US2268656A - Steam jet ejector - Google Patents

Description

Jan. 6, 1942. A. HALTMElE-R STEAM JET EJECTOR Filed March so, 1940 Patented Jan. 6, 1942 AlfredY Haltmeier,

Bergisch-Gladbach, Germany,

assignor, by mesne assignments, to Walther H.

Duisberg, New York, N. Y.

Application March 30, 1940,`Seral No. 32'7,061 y A In Germany May 31, 1938 This invention relates to the operating of steam jet ejectors, and more particularly to an improvement in -the designing of the nozzles u`s'ed in such ejectors.

The iigure attached to this specication shows 1 a steam jet ejector of the ordinary type. It comprises a nozzle l being inserted into the suction chamber casing 2, and a diffuser 3. High pressure steam enters the nozzle from above in the direction of the arrow, is expanded in the nozzle and, on itspassage from the nozzle through the diffuser to the condenser, pumps air or .other gases or vapors from the suction chamber in the pends on the outlet cross section area of the nozzle, (fs), if the steam is not over-expanded, i. e. expanded to a pressure lower than that existing in the suctionchamber. It is further known that the pressure nally obtained inthe suction .chamber depends from the amount of air, etc., pumped ofi by the ejector in the unit of time and also, within certain limits, from the back-pressure existing behind the diffuser. In designing nozzles for such ejectors, it has been customary to choose the cross section areas at th'e points fm and f such that, with' the desired quantity of gas or vapors to be pumped and at the desired back-pressure, the outlet pressure of the steam at the point fs, calculated on-the assumption that the expansion of the steam in the nozzle occurs adiabatically, would be equal to the pressure die--V sired in the suction chamber; it has even been proposed-to over-expand the steam, i. e. to expand it to a pressure lower th'an the pressure existing in the' suction room when the desired quantity of gas or vapors is cross section area has been so dimensioned that,

pumped. Ofi', the outlet at the highest vacuum obtainable with the suc tion pipe closed, the steam will expand /in the nozzle to the desired lowest pressure of the suction chamber (see Hfer, The Condensation in Steam Engines, Berlin, 1925, page 259, lines 9-10 from below).

I have now found that the efficiency of such' steam jet electors can be considerably increased by using nozzles having an outlet cross section area which is considerably smaller than it was hitherto thought to be necessary, so that Ithe steam leaves the nozzle with a pressure which, calculated on the assumption of adiabatic expansion, is substantially higher th'an the pressure existing in the suction chamber. bviously, this observation is quite contrary to what was commonly believed, viz. that a steam-'jet would pump a gas or vapor of the pressure ps only if it would previously be expanded in the nozzle to a pressure lower than ps (see Hfer, 1.o., Figure 2,59, and page 262, the last six lines).

My invention therefore broadly consists in operating steam jet ejectors with nozzles in which thev steam will not be expanded to a pressure equal to or lower than the pressure existing -in the suction chamber, but will leave th'e nozzles with a much higher pressure, the said steam pressure being always calculated on the assumption of adiabaticexpansion. In other words, for given conditions I use nozzles having a considerably smaller cross section area at the outlet than have been hitherto used. I have found that, for practical purposes, I can calculate the cross section areas of the steam nozzles to be used in my invention according to the formula:

wherein f. is the cross section area. of the outlet of the nozzle (mm.2); f.. is the cross section area at the narrowest point of the nozzle (mm3): ilss'fg geeislgrslkg; of the steam before it enters the i, is the enthalpy Ken/k Ome in the suction chamber;

s.) p. is the pressure mm. Hg) T. is the temperature (absolute); the steam would have i( it would i. is the enthalpy (Kcal/kg.) z. is the specific steam content f nozzle to the pressure p. 'n 1s a number which is at least equal to 2 and preferably is greater than, whereas, in the nozzleshithertoused, n was about equal to 1.

It is seen therefrom that, yaccording to my invention, the outlet cross section area of the nozzle is at the most one half of` that of the hitherto used nozzles, and preferably even less.

In order to illustrate the invention, the following lnumerical example may be given:

p1=11.5 kg./cm2. v1=0.176 vmii/kg. vi1=668 cal/kg,

adiabatically expand in the Properties the steam would have if n would adabatcally expand inthe nozzle to the pressure p.

lilifoxn'theseu data, I obtain trated my invention and in what manner it is to be performed, 'wh'at I claim is;

. In the operating of steam jet ejectors comprising a steam nozzle end a suction chamber, the improvement which comprises using a steam nozzle having an outlet cross section area' fs .cor- 1 responding to the following formula: FJLSWMJLUL "l 1in/ifi. wherein f. is the cross section area of the outlet of the nozzle (mm.2); A Y f.. is the cross section area at the narrowest point of the nozzle (mm.2);

p1 is the pressure (kgJemJ): v1 is the specic volume (m3/kg); oflgzezeam before it enters the il is the enthalpy (Kcal./kg.);

in the suction chamber;

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