US2322357A - Centrifugal fan - Google Patents

Description

June 22, 1943. H. F. HAGEN CENTRIFUGAL FAN l Filed Feb. 4, 1942 2 Sheets-Sheet l June 22, 1943. H. F. HAGEN l CENTRIFUGAL FAN Filed Feb. 4, 1942 2 Sheets-Sheet 2 Air Hecrer 644x040 F7 HAGEN y @fam/1@ M 'dll-'il UNITED STATES PATENT- OFFICE CENTRIFUGAL FAN Harold F. Hagen, Wellesley, Mass., assgnor to B. F. Sturtevant Company, Boston, Mass.

Application February 4, 1942, Serial No. 429,523

Claims. (Cl. 23o-132) This invention relates to centrifugal fans and has as its object the straightening of the spiral fluid how in the fan into straight line flow into the outlet ducts connecting the fans to loads.

In steam power plants, for example, it is customary because of limitations of space, to connect the outlets of centrifugal fans by relatively short outlet ducts to air heaters. The air heaters are relatively large and are connected by divergingr transformation plates to the relatively short outlet ducts previously mentioned. This causes a sudden expansion of the air before it has traveled but a short distance from the fan. As a result there is no opportunity for the flow lines to straighten out and there is considerable turbulence in the air flowing between the fan and the load with a corresponding loss in eiciency.

This invention provides transition vanes in the Fig. 1 how the position and shape of a transition vane are determined, and

Fig. 3 is a view partially in section and shown partially in dotted outline of a fan embodying this invention and connected by a short duct to an air heater.

Referring now to Fig. 2, a wheel circle having a radius of 16 units is drawn. A reference line is drawn horizontally through the center of the Wheel circle. The scroll of the fan is selected to start at a on the reference line where the radius ru=20 units and to extend through an angle of 270. Radial lines are drawn every 30 for plotting the scroll line and are indicated on Fig. 2 by r1, r2, r3, r4, T5, Tt, r'r, rs, and rf. The radius of the scroll point on each of the above mentioned radial lines is calculated by the formula:

outlet of a centrifugal fan and which extend from K log L points adjacent the delivery portion of the fan 20 y T0 wheel into the outlet duct and which are so m Whlch shaped and arranged that they intercept equal T0220 volumes of fluid and provide transition from the spiral flow which exists in the housing, to straight flow which is desired in the outlet connection.

Different flow conditions eXist in different portions of the fan housing and accordingly a num ber of transition vanes are provided, each being so shaped with respect to its location that the At the angle of 270 the terminating point of the scroll, shown as rf on Fig. 2 is selected as 33.7

air particles are directed Without turbulence into umts' Then the outlet. 700 K lo 3 3 .Z

For determining the shape and positions of the g 20 transition vanes, an elevation view in a plane and perpendicular to the axis of the fan is drawn and contains the scroll, the fan wheel and a portion of the outlet duct. A reference cylinder is selected and drawn in. The cylinder is then developed for forming a conformal chart. The scroll surface is laid out on this chart Where it appears as a straight line drawn at an angle to the base line because of its exponential shape. Reference lines in the fan for determining the shape of the transition Varies are drawn in their selected positions parallel to the developed scroll line. The positions of the fan outlet and of the =1190 log 2L() outlet duct are laid out on the conformal chart loef; Analog f and reference lines in the duct corresponding to the reference lines in the fan are plotted on the 02,

. t2 1.06 21.2 (r.) conformal chart. Lines connecting these lines on .0505 1.122 22.5 (r2) the conformal chart are the transition vanes gi; thereon. These lines are transferred back to the 21262 12340 65 (r2) elevation View and appear there in the proper positions for the transition vanes. 1202 1f 592 3119 (ri) The invention will now be described with refer- -227 M555 7 (fr) ence to the drawings, of which:

Fig. 1 is a conformal chart plotted from data obtained from Fig. 2.

Fig. 2 is a View of an outline of a centrifugal fan drawn in a plane perpendicular to the axis of the fan and illustrates in association with as follows: The sum of the x ordinates, the length of the unrolled cylinder The spacing between the :c ordinates every 30,

:9 '7: L: .7... 12 ..0.93-l-l 23R log [Au 92 log To From this dat-a the scroll line is plotted to scale on the conformal chart of Fig. 1 and appears as a straight line terminating at the ninth a: ordinate corresponding to p:270 where the scroll joins with the fan outlet as shown by Fig. 2.

The outlet duct joins the outlet of the fan along the vertical line connecting the points a-ai, of Fig. 2. The point a is on the horizontal reference line previously referred to of Fig. 2 where :0 and 360. The point a may therefore be plotted at 16:12 and y:0 on the conformal chart of Fig. 1,

The point ai of Fig. 2 happens to occur at o: 300 corresponding to :l0 on Fig. 1. The corresponding y ordinate on Fig. 1 is determined as follows: The distance from the center of the wheel of Fig. 2 to the point ai of Fig. 2 is scaled o and found to be 39 units 11:39). The formula gives for y a value of 26.6 units. This is plotted at :6:10 on Fig. 1 and establishes the position of the outlet duct, the line connecting a and ai on Fig. l, For properly establishing the position of the curved line connecting a and ai on Fig. 1, another point at pz-330 on Fig. 2 corresponding to 2:11 on Fig. 1, is selected and a radial line is drawn at 330a on Fig. 2 and where this line intersects the vertical duct line connecting a and ai on Fig. 2. the radius r is scaled and found to be 23.5 units. The formula y=2-3R log, -0=921og -20 gives y a value of 6.45 which is plotted at :1::11 on Fig. 1 and is shown at 1*:11 on the curved line connecting a and a1 on Fig. 1.

To show the position of the outlet duct at a point distant from the fan outlet, the radial line at qf :330c is continued on Fig. 2 to intersect the horizontal upper line of the duct at c. The distance from the center of the fan wheel to c is scaled and found to be r:67.5 units. This substituted in the formula r 67.5 Y :92 log l=92 log :20:

gives g/:84-6 which is plotted as y:84.6 and 33:11 on Fig. 1 and appears at c on Fig. 1. The line connecting c and ai on Fig. 1 corresponds to the horizontal line extending from ai to c on Fig. 2.

By way of example, the position and shape of a transition vane for connecting the mean line in the fan with the mean line in the outlet duct is determined as follows:

A line on Fig. l is drawn through 30:6 parallel to the scroll line as the mean line in the fan. The mean line in the outlet duct to be drawn in on Fig. l is determined as follows: The mean line of the duct is drawn in on Fig. 2 as half way between the upper and lower walls of the duct. At the angle :330 where the radial line drawn at this angle intersects the mean line of the duct of Fig. 2, the radial distance r is scaled and found to be 34 units. This substituted in the formula T o y 23R 10g Tu 9- log 20 gives y:21.2, which value is plotted to scale at x:11 on Fig. 1 to give one point on the mean line of the duct to be drawn in on the conformal chart of Fig. 1.

Another point on Fig. 2 is selected at p:340, corresponding to :11.5 on Fig. l. The radial line drawn at this angle intersects the mean duct line on Fig. 2 at a point which is scaled to give r:65.5 units. This substituted in the formula y=92 log 2% gives y:4'7.4 which is plotted to scale on Fig 1 at 3::115. These two y ordinates at :6:11 and :11.5 are sufficient to establish the mean duct line on the conformal chart and by means of a draftmans French curve a curved continuous line is drawn on Fig. l connecting the dashed mean line of the duct with the dashed mean line of the fan. This solid curved line is the developed mean line transition vane surface, and when the corresponding surface is plotted on Fig. 2 as will now be explained, the mean 4line transition vane may be drawn in there.

Nine equally spaced y ordinates are projected from the transition vane line of Fig. 1 onto the :c-Aline and are shown on Fig. 1 by the nine vertical dashed lines numbered 1-9 inclusive. Corresponding dashed radial lines are drawn on Fig. 2 to corresponding points on the reference cylinder' and are numbered there 1 9 inclusive. For the purpose of avoiding confusion, the radial lines just referred to are not continued all the way on Fig. 2, from the wheel axis to the reference cylinder surface, sufficient of the radial lines being drawn in to enable the points on the transition vane to be plotted as will now be described.

The y ordinate values for the transition vane line of Fig, 1 are scaled from the drawings and substituted in the formula The y values are known. The r values are to be determined and are found to be as follows:

These Values of r are scaled on Fig. 2 from the center of the wheel along the corresponding radial lines for establishing the points along the transitionvane, and plotted and thetransition vane is drawn through these points as illustrated by Fig. 2. The curved line so established is cona slight distance into the fan housing as shown,

on Fig.2 by the dashed lines connected to the left hand end of the transition vane.

Other points to the right and to the left of the transition vane line o! Fig. l may be scaled and calculations made to more definitely establsh continuations on Fig. 2 of the transition vane if this is desired.

It is now believed to be apparent-that other transition vanes placed at other positions in the fan housing and the outlet duct may be located by theA procedure described in the foregoing.

Fig. l3 illustrates three equally spaced transition vanes so determined. The center vane A is a mean transition vane. The vanes B and C are located the proper distances on each side thereof for intercepting and transforming equal volumes of fluid.

The outlet duct D connecting the fan h'ousing E and the air heater F is seen to be relatively short as is frequently required by space limitations in steam power plants. In an actual installation without the transition vanes of this invention, a fan supplying 60,000 cubic feet of air per minute gave a pressure of nine inches of water, less than expected. 'Ihe use of transition vanes of this invention as illustrated by Fig. 3. increased the pressure to the full ten and onehalf inches to agree with laboratory tests.

What is claimed is:

1. In a centrifugal fan having a scroll housing and having a duct connected to the outlet thereof forconnecting said fan to a load. the combination of a plurality of spaced transition vanes extending from points within said housing and through said outlet into said duct, said vanes having curved portions within said housing and having straight portions within said duct, said vanes converging towards each other within said housing.

2. In a centrifugal fan havirg ascroli housing and having a duct connected to the outlet there-- of for connecting said ian to a load, the combination of a plurality of spaced transition vanes extending from points within said housing and through said outlet into said duct, said vanes having curved portions within said housing and having substantially equally spaced, straight portions within said duct, said vanes converging towards each other within said housing.

3. A fan system comprising a centrifugal fan having a scroll housing, a fan load having a diverging inlet passage forming an expansion chamber, a duct connecting the outlet of said housing and said inlet passage, and a plurality of transition vanes extending from points within said housing and through said outlet into said duct, said vanes having curved portions within said housing and having straight portions within said duct, said vanes converging towards each other within said housing.

4. A fan system comprising a centrifugal fan having a scroll housing, a fan load having a diverging inlet passage forming an expansion chamber, a duct connecting the outlet of said housing and said inlet passage, and a plurality of transition vanes extending from points within said housing and through said outlet into said duct, said vanes having curved portions within said housing and having substantially equally spaced, straight portions within said duct, said vanes converging towards each other within said housins.

5. In a centrifugal fan having a fan wheel, a scroll housing and having a duct connected to the outlet thereof for connecting said fan to a load, the combination of a. plurality of spaced transition vanes 'extending from points within said housing and through said outlet into said duct, said vanes having straight portions within said duct and having portions within said housing which curve away from said wheel in the cut-oi! area of the fan, the degree of curvature being greater in the inner than in the outer vanes whereby the vanes converge towards each other within said housing.

HAROLD F. HAGEN.

Certificate of Correction Patent No. 2, 322, 357. vJune 22, 1943.

y HAROLD F. HAGEN It is hereby certified that errorappears in the printed specication of the above numbered patent requiring correction as follows: Page 2,- rst column, lines 6-8, for

and that the seid Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 10th day of August, A. D. 1943.

HENRY VAN ARSDALE,

Acting Commissioner of Patents.

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