Device for creating and exploiting a pressure difference and the

Details Device for creating and exploiting a pressure difference and the Device for creating and exploiting a pressure difference and the

1987-05-19

1988-12-20

Croyle, Carlton R.

Pumps

One fluid pumped by contact or entrainment with another

Jet pump with motive fluid generating pump

417 87, 417151, 417196, 417198, F04F 544, F04B 2304

Patent

active

047922842

DESCRIPTION:

BRIEF SUMMARY
The present invention deals with a process for creating a pressure difference by means of a tube of a certan shape, through which a fluid medium, i.e. a liquid or a gas is flowing. Furthermore the invention comprises a device suitable for carrying out the process as well as different technical applications of the process.
The process according to this invention is based on a modification of the venturi tube. This device, which has been known for nearly two hundred years, represents, by its shape, a body which is generated by rotating a complicated asymmetrical curve about an axis of symmetry. This body is a tube which, according to the form of the curve, along its longitudinal direction is narrowing and then again widening. If a liquid is flowing along the venturi tube, a reduced pressure (compared with the pressure at the entrance and exit cross-sections) is generated, whereby the pressure difference, following Bernoulli's law, reaches a maximum at the narrowest point of the tube.
Today the venturi tube still occupies a position of practical importance, e.g. as an instrument for the measurement of the flow velocity of liquids and gases along tubes, for the measurement of the speed of planes and ships, as a water jet pump (FIG. 2) for evacuating vessels, and furthermore in carburettors of internal combustion motors and in devices for the scrubbing of gases.
When using the venturi tube as a measuring instrument it proves to be of disadvantage, that the pressure difference read at the measuring point does not depend in a simple and calculable manner on the flow velocity. Many other factors, such as e.g. the viscosity and the density of the flowing medium, the pressure values at the entrance and exit and, last but not least, the exact geometry of the nozzle shape and the surface roughness of the wall influence the result in a decisive manner, from which follows that in practice a calibrating curve, which is valid only within narrow limits must be made for every measuring task. Certain simplifications and standardization of the nozzle shape (FIG. 3) have brought about some improvement and made possible a better reproducibility of the measuring results. However the correlation between the flow velocity and the pressure difference as measured remains complicated even for a standardized tube.
It has now been found, that some surprising results, which cannot be deduced from any literature known to date, can be achieved if the venturi tube of traditional shape is replaced by a simple double cone, whose angles at the entrance and exit sides satisfy the condition:
Such a double cone as is shown in FIG. 4, e.g. in a symmetrical form, i.e. with equal aperture angles of both of the opposed hollow cone trunks, not only makes possible an easier representation and calculation of the hydrodynamical situation and, within a wide range, a better conformity of measured and calculated data; very surprisingly there has also been found a higher efficiency. That is, with a given flow speed of the fluid medium, a higher pressure difference has been found between the entrance cross-section and the narrowest part of the double cone. This efficiency, which not only depends from the aperture angle of the two cone trunks, but in a certain degree from the length of the entrance and exit cones as well, can be evaulated from the numerical value of the function F. The more this value lies below the limit of 0.11, as given above, the higher is the efficiency of the double cone. Referring to the FIG. 4, in which the double cone according to the invention is represented, values of the function F are shown for some selected configurations:


TABLE 1 ______________________________________ F = (1 + sin.sup.2 .theta.) .multidot. sin.sup.2 .theta..sub.2 "efficiency factor" of the double cone for different aperture angles of the entrance and exit cones. entrance cone exit cone angle.degree. angle.degree. 1 3 6 10 15 ______________________________________ 1 0.0003 0.0028 0.0113 0.0312 0.0693 3 0.0003 0.0030 0.0121 0.03

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V.D.I. Zeitschrift, Bank 101, Nr. 34, Dec. 1, 1959, (Dusseldork, DE), F. Schupp: "Regelbars Mehrfach-Strahlsauger", siehe Figuren 1, 3-7.
Proceedings of the Instritution of Mechanical Engineers, Bank 185, Nr. 56, 1971, (London, GB), M. L. Hoggarth: "The Design and Performance of High-Pressure Injectors as Gas Jet Boosters", siehe Seite 756, Figur 1C.

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