Effect of nanoparticle deposition on rewetting temperature and quench velocity in experiments with stainless steel rodlets and nanofluids

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1 Eect o nanoparticle deposition on reetting temperature and quench velocity in experiments ith stainless steel rodlets and nanoluids The MIT Faculty has made this article openly available. Please share ho this access beneits you. Your story matters. Citation As Published Publisher Kim, H., et al. "Eect o nanoparticle deposition on reetting temperature and quench velocity in experiments ith stainless steel rodlets and nanoluids." Proceedings o the ASME 9 7th International Conerence on Nanochannels, Microchannels and Minichannels, ICNMM9, June -4, 9, Pohang, South Korea. American Society o Mechanical Engineers Version Final published version Accessed Sat Apr :5:36 EDT 9 Citable Link Terms o Use Detailed Terms Article is made available in accordance ith the publisher's policy and may be subject to US copyright la. Please reer to the publisher's site or terms o use.

2 Proceedings o the Seventh International ASME Conerence on Nanochannels, Microchannels and Minichannels ICNMM9 June -4, 9, Pohang, South Korea ICNMM9-88 EFFECT OF NANOPARTICLE DEPOSITION ON REWETTING TEMPERATURE AND QUENCH VELOCITY IN EXPERIMENTS WITH STAINLESS STEEL RODLETS AND NANOFLUIDS H. Kim*, J. Buongiorno, L. W. Hu, T. McKrell Massachusetts Institute o Technology Cambridge, MA 39, USA, hdkim@mit.edu ABSTRACT Quenching o small stainless steel rods in pure ater and nanoluids ith alumina and diamond nanoparticles at lo concentrations (. vol%) as investigated experimentally. The rods ere heated to an initial temperature o ~ C and then plunged into the test luid. The results sho that the quenching behavior o the nanoluids is nearly identical to that o pure ater. Hoever, due to nanoluids boiling during the quenching process, some nanoparticles deposit on the surace o the rod, hich results in much higher quenching rate in subsequent tests ith the same rod. It is likely that particle deposition destabilizes the ilm-boiling vapor ilm at high temperature, thus causing the quenching process to accelerate, as evident rom the values o the quench ront speed measured by means o a high-speed camera. The acceleration strongly depends on the nanoparticle material used, i.e., the alumina nanoparticles on the surace signiicantly improve the quenching, hile the diamond nanoparticles do not. The possible mechanisms responsible or the quench ront acceleration are discussed. It is ound that the traditional concept o conduction-controlled quenching cannot explain the acceleration provided by the nanoparticle layer on the surace. NOMENCLATURE Bi Biot number (=c/k) c Speciic heat (J/kg-K) Correction actor or ettability h Heat transer coeicient (W/m -K) k Thermal conductivity (W/m-K) q Heat lux (W/m ) R Radius o rodlet (m) t Time (s) T Temperature (C) T c Critical temperature o ater (C) T int Interace temperature (C) Maximum temperature o liquid phase(c) T MAX Minimum ilm boiling temperature (C) Reetting temperature (C) Temperature o rod specimen (C) T* Dimensionless temperature, ( Trod T ) ( Tre T ) u Propagation velocity o quench ront (m/sec) vol% Volume percent Wall superheat (C) T MFB T re T rod T sat Greek Letter Density (kg/m 3 ) Thermal eusivity (W/m -K) Subscripts Fluid sat Saturated Wall INTRODUCTION A number o recent investigations on boiling o nanoluids shoed that such engineered luids can eectively delay departure rom nucleate boiling (DNB) ith respect to pure luids (You et al., 3; Vassallo et al., 4). It as ound that the DNB heat lux enhancement is closely related to nanoparticle deposition, hich may change the heater surace roughness signiicantly (Bang and Chang, 5; Kim et al., 6). Moreover, the deposition o oxide nanoparticles like alumina and titania signiicantly enhances the ainity, or ettability, o the liquid to the surace (Kim et al., 7). These surace changes alter the boiling heat transer characteristics, e.g., they increase the value o the critical heat lux. Park et al. (4) perormed quenching experiments o a copper sphere in alumina nanoluids to investigate the eect o the nanoparticles on ilm boiling heat transer. Their results shoed that the ilm-boiling heat transer rate in nanoluids as somehat loer than in pure ater. Hoever, they observed Copyright 9 by ASME

3 an intriguing phenomenon: ater quenching a sphere in nanoluids, they repeated the test ith the same sphere, and ound that the sphere ould quench much more rapidly, apparently bypassing the ilm boiling mode altogether. This result suggested that nanoparticle deposition on the sphere surace prevents ormation o a stable vapor ilm, hich consequently promotes a more rapid quenching. Later, some investigations ere carried out by Xue et al. (7), Choo et al. (8), Kim et al. (8) ith similar results; hoever, the mechanism by hich nanoparticle deposition accelerates the quenching process is not clearly understood yet. To investigate the eect o nanoluids/nanoparticles on the quenching phenomena, e conducted quenching experiments ith stainless steel rodlets in ater and nanoluids. These experiments, their results and interpretation are reported in the present paper. NANOFLUIDS PREPARATION AND PROPERTIES We selected nanoluids ith alumina nanoparticles, as this material is idely used in previous investigations o nanoluid boiling heat transer, and also resulted in considerable enhancement o the critical heat lux. Also, diamond nanoparticles ere selected to explore the eect o a material ith very dierent physico-chemical properties. Water-based nanoluids o these to materials ere purchased rom Nyacol (alumina) and PlasmaChem (diamond). Nanoluids ith lo nanoparticle concentrations (.vol%) ere prepared by diluting the concentrated nanoluid purchased rom the vendors ith distilled ater. The size o the nanoparticles in the dilute nanoluids as measured ith the dynamic light scattering technique, and the averaged diameter as ound to be 39 nm or alumina and 65 nm or diamond, respectively. The surace tension, thermal conductivity and viscosity o the nanoluids ere measured by means o a Sigma 73 tensiometer, a KD thermal conductivity probe and a capillary viscometer, respectively. All the nanoluid properties ere ound to be ithin ±5% o those o pure ater, hich is not surprising, given the lo concentration o nanoparticles used in our experiments. EXPERIMENTAL DESCRIPTION Figure shos the details o the test specimen or the quenching experiments. A test specimen consists o a stainless steel rodlet (5 mm in length and 4.8 mm in diameter), a.5 mm-diameter K-type sheathed ungrounded thermocouple to record the temperature at the center o the rodlet, and a reinorcing precision tube to mechanically support them. The reinorcing tube is connected to a 9.5 mm-diameter connecting tube via a tube itting. The quenching experimental acility consists o a radiant urnace, an air slide, a quench pool, and a data acquisition system. The test specimen is preheated to 3C in the urnace. Then the test specimen is quickly plunged rom the urnace into the pool o the test luid, hich is maintained at atmospheric pressure and subcooled temperature o 3 or 8C. The quench pool is a mm rectangular vessel having depth o 5 mm, hich has an eectively ininite thermal capacity ith respect to the test specimen. The pool temperature is controlled by a programmable digital hot plate. The temperature history o the inserted thermocouple at the center o the specimen is recorded using a HP Agilent 3498A data acquisition system at a rate o Hz. Furthermore, the quenching process is recorded by a high speed video camera (Phantom v7.). Further details regarding the quench acility can be ound in a previous paper (Kim et al., 8). Figure Schematics o the rodlet specimens EXPERIMENTAL RESULTS Transient cooling curve Figure shos the temperature histories o the rodlet specimens during repeated quenching tests in ater, alumina and diamond nanoluids. Repetition o the quenching test in ater produced consistent cooling curves ith similar values o the rodlet temperature at hich the slope changes dramatically, in the range rom 4C to 43C. The initial quenching test in alumina nanoluids shoed a temperature history that is almost identical to that in the ater tests. Hoever, the quenching process in the subsequent repetitions ith the alumina nanoluids as considerably accelerated, ith rodlet temperatures at the transition point increasing up to 74C (4 th run). On the other hand, the repetitions ith diamond nanoluids did not display the same acceleration phenomenon, as shon in Fig. (c). (a) pure ater at 8C Measure temperature [ C ] st nd 3rd 4th 5th Time [ second ] Copyright 9 by ASME

4 (b) alumina nanoluids at 8C (c) diamond nanoluids at 8C Measured temperature [ o C] mm/sec, 74 C 5 mm/sec, 7 C 6.6 mm/sec, 6 C 6.5mm/sec, 4 C st nd 3rd 4th Measured temperature [ C ] ~ 46 C st nd 3rd 4th Time [second] Time [ second ] Figure Temperature history o quenched rodlets. (a) Water: t =,,, 3, 4, 5 sec; T rod ~ 4 C (b) st run in alumina nanoluids: t =,,, 3, 4, 5 sec; T rod ~ 4 C (c) 3rd run in alumina nanoluids: t =,.,.,.5,.,.5 sec; T rod ~ 7 C Figure 3 High-speed camera visualization o quenching phenomena or rodlets in pure ater and alumina nanoliuids at 8C. 3 Copyright 9 by ASME

5 Propagation o quench ront Quenching occurred through propagation o a quench ront on the rodlet specimen or pure ater and alumina nanoluids (Fig. 3). The edge o the quench ront as characterized by a line o vigorous boiling. The quench ront speeds ere measured rom the high-speed camera rames, and the values are reported in Fig.. With reerence to Fig. 3(a), the stable vapor ilm started to collapse rom the bottom o the rod at the rodlet temperature o 4 C. The quench ront moved up along the rod ith a moving speed o mm/sec. The initial quench ront speed in alumina nanoluids as ound to be ~7. mm/sec ith an associated rodlet temperature o 4 C, ithin the scattering range o the ater tests. Hoever, the subsequent test in nanoluids shoed quite a dierent behavior. The vapor ilm started to collapse at much higher temperature, ~7 C, and the quench ront propagated at a much higher velocity, ~.5 m/sec, hich is about three orders o magnitude higher than the values or ater. In act, the quenching process as so ast, that the transition rom ilm boiling to nucleate boiling seemed to occur almost simultaneously on the entire surace, as shon in Fig. 3(c). Unortunately, the diamond nanoluid as too opaque to visualize the quench ront. Eect o nanoparticle deposition It is ell knon that a nanoparticle deposition layer is ormed on the boiling surace due to evaporation o nanoluids (Kim et al., 7). This as observed also in our experiments. Since the accelerated quenching behavior observed in the alumina nanoluid tests is reproduced hen an alumina-nanoparticle-ouled rodlet is quenched in pure ater (6 th test case in Fig. 4), it is clear that the nanoparticles deposited on the rodlet surace (not the nanoparticles dispersed in the nanoluid) are responsible or the accelerated quenching. With subsequent quenches in pure ater, the quench ront velocity gradually decreases again, hich suggests that the particle deposition may be re-dispersed in ater. DATA INTERPRETATION The experimental results strongly point to the nanoparticle deposition on the surace to be responsible or the acceleration o the quenching process. In this section e discuss this eect in some detail. When the hot rodlet and the cold liquid put in contact ith each other, the instantaneous interace temperature assumes a value dictated by the thermal eusivities o the to materials (Carsla and Jaeger, 959), int T T T here k c () k c I this interacial temperature is higher than the reetting temperature or the luid/rodlet pair, quenching cannot occur. The reetting o the liquid on the heated surace is governed by the maximum alloable superheat o liquid near the interace at the moment o contact (Spiegler et al., 963), T int (T =T re, T ) = T MAX () Since the maximum alloable temperature depends on the physico-chemical properties o the surace, namely the ettability, Gereck and Yadigaroglu (99) suggested a ettability correction actor,, to correlate the maximum alloable temperature ith the critical temperature o the luid, as shon belo: T MAX ~ T C (3) here T c is the critical temperature o the luid, i.e., 374 C or ater. At T sat = C (T sat /T C =.58), is ound (Gereck and Yadigaroglu, 99) to be.8 and.89 or clean stainless steel surace ( ~ 8) and alumina nanoparticle-ouled surace ( ~ 5), respectively. The reetting temperatures on these to suraces are then calculated using Eqs. () ~ (3), and are 5C or the clean stainless steel surace and 33C or the alumina nanoparticle-ouled surace. The calculated values o the reetting temperature can be used to estimate the corresponding quench ront velocity, using a simple quench ront propagation model. It is traditionally assumed that the quench ront velocity is controlled by axial heat conduction ithin the solid substrate in the narro quench ront region. An approximate analytical solution o the todimensional (r and z) quench ront problem as derived by Duey and Pothouse (973), as given belo: For Bi <<, u R ( Trod T ) ( Trod Tre) c (4) hk ( T T ) re Figure 4 Quench ront velocity o ater and alumina at 3C. -5: test in pure ater or nanoluids; 6-: tests in pure ater or the rodlet previously quenched in tests -5. For Bi >>, u ( ) 4 c Trod T Tre T Bi h ( Tre T ) Trod T (5) 4 Copyright 9 by ASME

6 The density and speciic heat in these equations are or the stainless steel rod. Bi in our study is about 3.7. Thereore, e can use Eq. (5) to estimate the quench ront velocity. The boiling heat transer coeicient, h, can vary rom ater to nanoluids, but the deviation is usually not very signiicant. For example, experiments perormed in our laboratory shoed that the nucleate boiling heat transer coeicient o nanoluids is almost identical to that o ater (Kim et al., 9). Thereore, or this analysis a representative value o 5 4 W/m /K as assumed or both ater and the nanoluids. The temperature o the rod (at the time o transition rom ilm boiling to nucleate boiling), T rod, is directly measured in our experiments, hereas the reetting temperature is taken rom the estimates at the beginning o this section. The temperature o the luid is ixed at 8C. Table : Reetting temperatures and quench ront velocities T ( C) Trod (C) Tre Eqs. (~3) h (W/m K) Calculated by Eq. (5) u (mm/sec) Measured rom exp. Water Alumina NF st test Alumina NF 4th test Table reports the values o the quench ront velocity calculated by means o Eq. (5) or three representative cases. In spite o a higher reetting temperature, the model o Eq. (5) predicts a reduction o the quench ront velocity or the nanoparticle-ouled rodlet, mainly because the rod temperature or this case is very high. Hoever, the experiments clearly sho the opposite trend, i.e., the nanoparticle-ouled rodlet has a much higher quench ront velocity. This led us to question the physical validity o the model. Thereore, e decided to conduct numerical simulations o the to-dimensional quench ront propagation problem. Figure 5 shos the model or the simulation o the vapor ilm collapse. The Fourier equation or to-dimensional transient heat conduction as numerically solved or our rodlet geometry using the commercial code FLUENT 6.. To simulate the quenching process, the olloing assumptions ere used or the convective heat transer boundary conditions o the quenching surace: For T > T re, h = (ilm boiling region) For T T re, h = 5 4 W/m /K. (nucleate boiling region) Figure 5 Model o the vapor ilm collapse used in simulation Bi The rod temperatures in the simulation ere 4C and 75C, hich ere measured during our quenching experiments in pure ater and the 4 th alumina nanoluid tests, respectively. The 4 th test in nanoluid actually exhibited the extremely high quench ront velocity o 5 mm/sec. Quench ront velocity [mm/sec] Eq. (5) or Trod = 4 C Eq. (5) or Trod = 75 C Numerical simul. or Trod = 4 C Numerical simul. or Trod = 75 C T rod = 4 C Reetting temperature [C] T rod = 75 C Figure 6 Numerical simulation results o quench ront speed vs reetting temperature. Figure 6 shos the predictions o the numerical simulations, and compares them to the analytical solution o Duey and Pothouse (973). It is seen that the quench ront velocity predicted by the numerical simulation is relatively lo (and in good agreement ith the analytical solution) hen T re << T rod. On the other hand, hen the reetting temperature approaches the rod temperature, T re T rod, the quench ront velocity becomes very high, i.e., in the limit comparable to the experimentally observed velocity. The problem is that such a high reetting temperature (4-75C) is not physically possible, as it is ell above the critical temperature o ater (374C). Thereore, e can conclude that the very high quench ront speed is not compatible ith the notion o a quench ront that is controlled by axial heat conduction ithin the rodlet. CONCLUSIONS AND FUTURE WORKS Conclusions o this study are as ollos:. The nanoparticles dispersed in the luid at lo concentration (<. v%) do not change the quenching process appreciably.. The nanoparticles that deposit on the rodlet surace may accelerate the quenching process very signiicantly, up to three orders o magnitude in terms o quench ront propagation velocity, and up to 75C in terms o temperature at hich the transition to nucleate boiling begins. The acceleration strongly depends on the nanoparticle material used, i.e., the alumina nanoparticles on the surace signiicantly improve the quenching, hile the diamond nanoparticles do not. 3. Vapor ilm collapse in the accelerated quench tests does not seem to be controlled by axial heat conduction in the rodlet. 5 Copyright 9 by ASME

7 Further investigation and quantiication o the quench acceleration mechanism in the presence o nanoparticle deposition is underay. The results ill be presented in a uture publication. ACKNOWLEDGMENTS This research as supported by AREVA, a generous git rom Mr. Doug Spreng, and the Korea Research Foundation Grant unded by the Korean Government (MOEHRD) (KRF D6). REFERENCES. Bang, I. C., and Chang, S. H., 5, Boiling heat transer perormance and phenomena o Al O 3 -ater nano-luids rom a plain surace in a pool, Int. J. Heat and Mass Transer, 48, pp Berenson, P. J., 96, Film boiling heat transer rom a horizontal surace, J. Heat Transer, 83C, pp Carsla, H., Jaeger, J., 959, Heat conduction in solids ( nd Edn), Clarendon Press, Oxord. 4. Choo, Y. J., Chun, S. Y., Park, J. K., Song, C. H., Bang, I. C., 8, Experimental Study on Boiling Heat Transer using Standard Nanoluids, Proc. the 7th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, Operation and Saety, Seoul, Korea. 5. Duey, R. B., Porthouse, D. T. C., 973, The physics o reetting in ater reactor emergency core cooling Nucl. Eng. Design, 5, pp Gerreck, V., Yadigaroglu, G., 99, A local equation o state or a luid in the presence o a all and its application to reetting, Int. J. Heat and Mass Transer, 35, pp Henry, R. E., 974, A correlation or the minimum ilm boiling temperature, A.I.Ch.E. Symposium Series, 7, pp Kim, H. D., Kim, J. B., and Kim, M. H., 6, Eect o nanoparticles on CHF enhancement in pool boiling o nanoluids, Int. J. Heat and Mass Transer, 49, pp Kim, H. D., Buongiorno, J., Hu, L. W., McKrell, T., DeWitt, G., 8, Experimental study on quenching o a small metal sphere in nanoluids, Proc. ASME International Mechanical Engineering Congress and Exposition, Boston, USA.. Kim, H. D., DeWitt, McKrell, T., G., Buongiorno, J., Hu, L. W., On the Quenching o Steel and Zircaloy Spheres in Water-Based Nanoluids ith Alumina, Silica and Diamond Nanoparticles, Int. J. Multiphase Flo, (submitted).. Kim, S. J., Bang, I. C., Buongiorno, J., and Hu, L. W., 7, Surace ettability change during pool boiling o nanoluids and its eect on critical heat lux, Int. J. Heat and Mass Transer, 5, pp Ohtake, H., Koizumi, Y., 4, Study on propagative collapse o a vapor ilm in ilm boiling (mechanism o vapor-ilm collapse at all temperature above the thermodynamic limit o liquid superheat), Int. J. Heat and Mass Transer, 47, pp Park, H. S., Shiera, D., Sehgal, B. R., Kim, D. K., and Muhammed, M., 4, Film boiling heat transer on a high temperature sphere in nanoluid, Proc. ASME Heat Transer/Fluids Engineering Summer Conerence, Charlotte, USA. 4. Spiegler, P., Hopeneld, J., Silberberg, M., 963, Onset o stable ilm boiling and the oam limit, Int. J. Heat and Mass Transer, 6, pp Vassallo, P., Kumar, R., and D Amico, S., 4, Pool boiling heat transer experiments in silica-ater nanoluids, Int. J. Heat and Mass Transer, 47, pp Xue H. S., J. R. Fan, R. H. Hong, Y. C. Hu, 7, Characteristic boiling curve o carbon nanotube nanoluid as determined by the transient calorimeter technique, Appl. Phys. Letter, 9, You, S. M., Kim, J. H., and Kim, K. H., 3, Eects o nanoparticles on critical heat lux o ater in pool boiling heat transer, Appl. Phys. Lett., 83, pp Copyright 9 by ASME