Journal of Power and Energy Systems

Transcription

1 Energy Systems Inflence of Test Tbe Material on Sbcooled Flow Boiling Critical Heat Flx in Short Vertical Tbe * Koichi HATA ** Masahiro SHIOTSU *** and Nobaki NODA **** **Institte of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto , Japan hata@iae.kyoto-.ac.jp ***Professor Emerits, Kyoto University, Gokasho, Uji, Kyoto , Japan shiots@ji.energy.kyoto-.ac.jp ****National Institte for Fsion Science, 3-6 Oroshi-cho, Toki, Gif 59-59, Japan noda@lhd.nifs.ac.jp Abstract The steady state sbcooled flow boiling critical heat flx (CHF) for the flow velocities (=4. to ), the inlet sbcoolings ( T sb,in =48.6 to K), the inlet pressre (P in =735. to 969. kpa) and the increasing heat inpt (Q exp(t/τ), τ=1, and 33.3 s) are systematically measred with the experimental water loop. The 34 Stainless Steel (SUS34) test tbe of inner diameter (), heated length (L=66 mm) and L/d=11 with the inner srface of rogh finished (Srface roghness, Ra=3.18 µm), the Cpro Nickel (C-Ni 3%) test tbe of, L=6 mm and L/d=1 with Ra=.18 µm and the Platinm (Pt) test tbes of d=3 and 6 mm, L=66.5 and 69.6 mm, and L/d=. and 11.6 respectively with Ra=.45 µm are sed in this work. The CHF data for the SUS34, C-Ni 3% and Pt test tbes were compared with SUS34 ones for the wide ranges of d and L/d previosly obtained and the vales calclated by the athors pblished steady state CHF correlations against otlet and inlet sbcoolings. The inflence of the test tbe material on CHF is investigated into details and the dominant mechanism of sbcooled flow boiling critical heat flx is discssed. Key words: Critical Heat Flx, Sbcooled Flow Boiling, Test Tbe Material 1. Introdction *Received 1 Oct., 6 (No ) [DOI: 1.199/jpes.1.49] The inflence of test tbe material on steady state sbcooled flow boiling critical heat flx (CHF) is necessary to investigate the reliability of a divertor in a nclear fsion facility. The divertor is made of copper alloy tbe or copper alloy block whose thermal condctivity is very high. Divavin et al. carried ot the high heat flx experiments on rectanglar samples with cylindrical cooling dcts with one-side heating to the effect of a poros coating deposed on inner cooled srface on the Incident Critical Heat Flx (ICHF) performance at water sbcooled boiling regime. The different materials of samples were nder consideration as well: stainless steel, copper and copper alloys. They defined the empirical correlation between ICHF at one-side heating condition and geometrical parameters of elements of cooling design. The heat load tests have been nder way by the electron beam heating on a divertor 49

2 element which consists of the carbon armors joined to the copper heat-sink with a cooling tbe (). A helical type fsion experimental device which is Large Helical Device (LHD) located in the National Institte for Fsion Science, Japan, has two types of divertor element. One is Mono-block type (Cylindrical one), the other is Flat-plate type (Rectanglar one). The Mono-block type divertor is made of the oxygen-free copper cooling tbe with 1 mm inner diameter and 1.5 mm thickness, and the carbon armor (CXU) with 33 mm oter diameter and 1 mm thickness. The cooling tbe is located in the center of the carbon armor. The carbon armor is brazed to the cooling tbe. On the other hand, the Flat-plate type one is made of the oxygen-free copper block of 3 mm wide by 5 mm high and the carbon tile (CXU) of 3 mm wide by 1 mm high. The carbon tile is brazed to the copper block. The cooling tbe with the inner diameter of 1 mm is horizontally located at the height of 17 mm from the lower srface on the central line of the copper block. The critical heat flx (CHF) experiments for the different geometries (smooth tbe, finned swirl tbe, screw tbe and hypervapotron) were performed in the thermal hydralic conditions of fsion reactors: one-side heating, high heat flx and water-cooled by JAEA (Japan Atomic Energy Agency) (3). Test sections were made of two different materials: C (.%Ag) and OFHC-C (Oxygen Free High Condctivity Copper). Recently, three-dimensional thermal measrements for a one-side-heated mono-block were made for the robst design of one-side-heated plasma-facing components and other high heat flx components by Boyd et al. (4). The mono-block test sections were fabricated from Type AL-15 Glidcop Grade Copper. On the other hand, many researchers have experimentally stdied the CHFs on the niformly heated stainless steel test tbe by a steadily increasing crrent for the most part (5)-(11). We have already measred the steady state CHFs, q cr,sb,st, (9 points) on the niformly heated SUS34 test tbes by a steadily increasing crrent for wide ranges of experimental conditions to establish the database for designing the divertor of a helical type fsion experimental device, which is a Large Helical Device (LHD) located in the National Institte for Fsion Science, Japan -(19). It has been clarified that the q cr,sb,st against T sb,ot for T sb,ot 3 K are almost proportional to d -.4 and.4 for fixed T sb,ot and L/d, to ( T sb,ot ).7 for a fixed L/d, and to (L/d) -.1 for a fixed T sb,ot based on the experimental data -(19). We have given the following steady state CHF correlations against otlet and inlet sbcoolings based on the effects of test tbe inner diameter (d), flow velocity (), otlet and inlet sbcoolings ( T sb,ot and T sb,in ) and ratio of heated length to inner diameter (L/d) on CHF..1.1 d.3 L.7 Bo =.8 We Sc σ / g( ρl ρ g ) d for otlet sbcooling ( T sb,ot 3 K) Bo = C.1.1 ( L / d ) d.4.3 L C Re C 3 1 We e Sc* σ / g ( ρ ρ ) l g d for inlet sbcooling ( T sb,in 4 K) () where C 1 =.8, C =.53 and C 3 =.7 for L/d arond 4 and C 1 =.9, C =.85 and C 3 =.9 for L/d>arond 4. Bo, We, Sc and Sc* are boiling nmber (=q cr,sb,st /Gh fg ), Weber nmber (=G d/ρ l σ), non-dimensional otlet sbcooling (=c pl T sb,ot /h fg ) and non-dimensional inlet sbcooling (=c pl T sb,in /h fg ) respectively. Satrated thermo-physical properties were evalated at the otlet pressre. The correlations against otlet and inlet sbcoolings can describe the athors pblished steady state CHF data (9 points) for wide ranges of test tbe inner diameters (d= to 1 mm), heated lengths (L= to mm), L/d=4.8 to 74.85, otlet pressres (P ot =159 kpa to 1.1 MPa), flow velocities (=4. to ) and dissolved oxygen concentration (O =8.63 to.87 ppm) within 15 % difference for otlet 5

3 sbcoolings ( T sb,ot =3 to 14 K) and inlet sbcoolings ( T sb,in =4 to 151 K) on test tbes with rogh, smooth and mirror finished inner srfaces (srface roghness, Ra=3.18,.6 and.14 µm), althogh the CHF data (3 points) with the mirror finished inner srface (Ra=.14 µm) are distribted within -3 to +7.6 % difference of Eq. for 71.4 K T sb,ot 18.4 K. And frthermore, we have given the following transient CHF correlation against inlet sbcooling for the exponentially increasing heat inpts with wide range of exponential periods,τ, (Q=Q exp(t/τ), τ=19.4 ms to 8.3 s) based on the effect of the non-dimensional period clarified in the work (198 points) for the SUS34 test tbes of the inner diameters of 3 and 6 mm, the heated lengths of 66.5 and 6 mm and L/d=. and 1 with mirror and rogh finished inner srfaces (Ra=.14 and 3.18 µm) respectively at the otlet pressres of arond 8 and 11 kpa ()-(3). for inlet sbcooling ( T sb,in 4 K) (3) Most of the data (198 points) are within 15 % difference of Eq. (3). Recently, the steady state CHFs and the heat transfer coefficients (HTCs) in sbcooled flow boiling were applied to thermal analyses of the Flat-plate type divertor and the Mono-block type one of a helical type fsion experimental device (LHD). The incident CHF, q cr,inc, for the Flat-plate type divertor with the cooling tbe diameter, d, of 1 mm and the plate width, w, ranging from 16 to 3 mm and for the Mono-block type divertor with the cooling tbe diameter, d, of 1 mm and the carbon armor oter diameter, D, of 6 and 33 mm were nmerically analyzed based on the measred steady state CHFs, q cr,sb,st, and HTCs with the test tbe inner diameter, d, of 9 mm and the heated length, L, of 48 to 149 mm for the SUS34 test tbe. And the ratio of the one-side heat loading data, q cr,inc, to the niform heat loading data, q cr,sb,st, has been represented as the simple eqation based on the nmerical soltions (4)-(6). However, the divertor for a nclear fsion facility will be made of copper alloy tbe or copper alloy block for the most part, not of stainless steel ones. The objectives of present stdy are forfold. First is to measre the steady state CHF for test tbes of different wall materials with copper alloy (SUS34, C-Ni 3% and Pt) in the wide range of otlet and inlet sbcoolings and flow velocity. Second is to clarify the inflence of test tbe material on the steady state sbcooled flow boiling CHF. Third is to confirm the applicability of the steady state CHF correlations against otlet and inlet sbcoolings, Eqs. and (), based on the experimental data by sing the thin SUS34 test tbe. Forth is to discss the mechanisms of sbcooled flow boiling critical heat flx in short vertical tbe. Nomenclatre Bo =q cr,sb /Gh fg, boiling nmber C 1, C, C 3 constant in Eqs. () and (3) c specific heat, J/kg K c p specific heat at constant pressre, J/kg K d test tbe inner diameter, m G =ρ l, mass flx, kg/m s g acceleration of gravity, m/s h =(ρcλ).5, thermal activity factor, J/m Ks.5 h fg latent heat of vaporization, J/kg I crrent flowing throgh standard resistance, A L heated length, m 51

4 L e entrance length, m L ipt distance between inlet pressre transdcer and inlet of the heated section, m O dissolved oxygen concentration, ppm P in pressre at inlet of heated section, kpa P ipt pressre measred by inlet pressre transdcer, kpa P ot pressre at otlet of heated section, kpa P opt pressre measred by otlet pressre transdcer, kpa Q heat inpt per nit volme, W/m 3 Q initial exponential heat inpt, W/m 3 q heat flx, W/m q cr,inc incident critical heat flx, W/m q cr,sb transient critical heat flx for sbcooled condition, W/m q cr,sb,st steady state critical heat flx for sbcooled condition, W/m r i test tbe inner radis, m r o test tbe oter radis, m R 1 to R 3 resistance in a doble bridge circit, Ω Ra average roghness, µm Re =Gd/µ l, Reynolds nmber Rmax maximm roghness depth, µm Rz mean roghness depth, µm S srface area, m Sc =c pl T sb,ot /h fg, non-dimensional otlet sbcooling Sc* =c pl T sb,in /h fg, non-dimensional inlet sb-cooling T temperatre, K T in inlet liqid temperatre, K T ot otlet liqid temperatre, K T s heater inner srface temperatre, K T sat satration temperatre, K t time, s T sb,in =(T sat -T in ), inlet liqid sbcooling, K T sb,ot =(T sat -T ot ), otlet liqid sbcooling, K flow velocity, m/s V volme, m 3 We =G d/ρ l σ, Weber nmber δ wall thickness, mm λ thermal condctivity, W/mK ρ density, kg/m 3 ρ e electrical resistivity, µωm σ srface tension, N/m τ exponential period, s Sbscript cr critical heat flx g vapor in inlet ot otlet l liqid sb sbcooled conditions wnh with no heating. Experimental Apparats and Method The schematic diagram of experimental water loop comprised of the pressrizer is 5

5 Wat er Condenser El ectr o magneti c Val ve Pressrizer Vac m P mp Li qi d Te mp. St or age Tank Level Gage Heat er Pressre Gage Nitrogen Gas Heater Controller Wat er Safety Val ve Test Secti on Cool er Cooli ng Wat er Safet y Val ve Drai nage Pressre Gage Level Gage Expansi on Tank and Separat or By-pass Loop Ion Exchanger Test Tbe mm Inner Di a met er + 3mm + 6mm + + 9mm 1 mm + P mp Drai nage Pr e- Heat er Flow Meter Oxygen Met er Degassi ng Eqi p ment Flow direction Fig. 1 d Schematic diagram of experimental apparats. P C BL Flow direction T : Thermocople P : Pressre Gage C :Copper-electrode-plate BL : Bakelite SUS34 Test Tbe C SUS34 T P T L L+566 Heat Inpt Control Block Heat Inpt Si gnal Electronic Switch Power Sht off Si gnal Sht off Te mperat re Co mparator Data Processing Block D/A Converter Display Digital Co mpter Pri nter A/D Converter Amplifiers VT VR VTLi VI VF VTLo VPi VPo Data Si gnal 8channels + - Amplifier D.C. Sorce (3A,35V) Q T Mlti plier Divider VI VR VT VI Test Heater Block VR I RS R1 r a VI RT r r 3 VT Test Tbe R b R3 Fig. Vertical cross-sectional view of 6-mm inner Fig. 3 Measrement and data processing system. diameter test section. shown in Fig. 1. The loop is made of SUS34 stainless steel and is capable of working p to MPa. The loop has five test sections whose inner diameters are, 3, 6, 9 and 1 mm. Test sections were vertically oriented with water flowing pward. The two test sections of the inner diameters of 3 and 6 mm were sed in this work. The circlating water was distilled and deionized with abot 5-MΩcm specific resistivity. The circlating water throgh the loop was heated or cooled to keep a desired inlet temperatre by pre-heater or cooler. The flow velocity was measred by a mass flow meter sing a vibration tbe. The flow velocity was controlled by reglating the freqency of the three-phase alternating power sorce to the canned type circlation pmp. The water was pressrized by satrated vapor in the pressrizer in this work. The pressre at the inlet of the test tbe was controlled within ±1 kpa of a desired vale by sing a heater controller of the pressrizer. The cross-sectional view of 6 mm inner diameter test section sed in this work is shown in Fig.. The SUS34 test tbes with 3 different srface roghness have been generally sed. The test tbes with rogh and smooth finished inner srfaces (RF and SF) are 53

6 commercially available. The rogh finished inner srface was fabricated by annealing the test tbes first in the atmosphere of air and was then acidized, while the smooth finished inner srface was fabricated by annealing the test tbes in the atmosphere of hydrogen gas. The smooth finished inner srface test tbe was polished p to arond 5 µm deep by the electrolytic abrasive treatment to realize the mirror finished one (MF). Three different material test tbes which were the SUS34 test tbe with the rogh finished inner srface (SUS34-RF), Cpro Nickel one with the commercial finish of inner srface (C-Ni 3%) and Platinm one with the commercial finish of inner srface (Pt) were mainly sed in this work. Wall thicknesses of the test tbes, δ, were.,.3,.4 and.5 mm. The inner srface conditions of the test tbe were observed by the SEM photograph and inner srface roghness was measred by Tokyo Seimits Co., Ltd. s srface textre measring instrment (SURFCOM 1A). The silver-coated 5-mm thickness copper-electrode-plates to spply heating crrent were soldered to the srfaces of the both ends of the test tbe. The both ends of test tbe were electrically isolated from the loop by Bakelite plates of 14-mm thickness. The test tbes were also thermally inslated from atmosphere with a Bakelite block of 1 mm wide, 8 mm deep and L mm high. The test tbe was heated with an exponentially increasing heat inpt spplied from a direct crrent sorce (Takasago Ltd., NL35-5R, DC 35 V-3 A) throgh the two copper electrodes shown in Fig. 3. The common specifications of the direct crrent sorce are as follows. Constant-voltage (CV) mode reglation is.5 %+3 mv of fll scale, CV mode ripple is 5 µv r.m.s. or better and CV mode transient response time is less than µsec (Typical) against 5 % to fll range change of load. At the CHF, the test tbe average temperatre rapidly increases. The crrent for the heat inpt to the test tbe was atomatically ct off when the measred average temperatre increased p to the preset temperatre, which was several tens of Kelvin higher than corresponding CHF srface temperatre. This procedre avoided actal brnot of the test tbe. The transient average temperatre of the test tbe was measred with resistance thermometry participating as a branch of a doble bridge circit for the temperatre measrement. The otpt voltages from the bridge circit together with the voltage drops across the two electrodes and across a standard resistance were amplified and then were sent via a D/A converter to a digital compter. These voltages were simltaneosly sampled at a constant time interval ranging from 6 to ms. The average temperatre of the test tbe was calclated with the aid of previosly calibrated resistance-temperatre relation. The heat generation rate in the test tbe was calclated from the measred voltage difference between the potential taps of the test tbe and the standard resistance. The srface heat flx is the difference between the heat generation rate per nit srface area and the rate of change of energy storage in the test tbe obtained from the faired average temperatre verss time crve as follows: V dt q( t ) = Q( t ) ρ c (4) S dt where ρ, c, V and S are the density, the specific heat, the volme and the inner srface area of the test tbe, respectively. The inner srface temperatre was also obtained by solving the heat condction eqation in the test tbe nder the conditions of measred average temperatre and srface heat flx of the test tbe. The temperatre of the heater srface, T s, can be described as follows: qr TS = T 4(r o i ri 1 1 4ro ro lnro ri lnri ) λ 4 4 qri ( r r ) ( r r lnr ) o i (r r ) λ In case of the 6 mm inner diameter test section, before entering the test tbe, the test water flows throgh the tbe with the same inner diameter of the test tbe to form the flly developed velocity profile. The entrance tbe lengths, L e, are given 333 mm (L e /d=55.5). o i i o i (5) 54

7 The vales of L e /d for in which the center line velocity reaches 99 % of the maximm vale for trblence flow were obtained ranging from 9.8 to 1.9 by the correlation of Brodkey and Hershey (7) as follows: L e = 1 / Re (6) d The inlet and otlet liqid temperatres were measred by 1-mm o.d., sheathed, K-type thermocoples which are located at the centerline of the tbe at the pper and lower stream points of 83 and 63 mm from the tbe inlet and otlet points. The inlet and otlet pressres were measred by the strain gage transdcers, which were located near the entrance of condit at pper and lower stream points of 63 mm from the tbe inlet and otlet points. The thermocoples and the transdcers were installed in the condits as shown in Fig.. The inlet and otlet pressres of the test tbe were calclated from the pressres measred by inlet and otlet pressre transdcers as follows:.63 Pin = Pipt {( Pipt ) ( Popt ) } (7) wnh wnh.16 + L L Pot = Pin ( Pin Popt ) (8).63 + L Experimental errors are estimated to be ±1 K in inner tbe srface temperatre and ± % in heat flx. Inlet flow velocity, inlet and otlet sbcoolings, inlet and otlet pressres, and exponential period were measred within the accracy ± %, ±1 K, ±1 kpa and ± % respectively. 3. Experimental Reslts and Discssion 3.1 Experimental Conditions The initial experimental conditions sch as inlet flow velocity, inlet and otlet sbcoolings, inlet and otlet pressres, and exponential period for the flow boiling CHF experiments were determined independently each other before each experimental rn. The experimental conditions were as follows: Heater Material SUS34, C-Ni 3% and Pt Inner Diameter (d) 6 mm for SUS34 and C-Ni 3% test tbes and 3 and 6 mm for Pt ones Heated Length (L) 66 mm for SUS34 test tbe, 6 mm for C-Ni 3% one, and 66.5 and 69.6 mm for Pt ones L/d 11 for SUS34 test tbe, 1 for C-Ni 3% one, and. and 11.6 for Pt ones Wall Thickness (δ).,.3 and.5 mm for SUS34 test tbes,.3 and.5 mm for C-Ni 3% ones, and.5 and.4 mm for Pt ones Srface Condition Rogh finished inner srface for SUS34 test tbe and commercial finish of inner srface for C-Ni 3% and Pt ones Srface roghness for SUS34, C-Ni 3% and Pt test tbes 3.18,.18 and.45 µm for Ra, 7.8, 1.6 and.93 µm for Rmax and 1.16, 1.4 and 1.93 µm for Rz Inlet flow velocity () 4., 6.9, 9.9 and Inlet Pressre (P in ) 735. to 969. kpa Otlet Pressre (P ot ) 73.3 to 98.5 kpa Inlet Sbcooling ( T sb,in ) 48.6 to K Otlet Sbcooling ( T sb,ot ) 3.4 to K Inlet Liqid Temperatre (T in ) 88.9 to K Steadily Increasing Heat Inpt (Q) Q exp(t/τ), τ=1, and 33.3 s 3. Steady State CHF 3..1 In case of 34 Stainless Steel test tbe 55

8 Figre 4 shows the SEM photograph of the 34 Stainless Steel (SUS34) test tbe with rogh finished inner srface (RF). The inner srface roghness is measred 3.18 µm for Ra, 7.8 µm for Rmax and 1.16 µm for Rz respectively. The sbcooled flow boiling critical heat flx (CHF) for the flow velocities (=4. to ), the inlet sbcoolings ( T sb,in =48.6 to K) and the inlet pressre (P in =735. to 969. kpa) are systematically measred with the increasing heat inpt (Q exp(t/τ), τ=1, and 33.3 s). The CHF are almost constant for the exponential period ranging from 1 to 33.3 s for the same experimental conditions. The steady state CHFs, q cr,sb,st, against otlet sbcoolings for the inner diameter of 6 mm with the heated length of 66 mm at the otlet pressre of arond 8 kpa are shown verss the otlet sbcoolings measred, T sb,ot, with the flow velocities of 4., 6.9, 9.9 and in Fig. 5. The otlet sbcooling, T sb,ot, averaged over the cross sectional area was obtained from the measred otlet liqid temperatre, T ot, and otlet pressre, P ot. The figre illstrates the trends in the variation of CHF with increasing otlet sbcooling. The CHFs for the T sb,ot increase with an increase in T sb,ot. The increasing rate becomes lower for higher T sb,ot. The CHFs become higher with an increase in flow velocity at a fixed T sb,ot. These trends have been already reported by Hata et al. -(19) on steady state CHF data for the inner diameters of, 3, 6, 9 and 1 mm with the heated lengths of to 15 mm. The relation between q cr,sb,st and T sb,ot shown in Fig. 5 are rewritten on q cr,sb,st vs. T sb,in graph in Fig. 6 to know the inflence of T sb,in on the steady state CHF for flow velocities from 4. to. The inlet sbcooling, T sb,in, was obtained by the measred inlet liqid temperatre, T in, and inlet pressre, P in. The CHFs for the T sb,in increase with an increase in T sb,in. The increasing rate becomes also lower for higher T sb,in. The vales of CHF data show nearly the same trends of dependence on T sb,ot, althogh the vale of T sb,in at each CHF point is far higher than that of T sb,ot. Figres 7 and 8 show the ratios of the steady state CHF data obtained in this work (11 points) to the corresponding vales calclated by Eqs. and () verss T sb,ot and T sb,in RF Flow direction Fig. 4 SEM photograph of SUS34 test tbe with the rogh finished inner srface. q cr,sb,st (MW/m ) SUS34 RF L=66 mm L/d=11 P ot =8 kpa Eq. q cr,sb,st (MW/m ) SUS34 RF L=66 mm L/d=11 P in = kpa Eq. () T sb,ot (K) T sb,in (K) Fig. 5 q cr,sb,st vs. T sb,ot for SUS34 test tbe with an inner diameter of 6 mm and a heated length of 66 mm at an otlet pressre of 8 kpa. Fig. 6 q cr,sb,st vs. T sb,in for SUS34 test tbe with an inner diameter of 6 mm and a heated length of 66 mm at inlet pressres of 735 to 891 kpa. 56

9 (q cr,sb,st ) exp /(q cr,sb,st ) cal (q cr,sb,st ) exp : experimental vale (q cr,sb,st ) cal : calclated vale SUS34 RF L=66 mm L/d=11 P ot =8 kpa T sb,ot (K) +15% -15% Fig. 7 Ratios of CHF data for SUS34 test tbe with (RF) to the vales derived from the otlet CHF correlation, Eq., verss T sb,ot at otlet pressre of arond 8 kpa T sb,in (K) respectively. Most of the data for 53 K T sb,ot 11 K are within ±15 % difference of Eq. and those for 3 K< T sb,ot <53 K are within -5 to +35 % difference. And, most of the data for the tested range of T sb,in (48 K T sb,in 14 K) are within 15 % difference of Eq. (). (q cr,sb,st ) exp /(q cr,sb,st ) cal 3.. In case of Cpro Nickel test tbe Figre 9 shows the SEM photograph of the Cpro Nickel (C-Ni 3%) test tbe with commercial finish of inner srface. The inner srface roghness is measred.18 µm for Ra, 1.6 µm for Rmax and 1.4 µm for Rz respectively. The vales of Ra wold become approximately 18 times as smooth as that of the SUS34 test tbe with RF. The steady state CHFs, q cr,sb,st, against otlet sbcoolings for the inner diameter of 6 mm with the heated length of 6 mm at the otlet pressre of arond 8 kpa are shown verss the otlet sbcoolings measred, T sb,ot, with the flow velocities of 4., 6.9, 9.9 and SUS34 RF L=66 mm L/d=11 P in = kpa +15% -15% (q cr,sb,st ) exp : experimental vale (q cr,sb,st ) cal : calclated vale Fig. 8 Ratios of CHF data for SUS34 test tbe with (RF) to the vales derived from the inlet CHF correlation, Eq. (), verss T sb,in at inlet pressres of 735 to 891 kpa. Flow direction Fig. 9 SEM photograph of the C-Ni 3% test tbe. q cr,sb,st (MW/m ) C-Ni 3% L=6 mm L/d=1 P ot =8 kpa Eq. q cr,sb,st (MW/m ) C-Ni 3% L=6 mm L/d=1 P in = kpa Eq. () T sb,ot (K) T sb,in (K) Fig. 1 q cr,sb,st vs. T sb,ot for C-Ni 3% test tbe with an inner diameter of 6 mm and a heated length of 6 mm at an otlet pressre of 8 kpa. Fig. 11 q cr,sb,st vs. T sb,in for C-Ni 3% test tbe with an inner diameter of 6 mm and a heated length of 6 mm at inlet pressres of 75 to 93 kpa. 57

10 (q cr,sb,st ) exp /(q cr,sb,st ) cal C-Ni 3% L=6 mm L/d=1 P ot =8 kpa (q cr,sb,st ) exp : experimental vale (q cr,sb,st ) cal : calclated vale T sb,ot (K) +15% -15% Fig. 1 Ratios of CHF data for C-Ni 3% test tbe with to the vales derived from the otlet CHF correlation, Eq., verss T sb,ot at otlet pressre of arond 8 kpa T sb,in (K) in Fig. 1. The CHF for the T sb,ot increase with an increase in T sb,ot. The increasing rate also becomes lower for higher T sb,ot. The CHF also become higher with an increase in flow velocity at a fixed T sb,ot. The crves given by Eq. at each flow velocity are shown in Fig. 1 for comparison. The CHF data are in good agreement with the vales given by the correlation against otlet sbcooling, Eq.. The relation between q cr,sb,st and T sb,ot is rewritten on q cr,sb,st vs. T sb,in graph in Fig. 11. The vales of CHF data show nearly the same trends of dependence on T sb,ot, althogh the vale of T sb,in for each CHF data is far higher than that of T sb,ot. The crves derived from CHF correlation against inlet sbcooling, Eq. (), are shown at each flow velocity for comparison in Fig. 11. The CHF data are in good agreement with the vales given by Eq. () in the whole experimental range. Figres 1 and 13 show the ratios of the CHF data (4 points) to the corresponding vales calclated by Eqs. and () verss T sb,ot and T sb,in respectively. The ratios obtained with the athors correlations for T sb,ot p to abot K and for T sb,in p to abot K were almost within ±15 % differences of nity In case of Platinm test tbe Figre 14 shows the SEM photograph of the Platinm (Pt) test tbe with commercial finish of inner srface. The inner srface roghness is measred.45 µm for Ra,.93 µm for Rmax and 1.93 µm for Rz respectively. It is confirmed from these photos that the Cpro Nickel test tbe seems to be more flatly, althogh the cracks ranging from 1. to 3. µm extended vertically throgh the srface were observed clearly on the SUS34 test tbe with RF and qite a nmber of deep cavities ranging from 1. to 3. µm were also observed on the Platinm test tbe. The steady state CHFs, q cr,sb,st, for the inner diameter of 3 and 6 mm with the heated length of 66.5 and 69.6 mm respectively at the otlet pressre of arond 8 kpa are (q cr,sb,st ) exp /(q cr,sb,st ) cal C-N 3% (q cr,sb,st ) exp : experimental vale (q cr,sb,st ) cal : calclated vale L=6 mm L/d=1 P in : kpa +15% -15% Fig. 13 Ratios of CHF data for C-Ni 3% test tbe with to the vales derived from the inlet CHF correlation, Eq. (), verss T sb,in at inlet pressres of 75 to 93 kpa. Flow direction Fig. 14 SEM photograph of the Platinm test tbe. 58

11 (q cr,sb,st ) exp /(q cr,sb,st ) cal Pt L=69.6 mm L/d=11.6 P ot =8 kpa d=3 mm L=66.5 mm L/d=.17 P ot =8 kpa (q cr,sb,st ) exp : experimental vale (q cr,sb,st ) cal : calclated vale T sb,ot (K) +15% -15% Fig. 15 Ratios of CHF data for Pt test tbes with d=3 and 6 mm to the vales derived from the otlet CHF correlation, Eq., verss T sb,ot at otlet pressre of arond 8 kpa T sb,in (K) measred with the flow velocities of 4., 6.9, 9.9 and. The ratios of the measred steady state CHFs, q cr,sb,st, against otlet and inlet sbcoolings for d=3 mm and L=66.5 mm, and and L=69.6 mm (3 points) to the corresponding CHFs calclated from Eqs. and (), (q cr,sb,st ) exp /(q cr,sb,st ) cal, verss T sb,ot and T sb,in are shown in Figs. 15 and 16 for the otlet pressre of arond 8 kpa and the inlet pressres of 745 to 969 kpa, respectively. The ratios are within -4 to +17 % difference of Eq. for the whole T sb,ot range tested here and within arond ±15 % difference of Eq. () for the whole T sb,in range tested here. It will not be easy to complete wide distribtion database for heat flx with platinm test tbe in high pressre experimental condition by sing the existing direct crrent sorce (DC 35 V-3 A), becase electrical resistivity of platinm, ρ e, is very small as shown in Table 1. The steady state CHFs, q cr,sb,st, for the inner diameter of 6 mm with the heated length of 66.5 mm at the otlet pressre of arond 8 kpa were first measred at the otlet sbcooling of arond 6 K with the flow velocity of in this work and the q cr,sb,st for the inner diameter of 3 mm with the heated length of 69.6 mm were secondly measred for the wide range of otlet and inlet sbcoolings and flow velocity to confirm the applicability of CHF correlations against otlet and inlet sbcoolings, Eqs. and () for Pt test tbe. 3.3 Discssion Hata et al. -(16),(19) have clarified that the steady state CHFs, q cr,sb,st, against T sb,ot for T sb,ot 3 K are almost proportional to d -.4 and.4 for fixed T sb,ot and L/d, to ( T sb,ot ).7 for a fixed L/d and to (L/d) -.1 for a fixed T sb,ot based on the experimental data by sing the thin SUS34 test tbe. And, the steady state CHF correlations against otlet and inlet sbcoolings, Eqs. and (), mentioned above have been given based on the effects of test tbe inner diameter (d), flow velocity (), otlet and inlet sbcoolings ( T sb,ot and T sb,in ) and ratio of heated length to inner diameter (L/d) on steady state CHF for the SUS34 test tbe. And frthermore, the inflence of dissolved gas concentration, inner srface roghness and heating rate on the heat transfer characteristics and the CHFs are investigated in detail for the SUS34 test tbes of d=3 and 6 mm and L=66.5 and 6 mm with the inner srfaces of rogh, smooth and mirror finished (Ra=3.18,.6 and.14 µm) (17),(18),()- (3). (q cr,sb,st ) exp /(q cr,sb,st ) cal Pt L=69.6 mm L/d=11.6 P in = kpa d=3 mm L=66.5 mm L/d=.17 P in = kpa (q cr,sb,st ) exp : experimental vale (q cr,sb,st ) cal : calclated vale +15% -15% Fig. 16 Ratios of CHF data for Pt test tbes with d=3 and 6 mm to the vales derived from the inlet CHF correlation, Eq. (), verss T sb,in at inlet pressres of 745 to 969 kpa Inflence of srface roghness The critical heat flx (CHF) of sbcooled water flow boiling for the SUS34 test tbes of the inner-diameter (d=3 mm), the heated length (L=66.5 mm) and L/d=.17 with the inner srfaces of rogh, smooth and mirror finished (Ra=3.18,.6 and.14 µm) were systematically measred for the dissolved oxygen concentration (O ) of 8.63 to.88 ppm 59

12 Table 1 Thermo-physical properties of SUS34, C-Ni 3% and Pt. T (K) c (J/KgK) SUS C-Ni 3% (8) (1.13) (1.176) Pt (.357) (.36) λ (W/mK) (1.86) 43.9 (.31) 71.4 (4.46) 73. (3.84) ρ (Kg/m 3 ) (1.13) 888 (1.13) 146 (.71) 18 (.7) h (J/m Ks.5 ) (1. 5) 1333 (1.75) 1476 (.8) (1.95) ρ e (µωm) (.565).415 (.446).15 (.149).16 (.3) q cr,sb,st (MW/m ) d=3 mm L=66.5 mm L/d=.17 P in = kpa T sb,in =145 K Eq. () Satrated vapor pressre q cr,sb,st (MW/m ) Ra (µm) h (J/m Ks.5 ) Fig. 17 The q cr,sb,st for the inner diameter of 3 mm Fig. 18 The relation between q cr,sb,st vs thermal with the srface roghness, Ra, from.14 to 3.18 µm activity factor, h, for SUS34, C-Ni 3% and Pt test for the lowest dissolved oxygen concentration. tbes with the inner diameter of 6 mm. with the flow velocities (=4. to ), the inlet sbcoolings ( T sb,in =68.15 to K), the otlet sbcoolings ( T sb,ot =5.69 to K), the inlet pressre (P in =74.67 to kpa) and the otlet pressre (P ot = to kpa) nder the satrated vapor pressre (18). The CHFs on rogh, smooth, and mirror finished inner srfaces for the lowest dissolved oxygen concentration are shown verss the srface roghness, Ra, with the flow velocity as a parameter in Fig. 17. The q cr,sb,st for each flow velocity are almost constant independently of the srface roghness (Ra=3.18 to.14 µm). The corresponding crves for each flow velocity obtained from Eq. () are also shown in the figre. The q cr,sb,st for the SUS34 test tbes with Ra=3.18 to.14 µm are well expressed by the eqation. No Inflence of the srface roghness on CHFs was observed on the inner srface test tbes with Ra=3.18 to.14 µm. The range of Ra for the SUS34 test tbe of d=3 mm is a little wider than that in this work (Ra=3.18 µm for the SUS34 test tbe, Ra=.18 µm for C-Ni 3% one and Ra=.45 µm for Pt one) Inflence of test tbe material The thermo-physical properties of SUS34, C-Ni 3% (8) and Pt are shown in Table 1. It can be seen in the Table that the thermal condctivities for Cpro Nickel and Platinm are abot and 4.5 times as large as that for the SUS34 respectively. It was assmed before the experiment that the steady state CHFs, q cr,sb,st, for the Cpro Nickel and Platinm test tbes may become larger than the vales derived from Eqs. and () de to the following two reasons. One is that the steady-state heat condction in the longitdinal direction of Cpro Nickel and Platinm tbes with the same thickness will be larger than that for the L= mm L/d= P in = kpa T sb,in =9 K SUS34 Satrated vapor pressre Eq. () C-Ni 3% Pt 6

13 SUS34 one at a fixed heat flx level. This may case smaller temperatre difference between inlet and otlet for the Cpro Nickel and Platinm tbes. Another is that the occrrence of local heat spot at the critical heat flx may be sppressed by the increased transient condction heat from the nearby srface area. However, the steady state CHF correlation against otlet sbcooling, Eq., can almost describe the data for the Cpro Nickel test tbe with and L=6 mm within ±15 % difference at 46.4 K T sb,ot K and those for the Platinm one with d=3 mm and L=66.5 mm, and d=6 mm and L=69.6 mm within -4 to +17 % difference at 59.7 K T sb,ot 19.5 K. And the steady state CHF correlation against inlet sbcooling, Eq. (), can also describe most of the data for Cpro Nickel one at 68.8 K T sb,in K and those for Platinm one at 87.5 K T sb,in K within 15 % difference. For the SUS34 test tbe with and L=66 mm, Eqs. and () have also described the data within ±15 % difference at 53 K T sb,ot 11 K and within -5 to +35 % difference at 3 K< T sb,ot <53 K, and within ±15 % difference at 48 K T sb,in 14 K, respectively. It was assmed that the magnitde of the sbcooled CHF wold be affected considerably by that of the thermal condctivity and the heat capacity for the test tbe material difference. The steady state CHFs on the SUS34, C-Ni 3% and Pt test tbes for T sb,in =9 K are shown verss the thermal activity factor (9), h, with the flow velocity as a parameter in Fig. 18. The q cr,sb,st for each flow velocity are almost constant independently of the thermal activity factor (h= to 1476 J/m Ks.5 ). The corresponding crves for each flow velocity obtained from Eq. () are also shown in the figre. The q cr,sb,st are well expressed by the eqation for the test tbe material difference. Changes of test tbe material showed very little effect on steady state CHF nder wide range of otlet and inlet sbcoolings and flow velocity. It is expected based on this fact that Eqs. and () will give the general correlations for steady state CHF against otlet and inlet sbcoolings for the commercially obtainable pipes with varios thermo-physical properties. 4. Conclsions The steady state critical heat flx (CHF) of sbcooled water flow boiling for the 34 Stainless Steel (SUS34) test tbe of and L=66 mm and L/d=11 with the inner srface of rogh finished (Srface roghness, Ra=3.18 µm), the Cpro Nickel (C-Ni 3%) test tbe of, L=6 mm and L/d=1 with Ra=.18 µm and the Platinm (Pt) test tbes of d=3 and 6 mm, L=66.5 and 69.6 mm, and L/d=. and 11.6 respectively with Ra=.45 µm are systematically measred for the flow velocities (=4. to ), the inlet sbcoolings ( T sb,in =48.6 to K), the otlet sbcoolings ( T sb,ot =3.4 to K), the inlet pressre (P in =735. to 969. kpa) and the otlet pressre (P ot =73.3 to 98.5 kpa) nder the satrated vapor pressre. Experimental reslts lead to the following conclsions. Most of the CHF data for SUS34 test tbe with rogh finished inner srface (11 points) are within ±15 % difference of Eq. for 53 K T sb,ot 11 K and those are within -5 to +35 % difference for 3 K< T sb,ot <53 K. And, most of the data for the tested range of T sb,in (48 K T sb,in 14 K) are within 15 % difference of Eq. (). () Most of the data for C-Ni 3% test tbe with commercial finish of inner srface (4 points) are almost within ±15 % differences of Eqs. and () for T sb,ot p to abot K and for T sb,in p to abot K. (3) Most of the data for Pt test tbe with commercial finish of inner srface (3 points) are almost within -4 to +17 % difference of Eq. for 59.7 K T sb,ot 19.5 K and within arond ±15 % difference of Eq. () for 87.5 K T sb,in K. (4) Changes of test tbe material for 34 stainless steel, Cpro Nickel and Platinm with the thermal activity factor (h= to 1476 J/m Ks.5 ) showed very little effect on steady state CHF nder wide range of otlet and inlet sbcoolings and flow velocity. It is 61

14 assmed based on this fact that Eqs. and () will give the general correlations for steady state CHF against otlet and inlet sbcoolings for the commercially obtainable pipes with varios thermo-physical properties. Acknowledgements This research was performed as a LHD joint research project of NIFS (National Institte for Fsion Science), Japan, L-, 1 to 3 and was partially spported by the Japan Society for the Promotion of Science, Grant in Aid for Scientific Research (C), , 3 and 4. References Divavin, V.A., Grigoriev, S.A., and Tanchk, V.N., High Heat Flx Experiments on Mock-ps with Poros Coating on the Inner Srface of Circlar Coolant Channels, Proceedings of the ASME Heat Transfer Division, HTD-Vol , 1995 IMECE, (1995), pp () Kbota, Y., Noda, N., Sagara, A., Komori, A., Inoe, N., Akaishi, K., Szki, H., Ohyab, N., and Motojima, O., Development of High Heat Flx Components in Large Helical Device (LHD, Proceedings of the ASME Heat Transfer Division, HTD-Vol , 1995 IMECE, (1995), pp (3) Boscary, J., Araki, M., and Akiba, M., Analysis of the JAERI Critical Heat Flx Data Base for Fsion Application, JAERI-Research 97-53, Japan Atomic Energy Research Institte, (1997), pp.1-5. (4) Boyd, R.D., Ekhlassi, A., Cofie, P., and Zhang, H., High Heat Flx Removal from a Single-side Heated Monoblock Using Flow Boiling, International Jornal of Heat and Mass Transfer, Vol. 47, (4), pp (5) Bergles, A.E., Sbcooled Brnot in Tbes of Small Diameter, ASME Paper No. 63-WA-18, (1963), pp (6) Nariai, H., Inasaka, F., and Shimra, T., Critical Heat Flx of Sbcooled Flow Boiling in Narrow Tbe, Proceedings of the 1987 ASME-JSME Thermal Engineering Joint Conference, Vol. 5, Hemisphere, New York, (1987), pp (7) Celata, G.P., Cmo, M., and Mariani, A., Sbcooled Water Flow Boiling CHF with Very High Heat Flxes, Reve Generale de Thermiqe, n 36, (199), pp (8) Celata, G.P., Cmo, M., and Mariani A., Enhancement of CHF Water Sbcooled Flow Boiling in Tbes sing Helically Coiled Wires, International Jornal of Heat and Mass Transfer, Vol. 37, No. 1, (1994), pp (9) Celata, G.P., Critical Heat Flx in Sbcooled Flow Boiling, Heat Transfer 1998, Proceedings of 11th International Heat Transfer Conference, Vol. 1, (1998), pp Vandervort, C.L., Bergles, A.E., and Jensen, M.K., An Experiment Stdy of Critical Heat Flx in Very High Heat Flx Sbcooled Boiling, International Jornal of Heat and Mass Transfer, Vol. 37, Sppl. 1, (1994), pp (11) Mdawar, I., and Bowers, M.B., Ultra-high Critical Heat Flx (CHF) for Sbcooled Water Flow Boiling-I: CHF data and parametric effects for small diameter tbes, International Jornal of Heat and Mass Transfer, Vol. 4, (1999), pp Hata, K., Sato, T., Tanimoto, T., Shiots, M., and Noda, N., Critical Heat Flxes of Sbcooled Water Flow Boiling against Otlet Sbcooling in Short Vertical Tbe, Proceedings of the 1th International Conference on Nclear Engineering, Paper No. ICONE1-34, (), pp (13) Hata, K., Tanimoto, T., Komori, H., Shiots, M., and Noda, N., Critical Heat Flxes of Sbcooled Water Flow Boiling against Inlet Sbcooling in Short Vertical Tbe, Proceedings of the 11th International Conference on Nclear Engineering, Paper No. ICONE , (3), pp (14) Hata, K., Komori, H., Shiots, M., and Noda, N., Critical Heat Flx of Sbcooled Water 6

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