Improvements in Centrifugal Ventilating Fans and similar Machines.
Year: 1893

page_text: Date of Application, 30th Mar., 1893-Accepted, 24th June, 1893
COMPLETE SPECIFICATION.
Improvements in Centrifugal Ventilating Fans and similar
Machines.
I, CHARLES HERSCHER, of 95 Boulevard Beaumarchais, Paris, in the Republic
of France, Engineer, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
My invention relates to centrifugal fans and to similar machines such as
centrifugal pumps. My said invention is chiefly designed to provide an improved
fan for ventilating purposes, in which the parts are so arranged as to obtain the
highest efficiency both as regards the pressure, and the work which the fan is
capable of performing.
For this purpose I have sought, in designing my ventilator, to eliminate all
sources of loss of charge, or of eddies and shocks occurring during the passage of the
air or other fluid through the apparatus, and more especially ;-
1. Contraction of the fluid vein at the inlet of the ventilator.
2. Loss of suction due to the bend joining the inlet section and the entrance of
the channels formed by the vaues.
3. Contraction at the entrance of the said channels.
4. Eddies at the root of the vanes at the inlet apertures.
5. Loss of pressure of the fluid due to its passage through the channels formed
by the vanes.
6. Bad conduction of the fluid through the said channels.
7. Incomplete utilization of the working speed of the extremities of the vanes.
8. Unequal distribution of the fluid in the vortex-chamber at the delivery ends of
the vanes.
9. Shock to the fluid in passing through the channels into the vortex-chamber or
collector.
10. Friction and shocks to which the fluid is subjected during its passage through
the vortex-chamber or collector.
The arrangements whereby I am enabled to obviate the above mentioned
disadvantages, are shown in the accompanying drawings, in which :-
Figure 1 is a vertical section of a blowing fan, and
Figure 2 is a transverse section of the same.
Figure 3 is a section, parallel to the plane of the turbine, of a blowing and
exhausting fan, and
Figure 4 is a transverse section of the said blowing and exhausting fan.
Figure 5 is a diagram, drawn to an enlarged scale, showing one form of vane
developed or unrolled.
Figure 6 is a diagram in perspective, illustrating the formation of my improved
vanes.
Like letters indicate corresponding parts throughout the drawings.
I will now proceed to describe the apparatus and to successively analyze, in
detail, the arrangements adopted with a view to obviate the various losses of
pressure, eddies and shocks, enumerated above.
1. Means employed for preventing contraction in the cross-sectional area of the
inlet aperture.
The contraction in the inlet of a fan causes a loss of pressure corresponding to
the square of the difference between the velocity of the air in the contracted
section and the velocity of the air in the inlet ends of the moving channels between
the vanes.
In order to avoid the effect of this contraction, it is necessary that the velocity

page_text: imparted to the fluid, in its passage through the inlet aperture, should not be
diminished. For this purpose, I employ a trumpet-shaped mouth A, Figure 2,
placed over the inlet of the fan, in such a manner that the flow takes place, not as
in passing through a tube having thin walls or edges, or even as in passing through
a cylindrical tube, but as takes place with a conical tube the walls of which have
the proper convergence.
2. Diminution of the loss of charge due to the bend connecting the inlet section
to the entrance of the channels formed by the vanes.
The air enters the inlet in a direction perpendicular to that in which it moves
when entering the vortex-chamber or collector; from this fact results a loss of
pressure, which can be avoided by making the radius of curvature of the mean path
of the fluid large in proportion to the stream section.
Figures 2 and 4 show the radius of curvature obtained by the large amount of
convexity given to the inlet aperture.
3. Reduction of the contraction at the entrance to the moving channels.
The fans which have hitherto given the best results are those in which it has
been sought to give the fluid a constant relative velocity throughout its passage
through these channels. In fact the flow which thus takes place in a set of similar
sections, is comparable with that which takes place in a cylindrical tube, in which
the effect produced by a contraction of the inlet is well known. To obviate the
latter, the sections in my improved fan gradually grow narrower from the entrance
of the channels at E, F to their centre C, D, in order that the fluid may completely
fill the section (Figure 2).
4. Suppression of eddies at the root of the vanes near the inlet.
This result is achieved by giving to the different points of the inlet edges of the
vanes E, F normal to the curve E', F¹ described by the centre-line of the fluid-vein
at its entrance into the channels, an inclination corresponding to the speed at which
each of the said points is driven, in such a manner that the fluid enters the channels
between the vanes throughout the whole width of the vanes without shock.
:-
For this purpose each vane, mounted on the central plate M, M³, is formed as
follows, viz. The portion G, H of the vane is formed as if wound on an oblique
cone of circular section whereof the generating line, when at H, is perpendicular to
the plane of the turbine. Moreover the angle of the cone is selected in such a
manner that each of the points a, b, c, d, e, f, along the line G, L, Figure 5, receives
the fluid at a different angle, decreasing from a to f corresponding to their distance
from the centre of the turbine.
Since, on the other hand, the portion H, I of the vane is formed as if wound on
a cylindrical surface normal to the plate or disc M supporting the vanes, it follows
that the whole vane is capable of being developed or unrolled, a fact which
contributes to simplicity of construction.
In order that the formation of the vanes in my improved fan may be more
clearly understood, let it be supposed that the ellipse G H M, Figure 6, be the
trace, on the plane of the turbine, of an oblique cone of circular section, the apex
of which is at S. Let S H be the position of the generating line of the said cone
in which the said line is perpendicular to the plane of the turbine. The first
portion of the vane G Lh His formed as if it were wound upon the cone S G H M.
The distance G H is arbitrary and the point L is so chosen that the curve G L is
of the most suitable form for the entrance of the air.
Beyond the line Hthe vane is formed of a cylindrical surface h H IJ,
the generating line of which is parallel in all positions to the line S H. The
portion His made of suitable length in proportion to the dimensions of the fan.
I wish it understood that I do not limit myself to the use of the combination of
a cylindrical and a conical surface to form the curve of the vane, but I may employ
other surfaces capable of being developed or unrolled, with the exception of a
cylindrical surface alone.
5. Reduction of losses of air-pressure in the channels formed by the vanes.
This result is achieved partly by giving the mean stream-line of fluid passing

page_text: through the channels a large radius of curvature gradually decreasing, and partly
by limiting the section of the stream-channels formed by the vanes at their
smallest perimeter, the result varying according to the height and width of the said
channels.
6. Conduction of the fluid through the channels to the outlet thereof.
The curvature given to the vanes of the turbine has the effect of compressing
the air introduced into the moving channels. Therefore, the friction being greater
at the sides of the vanes than in the centre of the channel, the fluid moves under
the action of centrifugal force at unequal velocities, and a portion escapes at the
extremity of the vane without having attained the velocity which it is desired to
give it. To obviate this defect, it is necessary on the one hand that the length of
the channel should be proportioned to its width, so that the stream of fluid cannot
pass through without being acted upon by the sides of the vanes, and on the other
hand that the extreme length of the channels should be sufficient to ensure the
guiding of the fluid according to the desired angle of flow. This result J
accomplish in my fan by the peculiar arrangement of the vanes.
The vanes are of a convenient length (Figures 1 and 3) and are sufficiently
extended beyond the bend K to ensure the proper guiding of the fluid as it leaves
the channels.
7 and 8. Means employed to more effectually utilize the velocity of the turbine
at the extremity of the vanes and to throw the fluid into the vortex-chamber or
collector without eddies.
These objects are attained by giving to the vanes, at about the centre of their
length, widths gradually increasing from C, D to the outlet section M, P. This
special form of the vanes (see Figures 2 and 4) has the effect of imparting the
velocity at which the vanes are driven, not only from them to the fluid at the
medium line of the stream flowing through the channels but to a series of parallel
layers; whence it results, that for any given volume, a much greater number of
particles have the working velocity of the turbine imparted to them.
The gradual increase in the height of the vanes in the portion C, D,-M, P
further ensures that the fluid on its exit from the channels, shall be thrown at the
same time, to the centre and towards the circumference of the vortex-chamber or
collector, thus contributing to the avoidance of eddies in this part of the apparatus,
and to the equalization of the velocity of flow therein.
Further, since the transverse sectional area of the channels gradually increases
from the part C, D to the outlet section M, P, it follows, from what has been said
above in § 3 relative to the convergent form of the tube formed by the upwardly
extending part, of the said channels, that one of the characteristic features of my
fan consists in the use of convergent-divergent curvilinear channels obtained by
forming each vane of a successively decreasing and increasing width; the said
convergent-divergent channels permitting a full flow to be maintained throughout
their length and consequently obviating all eddies in their interior.
9. Diminition of shock as the fluid passes from the channels into the vortex-
chamber or collector.
The essential condition to be fulfilled in order to prevent shock between the
fluid leaving the channels, and that passing along the vortex-chamber or collector
is to give the same direction to the two bodies of fluid. It is therefore necessary,
that the direction of the absolute velocity of the fluid at the ends of the channels,
should not be opposed to that of the fluid in the vortex-chamber or collector, as is
the case in pans in which the vanes are inclined oppositely to the direction of
rotation, but that it should be as nearly as possible parallel to it. The curvature
of the vanes in a fan having an eccentric or concentric vortex-chamber or collector
should therefore be in the same direction as the rotation of the turbine.
This is accomplished in my improved apparatus by diminishing, as compared
with existing fans having constant relative speeds of flow, the angle between the
end portions of the vanes and the tangent to the external circumference of the
wheel.

page_text: 10. Reduction of friction in the vortex-chamber or collector.
This friction may be due to two different causes, firstly, to a perimeter too large
as compared with the section which it surrounds and secondly, to a too close
proximity of the walls of the vortex-chamber or collector upon which the fluid
leaving the channels is projected. These two disadvantages are obviated in my 5
improved apparatus by giving to the vortex-chamber or collectors of blowing or
exhausting fans of small diameter a circular section, which section offers, as is well
known, the minimum perimeter for any given area enclosed; and to the vortex-
chambers of blowing or exhausting fans or blowers of large diameter, such as the
mine ventilator shown in Figures 3 and 4, an approximately rectangular section 1
arranged in such a manner as to remove from the vanes the wall capable of
producing shocks.
DESCRIPTION OF THE APPARATUS.
Vane wheel. The vane-wheel is composed of a circular plate of sheet-steel M, M'
secured to the hub Q which is itself keyed to the rotating shaft R. Astride the 1
said plate are fixed from 24 to 30 sheet-steel vanes. These vanes are of simple
curvature and partly consist of conical or cylindrico-conical surfaces capable of
development, for example, bent round and forward towards the wheel so as to meet
the latter at an angle varying from 30° to 40°.
The vane-wheel is covered at its centre with a kind of conical torus S¹ of 2
stamped sheet brass, copper or other metal fixed at its small end to the shaft of the
vane-wheel and at its base to the plate at the root of the vanes. The wheel is
mounted on the shaft R which rests in two bearings T, T' placed symmetrically
on the right and left hand side of the turbine, and the said wheel rotates in a
casing U forming the vortex-chamber or collector. The position of the wheel with 2
respect to the vortex-chamber is such that its external circumference is tangential
at V to the interior wall of the vortex-chamber without intersecting it at any
point.
Shaft. The shaft R of the vane-wheel is made of decreasing transverse section
from the middle portion, where the wheel is fixed upon it, to its extremities, in 3
order to provide a body of equal resistance to torsion and bending.
It may be driven by two pulleys placed symmetrically, an arrangement which
possesses the advantages of reducing the section of the shaft in the bearings and
combining a rational well-balanced construction and avoiding all chances of mishap
with the minimum friction between the surfaces in contact.
Inlet aperture. Each of the inlet apertures is provided with a kind of bell-
mouth, fixed to the casing of the fan.
Mounting. In the mine ventilator, the rectangular delivery-pipe of which is
surrounded by a diffuser, the suction-orifice may take any direction whatever
around the trumpet-shaped pieces attached to the frame of the fan. It is only 4
necessary to vary the position of the bolts which hold the different parts together.
In the blowing-fan, any direction may also be given to the air delivery-pipe.
The casing of the fan is provided for this purpose with lugs m m', which may be
cast in any suitable position around the inlet-aperture.
The lower portion of these lugs in contact with the base-plate a, a carrying the
bearings, is of circular form, so that the setting of the lugs and of the pedestals
carrying the bearings determines at the same time the centre-line, the direction and
spacing of the bearings with respect to the vane-wheel shaft.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what 1
claim is :-
:―
The hereindescribed improved centrifugal apparatus more especially characterized
by:
First. The channels for the flow of the fluid, having the form of convergent-
divergent curvilinear tubes or ajutages and formed by vanes having their height 5

page_text: successively decreased and increased, or by other suitable means, the effect of
which is to obviate the contraction of the fluid when entering the said channels, to
increase its velocity at the extremities of the vanes, and to project it into the
vortex-chamber or collector without the production of eddies.
Second. The vanes having a form capable of development obtained by the
winding thereof on a cylindrical surface and on a cone of oblique base, in such a
manner that the various points on the internal edge of the vane at the entrance to
the channels are differently inclined according to their distance from the centre of
the turbine, in order that the fluid may enter throughout the whole height of the
channels, according to the angle of entrance found to be most suitable for
preventing eddies and shocks; I however claim the employment, for the purpose
above specified, of any surface capable of development, conical or otherwise, with
the exception of a cylindrical surface.
Third. The combination of the devices claimed in the preceeding claiming
clauses, with the various other arrangements described in the present Specification,
employed together or separately.
D101 3
CAL
1 1000
D. YOUNG & Co.,
11 & 12, Southampton Buildings, London, W.C.,
Agents for the Applicant.