14.05.2014 1 Numerical Modelling of DC Arc Plasma Torch with MHD Module BEYCAN IBRAHIMOGLU1,AHMET CUCEN1, M. ZEKI YILMAZOGLU2 1 Anadolu 2 Gazi Plasma Technology Energy Center Ankara University Department of Mechanical Engineering Ankara 1. INTERNATIONAL PLASMA TECHNOLOGIES CONGRESS 28-30 APRIL 2014 CONTENTS  INTRODUCTION  BACKGROUND  NUMERICAL ANALYSIS OF PLASMA APPLICATIONS  RESULTS AND DISCUSSIONS 2 1 14.05.2014 INTRODUCTION 1. INTRODUCTION  3 Numerical modelling of plasma state and industrial applications of this approach are of great importance due to its proved benefits. Industrial applications of plasma can be divided as engineering, medicine etc. Different types of plasmas are available for different types of specific applications and the numerical modelling of the plasma differs also the kind of the plasma and its application area. Numerical modelling of the plasma can be performed by using several CFD commercial codes. INTRODUCTION 1. INTRODUCTION (Cont.) 4  Ansys Fluent uses MHD module to simulate a electromagnetic field. Magnetohydrodynamic interaction between electromagnetic field and module allow us to model the behavior of a fluid electromagnetic field. fluid flow in an represents the fluid flow. MHD under DC or AC  In this paper, magnetohydrodynamic effects of a fluid flow is investigated. ANSYS FLUENT is used to model a DC torch. Boundary conditions, mass, continuity and energy equations are developed for the model and the results are shown below. 2 14.05.2014 BACKGROUND 2. BACKGROUND  5 Some of the codes, commonly used, are summarized below.  PTSG is an open source code developed by Michigan State University.  Altasim Technologies achieved modelling DC, inductively coupled plasma, capacitively coupled plasma and microwave plasma.  VizGlow is a plasma modeling software developed by Esgee Technologies for the simulation of DC, inductively, capacitively and microwave discharge, chemically reactive, non-equilibrium, multispecies, multi-temperature plasma discharge. BACKGROUND 6  COMSOL Multiphysics is especially used for low temperature plasma modelling.  PLASIMA developed by Eindhoven University is a commercial CFD software can simulate cold-plasma.  ANSYS FLUENT is most commonly used CFD software in thermal plasma applications. 3 14.05.2014 NUMERICAL ANALYSIS OF PLASMA APPLICATIONS 3. NUMERICAL ANALYSIS OF PLASMA APPLICATIONS  7 MODELLING ASSUMPTIONS  The model used in this study is based on these assumptions for numerical modelling of heat, mass, electromagnetic and fluid flow in plasma torch.  The fluid is considered as a continuum plasma gas and considered as a compressible, LTE (Local Thermal Equilibrium) condition.  Gravitation effects are taken into account  The fluid is turbulent and steady NUMERICAL ANALYSIS OF PLASMA APPLICATIONS 8 3.1. Conservation Equations Conservation of Mass (Continuity) ρ  (ρρV)  0 t Conservation of Energy h   hV   h  J  E  S rad t Cp Conservation of Momentum V  ( VxV )  p    JxB  g t 4 14.05.2014 NUMERICAL ANALYSIS OF PLASMA APPLICATIONS 3.2. Magnetohydrodynamic Model Theory  The coupling between flow field and electromagnetic field can be explained on two main effects.  These are induction of electric current because of the conducting material in a magnetic field and Lorentz force due to magnetic field and electric current interaction.  Inducted electric current and Lorentz force tend to oppose the mechanism that create these effects.  Electromagnetic induction can also form by availability of timedependent magnetic field. Stirring effect of fluid is related with Lorentz force and electromagnetic field can be identified with Maxwell equations. 9 NUMERICAL ANALYSIS OF PLASMA APPLICATIONS 3.2. Magnetohydrodynamic Model Theory (Cont.) 10  Many different plasma applications are being used in various different types of industrial areas. The main difference between these applications are diversity of energy transfer mechanism of electron and field. Being electron temperature much higher than neutral gas temperature characterize Low-pressure discharges. Increase of gas pressure boosts number of electron and neutral gas collisions. Electron and neutral gas temperatures are equal in local thermodynamic equilibrium state. 5 14.05.2014 NUMERICAL ANALYSIS OF PLASMA APPLICATIONS 3.2. Magnetohydrodynamic Model Theory (Cont.) 11  MHD module can be only activated by TUI (Text User Interface) in ANSYS FLUENT. UDF (User Defined Function) and UDS (User Defined Scalar) related to the MHD module are added to the drop-down lists. These added terms are able to model the Lorentz force and Joule heating as source terms. In the solution of these terms electrical potential method or magnetic induction method can be selected. In this study, the electric potential method was used due to its easiness of solving the source terms with one equation. NUMERICAL ANALYSIS OF PLASMA APPLICATIONS 3.3. Geometry Anode 12 Insulated Wall  The geometry used for modelling is SG-100 torch from Praxair Shown in Figure 1.  Geometry has 5 parts; Inlet Outlet Inlet  Inlet  Outlet  Anode  Cathode  Insulated Wall Cathode Figure 1. Plasma Modelling Geometry 6 14.05.2014 NUMERICAL ANALYSIS OF PLASMA APPLICATIONS 3.4. Thermal And Electrical Properties  We can define the electrical conduction properties of domains in MHD module.  In this study, anode is defined as a conducting wall and its current density is set to 0 A/m2.  The cathode is also defined as a conducting wall and its current density is set to 1e8 A/m2.  Insulated wall is defined as a non-conducting wall. 13 NUMERICAL ANALYSIS OF PLASMA APPLICATIONS 3.4. Thermal And Electrical Properties (Cont)  Total current of the cathode is 600 A, defined by current density.  Inlet velocity of the air is set to 7.16 m/s while the cathode temperature is set to 2000 K.  The convective heat transfer coefficient at the anode is equal to 20000 W/m2K and the temperature is set to 500 K.  Air is modeled as an ideal gas.  The electrical conductivity of air is shown in Figure 2. Two regions are given as boundary condition for the electrical conductivity. In the first region a polynomial approach is given for the temperature limit to 20000 K. In the second region the electrical conductivity of the air is taken as constant as shown in Figure 2. 14 7 14.05.2014 NUMERICAL ANALYSIS OF PLASMA APPLICATIONS 15 Elecrical Conductivity [S/m] 12000 10000 8000 6000 4000 2000 0 0 10000 20000 30000 40000 50000 60000 Temperature [K] 70000 80000 90000 100000 Figure 2. Electrical conductivity of air NUMERICAL ANALYSIS OF PLASMA APPLICATIONS 3.4. Thermal And Electrical Properties (Cont)  P1 radiation model is used to model the radiation losses.  The calculations are performed for a 3D geometry and it is meshed using 175000 tetrahedral cells that have 0.203 skewness value.  Mesh study has been made and medium mesh has 400000 cells. The temperature difference between course and medium meshes is %0.011.  Reliazible k-ε turbulence model was chosen for turbulence model. All boundary conditions are given in Table 1. 16 8 14.05.2014 NUMERICAL ANALYSIS OF PLASMA APPLICATIONS 17 Table 1. Boundary conditions of 3D MHD model Inlet Outlet U (m/s) 7.16 V (m/s) 0 W (m/s) 0 T (K) 300 300 0 0 J (A/m2) P (Pa) Ax (T.m) Ay (T.m) Az (T.m) Pin Ax 0 n Ay 0 n Az 0 n Walls Anode Cathode 0 0 0 0 0 0 0 0 0 300 Qa=hw.(T-Tw) 2000 0 1e8 u 0 n v 0 n w 0 n 101325 0 0 0 0 p 0 n Ax 0 n p 0 n Ax 0 n Ay Ay 0 n Az 0 n n 0 Az 0 n p 0 n Ax 0 n Ay 0 n Az 0 n RESULTS AND DISCUSSIONS 4. RESULTS AND DISCUSSIONS 18 Figure 3. Temperature distribution contour Figure 4. Velocity distribution contour 9 14.05.2014 RESULTS AND DISCUSSIONS 4. RESULTS AND DISCUSSIONS (Cont.)  Area average velocity and temperatures are found to be 300 m/s and 5000 K, respectively at the outlet region and the maximum values are 486 m/s and 6617 K at axis of the outlet region.  High Velocity mostly depends on high temperature and it causes an instant gradient changes in fluid domain. 19 RESULTS AND DISCUSSIONS Discussion  A DC arc thermal plasma torch was modeled in Ansys FLUENT with MHD module. The theory of the MHD module, governing equations in differential form, boundary conditions was given. According to the results Joule heat and Lorentz force are the main parameters which affect the fluid flow in a magnetic field.  This study intend to give a aspect modelling plasma with MHD module. Despite of progress in modelling algorithms and programs, more development have to be made. 20 10 14.05.2014 Acknowledgement  21 The research is supported by TUBITAK 1511/ 1120305 project named as Developing a Plasma Coal Combustion System for Soma Thermal Power Plant. References  [1] Internet, http://ptsg.egr.msu.edu/#Software Access date: 19/01/2014  [2] Internet, http://altasimtechnologies.com/technology-overview/plasma-modeling/ Access date: 19/01/2014  [3] Internet, http://esgeetech.com/products/vizglow/ Access date: 19/01/2014  [4] Internet, http://www.comsol.com/plasma-module Access date: 19/01/2014  [5] Internet, http://plasimo.phys.tue.nl/ Access date: 19/01/2014  [6] Ansys Fluent 14, Magnetohydrodynamics (MHD) Module Manual, 2011.  [7] Internet, COMSOL Multiphysics, http://www.comsol.com/ Access date: 19/01/2014.  [8] Lebouvier A., Delalondre C., Fresnet F., Boch V., Rohani V., Cauneau F., Fulcheri L., Three dimensional Unsteady MHD modeling of a low current high voltage non transferred DC plasma torch operating with air, IEEE Transactions on Plasm aScience, 39,9, 1889-1899, 2011.  [9] Huang R., Fukanuma H., Uesugi Y., Tanaka Y., An improved local thermal equilibrium model of DC arc plasma torch, IEEE Transactions on Plasma Science, 39, 10, 1974-1982, 2011.  [10] Internet, http://descanso.jpl.nasa.gov/SciTechBook/series1/Goebel_03_Chap3_plasphys.pdf 22 11 14.05.2014 23 THANK YOU 12