Multi-regionally coupled analysis of thermal fluid flow and heat conduction of solid using OpenFOAM is carried out to clarify the behavior of hydrothermal oxidative destruction reactor of polychlorinated biphenyls (PCBs). Internal fluid of the reactor assumes a single-phase hot water without chemical reactions considering temperature dependence of thermophysical properties. Compressible Navier-Stokes equation with buoyancy force and energy equation with gravity term are alternately solved for the thermal fluid analysis. In order to consider conjugate heat transfer between the internal fluid and the reactor vessel, two-regionally coupled analysis of the fluid and vessel was executed by chtMultiRegionFoam solver in the OpenFOAM. To verify coupling effect, the multi-regionally coupled analyses results were compared with thermal fluid analysis of the internal fluid or heat conduction analysis of the vessel

Kuramae, Hiroyuki

Matsumoto, Masahide

Sugimoto, Tokihiro

Watanabe, Nobuhisa

Scipedia

14th World Congress on Computational Mechanics (WCCM)ECCOMAS Congress 2020Virtual Congress: 11-–15 January 2021F. Chinesta, R. Abgrall, O. Allix and M. Kaliske (Eds)THERMAL FLUID COUPLED ANALYSIS OFHYDROTHERMAL DESTRUCTION REACTORTOKIHIRO SUGIMOTO1, HIROYUKI KURAMAE2,MASAHIDE MATSUMOTO3 AND NOBUHISA WATANABE41 Graduate School of Osaka Institute of Technology1-45 Chayamachi, Kita-ku, Osaka 530-8568, Japanm1m20r14@st.oit.ac.jp, http://www.oit.ac.jp/2 Osaka Institute of Technology1-45 Chayamachi, Kita-ku, Osaka 530-8568, Japanhiroyuki.kuramae@oit.ac.jp, http://www.oit.ac.jp/3 Osaka Institute of Technology5-1-16 Omiya, Asahi-ku, Osaka 535-8585, Japanmasahide.matsumoto@oit.ac.jp, http://www.oit.ac.jp/4 Osaka Institute of Technology5-1-16 Omiya, Asahi-ku, Osaka 535-8585, Japannobuhisa.watanabe@oit.ac.jp, http://www.oit.ac.jp/Key words: Polychlorinated Biphenyl, Hydrothermal Oxidative Destruction Reactor, Thermal FluidAnalysis, OpenFOAMAbstract. Multi-regionally coupled analysis of thermal fluid flow and heat conduction of solid usingOpenFOAM is carried out to clarify the behavior of hydrothermal oxidative destruction reactor of poly-chlorinated biphenyls (PCBs). Internal fluid of the reactor assumes a single-phase hot water withoutchemical reactions considering temperature dependence of thermophysical properties. CompressibleNavier-Stokes equation with buoyancy force and energy equation with gravity term are alternately solvedfor the thermal fluid analysis. In order to consider conjugate heat transfer between the internal fluid andthe reactor vessel, two-regionally coupled analysis of the fluid and vessel was executed by chtMultiRe-gionFoam solver in the OpenFOAM. To verify coupling effect, the multi-regionally coupled analysesresults were compared with thermal fluid analysis of the internal fluid or heat conduction analysis of thevessel.1 INTRODUCTIONHydrothermal oxidative destruction reactor decomposes polychlorinated biphenyls (PCBs, C12H(10−n)Cln)into water (H2O), carbon dioxide (CO2) and sodium chloride (NaCl) by dechlorination with sodium car-bonate (Na2CO3) and oxidative decomposition with liquid oxygen (O2) under high temperature 370 °Cand high pressure 26.5 MPa [1]. In these reactor vessels, wall thinning due to corrosion was observed onbottom inner wall. At present, the reactors have been safely maintained and operated by adding a bottom1Tokihiro Sugimoto, Hiroyuki Kuramae, Masahide Matsumoto and Nobuhisa Watanabepartition to prevent chemical sinking and supplying hot water to the reactor vessel bottom to control thetemperature. Thermal fluid analysis of the hydrothermal oxidative destruction reactors is necessary toclarify the corrosion mechanism.A finite volume analysis (FVA) code OpenFOAM [2] is used to perform a coupled analysis of the internalfluid flow and heat conduction in the reactor vessel with multi-region considering the conjugate heattransfer on the solid-liquid interface. This paper describes verification of the multi-regionally coupledanalysis by comparing with single region analysis, which is thermal fluid analysis of the internal fluid orheat conduction analysis of the vessel body.2 METHOD OF THE ANALYSIS2.1 Governing equationsIn this study, since chemical reactions in hydrothermal oxidative decomposition of PCBs are not consid-ered, the internal fluid in the vessel assumes a single hot water. To analyze steady state of thermal fluidbehavior in the vessel, the continuous equation, the compressible Navier-Stokes equations with buoyancyforce, and the energy equation per unit mass with gravity terms are as follows:∇ · (ρu) = 0 (1)∇ · (ρu⊗u) =−∇prgh +∇ ·[µ{∇⊗u+(∇⊗u)T}]−∇(23µ∇ ·u)−g · x∇ρ (2)∇ · (ρhu) + ∇ · (ρKu) = ∇ ·(λcp∇h)+ρu ·g (3)where u,h,K = 12 u ·u,µ,λ,cp,g,x and prgh = p−ρg · x are velocity vector, specific enthalpy, kinetic en-ergy per unit mass, viscosity coefficient, thermal conductivity, specific heat, gravity acceleration vector,position vector and the absolute pressure p minus the static pressure, respectively. Although the energyequation (3) does not include heat generation term, the heat of chemical reaction is considered by aboundary condition. The thermophysical properties λ,cp,µ depend on temperature T . Also, the equationof state, which describes density ρ, only depends on the temperature because of high pressure 26.5 MPain the vessel. The turbulence is considered using the standard k-ε model.The heat conduction equation without heat generation term for the reactor vessel body is as follow:∇ ·(λρcp∇h)= 0 (4)where the thermophysical properties of the vessel body λ,ρ,cp are assumed to be constant without con-sidering the temperature dependence.2.2 Method of the coupled analysis using OpenFOAMIn the coupled analysis of heat transfer between the internal fluid and the vessel body (solid), the conti-nuities of temperature T and heat flux (−λ∇T ) are satisfied on the solid-liquid interface as follows:Tsolid = Tfluid (5)λsolid∇Tsolid = λfluid∇Tfluid (6)2Tokihiro Sugimoto, Hiroyuki Kuramae, Masahide Matsumoto and Nobuhisa Watanabeheat conduction analysis(solid)thermal fluid analysis(fluid)N-SequationEnergyequationThermophysical propertiesEquation of stateHeatconductionequationEquation ofcontinuityFigure 1: Flowchart of coupled analysisFigure 1 shows flowchart of the coupled analysis. In the fluid region, the energy equation is solved toobtain specific enthalpy h and converted to temperature T . The thermophysical properties ρ,µ,λ,cp areupdated using temperature T , and fluid analysis is performed by solving compressible Navier-Stokesequation. In the solid region, the obtained temperature on the solid-liquid interface is used to analyze theheat conduction. The energy equation is updated using the solid-liquid interface temperature of the solidregion and kinetic energy K. This calculation process is repeated until all solutions converge.In this study, the standard solver chtMultiRegionFoam of OpenFOAM v7 [2] is used. In order to comparethe analysis results, the thermal fluid analysis of the internal fluid using buoyantSimpleFoam and theunsteady heat transfer analysis of the vessel body using the laplacianFoam are also performed to comparethe analysis results.3 FINITE VOLUME MODEL AND ANALYSIS CONDITIONS3.1 Construction of 3D finite volume modelIn this study, 3-dimensional (3D) solid model shown in Fig. 2 was constructed using a 3D CAD softwarebased on the configuration drawing of the actual reactor. Although there are various structure parts suchas pressure sensing tubes inside the actual reactor, in this study, the analysis domain is from the bottomof the vessel to the height of 5 m in order to focus on the thermal flow phenomena at the bottom of thevessel.3Tokihiro Sugimoto, Hiroyuki Kuramae, Masahide Matsumoto and Nobuhisa WatanabeBottom supply inlet336.1°COxygen inlet19.1°C15.364m Treatment fluid inlet286.8°CMixing fluid inlet288.2°C1.816m1.2m5m0.741m(a) without partition (b) with partitionFigure 2: 3D solid model of hydrothermal destruction reactor vessel(a-1) symmetrical plane (a-2) cross section (b-1) symmetrical plane (b-2) cross section(a) without partition, total 7,457,054 cells (b) with partition, total 20,299,821 cellsFigure 3: Finite volume mesh4Tokihiro Sugimoto, Hiroyuki Kuramae, Masahide Matsumoto and Nobuhisa Watanabe0 100 200 300600800100000.001Temperature [℃]Density [kg/m3 ]Viscosity coefficient [Pas]DensityViscosity coefficient0 100 200 3000.40.50.60.740005000600070008000Temperature [℃]Thermal conductivity [W/mK]Specific heat capacity [J/kgK] Specific heat capacityThermal conductivity(a) density ρ and viscosity coefficient µ (b) heat conductivity λ and specific heat cpFigure 4: Temperature dependent thermophysical properties of fluidTable 1: Thermophysical properties of inconel alloy (NCF690, 20 °C)Density ρ 8200 kg/m3Specific heat cp 450 J/(kgK)Thermal conductivity λ 12 W/(mK)Table 2: Boundary conditionsFluid region Solid regionTemperature [°C] Velocity [m/s] Pressure [MPa] Temperature [°C]Mixing fluid inlet 288.2 0.6950 288.2Side wall of mixing fluid nozzle 288.2 non-slip 288.2Treatment fluid inlet 286.8 0.6040 286.8Side wall of treatment fluid nozzle 286.8 non-slip 286.8Oxygen inlet 19.1 0.0467 19.1Side wall of oxygen nozzle 19.1 non-slip 19.1Bottom supply inlet 336.1 0.0176 336.1Outlet (top surface) 369.9 uniform 26.5 369.9Outer wall of vessel — — — insulationInner wall of vessel heat transfer non-slip heat transferBottom partition heat transfer non-slip heat transferThe analysis of half model of the reactor vessel is carried out considering symmetry structure. Two typesof FVA models are constructed with and without the bottom partition to compare results.Unstructured FVA mesh is generated using a standard meshing utility snappyHexMesh of the Open-FOAM based on 3D geometry data in the standard triangulated language (STL) format of the 3D solidvessel models. Figure 3 shows FVA mesh. In the figure, yellow and light blue cells represent solid andfluid regions, respectively.5Tokihiro Sugimoto, Hiroyuki Kuramae, Masahide Matsumoto and Nobuhisa Watanabe3.2 Thermophysical properties and boundary conditionsIn order to express temperature dependence of the thermophysical properties of the internal fluid, densityρ [kg/m3], viscosity µ [Pas], thermal conductivity λ [W/(mK)], and specific heat cp [J/(kgK)] areapproximated by polynomial equations of temperature T [K],f (T ) =N∑i=0aiT i (7)as shown in Fig. 4, where N is degree of the polynomial, a0,a1, . . . ,aN are coefficients and are calcu-lated by least squares approximation. For the heat conduction analysis of the vessel body, temperatureindependent thermophysical properties of inconel (NCF690) are shown in Table 1.Boundary conditions of multi-regionally coupled analysis are summarized in Table 2. At each inletof the fluid region, temperature and flow velocity are set based on the measured values during actualoperation of the reactor. Since the oxygen nozzle has a double circular structure and is constantly cooledby cooling water, temperature on the side wall of the nozzle is set to 19.1 °C. At the outlet, which is thetop surface of the FV models, pressure is set to 26.5 MPa due to the measured value inside the actualvessel, and the uniform velocity outlet condition is configured. In addition, the outlet temperature is setto 369.9 °C, which is also the measured value, to simulate the heat generated by the chemical reaction inthe hydrothermal oxidative decomposition of PCBs. On the outer wall of the vessel of solid region, heattransfer is insulated. The conjugate heat transfer is considered on the solid-liquid interface that are innerwall of vessel and surfaces of bottom partition.4 RESULTS AND DISCUSSIONS4.1 Temperature distributionFigure 5 shows a comparison of the temperature distributions among the coupled analysis of thermal fluidand heat conduction, the thermal fluid analysis for the internal fluid, and the heat conduction analysisfor the vessel body. In all analysis results, the top surface is uniform 369.9 °C, which is the temperatureinside the actual vessel. The oxygen nozzle is at the lowest temperature of 19.1 °C, which has a coolingeffect on bottom of the vessel.Comparing the temperature distribution results at the bottom of the vessel, the results of the thermal fluidanalysis for the internal fluid is the lowest temperature, and the heat conduction analysis for the vesselbody is the highest temperature. In the thermal fluid analysis for the internal fluid, since the solid-liquidinterface acts heat insulation, the temperature is reduced by the descent of the fluid cooled by the oxygennozzle. The heat conduction analysis of the vessel body retains the hot water temperature at the inlet ofthe bottom. In contrast, the results of the coupled analysis are distributed between the temperatures ofthe other two results because of the heat transfer on the solid-liquid interface.As shown in Fig. 5 (b), since heat conduction does not occur across partition in the thermal fluid analysis,the temperature differs significantly between top and bottom of the partition. The results of the coupledanalysis show that the temperature in the lower region of the bottom partition is lower than without thepartition because advection is blocked by the bottom partition.Figure 6 shows comparisons of temperature distributions on the solid-liquid interface along a path fromthe center of the vessel bottom to the side wall on the symmetry plane opposite the oxygen nozzle as6Tokihiro Sugimoto, Hiroyuki Kuramae, Masahide Matsumoto and Nobuhisa Watanabe[°C](a-1) coupled (a-2) thermal fluid (a-3) heat conduction(a) without partition(b-1) coupled (b-2) thermal fluid (b-3) heat conduction(b) with partitionFigure 5: Temperature distribution7Tokihiro Sugimoto, Hiroyuki Kuramae, Masahide Matsumoto and Nobuhisa Watanabe0 0.2 0.4 0.6 0.80100200300Arc length [m]Temperature [°C]coupledthermal fluidheat conduction0 0.2 0.4 0.6 0.80100200300Arc length [m]Temperature [°C]coupledthermal fluidheat conduction(a) comparison location (b) without partition (c) with partitionFigure 6: Temperature comparison at bottom of the vessel[m/s](a-1) coupled (a-2) thermal fluid (b-1) coupled (b-2) thermal fluid(a) without partition (b) with partitionFigure 7: Velocity distribution in the vertical direction[m/s](a-1) coupled (a-2) thermal fluid (b-1) coupled (b-2) thermal fluid(a) without partition (b) with partitionFigure 8: Stream line8Tokihiro Sugimoto, Hiroyuki Kuramae, Masahide Matsumoto and Nobuhisa Watanabeindicated by the orange line in Fig. 6 (a). With or without the bottom partition, the heat conductionanalysis results of the vessel show higher temperature than the others because there is no advection byliquid oxygen and the fluid cooled by the oxygen nozzle. The results of the coupled analysis are higherthan those of the thermal fluid analysis because of heat conduction in the vessel body.4.2 Velocity distributionThe velocity distribution in the vertical direction which is height direction of the vessel is shown in Fig. 7in comparison with the coupled analysis and the thermal fluid analysis. The outlet on the top surface hasa uniform flow velocity, which is 0.00129 m/s in the vertical direction. The actual average flow velocity3m/h = 0.00083m/s for the entire reactor of height 15 m with an in-vessel processing time of 5 h issimilar order as the result around the top surface. In the bottom of the vessel, the fluid is cooled by theoxygen nozzles and is descended, and the hot water from the bottom inlet flows upward in both analysisresults. In the coupled analysis, the downward flow is more extensive because the temperature betweenthe oxygen nozzle and bottom of the vessel is larger than in the thermal fluid analysis.Streamlines at the bottom of the vessel are shown in Fig. 8. The streamline color indicates the verticalflow velocity. The bottom supply inlet flow rises hot water flowing but the fluid is fallen down by theoxygen nozzle cooling, then causing circulation. In coupled analysis, the downward flow is larger thanthe thermal fluid analysis.5 CONCLUSIONSIn this study, multi-regionally coupled analysis of thermal fluid for the internal fluid and heat conductionanalysis for the vessel body is performed for hydrothermal oxidative destruction reactor of PCBs. It isconsidering the heat transfer on the solid-liquid interface. The heat generation of the chemical reactioninside the reactor is introduced by setting the temperature boundary condition as measured during theactual operation. The effect of the coupled analysis is clarified by comparing the results with and withoutthe bottom partition, and the coupled analysis with the uncoupled analyses.ACKNOWLEDGMENTThe authors would like to acknowledge providing actual data of the hydrothermal oxidative destructionreactors and the financial support of the Tokyo PCB Waste Treatment Facility, Japan EnvironmentalStorage & Safety Corporation (JESCO).REFERENCES[1] Maeda, T., Ueda, K., Fukusumi, T., Shinoda K. and Tateishi, M. Treatment of PCB by HydrothermalDecomposition. Mitsubishi Heavy Industries Technical Review, (2001) 38-1: 32–35 (in Japanese).[2] OpenFOAM (Free CFD Software) The OpenFOAM Foundation, https://openfoam.org/9

Thermal Fluid Coupled Analysis of Hydrothermal Destruction Reactor

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Thermal Fluid Coupled Analysis of Hydrothermal Destruction Reactor

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