US2072761A - Viscosity compensated flow control - Google Patents

Description

March 2, 1937. w. o. LUM

VISCOSITY COMPENSATED FLOW CGNTROL 4 Filed May l. 1935 Patented Mar. 2, 1937 UNITED sTATEs PATENT OFFICE 2,072,761 VISCOSITY COMPENSATED FLOW CONTROL Walter 0. Lum, Schenectady, N. Y., assgnor to y General Electric Company, a corporation of New York Application May 1, 1935, Serial No. 19,268

6 Claims. v (Cl. 137-78) .10 from a substantially constant low pressure source.

Thus, while it .will be understood by tho'se skilled in the art that the invention maybe used in other fluid flow control serv'ice, the principle of the invention and the best mode in which applicant.

has contemplated applying that-principle Will be explained in connection with an oil burner. g Viscosity compensated ow control is desirable in an ol burner due to the fact that it is and has been for-many years practically impossibleto expect any uniformity in the viscosity of fuel oils. Fuel oils even of the same commercial grade vary ln viscosity due'to the widely varying characteristics of the different crudes as well as the different mixes or blends.

Ordinarily variation in. fuel oil viscosity will result in serious difficulties in the operation of oil burners, particularly of the domestic type, utiliz- .ing relatively lo,w .atomizing pressures.l For eX- ample, the burnermay be designed or adjusted to ignite and operate satisfactorily on certain commercial grades of'fuel oil. However, when these burners are installed in homes in some other territory, it may be almost impossible to make these burners operate satisfactorily even on the same commercial gradesof oil. Likewise in theA same territory with fuel oil supplied by one dealer the burners may operate satisfactorily while with fuel oil of the same commercial grade supplied by another dealer the burners may fail to operate 40 satisfactorily- Even with identically the same fuel oil the viscosity will always vary widely with variations in its temperature. Y

The difiiculties outlined above are quite well known and many efforts have been made heretofore to maintain a substantially constant rate of feed of fuel oil of varying viscosity to anl oil burner. -complicated pressure regulating devices, steam and also electric oil heaters have been proposed for this purpose but have not proved entirely satisfactory.

By means of the present invention, a very simple-and inexpensive viscosity compensated flow controlis obtained which is capableof mainl"Htaining a practically constant oil rate in an oil Special metering types of oil pumps,

burner irrespective of variations of the viscosity of the fuel oil within predetermined limits, these limits being sufficiently wide to include the various grades of fuel oil ordinarily used in oil' burners of the domestic type. 5

Briefly, the viscosity compensated flow control of the present invention consists of a co-operating combination involving a specially proportioned thin walled, sharp-edged control orifice and a specially proportioned compensated fluid sup- 10 ply 'conduit connected with a source of uid maintained under substantially constant. pressure.l The control orifice is proportioned to determine the rate of fluid ow which may be any value desired. At the same time, the l5 control orifice is proportioned sothat it automatically increases its orice discharge coeicient under a constant orice pressure differential upon an increase in the viscosity of the fluid between the predetermined limits. Such control 20 orifice, if acting alone, would automatically increase the rate of fluid oW as the viscosity of the fluid increases due to the increasedorifice discharge coefficient thereof. However, the compensating fluid delivery conduit is proportioned 25 so as to function automatically to regulate the pressure differential of the control orifice as the viscosity of the fluid increases and thereby maintain the rate of fluid flow substantially constant. To accomplish this result the compensating fluid 30 delivery 'conduit is proportioned to provide a predetermined increased pressure drop upon the increase in viscosity of the uid between the predetermined limits. 'I'his increased pressure drop of the conduit functions toreduce the pressure 35 differential of the control orifice upon the increase in the viscosity of the fluid and thereby maintains a substantially constant rate of fluid flow through the orifice and conduit.

In the accompanying drawing, Fig. 1 is a sche- 40 matic diagram showing the general combination of the control orifice and compensating uid delivery conduit in the viscosity compensated ow control of the present invention; Fig. 2 is an enlarged vsectional view of the control orifice indi- 45- cating schematically the flow variation resulting with uids of high and low viscosity; Fig. 3 is a chart showing in Diagram A the relation between the rate of fluid flow at the value of Reynolds number and viscosity indicated and 50 'the inner diameter of the control orifice of Fig. 2

required to provide such rate and showing in Diagram B the corresponding relation between the rates of fluid flow indicated in Diagram A and the orifice pressure differentials required to pro- 55 vide such rates; Fig. 4 is a chart showing in Diagram C the variation of the discharge coeflicient of the control orifice of Fig. 2 under a constant pressure differential upon variation of the viscosity of the fluid between predetermined limits; Fig. 5 is a chart showing in Diagram D the variation of the pressure differential upon the control orifice of Fig. 2 required to provide a constant rate of fluid fiow with variation of the viscosity of the fluid between the limits shown in Diagram C and showing in Diagram E the variationl of the pressure stop provided by the compensating fluid delivery conduit with variation of the viscosity of the fluid flowing therein between the prede"- termined limits; and showing in. Diagram F the substantially constant combined total pressure required to produce a substantially constant rate of flow of fluid through the control'orifice and compensating fluid delivery conduit irrespective of variations in the viscosity of the fluid; and Fig. 6 is a chart showing in Diagram G the substantially constant regulation of the rate of fluid flow which may be obtained by means of the viscosity compensated control of the present invention with variation of the viscosity of the uid between.v the predetermined limits, this regulation being within one percent of the desired rateof fiow; and Fig. "1 shows the application of the viscosity compensated control of the present inventionto a preferred form of oil furnace.

Referring to the schematic diagram of Fig. 1, I0 represents a source from which fluid under substantially constant pressure is supplied to the fluid delivery conduit II. The flow control orifice I2 is located in an enlarged portion I3 of the conduit! I in co-operating'relation with the conduit for both determining the rate of fiuid iiow therethrough and maintaining the flow substantially constant irrespective of variations in the viscosity of the fluid between predetermined limits. It will be understood that the particular location of the control orice is not critical, as it may be located anywhere intermediate the ends of the fluid delivery conduit II or at either end thereof. g

As more clearly shown in Fig. 2, the control orifice I2 is preferably of the thin walled, sharpedged disc type having an inner diameter Di and and an outer diameter Dz. Such an 'orifice has the characteristic of automatically increasing the discharge coefficient thereof under a constant pressure dierential upon an increase of the viscosity of the fluid therethrough between predetermined limits. This characteristic may be explained by the increased adherence of the molecules of the more viscous fiuid tothe face of the orifice I2 as indicated schematically in Fig. 2 by the dotted line. Thus, with fiuids of high viscosity the radial component of fiow to the orifice is reduced and the diameter of the vena contracta of the stream of fluid passing through the orifice is increased over that obtaining with a fluid of lower viscosity as shown by the dotted lines in Fig. 2. With fluids of lower viscosity the radial fiow through the orifice is not impeded by adherence to the face of the orifice as indicated by the solid arrows adjacent the face of the orice I2 in Fig. 2. As a result of this radial iiow component, the stream of fluid of lower viscosity through the orifice has a vena contracta of less diameter than is the case with a fluid of' high viscosity.

Due to the variation in diameter of the vena contracta outlined above, the discharge coefficient of the orice I2 is dependent upon the viscosity of the fiuid flowing therethrough, the discharge coeflicient being greater for a' fluid of high viscosity than for a fiuid of low viscosity. To eX- tend the variation in discharge coemcient of the orifice I2 over a wide viscosity range, it is desirable that the face of the orifice be relatively large with respect to the oriiiceopening, that is, that the ratio be relatively small. For this reason, the diameter f ratio of the orifice I2 when used in oil rate con- Y2=soo whereinV is the flow velocity through the orifice, D the diameter of the orifice, u the kinematic viscosity and 300 is a Reynolds number pertaining to fluid flow and providing for a wide range of viscosity variation. This 'Reynolds number is not critical and may range from as low as 200 up to 400 or 500, although 300 is preferable. Upon simplifying and correlating this equation to the units of gallons per hour and inches as indicated in Fig. 3, it becomes D1=.013R, wherein D1 is the inner orice diameter in inches and R is the rate of fiow in gallons per hour for a viscosity oi '70 Saybolt seconds, which latter may be assumed to be the maximum viscosity of any ordinary heavy domestic fuel oil.

When the orifice diameter D1 and the desired rate of flow are once determined for the maximum viscosity flow, the differential pressure of the orifice becomes xed at a corresponding value. The relation between the orifice pressure differential and the rate is lindicated inDiagram B of Fig. 3, the value of the pressure differentials be.-

ing expressed as head in inches of oil. Diagram B is to be considered in connection with Diagram A. Thesediagrams show that when the orifice diameter is relatively small so as to provide a relatively low rate of fluid flow, ,the pressure differential on the orifice is correspondingly low. When the size of the orifice is increased as indicated by 'Diagram A to provide any desired increased rate of fiuid fiow, the pressure differential on'the orifice then must beA correspondingly increased to the value indicated by Diagram B to obtain the desired rate of vfluid flow. Thus for example, in case a rate of flow of 2.5 gallons per hour of oil of- 70 Saybolt seconds -viscosity should be desired, then an inner orifice'di-ameter of .0325 inch and a pressure differential head of whereinih is the orifice pressure. differential head vin inches of oil and R isthe rate in gallons per hour. This equation results from simplifying and correlating the proper units in the general equation II With the inner diameter D1 and pressure differential of the control orifice I2 determined for the desiredoil rate with the maximum viscosity oil as outlined above, Diagram C in Fig. 4 indicates the variation of the discharge coefficient of orifice I2 obtaining upon progressive decrease in the viscosity of the oil fiowing therethrough under a constant pressure differential. This variation in the orifice discharge coefficient is a phenomenon resulting from the reduction in the diameter of the vena contracta as the viscosity of' the oil is decreased as previously explained in connection with Fig. 2. To maintain a constant oil rate through the orifice I2 when the discharge coefficient thereof decreases due to the progressive decrease in viscosity of the oil as shown in Fig. 4, the pressure differential head on the orifice must be increased correspondingly. Diagram D in Fig. 5 indicates the progressive increase in the orifice pressure differential requiredV to maintain a constant rate of flow through the orifice I2 under these conditions.

In order automatically to vary the pressure differential head of orifice I2 in the manner indicated in Diagram D upon variation in viscosity of the oil iiowing therethrough, the compensating oil delivery conduit II is proportioned to provide a pressure drop therein which varies substantially inversely with the required variation of the differential pressure head of orifice I2. This variable pressure drop in the compensating oil delivery conduit II is indicated by Diagram E in Fig. 5. To obtain this result, the length and diameter of conduit I I are proportioned in accordance with the equation 1.1H1 Ru equation, the value 1.1H1 corresponds to the value H2 shown in Fig. 5 as the pressure drop in the conduit with fiuid of maximum viscosity flowingA through the conduit and expressed in head in inches of uid occurring between the maximum and minimum viscosity values as shown in Diagram D. Diagram F in Fig. 5 shows the combined total pressure head of the orifice and conduit expressed in inches of `oil under which the source I0 shown in Fig. 1 mustbe maintained in order to obtain a substantially constant rate of ow' therefrom through the compensating iuid delivery conduit II and the orifice I2. It will be observed that the total piessure'head indicated by Diagram F is substantially constant throughout the entire range of viscosity control. Hence after the conduit. II and orifice I2 are ,oncefproperly proportioned and connected in tio-operating', relation with the source I0, all that v'is required to maintain the liquid flow from the source I0 substantially constant irrespective of variations in the viscosity of the liquid is to maintain thesource III at the substantially constant pressure value indicated by Diagram F. This may be readily accomplished by any constant pres--4 sure regulating means well known to those skilled in the art.

In Fig. 7, the oil furnace is shown of the type described in the copending application of Aldo Macchi, Serial No. 505,867, filed December 31, 1930, and assigned to the assignee of the present application although the invention may be applied to any ordinarytype of pressure feed oil burner. In the type of furnace shown the oil atomizing nozzle .2 I extends into the top of the combustion chamber of the steam or hot water boiler 22 and is supplied with oil, atomizing air and combustion air from the electric motor driven blower compressor unit 23. The atomizng nozzle 2| is shown as of the type described and claimed in the copending application of John Eaton and W. O. Lum, Serial No. 691,320, led September 28, 1933, and assigned to the assignee of the present invention. The motor driven blower compressor unit 23 is shown as of the improved type described and claimed in my copending application, Serial No. 553,119, led July 25, 1931. In this unit the fuel oil and atomizing air therefor are maintained under pressure in the sump tank 24 upon operation of the electric motor driven blower and pumping mechanism. The fuel oil is conducted from the sump chamber 24 to the nozzle 2I through the pipe 25' and the atomizing air is conducted from the sump 24 through nozzle 2I through'the air line 26.

In order to maintain the rate of oil fiow through nozzle 2I substantially constant irrespective of variations in the viscosity of the oil, in accordance with the present invention a control orifice 30 is connected in the oil supply pipe 25. It will be understood that this orifice is proportioned as to diameter, size and ratio to provide the oil rate desired in the manner previously described. Likewise the pipe 25 is proportioned in length and diameter to co-operate with the control oice 30 so as to maintain the desired oil rate substantially constant irrespective of variations in viscosity in the same manner as described in connection with the compensating fluid supply conduit II of Fig. 1.

A substantially constant oil level is maintained in the sump 24 by means of a float operated bypass valve, not shown. The oil in sump 24 is maintained under a substantially constant pressure by means of the automatic air pressure regulating valve 3| which controls a by-pass from the atomizing air supply line 26 to the air inlet of the pump mechanism. Under these conditions, the rate at which oil is supplied from the sump 24 to the nozzle 2| is maintained substantially constant irrespective of variations in viscosity of the oil throughout a range suiiiciently wide to include the ordinary commercial grades of fuel oil.

In operation, the oil supplied to nozzle 2I is atomized and ignited by the electric spark from the electrode 32, low pressure combustion air is supplied from the blower 33 through the iiexible air pipe 34 to nozzle 2| and through the air conduit 35 to the air box 36 which extends into bottom of the combustion chamber of the furnace.

In accordance with the provisions of the patent statutes, I have explained the principles of operation of my invention and described the apparatus which I now consider represents the best embodiment thereof but Idesire to have it understood that the apparatus shown is only illustrative and that the invention can be carried out byv other means. It also should be understood that the invention may be' ycarried out with a. plurality of control orifices and conduits of the character described connected either in series to provide a desired rate of fiuid flow under high pressure or in multiple to provide an increased rate of fiow under low pressures.

What I 4claim as new and desire to secure by4 A,varying viscosity under substantially constant initial pressure comprising a delivery conduit having the 4pressure drop therein increasing as a function of the increase in viscosity of the fluid, and a thin wall sharp edge orifice connected with the delivery conduit and proportioned to increase the discharge coefficient thereof upon said increase of the viscosity of the fluid between predetermined limits to maintain the fuid ow through said conduit substantially constant.

3. Means for feeding fluids of varying viscosity at a substantially constant rate comprising V a reservoir for the fluids, means for maintaining a. substantially constant pressure in the res- 3 ervoir, a thin wall sharp edge orifice for determining the rate of fluid vflow from the reservoir Aand proportioned to increase the discharge coefficient thereof under a constant pressure diferential head upon an increase of the viscosity of the fluid between predetermined limits, and a iiui'd delivery conduit connected with the orifice and proportioned to decrease the pressure differential head of said orificel upon said increase of the viscosity of the fiuid to maintain-a substantially constant rate of fiuid flow through said orifice. A

4. An oil burner having a thin wall sharp edge orifice for determining the oil rate thereof and proportioned to increase the oil discharge coefficient upon increase of the oil viscosity between predetermined limits, and an nil delivery conduit proportioned to decrease the pressure dierential head of said orifice upon said increase of oil viscosity to maintain the oil rate substantially constant.

5. An'oil burner having means for supplying oil under pressure for combustion including an oil delivery conduit having the pressure drop.

therein increasing as a function of the increase in viscosity of the oil, and a thin wall sharpedge orifice for determining the rate of oil flow through the conduit and proportioned to increase the discharge coefficient thereof upon said increase of the viscosity of the oil between predetermined limits to maintain the oil flow through said conduit substantially constant.

6. An oil burner having an oil reservoir, means yfor maintaining a substantially constant pres-

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