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Design, construction and test of a steam air-ejector online

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N. CONSTKIJCTICH AND TES'i



ST1;AA AIR- EJECTOR



V. A. KHS^K
fv. A. TAYLOR



K il'lST



-} 1 8



621.64
K46




lUiaois iasdtote

of Tecliaology

UNIVERS)'Ty LIBRARIES



AT 491
Kerr, V. A.

Design, construction and
test of a steam air-ejector




Digitized by tine Internet Arcliive

in 2009 witli funding from

CARLI: Consortium of Academic and Researcli Libraries in Illinois



http://www.archive.org/details/designconstructiOOkerr



Design, Construction and
Test of a Steam air Ejector



A THESIS



PRESENTED BY

V. A. KERR AND K. A. TAYLOR

TO THE

president and faculty

OF

ARMOUR INSTITUTE OF TECHNOLOGY

FOR THE DEGREE OF

BACHELOR OF SCIENCE

IN

MECHANICAL ENGINEERING



MAY 29, 1918



APPROVED:



ILLINOIS INSTITUTE OF TECHNOLOGY ^c^^ J??^:^^//.*^.,.^/-

PAUL V. GALVIN LIBRARY ^-^^^^ — ^,.fM.d»„i»iB<«u>.«»,

35 WEST 33RD STREET U^^^yR^^.

CHICAGO. IL 60616 - 'iww^rin.s^ii-



^<^



DcAti of Ctlcurml ScudiM



TABLE OP CONTENTS

Pages

1. Introduction and Summary of

Machines already on the Market 1-15

2. Design of Theoretical Nozzle 15-20

3. Design of Working Nozzle 20-26

4. Method of Construction 26-29

5. Testing and Operating 29-48

6. The Proposed New Design of Steam

Air-Ejector 48-52



28097



ILLUSTRATIONS AND LOG SHEETS

Pages

1. The Radojet. (built by the C.?I,V/heeler ,

Mfg. Co. 6

2. Method of Utilizing The Heat in The Steam

& Freezing Air From Mixture. 9

3. Types of Pvimps Developed by 'Maurce

Leblanc ' * 11

4. Form ^Thich A Steam Jet Assumes During

Expansion Into A Partial Vacuum. 13

5. Log Sheet of Theoretical Nozzle. 19

6. Log Sheet of Working Nozzle. 24

7. Assembly of The Apparatus Used In Test-

ing The Steam Air-Ejector. 25

8. Photographs of The Actual Apparatus As

Used. 32 & 33

9. Log Sheets Of Tests Of the Steam

Alr-EJector. 37 & 38

10. Longitudional Section Of The New

Design Of Steam Air-£jector. 51



1.



STEAM AIR-EJECTOR
INTRODUCTION

The study of the steam air-ejector opens
up a field which is intensely interesting. This
thesis covers, of necessity, only a small area
in the search to find something useful to the
engineering profession. It is with this thought
and hope in mind that we have launched out on
new waters of experimentation. It is hoped that
our work will not he set aside, hut will be
carried on hy the future students at the Armour
Institute of Technology.

The authors desire to express their gratitude
and indebtedness to their teacher. Professor
George F. Gebhardt, whose deep interest and co-
operation have made this report possible.

The subject has herein been presented in
two parts:- the first, the general principles
and important factors which enter in, and second,
an application of these to a concrete example.



STEAI;! AIR-EJECTOR
A survey of what work and results of
experimentation has already been accomplished
is given in part #1. The design of some of
the machines, which are already on the market,
is also given.

The calculations, design, construction,
and testing of a particular apparatus for the
removing of air from condensers, when a high
degree of vaciaum, is desired are given in part
#2.

In this day of high efficiency, limited
floor space, low maintenance cost, and depend-
ability of machines, the steam turbine, as a
prime mover, has, no doubt, come to stay. With
the turbine came the demand for condensers of
a large capacity and capable of maintaining a
high degree of vacuum. It depended chiefly upon
the air pump to maintain this vacuum. Hence an
air pump of minimum space requirements, highest
efficiency, and lowest maintenance cost, is a



3.



STEAM AIR-EJECTOR
machine which is most desirable. Much has
yet to he done before such a machine will be
brought forth.

Steam air-ejectors, for removing air have
been known and used as early as 1868, but
never with the thought of producing a high vac-
uum, commercially. This was due to the fact
that the demand for a high vacuum was created
only when the steam turbine became one of the
standard prime movers for power plants.

The knowledge of the properties of steam
at this time was based mainly on the classic
investigation of Regnault.

Steam air-ejectors operate on the dry air
principle. It is desirable that they be highly
developed because of their mechanical simplicity,
ruggedness, absence of moving parts, (and hence
the absence of lubrication), and durability,
(because of their design and construction).

The Radojet Air Pvimp, which is built by the



STEAM AIR-EJECTOR
C« H. Wheeler Manufacturing Company, is
perhaps one of the most advanced air-ejectors
that is on the market at the present time.

The Radojet consists of two steam ejectors
working in series; the upper ejector being
called the first stage, and the lower one, the
second stage.

Referring to Pig. #1, the live steam is
delivered at 'L', and from there it passes
through a strainer #1, through pipe #2, auxil-
iary steam valve #3, strainer #4, and into the
expansion nozzles //5. It then crosses the suc-
tion chamber #6 of the first stage ejector.
This chamber is in direct communication with
the condenser through the opening #S.

The steam expands in the nozzles, leaving
them with a very high velocity. 7/hile passing
the suction chamber #6, it entrains the air and
vapors, which are to be compressed up to the
pressure of the atmosphere.



STEAM AIR- EJECTOR
The mixture then passes into the diffuser
#7. Here it is discharged at a higher absolute
pressure than that of the air entering at 'S'.
It then enters into a double passage #8, which
communicates with the suction chambers #9 of
the second stage. These two suction chambers
are annular, giving the commingled gases a
large entraimient surface.

Steam is simultaneously delivered through
the strainer ^fl into the passage #10. This
communicates with annular expansion nozzle,
which is formed between the two circular discs
#11 and #12. Disc #12 may be adjusted by means
of screw #13, to vary the cross section of the
nozzle passage. Hence the expansion ratio of
the steam is changed.

The steam, delivered radially by the annular
nozzle #11 and #12, expands leaving it as a jet
of high velocity in the form of a disc. In pass-
ing across the suction chamber #9, it entrains



6.




7.



STEAJ/1 AIR- EJECTOR
the air and steam coming from the first stage.
The commingled air and steam passes into the
annular diffuse #14, and the mixture is then
compressed up to atmospheric pressure. The
mixture is then discharged into casing #15,
which has a discharge opening #D.

The steam nozzles and the diffuser are de-
signed scientifically to give the highest over-
all efficiency. The nozzles of the first stage
are bronze and those of the second stage are
of a bronze steel. The diffusers of bronze and
accurately machined. In the smaller sizes, the
diffusers are a part of the casting, v;hile in
the large sizes the diffusers are secured to a
cast iron casing by bolts. These form a ground
metal to metal, joint with the casing.

The strainers ahead of the nozzles are
easily removed for cleaning.

Figure #2 shows a method of discharging the
mixture into a tank supplied with fresh water



8.



STEAM AIR-EJECTOR
for the boiler. The steam contained in the
mixture is condensed and the heat transmitted
to the boiler feed water, raising its tem-
perature. The air frees itself from the rais-
ing water and escapes through a vent to the
atmosphere.

Another design of an ejector air-pump,
or steam air-ejector, is being put on the
market. After many months of arduous research
work, during which time many set-backs and
innumerable difficulties were overcome, the
inventor, Maurce Leblanc, evolved a fairly high
class pump.

Figures #5 and #6 show the general arrange-
ment of this apparatus. The pump is arranged
to work in two stages, steam being admitted
to the second stage by the valve 'C'. Imme-
diately 'C* is opened, steam fills the annular
space behind the nozzle plate and finds its
way into the throats of the group of nozzles,



STEAM
FROM BOILER



GATE VALVE



OVERFLOW




WATER
INLET



CONDENSING
TANK



10.



STEAM AIR-EJECTOR
'Y', which are attached to this plate. The
method of supplying the first stage with steam
is readily seen from the pictujfe. The pump is
connected to the condenser at the branch 'd',
which is the air inlet. At the entrance to
each of the steam spaces back of the nozzles,
fine wire gauze strainers are fitted to prevent
any foreign matter, which may have primed over
from the boiler, from entering the nozzles.
A stoppage of one or two of the nozzles might
mean a loss of the vacuvun.

The nozzles are securely locked to the
nozzle plates. The mixture Of air and steam
is discharged at the mouth of the cone 'Y ,
and lead away to a feed water heater of the
open type. In this mam er a part of the heat
of the steam is reclaimed.

To start the pump, the valve 'c' is opened
and a certain degree of vacuum is attained in
the condenser. When the needle of the vacuum



11.




12,



STEAM AIR- EJECT OR
gauge becomes stationary, the inlet steam
valve for the second stage is opened and the
maximum degree of vacuum is obtained in a short
time.

A very important factor in this type of
pump is the absence of moving parts.

This Leblanc air pump, although apparently
having a rather high steam consumption is really
very efficient and economical. This m^achine gives
back about ninety-five percent of the original
heat of the steam.

Figure #7 shows the form which the steam
jet is though to take, upon expansion into a
high vacuiim. The steam, issuing from the mouth,
expands and contracts alternately. It ultimate-
ly assumes a constant cross sectional area.
Leblanc found that a nximber of these nozzles
grouped together gave far better results than
a single nozzle with a throat area equal to the
aggregate area of the smaller nozzles. The



13.



14.



STEAM AIR-EJECTOR
reason for this is that the alternate increas-
ing and decreasing of the cross sectional area
of the jets is minimized by the contact of one
steam jet with next, when groups of nozzles are
used. This helps considerably to increase the
surface available for entrainment of the air.



15.



STEAJf AIR- EJECTOR
DESIGN OP PRIMARY NOZZLE (theoretical)

The design of the first stage nozzle
resolves itself into the following problem:-

Assume a diameter of throat opening and
back pressure at end of nozzle. Having given
the available steam pressure, follow through
the calculations and design of a nozzle. Compare
these calculated dimensions with the required
ones for such a nozzle.

Hencf, given 100# gauge, (or 115# abs.),

initial pressure, .94# abs. back pressure and

1/4" diameter throat. Initial steam assiimed as

dry.

Dia. z 1/4"

Bg z 'SS X 115# ; 66. 7# abs. press,
in the throat.

?! = 100#-f-15# z 115# abs.

Yrj - 28# vacuum z 1»92 x .49 = .94#

abs.

Area of 1/4" throat = .4915 sq. in.

- .000341 sq. ft.



16.



STEAM AIR-EJECTOR
V = 224 ^H^ - Hg
where, H^. = ^eat at 115# z 1188.7 B.T.U.

" H2 = heat at 66. 7# = 1145 B.T.U.
Assuming adiabatic expansion.



Vg ; 224 Y 1188.7 - 1145 = 1480 ft. /sec,

Prom Moller diagram,

V]_ = 3890 ft. /sec. velocity.

Xg - .964

'S' at 66. 7# = 6.48 (from steam tables)

.964 X 6.48 = 6.25 cu. ft./#

also

Vo = 224 \/ Hn - Ho~(where Hi at 115# A
^ "• ° " Hq at .94#)

_2 224 \/ll88.7 - 885

3 3890 ft. /sec. (check)

El :: 778 (1188.7 - 1145)

r 34400 ft./# of energy in the steam.

A r WS/V

where ]_A = area in sq. ft. of nozzle opening.

" W z w't" of steam,

" S ; specific volume



17.



STEM AIR- EJECTOR
where V r vel. ft. /sec.

.000341 - W X 6.49
14B0

; ,Q11Q# steam/sec.

or .0778 X 3600 = 284# steam/hr.

This is theoretically the amount of steam
which will pass through the nozzle per sec. by
expanding from 115# abs. boiler pressure, to
66. 7# pressure in the throat.

The areas, or diameters, of the different
sections at the respective pressures of 66. 7#;
40#; 14. 7#; 8#; 4#; 2#; & .94# (discharge press.)
were obtained in the following manner; i.e. at
8# pressure.

A - .0778 (lbs, steam/sec.) x S(sp ec ific vol. @ 8#)
3060 (vel. in ftT/sec.)

- .475" dia.

- .00121 sq. ft. area.

This method gives a diameter of 1.156" at
.94# back pressure. There are losses which enter
in and change the quality, volume, and velocity



18.



STEAM AIR-EJECTOR

of the steam. It is necessary to allow for

these in the working nozzle. The calculations

for this nozzle will be given later.

The total heat, quality and velocity used

in these calculations were obtained from the

Moller diagram, (the velocity being checked by

calculation) .

F : W X V
S

where F r no. foot-lbs.

" W : wt. of steam,

" V = vel. in ft. /sec

" g r 32.2 ft. /sec. /sec.
F (at 4#) = 1 X 3370

= 104.6 ft. -lbs.

also

d - /144 X 4 X A, (where A = area in sq.
~ V 3 . 1416 ^*" °^ cross section.

:: 13.65 ^.00705

- 1.15" dia. at discharge.



19.




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20.



STEAM AIR-EJECTOR
DESIGN OF WORKING NOZZLE

The design of this nozzle takes into
consideration the increasing quality of the
steam, due to the friction in the nozzle.

The length of the nozzle will not change
from the theoretical.

This nozzle, like the theoretical one,
presents the following problem:

d^ z 1/4" = .4915 sq. in. r .000341 sq.ft.

Pi z lOC^ ga. = 115# abs.

P2 = .58 X 115# z 66. 7# abs. pressure in
throat.

Pg r 28" vacuum r 1.92 x .49 = .94# abs.
pressure.

The energy loss is converted into heat and
hence tends to dry out the steam. Assuming a
10^ energy loss and calling this loss = 'y'
V : 224 \J(1 - y) (H^ - Hg)



21,



STEAM AIR-EJECTOR
where H^ = heat at 115# = 1188.7 B. T. U.
" H2 = heat at 66. 7# = 1145 B.T.U.

V = 224 V (1 - O'l) (1188.7 - 1145)
: 224 \/' .9 X 43.7

z 1405 ft/sec. vel. of steam in the
entrance.
QUALITY OP THE STEAM AT VARIOUS POINTS
Xi = real quality,
Xq - theoretical quality
r3 = latent heat of vaporization
Xi = Xg - Iq = Xq - y (Hi - Hq)
Increase in quality;

- ,1 X (1 188.7 - 886)
' 1035.6

: .0294
Real quality = .0294 - X
z .0294 - .791

:: .810 for the discharge quality.
POOT-LSB. OF ENERGY IN THE STEAM.
E 1 778 X \f{l ' y) (^r^^H^T"



- 778 X \/{l - 0.1) (1188.7 - 1145)



22.



STEAM AIR-EJfiCTOR
■; 31,000 ft. lbs. of energy at throat

AREA IN SQ. FT. OF NOZZLE
Aq - TSX]_ X U
V
where A = area in sq. ft.

" W 2 ■»<^t. of steam passing through nozzle.

" X3 I quality of steam (real).

" Uo - specific volume of steam at .94#

A3 z . 0778 X 81 X 550.8
3760

z .00588 sq. ft.
but, Ai z 1/4 X 3.1416 X d2 r *7b8d.^
d = \/. Q05Q8

:: .0865 ft. dia.

z 1.038"; say 1" at end of nozzle.

FOOT-LBS. OF ENERGY

F z W V
g

- .0778 X 5760
52.2

r 116.7 ft. IbB.



23.



STEAM AIR-EJECTOR
LENGTH OP NOZZLE.
'L' rV15 X a where 'a' ; dia. at throat.

r Vl5 X .25"

z 1 & 15/16" length from throat.



24.













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26.



STEMt AIR-EJECTOR
METHOD OF CONSTRUCTION

The upper combining shell was made of cast
iron. The surface of the top joint was turned
corrugated to prevent the packing from blowing
out. A light cut was taken from the inside of
this piece. This lessened the friction of the
gases, which are traveling at a high velocity.

The surfaces of the lower joint were turn-
ed smooth in order that the joint might not
leak when a metal to metal contact was desirable.
The inside of the lower nozzle, forming this
piece, was turned central with the outer edge
of thesteam passage. This outer edge was made
with a sliding fit, over the shoulder of the
lower combining shell. It was in this manner
that the nozzle was centered.

The lower combining shell was finished with
a light cut on the inside to reduce friction
on the high velocity gases. The outer edge of



27.



STEAlvl AIR-EJECTOR
the lower nozzle, (on the inner side of the
upper combining shell), was finished smooth
to exact size.

The upper and lower combining shells were
fitted together, by means of the centering
shoulder. When the two smooth surfaces came
in contact, it left an opening of between 1/64
and 1/100 of an inch all around the circamference
of the secondary nozzle. By inserting a pack-
ing of a known thickness in the joint, a known
width of opening of the nozzle could be obtain-
ed. Thehozzle was made of brass and filled on
the inside to reduce the friction, which causes
a loss of energy in the steam. Threads were
cut, on the opposite end from the discharge,
leading up to the shoulder, so that the nozzle
could be screwed tight up against the top plate.
By this means washers could be inserted between
the shoulder and the top plate, if it was desir-
able to change the position of the nozzle.



28.



STEAiVl AIR-EJECTOR
The calculations show that the nozzle
should not be as long as the blueprint calls
for. The authors thought that with the extra
length of nozzle, a 'rolling action' could be
produced on the sides of the jet that would
cause a greater entrainment of air. The nozzle
is so designed that it could be cut off to the
theoretical length, if it is shown through the
subsequent tests that the extra length of
nozzle is not desirable.



29.



STEAM AIR- EJECTOR
TESTING AND OPERATION



The ejector was set up for testing in the
north-east end of the engine room of the Armour
Institute of Technology. A plan of the apparatus
and its construction is given in the illustration
#A2. In this illustration all the fittings and
apparatus are sho;vn to be swung up into the plane
of the paper. In illustrations #k-^ and #A3 the
actual apparatus is shown as it was when it was
being tested. The live steam pipe, #9 in #A3,
feeds direct from the boiler to the ejector. The
steam coming so direct from the boiler, it was
permissable to assume that it had a quality of
100^, in the calculations of the tests that
follow. This was also assumed in the calculations

of the nozzle.

The live dry steam, coming through pipe #9,
goes through valve #8 and enters the primary
nozzle at #1. It then goes through the ejector
and out the exhaust #14. This gives the opera-



30.



STEM AIR-EJECTOR
tlon of the first nozzle alone, assuming that
valve #16 is closed.

To operate the secondary nozzle alone,
valve #8 was closed and the live steaii goes
through valve #16 and into the secondary nozzle
at #la» The commingled air and steam then pass
out the exhaust #14. To operate both nozzles,
valve #8 and #16 are both opened and the steam
passir\g through them comes together again in
the lower combining shell, #1^* and hence to
the exhaust. The air that was sucked in came
through the pipe #17 and valve #6. This pipe
connected on to a displacement air meter #11,
which was capable of handling abcut 125 cu. ft.
of air per minute. This was sufficient for the
ejector.

The exhaust leads to a counter-current
condenser, #2, that had beer; opened to the at-
mosphere. This virtually makes it an open type
of condenser. This was necessary in order that



31.



STEAM AIR-EJECTOR
the air, which had been entrained in the
steam, could have an outlet.

A reciprocating pump was situated direct-
ly under the condenser. This machine pwaped
the condensed steam, and a certain amount of
air, into either one of two weighing tanks.
These tanks were situated about 10 feet back
of the condenser and in the south end of the
wash and locker room. The live steam, to ac-
tuate the pump, was admitted through the valve
#18.

In starting to run a test on the ejector
as a whole, the steam was first admitted slow-
ly to the line #9, by means of a gate valve and
a separator (not shown), so as not to cause
'Water-hammer'. The valve #16 was then cracked
open and the drip of valve #19 was allowed to
drain off through valve #16, down through the
drip-cock #13, and into a pail on the floor.
The cooling water from the city mains was then



32,




33,




34.



STEAM AIR-EJECTOR
Started through the condenser. This was forced
through by city pressure alone, no pump being
used for this circulation. The condenser pump
was then started by admitting steam through
the valve #18. This pump pumped the condensed
steam into the above mentioned tanks which
rested on platform scales and were capable of
holding about 1600 to 2000 lbs. of water.

When the drip was drained off, the valve
#16 was opened full. This let steam to the
secondary nozzle. It was thought best to let
the steam through the secondary nozzle, first,
in order to build up a vacuum in the upper
combining shell. The valve #8 was now opened
and the steam was admitted to the primary, or
first stage nozzle, after having created as
high a degree of vacuum as possible. The valve
#6, from the air meter, was now cracked open.
This was done because the drip from the steam
pipe had collected in the air pipe above the



35.



STEAM AIR-EJECTOR
valve #6. In this way the collected water
was gradually taker, into the ejector and
hence into tho condenser. When the ejector
was well heated up, the air valve, #6, was
opened full.

The boiler pressure was read on gauges
#4 and #5. The degree of vacuvun was read on
gauge #3, and also on the manometer, frlO, This
manometer lead to the suction pipe by means of
the tube, #7. The amount of air drawn in was
read from the meter at #11. The amount of
condensed steam was weighed by means of the
tanks on the platform scales in the locker-room.

In starting the first test, the secondary
was turned on first. Instead of creating the
desired vacuum, it caused a back-pressure. The
authors thought that the reason for this was
that this secondary nozzle had too wide an open-
ing. Because of this, the steam was not direct-
ed down, but rather in a course that was diagonal



36.



STEAM AIR-EJECTOR
across the lower combining shell. By follow-
ing this course, the steam from one side of
the nozzle met the steam coming from the other
side at a comparatively wide angle. >^s a re-
sult of this there was a combined, splash and
'rolling-back' action produced, causing the
steam to build up pressure in the upper combin-
ing shell.

The first nozzle was turned on at this
time with the secondary nozzle and a vacuum of
about 1" was created. Vi/hen the secondary nozzle
was turned off and the 1st left on running, with
wide open valve and under 93# pressure, a vacuum
of 2.75" Hg. was created. When the air was shut
off fully and maintained about l" Hg. vacuum
and pulled about .47# of air per # of steam.
(see log blue print for test #1).

The above results were of little value, hence
more elaborate tests and data were unnecessary.

The gasket from the lower joint was taken



37.



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Online LibraryV. A KerrDesign, construction and test of a steam air-ejector → online text (page 1 of 2)