Sino-German-Workshop October 11-12, 2004, Shanghai (China) Experimental investigations and numerical modelling of metal melt flows in induction furnaces Egbert Baake, Andrejs Umbrashko Institute for Electrothermal Processes University of Hannover Contact: Prof. Dr.-Ing. Egbert Baake Tel.: +49 511 762 3248 Institute for Electrothermal Processes Fax: +49 511 762 3275 University of Hannover e-mail: baake@ewh.uni-hannover.de Wilhelm-Busch-Str. 4 Internet: www.etp.uni-hannover.de D-30167 Hannover Germany 1
Contents � Introduction � Characteristics of turbulent metal melt flow in induction furnaces - low frequency oscillations - 3D flow structure � Melt flow in cold crucible furnace - experimental work - 3D tansient numerical simulation � Conclusions 2
Industrial process requirements for melting in induction furnaces � Mixing and homogenisation of the entire melt � Homogenisation of the temperature, avoiding of local overheating, but realizing of sufficient superheating of the entire melt � Intensive stirring at the melt surface (melting of small-sized scrap, carburization process) � Avoiding of erosion and clogging of the ceramic lining � Optimisation of the heat � Avoiding of melt instabilities, and mass exchange in splashing or pinching the melt � Intensive stirring for cleaning of the melt (zinc removing) 3
Main features of the induction furnace metal melting processes � Heat and mass transfer and the temperature distribution in the melt are determined by 3D instationary turbulent melt flows � Experimental investigations, e.g. measurements of the turbulent melt flows are very limited in industrial furnaces, experimental investigations are possible in model furnaces with model melts � Optimal design and optimisation of the operation behaviour of induction furnaces needs 3D instationary numerical simulation of the turbulent melt flow and the heat and mass transfer using experimentally verified models 4
Physical Correlations magnetic field meniscus shape - distribution of power geometry of melt - el. efficiency temperature field velocity field - superheating homogenisation of - heat flow melt - crucible temperature skull liquid-solid-interface optimization of design and operating parameters 5
Melt flow measurements in induction crucible furnace Crucible wall V max ≈ 20 cm/s Crucible bottom ′ max ≈ v 1 v max Baake, E. et.al.: 1994 6
Measurement of local flow velocity (ICF): near the crucible wall between the main flow eddies 25 20 15 Geschwindigkeit in cm/s 10 5 0 � 0 10 20 30 40 50 -5 -10 -15 -20 Zeit in s -25 � Low-frequency oscillations � Oscillation period: 8...12 sec 7
Application of 2D and 3D RANS (k- ε ) turbulence models: Calculation results of turbulent characteristics are different from measurement results crucible wall crucible bottom 8
RANS (k- ε model) DNS RANS (k- ε model) DNS • Whole energy spectrum is modelled • All scales are resolved directly • Whole energy spectrum is modelled • All scales are resolved directly • Relatively low mesh resolution • Very high requirements for • Relatively low mesh resolution • Very high requirements for requirements computational resources requirements computational resources • Steady-state simulations • Simulations of industrial installations • Steady-state simulations • Simulations of industrial installations are impossible are impossible CFD problem CFD problem Re ≥ 10 4 Re ≥ 10 4 LES LES • Large scales are resolved directly while only small • Large scales are resolved directly while only small scales are modelled scales are modelled • Relatively high mesh resolution requirements • Relatively high mesh resolution requirements • Transient 3D simulations • Transient 3D simulations 9
Calculated local flow velocity: (3D transient LES) 0,25 r = 0.155 r = 0.14 0,2 r = 0.075 0,15 0,1 Geschwindigkeit in m/s 0,05 0 � � 0 10 20 30 40 50 60 -0,05 -0,1 -0,15 -0,2 Zeit in s -0,25 � Low-frequency oscillations � Oscillation period: appr. 10 sec 10
Fourier analysis of the measured and calculated oscillations of the axial velocity components near the crucible wall between the main flow eddies Amplitude Frequency (Hz) Measurement Calculation 11
Long-time period averaged velocity field in the melt of the ICF (3D transient LES) azimuthal velocity particles trajectories velocity magnitude 12
3D hydrodynamic model of an industrial induction crucible furnace P = 4540 KW H ind = 1.33 m R cr = 0.49 m Filling level 90 % 13
Kinetic energy of the oscillations Experiment Calculations (model furnace) (industrial furnace) 14
Time-averaged flow pattern [m/s] 15
Transient flow development [m/s] 16
Transient flow development (cross-section) [m/s] 17
Calculation of the particle tracing in the melt of the ICF (3D transient LES) 18
Features of the Induction Furnace with Cold Crucible � slitted crucible to realize melt flow radiation efficient electromagnetic transparency slit � free melt surface, based crucible on electromagnetic forces segment (water cooled) inductor � water cooled bottom and (water cooled crucible segments leads to current solid layer (skull) melt with meniscus EM-forces � heat losses by radiation shape and conduction depending bottom on the meniscus shape skull (water cooled) heat conduction 19
Cold crucible induction furnace crucible inductor free surface Optimisation of electromagnetic and real thermal parameters ideal � Maximisation of the overheating temperature, which is the key parameter of the process � Improvement of the total efficiency of contact point process wall-skull bottom-skull � Reliable, reproducible and stable melting process crucible-bottom 20
Experimental set-up for semi-levitation melting R c = 72.5 mm R c = 72.5 mm H i = 208 mm H i = 208 mm 5 coil turns 5 coil turns P = 200 kW P = 200 kW f = 9.2 kHz f = 9.2 kHz T = 660-720°C T = 660-720°C 21
Melting process of Aluminium 22
Temperature measurements in Aluminium 23
Measured temperature field in Aluminium 24
Melt flow measurements in Aluminium with the electromagnetic velocity probe stainless- steel holder stainless- steel case coil 6 14 35 magnet core electrodes 25
Flow pattern and temperature distribution simulated with 2D RNG k- ε turbulence model 26
3D LES-model for Aluminium melting ~3.8•10 6 elements ~3.8•10 6 elements Time step 10 ms Time step 10 ms Smagorinsky-Lilly subgrid Smagorinsky-Lilly subgrid viscosity model viscosity model Parallel computations with Parallel computations with FLUENT 6.1 software at FLUENT 6.1 software at the HLRN*-system the HLRN*-system *HLRN – scientific supercomputer network of North Germany 27
Results of 3D transient LES modeling [m/s] v m ~40 cm/s [m/s] Time-averaged flow pattern An intermediate flow pattern Time-averaged flow pattern An intermediate flow pattern 28
Results of 3D transient LES modeling 29
Results of 3D transient LES modelling ºC ºC Time-averaged temperature Measured temperature Time-averaged temperature Measured temperature distribution distribution distribution distribution 30
Results of 3D transient LES modelling 31
Results of 3D transient LES modelling 32
Conclusions � Heat and mass transfer processes in the melt of induction furnaces are significantly influenced by large scale low-frequency oscillations of the recirculating flow main eddies � Comparison of the LES modelling results with experimental results show good agreement � 3D-transient LES is a reliable numerical tool to simulate the turbulent melt flow with in-stationary low-frequency flow oscillations in induction melting installations 33
Recommend
More recommend
