optimal à partir de la plage de valeurs en déterminant une force axiale nette pour la plage de valeurs; et déterminer la hauteur de nervure optimale pour la densité de nervures et l'angle d'hélice optimaux, de telle sorte qu'une diminution du frottement entre le câble et le conduit sans réduction significative voire sans réduction de la force axiale soit obtenue.
PCT/IN2007/000228 2006-06-14 2007-06-06 Conduit comportant des nervures hélicoïdales internes WO2007144899A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IN1409DE2006 2006-06-14
IN1409/DEL/2006 2006-06-14

Publications (2)

Publication Number Publication Date
WO2007144899A2 true WO2007144899A2 (fr) 2007-12-21
WO2007144899A3 WO2007144899A3 (fr) 2009-04-16

Family

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Family Applications (1)

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PCT/IN2007/000228 WO2007144899A2 (fr) 2006-06-14 2007-06-06 Conduit comportant des nervures hélicoïdales internes

Country Status (2)

Country Link
MY (1) MY180662A (fr)
WO (1) WO2007144899A2 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11815216B2 (en) 2020-06-18 2023-11-14 United Pipeline Systems, Inc. System and method for installing pipe liners

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5692560A (en) * 1993-06-07 1997-12-02 Trefimetaux Grooved tubes for heat exchangers in air conditioning equipment and refrigerating equipment, and corresponding exchangers
US20030173071A1 (en) * 2002-03-12 2003-09-18 Pascal Leterrible Reversible grooved tubes for heat exchangers

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5692560A (en) * 1993-06-07 1997-12-02 Trefimetaux Grooved tubes for heat exchangers in air conditioning equipment and refrigerating equipment, and corresponding exchangers
US20030173071A1 (en) * 2002-03-12 2003-09-18 Pascal Leterrible Reversible grooved tubes for heat exchangers

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11815216B2 (en) 2020-06-18 2023-11-14 United Pipeline Systems, Inc. System and method for installing pipe liners

Also Published As

Publication number Publication date
MY180662A (en) 2020-12-04
WO2007144899A3 (fr) 2009-04-16

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