The selected receiver concept is a direct-heated, once-through, monotube boiler operated at supercritical pressure. The cavity is formed by a cylindrical copper shell and backwall, with stainless steel tubing brazed to the outside surface. This core is surrounded by lightweight refractory insulation, load-bearing struts, and an outer case. The aperture plate is made of copper to provide long life by conduction and reradiation of heat away from the aperture lip. The receiver thermal efficiency is estimated to be 97 percent at rated conditions (energy transferred to toluene divided by energy incident on aperture opening). Development of the core manufacturing and corrosion protection methods is complete

Haskins, H. J.

English

NASA Technical Reports Server

ORGANIC RANKINE CYCLE RECEIVER DEVELOPMENT 
3 
bT- 
H. J. Haskins 
Ford Aerospace & Comnunications Corporation 
Aeronutronic Division 
Newport Beach, CA 92663 
ABSTRACT 
A so l a r  receiver  i s  being developed fo r  use with an organic Rankine cycle  (oRC) 
engine a s  par t  of the Smdl  Comrmnity Solar  Experiment (SCSE). The selected 
receiver  concept i s  a  direct-heated,  once-through, monotube b o i l e r  operated a t  
supe rc r i t i ca l  pressure. The cavi ty i s  formed by a  c y l i n d r ~ c a l  copper s h e l l  and 
backwall, with s t a i n l e s s  s t e e l  tubing brazed t o  th: ou ts ide  surface.  This core 
i s  sczrounded by lightweight r e f r ac to ry  insu la t ion ,  load-bearing s t r u t s ,  and an 
outer  case. The aperture p l a t e  i s  made of copper to  provide long l i f e  by 
conduction and re rad ia t ion  of heat away from the aper ture  l i p ,  The rece iver  
thermal eff ic iency i s  estimated t o  be 97 percent at: ra ted  condit ions (energy 
t ransferred to  toluene divided by energy incident on aperture opening). Devel- 
opment of the core manufacturing and corrosion pro tec t ion  methods i s  complete 
with development t e s t i ng  of the core t o  be completed i n  January 1981. A 
prototype receiver  w i l l  be supplied in  March 1981 for  in tegra t ion  and t e s t  a t  
the engine suppl ie r ' s  f a c i l i t y .  
The SCSE Phase I1 program in progress a t  Ford Aerospace & Cormnicat ions 
Corporation (FACC) includes development of s prototyr  power conversion 
a~semblp (PCA).  The PCA w i l l  be mounted a t  the foca l  point of a  1 2  meter 
parabolic dish and w i l l  output approximately 20 kW of 3 kHz ac power t o  a  
ground-mounted r e c t i f i e r .  The PCA includes a  cavity receiver  coupled t o  an 
OW engine. The engine working f lu id  i s  toluene with a nominal bulk tempera- 
tu re  l imi t  of 399°C (750%') a t  the receiver e x i t .  The receiver  design 
requ' -ements inc'ude input thermal power up t o  95 kWt, toluene flow from 54 t o  
545 kg/h ,  operating pressure up to  5862 kPa (850 p s i a ) ,  and a  nominal 30 year 
conponent l i f e .  The two pr inc ipa l  cons t ra in ts  on the design a r e  1 wcight l i m i t  
of 272 kg (600 lhm) anJ a  maximum toluene pressure loss  of 448 kI'4 (65 p s i ) .  
The performance goals of the receiver  design a r e  t u  maximize the thermal 
eff ic iency,  and t o  maximize the hes t  capacity of the core.  The l a t t e r  goal i s  
desired f:-r s t s b i l i z i n g  the PCA operation during in te rmi t ten t  c l m d  cover. 
C3NC EPT SELECTION 
- ' n  or ig ina l  basel ine receiver  concept for  the XSE program was a  pool-boiling 
c , f  bguration using 3 secondary f  h i d  and separate  toluenc heat exchanger ( 1 ) .  
A ? ta i led  evaluation of candidate secondary f l u i d s  Zed t o  the conclusioc t h a t  
https://ntrs.nasa.gov/search.jsp?R=19810021993 2020-03-21T09:47:16+00:00Z
t h i s  concept was not p rac t i ca l  f o r  t he  ORC temperature of 4 0 0 ~ ~ .  Al te rna te  
concepts were then considered including use of a pumped secondary l i qu id ,  use 
of a non-boiling sodium pool, and f i n a l l y ,  a direct-heated copper s h e l l  with 
tubing brazed t o  the  outs ide.  After devzlopment of a f e a s i b l e  manufacturing 
process, the  copper shel l /brazed tubing concept was se lec ted  a s  the  base l ine  
receiver.  This concept o f f e r s  the maximum i n  se rv i ceab i l i t y  i n  i ts  f ab r i -  
cat ion,  operation, and maintenance. 
Several toluene boi le r  Zesign options were a l s o  considered a s  pa r t  of the 
receiver  concept evaluation. A once- thr~ugh configurat ion was chosen over a 
rec i rcu l  z t ing boil  r :/superheater combination i n  order  t o  minimize hardware 
comple,dty. ? mc.. >tube, r a the r  than mult iple  p a r a l l e l  tubes,  was selected t o  
help avoid flow i n s t a b i l i t i e s .  An important receiver/engine cont ro l  dec is ion  
was to  t h r o t t l e  the toluene flow a t  the rece iver  e x i t  (vapor phase) ra ther  than 
a t  the i n l e t  ( l i qu id  phase). The receiver  then operates  a t  an approxima:eiy 
constant toluene pressure over the f u l l  range of flows. This minimizes the  
r i s k  of boi l ing i n s t a b i l i t i e s  and burnout occurring i n  the  rece iver  tubing. A 
f i n a l  bo i le r  design trade-off was t o  s e l ec t  the toluene pressure l eve l  a t  the  
receiver .  A minimum value of 4482 kPa (650 xis) i s  used (which i s  about 10 
percent above the c r i t i c a l  pressure of toluene) t o  fu r the r  reduce the  possl-  
b i l i t y  of tube burnout. 
In  performing the rece iver  concept t radeoffs ,  i t  was found t h a t  the weight and 
complexity of an aper ture  door assembly could not be j u s t i f i e d  i n  comparison 
with the s l i g h t  reduction i n  energy losses  during t r ans i en t  cloud passages. 
In  addi t ion,  the receiver  performance was maximized by flowing the toluene 
from the f ron t  (aper ture  end) of the cavi ty to  the r ea r ,  and by using a 
tcluene-cooled backwall instead of an insulated backwall. The receiver  
t rans ien t  performance was found t o  be best  fo r  a uniformly d i s t r i bu ted  heat  
cspaci ty (uniform thickness) i n  the cavi ty wall .  
DESIGN DESCRIPTION 
The pr inc ipa l  receiver  components a r e  the core assembly, core support s t ruc tu re ,  
thermal insu la t ion ,  ou ter  case,  and the aper ture  p l a t e  ( s ee  Figure 1 ) .  
The core cons i s t s  of , ba r re l  sec t ion  and a f l a t  p l a t e  backwall. These copper 
pieces have grooves machined i n  t h e i r  ou ts ide  s ~ r f a c e s  t o  match a h e l i c a l  c o i l  
and a s p i r a l  c o i l  o; 347 s t a i n l e s s  tubing. The tubing is mechanically held 
within the grc Jves and brazed t o  assure good thermal contact  with the copper. 
The overa l l  coppershell  thickness is  1. 7 1  cm ( 0 - 7 5  i n . )  with a nominal groove 
depch of 1 . 2 7  cm (0.5 i n . ) .  The cavi ty diameter and length a r e  0.61 m 
(24.0 i n . )  by 0.56 m (22.0 i n . ) ,  respect ively.  The tubing outs ide diameter 
and wall thickness a r e  1.59 cm (0.625 i n . )  by 0.889 nu11 (0.035 i n . ) ,  respec t ive ly ,  
and the t o t a l  tube length i s  63.1 rn (207 f t . ) .  The core accounts fo r  147 kg 
(325 lbm.) of the t o t a l  receiver weight of 271 kg (597 lbm). 
The copper s h e l l  and tube /she l l  braze jo in t  a r e  protected from corrosion i n  
a i r  by an appias - t i on  of e l e c t r o l e s s  nickel p la t ing .  The cav":? i n t e r i o r  is 
then given a cC::k of f l a t  black high temperature pa in t  t o  increase i t s  sur face  
so l a r  sbsorp t iv i ty  t o  about 0.95. 

The core temperature w i l l  be monitored a t  s i x  loca t ions  using type K thermo- 
couples. Four locat ions a r e  on the  cy l ind r i ca l  s h e l l  and two a r e  on the c e n t r a l  
region of the backwall. The two thermocouples on the backwall provide an 
estimate of the cavi ty f l u x  which may be used i n  the PCA cont ro l  system i f  
necessary. 
The core support s t r u c t u r e  fea tures  a  ci.-cumf e r e n t i a l  band around the core a t  
i t s  center-of-mass. Four s t r u t s  t i e  t h i s  "belly band" t o  the main support 
r i ng  of the receiver  which i s  i n  turn attached t o  the four mount r a i l s  of the  
PCA s t ruc ture .  These cen t r a l  s t r u t s  provide complete l a t e r a l  support fo r  t he  
core. Support against  a x i a l  and pitchlyaw loads i s  provided by four addi t iona l  
s t r u t s  running from the cylinder/backwall junction of the core out t o  the main 
support r ing.  The s t r u t s  a r e  length-adjustable and a r e  pinned a t  each end t o  
accommodate thermal expansion of the core r e l a t i v e  t o  the support ring. 
The insu la t ion  around che core i s  formed from a low densi ty  re f rac tory  wool. 
Insulat ion pieces a r e  molded t o  the desired shape and s e t  using a  r i g i d i z e r  
compound. After forming, the pieces a r e  given a water - res i s tan t  treatment. 
Although the insu la t ion  proper t ies  a r e  unaffected by cyc l i c  moisture 
absorption and dryout, the coating minimizes the  r i s k  of insu la t ion  damage 
from rapid heating while moisture i s  present.  
The outer case forms a pro tec t ive  enclosure for  t he  insu la t ion  against  the 
external  environment. It a l so  serves to t i e  the  aper ture  p l a t e  t o  the  main 
support r ing.  The case segments a r e  fonced from aluminum sheet except fo r  
the forward segment and the support r ing ,  which a r e  s t a i n l e s s  s t e e l .  
The aperture p l a t e  i s  made of 3.2 mm (0.125 in.)  copper sheet ,  with a  thicker  
copper r i ng  weldrrd t o  the sheet  metal to  form the aper ture  l i p .  The nominal 
aperture  diameter LS 37.95 cm (14.94 in. ) , providing a  co l l ec to r  concentrat ion 
r a t i o  of 1000. The assembly i s  n icke l  plated t o  prevent oxidation and is 
painted with high temperature black pa in t  02 the ex te r io r .  In  normal operat ion,  
the concentrated so l a r  beam is subject  t o  d>.ilamic and s t a t i c  point ing e r ro r s  
which r e s u l t  i n  t r ans i en t  l i p  heating. Circumferential  conduction i n  the l i p  
r ing  helps average out t h i s  heating. Radial conduction from the l i p  i n t o  the 
face p l a ~ c  i s  a  major f ac to r  i n  maintaining a  low ( <  400'~) l i p  temperature. 
The heat conducted i n t o  the face  p l a t e  is re jec ted  t o  the environment by 
reradiation and f r e e  cenvection. This simple, passive approach provides fo r  
very long l i f e  fo r  t h i s  important component. Normal sun acquis i t ion  and 
derrack mancuvers, performed a t  nominal r a t e s  o i  2 degrees fn  each of two axes, 
r e s u l t  i n  a  t r ans i en t  heat pulse for  the face p h t e  a s  the so l a r  beam sweeps 
off the receiver  ax is .  The heat capacity of the copper is  s u f f i c i e n t  t o  
l i m i t  the t rans ien t  temperature r i s e  i n  the face  p l a t e  t o  about 55Oc ( 1 0 0 ~ ~ ) .  
The receiver  thermal e f f ic iency  is estimated t o  be b e t t e r  than 97 percent a t  
ra ted conditions.  These condit ions include a  d i r e c t ,  normal so l a r  i n so la t ion  
on the concentrator of 1000 w/m2,  ambient temperature of 2 8 ' ~  ( s ~ O F ) ,  and 
the nominal concentrator parameters of 0.78 r e f l e c t i v i t y ,  0.95 dus t  f ac to r ,  
aria 0.932 blockage fac tor .  With the  exception of a small r e f l e c t i o n  loss ,  the  
receiver  thermal losses  a r e  independent of inso la t ion  and a r e  t yp ica l ly  2 t o  
2.5 kWt. This i n s e n s i t i v i t y  of l o s s  t o  so l a r  input is due t o  the  nearly 
constant rece iver  cavi ty temperature w e r  the  range of input thermal power. 
The average cavi ty surface temperature i s  360°C (680'~). 
The core heat  capacity is approximately 13 Wh/OC (25 B~u/ 'F),  which provides 
some t r ans i en t  operating capabi l i ty  fo r  the engine during cloud passages. I f  
the  sun i s  suddenly obscurred by a cloud, the eagine can be run a t  ra ted  power 
f o r  about one minute o r  f o r  about 2 1/2 minutes a t  40 percent of ra ted  power. 
During these periods, the toluene vapor temperature a t  t he  turbine i n l e t  would 
be reduced about 5 5 ' ~  (100%). 
MANUFACTURING DEVELOPMENT 
The f e a s i b i l i t y  of the copper shel l /brazed tubing concept f w  the  receiver  core 
was i n i t i a l l y  establ ished using small, f l a t  braze samples. These samples 
ve r i f i ed  the material  se lec t ions  ;or the brazing process and iden t i f i ed  the 
leve l  of manufacturing tolerances desired t o  obta in  a low porosi ty  j o in t .  
Cylindrical  samples have now ve r i f i ed  the method of assembling the tubing onto 
the s h e l l s ,  and the technique fo r  r e t a in ing  the tubing i n  int imate -ontac t  with 
the s h e l l  during the braze cycle. A complete development rece iver  core w i l l  
be used t o  demonstrate the performance cf  the rece iver  concept. A complete 
prototype receiver  w i l l  t.len be fabricated fo r  use i n  the SCSE prototype 
power module. 
The i n i t i a l  core development t e s t i ng  w i l l  be conducted P ?  FACC using a toluene 
t e s t  loop t o  simulate the ORC engine, and using a -100 kW radian t  cavi ty 
heater  to  simulate the input so l a r  beam. The t e s t s  w i l l  include s t a t i c  thermal 
performance measurements a t  several  input power leve ls .  Following these, the 
dynamic (open-loop) response of the rece iver  to  s tep  changes i n  input power and 
toluene flow w i l l  be measured. These da ta  w i l l  permit optimization of the PCA 
control  system t o  maintain s t a b l e  operat ion of the engine a t  a nominally 
constant turbine i n l e t  temperature. Thrs, engine e f f ic iency  w i l l  be maximized 
over a wide range of input power. 
The complete prototype receiver  w i l l  be sent  to the engine vendor's f a c i l i t )  
following i n i t i a l  proof t e s t i n g  and performance checks. There i t  w i l l  be 
integrated with the ORC engine fo r  qua l i f i ca t ion  t e s t i ng  of the complete PCA 
and cont ro l  system. 
The present SCSE program schedule c a l l s  fo r  completion of the core development 
t e s t s  i n  January 1981 and shipment of the prototype rece iver  to  the engine 
suppl ier  i n  March 1981. 
REF ERENC E 
1. Osborn, D. B. , "An Organic Rankine Receiver fo r  the SCSTPE Program", 
paper presented a t  the F i r s t  Semi-Annual Distr ibuted Receiver Systems 
Program Review, Lubbock, Texas, January 22-24, 1980. 
'4 


Organic Rankine cycle receiver development

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