The laboratory scale testing of a modified anhydrous NaOH latent heat storage concept for small solar thermal power systems such as total energy systems utilizing organic Rankine systems is discussed. A diagnostic test on the thermal energy storage module and an investigation of alternative heat transfer fluids and heat exchange concepts are specifically addressed. A previously developed computer simulation model is modified to predict the performance of the module in a solar total energy system environment. In addition, the computer model is expanded to investigate parametrically the incorporation of a second heat exchange inside the module which will vaporize and superheat the Rankine cycle power fluid

Rice, R. E.

Rowny, P. E.

English

NASA Technical Reports Server

DEVELOPMENT OF A THERMAL STORAGE MODULE USING MODIFIED 
ANHYDROUS SODIUM HYDROXIDE 
Richard E. Rice and Peter  E. Rowny 
Comstock & Wescott, Inc .  
PROJECT OUTLINE 
P r o j e c t  T i t l e :  La ten t  Heat (NaOH) Storage fo r  To ta l  Energy Systems 
P r i n c i p a l  I nves t i ga to r :  Richard Rice 
Organizat ion: Comstock & Wescott Incorpora ted  
765 Concord Avenue 
Cambridge, MA 02238 
Telephone: (617) 547-2580 
P ro jec t  Goals: To conduct l abo ra to ry  scale t e s t i n g  o f  a mod i f i ed  anhydrous 
NaOH 1 a ten t  heat s torage concept f o r  small so la r  thermal 
power systems such as t o t a l  energy systems u t i l i z i n g  
organic Rankine systems. 
P r o j e c t  Status: Under a prev ious cont rac t ,  NAS3-20615, a module was tes ted  
and a computer s imu la t ion  code developed. This  f o l l  ow-on 
e f f o r t  cons i s t s  o f  d iagnost ic  t e s t  on the  module and 
i n v e s t i g a t i o n  o f  a1 t e r n a t  i ve heat t r a n s f e r  f 1 u i  ds and heat 
exchange concepts. 
Post t e s t  analys is  o f  t he  p rev ious l y  tes ted  module 
i n d i c a t e d  no i n t e r n a l  cor ros ion  or leakage. The module has 
been r e f i l l  ed w i t h  Thermkeep (91.8% Anhydrous NaOH, 8% 
NaN03, and 2% Mn02) and prepared f o i r  a second t e s t  
se r i es  us ing  an a1 t e r n a t i v e  heat t r a n s f e r  f l u i d ,  Cal o r i  a 
HT-43. S i l i c o n e  B was i n i t i a l l y  t o  be used; however, t h i s  
f l u i d  was found t o  be m i l d l y  r e a c t i v e  w i t h  the  NaOH. The 
computer simul a t i  on model has been mod i f i  ed t o  p r e d i c t  t he  
performance o f  t h i s  module i n  a so la r  t o t a l  energy system 
environment. I n  add i t ion ,  the  computer model has been 
expanded t o  i n v e s t i g a t e  p a r a m e t r i c a l l y  t h e  i nco rpo ra t i on  of 
a second heat exchange i n s i d e  the  TES module which w i l l  
vaporize and superheat t h e  Rankine c y c l e  power f l u i d .  
Contract  Number: DEN3-138 
Contract  Period: May 1979 t o  February 
Funding Level: $92,500 
Funding Source: NASA Lewis Research Center 
https://ntrs.nasa.gov/search.jsp?R=19800014316 2020-03-21T18:14:49+00:00Z
DEVELOPMENT OF A THERMAL STORAGE MODULE USING 
MODIFIED ANHYDROUS SODIUM HYDROXIDE* 
Richard E. Rice and Pe te r  E. Rowny 
Comstock & Wescott ,  Inc .  
Barry M.  Cohen, Consultant 
INTRODUCTION 
The program repor t ed  h e r e i n  i s  a cont inua t ion  of a p r i o r  program ( r e f .  1) 
which included t h e  des ign ,  c o n s t r u c t i o n ,  and t e s t i n g  of an experimental  one- 
t e n t h  scale-model of a phase change thermal  energy s t o r a g e  (TES) system s u i t -  
ab l e  f o r  use i n  e l e c t r i c i t y  gene ra t ing  systems such as t h e  Sandia So la r  T o t a l  
Energy Test  F a c i l i t y  (SSTETF) a t  Albuquerque, New Mexico. This was used t o  
genera te  d a t a  with which t o  v e r i f y  a prev ious ly  developed computer model of 
t h e  TES u n i t .  The TES u n i t  employs a s i n g l e  pas s ive  i n t e r n a l  h e a t  exchanger 
which i s  used both f o r  charging and d ischarg ing  h e a t  by means of a non-phase 
change h e a t  t r a n s f e r  f l u i d  such a s  ~herminol -66 .  The TES u n i t  and t e s t  bed 
a r e  descr ibed i n  r e f .  1. 
The nominal composition of  t h e  TES medium (Thermkeep) i s :  
Anhydrous NaOH, commercial grade 91.8% ( w t )  
NaNO 8.0 
&02 0 .2  
The commercial grade of N a O H  t y p i c a l l y  con ta ins  1-2% of NaCl and 1-2% 
of Na2C03. 
The program which i s  approximately 50% completed inc ludes  t h e  fol lowing 
t a s k s  : 
1. The experimental  model developed under t h e  p r i o r  c o n t r a c t  i s  t o  be 
examined t o  determine whether o r  no t  d e t e r i o r a t i o n  has occurred dur- 
ing  t h e  t e s t i n g ,  such a s  mechanical damage t o  t h e  h e a t  exchanger,  o r  
chemical changes i n  t h e  TES medium. 
2. Res tora t ion  of t h e  TES system t o  opera t ing  cond i t i on ,  i n s t a l l a t i o n  of  
a d i f f e r e n t  h e a t  t r a n s f e r  f l u i d  approved by t h e  NASA Program Manager, 
and t h e  running of a s e r i e s  of thermal  charging and d ischarg ing  cyc le s  
t o  ob ta in  a d d i t i o n a l  experimental  d a t a  f o r  c o r r e l a t i o n  wi th  t h e  compu- 
t e r  model f o r  f u r t h e r  v a l i d a t i o n .  
* The program i s  be ing  performed under Contract  No. DEN3-138 i ssued  
by NASA Lewis Research Center .  
3. Extension of t h e  computer model of t h e  TES system t o  include a sec- 
ond hea t  exchanger i n  t h e  TES u n i t ,  so t h a t  t h e  u n i t  can be  charged 
by means of a non-phase change f l u i d  (e.g.  from s o l a r  c o l l e c t o r s )  
flowing i n  one hea t  exchanger, and discharged by a phase change f l u i d  
flowing i n  t h e  o ther  (e .g .  t h e  power f l u i d  of a Rankine cycle engine).  
4. Upon completion of t h e  computer model a reference design of a lowest 
cos t  TES system i s  t o  be developed s u i t a b l e  f o r  use i n  s o l a r  e l e c t r i c  
power generat ion.  
POST-TEST ANALYSIS OF TES UNIT 
During t h e  p r i o r  program t h e  TES un i t  was used t o  obtain da ta  from 23 
cycling tests which ranged i n  durat ion from 4 hours t o  48 hours, and i n  temp- 
e ra tu re  from approximately 230 C t o  315 C .  These t ' es ts  extended over a period 
of about 5 months during which t h e  un i t  was maintained continuously within t h e  
operat ing temperature range. Thereafter  t h e  un i t  self-cooled very slowly t o  
ambient temperature. 
Chemical Analysis of Thermkeep 
The f i r s t  s t e p  of t h e  pos t - tes t  analys is  was t h e  removal of samples of 
Thermkeep f o r  chemical ana lys i s  t o  determine whether or  not segregation of 
components occured (Thermkeep being a non-eutectic mixture) ,  and whether r e -  
duction of NaNO r e s u l t e d i n  an increase i n  NaNO The l a t t e r  i s  formed a t  a 2 2 ' very slow r a t e  y oxidation of t h e  s t e e l  tank and heat  exchanger and i s  reoxi-  
dized t o  NaNO by a i r  "breathedt' i n t o  t h e  clearance space above t h e  Thermkeep 3 during cycl ing,  thus  maintaining chemical s t a b i l i t y .  Samples f o r  analys is  
were obtained through holes  cu t  i n  t h e  wa l l  of t h e  tank.  Because t h e  hea t  ex- 
changer s u s t a n t i a l l y  f i l l s  t h e  tank,  t h e  samples were removed from loca t ions  
within 5 cm o f ' t h e  tank wal l .  Tank height  i s  244 cm and diameter i s  71.8 cm. 
The samples were analyzed i n  p a i r s ,  one p a i r  taken from t h e  o r i g i n a l  l o t  
of Thermkeep and seven p a i r s  taken from seven locat ions  i n  t h e  tank.  The re-  
s u l t s  of t h e  ana lys i s  a r e  shown i n  t a b l e  I .  The s i x  components were inde- 
pendently determined and t h e  small deviat ion of t h e  t o t a l  from 100% ind ica tes  
t h e  precis ion of t h e  analyses.  The analyses show t h a t  t h e  NaN02 content of 
t h e  Thermkeep d id  not increase  i n  t h e  TES u n i t ,  ind ica t ing  chemical s t a b i l i t y  
of t h e  system. 
The NaNO content of Thermkeep (8%) i s  lower than t h a t  of t h e  NaOH-NaNO 3 
e u t e c t i c  (33% N ~ N o , ) .  Upon cooling, t h e  s o l i d  phase which forms on heat  ex- 3 
changer surfaces ,  &d on t h e  tank wal ls  due t o  insu la t ion  l o s s ,  has a higher 
r a t i o  of NaOH t o  NaNO than t h e  l i q u i d  phase. The samples of Thermkeep (which 
were c lose  t o  t h e  t a n 2  w a l l )  a l l  show an increased NaOH/NaNO, r a t i o .  Since it 
.J 
i s  believed un l ike ly  t h a t  n i t rogen was l o s t  from t h e  system, t h i s  i s  tenta-  
t i v e l y  a t t r i b u t e d  t o  a small-scale segregation of cmponents during s o l i d i f i c a -  
t i o n ,  which would be reversed upon remelting. To obta in  more information on 
t h i s  p o i n t ,  a d d i t i o n a l  samples which a r e  awai t ing  a n a l y s i s  were taken  a f t e r  
t h e  Thermkeep had been completely remelted by  a method which prevented segre-  
ga t ion  of components dur ing  sampling. 
The cyc l ing  mode of t h e  TES u n i t  dur ing  t h e  t e s t i n g  program t h a t  preceded 
t h e  sampling w a s  such t h a t  t h e  Thermkeep near  t h e  bottom ( l o c a t i o n  7 )  w a s  
permanently s o l i d .  The upper po r t ion  ( l o c a t i o n s  1-41 w a s  s ~ ~ b s t a n t i a l l y  com- 
p l e t e l y  l i q u e f i e d  dur ing  each cyc le .  Table I shows t h a t  t h e  N ~ O H / N ~ N O ,  r a t i o  
2 
i s  h ighe r  a t  sampling l o c a t i o n s  5 and 6 than  a t  o t h e r s .  This i s  be l i eved  t o  
i n d i c a t e  a s m a l l  degree of v e r t i c a l  segrega t ion  of  t h e  components of  Thermkeep 
i n  t h e  tank .  Fu r the r  t e s t i n g  i s  r equ i r ed  t o  determine whether o r  no t  t h i s  
r e p r e s e n t s  a s t a b l e  s t a t e  i n  t h e  TES t ank  o r  whether f u r t h e r  s eg rega t ion  would 
occur with cont inued cyc l ing .  In  e i t h e r  case  t h i s  cond i t i on  could b e  reversed  
by p e r i o d i c a l l y  remel t ing  t h e  Thermkeep i n  t h i s  zone of t h e  t ank .  
Examination of Heat Exchanger 
Following removal of  t h e  Thermkeep samples,  t h e  Thermkeep was melted and 
p a r t i a l l y  dra ined  t o  expose t h e  upper t h i r d  of t h e  h e a t  exchanger. The h e a t  
exchanger c o n s i s t s  of 25 h e l i c a l  c o i l s  of .64 cm diameter s t e e l  t ub ing  formed 
i n  a h e l i x  10  cm i n  d iameter ,  manifolded a t  t o p  and bottom f o r  p a r a l l e l  flow 
of t h e  hea t  t r a n s f e r  f l u i d .  F igure  1 shows t h e  h e a t  exchanger dur ing  f a b r i -  
c a t i o n  and f i g u r e  2 shows it i n  t h e  t a n k ,  exposed f o r  examination. No s i g -  
n i f i c a n t  changes were observed and it was concluded t h a t  no r e p a i r  w a s  r e -  
.': qu i r ed  be fo re  proceeding with t h e  t e s t  program. 
EXPERIMENTAL VALIDATION OF COMPUTER MODEL 
The s e l e c t i o n  of a h e a t  t r a n s f e r  f l u i d  f o r  t h e  computer model v a l i d a t i o n  
program was based on s e v e r a l  f a c t o r s .  It must have thermo-physical p r o p e r t i e s  
s i g n i f i c a n t l y  d i f f e r e n t  from those  of ~herminol -66  which w a s  used i n  t h e  p r i o r  
program i n  order  t o  extend t h e  range of c o r r e l a t i o n .  It must no t  r e a c t  vio-  
l e n t l y  nor produce t o x i c  r e a c t i o n  products  when i n  con tac t  w i t h  Thermkeep a t  
t h e  ope ra t ing  tempera ture ,  and it must be  a f l u i d  which would b e  s u i t a b l e  f o r  
use i n  a demonstration system. From among t h e  cand ida t e s ,  t h e  NASA Program 
Manager approved Ca lo r i a  ~ ~ 4 3 ,  a product of Exxon Corp. The h e a t  t r a n s f e r  
f l u i d  system has been f lu shed  and recharged with ~ ~ 4 3 .  
Data f o r  experimental  v a l i d a t i o n  o f  t h e  computer model ( d e t a i l s  of which 
can be  found i n  r e f .  1) a r e  t o  be  obtained from s e v e r a l  t ypes  of charging and 
d ischarg ing  runs during which ~ ~ 4 3  flow r a t e s  and tempera tures ,  t h e  Thermkeep 
tempera ture ,  and t h e  TES tank  su r f ace  temperature w i l l  be  measured. The runs 
w i l l  inc lude  charging and d ischarg ing  at cons tan t  r a t e s ,  consecut ive cyc l e s  
a t  cons tan t  charge and d ischarge  r a t e s ,  and cyc le s  s imula t ing  a s o l a r  d a i l y  
cyc l e .  This a c t u a l  performance i s  t o  be  compared wi th  performance p r e d i c t e d  
by t h e  computer model. 
This phase of t h e  program i s  j u s t  s t a r t i n g  and only pre l iminary  r e s u l t s  
a r e  a v a i l a b l e .  F igures  3 and 4 show p a r t i a l  r e s u l t s  of a slow d ischarge  t e s t  
with ~ ~ 4 3  enter ing a t  235 C and flowing upward through t h e  heat  exchanger a t  
0.0489 kg/s ( 1 . 1  gal /min).  The temperature of t h e  Thermkeep i n  t h e  TES tank 
was measured by thermocouples loca ted  i n s i d e  t h e  tank,  11 cm ( 4 . 3  i n )  and 
27 cm (10.8 i n )  f r o m t h e  w a l l ,  and o thers  on t h e  wa l l .  Temperatures of t h e  
Thermkeep a r e  p l o t t e d  aga ins t  d is tance  from t h e  t o p  of t h e  tank,  a s  measured, 
and as  predic ted  by t h e  computer model. Figure 3 shows t h e  i n i t i a l  condit ion 
of t h e  TES tank r e s u l t i n g  from an immediately preceding charging which l e f t  
t h e  temperature of t h e  wa l l  about 17 C lower than t h e  i n t e r i o r .  The computer 
response t o  t h e  i n i t i a l  temperatures i s  a l s o  shown. Figure 4 shows t h e  s t a t e  
a f t e r  one hour of discharging and t h e  computer p red ic t ion .  The Thermkeep i s  
l i q u i d  above 292 C and most of  t h e  l a t e n t  heat  i s  del ivered  between 292 C and 
270 C .  This %s r e f l e c t e d  i n  f i g u r e  4 by an increase  i n  t h e  v e r t i c a l  thermal 
gradient  below t h e  l a t e n t  hea t  range, and a decrease wi th in  it. The loca t ion  
of t h e  upper su r face  of t h e  Thermkeep i s  a l s o  shown. This w i l l  move downward 
due t o  t h e  decrease i n  s p e c i f i c  volume of t h e  Thermkeep a s  s o l i d i f i c a t i o n  
continues i n  l a t e r  s t a g e s  of t h e  run ,  which w i l l  be continued t o  a t o t a l  of 
about 6 hours.  
ADVANCED HEAT EXCHANGER MODEL 
Figures 5 and 6 show schematical ly how the  TES u n i t  can be used i n  a s o l a r  
powered e l e c t r i c i t y  generat ing system such as  t h e  SSTFTF. The experimental 
TES u n i t  and computer model p resen t ly  being t e s t e d  correspond t o  f i g u r e  5 .  
Heat t r a n s f e r  f l u i d  heated by s o l a r  co l l ec to r s  t o  approximately 310 C flows t o  
a hea t  exchanger where t h e  Rankine cycle f l u i d  ( e . g .  to luene)  i s  vaporized and 
superheated. Excess heat  i s  del ivered t o  t h e  TES u n i t .  The r e t u r n  tempera- 
t u r e  t o  t h e  c o l l e c t o r s  i s  243 C .  I n  t h e  absence of s o l a r  h e a t ,  flow through 
t h e  TES i s  reversed.  
The advanced computer model w i l l  provide f o r  two hea t  exchangers i n  t h e  
TES u n i t ,  one f o r  t h e  hea t  t r a n s f e r  f l u i d  and one f o r  t h e  Rankine cycle f l u i d ,  
as  i n  f i g u r e  6 .  The algorithms provide fo r  hea t  t r a n s f e r  wi th in  t h e  TES u n i t  
from t h e  hea t  t r a n s f e r  f l u i d  t o  Thermkeep, from Thermkeep t o  t h e  Rankine f l u i d ,  
and d i r e c t l y  from t h e  heat  t r a n s f e r  f l u i d  t o  t h e  Rankine f l u i d .  This w i l l  
allow ana lys i s  of two configurat ions:  1) two independent hea t  exchangers with 
t h e  t o t a l  output from t h e  s o l a r  co l l ec to r s  flowing through t h e  Thermkeep; 2 )  
two thermally coupled exchangers with only s to red  heat  flowing through t h e  
Thermkeep. P o t e n t i a l  advantages of t h e s e  configurat ions a r e  t h e  e l iminat ion  
of t h e  ex te rna l  heat  exchanger and, more importantly,  p o t e n t i a l  improvement 
i n  performance of t h e  TES u n i t  r e s u l t i n g  from t h e  f a c t  t h a t  during discharging 
t h e  temperature of  t h e  Rankine f l u i d  enter ing  t h e  bottom of t h e  TES i s  much 
lower than t h a t  of t h e  heat  t r a n s f e r  f l u i d  i n  t h e  case of t h e  s i n g l e  hea t  ex- 
changer . 
REFERENCE 
1. Development of a Phase-Change Thermal Storage System Using Modified 
Anhydrous Sodium mdroxide  f o r  Solar  E l e c t r i c  Power Generation, 
DOE/NASA/0615-7911, NASA CR-159465. 
t
-
t
-
C
U
a
3
d
w
M
t
-
m
C
O
d
 
t
-
w
C
U
a
 
w
t
-
-
L
n
C
-
-
f
C
U
O
e
-
c
u
.
t
-
m
 
I
0
3
t
-
~
 
f
f
 <
;
C
U
.
O
.
M
L
~
M
U
~
~
I
-
 
I 
r
-
n
t
-
r
i
 
$1 
.
 
.
 
.
 
.
.
 
.
 
.
 
.
 
I
.
.
 
.
 
.
 
a
t
-
-
3
 
L
~
L
~
L
~
;
~
-
=
T
c
u
 
C
u
C
u
L
n
L
n
 
.
.
.
.
.
.
.
.
.
.
 
.
 
-
.
 
I
.
.
.
.
 
2
I
W
r
n
,
-
+
-
l
i
3
4
d
c
u
m
 
c
o
a
3
m
m
m
m
m
m
a
3
m
m
 
m
a
m
m
 
m
m
a
3
0
3
 
3
 
t- 
3
 
rl 
d
 
r-! 
2
 
L
n
w
 
Fig.  1. Heat Exchanger During Fabr ica t ion  
Fig. 2 .  Heat Exchanger Exposed for Examination 
A =  Deep Thermocouples 
O =  Shallow Thermocouples 
8 = Tank Surface 
+Themkeep Surface 
Distance from t o p  of s to rage  v e s s e l ,  cm 
Fig. 3. Thermkeep Temperature vs .  Axial Distance,  I n i t i a l  Condition 
2 50 
25 50 75 100 125 150 175 200 225 
Distance from t o p  of s to rage  v e s s e l ,  cm 
A =  Deep Thermocouples 
0 = Shallow Thermocouples 
- 8 = Tank Surface 
- 
- 
- 
-Themkeep Surface 
- 
- 
\ 
I I I I I I I I I 
Fig.  4. Thermkeep Temperature vs. Axial Distance,  a f t e r  1 Hour. 
180 
r 
310 C 309 C 
TES Two Heat 
Exchanger S to r -  
Solar  
Collec- 
t o r s  
. 
Heat Transfer  Rankine Cycle 
F l u i d  F l u i d  
243 C 
. ... . 
Fig .  6. Advanced Computer Wodel 
181 
310 C -------t 309 C 
L 
Charge \1 F i s c h a r R e  
1 
Sola r  
Collec- 
-t;ors 
4 
- 
Fig .  5. Schematic of S o l a r  Powered E l e c t r i c i t y  Generating System 
t Heat Transfer  F l u i d  
Char? 1 k s c h a r g e  
242 C 243 c , 
Rankine Cycle 
F l u i d  
b 


Development of a thermal storage module using modified anhydrous sodium hydroxide

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server