(. IKST. SEP 141914 4I8R A AN IN V WA0 T H R-0 U G S T I G A T ION 91Q A _L1I AI N T U RI L Thesis of Signature redacted Submitted to M. I. DEPT., M.I.T. 1 9 1 4. .1 HE T R Acknowledgement. This is to thank Professor C. W. Berry for his general interest in my work, and for his kind suggestions and assistance given to me from time to time in completing the thesis. I Introduction. Long since the investigation of the Venturi Meter by Herschel in 1887, it was experimented upon by the inventor himself on large size meters fitted- to 12 and as large as 108 inch pipes. accurate. The results were fairly However, experiments made by Professor Cokes on a small meter showed very variable results. So in hydraulic work, the meter is more advantageously used to measure large quantities of water flowing in pipes. While in gas and air measurements, though there is not much data fream which to draw any conclusions, it seems so far that in measuring large quantities of gas and air the Venturi meter gives fairly accurate results. Experiments made by E. P. Coleman in 1906, and by K. Bush and I. U. Guilford in 1908, all C. showed that the Venturi meter is valuable for measuring large quantities of air. At present the meter is manufactured by the Builders' Iron Foundry in Providence, R.I. in large sizes. These are used as air and gas meters. But for small quantities of fluids (air or steam) flowirig in pipes, the use of a Venturi meter has not yet been experimented on; although in injector works and in Carburettor works for gas engines the principle of the Venturi 99 3.4 2 meter has been already employed. So this investigation is made to test the accuracy of the Venturi meter in measuring small quanities of air flcwing in pipes. To make the investigation a successful one, the following conditions were imposed at first: 1) That the drop in pressure shall not exceed one pound. 2) That the moisture in air shall be considered. 3) That the results shall agree closely with Fliegner's equations. 3. EIEENOES. The only published reference that has direct bearing on the subject is an article entitled 'The Flow of Fluids in a Venturi Tube*. It was written by Mr. E. P. Coleman and published in the A.8.M.E. Transactions, Nov., 1906, page 391, and Mar., 1907, page 1207. I was given the privilege also to use the thesis work of K. 0. Bush and I. IL Guilford in 1908. By kindness of Prof. C. W. Berry I was allowed to use a special paper which he has written on the thermodynamics of the Venturi Meter. In designing the meter the following were consulted: 1) 'The Venturi Air and Gas Meter', published by the Builders' Iron Foundry in Providence, Rhode Island; 2) Pitot Tubes for Gas Measurements' written by V. C. Rowse in A.S.M.E. Journal, Sept.1913. Other books which have some general relation to the matter are: 'Thennodynamics of the Steam Engine' by Prof. 0. H. Peabody, 'Engineering Thermodynamics" by Prof.O. E. Lucke; 'Flow of Steam Through Nozzles" by Rateau. 4 Object of Investigation. The main object of the investigation was to test the accuracy of the Venturi meter in measuring smell quantities of air flowing in pipes. It is claimed by the G and A Carburettor makers that a Venturi meter having angles of convergence and divergence of 300 and 70 respectively will give the maximum flow. While Wimperis in his vInternal Combustion Engines* asserted that a Venturi meter of 130 convergence and Sodivergence will have the maximum flow. It was my first intention to make a series of tests with different angles of convergence and divergence, keeping the throat areathe same. For if the best angles would be more favorable that those above quoted, or a few degrees deviation from them would not make much difference in the maximum flow, the commercial difficulties in making these long slender tapering nozzles would be much diminished. However, it is too long and expensive a task to be performed at the present. I hope that my experiments may be the first of the series; other students may finish the task later on. 6 Desian of the Meter. A considerable time has been used in the design of the meter in attaining arrangements for accurate measurements and in obtaining simplicity for machine work. Though the meter is to be used for measuring small quantities of air, it was found that a throat area of less than one square inch has no commercial value. By recommendation of Mr. Hopwell experienced in the use of the Venturi meter in carburetors of gasoline engines, the angle of convergence and divergence was made thirty degrees and seven degrees respectively. By referring to Mr. W. 0. Rowsels experiments on pitot tubes for gas measurementsthe holes in the piezometer rings were drilled with 450 inclination. A set of radial holes were also drilled at the throat section to check the reading. A set of tracings of the design are inserted at the back of the thesis, the computations though simple are given as follows: Diameter of the 8 inch pipe with which the meter will be used is 3.08655. Diameter of I sq.inch circle = 1.12849 Use angle of convergence = 300. 8 .. the length of the converging portion (3.0665 - S--------- 1.1284) .98861 ------ tan 150 =3.814 .28795 The length of the cylindrical portion is made as short as possible. so tbAt it It is made half an inch in this case can accomodate the two sets of piezometer holes. Use angle of divergence = TO . The length of the diverging portion } (3.0655 =-------------- - 1.1284) tan Sij .98851 = ------ = 15.836Y .06116 7 TMEUJIYNAMIOS OF THE VENTURI 32TER FOR AIR )MAUREMENT. In establishing the theoretical equations for the operation of the meter, great assistance has been given by Prof. 0. W. Berry. The following equations are based almost entirely on a special paper written by him some time ago. The action of air in expanding through the throat is assuled to be adiabatic, as the flow of fluids through orifices and nozzles. The air is flowing from the lar- ger pipe into the throat, and there will be a drop in pressure and increase in velocity. As the velocities are different in the two sections there will be a change in kinetic energy. So, the equation expressing the first law of thermodynamics, with an additional term taking care of the change in kinetic energy, suffices to express the change of air in the meter. The oquation in its general way may be written dQ = A (d E + dW + dK), where dK is the change in kinetic energy. Por further development of the equation the following notations are employed: 8. V = velocity in feet per sec. v = volume in cubic feet a = area in square I5e4 ^ P = pressure in pounds per sq.inch. E = internal energy in foot pound.,units. T - temperature absolute in OF. subscript 1 concerns section I. subscript 2 concerns section 2. T = weight of air passing through per sec. Since there is no heat added to or radiated from the air the sum of the external work, intrinsic energy, and kinetic energy must be the same at section 1 as at section 2, so that = P 2 v2 + E2 + PIv1 + E, + -P4 2 g also for adiabatic expansion, p:vIj and U ajiv. P2 ' 2 --- -m---- ....... ............ .. ... Combining (1) & (2) 2 2 V1 .- 2g The intrinsic energy of a unit weight of air is P V = + constant, --- (2) ap, VR' K-i 2g K so the above reduces to .... (3) s. Using the relation PV - RT 2g RK 2 2 V V2 K-i Pp V 1 Pa - -Pi ( 29 KR a2 2 a2 a1 a1 (4) kJ vi I--- V2 - " = P2 a2 I PJL 2 P2 2 K- I P1 Combining (2) & (3), V: V,2 = 2 P2 F K-i I (2) - 2g R - ----K-1 P 2 vY 2 k PI 0'' ''.' ''..... ''* * e (5) Combining (4) & (5) 2. P 2 --k )p)(---)P a V2.2 PI a1 L - P2 K-i P1 K-)Z P1 Ik RTj (1 2g XR (--) P1 e 0 0 0 (a) ...........- a a2 P1 Oombining (2) (a) and (8) V1 2 T 1 k- X-1 iR - L 2 P, a 2 (2)2 1 I 7 2.- -( a1 P2 -- ) (---) Pj 2 k R lvi P1 T1 10. K--I W 2 P1 P1 2g K I2 - a-k P2 2K 4 a-TP, (K-1)R 4)D ) P -3 10L EFIMOT OF MOISTURE IN THE AIR. If there is any moisture in the air, the ratio of the specific heats of air will not hold good. The proper value to be used should be the ratio of the specific heats Of the mixture of water vapor and air . Since air always contains some moisture, it was decided in the following experiments to determine a new Nn' to fit the particular case. It is accurate enough to take Yny of the mixture as equal to p T vO, , which is equal to Wax .2375 + V3 X Wa X.1890 + To X 0 pe 0 y8 where Va is the weight of air and W. is the weight of water vapor.. The water vapor being compressed to a high pressure will remain superheated after expansion in the receiver. 11 The matter now simplifies to the determination of the specific heats of superheated steam and the weight of water vapor and dry air in a cubic foot of mixture. As there is no way to determine the specific heats of superheated steam readily without going into a hard task, these constants were extrapolated from Mollier's total heat pressure diagram. The weight of a cubic foot of moist air was obtained from a chart in Professor Miller's "Notes on Heating and Ventilation3 . A numerical example for finding Yn* is given on Page TJS 7ESTIN APPAATUSAN Mi HR AMRANGE NTS. The apparatus at my command was a Norwalk three-stage Air Compressor driven by Tandem Qompound Engine, ten storage tubes, and a big steel receiver. A throttling valve letting air into the receiver keeps the pressure constant in the latter. Three-inch discharge pipe leading out from the receiver turns around the storage tubes; the Venturi meter comes next to the pipe and a standard orifice cut in a bolting flange comes at the end of the pipe line. Diam- eter of orifice = .6005m. The measuring device consisted mainly of getting the drop in pressure in the throat by a differential gage. Water was used for it gives more accurate readings in small I 4 re #//,r~ I T~ I #9 0dw C 7VhPl#1ve I 7k.f~oe-e- /iVcAh tooye I I I I I I I i /7eeeire I I I I I 12 drop of pressure. 1/4N pipe was used to communicate pressure to the differential gage or U-tube. Valves were used for p2 and p3 so that only one could be connected at a time with pl. S Three gages were calibrated to get the pressure P1 and P 4 and pressure in the receiver. used to indicate t1 and t4 . Two thermometers were A sling psychometer was used to serve the purpose of a wet and dry bulb thermometer. EITHOD OF MAKING A TEST. It is only after a day's hard work that things went apparently right at low pressures. In making the test, two fellow students kindly helped me as it needed three to run the test. One man had to stay at the throttling valve to keep the pressure constant in the receiver. One of the remaining two took care of the readings of the , differential gage, and the last one took readings of P1 P4 , tj and t4 . The tests lasted about five minutes and as many readings as time allowed were taken in each test. dED OV $:"~~ pi 7 j-0 f ~~'-6lc. 9xjA1A _ _ 4 4- 7 7-0 7 6-5 _ _ --5 _ -3 -4.Q e 3. -4-4 57--- O3 '7. -41 o- 7.1 3l 4-7 3- 7.0 -44 4- 00 - 54 20 02.3 7-s- ZO #I3 80-5 82 goe- .o Z-4 s'75 3 eo4-5 -0 7 J0 '4~/ -- Jo-/a0 z o-ic. / - 3 oVe. 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I I II I I [ Il i [ ki l l f i ll Ti l l f i ll itli lilt l i l t II 11 iI fI IfIf I t t i l l- I II I II I l l I TT $ I I I I I I F l i l t ] If I I II It It I T I i t [Ili I f I if T IT M l il t l il t I 1 1 ] f i l l IFI I I I I I I I I f I II I I II IIIII :V l l IIIIIII f i -LI-LLLM ] 4ASGACHUGLITTO INSTITUTE OF TEOMMOLMY.