US 2990107 A
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R AY C. EDWARDS INVENTOR June 27, 1961 R. c. EDWARDS COMPRESSOR Filed Nov. 30, 1956 United States Patent 2,990,107 COMPRESSOR Ray C. Edwards, Pompton Plains, NJ. (Ski Trail, Sm'oke Rise, NJ.) Filed Nov. 30, 1956, Ser. No. 625,456 9 Claims. (Cl. 230-127) This invention relates to centrifugal compressors and more particularly to a new and novel type of centrifugal compressor whose novelty is based on the compression of the medium to be pumped within the rotating wheel. The basis of the invention is based on the premise that the material to be pumped can be compressed, such as gases, and the compressor of the present invention is particularly adaptable for conpression of high density refrigerants such as Freon 12 or 22 for use in relatively small refrigeration systems, such as employ a two to five ton compressor, but it is to be understood that the invention is not so limited and that the compressor hereof may be employed in any work to which it is adaptable.
The invention is based on the phenomenon that in rotating about its axis, a completely closed cylinder containing a compressible medium such as a gas, the gas within the cylinder will eventually assume the rotative velocity of the cylinder and will be compressed by centrifugal force from the center outwardly and that by regulation of the ratio of the area of the discharge port to the area of the intake port the degree of compression may be regulated or the desired compression be obtained. Also by regulation of the discharge direction of the discharge port of the wheel, the conversion of discharge velocity pressure as the gas leaves the port in the periphery of the wheel into static pressure may be provided. Therefore, two compression phenomena may be added together to produce the total pressure of the com:- pressor of the present invention, namely, compression the wheel plus the conversion of velocity pres-'' sure to static pressure.
Specifically the invention consists of a cylinder rotatable about its axis at predetermined speeds, which cylinder is provided with an axial inlet and peripheral outlet for the medium compressed and with various "forms of vanes formed upon and rotatable with the cylinder.
The accompanying drawings show one construction of the compressor of the present invention wit-h'various vane structures, but it is to be understood that the invention is not limited to the specific structures shown, which may be widely modified within the limits defined by the claims hereof.
In the drawings:
FIGURE 1 is an end elevation of the compressor.
FIGURE 2 is a vertical section through the compressor, taken on line 22 of FIGURE 1.
FIGURE 3 is a section through the cylinder of the compressor showing one form of vane.
FIGURE 4 is a cross section taken on the line 44 of FIGURE 3.
FIGURE 5 is a section through the cylinder showing straight radial vanes.
FIGURE dis a detail section taken on line'66 of FIGURE 5, i.e. a fragmentary section taken at right angles to the section shown in FIGURE 5.
7 is a section through the cylinder showing Patented June 27, 1961 a single spiral vane, spiralling from the axial inlet to a single discharge port.
FIGURE; 8 is a section through the cylinder showing double spiralling vanes, spirallingfrom the axial inlet to a pair of diametrically opposed discharge ports.
The construction of the forms of the compressor, shown will be first described, and the theory and operation thereof will follow.
The compressor is of simple construction comprising a sationary casing 1, one side of which is closed by a removable closure plate 2, to permit insertion of the rotative cylinder 3 into the casing 1.
The cylinder 3 is completely closed except for an axial opening 4 which forms the inlet for gas or the medium to be compressed, and through which the rotating shaft 5 extends. The shaft 5 may be supported by any suitable type of bearing shown at 6 and rotated by any suitable means. A sheave 7 for receiving a 5 and cylinder 3. The cylinder 3 is provided with a discharge port'7 in its perimeter and a suitable seal 8 of any approved type is provided to prevent leakage of the medium being compressed into the casing 1 surrounding which surrounds the cylinder. The compressed gas or other medium is discharged into the space 8' from the interior of the cylinder 3 through the discharge port 7 and leaves the casing for use through an outlet 9.
Various forms of vane structures may be employed in the cylinder 3 and all such vanes, regardless of shape,f
type or form are formed within or attached to the inner surface of the cylinder and rotate therewith.
In FIGURE 4 of the drawings the vanes 10 are arranged to form substantially a diametrically extending cylinder 11 within the rotating cylinder 1 with the inlet- 12 opening transversely into the inner cylinder 11 at its longitudinal center. Discharge passages 13 of greatly reduced area with respect to the cross-sectional area of the inner cylinder 11, and in proper ratio-to the area of the inlet 12 (as hereinafter more specifically referred to) are provided at each end of the inner cylinder 11. The discharge passages 13 open out through diametrically opposed discharge openings 14 in the perimeter of the cylinder 1'.
In FIGURE 5 of thedrawings a plurality of straight vanes 15 are attached to the sides 16 of the cylinder 1 and radiate from: the axis of rotation of the cylinder 1 The inner ends of the vanes 15 terminate a predetermined distance outwardly of the perimeter of the inlet opening 17 in one side of the cylinder 1 and also terminate a predetermined distance inwardly of the perimeter of the cylinder 1 as clearly shown in FIGURE 5, so
as to permit flow of the medium being compressed to the discussion of the theory and operation of the compressor.
FIGURE 7 shows a deviation from the straight vane structures of FIGURES 3 and 5 in that it shows a spiral vane 20 which spirals outwardly in a uniform spiral from the perimeter of the inlet port 21 of the cylinder 1 to the 1 inner perimeter of the cylinder, to which it is. joined at a point a predetermined distance beyond the discharge port 22 in the perimeter of the cylinder 1 Thus the spiral passage from the intake 21 first gradually increases in area for a short distance outwardly from the intake then continues in uniform area to and throughout a portion of the outermost spiral, gradually decreasing in cross-sectional area as it approaches the discharge port 22 and finally, at a predetermined distance beyond the discharge port 22 it merges to the inner periphery of the cylinder '1". The proportionate areas of the intake port 21 and the discharge port 22: are as described in connection with FIGURES 3 and '5'. The'spiral vane ex-;
tends from one side of the cylinder 1} to the other,'as thevanes 15 in FIGURE 5, and-is attachedito the cylinder to rotate therewith.
FIGURE 8 employs the same type of spiral vane as shown and described in FIGURE 7, differing therefrom in that two spiral vanes and 26 are provided which spiral in uniformity from the intake port 23 in the cylinder 1 to the two discharge ports 24in the perimeter of the cylinder. The discharge ports 24 are diametrically opposed in the perimeter of the cylinder 1 and are located predetermined distances forwardly of the termination ofthe spiral flow passages formed by the vanes 25 and 26. The proportion of the areas of the intake port 23 to the combined areas of the discharge ports is regulated as in the other forms of the. cylinder above described.
While in the drawings the vanes are shown'as extending from side to side of the rotative cylinders, it is to be understood that the invention embraces stnlctureswherein the vanes extend into the cylinderonly a part of its width and not completely from side to side thereof.
The invention is based upon the observed phenomenon that if one rotates a completely closed cylinder containing a compressible medium such as gas about its axis, the gas within the cylinder will eventually assume the rotative velocity of the cylinder and will be compressed by centrifugal force from the center outwardly.
In a non-rotating cylinder the gas will obey Boyles law which states that Pp=RT. Where P is the pressure in. pounds per square foot, p is the density in pounds per cubic foot. R is the universal gas constant which is a constant for any given gas and T=the absolute temperature degree Rankine (degrees F.+460).
If the cylinder is rotated with an angular velocity of w radians per second about its axis and the gas rotates about the axis of the cylinder, then the law determining the pressure in the cylinder measured along the'radius of the cylinder as a function of w, r and R and is given by the equation:
This relationship is based on isothermal compression of the gas within'the wheel. With the proper construction of the wheel, isothermal compression'can be realized. P is the pressure at the center of the wheel.
The gas will tend to be compressed along an isothermal path rather than an adiabatic path, because the discharged part is so minute in size as compared to the inlet opening to the compressor wheel, and'the gas will be cooled as it is compressed. This trend toward isothermal compressionwill aid in reducing the RP. requirements of the compressor for a' given head.
The above relationship is derived through the following steps:
The force on the shell of the cylinder is equal to the pressure in the cylinder times the surface area. An elemental change in the surface force is equal to the surface area times-an elemental change in the pressure dp 4 or- 21rrl dp.- This elementalchange -in-surfaceforce equal to the elemental change in centrifugal force of an elemental section of the cylinder.
Now if we equate the elemental change in surface force with the elemental change in centrifugal force, we arrive at the following:
P1 T1402 t t f 11 d f d =f a a can ero cy n er pop p rokgr r Integrating-this equation from r 0 to r we" have Therefore p=p e where p is the pressure'at the center ofthe cylinder. It also follows that Where isithe density of the gas at the center of the cylinder.
In a centrifugal compressor the head produced-is give by thefollowing formula:
Head= From the formula we see that the head is purely a function-of the rotor velocity and the angle of discharge.
However, thestatic-pressure in pounds per 'sq. in. pro duced by the compressor is directly proportional to the density of the discharge gas. Therefore, if we can cause compression to take place within the wheel we can reduce the required head for a given required compression in direct proportion to the increase in density of the gas being compressed. In effect We can markedly reduce the r.p.m. at which the compressor must operate. This, in essence, is the basis of our entire invention.
"A typical application for the compressor would be in the refrigeration field. The equation shows that f p=pv The ratio of compression R Po Then For the refrigerant dichlorodifluromethane, more commonly known as Freon 12, the value of k is5900 when calculated from the state of the saturated gas at 40 degrees F. to in radians per second is equal to 211' r.p.m. 60
=.105 r.p.m. or=.105 n where n=r.p.m.
r n (3.46X 10 r n =3.46) 10 10g R The following table calculated from this equation shows that very useful amount of gas compression can take place within the compressor wheel.
THEORETICAL COMPRESSION OF FREON 12 IN THE CLOSED WHEEL COMPRESSOR AS A FUNC- V TION OF RADIUS AND R.P.M.
From this table it can be noted that for a compression ratioof 3 to 1 and a wheel radius of .75 feet a speed of only 8250 r.p.m. is required.
:If a commonly used non-over-loading type of com- 75 pressor wheel were used with backward curved blades withan angle of between and 60, then the r.p.m.
required for a 3 to 1 compression ratio would be:
2.... head U [Z 111 GOS The equation relating head in feet, density of this gas in lbs. per cubic foot and pressure at the bottom of column is:
v hp p.s.1. 144
h =-density of gas in lbs/fu "I For Freon 12 at suction condition the head in feet required for a compression ratioof 3 to 1 is:
h=144 51.68 X3 X .792=17,700 feet I Where 51.68 is vapor pressure of Freon at 40 F. an 1 .792 is the cubic feet per pound of gas Assume that the cos 0c=.5 then V .5 U
U 1065 feet/sec.
Assuming a wheel .radius 'of .75 feet and a wheel .cir-' cumference of 4.7 feet the revolutions per second of the Wheel would be 1065/ 4.7 or 227 per second or 13600 per minute. .This 13 600 r.p.m. compares with 8250 r.p.m. as given in the Table 1 for compression within the wheel." However, a further and very important advantage of the invention is that the gas after-being compressed within' the wheel can be discharged through a port in the wheel so that its velocity pressure canbe converted into static pressure. This static pressure can .then be added to the compression ratio obtained within the wheel. The Freon 12 gas may be ejected through a port in the circumference of the compressor wheel. The port may be oriented in a forward, radial, or backward direction with respect to,
the rotational of the compressor wheel. The head produced by this discharging gas will obey the same equation type wheel of the conventionaltypq as used for an open namely,
h: U fuw C08 C1 g The gas leaving the wheel described above and rotating at 8250' r.p.m. willbe compressed to a pressure of 172lbs.
(Cubic feetper pound at 40 suction=.792.)
These calculations are based on the same ang1e ofdischarge as used in the calculations for a standard wheel. 1 If a, forward discharge port were used, the theoretical I head vproduced would, of course, be far greater.
Typical types of wheel that could be used to these results are shown in the drawings.
The above shows that gas to be compressed can be I compressed within the cylinder and then discharged after the compression has taken place; therefore the present. invention consists of an entering opening at the axis'of a closed cylinder containing vanes to cause the gas to rotate with the cylinder and a discharge port on the outer perimeter of the cylinder as is shown in the drawlugs and hereinbefore described.
produce The ratio of, the area of the discharge port to that of the area of the intake port at the axis of the cylinder must be quite small so that the gases are forced to compress within the cylinder before a they are discharged. Compression within the cylinder may be caused to occur. when thisratio is in the neighborhood of 1 to- 10 or less; Itisith'e present practice in constructing centrifii oi'ie foot the' peripheral velocity of, thewheel'must be- 725 feet per second. However; if compression is caused to take place within the wlieel; asifi'the' cylinder 'ofthe present invention, the peripheral velocity of the wheel may be reduced to 475 feet per second. This reduction in peripheral velocity, is of particular importance in the refrigeration industry where it is highly desirable to provide a low tonnage refrigeration compressor of the order of magnitude of two to five tons. To date this has-been impossible from a practical standpoint because rotative wheel speeds of the order of 15,000 to 25,000 revolutions per minute and greataer are required. However, if compression is caused to take place within the wheel, as ihthecylinder of the present invention, the rotative speed may be reduced to approximately 10,000
rpm. which'iswell within a practical range for use in practical equipment now available on the market.
Also, in the construction of a two to five ton centri fugal compressor of present day best design'using a conventional type of wheel, a low density refrigerant gas mutsbe used in order to obtain a good hydraulic efnciency. Low density? refrigerant gas does not have the frictional losses that a high density gas has within awheel. Howeventhe low density gasesstill have suffi cient functional losses within the wheel that mak'es ther'nimpractical for use in small tonnage machines of present day design.
With the compressorof thepresent invention, in which the compression takes place within the wheel, friction losses within the wheel can be almost ignored because they will so "small when high density; refrigerants, such =as'Fre'on12 and 22 are employed. High density refrigerants are ideal for use in a compressor of this new de sign.
Table A (above) shows'the compression ratios that may be obtained within the wheel, using 40 F. suction temperature with Freon, 12 and'various r.p.m. :It will be noted that with moderate speeds, compression ratios of two to three to onepan be"; obtained-within the wheel. Added to this compression ratio within the wheel, is (in the present invention) the'conversionof the discharge velocity pressure-asthegas leaves" the discharge port in the perimeter of the wheel to; static pressure; Therefore, two compression phenomena are added together to'produce the totalpressure of the centrifugal compressor of the present invention, namely, compression within th'e'wheel plus the conversion-of the velocitypressure to" static pressure.
The conversion of the velocity pressure to staticpressurecan be controlled by the direction in which the gas is discharged from the periphery. of the cylinder 3. The dischargeport may be directed forwardly with respect to'"the"'direction of rotationof the cylinder, radiallyor backward, depending on' the necessity for using thevelocity pressure to augment the compression within the wheel.
It is-the practice in the field to use reciprocating compressors forrefri'geration systems of small'tonnage due to;the inability to heretofore provide a practical centrifugal compressor for such use. compressorsjthe obtaining of capacity control is difli cult and requires expensive relative, delicate and. sensitive mechanisms for such control, but with a compressor of thepresentinvention accuratecapacity control is provided merely by changes in speed of rotation of the 'wherein said vanes constitute a plurality of straight 'vanes 7 cylinder 1. With a centrifugal compressor the compressor capacity varies with the square of the wheel velocity.
It will be understood that the invention is not to be 1 limited to the specific constructions shown, but that they may be widely modified within the invention defined by the claims.
What is claimed is:
1. A centrifugal compressor including a closed cylinfder having flat ends and means for rotating said sylinder wherein a compressible gas within the cylinder will assume the rotative velocity of the cylinder and will be compressed by centrifugal force from the rotative center of the cylinder outwardly, the'inner surface of the perimeter of said cylinder being in the form of a continuous circle and free from irregular surface areas, at least one vane within said cylinder and rotatable with the cylinder, said vane spaced with relation to theinner surface of the perimeter of said cylinder as to permit unimpeded rotary movement of the compressed gas along the inner surface of the perimeter of the cylinder, the perimeter of said cylinder having at least one discharge port therein, and'said cylinder provided with an inlet port at its axis the total discharge area of the cylinder with respect to the total intake area of the inlet to the cylinder bing of a ratio in the neighborhood of one to five for forcing gas within the cylinder to compress before being discharged.
2. A centrifugal compressor as claimed in claim 1, wherein said outlet port is directed forwardly with respect to the direction of rotation of said cylinder to convert a predetermined percent of velocity pressure of the compressed gas to static pressure.
3. A centrifugal compressor as claimed in claim 1,
wherein said outlet port is directed backward with respect to the direction of rotation of the cylinder to conver: a predetermined percent of velocity pressure of the compressed gas to static pressure.
4. A centrifugal compressor as claimed in claim 1, wherein said outlet port isdireoted radially of the rotative axis of the cylinder to convert a predetermined percent of thevelocity pressure of the compressed gas to static pressure.
5. A centrifugal compressor as'claimed in claimv 4,
wherein the'ratio of the area of said'discharge portto that'ofs'aidinlet port is in the neighborhoodof one to ten. I
6. A centrifugal compressor as claimed in claim 1,
radiating from the axis of said cylinder and said inlet port with their inner ends spaced from the inlet port to provide an obstruction free annular space between the inner ends of the vanes and the outer edge of the inlet opening.
7. A centrifugal compressor including a closed cylin der having flat ends, means for rotating' said cylinder wherein a compressible gas within the cylinder'will assume the rotative'velocity of the cylinder and will be com- In such reciprocating the perimeter of the cylinder as to permit unimpeded rotary movement of the compressed gas along the inner surface of the perimeter of the cylinder, said cylinder provided with an inlet port at its axis and at least one discharge port therein, said vanes spaced outwardly of the inlet port so as to provide a curved obstruction free passage for gas about said inlet, the edges of said vanes extending to and engaging the inner sun-faces of the ends of said cylinder, whereby the only obstruction free curved passages for gas within the cylinder are at the inner and outer ends of said vanes, the total discharge port area of the cylinder with respect to the total inlet area of the cylinder being such that the compressible gas within the cylinder will assume the rotative velocity of the rotating cylinder and will be compressed along an isothermal path.
8. A centrifugal compressor as claimed in claim 7, wherein the discharge port of said cylinder is disposed at an angle to the direction of rotation of the cylinder so as to convert a portion of the discharge velocity of the compressed gas to static pressure.
9. A centrifugal compressor as claimed in claim 7, wherein the ratio of the area of the discharge port to that of the inlet port is greater than one to four.
References Cited in the file of this patent UNITED STATES PATENTS Barber Mar. 31, 1896 Harris Jan. 26, 1897 Brooks Jan. 28, 1908 Austin June 9, 1908 Trent Nov. 24, 1908 Richardson Mar. 23, 1909 Upton et a1. Dec. 11, 1917 Carson June 21, 1921 Woody Oct. 10, 1922 Danford et al. Dec. 30, 1924 Germeyer Oct. 5, 1926 Linderman, Jr. Sept. 4, 1928 Curtis Jan. 15, 1935 Denys Jan. 11, 1946 Grantham Oct. 2, 1951 Ifield Aug. 24, 1954 FOREIGN PATENTS Great Britain of 1903 Switzerland Oct. 1, 1919 Germany Mar. 30, 1920 Great Britain Jan. 4, 1956