Pipe joints or couplings – Elbow
Reexamination Certificate
1999-06-11
2001-01-30
Nicholson, Erik K. (Department: 3629)
Pipe joints or couplings
Elbow
C285S129200, C285S133110
Reexamination Certificate
active
06179342
ABSTRACT:
The design of this invention relates to the shape of a bend conduit for which its function is to eliminate pressure loss in a pipeline system caused by fluid turbulence, centrifugal force, and the boundary layer between the fluid and conduit.
BACKGROUND OF THE INVENTION
A conventional bend conduit
3
, as shown in
FIG. 1
, normally has a relatively large pressure loss when used with straight pipes
4
,
5
and
6
. The invention discussed forms a pipeline system, of which the fluid dynamic properties obey the following formula:
H=
(
p
1
−
p
2
)/&ggr;=&lgr;(
L/D
)(
Vm*Vm/
2
g
)+&zgr;(
Vm*Vm/
2
g
),
Wherein
H stands for the (measured) total pressure loss
P
1
: the static pressure of the fluid at point
1
in
FIG. 1
P
2
: the static pressure of the fluid at point
2
in
FIG. 1
&lgr;: the friction factor of the straight pipe
Vm: the mean velocity calculated from orifice readings
&ggr;: the specific weight of the fluid
Lu: the distance between the upstream measured tap (point
1
) and the entrance of the first bend conduit
Lm: the distance between the exit of the first bend conduit and the entrance of the second bend conduit
Ld: the distances between the exit of the second bend conduit and the downstream measured tap (point
2
)
L: Lu+Lm+Ld
g: the acceleration of gravity
&zgr;: total pressure loss coefficient due to two bend conduits in
FIG. 1
d: the diameter of the straight pipe
It is thus known that the total pressure loss (H) will be reduced if the total pressure loss coefficient(&zgr;) is smaller. In a pipeline system having two elbows, the value of pressure loss coefficient of the second elbow will be twice that of first elbow if the distance (Lm) is too short or two elbows are in a different plane (see FIG.
1
). If a pumped fluid passes through the first elbow, as shown in
FIG. 1
, a strong spiral motion is produced before entering the second elbow, which results in an additional pressure loss. The pressure loss occurs because the fluid cannot travel enough length to eliminate the spiral motion and recover to its normal velocity distribution. An analysis of a fluid flowing through bend conduits will be made hereinafter by means of principles of fluid dynamics. Upon a fluid flowing through a conventional bend conduit, as shown in
FIG. 2
, the fluid passes from the straight pipe section to the inner
7
and outer
8
curved portion and to the adjacent straight pipe. The passage has a high pressure vortex zone
9
and low pressure eddy zones
10
,
11
wherein the former will increase the resistance of friction along the fluid flow and the latter will induce a relatively large turbulent flow. This decreases the mean fluid velocity (Vm) and in turn increases the pipe cross sectional local velocity, or the pressure variations, thereby increasing the value of the pressure loss coefficient. The resistance of friction includes the inertial forces, caused by the centrifugal forces directed from the center of curvature acting at the vortex area
12
, and the frictional shear force resulting from the boundary layer acting at the boundary area
13
. In order to reduce the inertia forces caused by the centrifugal forces, it is proposed to decrease the acceleration of centrifugal force (V*V/R) (V stands for angular velocity) by increasing the radius of curvature (R) of the bend conduit. Prior arts are in the Bennett, U.S. Pat. No. 298,059. Bennett's bend conduit discloses forming an elbow conduit in such a way as to achieve an area of the inlet and outlet ends which join the main pipe to reduce the effects of friction and obstruction on the fluid thereby requiring less power to move the fluid. However, the Bennett patent is based on the area of the bend of intermediate section being twice the area of the first and second ends. Applicant's application is to increase the intermediate section by cutting off the corner of the inner portion and outwardly expanding the outer portion to a ball-like shape, and the area of the intermediate section is larger than the first end only. The second end may be either more or less than the area of the first end. The reason is very clear: wherein the intermediate section is enlarged by cutting off the edge of the inner corner and outwardly expanding the outer portion as a ball-like shape to provide the bend conduit with a low pressure loss coefficient whether the second end is large or small. Shaefer, U.S. Pat. No. 4,514,244, which is the same as Bennett, requires that opposite ends be of the same area size.
SUMMARY OF THE INVENTION
The objective of this invention is to provide a bend conduit design resulting in a low pressure loss coefficient The further objective of this invention is to decrease the desired pump power needed to drive a fluid through bend conduits resulting in saving energy. In addition, the objective of the present invention is to provide many band conduits with lower pressure loss coefficient in which the spiral motion within the first and adjacent second bend conduit will be greatly reduced. Then a pipeline system of many bend conduits is to decrease total pressure loss. The present invention is based on the above analysis and by means of the following measures: 1) In order to reduce the pipe cross sectional local velocity variation caused by the turbulent flow or to reduce the turning pressure loss, the low pressure eddy zone
10
of a conventional conduits in
FIG. 2
needs to be as small as possible. This can be done by cutting off edge
14
to increase the radius of curvature of inner curved portion
7
wherein the angle of the incidence(&agr;) is between 40° to 50° with reference to the direction of inlet of the flow as in
FIG. 3
, preferably 45°. 2) In order to reduce the acceleration of centrifugal force (V*V/R) in the bend conduit to decrease the resistance of friction acting at vortex area
12
, another method is to enlarge the cross section of the turning portion by outwardly expanding the outer curved portion
16
to be a ball-like shape as in FIG.
3
and/or expanding the opposite sides
17
,
18
to be a ball-like shape as in
FIG. 4
, then increasing the cross sectional area and decreasing the angular velocity (V). This will help to eliminate the low pressure eddy zone
11
; 3) In order to reduce the pressure gradient caused by the boundary layer or to minimize the frictional shear force at the boundary area
13
, the best way is to expand the intermediate area from the bend conduit inlet to the middle of the intermediate section. Furthermore, in order to minimize the drag force caused by the frictional shear force, the streamlined design will achieve a more uniform velocity variation. The cross sectional area ratio between the middle of the intermediate section and the bend conduit inlet section is 1.2 to 2.0, or even more than 2.0. The present invention can effectively achieve the objective in that it is contrived after having fully and carefully considered and studied factors possibly influencing the pressure loss coefficient. The conventional elbow has a pressure loss coefficient of 0.8-1.4; the value can be reduced to smaller than 20% according to the present invention. The present invention may best be understood through the following description with reference to the accompanying drawings.
REFERENCES:
patent: 836320 (1906-11-01), Hanlon
patent: 917395 (1909-04-01), Wise
patent: 977740 (1910-12-01), Higgins
patent: 1989608 (1935-01-01), Reed
patent: 2286565 (1942-06-01), Norton
patent: 2879848 (1959-03-01), Drummond
patent: 5054819 (1991-10-01), Grunwald
patent: 598919 (1934-06-01), None
patent: 1102040 (1961-03-01), None
patent: 1120367 (1961-12-01), None
patent: 1123256 (1962-02-01), None
patent: 1146808 (1963-04-01), None
patent: 184082 (1922-08-01), None
patent: 601130 (1959-12-01), None
patent: 404362394 (1992-12-01), None
patent: 406109192 (1994-04-01), None
patent: 505850 (1976-03-01), None
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