US 1745441 A
Description (OCR text may contain errors)
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ER FAN Inventor* Patented Feb. 4, 19307 UNITED STATES- ra'rlzu'r OFFICE' CLIFFORD M. NORBERG, NEW YORK, N. Y., ASSIGNOR TO BRUNNER ENGINEERING CORPOB/AfTIONOF NEW YORK, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK PROPELLER FAN Application filed October 14, 1927. Serial No. 226,057.
My invention relates to propeller fans. The object is to provide a propeller fan which shall have a' substantially linear power input characteristic. By such a structure a larger motor is not required than that necessary for normal load. It is known in the art that the power input characteristic of an ordinary propeller type fan rises as the inlet or outlet to said fan is restricted, and it is the usual practice to provide a motor therefor with sufficient reserve power to take care of such emergency.
The linear characteristic of the power input of the fan in accordance with my invention eliminates the necessity of providing such reserve power; o
The increased efficiency resulting from my v invention will .be apparent from the followytion is to increase the working pressure and ing description.
The object of my invention -is also to increase the efficiency for moderate or normal working pressures.
A propeller type of fan is not usually employed where it is required to function against even' very low working pressures, because its efficiency falls rapidly as its working pressure is increased. On the other hand the propeller type of fan is the most efficient instrument to use where large volumes of air are to be handled at atmospheric pressure, and at fairly low velocities.
The object therefore of the present invento take advantage of its large volume output Without materially affecting its eiliciency. This object is secured by the design and proportions of the various parts.
My researches have proved that these design proportions are effective for commercial sizes of from six to sixteen inches in diameter,
but I have no reason to lbelieve that my irlvention is not equally applicable to all diameters. l
Another object of my invention is to secure simplicity of construction, in lthatthe device in accordance with said design may be readily cast either bysand, die or other casting or construction methods. v
Anotherobject of my invention is to secure quietness in operation. The proportions and formations being such as to eliminate, especially at moderate speeds, practically all noise.
The structure in accordance with m invention secures a vcomparatively large open area through the fan. This is particularly important when appliedto coal burning furnaces for forced draft purposes.
In the general layout of such forced draft equipment, the blower or other draft inducers are .usually controlled by either'a Athermostatlc or pressure actuated electric switch, which in general practice, is connected in the motor circuit driving the blower. Such a device is a limiting control and is usually set to shut oil' the current to the motor when a certain desired high temperature or pressure has been reached, and conversely it closes the motor circuit when a predetermined low temperature or steam pressure has been attained. The blower thus functions intermittently throughout the day. By such action as described above, the blower or draft inducer remains idle part of the time. Now, if the construction of the fan is such as to greatly impede the air flow through it, while same is idle, the natural draft ordinarily 0btained from the created hot gases of the flue will be checked and will not allow the 'passage through the fan of the necessary amount of air to maintain the proper rate of combustion. The rate of combustion being thus curtailed, the result will be a quick reduction V,of pressure or temperature, as the case may be. The usual control apparatus attached to the blower equipmentund'er these conditions will keep the blower in operation more frequently than should be necessary. The result is obvious; artificial draft costs money to maintain, while natural draft has practically no cost, any device which will prolon the use of the latter in its cyclic operatlons, will also increase the general operating eliciencv of the whole system.
Referring to thedrawi-ngs, which illustrate merely by way of example, a suitable embodiment of my invention- Fig. 1 is a front elevation of the fan.
Fig. 2 is an'edge view of' same.
Fig. 3 is a fragmentary view on an enlarged scale.
Similar numerals refer to similar parts throughout the several views.
tion to radius 14. The edge 11 of the bladeY 8 will then be made with a fortyefve degree angle 10 to the tangent 16. The angular of the fan so that it will be driven forwar position of blade 8 with respect to the medium upon which it acts, is such as to slice the medium, thereby reducing the eddy currents which normallyfexist at the back of the leading edge of such blades. The edge 11 is parallel to the edge 1'1, but is offset on the tangent 16 equal to the distance shown at 17. This distance also determines the pitch of the blade 8 and is one-sixth of the length of radius 15. Both edges 11 and 11 are feathered7 to reduce their air resistance.
The active area of blade 8 is dependent upon the number of blades used with a given diameter, and also upon the length and angular displacement of the sectors orwebs 9. This fan is intended to be mounted directly to a motor shaft and is secured to same by means of the hub 7 and set-screw 18, but it is understood that the fan can be attached to other devices and devices and driven from an independent source of power. The vfan is adapted to be mounted directly to an electric motor, both being housed in a suitable casing comprising a blower unit. Such housing usually provides a ring for the fans periphery, which clears the fan by 1A.; inch. The purpose of the ring is to keep the air ue to centrifugal action, in thel active port on as shown by line AC in Fig. 3. l
From my researches and tests in a windtunnel set-up which is in accordance with the National Fan Mfgs. Test Code for Centrifugal and Propeller Fans, I have deduced the following:
Air fromv a fan such' as is described here is a. result of-forces from several sources and acti-ng at different angles to each other. They combine to form one'resulting force as a rule. In the parallelogramof forces line A represents the resulting centrifugal force which has been deflected according to the angular position of sector'or web' 9. Line D represents the force resulting from the direction or rotation. The vectorial Sum of these two forces gives us the forcerepresented by line-Bf which also represents its comparative magnitude' and direction. New, the blade 8 acts upon the force B and also produces a centrifugal force of its own, represented by the vector A. Combining these two forces we get the force C, which is shown as being in the same plane as the force from sector or web 9; the actual direction of this force is toward the observer as he looks at Fig. 1. Fig. 3 shows this force as it actually occurs.
Fig. 3 also shows the probable combination occuring between forces A and B.
With further reference to Fig. 3 to the vectorial diagram, we see the effect of eliminating theI sector 9. This effect is shown by the dotted portion of the vector, lines y and a.
Line a: would then indicate the magnitude and direction of the air forcel delivered by the fan under that condition. Besides raising the pressure of the fan, the sector 9 fills in that portion of the fan which produces a relatively low pressure and which is the source'of back pressure. As such back pressure or slip lowers the operating efficiency when the fan is working against a pressure above atmospheric pressure, the inclusion of sector 9 is well worth while. The sector or web 9 fulfills a third function, and that is the bracing and addition of mechanical strength to the blades 8. The pitch of blade 8 and its curvature are important factors in the fans operating characteristic. The pitch is determined from wind-tunnel test data.
What I claim is:
1. A propeller fan comprising a hub and radiating blades, having the angular displacement of the forward edges of the blades defined by describing a circle with a radius in length approximately two-thirds that of the fan radius, describing a tangentat the point of intersection of said first radius and said forward edge, said forward edge then being positioned at an angle of forty-five, degrecs to said tangent, then forming the rear vedge of the preceding blade parallel with the said forward edge but offset a distance approximately one-sixth of the fan radius.
v 2. A propeller fan comprising a hub and radiating blades, having the angular displacement of the forward edges of the blades denedby describingv a circle witha radius in length approximately two-thirds that of the fan radius, describing a tangent at the point of intersection .of said first radius and said forward edge,said forward edge then being y positioned at an angle of forty-five degrees,-
to said tangent, then forming the rear edge of the preceding blade parallel with the said forward edgebut-oiset a distance ap proximately one-sixth of the fan'radius and providin a web between adjacent blades extending rom the hub to saidI tangent.
3. A propeller fan comprising a hub and radiating blades, having the angular displacement of the forward edges of the blades the fan radius, describing a tangent at the point 'of intersection of said first radius and said forward edge, said forward edge then being positioned at an angle oit forty-five 5 degrees to said tangent, then forming the rear edge ofthe .preceding blade parallel with the said forward edge but oil'set a dis; tance approximately one-sixth of the fan rai dius and providing a web between adjacent m blades extending lfrom the hub to said tangent', said web lying in a plane at an angle approximately ninety degrees to the plane of the hub. Y
4. A propeller fan comprising radiating f 15 blades and sector shaped webs between the inner portions of adjacent blades, said blades having straight longitudinal margins from web to -fan periphery, and adjacent straight margins havin an angular displacement de- A2@ fined by'descri inga circle having a radius approximately two-thirds the total radius of the fan, describing a tangent in said circle where it intersects the blademargin, 'and forming the blade with approximately a 25 forty-five' degree angle to said tangent.
y CLIFFORD M. NORBERG.