Jet proptilrion principles have prac
tical uie» in th« engineering world.
Q wen i town
v
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g e n e r a l m isconception has been prevalent lately th a t ' • je t propulsion is new, one of the m arvels of the present war.A strenuous b it of trav el recently showed th e w riter th a t m any well inform ed people are overlooking th e historical facts and tim ing connected w ith hundreds of useful applications of jet- propelled devices. T he P ullm an smoking-room experts, even those m echanically inclined, invariably gave th e impression th a t jet-propelled devices are th e late st an d m ost w onderful in
ventions ever produced by th e supercreative G erm an mind.
I t is th is last in terp retatio n , as m uch as th e error in timing, which has inspired this article.
A sh o rt b u t inclusive search failed to reveal ju s t when the first “injector” was used to pum p feed w ater in to a steam boiler, b u t th ey were in common use on locomotives in 1881. This simple light-w eight device then, as today, received steam from the boiler it was feeding, discharged this steam through a jet, and im parted to th e feed w ater sufficient velocity to force it into the boiler against th e working pressure. T he use of je t energy for m any simple purposes is certainly over one hundred years old.
D uring this period th e developm ent an d application of jets have led to such uses as pum ping, circulating, compressing, evaluating, agitating, mixing, an d refrigerating. Design im
provem ents 'have greatly increased th e efficiency of operation w ithout increasing the num ber or complication of th e p a rts re
quired. A typical jet ejector consists of three pieces, w ith two gaskets an d th e necessary bolts to join th e steam nozzle, th e suc
tion chamber, an d th e diffuser th ro at. Since there are no moving parts, m aintenance is very low an d efficiency of operation is maximum throughout th e life of th e equipm ent. T he pressure on th e steam or other fluid used in th e je t should ordinarily be higher th a n the discharge pressure a t th e diffuser th ro at. In je t devices th e am ount of steam used is sometimes ra th e r high, b u t in m any applications th e therm al efficiency is nearly 100%.
This is especially tru e when a steam je t ag itato r is used in a tan k of liquid to be heated.
An interesting exam ple of je t power applied to circulation was dem onstrated ab o u t 1927 in a E uropean synthetic ammonia process. A characteristic of m ost processes is th e “ circulating loop” a t th e end of th e purification train . Because only one fifth to one sixth of th e gas is converted to amm onia a t each contact w ith th e catalyst, it is necessary to condense o u t th e ammonia, renew th e gas volume, an d re tu rn th e m ixture to th e catalyst. A one-stage circulating compressor is used in m ost processes to m ain tain even uniform flow of gas in th e loop. One process uses a n injector to produce th e desired circulation, w ith som ew hat questionable results. T he purified m ake-up gas, rep
resenting a t least one fifth th e to ta l gas volume in circulation, is compressed to 950 atm ospheres; a t th is pressure it is used in the p rim ary nozzle of a je t ejector w ith th e suction cham ber and dif- fusor discharge a t 600 atm ospheres pressure connected in to the circulating loop. T he circulating compressor would cost about five or six tim es th e cost of th is ejector, b u t th e increase in size of th e m ain compressors an d driving engines, an d th e difficulty of operating th e entire purification tra in a t different pressures from 800 to 950 atm ospheres m akes th is process u n attractiv e, even though it is less expensive to install.
J e t ejectors of excellept efficiency have been developed by Ingersoll-Rand, Croll-Reynolds, S chutte & K oerting, and other advertisers in these pages, for a large variety of uses in the con
densation of vapors an d th e production of high vacua. The device is so simple th a t stock ejectors are available for alm ost any capacity or back pressure, an d nearly top economy is thus provided in all applications. C apacity of an ejector is usually expressed on a w eight basis in pounds per hour, ra th e r th an in cubic feet per m inute. F or all applications where very low pressures are required or where th e vapor handled contains non- condensable gas, th e practice is to use two or three ejectors in series, w ith precondensation an d also interstage coaling or con
densing when required. One line of ejectors is designed for capacity load a t 4 inches of m ercury absolute suction pressure.
If operated a t th e same steam pressure to produce 2 inches of m ercury absolute suction pressure, th e capacity falls to 21% of design capacity a t 4 inches of m ercury absolute pressure, b ut 200% of capacity operation can be obtained if the suction pres
sure is raised to 7.7 inches of m ercury absolute. W hen three suitably designed ejectors are used in series, th e set will move 25% of rated capacity a t 0.2 inch of m ercury absolute pressure, 100% a t 0.5 inch, an d 225% of capacity a t 1.5 inches. T his wide range of usefulness is indicative of th e im portance of these low- cost stationary devices. Compression of waste or exhaust steam from a low pressure to a pressure two or three tim es higher can be carried o ut by noncondensing jet ejectors. Steam a t considerably higher pressure th an th e discharge pressure m ust be supplied to th e nozzle, an d th e economy of use is somewhat poor. T he therm al efficiency is relatively high because all the steam used in th e nozzle as well as th e steam compressed is avail
able a t th e higher pressure.
Because th e capacity of ejectors is usually expressed on a weight basis, one seldom realizes th e enormous volume of vapor these small devices can handle. I t is so large th a t a jet-propelled pum p or compressor is often used to cool, or refrigerate w ater by self-evaporation. B y placing a je t ejector suction cham ber on a baffled ta n k containing w ater and th en evacuating the w ater vapor a t 1 or 2 inches m ercury pressure absolute, the w ater in the ta n k is cooled by evaporation. B y adm itting ordinary tem pera
tu re w ater a t th e proper ra te an d pum ping o ut th e cooled w ater, a continuous supply of w ater a t tem peratures as low as 38° F.
can be obtained. T he vaporization of ab o u t 1 % of th e w ater in the tan k cools the rem ainder 10° F . T his type of equipm ent is light in w eight an d com pact in size, and operates w ithout vibration or noise. Steam an d w ater are th e only costs of operation, as m aintenance is negligible and there is no refrigerant to handle or replace.
N um erous inventors an d hundreds of inventions were offered to win th e first W orld W ar; b u t we seemed to possess more common sense back in those days, and no one dream ed th a t a Technical M obilization Act was needed to handle th e problems.
In stead it was realized th a t the situation required only a small com petent group to interview an d appraise th e inventions. The m ain problem was to direct inventors to a group suitably trained to evaluate th e proposal. T he money required came from a fund known as A rm am ents (Continued on -page 80) 79
in terestin g b u t for certain p a tte rn s of hum an n a tu re w hich were encountered a t once. H isto ry seldom records th e acceptance of adverse decisions b y inventors of dream gadgets no m a tte r how fair a n d accurate th e y m ay be. T his was p articu larly tru e of th e m any inventors of “electrical d eath ra y ” devices, w hich were considered so im p o rta n t th ey could n o t be p a te n ted a n d so pow er
ful whole populations could be killed in a few m inutes. T h e dis
agreeableness usually sta rte d w hen one inquired a b o u t th e degree of im m unity for th e o p erato r or ju s t w h at te s ts h a d actu ally been m ade a n d th e num ber of people killed by coroner’s count. I t w as astounding to w itness th e im patience of th e inventors over th e least criticism of th eir unproved statem en ts. Second only to th e “electrical d eath ra y ” were th e num erous ro ck et devices, including rocket-propelled airplanes.
In to th is Tom m y T in k er atm osphere cam e F arley G. C lark to propose th e developm ent of jet-propelled m ilitary planes. As chief engineer of th e T o ro n to Pow er C om pany, a large C anadian firm a t N iagara Falls, his able, technical appeal for th e develop
m en t of jet-propelled m ilitary planes w as refreshingly scientific.
B ased upon m em ory only, his rough specification appears strik ingly like th e je t applications being trie d to d ay . C lark pro
posed a plane of conventional design, w ith o u t a m otor a n d driven only by fuel burned un d er forced com bustion, w ith th e products passing th rough a je t whose reaction against atm ospheric resist
ance w ould drive th e plane. C lark a d m itte d his studies were prelim inary, b u t he had figures to show th a t th e required energy was there. H e m ade no e x tra v ag a n t claims for fuel consum p
tion, b u t took reasonable credit for th e sm all w eight an d to ta l absence of drag of je ts ag ain st th e w eight an d fro n t resistance of airplane m otor an d propeller of those days. H is m ost logical an d im p o rta n t arg u m en t for th e adoption of jet-propelled planes was based on sound economic engineering. W hy p u t a m otor w ith severe vib ratio n characteristics in to a plane, a t a cost of 12,000 to 14,000 m an-hours an d $50,000 to $60,000 w hen its useful com
b a t life m ight be 10, 8, or even fewer air-hours, ju s t to obtain a little fuel economy. T his was a n early lesson in th e peculiar economics of m ilitary m achines which m ight have borne valuable fru it except th a t it had a pow erful com petitor. W ide publicity com bined w ith com plete m y stery already surrounded th e m ost glam orous L iberty m o to r being designed beyond locked doors, a n d th e je t propulsion theory was filed.
A valuable developm ent of je t energy has been successfully applied to hydroelectric in stallatio n s by O scar G. Thurlow , form erly chief engineer of th e A labam a Pow er C om pany. I n m ost hydroelectric p lan ts th e w ater tu rb in e is placed some several feet above th e m ean w ater level below th e dam , an d this distance is filled in w ith th e discharge d ra ft tu b e. T he pull of th e w ater in th e d ra ft tu b e together w ith th e im proved flow characteris
tics due to th is tu b e m ake th e fall below th e w heel quite as ef
fective as th e head above th e wheel in norm al operation. W hen flood w aters occur, all this changes. T he w ater due to th e flood volum e backs up below th e dam an d gj-eatly decreases th e effec
tiv e useful head. T here is too m uch w ater everyw here. B y m eans of several je ts properly placed near th e discharge tu b es of th e turbines, th is troublesom e excess w ater is p u t to work.
Some of th e useless flood w ater is tak en from th e high level above th e dam an d discharged th ro u g h these jets, w here th e energy in th e jets is used to pum p w ater aw ay from th e discharge of the turbines. T his gives th e effect of lowering th e level of th e
“ tail w ater” . W hen in operation these je ts te n d to restore th e m axim um difference in level betw een th e h eig h t of w ater above a n d below th e dam . T his je t application has recovered a large a m o u n t of energy which w ould otherw ise be lo st a n d has won honors from T h e F ran k lin In s titu te for T hurlow .
80
^ M A / ie s u , i s t
Th* analysis of sat«* by thermal conductivity method* Is discussed.
c<=~ ~ t) is c u ,M e ( l
( u J ^ a lv l i y ^ P tu n c L
/ )a s t m onth th e infrared gas analyzer m ade by B aird Associ- JLm ates was discussed in this column. P ractical application of th a t m ethod for industrial control purposes is very recent, al
though th e possibility of infrared gas analysis has been known for a long tim e. T herm al conductivity m ethods have, on th e other hand, been used to perform continuous gas analyses for recording and control applications for m any years. One of the earliest in
dustrial applications was th e in stru m en t perfected in 1909 in Germ any by K opsel for m easuring hydrogen in producer gas.
D uring W orld W ar I th erm al conductivity gas analyzers, de
veloped in E ngland an d in th is country, were used to tes t the purity of balloon gas and th e perm eability of fabrics for balloons.
From those early beginnings, to d ay ’s highly developed equip
m ent has evolved.
To give some idea of th e differences in therm al conductivity which form th e basis for this m ethod of gas analysis, d a ta for some of th e m ore im p o rta n t gases are given in T able I. As a first approxim ation, th e therm al conductivity of a gas m ixture m ay be considered to be a linear function of th e concentration.
Using d a ta from th e table, we m ay calculate th e conductivity of a m ixture containing 10% carbon dioxide an d 90% air to be 2.77 a t 100° C. T he value for dry a ir a t 100° C. is 2.85. T hus, 10%
carbon dioxide causes a 2.8% change in conductivity. T his rep
resents ab o u t the m inim um change in th erm al conductivity which can safely be m ade equal to full scale for a comm ercial gas an a
lyzer. I t will be noted th a t a binary m ixture is assum ed in this discussion. If w ater vapor is present, it m u st either be removed by drying agents or k ep t a t a co n stan t value by bringing th e gas m ixture to equilibrium w ith w ater a t a fixed tem perature. Small am ounts of sulfur dioxide or carbon monoxide cause appreciable errors in th e reading of th e in stru m en t; sm all am ounts of hydro
gen cause serious errors, as w ould be expected from th e therm al conductivities in T able I. T hus, th erm al conductivity gas analyzers by them selves do n o t possess th e ab ility to distinguish among gases to such a high degree as do infrared gas analyzers, nor is th eir sensitivity so g reat in m any cases.
Figure 1 is a schem atic diagram of a th erm al conductivity gas analyzer of th e ty p e m ade by Leeds & N o rth ru p Com pany, Philadelphia. T he filam ents of tw o therm al conductivity cells, M and N , and two resistors form th e arm s of a W heatstone bridge. T he cells are tu b es containing fine platinum filam ents stretched along th eir axes. Cell N is filled w ith a stan d ard gas; th e sam ple flows th rough cell M . T he cu rren t flowing through the W heatstone bridge heats th e filam ents of th e con
ductivity cells to a tem perature depending on the conductivity of the gas around them . Since the resistances of th e filam ents are a function of th eir tem perature, changing th e com position of gas in M alters th e bridge balance. T he o u tp u t from the bridge is m easured by an altern atin g -cu rren t potentiom eter recorder w ith a scale calibrated in term s of gas concentration.
Figure 2 is a photograph of th e therm al conductivity cells used in Leeds & N o rth ru p instrum ents. To avoid change in calibra
tion due to corrosion, th ey are constructed so th a t th e sample does n ot come into contact w ith any m aterial except glass; even the platinum filam ent and tension spring are glass-covered. The left-hand cell is th e reference cell; th e right-hand, th e measuring cell. Sample flows downw ard through th e right-hand m em ber of th e m easuring cell. A sm all portion of this gas is carried by con
vection up through the diagonal tu b e to th e cell, down through it, and back to th e m ain sample stream . (Continued on page 86)
Table I. Thermal Conductivities of Gases
,--- k in Kilo-Ergs, Cm. “2 Sec. -1--- * W ater
T° C. Air N2 O2 H2 CO2 SO2 vapor N H3 CI2
0 2 .2 3 2 . 2 8 2 .3 3 1 5 .9 1 .3 7 0 .7 6 8 . . 2 .0 0 0 .7 1 8 50 2 .5 4 2 .6 0 2 .6 8 1 8 .0 1 .7 0 . . . 1 .83 ...
100 2 .8 5 2 .9 0 3 .0 1 2 0 .0 2 .0 7 . . . 2 .1 7 3 .1 0
Figure 1 (Below). Diagram of Leeds & Northrup Ther
mal Conductivity Gas Analyzer Figure 2 (Right). Thermal
Conductivity Cells
IIS VOLTS A - C
A-C WHEATSTONE BRIDGE CELL
ASSEMBLY
A -C POTENTIO METER RECORDER
A - C GALVANOMETER AND FIELD COIL
9 n A ^ u im e * U a tio * i
T his arran g em en t gives a uniform flow ra te th ro u g h th e m easur
ing cell. T h e tw o cells are m ou n ted in a sep arate enclosure in a th erm o stated cham ber along w ith a s a tu ra to r to keep th e w ater v ap o r pressure c o n stan t. Figure 3 represents th e com plete as
sem bly. T h is equipm ent requires little m aintenance because it is o perated by a lte rn atin g cu rren t a n d sa tu rate s in stead of drying th e sam ple. P erh ap s th e g reatest num ber of th erm al conductiv
ity gas analyzers are carbon-dioxide recorders for com bustion con
trol. I n addition, th ere is a g reat v a rie ty of m iscellaneous a p plications, w ith several installations for m easuring hydrogen in m ixtures w ith nitrogen, air, oxygen, or chlorine. D eterm ination of am m onia, sulfur dioxide, oxygen, hydrocarbons, carbon m on
oxide, hydrogen sulfide, helium , an d argon are am ong th e com
m ercial applications. T h e m ethod has m any ad v an tag es for th e m easurem ent of h um idity. F o r some applications it is possible to increase th e sensitivity an d selectivity of th e m ethod by using a double-flow cell arranged so th a t th e co n stitu en t to be d eter
m ined is rem oved from th e m ixture by reaction o r absorption after th e sam ple has passed th rough one cell. T h e rem ainder of th e m ixture is th e n passed th rough th e second cell. T h is differ
ential m ethod also m akes possible th e analysis of m ulticom pon
e n t m ixtures for one co n stitu en t w hen th e relative am ounts of th e others are n o t constant. One exam ple of th is ty p e is th e analysis of electrolytic chlorine, containing variable am ounts of oxygen, nitrogen, an d carbon dioxide, for hydrogen. A fter passing through the first cell, th e hydrogen is reacted catalytically w ith chlorine an d passed through th e second cell.
Rotameter Nomograph for Steam. Fischer & P o rte r Com pany, H atboro, Pa., has available a nom ograph to determ ine th e proper size ro tam eter for a given steam m easurem ent application. T he range is 50 to 500,000 pounds per hour of steam . Also available are C atalog 43-E on A rm ored R o tam eters an d B ulletin 82-A covering Rotasleeves.
Apparatus (or D-C Resistance Measurements. Leeds & N o rth ro p C om pany has released a 36-page edition of “A p p aratu s for D -C R esistance M easurem ents” . T his catalog lists equipm ent ranging from K elvin bridges to insulation te s t sets an d from precision bridges for lab o rato ry stan d ard s to per cent lim it bridges for routine production testing. I t gives inform ation on selecting th e proper in stru m en t an d accessories to go w ith it.
Figure 3. Interior V ie w of Thermal Conductivity Gas A nalyzer for Use with Leeds & Northrup Micromax M o d e l R or S Recorders