fEc : '60

NBS

PB 151398

ecUnlcai ^lote

j$oulder laboratories

92o. 39

HELIUM REFRIGERATION AND LIQUEFACTION

USING A LIQUID HYDROGEN REFRIGERATOR

FOR PRECOOLING

BY D.B. CHELTON, J.W. DEAN, T.R.STROBRIDGE, B.W. BIRMINGHAM

AND D.B. MANN

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended hy Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent with these standards: the determination of physical constants and

properties of materials: the development of methods and instruments for testing materials, devices,

and structures; advisory services to government agencies on scientific and technical problems: in- vention and development of devices to serve special needs of the Government; and the development

of standard practices, codes, and specifications. The work includes basic and applied research,

development, engineering, instrumentation, testing, evaluation, calibration services, and various

consultation and information services. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau's unique competence is required. The scope of activities is suggested by the listing of

divisions and sections on the inside of the back cover.

Publications

The results of the Bureau's work take the form of either actual equipment and devices or published papers. These papers appear either in the Bureau's own series of publications or in the journals

of professional and scientific societies. The Bureau itself publishes three periodicals available from

the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary

and preliminary reports on work in progress; and Basic Radio Propagation Predictions provides

data for determining the best frequencies to use for radio communications throughout the world.

There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series,

Handbooks, Miscellaneous Publications, and Technical Notes. Information on the Bureau's publications can be found in NBS Circular 460, Publications of the

National Bureau of Standards ($1.25) and its Supplement (SI. 50), available from the Superintendent

of Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS

technical ^lote

39

January 27, I960

HELIUM REFRIGERATION AND LIQUEFACTION USING

A LIQUID HYDROGEN REFRIGERATOR FOR

PRECOOLING

by

D. B. Chelton

J. W. Dean

T. R. Strobridge

B. W. Birmingham

D. B. Mann

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature. They are for sale by the Office of Technical Services, U. S. Department of Commerce, Washington 25, D. C.

DISTRIBUTED BY

UNITED STATES DEPARTMENT OF COMMERCE

OFFICE OF TECHNICAL SERVICES

WASHINGTON 25, D. C

Price $ .50

TABLE OF CONTENTS

*

Abstract 1

Introduction 2

General Discussion 2

Hydrogen Refrigerator 5

Helium Refrigerator 10

Helium Liquefier 21

Bibliography 31

Helium Refrigeration and Liquefaction Using

a Liquid Hydrogen Refrigerator for

Precooling

by

D. B. Chelton

J. W. Dean

T. R. Strobridge

B. W. Birmingham

D. B. Mann

ABSTRACT

Consideration is given to the use of a hydrogen refrigerator to

assist in the production of temperatures below those obtained with

hydrogen. A hydrogen refrigerator is used to maintain a precooling

evaporator at or near 21 K in a helium gas circuit. The helium

circuit may be arranged to produce liquid for external use or to produce refrigeration between 21 K and 4. 2 K in a closed system.

Charts have been developed that show the requirements of the

composite helium - hydrogen system and the effect of heat exchanger

performance. The relative quantities of refrigeration (hydrogen and

helium) at various temperature levels have been determined.
INTRODUCTION

At the present time, a number of hydrogen refrigerators and

liquefiers are being used to maintain experimental apparatus at low

temperatures. For example, several 21-27 K hydrogen refrigerators

are used for continuous refrigeration of liquid hydrogen bubble chambers* » 2. Refrigeration at this temperature level is also being planned

for experimental apparatus associated with nuclear reactors and

electromagnets. Certain applications may require temperature below

those obtainable with hydrogen.

Hydrogen refrigerators can be used for the production of lower

temperatures by using a hydrogen evaporator to precool a stream of

helium gas in an additional circuit. In some instances, it may be

feasible to convert a hydrogen liquefier to perform the function of a refrigerator for this precooling.

This paper discusses a relatively simple method of using a hydrogen refrigerator to assist in the production of temperatures

from 21 K to liquid helium temperature. With proper considerations

it should be possible to operate the hydrogen precooled helium system

at any temperature within these limits. Consideration in the text is

also given to the production of liquid helium for external use. Cycle

information is presented with text only sufficient to define the particular conditions or assumptions upon which the calculation is based.

GENERAL DISCUSSION

A schematic arrangement of the composite helium-hydrogen

low temperature apparatus is shown in Figure 1 . Symbols indicated

on the schematic are used throughout the text. The automatic control

of such a unit has been discussed elsewhere and will not be considered

here. Both the helium and the hydrogen circuits use liquid nitrogen

precooling at 65 K, although 78 K is considered in a few instances.

The liquid nitrogen required as precoolant is given in liters per hour

since, for most applications, it will be supplied as liquid from an external source. It is further assumed that the nitrogen will be supplied

to the unit as saturated liquid at 2 atmospheres.

The hydrogen gas is further cooled, after liquid nitrogen precooling, in a final heat exchanger and expanded at the hydrogen throttle

valve to produce liquid in the evaporator. The evaporator can be a reservoir as shown, or a bundle of heat exchanger tubes. Hydrogen

evaporator temperatures from 21 K (1.23 atm) to 1 5 K (0.13 atm) are

studied.
CM

I

LIQUID NITROGEN

EVAPORATORS

( PRECOOLANT )

H2 Throttle Valve

LIQUID HYDROGEN

EVAPORATOR

( PRECOOLANT)

He Throttle Valve

Q2 or-x->

HELIUM RESERVOIR

or EVAPORATOR

Figure I. schematic arrangement of low

TEMPERATURE CYCLE
The helium gas, after liquid nitrogen precooling, is passed

through a counterflow heat exchanger and further cooled in the liquid

hydrogen evaporator. The temperature of the gas is still further

reduced in a final heat exchanger and expanded at the helium throttle

valve where liquid can be formed. Liquid formed in the expansion

process can be evaporated in the reservoir, as in a refrigerator, or

can be extracted from the reservoir, as in a helium liquefier. If refrigeration is required at temperatures above liquid helium, the

final heat exchanger is partially by-passed. The quantity of by-passed

gas determines the operating temperature of the refrigerator.

If a hydrogen refrigerator is available, the method described

above is a very simple way of producing temperatures lower than that

obtainable with hydrogen. An alternate method for the final stage

cooling of the helium gas stream would utilize an expansion engine as indicated by the dotted lines of Figure 1. The expander inlet temperature could range from the temperature of the hydrogen evaporator

to some lower temperature. This method requires the use of an expansion engine operating at low temperatures, but it substantially

increases the thermodynamic efficiency of the cycle. Additional

improvement in the thermodynamic efficiency of the cycle can be

obtained by replacing the helium throttle valve with an expansion

engine. Use of such an expander is limited to temperatures above

that of liquid helium if condensation in the expander is to be avoided.

The performance of this alternate cycle must be computed for the

refrigeration temperature desired. These more extensive calculations have not been considered in the present paper.

Small capacity refrigeration systems do not necessarily

require a high thermodynamic efficiency. Often the simplest cycle is

desirable for reliability and ease of operation. For any cycle,

however, it is desirable to produce refrigeration with a minimum expenditure of energy, since the cost of gas compression equipment

materially affects the total capital investment. Compression equipment may account for 20-40 percent of the total system cost.

Sufficient information is presented later to determine the performance of a practical helium refrigeration or liquefaction system

based on the cycle indicated by the solid lines in Figure 1. A convenient reference is the theoretical performance based on a heat exchanger

efficiency of 100 percent. For the final heat exchangers in the cycle

under consideration, this corresponds to AT = AT. = 0. The design

parameters considered are:
5

1) heat exchanger efficiency (presented as

functions of AT through AT ) 1 5

2) liquid nitrogen consumption

3) mass flow

4) power required for compression

The power required reflects only that necessary for compression of

the gas in each circuit. A 65 percent isothermal compression

efficiency is used for the calculations. With the aid of the design

charts presented, it is possible to determine the quantity of refrigeration (Q ) required at liquid hydrogen temperature for a given quantity

I; of refrigeration (Q_) at lower temperatures or for a given quantity of

helium liquefied (x).

All helium calculations are based on the thermodynamic pro-

's A 5 perties presented by Mann and Stewart , Keesom and Zelmanov a The hydrogen calculations are based on the properties given by

Woolley, Scott and Brickwedde . The results of the calculations have

been smoothed where necessary since they require greater accuracy

than obtainable from the above properties.

HYDROGEN REFRIGERATOR

Hydrogen refrigerators usually operate from 21 K to 27 K.

For efficient operation of the helium refrigerator or liquefier, it is

desirable to maintain the hydrogen evaporator as low in temperature

as possible. In fact, it would be desirable, on this basis, to operate

the evaporator at a reduced pressure. Practical considerations

usually limit the precooling temperature to about 15 K (0. 132 atm),

slightly above the triple point of hydrogen. Operating the hydrogen

evaporator at a reduced pressure results in a substantial increase in

the work of hydrogen compression although there is a considerable

reduction in the work of compression for the total cycle in Figure 1.

Figure 2 shows the work of hydrogen compression (kw) required per

unit (kw) of refrigeration at the evaporator temperature for theoretical performance (100 percent efficiency) of the final heat exchanger.

Minimum work occurs for an inlet high pressure near 120 atmospheres

and this pressure has been used throughout the remainder of the calculations. The power required to compress 1 scfm (1 atm, 20 C) of

hydrogen gas from 1 atmosphere to 120 atmospheres is equal to 0. 37

kw„ Compression from 0. 132 atm requires 0. 52 kw per scfm (1 scfm=

0. 04 gm/sec).
The refrigeration available as a function of heat exchanger

performance is shown in Figure 3. It is observed that the quantity of

refrigeration is reduced because of finite temperature differences,

by 5 percent per degree K for 65 K precooling and by 6.7 percent per

degree K for 78 K precooling.

The liquid nitrogen required in the precooling evaporator is

affected by both AT and AT.. A lower limit is imposed on the value

of AT. because of the variation in the specific heat of hydrogen. This

limit can be seen in a cooling curve analysis . The quantity of

nitrogen is shown in Figure 4 in units of liters per hour per watt of

refrigeration (Q ) at the hydrogen evaporator. Both Figure 3 and 4

are independent of the hydrogen evaporator temperature.

Since it is thermodynamically advantageous to reduce the

temperature (and pressure) of a hydrogen evaporator, it is of

interest to determine the effect of a reduced pressure on the performance of a hydrogen refrigerator not specifically designed for such

operation. The reduction in temperature (and pressure) will require

that the heat exchangers operate under conditions other than the

original design. The important design parameters influenced by

reduced pressure operation are the heat exchanger efficiency and the

pressure drop across the heat exchangers. The heat exchanger

efficiency is affected by both the quantity of heat transferred and the

heat transfer coefficients within the heat exchanger.

By considering the basic equations of heat transfer, it can be

shown that the heat transfer coefficients will remain approximately

the same for a given flow rate regardless of pressure. The change

in efficiency of a heat exchanger will therefore be determined by the

additional heat removed and its effect on the log mean temperature

difference. However, for the case considered this effect has been

calculated and found to be insignificant. Thus, neither the change in

the heat transfer coefficients nor the quantity of heat transferred has

an appreciable effect on the heat exchanger efficiency.

The pressure drop across a heat exchanger, for a given flow

rate, is proportional to the specific volume of the process fluid. For

a given heat exchanger, the pressure drop in a 1 5 K hydrogen refrigerator will be approximately 10 times the pressure drop in a 21 K

refrigerator. Therefore, the lowest attainable operating temperature

of the evaporator will usually be dictated by the heat exchanger

pressure drop. However, the actual value must be determined for

each heat exchanger design and cannot be computed on a generalized

basis.
E

o

LUor

CO

C/) LU

tr

Q.

X

O

a: o

CM

LU

D

Ll

•J9*d 2H m>|/aa>| • N0ISS3ddlAI00 ZH JO >JHOM
Af\ - 1U - p>

. c

- Precoo in «ja TemD. w i ii ^

.

~ **--*-.. 65 ° < " _r iz

**- "tj O ""''" !"»«i-

</) *""«; \^ Qy _- - — _________

*"

+- ------ o _ ______

£

Q _ ~_ _ O

ll 1 _l

flO « .. ^*' - Precoo 1

1

1 i a Tfi md

, * —

B -» 7 3° < —

' 7 -"-*_Li

r *

Bi -»^

^r *•-= ^i *> >

^ - -

• u_

i i GL Lu ©

/VQu

AT3 i K

Figure 3. hydrogen refrigerator

refrigeration available
H CD CL or 5 CM 3 X

CO

"Z. •*- o o

o $N CM k_ z .c

*~\ \ L_J V)^ 3 CD O .t:

N2 Precooling Temp. = 65 °K

t j

1 ftOC 1 Utb 1

. A 4= 15 K „---""

— ^** "T*

i~ ^^w^

m^** 9 ^

m m m mm OCA "^

UeiH- i 1

1

1 T|

"" X

1

1

•

1 '

!

1 1

1

1 C\0 O ' 'ii

VtLeL . ^ "A"Vi=m°k ' 1 i LL_L44-+M

I £S 4 - \\J r\ j j_li_—H""TT I

I I j j L- ^"^" e^^^* * ^m^m mmm

m m^^~ m

... | AOA i

' ; i M

_[__ _, . UdO i i I

I

i

I I . __ _, L _4_1__L , J _, I

! I

I

I

i _j_ __ __u J ,_ -n_ 4_,_ .. J L j_ _L

; i I A|Q I I I I • I 1 , UltJ A 4- - «. J .—+—'""^ ATa = 5 °K I , , .,—>--" ^

-Li-^+* "^Ti

— J^^H 1 I—" m^**^^ »* 1

I ! 1

1 !

i nin ' !

1 1

!

' ; 1

i Ulo I Ml ,

; |

1

1

1 ' 1

i !

'

;

1 ! ! ! 1 1 1 I II! 1 1 ! II 1 1 iq1

II hi i ! i i ! I ! I :

i i !

'

!

i . i i i !

AT3 , °K

Figure 4. hydrogen refrigerator

liquid nitrogen consumption
10

HELIUM REFRIGERATOR

The performance of a helium refrigerator with liquid hydrogen

precooling has been calculated on the basis of the assumptions set

forth in the General Discussion. The design charts presented

(Figures 5 through 12) are applicable to refrigeration temperatures

from the temperature of the liquid hydrogen evaporator to the temperature of liquid helium.

Figure 5 shows the work of compression (kw) required per

unit (kw) of refrigeration at the helium evaporator temperature for

theoretical performance of the final heat exchanger, AT_ - 0.

Minimum work occurs for an inlet high pressure near 30 atmospheres

and this pressure has been used throughout the remainder of the calculations. The compression of 1 scfm (1 atm, 20 C) of helium gas

from 1 to 30 atmospheres requires 0.274 kw (1 scfm = 0.0835 gm/sec).

As previously indicated, the quantity of helium refrigeration

(Q_) available is substantially influenced by the hydrogen precooling

temperature. Theoretical refrigeration as a function of the precooling

temperature is shown in Figure 6. It can be seen that an increase in

refrigeration of 80 percent is achieved by reducing the precooling

temperature from 21 K to 1 5 K when the return helium stream is at

a pressure of one atmosphere. An increase in the low pressure of

the system will decrease the available refrigeration but will also

decrease the power of compression. A low pressure of 5 atmospheres

results in a decrease in the work of compression of 47 percent (30

atmospheres high pressure) while the theoretical refrigeration available is decreased by 20-25 percent. Thus, operation at a slightly

elevated low pressure may be beneficial if refrigeration temperatures

above liquid helium are desired. If refrigeration is required near

the normal boiling point of helium (4. 2 K), it is important to keep this

pressure as low as practicable.

Applying the First Law of Thermodynamics to the process

shown in the schematic of Figure 1 shows that AT. affects the final

quantity of refrigeration (Q_) and that AT affects the relationship of

Q to the quantity of refrigeration required in the hydrogen evaporator

(Q- ). Figures 7 and 8 indicate the ratio of refrigeration, Q /Q , as a function of both AT and AT for 21 K and 15 K precooling, respectively. The temperature difference at the warm end of the final helium

heat exchanger (AT ) has a profound influence on the refrigeration

available - considerably greater than the influence of AT . In fact,

when AT = 1. 9 K with 21 K precooling, no refrigeration is available

below the hydrogen evaporator temperature. The point of zero refrigeration with 1 5°TC precooling occurs when AT. = 3. 1°K.
11

The basic assumption of theoretical refrigeration, AT = 0,

requires further consideration for the helium refrigeration cycle. By

a cooling curve analysis , for the conditions under consideration, a violation of the Second Law of Thermodynamics is observed. To

avoid this difficulty, a modification to the schematic shown in Figure

1 must be made for the portion of the helium circuit below the

hydrogen evaporator. This modification is shown in Figure la below.

High

Pressure

Low

Pressure

I

EVAPORATOR

SECONDARY

THROTTLE

VALVE

SECONDARY

PRESSURE

HX I

Figure la Modified

Schematic for Helium

Refrigerator

hx n
12

The final helium heat exchanger of Figure 1 is subdivided

into two heat exchangers by the addition of a secondary throttle valve.

The inlet temperature of this valve and the resulting down stream

pressure is selected to prevent a violation of the Second Law of

Thermodynamics. A cooling curve for this arrangement is shown in

Figure 9. For a 30 atmosphere high pressure and the precooling

temperatures under consideration, a secondary pressure of 5-10

atmospheres is sufficient.

To be consistent with the Second Law of Thermodynamics, if

provisions for the two throttle valves are not made, the minimum

values of AT are 0. 5 K for 21 K precooling and 1.7 K for 15 K

precooling. These temperature differences are sufficient to provide

a AT = at the cold end of the final heat exchanger. The effect of

this AT. can be seen from Figures 7 and 8.

Additional design parameters are given in Figures 10 and 11.

From these figures, it is possible to determine the helium flow rate

and the consumption of liquid nitrogen for a helium refrigerator.

The liquid nitrogen consumption shown in Figure 11 is independent of

the hydrogen evaporator temperature.

The effect of eliminating the nitrogen evaporator in the helium

circuit is shown in Figure 12 for a 21 K hydrogen evaporator. The

ratio of the quantity of helium refrigeration to the quantity of

hydrogen refrigeration is greatly reduced, conclusively indicating the

desirability of this precooling in the helium circuit.

As indicated in the General Discussion, the installation of an

expansion engine across the final helium heat exchanger, as shown by

the dotted line in Figure 1, adds substantially to the thermodynamic

efficiency of the cycle. Preliminary calculations indicate that the

addition of an expansion engine having a 21 K inlet temperature and

an 85 percent isentropic expansion efficiency will decrease the work

of compression by at least a factor of 2 and will increase the available refrigeration (Q ?

) by a considerable factor. The optimum high

pressure, based on work of compression, is reduced to about 15

atmospheres.
13

0)

OC

X

-ST

in

en

UJ

rr

gl

o

o

a> X

rro

Low Pressure = 1 atm

AT2

=

. ac\c\ bUU v\

i_ i vA i \

\ "i

L-i, rrecooiing lemp.

- . _ \ 21 K :

' i

i ~1 . V

^

I.X

C

W i- HKJKJ /AA VV ^

\ *^

^ j?

Sfc. *?^ ^* m — J^*^

| i L "1—

1 ~ +" ~n~ " ~^~

i _l _. q

v rrecoo ling i e m p.

~ ~~

... ~ S^ : 15 < : . . ^ *- * ^^ *^** 200 ~i T"*J """

_

i j >-v 10 20 30 40

HIGH PRESSURE , atm

Figure 5. helium refrigerator

work of helium compression
14 —rr t r

- 1 -

'

'

i

1 TM iT r 1 ± : ± ±4- . ^ X i 1

• yi ts: r te I 1.4 | V

0) " "L _S~ "" '" * |

i T* S ! s c

LI £ ""' ' """ \ " ± X ..

' "

. m- +- " ^rt 4- ' " ' o X u . . .-i ._ »-/ -+- \

</} 1 - V ^ 1 \

1 ^

(/) *~ ^

^ \

* . -

|

, t o 1.2 ~ x __ ^v' • •* - -4 \0, . > X Ji -. Cox X - T - - - V^fc - * V j* VO*. - -» -^ . -t . . VO/^ 2 ± . V^n O X i_ X ^>0 ± V/i ._X - X- X i -Xl x-xv it 1— - s K X .__ ±i . ± SStv .... _. 'it- - h

^-r ^ k. Sl^rv <L V VJVr I fXIX.

4 - S^^ \*o - ^x

-sr^G xx lit v \PUs X 4i LU X •— -04-V - N ^ - CO i n V \.t- -1- ^ v-/ I.U V *~~

VI n" -j s r «- 1 IS.

Li_ - -- -ps 5

s. -j- - x ~ _ " s s^ .^4~ -" \ \J x 5

^ X

OC J. X it. _. S

SL-

<V^ 4- sl/^> _ H ^ J

7 / ~k

i X X- 4X 7t s v<n k. -d - sl u£t. <r . _ .it __ . . V^ N 7t - 7 ^

V j<S Sc

' (J X 4_X , , ... _ n sm/ /? ^L. /^C* 4- 3 t s o i? r ^. I— I: ~

" _

" S SL°V?X S^ -+-4-

i n ft sl°^/r "^ _ s

li 1 u.o s ^ ^^- s rv X "" "'X _ it "

.. -s^7v^- jr --^ ^r ± "- !-t \i^ , V

r>> 1 _ 4 K\J £ ^ . Ik III i ^kv ^ . LU

x V I— ___ ___x_ _ _x v

%i. 1 ^v X . c 4xt s ». 47 7t

_L V +

__4_4_ ._ I" "" I|_ j_ i V i >». i J.j _i-4 ,--

" ~ -!--.

^s j. xixr - x ~"

'

r» «? i ii _l. ~' S ! u.t> _L4-i-L -X _...

' _ 4 ^ Sk 4XQXJ X X ' 1 1^ ' 7P4X J... .. _ t j 1 - n

-

' ' "'" ^ '_ "„ ±'"_x_^ il . ,

'

T'4-i . |_ „. X-. J t i ill

i t r X ^

-J f++7

- X i 1 1 i 15 16 17 18 19 20 21

precooling temperature , °k

Figure 6. helium refrigerator - theoretical

REFRIGERATION
15

: _ x

"" "

: -F-

• -^- T

I

i x

_ X iH

. x

! /

i '/

4*

i x

1 * i [y / / /

!

'

! I

; !

1 /S'f/

y l/

i y [ /\ 11 l/ \ / ' /' 'v > ./

1 >' ,/ j j 1

I

i ! I

1 cK / i/

_*n^ y^ ' # M jT- X /

<> y /

1 ! '

, ! | >T 1 ,' 1 f\ |

i

! Ml

j* j

/l / i

1 II 1 IN' /

\

1 i 1

1

| L/l | 1 1 l>" >' !

! LLf li!' i m I 1 >T \j f .^ .^r M \ Xj?*\ * 'n ^

'

i ' >^i Mm 1>+T j ! >n !

'

'

1 ! U^T ' M >f II i

! _> fTI '

; T ^M[\ II" in .**^ i III! : j^xt ! ^ !

l Ml o^T ! ^^ •^ ui

: LU"^ ' / 1 %• ^ ' i

; Vn .

' .? n o 1 M L^ y

* III! | 1 | _>>^ ^r I y — «fi !

i

!

i

' LL-rTl M " !

i i

' .uh i #

f\l IA «-> 1 J*^" i U^ 1 1 !

i

| ] i/1 ^ **> ! 1 lO^-M : ! I 1 !

1 |1 1

" "

II

I -*^ / 1 O ' ': ' I'm 1 I _^* 1 ; ^^^M \ f\' 1 1 jH

f\ ^m^ -— l ' / O- 'v^ Mi ±**^

£ £ \ ir 1 Li- ,Ti '

I

;

j m !

1 "1/K^ I

'

' c c 1 1 O M _^«**T^ il'l MM 1 r«f| a> © «— v_***f i mm 1

1

' •" : 1— •— ftJ O >"f i

i -.'*' 1

i 1 c^ ll ! ! %J* **• ~ O - -

i C C -

I j -" i ^+ l 0*

O O i -- -4- ^? o ft ____: _zji =- -^—

'i O O i

| *«"

a> a> ^^^-'wrr

^- *- lO -4""""

q_ q.

U,!---"T _

CM CM T ^ ' -1- ^ > 1 1 j

1 i!i

i i

' i

i

' i

1 1 1 'III i !

' '

|

i

' 1 !

!

1 i

' '

I i _l_ _l LI t ! II II 1 II 1 INI i 'I i I i i 1 J - ... _-

X

UJ

e)

z

< 00 i

o

UJ — Si — T o

\ Ll

CO co o Z

6 <J _l

Li. 5

8

UJ |L

tr ll. Lu

CO X

UJ

I Q.

o IT ^y;

*-6 l±_' 1- CM

UJ

cc UJ UJ

a> X

**-o Li- Li

z

<

o a: or

CVJ d

1-

<

or 2

D

2

or

LU _l a.

<M

>1<

* I IV

UJ

I

UJ

o:D

Ll
16 1 1 1 1 u 1 ! ' Mil 1 ii j 1 i i i i V ^^ i L ^ J/^ / 1 ^ -^ ^ > !

>*'' >*^ ? d ! if .^ _*^ ! X r^

i*x / ' / ' X ^^ j/ 1 ./ i n * / ' / + ** ** ^ 4 ^ *^ V J

O

_ >^ _V .r ^ ^ ^ -^' >T l> lO -" ^ r d ± y£ r

_i> i ov* • ' I jf

v^ ^ ^^ ^ o

in 32

p * p * ~X- lO •" T — <£>

ii ii • • a. a. i e c o +* C t

<D <D C\J_ 1— 1— 1 9 o» • C "" _ * — O /-i So 2O 1 o o _ : ±1 nLL nU>

CM CM X z . j ^ ^L —

CDddd

CMd

CM o

LJor

CM X

UJor

CD XoO

h-<

or

UJz<

UJ

— h- 3 UJI ^

CM

>!, 'IV

U.o&

Ll

LLUJ

a:

UJ

LLUJ

ITD

-I

UJI

CO

UJD

Ll

Ul

LlT uz<£

UJ

Ql
17

LlI

<

LU

Q_

LU

HIGH PRESSURE

LOW

PRESSURE SECONDARY

PRESSURE

hxh \

HEAT TRANSFERRED

Figure 9. helium refrigerator -cooling

CURVE FOR MODIFIED CYCLE
18

q —-—n— n r

! ° ±T i- -4- -i -a L . -+. lu l

i

1

' U

1 MM! i i

j + 1 t i 1 ! i h

1

i 1

''

I

1 1 1

i

'

'

i

. — — [ | i i i i . . -+--+---- ; i : ! """ | | 4 " " "

! I i M

! MM 1 1

1

i

'

!

1

!

1 i

1

1 1 1 i1

! 1

1 T~i ^

h l| ' , M iq- - Ml 1

i {

f

f 1 !

1 Ml' til '

'

1

!

! Mi, iji mi j J | III c m ' J '

: M i

i j

i

;

1 b M / '

i i \ '

'

'

' ' M Pf a/> nn linn To m n Tp ;

! Ml i i

:

i i ! *4— l|| 1 rTCVsUUIIiiy ICIMJJ. i 0) ?| °K / i M II 1 ^3 || ! fc. 1 r\ / I I I | || | j 0- i

! 1 1 j

1

1 j

I

1 1 *» T i

1 / j I

j

'

' I

1 ! I

1 1] "T" ' ' ' / | i

i M i i M i •*• j

j j

i 1 j

i i i

j | | i |

| *

i/ 1 i

!

'

i

j • H !

i o i 1 / 1

i zr 1 i

'

' / i I

' I

! !

'

' $ In i j

! i

i j

i I \ " 1 ^ 1 y j

i ; ,

j c /i ! "^ ^

"^ 1 / '

i "^ li'M *— ~r i i i f

! n i

i ««-n*» \ i'// 1

< II I'MMlilM M 1 M 1 (/) /

j'

•* cx

LUUJ // 1 U |

1 | j | | | ] 1— / i Sr / I M <*

/v- iy/ M MMii

i Q- y^r / > y i

i ii

' ^ i ^n~zt O O ^ ' ' J* ~j ^ • ' ' i ^."^ '

1 _*^ i^'' LL- ^f' ^^T

jdrf^*' Irf^ ^

CD *** m**^' x "^ .— '" I

~l i= 1 l~

1 j* - """ -Yeeoolina TemD ' - --«-" **"". |«n oiv- ^t-----"* IO «A

1

l

l~

1

| | ^ - , , , . .1....

I 2

AT2 f °K

Figure IO. helium refrigerator - helium

flow rate
19

N2 Precooling Temp . = 65 °K __ _ _j_ TT'TT ""

^TT"-j MX—"' "'

.

l tti

i

i

i J ® no ^ -j_ 1 -r- .08 ^"""»~v_L 1 >\-r

'"

! |

' -1- ta H h ->--^L *iie - i *»-M_l? ' 5 o^ , _+_ _L _j_ t-C ! ^TH-M-aL ^-»H* — 1 L | K

*- 1 TrH-, f

1

1 H— 1 --«.. 1 O | </> 1 *"**-L 1

! TT*- 1 >s I

1

i

1 V. 1 "*-C 1 I' ! >s

(/)

i

i Ti r\r i

i i ] o> .Ub I ^M I ._

' _• !

1 ' !

i ""'— ! M 1 l ""••.^ i

i I

i ^""+4-* ATi

' 'MM Mi l -^ !

i M -T*-^'*! ^^"s-kr

=? /0iA

°z^

' M'-J- J- _i L_!

i r^"**H». a i

i i O i ! ~"-»-4_1j 1 1

I ^*"1—J_i 1

1 ^"*^>_L 1 i_ — -h i- r ft n 1

j

1 r^",W».^ j • ' i i i

i II ; I r ^ ! ^

0- -txx X^X Ml MM' r ^ !

I Mil ~^ "^ ~l T I'll ! ""> rid ! ' ii 1

i

! 7k - u^"

i

1 Mi CO t X X j 1 M Ml

-7 ; i

1

i

! 2 1 1 ! ! I

i

J

! r\ >

i I *-'

i

' 1

i ! o

' T i

i

: r 1

1 1 ^^ i i

i

i i i j

i

I

i

'

i *M [.. i

i * -+»»-,_ ' 1 •

i M M ' ' ^ """-•L ! 1 |jl M!|| 1 I """»».. y\ t ' Mi MM • "-^-r-L^f1 1 5 = e- ' Mil 1 (~\ ^"""4-4 r D °if

' Ti ^***-hi_L_i ' • ^— l rt""4»Lj

""i X - . _|_ X M*""

4-)-.^'

'"" —

d r\r> w

*"^ ^^—1_ .Ot f" *"^ 5*1

i

1 _l !

j

1

1 i i

. 1-j i

]

! !

!

' M

! 1

i 1

| Ii! i

i ! 1 i ill III ! II! lilt MM

AT, , °K

Figure II. helium refrigerator - liquid

NITROGEN CONSUMPTION
20

H2 Precooling Temp. = 21 °K

No N2 Precooling

AT2

= <;u ^r

ie _ _ __ lb

1 \

\

.

% ^^

\

^

%

.

10 \

-£ '-- % ±

s_^^

If} £_

i-i **%

I"" s s <1 - s ^ *_ Q - _______ *-*,

***

** s fc ^s^ "^

s ^*" *^ ~'* ^ *** s» * — » «l Zl - - - *T

.08 .12 .16 .20

RATIO of He REF.to H2 REF. (Q2 /Q| ) Figure 12. helium refrigerator - effect of heat

exchanger performance ( no nitrogen precooling )
21

HELIUM LIQUEFIER

Essentially the same principles apply to the helium liquefier

that apply to the helium refrigerator discussed in the previous section.

However, for the pressures and temperatures considered, there is no

danger of violations of the Second Law of Thermodynamics. Although

the work of helium compression in a helium liquefier differs from

that of a refrigerator, the level of optimum high pressure remains

the same. This is shown in Figure 13 where the work of helium compression per unit of helium liquefied is presented as a function of the

high pressure. The liquid produced is calculated assuming theoretical performance of the final heat exchanger, AT. = 0, and a low

pressure in the cycle of one atmosphere. The remainder of the calculations are based on the optimum high pressure of 30 atmospheres.

The influence of the heat exchanger temperature difference (AT ) on

the quantity of liquid produced (fraction liquefied) is shown in Figure

14. If liquid helium at one atmosphere is desired as an end product,

increasing the low pressure will both reduce the fraction liquefied

and cause flashing losses when the liquid is transferred from the

liquefier to an external storage container. It is particularly important therefore, to keep the low pressure as near one atmosphere as

possible. The pressure drop on the low pressure side of the helium

system must be carefully evaluated.

The ratio of helium liquefied to the quantity of hydrogen refrigeration required is shown in Figures 15 and 16. The effect of heat

exchanger performance can clearly be seen from these figures. With

21 K precooling, no liquefaction occurs when AT. a 1 . 9 K. With

15 K precooling, no liquefaction occurs when AT =3.1 K. The

required helium flow rate and liquid nitrogen consumption are shown

in Figures 17 through 20.

The effect of eliminating the liquid nitrogen evaporator in the

helium circuit is shown in Figure 21. The ratio of helium liquefied

to the quantity of hydrogen refrigeration required is greatly reduced,

again indicating the desirability of this precooling in the helium

circuit.
22

a>

+—a

5

2400

2000

600

C/) CO

UJ 1200

rr

Q.

S

O

o

a> 800

X

H—O^

cr 400

.... ,

1 ! |

1 L

\I\

"A

~1\

~1 c

* -. . rtl . _

V 21 °K Drecoo inq i . *

\

L*

IV j \]iv J^

I [j i A H

nlj l—5r W I ^r

N*_ rf**^^

'

i ^ ^^ j

i ^^ |

' ^W» w*^^*

1 1 _l_ _l_ 1 _J , j_ _^_

1

4- - -4T^t i

i -C ^t

!

I

I 1

i ! 1

1 j \

S.

""^W~j

T" it S -15 K Precoo ing z:

n**-L^ NT"— M L^-^-r^ T Li J j_44--rTi i

i

" — T ! '

!

'

! Il 1 1 ! |

1 i ! i ' i

i

i

! I...L 1

i

:

i i I i

;

: g 10 20 30 40

HIGH PRESSURE , atm

Figure 13. helium liquefier - work of

helium compression.
23

q x

?f\ «-U v

r>^ S^

s.^^

^^

s^ O ^^S. /^T

1"-I 11 .lb1 c s,VwV

'\S a

°JL.

. . ... — 4 S si/T iCr*" _. U_ ^.^/tv* - nJT®*v. IP

lu _ s *j>o M 41 3

--* ^kt //^ sJOn ^» it it .. z^y ^

HlT

-'^ ~ ~ x X

S

_J _j T

-*» rs X s

_. *^^ —^ s^

^- ^

t~\ S|s

V-> S.

«HW s^

1 AQ ». \, r— .Uo v n»j

( } s v^ * fc*< s <r ***».« -i -+- .s. . «-> __ OC -+- 4- *% = </ o. tT *-h2 k a. t-L % >kL^ f^f ' -n/ rQr^ ' Hid ' s h_T c°o/- • u^ i "«<- W'//>^ T*>sj ''O ^ sJj^^^

fc ^^

^s ^

*^_^^ O" 1 Hi Mill II ill Mill Mill MM 1 Mil llmllll II II

AT2 , °K

Figure 14. helium liquefier - fraction

liquefied.
24

TTTT "TTT TTTT

-! '-U

1

]

| _

;

| .

i

'

'

i

. !

| i !

'

1 ;

1

' .^H-*"*^ n

,.,,,! ,, !,

1 ill "X — L i . i . —-^ .awri - - 1—

.

, J—H-H-H—— \

<

\ -U —-~—1}— \ :S::'CH-i-rTT:. .._..., -j-p

__^rr__g#ip [

|

i i

|

'

.

' !

. '

' ' ' 1 i< —i -*^

, 1 ,-** J/i 1

tm

i

' 1 1 ] v~ ' |

I :

i

1

1 1 ' III 1

1 _->^'r:

1 o ' l

! ":..-*- f^T. " ! - ...<- r ~

q * ^ = N o ° rH

CO <o | ^

:

:

Q. Q. -n

'

1

' ***^* *- i- '+'-'-'-^

o* v :_^i".^ ,, ^^ . r- e i r

:

1

*->

f-i O O gM i

: :

i

: i

, :

i i

i

i

! .

j

! 1 I

i i

! o ! i 1

'

'

' I

i

; ! Of 1

1

l i ::' :';;:! L.

-i h i .l^al-lkiliiijli_!~ 4444- u _

00O

toO

CM

O

CMO

>i< 'IV

UJZ

<

I

<*— u •— X

o UJ

£. \ 1-

c < • \ Ul

i_ I

CO u. z

• H

Ll_ u u LlI UJ UJ

or u. X

OJ Li. d

X UJ

1 *

o*~ X

o UJ CM

LJ

u.

U_ UJ UJ

UJ _)

Z> a z O _i <

_l ?

a> ^ q: X _>

•^ _i u. o UJ tr o I UJ

V- • a. <

or 10

UJX

D

o

Ll
25 o5 XWOz<IoX

UJ - I

UJ

or

CM XQ

UJ

UJO

CD XOO

I-<

a:

>1, * l IV

I-U

UJ

Ll

u_UlX

UJ

u.UJDg

_jD

_l

UJI

CO

UJXD2 z

_ioou

UJX

Q. o

10

UJuz<o

u.X

UJ

0.
26

Precooling Temp.= 2l°K

80

Q)

0)

.2" 60

0)

o 40

(A

UJ

i-

<

o

<D

20

i I ZH i I lj lIIj i 1

i ~l~ i I

I 2

AT2 , °K

Figure 17 helium liquefier - flow

rate (21° k precooling) .
27

Precooling Temp. = I5°K

o

a>

j= 4

Q>

(/)- 3

UJ

(Z

a> 2

, ,

,

! j

! i

1 f /

/

_J^~

. t

f~

i /] *

Jf lA

i

t / j f~

i /

_j/

j

/

]f ~i

f /

f //

w\ J

' i" /

~i ¥

/[

i

. /

\/

J\ i

j Jf /^

\j I jr ' f : ^r 1 \f

Jf

\J \ Jf

s\ \a*

'jr J 1 j/^ [x

^^—

1> ^

!

! V^ i 1 1 ' 1

!

i i ^n i

i M i

i ^.^ i

i II '

'

^ri

^^^i ^-^r

I

1

i

'

!

i

!

!

1 |

> Mil 1

i

!

1 . 1 1 1 1 i_ I !

!

i

: 'I'M 1 III ...... IIj

1

j

!

1"

'"

! E j ^

•

i

I !

I !

'

i i III | ; r i T !

i

i !i i i 1

1

i i i

i i (I { j j _j ] j |

I 1

! 1 1 i 1 1 J_J1. \x ! 1 i i i

, i, i ;| :

i LJJJJ

AT2 , °K

Figure 18. helium liquefier -flow

rate (15° k precooling) .
28

Q> X

o

(A

to

0.16

0.14

£ 0.12

o 0.10

hQ.

^ .08

O

.06

H 2 Precooling Temp. = 21 °K

N2 Precooling Temp. = 65 °K

AT5

= 10 °K

_______

-1- -

--__«_— . ATo - r\ — rn *

" "*T 1 -J- """"------B...

_T

*

1 _ A »•

j "*—-— ** ? = n k 0.^ ' M-t4-f U - 5 K

__l_ . . _,_ .„rp ""-•i..^^^ *u

1

j 1

'

1 1 r~ --«-„.„ AT« _-_ - -"-, h=ti 1 ? °K 41 ^TM H *^^^*4^_i_^"" "**"_ m ^ mm * mm ^mm

--__~- AT - -

*•"»--- : ^'p = 5 °w 1 1 _ CI ,

, ""' \ ** TM " — — — 1 „ 1 1

1

, ---_____

. „__ ... . _-__

-J- -\-i- -\- -4-

. _ ... ~T -J- -L-

,—

1

1 1 . „_r __. 3

O

- .04 -1

I 2

AT, , °K

Figure 19. helium liquefier - liquid nitrogen

consumption (21° k precooling) .
29

H2 Precooling Temp. = 15 °K

N2 Precooling Temp. =65 °K

AT5

= 10 °K

_p

028 r\ oq ---___ : A

- = __ z ":'"f"::::::

\j -\~ ii

^»

h- • 0,24 H-l i 441y\\

A 2=0

; 5

1 ^ff%m#ww^ ._^ =p 4= H - 1? p it it ^ :+:._ r? c

-r h- MM

z S kl+HH irrmfTr

°°

K 111 llll4Ufflm \ 0.20

^ ^=—+ +T"~=^=-r^ — »- ^ + "^

It111 lllllllllllllill AT?

S fi °K 1

| |

1

|

' | ^. </> ===-b----l.j

""TITT 11 ---' ~ Q <D n 1 c _ it ^_ u. 1 —^

v — 4- it AT « ~ ~ ' O - —======== AT2 *2.:i°<— 11 11

-1 -- - - ___^«= = «L_±

A lO U. 1 L. ' ^ l_3: . „, i__

AT, , °K

Figure 20. helium liquefier - liquid nitrogen

consumption (15° k precooling) .
30

cm

ii

Q.e

o>cooo

<D X 1

o>c_o

r\O

<u > O - Q_ *-'

(M " . Z^»

(M. ~ 1— ° ^1 2 <J

:.. 1 i o

CM

CO CVI CO *9

», MV

111

JO

4—

CDz o •-o <I

V.

k.

X £ UJ CD \ Z o

CD <

UJI

_l

n U. UJ

Li. hi

X

a.

rr 1- z

CM X UJu.

UJ

CD

ro o U. O *

UJ

X

Q 1 H

UJ

X 7

l! UJ

UJ U. 3 UJ z o D

CM

n

a UJ

q

co X

**-o D z<X o -1

UJ Ll. <

a: I• UJ

CL

_ CM o

UJxD

CD

Ll
31

BIBLIOGRAPHY

1. B. W. Birmingham, D. B. Chelton, D. B. Mann and H. P.

Hernandez, n Cryogenic Engineering of Hydrogen Bubble

Chambers", ASTM Bulletin, No. 240, pp. 34-39 (1959).

2. D. B. Chelton and J. W. Dean, "Design and Construction of a Liquid Hydrogen Temperature Refrigeration System",

National Bureau of Standards Technical Note No. 38 (I960).

3. D. B. Mann and R. B. Stewart, "Thermodynamic Properties

of Helium at Low Temperatures and High Pressures",

National Bureau of Standards Technical Note No. 8 (1959).

4. W. H. Keesom, A. Bijl and L. A. J Monte, "Le Diagramme

log T, Sde l'helium, Leiden Communication, Supplement

No. 108c.

5. J. Zelmanov, "The Entropy Diagram for Helium at Low

Temperatures", Journal of Physics (USSR), Volume 8,

Number 3, (1944) pp. 135-141.

6. H. W. Woolley, R. B. Scott and F. G. Brickwedde,

"Compilation of the Thermal Properties of Hydrogen in Its

Various Isotopic and Ortho-Para Modifications", Journal of

Research, National Bureau of Standards, 41, 379 (1948)

RP 1932.

7. I. L. Zelmanov, Comptes rendus (Doklady) Acad. Sci. URSS,

22, 25 (1939).

.S. DEPARTMENT OF COMMERCE

Frederick H. Mueller, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., and

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

In general, each section carries out specialized research, development, and engineering in the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the front

cover. WASHINGTON, D.C.

Electricity and Electronics. Resistance and Reactance. Electron Devices. Electrical Instruments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Photographic Technology. Length. Engineering

Metrology.

Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Molecular Kinetics. Free

Radicals Research. Atomic and Radiation Physics. Spectroscopy. Radiometry. Ma6s Spectrometry. Solid State Physics. Electron Physics. Atomic Physics. Neutron Physics. Radiation Theory. Radioactivity. X-rays. High

Eneigy Radiation. Nucleonic Instrumentation. Radiological Equipment.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic

Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics. Mass and Scale. Capacity, Density, and Fluid Meters. Combustion Controls.

Organic and Fibrous Materials. Rubber. TextUes. Paper. Leather. Testing and Specifications. Poly- mer Structure. Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal

Physics.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Air Conditioning, Heating, and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat Transfer. Concreting Materials.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Data Processing Systems. SEAC Engineering Group. Components and Techniques. Digital Circuitry.

Digital Systems. Analog Systems. Application Engineering.

• Office of Basic Instrumentation. • Office of Weights and Measures. BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas Liquefaction. Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular Propagation

Services. Sun-Earth Relationships. VHF Research. Radio Warning Services. Airglow and Aurora. Radio

Astronomy and Arctic Propagation.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Research. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Propagation Obstacles Engineering. Radio-Meteorology. Lower Atmosphere Physics.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. High Frequency Impedance Standards. Electronic Calibration Center. Microwave Physics. Microwave Circuit Standards. Radio Communication and Systems. Low Frequency and Very Low Frequency Research. High Fre- quency and Very High Frequency Research. Ultra High Frequency and Super High Frequency Research. Modulation Research. Antenna Research. Navigation Systems. Systems Analysis. Field Operations.
NBS