FIELD OF THE INVENTION
This invention refers to the development of an internally finned tube with axial or
longitudinal ribs and its manufacturing for the heat transfer applications
adaptable to single-phase flow, two-phase flow, boiling, evaporation and
condensation.
BACKGROUND OF INVENTION
The axial or longitudinal ribs are used for enhancing the heat transfer in both
single and two-phase flow applications. Wolverine tube manufactures straight
inner finned tubes, which are drawn or swaged and have around 6 to 50 axial
ribs of 0.635 to 1.575 mm over diameter range of 8 to 20 mm (wolverine tube
Catalogue). These ribs are not microfins, which are better in application of
interest stated above.
An Us patent number 3422518 discloses a method involving externally swaging a
cylindrical tube black against a grooved mandrel, which displaces metal from
blank wall into the grooved mandrel to form fins. This also leads to extensive
elongation of blank resulting into considerable reduction of wall thickness, which
is advantageous for heat exchange. The disadvantage with this approach is that
large reduction are present, which adds load to the machine.

A German patent number 3231318 (A1) discloses internally ribbed tube
comprising of shell strips bearing plurality of ribs in the longitudinal direction and
welded together at the longitudinal sides. This tube is manufactured for heating
boilers heated by means of pressurized gas or oil. The disadvantage of this
method is number of welded joints, which limit the use to lower operating
pressures and leak proof operations.
Another German patent number 3222944 (C1) discloses internally ribbed tube for
central heating boilers of low temperature systems. It is made of integral casing
strips of T or U shaped rolled or folded chamfered profiles of appropriate length,
with longitudinal ribs are welded together along the side. One T and one U
profile are fastened alternately to each other thus forming an internally ribbed
tube. The disadvantage of this method like above invention is number of welded
joints, which limit the use to lower operating pressures and leak proof
operations.
With the HFIW or ERW tube as the base tube, thickness can be controlled in the
beginning of the fin manufacturing process. The axial ribbed tube of present
invention is made by using a cold-drawing process with a die and profiled plug,
which uses an ERW or HFIW tube as base tube and produces longitudinal ribs
along the tube length. The ribs have trapezoidal cross-section, which makes this
tube versatile for heat transfer application in single-phase flow, boiling,
evaporating and condensation.

To achieve the objectives of this invention, the flat topped trapezoidal rib shapes
are designed with underlying basis of fully developed fluid flow and Nusselt
number characteristics of trapezoidal ducts having tube inner wall surface of
length equal to distance between two consecutive ribs at the base of ribs and
these rib sides forming a trapezoidal channel. The rib geometry is shown in
Figures 1(a) and (b) and has following characteristics:

The axial ribbed tube (inside diameter d) of present invention is manufactured
using a cold drawing process with a die and profiled plug.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose the development of
an internally finned tube with axial or longitudinal ribs adaptable to heat transfer
application which eliminates the disadvantages of prior art.
Another object of the present invention is to propose the development of an
internally finned tube with axial or longitudinal ribs adaptable to heat transfer
application which is applicable to single phase flow, two phase flow, boiling,
evaporation and condensation.
A further object of the present invention is to propose the development of an
internally finned tube with axial or longitudinal ribs adaptable to heat transfer
applicable of flow of water, calcium chloride line solutions and ethylene glycol
line solutions.
A still further object of the present invention is to propose the development of an
internally finned tube with axial or longitudinal ribs adaptable to heat transfer
application which is applicable for heat transfer of medium and high pressure
water boiling inside the tube.
An yet further object of the present invention is to propose the development of
an internally finned tube with axial or longitudinal ribs adaptable to heat transfer
application which is applicable for heat transfer of low pressure in tube
refrigerant and water evaporation and condensation.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Fig - 1 (a) & (b) shows a schematic view of an axial ribbed tube along with the
cross-sectional view showing flat topped trapezoidal rib configuration.
Fig -2 (a) & (b) shows a photo-view of cross section of tube and an enlarged
view of inside finned rib along the cross-section.
SUMMARY OF THE INVENTION
Accordingly there is provided internally ribbed tube with an inside diameter d, for
heat transfer application comprising regularly spaced axial or longitudinal ribs
having flat topped trapezoidal cross-section for efficient heat transfer
applications in one of a Single phase flow, a two phase flow, a boiling, an
evaporation and a condensation, said internal ribs configured by maintaining the
device parameters relationship, in which

The internally ribbed tube (inside diameter d) of present invention is
manufactured using a cold drawing process with a die and profiled plug.
In the cold drawing step, axial or longitudinal ribs are formed on the inside of an
ERW or HFIW tube using a plug having plurality of axial or longitudinal grooves
on its surface.
DETAILED DESCRIPTION
Figures 1 (a) and (b) show axial ribbed tube of this invention along with the
cross-sectional view showing schematically flat topped trapezoidal rib geometry.
This invention refers to a developed configure of an axial ribbed tube using axial
or longitudinal ribs having flat topped trapezoidal cross-section and
manufacturing of these internally ribbed tubes for heat transfer applications
involving single-phase flows, two-phase flows, boiling, evaporation and
condensation. The present invention overcomes the limitations as posed by
applications of prior art. This invention refers to the design of an axial ribbed
tube using axial or longitudinal ribs used for both boiler and low pressure
evaporators and condensers. More importantly, the present invention provides
longitudinal or axial regularly spaced ribs, which are also useful for medium and
high pressure water boiling inside tubes and low pressure in tube refrigerant and
water evaporation and condensation, including heat transfer applications in
single and two phase flows.
The flat tapped trapezoidal ribs (refers Figuresl (a) to (d)) are longitudinal and
regularly spaced with following geometric characteristics:

The internally roughened tube (inside diameter d) of present is manufactured
using a cold drawing process with a die and profiled plug. In the cold drawing,
spiral lands are formed on the inside of an ERW or HFIW tube using a plug
having plurality of axial or longitudinal grooves on its surface.
Fig 2 presents axial ribbed tube manufactured with above geometric
characteristics. It has following dimensions and characteristics:
Outer diameter: 25 - 25.02 mm, Thickness: 2.2 - 2.39 mm, Rib angle at rib
base: 137°-147°, Rib height:0.21-0.28 mm, Rib width (top): 1.06-1.11 mm, Rib
width (bottom): 1.33-1.39 mm, No. of ribs: 15, pitch: 4.23 mm, Heardness: as
drawn - on rib 176/177 VPN & between ribs -185/187 VPN
This tube has performance in laminar flow as computed using correlation given
by Compo and Chang (1997) and presented below as

This tube has perform in turbulent flow as computer using correlations given by
Cornavos (1980) for 0.7 = Pr = 25 and presented below as

It is seen that same performance in heat transfer and same efficiency index
value is achieved for length of 4.5619 m. Shorter tube length than 4.5619 m
provided heat transfer performance and higher efficiency index values.
REFERRED PATENTS
1. French, F.W., 1969, Method of reforming tubular metal blanks into inner-
fin tubes, US Patent No. 3422518.
2. Heim, K., 1984, Internally ribbed tube for heating boilers heated by
means of pressurized gas or pressurized oil, DE 3231318 (A1).
3. Schuster, O., 1987, internally ribbed tube for central heating boilers
consists of welded rolled or bevelled profiles of T-shape, or U = shape,
DE 3222944 (C1).
4. Campo, A. and Chang, 1, 1997, Correlation equation for friction factors
and convective coefficients in tubes containing bundles of internal,
longitudinal fins, Heat and Mass Transfer, Vol. 33, pp. 225-232, 1997.
5. Kim, N-H. and Webb, R.L., 1993, Analytic prediction of the friction and
heat transfer for turbulent flow in axial internal fin tubes, Journal of Heat
Transfer, Vol.115, pp.553-559.
REFERENCE
1. Wolverine Tuber Catalogue.
WE CLAIM
1. Internally ribbed tube with an inside diameter d, for heat transfer
application comprising regularly spaced axial or longitudinal ribs having
flat topped trapezoidal cross-section for efficient heat transfer applications
in one of a Single phase flow, a two phase flow, a boiling, an evaporation
and a condensation, said internal ribs configured by maintaining the
device parameters relationship, as given below
- a/e < 2
- 0.66 = a/b = 0.99
- 0.3 < s/e < 20
- 0.01 = e/d = 0.07
Where,
a = top width of the rib
b = base width of the rib
s = distance between the two consecutive ribs at base
e = height of the rib
d = internal diameter of the tube
2. Internally ribbed tube as claimed in claim 1 for heat transfer applications,
wherein the device parameters are maintained as follows:
Outer diameter of the tube: 25-25.02 mm, Thickness of the tube: 2.2-2.39
mm, Rib angle at rib base: 137-147°, Rib height:0.21-0.28 mm, Rib width
(top): 1.06-1.11 mm, Rib width (bottom): 1.33-1.39 mm, Number of ribs:
15, Pitch: 4.23 mm, Hardness when drawn - on rib 176/177 VPN &
between the ribs - 185/187 VPN.
3. Internally ribbed tube for efficient heat transfer applications as herein
substantially described and illustrated with reference to the accompanying
drawings.

The present invention relates to an internally ribbed tube with an inside diameter
d, for heat transfer application comprising regularly spaced axial or longitudinal
ribs having flat topped trapezoidal cross-section for efficient heat transfer
applications in one of a Single phase flow, a two phase flow, a boiling, an
evaporation and a condensation, said internal ribs configured by maintaining the
device parameters relationship, as given below
- a/e < 2
- 0.66 ≤ a/b ≤ 0.99
- 0.3 < s/e < 20
- 0.01 ≤ e/d ≤ 0.07
Where,
a = top width of the rib
b = base width of the rib
s = distance between the two consecutive ribs at base
e = height of the rib