Coupled Conjugate Heat Transfer Research Articles

Thermal-fluid-structure coupling progressive failure analysis for the type III composite cylinder under localized fire

Predicting the failure characteristics of composite cylinders under fire is the key to improve the fire resistance and safety of cylinders. However, the current thermal-mechanical coupled failure analysis methods for composite cylinders under fire have several limitations such as oversimplification of the cylinder dome's geometric model and the fire source. To solve these problems, a comprehensive three-dimensional thermal-fluid-structure coupling progressive failure analysis method is developed. This method encompasses a fully coupled conjugate heat transfer model, a FLUENT-ABAQUS data transfer method, and a progressive failure analysis model integrates the Hashin failure criterion and nonlinear damage evolution for fiber reinforced composites. The method is adopted to analyze the fire-resistant performance of a type Ⅲ cylinder to obtain the fire-resistant time, failure pressure and burst location of the cylinder, finding that the pattern of failure pressure depreciation correlates with the burst location of cylinder under localized fire. Besides, the influence of the glass-fiber/epoxy layer on the fire-resistant performance of the cylinder is discussed, demonstrating that even a thin layer of glass-fiber epoxy can significantly increase the fire resistance time of the cylinder.

Two‐scale conjugate heat transfer solution for micro‐structured surface

AbstractThe primary challenges for simulating a turbulent flow over a micro‐structured surface arise from the two hugely disparate spatial length scales. For fluid–solid coupled conjugate heat transfer (CHT), there is also a time‐scale disparity. The present work addresses the scale disparities based on a two‐scale framework. For the spatial scale disparity, a dual meshing is employed to couple a global coarse‐mesh domain with local fine‐mesh blocks around micro‐structures through source terms generated from the local fine‐mesh and propagated to the global coarse‐mesh domain. The convergence and robustness of the source terms driven coarse‐mesh solution is enhanced by a balanced eddy‐viscosity damping. In this work, the two‐scale method previously developed only for a fluid‐domain is extended to a solid domain so that thermal conduction around micro‐elements can now be resolved accurately and efficiently. The fluid–solid timescale disparity is dealt with by a frequency domain approach. The time‐averaged (zeroth harmonic) is effectively obtained in the same way as steady CHT. And remarkably, wall temperature unsteadiness can be simply obtained from the fluid temperature harmonics through a wall fluid–solid temperature harmonic transfer‐function at minimal computational cost. The developed CHT capability is validated for an experimental internal cooling channel with multiple surface rib‐elements. For a test configuration with 100 micro‐structures, the fluid domain‐only, the solid domain‐only and the fluid–solid coupled CHT solutions are analyzed respectively to examine and demonstrate the validity of the present framework and implementation methods. Some of the results also serve to illustrate the primary underlying working of the methodology.

A coupled conjugate heat transfer and CFD model for the thermal runaway evolution and jet fire of 18650 lithium-ion battery under thermal abuse

Thermal runaway (TR) is a major safety concern for lithium-ion batteries. A TR model incorporating the resulting jet fire can aid the design optimization of battery modules. A numerical model has been developed by coupling conjugate heat transfer with computational fluid dynamics (CFD) to capture the cell temperature and internal pressure evolution under thermal abuse, venting and subsequent combustion of 18650 lithium-ion batteries. The lumped model was employed to predict the thermal abuse reactions and jet dynamics, while the vented gas flow and combustion were solved numerically. Model validation has been conducted with newly conducted experimental measurements for the transient flame height of jet fire and temperatures at selected monitoring points on the cell surface and above the cell. The validated model was then used to investigate the effect of the SOCs on the evolution of TR and subsequent jet fires. Increasing SOCs shortens the onset time of TR and enlarges the peak jet velocity. The peak heat release rates and flame height of the jet fire increase with the increase of SOC. The developed modeling approach extends the TR model to jet fire and it can potentially be applied to assist the design of battery modules. • A coupled conjugate heat transfer and computational fluid dynamics model. • Dynamic boundary conditions to couple internal and external parameters. • Capturing thermal runaway and jet fire behavior of lithium-ion battery.

Experimental and numerical investigation of the thermomechanical load on a turbine housing in a radial turbocharger

The fatigue life of turbine housing is an important index to measure the reliability of a radial turbocharger. The increase in turbine inlet temperatures in the last few years has resulted in a decrease in the fatigue life of turbine housing. A simulation method and experimental verification are required to predict the life of a turbine housing in the early design and development process precisely. The temperature field distribution of the turbine housing is calculated using the steady-state bidirectional coupled conjugate heat transfer method. Next, the temperature field results are considered as the boundary for calculating the turbine housing temperature and thermomechanical strain, and then, the thermomechanical strain of the turbine housing is determined. Infrared and digital image correlations are used to measure the turbine housing surface temperature and total thermomechanical strain. Compared to the numerical solution, the maximum temperature RMS (Root Mean Square) error of the monitoring point in the monitoring area is only 3.5%; the maximum strain RMS error reached 11%. Experimental results of temperature field test and strain measurement test show that the testing temperature and total strain results are approximately equal to the solution of the numerical simulation. Based on the comparison between the numerical calculation and experimental results, the numerical simulation and test results were found to be in good agreement. The experimental and simulation results of this method can be used as the temperature and strain (stress) boundaries for subsequent thermomechanical fatigue (TMF) simulation analysis of the turbine housing.

Fully Coupled Large Eddy Simulation-Conjugate Heat Transfer Analysis of a Ribbed Cooling Passage Using the Immersed Boundary Method

Abstract The study focuses on evaluating fully coupled conjugate heat transfer (CHT) simulation in a ribbed cooling passage with a fully developed flow assumption using large eddy simulation (LES) with the immersed boundary method (IBM-LES-CHT). The IBM-LES and the IBM-CHT frameworks are validated by simulating purely convective heat transfer in the ribbed duct, and a laminar boundary layer flow over a 2D flat plate with heat conduction, respectively. For the main conjugate simulations, a ribbed duct geometry with a blockage ratio of 0.3 is simulated at a bulk Reynolds number of 10,000 with a conjugate boundary condition applied to the rib surface. The nominal Biot number is kept at 1, which is similar to the comparative experiment. It is shown that the time scale disparity between turbulent fluid flow and heat conduction in solid can be overcome by using an artificially high solid thermal diffusivity. While the diffusivity impacts the instantaneous fluctuations in temperature and heat transfer, it has an insignificant effect on the predicted Nusselt number. Comparison between IBM-LES-CHT and iso-flux heat transfer simulations shows that the iso-flux case predicts higher local Nusselt numbers at the back face of the rib. Furthermore, the local Nusselt number augmentation ratio (EF) predicted by IBM-LES-CHT is compared with experiment and another LES conjugate simulation. The present LES calculations predict higher EFs on the leading face of the rib and show a different trend at the trailing face when CHT is activated.

Coupled conjugate heat transfer model for melting of PCM in cylindrical capsules

Phase change processes in latent heat thermal energy storage (LHTES) units are relevant, due to their ability in storing surplus power generated from renewable and conventional power plants. Macroencapsulation of phase change material (PCM) is one of several approaches to increase the mean discharging and charging power of such storage units. Numerical modelling and simulation in this context is a necessary alternative to rapid-prototyping to study solid-liquid phase change in latent heat thermal energy storage units. In this work, a numerical model is developed to represent the detailed thermal coupling between the heat transfer fluid (HTF) and phase change material capsules in a storage unit. An optimized iterative approach to represent the non-linear enthalpy-temperature and variable viscosity method for fixing and settling of solid phase in the capsule are employed in this work. Different computational domains for phase change material (PCM), heat transfer fluid (HTF) and capsule wall are employed, whose conjugated heat transfer is modelled in this work. A small representative latent heat thermal energy storage container is conceptualized to validate the developed conjugated heat transfer model. The melt front of phase change material is captured using photographic measurement in experiments over the complete melting time. The developed computational fluid dynamics (CFD) based conjugated heat transfer model has shown a very good agreement with experiments to estimate the heat transfer and melting of phase change material in the cylindrical capsule of a small scale latent heat thermal energy storage unit.

The effect of convective motion within liquid fuel on the mass burning rates of pool fires – A numerical study

To improve numerical simulation of liquid pool fires and remove the need for experimentally measured or empirically calculated mass burning rates as boundary conditions, a fully coupled three-dimensional (3-D) numerical formulation, which directly solves convective motion in the fuel region by incorporating inhomogeneous heat feedback, is formulated. The fire dynamics is modelled using the large eddy simulation (LES) approach. Incompressible laminar flow formation is applied to the liquid fuel region, assuming constant thermo-physical properties except for the density which follows the Boussinesq approximation. The numerical formulation of the two phases is solved using a fully coupled conjugate heat transfer approach at the pool surface. The coupled model is validated against published measurements for a thin-layer heptane pool fire and a deep methanol pool fire. The convective motion within the liquid phase is found to have important effects on the pool fire mass burning rate and its neglection would result in a fast rise and over-prediction of the mass burning rate.

Large-Eddy Simulation of a Model Aero-Engine Sooting Flame With a Multiphysics Approach

In this work, an in-house developed multiphysics unsteady approach (U-THERM3D) is employed to compute wall temperatures in a loosely coupled manner for a model aero-engine combustor, fueled with a non-premixed ethylene/air mixture and representative of the RQL technology. Large-Eddy Simulation (LES) is carried out to prove that scale-resolving approaches are required for a reliable prediction of turbulent mixing with respect to steady-state methods. A Flamelet Generated Manifold approach is adopted to describe the reactive flow, whereas two additional transport equations are included to predict the soot concentration. For a thorough investigation of the considered aero-engine combustor, cold flow results are firstly presented, highlighting the importance of an accurate predictions of general flow features. Then, the aerothermal fields are analysed to show the overall accuracy of the developed approach and so the impact of heat losses, comparing the results of an adiabatic simulation with respect to the loosely coupled conjugate heat transfer calculation. Finally, the investigation is focused on the prediction of the wall temperature distribution to prove the advantages of the U-THERM3D procedure with respect to steady-state approach.

Closely coupled fluid-solid interface method with moving-average for LES based conjugate heat transfer solution

Fluid–solid coupled Conjugate Heat Transfer (CHT) simulations are relevant to many practical problems. Most existing interfacing methods have been developed for Reynolds averaged Navier-Stokes solvers. For high fidelity turbulence scale-resolved flow solvers however, the CHT interface methods face significant challenges arisen from a wide frequency spectrum of unsteady disturbances to be dealt with, compounded by the huge time scale disparity between fluid and solid domains.In this paper, a closely coupled non-partitioned (monolithic) CHT method is presented. The main issues of interest are the prohibitive time costs of direct time domain CHT methods and an extra mesh dependency in the solid domain when resolving high frequency turbulence disturbances. Based on a temporal Fourier spectral framework, the present CHT interface method entails a moving-average for the time-mean flow and a discrete Fourier transform on-the-fly at each time step. Taking advantage of a semi-analytical transfer function and harmonic balancing for the CHT interface, we can achieve solving the solid domain completely in its own time step (3–5 orders of magnitude larger than that of the fluid domain). The present interface method can effectively circumvent aliasing errors and extra solid domain mesh-dependence encountered by other time-domain coupling methods when applied to turbulence scale-resolved CHT solutions. Illustrative stability analyses also show that the numerical stability of the present CHT interface should require no more stringent conditions than that in either fluid or solid domain. The computational results and analyses highlight the advantages of the present methodology in terms of both the computational efficiency and accuracy, in comparison with a conventional directly coupled interface method. Furthermore, a case study aided by a simple interface response analysis highlights much augmented wall temperature fluctuations and higher sensitivity to the interface treatment when a low conductivity protection layer (Thermal Barrier Coating, TBC) is added. The present study underlines the relevance of accounting for fluid disturbances over a range of frequencies in an effective and accurate CHT interface treatment.

Coupled conjugate heat transfer and heat production in open-cell ceramic foams investigated using CFD

Combining low pressure drop and remarkable heat transport properties, open-cell foams offer a combination that makes them a highly attractive option as monolithic catalyst support. The coupled thermal behavior of foams and fluids during heat production, e.g., exothermic chemical reactions, is still not thoroughly described despite their potential to optimize temperature control in fixed-bed reactors. Hence, the aim of this study is to get deeper insight into coupled conjugate heat transfer and heat production in open-cell foams used in a tubular reactor with constant wall temperature. Therefore, we conducted - μCT-based CFD simulations of open-cell foams with artificial heat sources that mimic the heat of reaction during an exothermal chemical reaction and allow to study the effect of heat production on heat transfer while requiring lower computational cost than simulating actual chemical reactions. We implemented a range of heat source intensities, that covers typical exothermic reactions, to study their effect on heat flows as well as temperature fields and used CO2 methanation as a case study. We further quantified the influence of superficial velocity, heat source intensity, and material on the temperature fields inside the foam and found conduction being the dominant heat transport mechanism. We further evaluated the feasible range of even more simplified pseudo-homogeneous models and found high thermal conductivities and low superficial velocities to be appropriate. In conclusion, the presented approach offers the possibility to study thermal effects regarding catalytic supports and give valuable insight in heat transport mechanisms under relevant process conditions in heterogeneous catalysis (heat sources: 5–150 W for a reaction volume of 1.2 × 10−5 m3, superficial velocities 0–0.51 m s−1, thermal conductivities 5–50 W m−1 K−1).

Numerical modelling of transient heat transfer of hydrogen composite cylinders subjected to fire impingement

To improve the current design standards of the hydrogen composite cylinders, it is essential to understand the thermal response of the hydrogen composite cylinders subjected to fire impingement. In the present study, a fully coupled conjugate heat transfer model based on a multi-region and multi-physics approach is proposed for modelling the transient heat transfer behaviour of composite cylinders subjected to fire impingement. The fire scenario is modelled using the in-house version of FireFOAM, the large eddy simulation (LES) based fire solver within the frame of OpenFOAM. Three dimensional governing equations based on the finite volume method are written to model the heat transfer through the regions of composite laminate, liner and pressurized hydrogen, respectively. The governing equations are solved sequentially with temperature-dependent material properties and coupled interface boundary conditions. The proposed conjugate heat transfer model is validated against a bonfire test of a commercial Type-4 cylinder and its transient heat transfer behaviour is also studied.

Flame–wall interaction effects on the flame root stabilization mechanisms of a doubly-transcritical LO2/LCH4 cryogenic flame

High-fidelity numerical simulations are used to study flame root stabilization mechanisms of cryogenic flames, where both reactants (O2 and CH4) are injected in transcritical conditions in the geometry of the laboratory scale test rig Mascotte operated by ONERA (France). Simulations provide a detailed insight into flame root stabilization mechanisms for these diffusion flames: they show that the large wall heat losses at the lips of the coaxial injector are of primary importance, and require to solve for the fully coupled conjugate heat transfer problem. In order to account for flame–wall interaction (FWI) at the injector lip, detailed chemistry effects are also prevalent and a detailed kinetic mechanism for CH4 oxycombustion at high pressure is derived and validated. This kinetic scheme is used in a real-gas fluid solver, coupled with a solid thermal solver in the splitter plate to calculate the unsteady temperature field in the lip. A simulation with adiabatic boundary conditions, an hypothesis that is often used in real-gas combustion, is also performed for comparison. It is found that adiabatic walls simulations lead to enhanced cryogenic reactants vaporization and mixing, and to a quasi-steady flame, which anchors within the oxidizer stream. On the other hand, FWI simulations produce self-sustained oscillations of both lip temperature and flame root location at similar frequencies: the flame root moves from the CH4 to the O2 streams at approximately 450 Hz, affecting the whole flame structure.

Full conjugate heat transfer modelling for steam turbines in transient operations

Steam turbines are increasingly required to operate more flexibly, leading to a need for more detailed calculations and design considerations of the thermal conditions during transient operations. A major challenge in transient thermal designs is the time scale disparity. For the natural cooling of a turbine, the physical process is typically in hours or tens of hours, but on the other hand, the time step sizes typically usable tend to be very small, in seconds or sub-seconds, due to the numerical stability requirement for natural convection as often encountered.The present paper reports a validation and demonstration study of a new loosely coupled conjugate heat transfer (CHT) approach developed for efficient and accurate simulations of steam turbine transient operations (Shut-down/Natural cooling). The verification and validation have been carried out for a complex 3D geometry configuration with attributes of realistic but geometrically simplified full-scale steam turbines and compared with a well-established simplified working method backed up by experimental data. Further comparisons are made against a direct baseline CHT method. The present results demonstrate a generally good agreement with the simplified working method. The new loosely coupled method is shown to give a marked speed-up (by a factor of 240) compared to the baseline directly coupled method with the same accuracy. It thus offers the potential for significant improvement in predicting the long-duration transient natural convection conjugate heat transfer problems of steam turbines in terms of computational efficiency and accuracy.

The Simulation Investigation on Fluid-solid Coupled Conjugate Heat Transfer for Spool Valve Based on COMSOL

The Simulation Investigation on Fluid-solid Coupled Conjugate Heat Transfer for Spool Valve Based on COMSOL

Self-adaptive coupling frequency for unsteady coupled conjugate heat transfer simulations

Tackling transient conjugate heat transfer with high-fidelity methods such as large-eddy simulation (LES) requires to couple the LES solver with a heat transfer solver in the solid parts of the computational domain. Challenges include performance scalability, numerical stability and accuracy. In such unsteady simulations, both solvers integrate their respective set of equations in time independently for the sake of computational efficiency, and during a physical time corresponding to a coupling period to be specified. During the separate temporal integrations, the thermal state at the wall interface is typically set as a Dirichlet condition in the flow solver while a Neumann condition is imposed in the heat transfer solver to enhance numerical stability. When carefully validated, the chosen value of the coupling period which optimal value is initially unknown can be compared a posteriori with a refined solution. However, this optimal value of the coupling period (neither too large to remain accurate nor too short not to penalize the computational cost) is case-dependent.In this study, an approach to automatically adapt the coupling period is presented. It relies on a describing the temporal evolution of the boundary temperature in hybrid cells composed of the neighboring fluid and solid mesh cells. Then, between coupling iterations, each solver advances separately with the same Dirichlet boundary condition on the computed interface temperature. Yielding a first order Ordinary Differential Equation (ODE) for the boundary temperature, the method allows using automatic adaptation of the step size to control the numerical integration error based on a prescribed tolerance by using controllers.The coupling method is studied on 1D unsteady configurations where the results demonstrate that this energy conserving method is able to determine the coupling period automatically and efficiently for different configurations. The impact of excitation frequency and prescribed tolerance enables to select a specific PID controller which remains robust in spite of not carrying out step rejections for the sake of computational performance in the context of an LES application.

Efficiency of coupling schemes for the treatment of steady state fluid-structure thermal interactions

Partitioned approaches for the simulation of coupled conjugate heat transfer are gaining popularity in fields that require accurate thermal predictions. Considerable efforts have been put into determining stable coupling schemes, but performance enhancements have been neglected. This paper presents, for the first time, a detailed and comprehensive study of the numerical properties of Dirichlet-Robin coupling procedures, used in conjugate heat transfer simulation, with emphasis put on the optimal local coupling formulation that was recently derived from a stability analysis. This all-new optimal coupling approach provides local adaptability and has never been tested on a complex setup. This investigation looks to determine the relevance and the limitations of the theory when applied to complex conjugate heat transfer setups. The stability theory of the optimal Dirichlet-Robin coupling scheme is first recalled, then, a realistic 3D application, with complex geometry and flow structures, is used to evaluate the performance and sensitivity of Dirichlet-Robin couplings, with respect to various numerical parameters. This detailed study allows, for the first time, to evaluate the advantages and limitations of the recently proposed optimal procedure, when used on realistic 3D CHT problems. It turns out that the local optimal Dirichlet-Robin formulation outperforms all what is found in literature, and insures unconditional stability with monotone convergence for all considered setups of the 3D model.

Use of the method of manufactured solutions for the verification of conjugate heat transfer solvers

This paper demonstrates the use of the method of manufactured solutions to verify the implementation of tightly coupled conjugate heat transfer for fluid-solid solvers. The interface conditions in the prescribed manufactured solutions were implemented to mimic real effects such as no-slip, and temperature/heat flux match between the solid and fluid domains. The newly developed solid heat transfer solver was verified in standalone mode using this prescribed manufactured solution and was found to have no apparent coding errors. Our pre-existing in-house compressible fluid solver (Eilmer) was used to demonstrate the conjugate heat transfer implementation. Both the fluid and solid solvers showed an expected spatial order of convergence of 2.0 in the standalone mode. The coupled conjugate heat transfer mode also showed no coding errors and demonstrated that the spatial order of convergence was again 2.0. The one-sided spatial discretisation utilised to enforce the tight coupling for the interface conditions were effectively equivalent to a central difference. Hence, the overall spatial order of the error convergence for the entire domain, including the interface, was 2.0. The method prescribed in this work can be extended for verification of other conjugate heat transfer solvers, in particular for compressible flow scenarios where analytical solutions may not be readily available.

Conjugate heat transfer analysis for in-vessel retention with external reactor vessel cooling

A conjugate heat transfer analysis method for the thermal integrity of a reactor vessel under external reactor vessel cooling conditions is developed to resolve light metal layer focusing effect issue for in-vessel retention. The method calculates steady-state three-dimensional temperature distribution of a reactor vessel using coupled conjugate heat transfer between in-vessel three-layered stratified corium (metallic pool, oxide pool and heavy metal and polar-angle dependent boiling heat transfer at the outer surface of a reactor vessel). The three-layer corium heat transfer model is utilizing lumped-parameter thermal-resistance circuit method. For the ex-vessel boiling boundary conditions, nucleate, transition and film boiling are considered. The thermal integrity of a reactor vessel is addressed in terms of heat flux at the outer-most nodes of the vessel and remaining thickness profile. The vessel three-dimensional heat conduction is validated against a commercial code. It is found that even though the internal heat flux from the metal layer goes far beyond critical heat flux (CHF) the heat flux from the outermost nodes of the vessel may be maintained below CHF due to massive vessel heat diffusion. The heat diffusion throughout the vessel is more pronounced for relatively low heat generation rate in an oxide pool. Parametric calculations are performed considering thermal conditions such as peak heat flux from a light metal layer, heat generation in an oxide pool and external boiling conditions. The major finding is that the most crucial factor for success of in-vessel retention is not the mass of the molten light metal above the oxide pool but the heat generation rate inside an oxide pool and the three-dimensional vessel heat transfer provides much larger minimum vessel thickness.

Low Energy Direct Contact Membrane Desalination: Conjugated Heat and High Fidelity Flow Simulation

The steady state performance of Low Energy Direct Contact Membrane Distillation (DCMD) is numerically investigated. A case of uniform flow is considered entering both the feed side at a temperature above the permeate side. The developed fluid model is governed by the Navier-Stokes flow and energy equation in a coupled conjugate heat transfer formulation to the flow and the solid membrane. Across the membrane and depending on the membrane parameters including permeability, thickness, pore size and conductivity the local temperature difference creates a driving pressure gradient responsible of evaporation part of the feed adjacent to the membrane surface, transport it through the pores, and condense it at permeate side through the hydrophobic membrane. The membrane's coefficients of DCMD membrane is evaluated along with the mass flux, heat flux, temperature polarization factor, and thermal efficiency. In this paper, two flow configurations are studied: Counter and Parallel flow. A parametric study is conducted incorporating velocity combinations and concluding an optimum configuration in terms of DCMD efficiency, mass flux. In view of these plausible results, a sensitivity study to the flow rates is carried out to gain better insight to the temperature polarization, heat flux including convective, conductive and the associated latent heat as well as in understanding its effect on the process metrics and yield.

A heat exchanger analogy of automotive paint ovens

Computational prediction of vehicle temperatures in an automotive paint oven is essential to predict paint quality and manufacturability. The complex geometry of vehicles, varying scales in the flow, transient nature of the process, and the tightly coupled conjugate heat transfer render the numerical models computationally very expensive. Here, a novel, simplified model of the oven is developed using an analogy to a three-stream cross flow heat exchanger that transfers heat from air to a series of moving bodies and supporting carriers. The analogous heat exchanger equations are developed and solved numerically. Steady state Computational Fluid Dynamics (CFD) simulations are carried out to model the flow field and to extract the heat transfer coefficients around the body and carriers. The air temperature distribution from the CFD models is used as a boundary condition in the analogous model. Correction coefficients are used in the analogy to take care of various assumptions. These are determined from existing test data. The same corrections are used to predict air temperatures for a modified configuration of the oven and a different vehicle. The method can be used to conduct control volume analysis of ovens to determine energy efficiency, and to study new vehicle or oven designs.