Flow distribution and turbulent heat transfer in a hexagonal rod bundle experiment

Flow distribution and turbulent heat transfer in a hexagonal rod bundle experiment K. Litfin, A. Batta, A. G. Class,T. Wetzel, R. Stieglitz Karlsruhe Institute of Technology Institute for Nuclear and Energy Technologies Litfin@kit.edu

Introduction Liquid metal cooled reactors (ADS) Motivation Minimization of radiotoxicity of long lived fission products (Am,Cu,Np,..) Realisation options Accelerator Driven Systems Fast critical reactors Heavy liquid metal (Pb or LBE) as coolant High neutron production rate low reactivity Open issues Turbulent liquid heat transfer of HLM along fuel pins and bundles Sketch of ADS

Experimental overview: Experimental campaign at in the framework of IP-EUROTRANS: LBE single rod experiment Heat transfer for forced, mixed and buoyant convection Test of heater performance Validation and qualification of measurement techniques Water rod bundle experiment Pressure drop in subchannels / rod bundle area Fluid-structure-interaction (flow induced vibrations) Validation and qualification of measurement techniques 2dim flow distribution in sub channels (turbulent mixing) LBE rod bundle experiment Pressure drop in subchannels / rod bundle area Temperature distribution of the rod bundle in the forced convection regime Heat transfer of the hexagonal rod bundle geometry

ADS Fuel assembly design Upper plenum Fuel pin Inlet Foot Parameter PDS-XADS Experiment MYRRAH Design of FA hexagonal hexagonal hexagonal Total Power 0.775 MW 0.43 MW 1.466 MW Number of fuel pins 90 19 91 Pin diameter 8.5 mm 8.2 mm 6.55 mm Pitch 13.41 mm 11.48 mm 8.55 mm P/D ratio 1.57 1.4 1.3 Pin length 1272 mm 1272 mm 1200 mm Active height 870 mm 870 mm 600 mm Nr. of grid spacers 3 3 3 coolant mean velocity 0.42 m/s 2 m/s 2.5 m/s mass flow ~ 40 kg/s ~ 26 kg/s ~ 71 kg/s sub channel area 9330 mm² 1260 mm² 2760 mm² mean heat flux 38 W/cm² 100 W/cm² 131 W/cm² Inlet temperature ~ 300 C ~ 300 C ~ 200 C outlet temperature ~ 400 C ~ 415 C ~ 337 C 1 7 9 84 1 7 7 1 8 0 85 138 137 83 1 7 6 1 8 1 86 140 139 56 136 135 1 8 2 87 142 141 57 87 86 55 134 1 8 3 88 144 143 58 89 88 89 146 145 91 90 34 48 185 147 93 90 148 94 186 149 91 150 47 20 5 3 12 33 66 85 46 19 4 13 34 67 112 84 59 32 83 153 101 59 102 60 61 38 39 40 65 92 35 50 49 33 17 45 36 52 51 18 21 16 44 95 53 19 23 22 6 18 96 37 54 24 7 6 5 17 151 97 55 25 8 7 1 1 16 62 98 56 26 8 2 2 4 15 152 99 57 27 9 10 3 14 63 100 58 20 21 9 28 29 10 11 12 36 60 22 30 31 11 35 64 103 41 61 62 23 32 25 69 1 5 5 104 105 42 63 64 24 68 1 5 6 66 106 107 43 65 45 114 1 5 7 67 108 109 44 113 111 1 6 2 1 5 8 68 110 70 1 6 1 1 5 9 69 42 25 19 8 9 2324 7 8 9 18 7 2 10 2122 6 1 2 1011 17 6 1 3 11 2019 5 4 3 1312 16 5 4 12 1817161514 15 14 13 34 33 39 3 7 40 3 6 2 7 31 2 8 30 Head Test section Flow equilizer & straightener Foot 82 54 31 15 14 13 26 46 71 1 7 5 133 132 82 81 43 42 41 40 39 38 37 71 70 116 115 1 6 3 81 1 7 4 131 80 53 130 80 52 30 79 78 51 29 77 76 50 28 75 74 49 27 73 72 48 47 118 117 73 1 6 4 72 1 7 3 129 79 128 171 127 78 126 170 125 77 124 169 123 121 122 76 75 120 168 167 119 74 1 6 5

LBE Single rod experiment Experiment carried out at LBE Loop Thesys 2 Technology for Heavy Liquid Metal Systems 2nd Version Medium: Pb 45 Bi 55 Inventory: 222 l Flow rate: 2-14 m³/h Diameter: 60 mm 4 different flowmeter Accuracy + 0,5% Oxygen control

LBE Single rod experiment Single rod layout: Total power 22,4 kw heated length 870 mm Power density 100 W/cm² Rod diameter d r 8,2 mm Tube diameter D 60 mm Measurement Range: Temperature 200 C - 400 C Velocity 0-1.6 m/s Prantl 0,016-0,03 Reynolds 5 10 4-5,6 10 5 Thermocouple spacer Results will be presented in Talk 6-16 "Turbulent liquid metal heat transfer along a heated rod within an annular cavity"

Water rod bundle experiment Experiment carried out at water loop Technical details: Temperature 20 C - 100 C Flow rate 130 m³/h Pressure 14,7 bar H 2 O inventory 8 m³ Water rod bundle design identical with LBE rod bundle except for PMMA in active Zone needed for LDA measurements Isothermal experiment Measurement Range: Velocity: 0.1-10 m/s Reynolds: 10 3-9 10 4

Water rod bundle experiment Sensor instrumentation: Head P g P f,e Test section Flow equilizer & straightener Foot P a V T 2 utlet spacer position LDA 3 LDA 2 LDA 1 P d,c,b g T 1 Inlet Pressure measurements Fast pressure sensors P a to P g for component specific pressure loss, flow metering and vibration measurements Temperature measurements Static temperature sensors T 1 and T 2 for overall temperature change LDA velocity measurements LDA 1 downstream venturi nozzle for inlet conditions LDA 2 upstream fist spacer for lateral flow distribution due to the bundle LDA 3 downstream 2 nd spacer for lateral redistribution UDV velocity measurements Measurement in each sub Channel type

Water rod bundle experiment Measurements of pressure loss P a to P g in different configurations to characterize loss coefficient of Inlet section with foot and riser Flow straightener Test section Spacer Inlet section Flow straightner Spacer Test section Exp Pressure loss 0.60 bar 0.66 bar 0.38 bar 2.58 bar Loss coefficient -- -- 0.78 5.7 Experimental results of pressure loss measurements at max velocity of 10m/s (Re 88.000) Loss coefficient C D Loss coefficient C D 2,5 2,0 1,5 1,0 0,5 Measured Spacer Loss Coefficient Calculated Spacer loss coefficient 0,0 0 20.000 40.000 60.000 80.000 100.000 11 10 9 8 7 6 5 4 Loss coefficient of the spacer Re Measured Test Section Loss Coefficient Calculated Test section loss coefficient 3 0 20.000 40.000 60.000 80.000 100.000 Re Loss coefficient of the test section T spacer position LDA 3 LDA LDA T 2 u 2 Pd,c,b 1 0 1 Outlet g Inlet UDV Pg Pf,e Head Test section Flow equilizer Foot P a

Water rod bundle experiment Comparing experimental results: Simple calculation of loss coefficient for used spacer given by average blockage ratio calculates a loss coefficient of 0.65 g f e C D AS = 7 A 2 C D p = 0.5 ρ u 2 Calculated pressure losses for water and lbe experiment: d b H 2 O Exp. LBE Exp 200 C LBE Exp 300 C Spacer pressure loss 0.38 bar 0.20 bar 0.20 bar Test section pressure loss 2.58 bar 2.26 bar 2.21 bar a

Water rod bundle experiment CFD of the test section area Calculated pressure loss of the spacer geometry agrees very well with measured pressure loss. 0.40 Bar calculated pressure loss of the test section near a spacer CFD 1/6 of the test section with modelled spacers (1.2M cells, kε model) T spacer position LDA 3 LDA LDA T 2 u 2 Pd,c,b 1 0 1 Outlet g Inlet UDV Pg Pf,e Head Test section Flow equilizer Foot P a

Water rod bundle experiment Measurements of pressure loss on inlet and test section area with high time resolution: Negligible influence of flow induced vibrations onto the experimental setup. Amplitude 1,0E-04 1,0E-05 1,0E-06 1,0E-07 1,0E-08 1,0E-09 1,0E-10 dg dp103 0,1 1,0 10,0 100,0 Frequency [Hz] Amplitude 0,3 0,2 0,1 0,0 ab dg dp101 103-0,1-2,0-1,5-1,0-0,5 0,0 0,5 1,0 1,5 2,0 Time [s] T spacer position LDA 3 LDA LDA T 2 u 2 Pd,c,b 1 0 1 Outlet g Inlet UDV Pg Pf,e Head Test section Flow equilizer Foot P a FFT of the time resolved pressure of the test section Cross correlation calculation of the time resolved pressure of the inlet and test section

Water rod bundle experiment LDA Measurements of 1d velocity downstream the venturi nozzle at the end of the flow straightening section : Symmetric flow distribution, flow conditionning works more reliable compared to the single rod experiment. 1,60 1,40 1,20 1,00 u/umean 0,80 0,60 0,40 Re = 5.000 Re = 8.000 Re = 10.000 Re =26.000 LDA 0,20 0,00-1 -0,8-0,6-0,4-0,2 0 0,2 0,4 0,6 0,8 1 rel. distance Normalized velocity profile downstream the venturi nozzle at the end of the flow straightening section

Water rod bundle experiment CFD of the velocity profile at the end of the flow straightening section: LDA Velocity profile downstream the venturi nozzle at the end of the flow straightening section with Re 8000. (cfd with 960.000 cells, kεmodel)

Water rod bundle experiment 1d Measurements of the velocity profile in the testsection area: LDA 1d velocity profile at the beginning of the testsection (5m/s Re 38000) 2d Measurements of the velocity profile in the testsection area are planned. Additional cfd planned.

LBE rod bundle experiment Experiment to be carried out at LBE Loop THEADES (THErmalhydraulics and Ads DESign) Technical details: Temperature 190 C - 450 C Flow rate 47 m³/h Pressure 5,9 bar Test ports 3 Usable height 3405 mm O 2 Control LBE-Inventory 4 m³ (42 to) Tube diameter 107mm LBE rod bundle experiment

LBE rod bundle experiment Sensor instrumentation: Head P P Test section P P P Flow equilizer & straightener Foot T P T tlet spacer position TC-Spacer moveable TC-Spacer TC-Pinfixer P d,c,b g Inlet Pressure measurements Fast pressure sensors for component specific pressure loss, flow metering and vibration measurements. Pitot tube for pressure distribution in sub channels Temperature measurements Static temperature sensors T for overall temperature change Fast TC equipped spacer and Pinfixer for subchannel and rod surface temperature distribution

Conclusions Single rod experiments show a large influence of buoyancy on the velocity profile even at relatively high Reynolds Numbers while the temperature field is less influenced. This yields to an enhanced heat removal. Currently used Nusselt correlations are rather conservative. Water rod bundle experiments show very good agreement of measured pressure loss with numerical predictions in the fully turbulent flow regime whereas in the transitional regime secondary flow leads to a rising loss coefficient Measurements show negligible flow induced vibrations onto the setup LBE rod bundle experiments will be conducted soon and hopefully give new insights onto the heat transfer. Acknowlegement The work is supported in the framework of the IP-EUROTRANS project; contract number FI6W-CT-2004-516520