NASA Technical Reports Server (NTRS) 19910018192: Heat transfer in a compact heat exchanger containing rectangular channels and using helium gas

101 Pages·3.5 MB·English

by  NASA Technical Reports Server (NTRS)

PB91-184804
Heat Transfer in a Compact Heat Exchanger Containing
Rectangular Channels and Using Pclium Gas
(C1.S.) National inst. of Standards and Tcihnc.logy (NML), Boulder, CO
Prtparea for:
National Aeronautics and Space Ahinistr&tion, Hampton, VA
3an 91
I
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National Institute of Standards and Technology
NISER 3959
HEAT TRANSFER
IN A COMPACT HEAT EXCHANGER
CONTAINING RECTANGULAR CHANNELS
AND USING HELIUM GAS
Douglas A. Olson
REPRODUCED RY
US. DEPARTMENT OF COMMERCE
NAnoNALTEcHNlcAL
INFORMATIONSERVlCE
SPRINGFIELD, VA 22161
HEAT TRANSFER
IN A COMPACT HEAT EXCHANGER
CONTAINING RECTANGULAR CHANNELS
AND USING HELIUM GAS
January 1991
US. DEPARTMENT OF COMMERCE, Robert A. Mosbacher, Secretary
NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY. John W. Lyons. Director
Page
~omenclatur.e. .......................................................... vii
Abstract ................................................................. 1
1 . Intr~ductio.n. ....................................................... 2
2 . Description of experimental apparatus ............................... 2
2.1 Flow apparatus ................................................. 3
2.2 Channel specimen .............................................. 3
2.3 Instrunentation ................................................ 4
3 . Description of experiments and analysis techniques ................... 5
3.1 Experiments conducted .......................................... 5
3.2 Friction factor ................................................ 6
3.3 Heat transfer coefficient ...................................... 7
3.4 Uncertainty analysis ........................................... 10
4 . Results of experirPents ............................................... 11
b.1 Friction factor ................................................. 11
4.2 Temperature distributions and heat transfer ..................... 12
5 . Summary and conclusions .............................................. 15
6 . References ........................................................... 16
Amendices
A . Heat €1.- distribution in reflective furnace ......................... 17
B . Method of calculating flow distribution in specimen .................. 18
LIST OF TABLES
Tahla Page
1. Uncertainties in experimental measurements and gas properties at a
95% confidence Lncerval ............................................. 21
2. Summary of geometrical parameters and experimental conditions for
...................................................
channel specimer 22
3. Data tables for all experiments ..................................... 23
4. Uncertainties in data analysis parameters and calculated
quantzties.. ...................................................... 76
5. Predicted flow distribution in heat transfer experiments using
method of Appendix B ................................................ 77
iv
LIST OF FIGURES
1. Helium flcr apparatus ............................................... 79
2. Specireen furnace, showing location of inlet gas tamperature (A),
upstream pressure (0). outlet gas temperature (B), and downstrear
przrsure (1) ....................................................... 80
3. Channel specimen .................................................... 81
6. Top view of channel specimen shoving locations of blockdge in flou
ct,.mels due to braze fillets ....................................... 82
S. Friction factor (f) as a function of Reynolds number (Re) for
experiments 1 and 2, no heating, compared to tube spezimen
.............................
correlation and smooth tube correlation 83
6. Percent difference betueen predicted and measured pressure drop
(Po-P,) as a function of heliurr flow rate (m) for heat transfer
.........................................................
exileriments 8L
-
7. Wall (T,) and gas (S,) temperatures as a function of x/L;
................
experiment 8, 13.8 kg/h helium flow, and y/U .0.04 85
8. Val1 temperature (T,) as a function of y/U at several x/L locations;
experiment 8, 13.8 kg/h helium flow ................................ 86
9. Wall-t o-gas temperature difference (T,-T,) and heat transfer
-
coefficient (h) as a function of x/L; exFtriment 8, 13.8 kg/h helium
flov an6 y/U -0.04............... ................................ 87
10. Reynolds number (Re), Nusseit rmnber (Nu), m d modified Nusselt
number (NuJ a-s a functior. of x/L; experiment 8, 13.8 kg/k helium
flow and y/W .0.04 ........................................... 88
11. Modified Nusselt number (NIL) as a function of Reynol-d s number (Re);
all heated experiments with 0.2 .c x/L < 0.8 acd y/V -0.04......... 89
-
4.1. Normalized meter heat floc.. as a function af x/L for yfi 0.12,
......................
368 voltage, reflective furnace calibration 90
B.1. Ratio of predicted chmnel flow to average channel flow, as a
function of y/U at several tot21 flou rates for experiment 8 ........ 91
V

Nomenclature
-
a - coefficient of Re in Nu vs Rr. and Pr correlation
A - inlet manifold location
- -
A, channel normal area = hew,
A, - flow noma1 area nh,w-,
A,, - specimen normal area L-W -
A,, - wetted wall area (total wall area exposed to fluid) 2n!~,+h,)L
b - coefficient of Pr in Nu vs Re and Pr correlation
0 - outlet eanifold location
-
c leading coefficient in Nu vs Re and Pr correlation
cp - specific heat at constant pr-es sure
4 - specimen hydraulic diameter 2wchc/(wc+hc)
-
f friction factor
fq - heat flux distribution function - -
C mass flow rate per unit flow normal area in channel mJAE pV
h =- heat transfer coefficient
-
h enthalpy
h, - height of channel
k - thermai conductivity
L - heated length of specSmen
-
m MSS flow rate
m, mass flov rate per channel
- -
n = number of charnels
Nu Nusselt n d e r h e w -
-
ICs- modified Nusselt number Nu-( TJTf)O-’’
P - pressure
Pr Prandtl nunber = p-c+
q, = local normal heat flux
-
Qp,- fraction of tota; heat flow on specimen added up to position x
integration af furnace calibration function fq, 0 to x
-
Qr = total heat transfer to specimen
qr local heal f;w (hefit flow per unit area) into the cooling fluid based
-
on total wette3--w all area of the specimen
r - recovery factor - pr113 for turbulent flow
Re - Re-olds num5er p”4JIr
T - temperature
T, - cooling fluid adiabatic wall temperature
TI - local bulk fluid temperature
T, - specimen wall temperature
V velocity
V, - heater voltafe
.I
-
W width of specimen
w, - width of channel
U, - uncertainty in friction. factor
W, uncertainty in heat transfer coefficient
Unu- uncertainty in Nusreit number
WG- uncertahty in totel heat trarlsfer
Ura- uncertainty in Reynolds nlmber
Wtr- uncertainty in fluid temperature
Ut“- uncertainty in wall temperature
vi i
-
x - position coordinate parallel to flow direction
y position coordinate perpendicular to flow direction
-
-
@ coefficient of thermal expansion
--
p d-ic viscosity
- kinezsa: viscosity
Y
p density
-
0 - location where heating begins (x/ti))
1 location where heating ends (x/Gl)
viii
Heat Transfer in a Compact Heat Exchanger Containing
Rectangular Channels And Using Helium Gas
Douglas A. Olson
Chemical Eqineering Science Division
National Institute of Standards and Technology
Boulder, CO 80303-3328
Abstract
W e have constructed a compact heat exchanser cotsfsting of 12
parallel, rectangular channels in a flat piece of comercially
pure nickel. This channel specimen was radiatively hehted on the
top side at heat fluxes of up to 77 U/cd, insulated on the back
side, and cooled with helium gas flowing in the channels at 3.5 to
7.0 MPa and Reynolds n d 6 r 8 of 1400 to 23 900. The measured
friction factor was lower than that of the accepted correlation
for fully developed curbulent flow, nithough our uncertainty was
high due to uncertainty in the channel height and a high ratio of
dynamic pressure to pressure drop. The aeasvced Nusselt nunber,
vhen modified to account for differences in iluid properties
between the wall and the cooling fluid, agrctd with past
correlations for fully developed turbulent flow in channels.
Flow nonunifornity from channel-to-channel was as high as 12%
above and 19r below the mean flow.
Kf-y words: apparatus; compact heat exchanger; convection heat
transfer; frictioc factor; high temperature: National Aerospace
Plane; radiative furnace; rectangular channel; turbulent flow;
variable property effects.
This work was supported by NASA Langley Kesearch Center under contract L74c)OC.
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