8/3/2019 2011.09.30 - Scientific American - The Tesla Steam Turbine

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296 SCIENTIFIC AMERICAN Sept emb er 30, 1\1

Th e tO I? half of i l f . ; ' ~ is renl o.vccl ., two roto rs. E a . c ro tor S L S o f 25 di8k ! %- iuc;h tbi c li .iJY i!lCh di umeter. '1' 1! e steam enters a t t!J e r i p h und rtow :5 in spiral patlls to exhaust at th e ecuter of theL11 sks. Th e driVlllg t nrbme 1s to the Jeft , t he brake tnrlnne to t he r1 ght. Between tlietn IS a ton:uou spring. 'l'he 8ten m m lets are on opp osite sides on the two roto rs · the drivinO' rotorm ovin tr cloc l·wi se

Th e torsion of th e spring is automat ically shown hy beams of li ght 1tnd mirrors anu the horse-power is read off a scale. At 9,000 revolutions per mi nute, with 125 ponnd;at the thr ot tie ' •n11d fre e ex lwn Kt . thi s tnrhine d e v c l o p s 200 hor se-pow er. It weig hs t wo per o w e r .

The Tesla turbine testing plant at th e Edison Waterside Station, •New York.

The Tesla Steam Tu rbineThe Rotary Heat Motor Reduced to Its Simplest T erms

I T will in teres t th e rPa.dPrs .of the Sc lE :-> 'I'JFW AMF.RI

f'A.N to know tha t Nikola T'Psla, whose reputation

must , na turall y, st and upon the rontribution s he made

to e lE•C'triral engineering when th e ar t was yet in it s

comparat :ve. in fan cy, is by t rainin g and choice a mechanicaI engineer , with a strong leaning to that bran ch

of it whi ch is covered by th e term "ste am enginee r

ing." Fo r severa l years past he bas devot ed much of

his at tention to improvement s in th .ermo-dynamic con:

ve rsion , and th e resnlt of his theories and practical

experimPnt s is to be ~ o u n d in an entirely new form

or prim P movf' rs shown in opf'ration at th e Waterside

s ta tion of th e. New York Edi son Company, who Jdudly

pla ced the facilities of their great plant at hi s disposa.l

for carrying on experimental work.

By th e courtesy of the inventor, we ar e enabled to

publish th e accompany'ing vie ws, representing th e

tes ting plant at the Waterside station, which ar e the

first photographs of this interesting motor that have

ye t been made public.

Th e basic principle which determined Tesla' s in ves

tigations wa s the well-known fact th at when a fluid

(s team, gas or water) is used as a vehicle of energy,

the highest possible economy can be obtaine.d only

when the changes in velocity and direction of th r

movem ent of the fluid are made as gr adual and easy

as poss ible. In the present forms of turbines in 'i\'hi ch

th e energy is transmitted by pr essure, reaction or

impact, as in the De Laval , Pa rsons, and Curtiss

• ty]Jes, mo re ·or less sudden h ~ n g both of speed and

direction ar e involved, with consequent shocks, vibra

tion and -destructive ed.dies. F u r t h e r m o r e , th e intro

duction ·of piston s, blades , bu ck ets , and intercepting

devices of this general class , into th e path · of the

fluid involves much delicate and difficult mechanical

construction which adds greatly to the cost both of

production and maintenance.

Th e -desidera ta in an ideal turbine group themselves

under the heads of th e theoretical and the mechanical.

Th e th eoretically perfect turbine would be one In

whi ch the fluid was so controlled from th e inle t to thE)

r.xhau st. that its energy wa s delive red to th e driving

shaft. with the least possible losses due to th e mechan

ical means employed. Th e mechanically perfect tnl' -

bin e would be one which combined simpli ci ty ancl

cbe.apness of construction, d u r ~ b i l i t y ease and rapidity

of repairs, and a small ratio of weight and space oc

cupied to th e power delivered on the shaft. Mr. Tesla

maintains that in the turbine which forms th e snbj er t

of this article, he ha s carried th e steam and gas motor

a long step forward toward the maximum attainabl e

efficiency, both theoretical and mechanical. That these

clai.Ins ar e well founded Is shown by the fact that in

the plant at th e Edison station, he is securing an

Th il5 litt le pu m p, dl'iven by a motor of 11: hor:-:e.pow cr. is here s how n

delivering 40 gnllons of water p er minu te n 9-foot heat!,

The turbine used as a pump.

'!'his vi ew eh o ws one comp lete h.tg-h J11'C-tslli'C nllit, with th e s ten mt.l1rottle above, u. nrl below it the vulvc and the comp ac t

tnrh 1nP. Note th e mauy gages <e:f?d in t he te:='ts.

A 200-horse-power hiith-pressure turbine.

outp ut of 200 horse-power from a s ingle-stage steam

turb ine with atmospheri c exh aust, weighing less than ·

2 pounds per horse-power, wh irh is contain ed wit hi n

a space measuring 2 feet by 3 feet , by 2 fee t in height,

and whi ch acc omplishes th ese r esul ts with a th ermalfa ll of onl y 130 B.T.U., that is, about one-third of the

t otal drop available. F urthermore, considered from

the mechanical standpoint, the turbine is astonishingly

simple and economical in construction, and by the

very nature of its construction, should prove to pos

sess such a dur abili ty and fre edom from wear and

break down as to 11lace it, in th ese respects , far in

adv ance of any typ e of steam or gas motor of the

pr esent day.

Briefly stated, Tes la's steam motor consists of a se t

of fiat stee l disks mounte.d on a shaft and rotating

withi n a casi ng, the s team ent erin g with high velocity

at the peri phe ry of the disks, flowin g between them in

free spiral paths, and finally escaping through e.xhaus t

ports at their center. Instead of developing the energy

of the steam by pressure, re action , or im pact, on a

series of blades or vanes, Tesl a depends upon the fluid

pro perties of adhesion and viscosit y- th e attraction ofth e stea.m to th e faces of th e disks and the r esistance

of it s particles to molecular separation combining in

transmitting the velocity energy of the motive fluid to

the plates and the shaft.

By reference to th e a ccompanying ph otographs and

lin e drawings, it will be seen that th e turbine ha s, a

ro tor A which in the presen t case consists of 25 fiat

steel ' disks, one thirty-second of an inch in th ickness,

of hardened and carefully tempered steel. The rotor

as assembled is 3% . inche..s wide on the face, by 18

in ches in diameter, and when the turbine is r unning

at its maximum worki ng velocity, the material is

never un der a tens ile stress exceeding 50 ,000 pounds

per square in ch. Th e rotor is mounted in a casing

D, which is provided with two inlet nozzles, B

for use in running -direct and B' for revers ing. Op en

ings C are <'ut ou t at th e cent ra l portion of the disks

and these communicat e directly with exhaust ports

formed in the side of the cas ing.In operation, th e steam, or gas, as th e case may be,

is directed on th e periphery of th e disks through the ·

nozzle .B (which may be diverging, straight or con

verging) , where mo re or less of its expan sive energy

is converted into velocity energy . Wben th e machine·

is at rest, th e radial and tangential forces -due to the

pressure and velocity of the steam cau se it to travel in

a rather short curved path tow ard th e central exhaust

opening, as indicated by th e full black line in the

accompanying diagram; but as the disks commence to

rotate and th eir speed increases , the steam travels in

spiral paths the length of whi ch in creases untli. as

8/3/2019 2011.09.30 - Scientific American - The Tesla Steam Turbine

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;mber SO, l 911

in th e case of t he present turbine, the particles of

the fluid comp lete a number of turns around th e

shaft befo re r eaching th e exhaust, covering in the

meantime a lineal path some 12 to 16 feet in

length. During its progress from inl€t to exhaust,

th e velocity and pressure of rthe steam ar e reduced

until it leaves th € <Jxhaust at 1 or 2 pounds gage

pr€ssure.

The resistance to tl).e passage of the st<Jam or gas

between adjoining plates is approximate ly proportion

.at€ to the square of th e re lative spe€d, which is at

a maximum toward th e center of th e disks an d is

eq ual to th e tangential velocity of the steam. Henc€th e .r<Jsistance to . radial escape is very gr<Jat, being

furthermor e enhanc€d by th e centrifugal force acting

outwardly. One of the most des ir-

ab le elem ents· in a perfected turbine

is that of r ev<Jrsibility, and we ar e

all familiar with th e many and fre

quently cum be rsome means which

have been employed to secure this

end . I t will be seen tha t th is tu r l1ine

is admirably adapted for reversing,

si nce th is effec t can be secured by

m erely clos in g th e right-h and valve

an d opening that on th e left.

I t is evi dent tha t the principles of

this turbine ar e equally a p p l i c a b lby slight mo difi cations of design, for

it s us e as a p um p , an d we present a

photograph of a demonstration model

which is in operation in Mr. Tesla's

offi ce. 'f 'hi s little pump, driven by

an electric motor of 1/12 horse-power ,

delive rs 40 gallons per minute against

a hea d of 9 feet. Th e discharge pipe

lead s up to a horizontal tube provided with a wire

mesh for :;;creening th e water and checking th e eddies.

The wa te r fa ll s through a slot in the bottom of

this tube an d passing below a baffle plate flows

in a steady stream about in ch thick by 18 inch€s

in width, to a trough from which it returns to th e

pump. Pumps of this character show an efficiency

favorably comparing with that of centrifugal pumps

and they have th e advantage that great heads ar e ob

tainable economi ca ll y in a single stage. Th e runn er is

mounted in a two-part volute casing and except for

the fact tha t th e place of th e bu ckets, vanes, et c., of th e

ordinary centrifugal pump is taken by a se t of disks,

the constr uct ion is generall y similar to that of pumps

of the standard kind .

In conclusion. it should be no ted that although th e

experimental p lan t at th e Waterside station deve lops

200 ho rse-power with 125 pounds at th e supply

pipe an d 1'ree exhaust, it could show an output

of 300 horse-power with the full pressure of

the Edison supply circuit. Furthermore, Mr.

T esla states that i f it were compounded and

th e exhaust were led to a low pr ess ure unit,

carrying about three times th e number of disks

contained in the high pressur e element , with

connection to a condenser affording 28% to 29

inch€s of vac uum, t he results obtained in the

present high-pressure machine indicate that th e

compound unit would give an output of 600

horse-power, withou t great in crease of dimen

sions. This estimate is conservative.

SCIENTIFIC AMERICAN

high efficiency when we consider that th e heat-drop,

measured by thermometers, is only 130 B.T.U., an d

that the energ y transformation is effected in on e

s tage. Si nce about three times this number of hea t

units ar€ available in a modern plant with super

heat and high vacuum, the above means a consump

tion of less than 12 pounds pe r horse-power hour in

such turbin es adapted to take up th e full drop.

Under certain conditions, ho weve r, very high ther

mal efficiencies have been obtained which demon

strate that in large machines based on this prin·

ciple, in which a very small slip can b€ secured, th e

steam consumption will be mu ch lower an d should,Mr . Te.sla states, approximate th e o r e t i c a l mini

mum , thus resulting in nearly frictionless tur-

£

297

while al l th e coal which had been mined prior to

1895 was 3,138,174,119 tons.

In credible as i t' may seem, at th e present ra te of

in crease th e ten-year period betw een 1905 and 1915

will show a production greater than a ll th e coal mi ned

in the United St ates prior to 1905. In 1850 th e per

capita product ion of coal was a little ·over one-fourth

of a ton. In 1870 the per capita production had in

creased to nea rl y one ton; in 1890 it was 2% tons;

in 1900 it was 3% tons, and in 1910 with th e popula

tion of 91,972,266 th e production wa s near ly ton s

for each person.

Last year 725,030 men mi ned coal in the UnitedStates. Th e great coal production record of 1910 was

made in spite of a series of labor s trikes participa ted

in by 215,640 men. Th e loss in

wages alon€ amounted to nea rl y

$30,000,000.

Th e quantity of 'coal used fo r

making coke in th e . United States

for metallurgical· purposes was 52,-

187,450 tons. This is additional to

by-product coke produced in gas

manufacture.

Sectional views. Spiral path of steam.

Th e total prddudion of coa l in th e

United States at th e close of 1910

was 8,243,351,259 short tons. This

plus the es t imated loss incident to

mining makes a total exhaustion of

13 ,395,000,000 tons. Th e United

States Geological Surve.y estimateflthe original supply of coal in the

ground in the United States, ex-

Details of turbine.

bine transmitting almost the entire expansive energy

of the steam to th e shaft.

Some Str iking Coal Facts

L AST year the United States mined 501,596,378

short tons of coal or nearly two-fifths of the year's

total production for th e wo r ld. This coa l wou ld load

a train stretching back and forth across th e United

States from th e Atlantic to th e Pa cific 33 times-a

t rain approximately 100,000 miles long. Eleven year s

ago th e United States for th e first time surpassed

Great Br i tain with a prod uction of 253 ,741,192 tons,

only a little more than half of last year's output.

The m er e in crea se of th t: coal output of th e Un it ed

States fo r 1910 over that of 1909-40 ,781,762 tons

was greater th a n th e total production of any foreign

clusive of Alaska, at 3,076,2 04 ,0 00,000

tons. Th is original suppl y less th e

exha ustion at th e close of 1910 leaves

an apparen t sup ply st ill av a ilable of 3, 06 2,808,972,0 00

tons, or 99.6 pe r cen t of the original supply . In oth e1·words, in all the time since coal mining began in the

United States th e draft upon th e origina l supply in

cluding loss in mining, ha s amount€d to less than

one-hal f of one p€r cent. At th e presen t rate of pro

duction of approximately half a billion tons a year

th e coal reserv e of the United States would therefore

last 6,000 years. At the present ra t€ of increase in

production. however, th es e three thousand billion ton s

of coa l in th e ground would last only a few genera-

tions.

Foreign Students in America

ADDRESSING th e Hou se of R epr esentatives on th e

many new activities of th e United States diplomatic

servi ce, Representative Foster, of Ver mont, la te

chairman of. th e House Fo reign Affairs Com

mittee, recently called attention to th e effort

made by our diplomatic an d consular repre

sen tat ives t o advertise th e United States as an

educational center, an undertaking that ha s

bee n fruitful of results.

One of th e outcom<Js of this program was

th e formation in Bueno s Ai res two years ago

of a United States University Club, which ha s

been the means of sending a t least 20 young

Argentinians to this cou ntry to be educat€d.

Under th e auspices of this clu b lectur es ar e

given on univer sit y life in the United States,

ill ustrated with a large number of appropriatestereopticon views. Negotiations are now un der

way for an interchange. of schoolboys between

the Boston High School of Commerce and t he

preparatory department of th e Uni versity of

La Plata. The re ar e no w at l<Jast 400 Latin

American s studying in th e United S tates, an d

the number is steadily increasin g.

The t esting p la n t consists of two identical

tu rbines connected by a care.full y calibrated

torsion spring, th e machine to th e left being

th e driving element, th e oth€r th e brake. In

th€ brake e lement, the steam is deliver ed to

the blades in a direction opposite to th a t of

th e rotation of th e disks. Fas t ened to th e

shaft of the brake turbine is a hollow pulley

pr ovided w it h tw o . diametrically opposite nar

row slots, and an incand escent lam p placed in ·

side clos€ to th e rim. As the. pulley rotates,

two flashes of light pass ou t of th e same; an d

by means of reflecti ng mirrors and lenses, they

ar e carried around the plant an d fall upon tw o

rotating glass mirrors placed back to back on

This turbine, who se rotor wnsists simply of a set of fiat disks 18 inches in diameter,develops 200 brake hor se-power on test.

'fhrough • th e efforts of our ambassa dor at

Constantinopl e, s upported by th e State D€part

ment, Columbia University ha s voted to 'r e·

ceive, . free of al l tuition charges, three students

annually from 'the Ottoman Empih for th e

next ten years, to pursue courses of study in

any of the ' departments of th e university.

These students ar e to be · sel<Jcted by th e Otto-the shaft of th e driving turbine. so that th e

center lin e of th e silver coatings coincides with

th e axis of the shaft. The mirrors ar€ so se t tha t

when there is no torsion on the spring, th e lightbeams produce a luminous spot s tationary at th e

zer0 of the scale. Bu t as soon as load is pu t on, th e

beam is d·eflected through an angle which indicates

dir<J ctl y th e tors ion . Th € scale and sp r ing ar e so

propor tion ed a nd adjustea . that th e horse-powe.r can

be read di rec tly from the deflections · noted. The

in dication s of this dev ice are very accur ate and have

s h,own that when the turbine is running at 9,000

revolutions und e.r an inlet pressure .of 125 pou nds to

th e squar e inch, an d with free ex_haust . 200 ·brake

horse-power ar e developed . Th e consumption un d er

t hes€ conditions of maximum output is 38 pounds

of satura te d steam pe r horse-power pe r hour -a very

Turbine with upper half of casing removed.

country except Great Britain, Germany, Austria, H;un

gary, or France.This increase alone was one and on€-fifth times as

great as the entire production of th e United States

in 1870. Excep ting only Great B: itain and Germany,

either of th e States of Pennsylvania or Wes t Vir

ginia produced in 1910 more coal than an y foreign

country. Fo r th e past seven or eight 10-year periods

th e coal production for .each decade has been about

equal to th e entire amount of coal pr e.v iously mined

in the United States . Thus in th e 10 year s bet ween

1885 an d 1895- th e · product ion · was 1,586,098,641 tons ;

whil e th e entire amount of coal mined prior to 1895

was only 1,552,080,478 tons. In th e 10 years be tweeen

1895 and 1905 the production was 2,832,402,746 tons ,

' ma n gov ernment , with the advice an d approval

of th e ambassador at Con'stantinople.

Th e education of Chinese stu dent s in Am eri ca, a m atte r in wh ich th e United States government ha s always

taken a kindl y interest, is assuming ever large r pro

portions . Th ese st ud ent s no w number between 80 0

and 900. Half of these ar e "government students, ' '

supported by th e differ·ent Chinese provinces, and by

the remitted portion of th e Boxer indemnity fund. 'TJ

insure that the indemnity students com in g to th e

United States should no t start with a serious

handicap, bu t be fully prepared to enter th e Ameri

can . coll e.ges, an acade!llY- ha s been established in

Peking by th e Chi nese government, wher€ these st u

dents r eceive preliminary instuctions under An:erkan

teac he rs.