Investigation was made of the unstable behavior of a heat-transfer loop operating at a supercritical pressure. Natural convection operation of the loop, with observations on acoustic and slow oscillatory behavior, was emphasized during testing. The basic cause of both types of behavior appeared to originate in the heated boundary layer

Cornelius, A. J.

English

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AEC-NASA TECH BRIEF H 
ICYCl., 
FES
February 1969
	
Brief 69-10042 
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
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the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Instabilities Encountered During Heat Transfer to a Supercritical Fluid 
An investigation has been made of the unstable be- 	 When the outlet bulk temperature was slightly 
havior of a heat-transfer loop operating at a super-	 below the pseudocritical temperature, a different type 
critical pressure.	 of oscillation was observed. This oscillation was char-
In recent years, studies of heat transfer to fluids	 acterized by a frequency two orders of magnitude 
near their critical point have revealed that severe 	 slower than the sonic oscillations. The frequency of 
pressure and flow oscillations spontaneously accom-	 the acoustic oscillations decreased with temperature, 
pany the transfer of heat in this region. Since no 	 while the frequency of the slow type increased with 
plausible explanation has been advanced, the purpose 	 temperature. 
of this study was to investigate this unstable be-	 The data indicates that this type of oscillation was 
havior, which occurs in connection with the transfer 	 initiated and sustained by a sudden improvement of 
of heat to a fluid near its thermodynamic critical 	 the heat transfer coefficient, which attributed to the 
point.	 occurrence of a "boilinglike" phenomenon in the su-
The instabilities were studied in a heat transfer loop	 percritical fluid. An approximate numerical solution, 
designed to operate by either natural or forced convec- 	 which closely matched the experimentally observed 
tion. Since the instabilities were strongly damped 	 results during the slow oscillations, verified the 1111- 
during forced-convection, attention was concentrated	 portance of the heat transfer improvement in trigger-
on natural convection operation.	 ing and maintaining the oscillations. 
Two types of oscillatory behavior, acoustic and
	 Both the acoustic and slow oscillations also occur 
slow, were observed during the tests. Pressure and
	 during subcritical boiling heat transfer. Generally, 
flow oscillations occurred with bulk temperatures be- 	 the acoustic type has been considered of secondary 
low the pseudocritical temperature and with heater	 interest, but a large amount of attention has been 
wall temperatures exceeding the pseudocritical tem-	 focused on the slow type due to its importance in 
perature. The basic cause of both types of oscillatory 	 nuclear reactor applications. 
behavior appeared to originate in the heated boundary 
layer.	 Notes: 
The first type of oscillation was of an acoustic na- 	 I. These results are reported in "An Investigation of 
ture, exhibiting harmonic pressure and now oscilla- 	 Instabilities Encountered During Heat Transfer to 
tions in the range of 5 to 30 cps. The acoustic oscilla- 	 a Supercritical Fluid", by A. J. Cornelius of 
tions are believed to have been initiated by a local dis- 	 Argonne National Laboratory, ANL-7032, April 
turbance, which resulted in pressure waves being pro- 	 1965. This report is available from the Clearing-
pagated at sonic speed away from the disturbance. 	 house for Federal Scientific and Technical Infor-
For the oscillation to have been maintained, the	 mation, Springfield, Virginia 22151; Price—$3.00 
acoustic pressure wave would have to be reinforced
	 (microfiche $0.65). 
upon passing a given point in the system. A mech- 	 2. The report includes the experimental apparatus 
anism that would cause the acoustic pressure wave to 	 and procedure used, the experimental results, and 
be reinforced is postulated in the report. 	 an analysis of slow oscillations.
continued o"erleaI) 
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Inquiries concerning this report may be directed 
to:
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Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B69-10042 
Source: A. J. Cornelius 
Reactor Engineering Division
Argonne National Laboratory
(ARG- 10266)
Patent status: 
Inquiries about obtaining rights for commercial use 
of this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439
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Brief 69-10042	 Category 02


Instabilities encountered during heat transfer to a supercritical fluid

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