· I ip o t AN - : ; . are not .. L ' I OFI ORNL P 3190 They soos 4 . i - i + in . . 21 1 1 : . . 1 - . - .. 0 4.5 E 50 - W ool 1 1 STUI TUI SZILI MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS - 1963 . ORNA-p-3190.. Conf-670916--2. MASTER Ite AUG 22 1967 2.c. 13.00, mw .65 LEGAL NOTICE This report was prepared as an account of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commission: A. Makes any warranty or representation, expressed or implied, with respect to the accu- racy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities raith respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report, As used in the above, "person acting on behalf of the Commiselon" includ: 1 any em- ployee or contracor of the Commission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminal.es, or provides access to, any information pursuant to die employment or contract with the Commission, or his employment with such contractor. AN EXPERIMENT EMPLOYING ULTRASONIC ENERGY TO. PROMOTE BOILING IN LIQUID METALS M. M. Yarosh Oak Ridge National Laboratory Oak Ridge, Tennessee ABSTRACT - The tendency for liquid metals such as sodium and potassium to undergo substantial liquid superheating and subsequent explosive boiling has been demonstrated at Oak Ridge National Laboratory and at other research instal- lations. An experiment was conducted employing ultrasonic energy excitation to initiate and maintain stable boiling in potassium under conditions that normally produced liquid superheating and unstable, explosive boiling. Unstable boiling is characterized by large and erratic temperature differences between the tem- peratures of the liquid and vapor. These temperature differences were signifi- cantly reduced or eliminated upon excitation of the ultrasonic probe. The tendency toward liquid superheating was substantially eliminated under many operating conditions. *Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation. DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED INTRODUCTION In the design of liquid metal cooled reactors, in reactor designs having intermediate liquid metal heat removal systems, and in many liquid metal exper- imental systems, predictable behavior of the metal coolant under all possible operating conditions is imperative. It is therefore important that we be able to operate such a coolant system under conditions which avoid cyclic boiling instabilities. In the past several years, investigations at a number of research instal- lations have reported encountering significant instabilities occurring in ex- periments involving boiling of liquid metals, particularly sodium and potas- sium. (1,2,3) At the Oak Ridge National Laboratory, these instabilities were observed to occur during attempts to establish conditions of stable boiling in pools of soäium and potassium and in natural and forced convection systems. \4979 Boiling instabilities occurred when the liquid pool was heated to above saturated temperature conditions without subcooled or nucleate boiling having been estab- lished. Continued addition of heat resulted in substantial superheating of the liquid above the saturation temperature corresponding to the system pressure until a sudden and sometimes violent explosive boiling occurred. This explo- sive boiling or "bumping," as it was termed, was accompanied by sharp tempera- ture reductions in the liquid pool, by rapid temperature rises in the vapor space above the pool, and by rapid pressure fluctuations. Liquid superheats of several hundred degrees Fahrenheit and rapid temperature changes of well over 100°F have been measured. Figure I shows typical traces of the tube wall tem- perature from boiling instabilities occurring in a natural circulation potassium system. (1) . ... .. - OLE. ORNL-DWG 63 - 7539A 1700 4680 HEATER 1660 1640 1620 1600 4580 TUBE OUTER WALL TEMPERATURE (°F) 1560 40 1520 1500 CONDENSER 1480 1460 1440 2 TIME (min) Temperature Traces During Boiling Instabilities in a Natural Convection Potassium System CYCLIC BOILING INSTABILITY The phenomenon of cyclic boiling instabilities, or explosive boiling due to highly superheated liquid, is not peculiar to liquid metal systems out has been observed for many yeai's in water under pool boiling conditions.'°). The phenomenon is associated with the physical properties of the fluid, the liquid to surface wetting characteristics, the presence of dissolved gases, and the characteristics of the heated surface. In liquid metals such as sodium and potassium, the tendency for bulk superheating of the liquid is increased by the high thermal diffusivity of the metal and the relatively high saturation tem- peratures which correspond to expected reactor operating conditions. Krakoviak, by use of an equation suggested by Ellion, has calculated possible superheats for sodium of several hundred degrees Fahrenheit under surface conditions which for water yielded superheats of the order of 30°F.1°) Marto and Rohsenow have studied the effect of surface conditions and cavity shapes on nucleate pool boiling instabilities. 1399) Several techniques have been studied at the Oak Ridge National Laboratory in efforts to promote stable boiling, including mod- ification to the heated surface, vapor addition through vapor generation by special separate heated surfaces, and effects of dissolved gas as a potential nucleation promoter in such systems. ULTRASONIC EXC.LTATION Studies had been underway for some time on the use of a technique employ- ing ultrasonic energy for detecting incipient boiling conditions in channels of water-cooled reactors. It.) The detection scheme was based on the theory that the energy requirements to cause cavitation by ultrasonic energy imposed on a surface immersed within a subcooled liquid pool decreased as the pool temperature approached saturation conditions.itc) Calibration of the energy requirements for cavitation within a given system migh; then permit prediction of the approach to incipiert boiling conditions. An extension of this detection scheme was proposed for use in liquid metal systems as a possible means for determining the presence and degree of superheat in the liquid metal pool. (12) The des re to achieve stable nucleation in liquid metal systems led to the investigation of the use of a modification of the ultrasonic detection scheme as a means for stimulating nucleation in a saturated fluiå. It was reasoned that if cavitation could be generated within a saturated fluid it should be possible to use this technique to prevent the buildup of a substantial liquid superheat. Analysis indicated that the localized vapor voids generated by the high fre- quency minute vibrations should in turn serve as effective nucleation sites for the generation of additional vapor. This could effectively eliminate the cyclic boiling instability. The ultrasonic frequency imposed on the liquid system results in pressure fluctuations i, o nin the liquid which produce tensile forces in the liquid suffi- cient to generate vapor voids.'-) These voids correspond to a condition during the pressure fluctuation wherein the localized pressure is reduced below the saturation pressure corresponding to the lucalized temperature. The collapse of the voids produces a wide band noise spectrum which can be detected on a fre- quency spectrum analyzer. The fixed frequency imposed on the driver element or vibrating probe, can be distinguished easily from the random spectrum noise in- dicative of cavitation voids. In order to test the feasibility of the idea quickly and inexpensively, a 1/2-in.-diam electrical heater element was installed in a 2-in.-diam glass cap- sule as shown in Fig. 2. The heater element was completely submerged in dis- tilled water end ultrasonic energy was imposed on the surface probe introduced . . . . . . . - CONDENSER 2 . Ico — VAPOR THERMOCOUPLE --- LIQUID DEFLECTOR allaw -...--LIQUID LEVEL -ULTRASONIC PROBE X -GLASS CYLINDER LIQUID THERMOCOUPLE -HEATER ELEMENT (1/2" DIA.) ULTRASONIC BOILING EXPERIMENT IN WATER í Glass Capsule for Ultrasonic Boiling Water i Experiment through the Tee section shown on the figure. The results obtained from this experiment indicated that ultrasonic energy would promote nucleation in water. When operating the system at temperatures of approximately 100°F to 120°F with- out ultrasonic input, slight liquid superheating was obtained, ani periodic cyclic boiling occurred as shown in Fig. 3. As seen in Fig. 3, ercitation of the ultrasonic energy probe stabilized the temperatures. BOILING POTASSIUM EXPERIMENT The success of the water experiment lead to the design of an experiment for testing the concept in liquid potassium. A 2-in.-dian, 30lt-austenitic stainless steel capsule, 54-in. long was adapted from an existing design and fitted with a heater element mounted internally and axially concentric with the capsule wall as shown in Fig. 4. The stainless steel ultrasonic probe (or vi- brating face), shown in Fig. 5, consisted of a 3/8-in.-diam rod approximately 31-in. long on the end of which was mounted a flat 1 5/16 ~ 5/8 x 1/16-in.-thick active ultrasonic vibrating surface. The probe was welded into the top of the capsule and the vibrating surface was submerged 3/4-in. below the liquid sur- face or about l-in. above the top of the central heater element. Mounted above the rod extemal to the capsule was a magnetostrictive ultrasonic transducer and a piezoelectric receiving crystal, which was sensitive to the presence of cavitation voids within the liquid. Energy input was supplied by a variable frequency RC oscillator, amplified and imposed on the ultrasonic transducer. The acoustic conductor path leaving the transducer passed through the capsule sitive mount. The mount is designed to prevent dissipation of the energy through the support system by being located at a node in the acoustic path.* Power input "A development of Aeroproducts, Inc., West Chester, Pennsylvania, U.S.A. I ORNL-DWG 65-12596R LILII -ULTRASONIC GENERATOR STARTED . TIME ГТ ТТ .... LULUH LUULUU LIQUID TEMPERATURE (°F) VAPOR TEMPERATURE (°F) Temperature Traces During Ultrasonic Experiment with Boiling Water . . . . . . ... ... ... -. . E -PRESSURE TAP ---AIR ANNULUS -CALROD HEATER 31 1/2" OSOITE LIQUID LEVEL JA - ULTRASONIC VIBRATION FACE -CALROD HEATER HEATED LENGTH MICROPHONE HEIBEN HEATER ELEMENT (1/2 DIA.) THERMOCOUPLE WELL- 24 -DRAIN ULTRASONIC BOILING EXPERIMENT IN POTASSIUM Experimental Capsule for Ultrasonic Tests in Boiling Potassium LE PHOTO 73453 linii oma in MAGNETOSTRICTIVE TRANSDU JCER intens More Dani-jodohrmasis na m ! . vo.. PRESSURE TAP CAPSULE HERMETIC FLANGE t e verwarmin ULTRASONIC VIBRATING PROBE FACE Ultrasonic Probe for Boiling Potassium 11 and frequency were monitored with appropriate equipment.* The wide band spec- trum energy reflections produzed by cavitation within the liquid were trans- mitted from the sensitive crystal pickup located just below the input transducer to a Panoramic frequency spectrum analyzer. A single line block diagram of the electronic equipment is shown in Fig. 6. Potassium liquid and vapor temperatures were measured with Chromel-Alumel thermocoupies inserted through the thermocouple well shown in Fig. 4. TWO couples were mounted in a manner which permitted individual adjustment of the couple elevation. Temperatures were recorded on a two-channel, high-speed Sanborn recorder. System vapor pressure was measured with a Taylor absolute pressure gage graduated in 1/2 psi increments with an estimated precision of 0.2 psi. A crystal pickup microphone was mounted on an elongated metal rod attached to the exterior wall at the liquid filled section of the capsule. Boiling noises were monitored with ear phones and were simultaneously recorded on magnetic tape. The sound was also converted to a millivolt signal and re- corded on a two-channel, high-speed Sanborn recorder. The vapor released from the liquid pool was condensed on the upper section of the capsule wall. This wall was cooled by air flowing external to the capsule through an air jacket. Calrod heaters wrapped around the capsule wall, as shown in Fig. 4, were con- trolled by individual variacs. This permitted separate control of the heat in- put to the liquid and vapor wall sections. The entire assembly was wrapped with high-temperature magnesia insulation. Prior to filling the system with potassium it was pumped down to a pres- sure of less than 50 microns under elevated temperatures for 48 hours. This was done to "outgas" the capsule and reduce the influence of noncondensibles on the experiment. *A tabulation of equipment is included in the Appendix. ORNL-DWG 67-6512 ULTRASONIC TRANSDUCER WATTMETER POWER AMPLIFIER SENSING CRYSTALS FREQUENCY COUNTER ULTRASONIC SPECTRUM ANALYZER AMPLIFIER VARIABLE FREQUENCY OSCILLATOR OSCILLOSCOPE HEAD PHONES -VIBRATING PROBE FACE MAGNETIC TAPE RECORDER MICROPHONE CONVERTER TWO-CHANNEL HIGH-SPEED RECORDER - - - - - .- BLOCK DIAGRAM FOR ELECTRONIC INSTRUMENTATION FOR ULTRASONIC BOILING EXPERIMENT. Block Diagram of Electronic Instrumentation for Ultrasonic Boiling Potassium Experiment EXPERIMENTAL PROCEDURE The objective of the experiment was to determine whether ultrasonic exci- tation of potassium at various pool temperatures and heater element heat flux conditions could serve to stabilize otherwise cyclic boiling conditions. Two experimental methods were used. The heater element power input was fixed and the potassium liquid and vapor temperatures were varied by adjustment of the variacs controlling the liquid and vapor calrods and adjustment of the condenser cooling air flow. The pool temperature was gradually increased, first without and then with ultrasonic input to determine the effect on conditions for achieving stable nucleate boiling. The effect of ultrasonic energy input was also studied by maintaining an approximately constant pool temperature through adjustment of the external calrod heater and varying the heat flux on the cen- tral heater element until defined conditions were achieved. Liquid and vapor temperatures, audio signals, and potassium vapor pressure were all monitored. Variation of the power input and frequency permitted a search for favorable energy input conditions for inducing nucleation. The maximum power output from the ultrasonic generator was 100 watts. In general the power output was well below the maximum. The frequency output from the generator could be varied up to approximately 100 kc, but a value of 52 kc was commonly employed for most runs. TEST RESULLS A control test of the system to establish typical temperature patterns . under normal operating conditions without ultrasonic excitation was conducted at a constant central heater element input of 1 kw (heat flux :: 25,550 Btu/ft- hr). The potassium pool temperature was gradually increased by raising the power input to the lower external calrod. Temperature traces from the Sanborn 24 recorder are shown in Fig. 7. A close examination of Fig. 7 reveals that the liquid and vapor temperature move in opposite directions. As the liquia tem- perature increases and the liquid is superheated under relatively quiet pool conditions, little vapor is generated and the vapor temperature is seen to de- crease. Periodically, a sharp drop in liquid temperature occurred, triggered as a result of sudden explosion-like pool vaporization which resulted in hot vapor being pushed into the vapor section of the capsule. A rapid rise in vapor temperature is seen to follow closely the drop in liquid temperature. The duration of active boiling was short and was followed by a repeat of the cycle of a slow rise in the liquid temperature and a slow drop in the vapor tem- perature as the vapor generation rate again almost ceased. The frequency of such explosive boiling occurred at approximate y 1 1/2-min intervals, but occa- sionally significantly different intervals occurred. The "sawtooth" pattern of the liquid temperature trace is typical for a pool boiling system under unstable conditions. The sudden drop in liquid temperature was immediately preceded by an audi- ble explosion-like report followed by vigorous boiling noises which correlated well with the corresponding temperature traces. The data of Fig. 7 showed liquid-to-vapor temperature differences of as much as 125°F. Measured liquid-to-vapor temperature differences varied from this maximum to less than 10°F. In the test represented by Fig. 7, the pool temperature was raised to a maximum of approximately 1440°F and stable boiling conditions were not achieved. The control experiment represented by Fig. 7 was repeated using a heater element input of 1 kw, but with a 52 kc ultrasonic energy input to the vibrating probe. With a 1 kw power input, an equilibrium pool temperature below 1000°F could not be maintained and the pool temperature stabilized at about 1050°F. ORNL-OWG 66-9825 FIREROD TURNED OFF TIME min POWER = 1 kW 009 1460 280 000 LIQUID TEMPERATURE (°F) VAPOR TEMPERATURE (OF) Temperature Traces During Potassium Boiling Without Ultrasonic Input Although completely stable boiling was not indicated by the liquid temperature trace, the temperature did not exhibit the clear "sawtooth" characteristics seen earlier. At a temperature of approximately 1100°F, the boiling temperature did stabilize and the liquid and vapor temperature pattern appeared as shown in Fig. 8. Note that fluctuations in temperature are less than 10°F, and that the liquid-to-vapor temperature difference is, in almost all cases, less than 20°F. To further demonstrate the effectiveness of the ultrasonic input as a means for stabilizing boiling under given conditions, the system was operated under stable boiling conditions at a power level of 2 kw to the heater element with the ultrasonic generator in operation at a frequency of 53.7 kc. The liquid temperature was slowly rising, and at approximately 1200°F the iltrasonic gen- erator input was stopped for a period of 4 min and then reactivated. The re- sults are shown in Fig. 9. Prior to time 1612, although an equilibrium temper- ature iad not been achieved, the temperature traces were rational and both liquid and vapor tenperatures followed a consistent and rising pattern. Temper- ature differences between the liquid and vapor were generally around 10°F. At time 1612 (point A), the ultrasonic input was stopped and, within less than one minute, the liquid and vapor temperatures began an erratic behavior character- istic of the type of boiling instabilities discussed earlier. Liquid and vapor temperatures began to move in opposite directions throughout the 4-min period. At point B on the graph the ultrasonic generator was reactivated and the re- sulting stabilizing effect on the system temperatures is evident. Monitoring of the boiling noises with ear phones was an effective technique as it proved possible to distinguish between ultrasonic cavitation with non- sustained boiling, sustained boiling, and cyclic boiling. A technique for core- lation of sound generation with boiling heat transfer has been reported on by Schwartz and $11er. (13) Cyclic boiling consisted of long quiet periods with ORNL-DWG 66 - 9826 TIME POWER -I kW 1070 LIQUID TEMPERATURE (°F) VAPOR TEMPERATURE (°F) Temperature Traces During Potassium Boiling with Ultrasonic Input ORNL-OWG 66-9827 TIME 1616 TIME 1612 TIME I min POWER * 2 kW PER ROD A= ULTRASONIC GENERATOR OFF 8 = ULTRASONIC GENERATOR ON 1130 06 130 0621 LIQUID VAPOR TEMPERATURE (°F) TEMPERATURE (OF) Effect of Cessation of ultrasonic Excitation on Boiling Stability - -- - - - - - - sudden, very loud, sharp explosion-like noises followed by short periods of boiling, which gradually diminished to the quiet periods.* Agreement between the temperature traces and the audio monitoring of the boiling noise with stable boiling was excellent and was accepted as confirmation of stable nucleate boil- ing conditions. A visual trace of the boiling noise was recorded and a typical trace is shown in Fig. 10. The lower portion of the curve was traced during non-boiling conditions with the ultrasonic generator turned off. At the point indicated the ultrasonic generator was started with the effect shown. The decibel scale represented by the abscissa was not calibrated. A characteristic noise trace recorded during a period is shown in Fig. 11. The abscissa scale sensitivity in this case was reduced by a factor of 100 from that of Fig. 10 to prevent the recorder from driving off scale. Magnetic tape record- ings for each of the conditions covered by Figs. 7 through 11 were obtained. Under low temperatures (below approximately 750°F), saturation pressures for potassium are very low (below approximately 0.1 psia) and it is therefore -.* - .-. important to consider the liquid pool depth at which temperature measurements are made in order to know the condition of the liquid. A traverse of the potas- re-run-- -- -. sium pool temperature was made to determine the temperature gradient as a function of pool depth with and without the ultrasonic generator in operation, and with constant power on the heater element. From Fig. 12, the temperature gradient is seen to be significant, and the effect of ultrasonic operation is clearly evident at the higher temperatures. The change in slope of the curves at a depth of approximately five inches coincides with the top of the heated section of the heater element. The sharper break in the curve with the gener- ator off is the result of increased liquid stratification because of the absence The magnetic tape recording for typical cases will be presented at the conference, and is available for loan. ORNL - DWG 66 - 9828R hahahahahahhahaha TIME GENERATOR ON 1sec -GENERATOR OFF SENSITIVITY = 100 NOISE LEVEL Noise Trace Showing Effect of Ultrasonic Boiling ORNL-DWG 66-9829A BUMPING BOILING TIME 1 sec SENSITIVITY = 1 NOISE LEVEL --- Noise Trace Showing Effect of Explosive Boiling Instability 4400 ORNL-DWG 66-9830 • ULTRASONIC GENERATOR OFF O ULTRASONIC GENERATOR ON SATURATION TEMPERATURE (p=46 lb/ft?) - POOL TEMPERATURE (°F) 700 10 DEPTH BELOW LIQUID SURFACE (in.) Effect of Ultrasonic Excitation on Potassium Pool Temperature vs Depth 23 of boiling. The slope appears to change again at the bottom of the heated section (approximately the 15-in. depth). With no ultrasonic input, vapor is generated primarily by evaporation from the liquid surface, and the upper liquid layer is cooled by this process. The liquid temperature adjacent to the heated section of the heater element (at approximately the 5- to 15-in. depth) is increased. The dashed curve of Fig. 12 represents the approximate, saturation tempera- ture vs pool depth for an assumed constant liquid density of 46 lb/ftö (800°F). The curve position shown is for the case where saturation conditions exist at the liquid surface. At a temperature of 700°F the vapor pressure of potassium is approximately 0.05 psia, and potassium pressures this low could not be accu- rately measured in the system; therefore liquid conditions at the surface were not well defined.. From the discussion which follows, however, it appears prob- able that the vapor pressure may have been substantially lower, and that much of the liquid pool may have been superheated. Thus the dashed curve would have to be much lower to represent true pool saturation temperature conditions. When the ultrasonic generator was activated, the liquid temperature adja- cent to the heated section of the heater element dropped, as shown in Fig. 12. The rise in liquid temperature above the 5-in. depth suggests that vapor was generated adjacent to the heated section and that vapor bubbles rising through the liquid heateå the cooler upper liquid layer, hence the crossover of the curves at the 5-in. depth. The drop in liquid temperature at the heated section and apparent vapor bubble stability suggests that the liquid at this depth was actually superheated. The importance of recognizing the existence and effect of significant temperature gradients in pool boiling is apparent, but the need for better data is also apparent. During operation of the system with ultrasonic input, a scan in input fre- quency was made, and strong effects of certain input frequencies were detected. At these frequencies, pronounced effects on boiling occurred, while at inter- mediate frequencies the effects on boiling were minor. The favored frequency input seemed to vary as a function of pool temperature so that the most favored input frequency was not a constant. This suggests that under conditions of system startup a variable frequency input might be desirable to establish boiling conditions initially. An examination of the ultrasonic probe after test termination was made to determine if evidence of cavitation damage to the active probe surface had occurred. This is particularly important since ultrasonic induced cavitation has been emp3.oyed to permit accelerated studies of damage which may occur as a result of cavitation under normal system design conditions The examination of the probe surface revealed no evidence of cavitation damage, but cracks were found on the support rod behind the active surface as seen in Fig. 13. These appeared to be fatigue cracks. The 31-in. long unsupported acoustic rod length required for this capsule was recognized as undesirable, and the cracks are be- lieved to be associated with this specific design. Roâ length can be any inte- gral function of the ratio of acoustic velocity in the rod to a resonant har- monic frequency so that it is essentially governed by the system geometry. In this experiment, the length was required to permit the probe to be inserted through the capsule top and to reach the liquid surface. DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS The work reported on in this paper permits some preliminary conclusions, but it clearly indicates the need for additional and more detailed work. The experiment was terminated when funds were no longer available. Some of the recommendations included here, therefore, were part of the original experimental 1 . r . 1. Y - A C - . . .. w V IN en nie. . * . .. 1.- . . - - .-. , + . ... EL . .! ! . !. . . . . .. . Y . - -. .. . :- - - . - -- . . . - - - - -. - .. W e s nie in . NU someth MT is increase this little biti samo tako Cracking on Support Roâ of Boiling Potassium Ultrasonic Probe ***; :.. .... .. - - - . . -. -. . 26 test plan, but the early termination of the experiment prevented a more complete investigation. 1. The tendency for cyclic boiling instabilities in liquid metals, because of the liquid superheat phenomenon, can be eliminated under many operating con- ditions through the use of a vibrating surface receiving ultrasonic energy input. 2. Systems operating under conditions where stable boiling cannot be achieved might be stabilized using ultrasonic energy input, while systems oper- ating stably with ultrasonic energy input may go unstable with cessation of the ultrasonic energy input. 3. Ultrasonic energy input may permit the initiation of nucleation for stable boiling in liquid metals at substantially lower temperatures than other- wise possible. 4. Very cursory experimental studies indicate a high peaking of boiling response to frequency input with some sensitivity to the system pool tempera- ture. This suggests that a variable frequency sweep input may be desirable. 5. Power input requirements are only a relatively few watts and these can he utilized, if desired, during startup or transient periods during which assured boiling is required. 6. This technique for initiating and stabilizing boiling eliminates trou- blesome additional heat sources within the reactor or heat exchanger vicinity and permits all sensitive equipment to be located external to and remote from the reactor. In preliminary work referred to earlier, system boiling responds best to different input frequencies as system temperature is changed. Results indicated that it is necessary to investigate the effect of using a variable sweep input frequency during a system warmup period to determine favorable frequencies as a function of system temperatures. Investigation of the system performance at temperatures in the range of 200 to 700°F should be made with improved geon- etries and with variable frequency input to determine the potential for early The geomatry utilized in the subject experiment is particularly poor be- cause of the relative orientation of the vibrating face with respect to the heated surface. Tiere is a "focusing effect" from the ultrasonic vibrating face, and it is therefore desirable that the active surface be located so that focusing onto the heated surface is possible. This may substantially improve system performance and should be studied. The possibility of imposing an ultrasonic energy input within fuel element clusters, or on fuel elements themselves during periods where stable boiling is essential, suggests itself as a future possibility. It will be necessary to investigate more thoroughly for cavitation damage which may occur on the probe face as a result of ultrasonic energy input. Some damage may of course be tolerable. The experimental work reported on in this paper was conducted in collabora- tion with Mr. J. K. T. Jung now with Jow Chemical Corporation. 4 U 28 Appendix MAJOR ELECTRONIC EQUIPMENT 1. General Radio Model 1210-CRC Variable Frequency Oscillator. -2. "Sonobond" Model 1040A 100 Watt Amplifier. 3. Panoramic Radio Products Frequency Spectrum Analyzer Model 513-15a. 4. Flude Mode 102 Volt Ammeter Wattmeter. 5. T.S.I. Frequency Counter. . . . . . . 7. Techtronix Oscilloscope. -. . . ...... . ... ., . . o . -- REFERENCES 1. J. A. Edwards and H. W. Hoffman, Superheat with Boiling Alkali Metals, Proceedings of the Conference on Application of High Temperature Instrumentation to Liquid Metal Experiments, USAEC Report ANL-7100, September 28-29, 1965, Argonne National Laboratory.. : 2. R. E. Balzhiser, Boiling Studies with Potassium, Proceedings of 1963 High Temperature Liquid Metal Heat Transfer Technology Meeting, USAEC Report ORNL-3605, Oak Ridge National Laboratory, 1964. ' ." 11141 3. P. J. Marto and W. M. Rohsenow, Nucleate Boiling Instability of Alkali Metals, ASME-AICHE Heat Transfer Concerence, Los Angeles California, August 8-11, 1965, Paper 65-HT-22. ...- - 4. E. E. Hoffman, Boiling-Potassium Stability Studies, Metals and Ceramics Division Annual Progress Report for Period Ending May 31, 1963, USAEC Report ORNL-3470, Oak Ridge National Laboratory, Nov. 4, 1953. 5. H. W. Hoffman and A. I. Krakoviak, Convective Boiling with Liquid Potas- sium, Proceedings of 1964 Heat Transfer and Fluid Mechanics Institute, Stanford University Press, Stanford, California. 6. Max Jacob, Heat Transfer Vol. I, John Wiley & Sons, 1949, pp. 615-618. .' -. _ - 7. L. S. Tong, Boiling Heat Transfer and Two-Phase Flow, John Wiley & Sons, 1965, pp. 32-36. !-www ci . 8. . .. . . . A. I. Krakoviak, Superheat Requirements with Boiling Liquid Metals, Pro- ceedings of the 1963 High Temperature Liquid Metal Heat Transfer Technology Meeting, USAEC Report ORNL-3605, Oak Ridge National Laboratory, 1964. .... www. . . . .. . . . . 9. P. J. Marto and W. M. Rohsenow, Effects of Surface Conditions on Nucleate Pool Boiling of Sodium, ASME Paper 65-HT-51. 1 10. R. E. MacPherson, Techniques for Stabilizing Liquid Metal Pool Boiling, to be presented, International Conference on Safety of Fast Reactors, Bouches du Rhone, France, September 19-22, 1967. * 11. Carmine F. De Prisco et al., Ultrasonic Instrumentation in Nuclear Applica- tions, I - Ultrasonic Detection of Incipient Boiling and Cavitation, USAEC Report NYO-10010, Aeroprojects Incorporated, March 1962. 12. Aeroprojects Incorporated Progress Report No. 22, Applications of Ultra- sonic Energy: Ultrasonic Instrumentation for Nuclear Applications, USAEC Report NYO-2910-10, June 1965. . ... 13. F. L. Schwartz and L. G. Siler, Correlation of Sound Generation and Heat Transfer in Boiling, ASME Paper 64-WA/HT-24. . 14. R. Garcia and F. G. Hammitt, Ultrasonic-Induced Cavitation Studies, University of Michigan Technical fieport 05031-1-T, October 1964. mest interestimimaan, 's .. r ove emege p papel para co *** them and painter to come photo travel UNE DATE FILMED 9 / 28 /167 HES . . a H i ! Io Pre--...