Thermal Fluid Flow Research Articles

Investigation of thermal evolution and fluid flow in the hot-end of a material extrusion 3D Printer using melting model

This work presents Computational Fluid Dynamics (CFD) simulations of the thermal evolution and fluid flow in the hot-end during material extrusion in fuse filament fabrication (FFF) additive manufacturing. The hot-end is the most fundamental and complex part of a FFF 3D printer. The fluid dynamics during material extrusion depend on the hot-end design while the printing speed depends on the speed at which the hot-end can melt the filament. In this work, a new melting model developed specifically for the FFF process is introduced. The CFD melting model incorporated the liquid fraction evolution to account for the presence of an air gap between the liquefier wall and the solid filament. For the first time, the thermal contact resistance was implemented using a melting model. The governing transport equations for the melting model were presented both in the dimensional primitive and non-dimensional primitive representations to understand the relevance of each term in a physical sense. The model equations were implemented with the aid of written user-defined function (UDF) codes coupled in the ANSYS Fluent. The grids were refined systematically to ensure that the influence of the mesh size on the computational results is minimized. The Richardson extrapolation technique was used to estimate the grid convergence index (GCI) and to quantify discretization error. The maximum discretization error is found to be 1.68%, which is an indication that the solution is in the asymptotic range. The thermal boundary conditions were implemented using simple liquid fraction-heat transfer coefficient relation and the results were validated using previously measured feeding force by Serdeczny et al. [1]. The predicted feeding force agrees reasonably with the measured feeding force. The model predicted a strong counter-clockwise recirculating vortex close to the barrel inlet. The further simulation revealed that the filament did not melt immediately at entry into the heated barrel, and variation in the barrel length indicates that the solid penetration depth ratio increases with an increase in the P é clet-number ( Pe ). Since high-speed 3D printing depends on the flow rate, an optimized thermal dissipation is desired in the hot-end. Our approach in presenting the model equations and subsequent results obtained should advance the understanding of the flow characteristics in the liquefier hot-end and thermal history within the barrel and the nozzle exit. Hence, the presented melt flow dynamics model would help in developing hot-end designs for 3D printers capable of melting filaments at an improved rate, by reducing the barrel length and printing at a higher liquefier temperature, while preheating the solid filament. • A new CFD melting model developed specifically for the FFF process is introduced. • Thermal contact resistance was implemented using the CFD melting model. • Effect of the air gap between the filament and the liquefier wall was implemented. • The true position of the melting front at the liquefier center was identified. • CFD Grid Sensitivity Analysis reveals solution is within the asymptotic limits.

Coupled thermo-hydro-chemical effect on rheological behavior of fresh cemented tailings backfill

Cemented tailings backfill (CTB) is a mixture of tailings, binder and water. The freshly prepared CTB slurry is commonly transported into underground mined-out areas via pipeline. The flowability of fresh CTB slurry is significantly affected by the coupled thermal (T), hydraulic (H), rheological (R) and chemical (C) processes. Therefore, this paper develops a THRC coupling model, which considers the evolutions of thermal conduction, fluid flow, rheology, and binder hydration to predict the fluidity of fresh CTB slurry. Rheological testing experiments are conducted to verify the availability of the developed model. The validated model is used to further investigate the effect of time and temperature factors on the hydraulic behavior of the hydrating CTB slurry. The obtained outcomes can make contributions to a better regulation of the time and temperature factors in the preparation and transportation of fresh CTB slurry.

The relationship between the macro- and microstructure and the mechanical properties of selective-laser-melted Ti6Al4V samples under low energy inputs: Simulation and experiment

The occurrence of structural defects in selective laser melting (SLM) damages the mechanical properties and fabrication accuracy of components and is closely related to the processing parameters. Therefore, having a good grasp of the interaction mechanism between the material and laser is useful for designing an improved process window. In this study, we experimentally investigated the relationship between the samples' macro- and microstructure and their mechanical properties under low energy inputs, and the response behaviour of as-built parts under these parameters was calculated using a thermal fluid flow (TFF) model with a modified and surface-tracking heat source. The results showed that Ti6Al4V parts obtained via SLM under low energy inputs exhibited a strong relationship between the macro- and microstructure and the mechanical properties. Single-track TFF models were built to better understand the underlying phenomena that are influenced by process parameters and then affects the depositing process. The models provided insight into the thermal history, deposition behaviour, densification, size accuracy, and surface morphology and by considering the velocity field, the phenomenon of powder adhesion caused by the Bernoulli effect could be investigated. Interestingly, the TFF model with a volume energy density (Ev) of 90 J/mm3 captured the formation of pores, however, high smoothness of the surface and size accuracy was obtained in the sample. It can be proved that densification is hardly related to the surface morphology or the fabrication precision. In addition, our experiments showed that the fabrication process was less sensitive to process parameters at Ev = 38 J/mm3. Densification was also more sensitive to the laser power than to the scanning speed.The results suggest that good-quality samples can be synthesised via SLM under low energy inputs, and the TFF model is a powerful tool for the systematic optimisation of the process parameters. Our findings could be applied to improve the controllability of the overhang surface with severe powder adhesion in further studies.

Experimental and Simulation of Solar Drying Cabinet with PCM and SiO2 Materials

Solar energy is a potential renewable source in Indonesia, especially for the drying process. The process needs a drying cabinet as a support component to store the drying product. A high-quality drying cabinet to store heat for a long time is needed. This research aims to compare the thermal performance of the drying cabinet without PCM (phase change material) and SiO2 materials or DC I (drying cabinet I) with the drying cabinet that uses PCM and SiO2 materials or DC II (drying cabinet II). The research was carried out by experimental and simulation to investigate thermal performance and fluid flow characteristics. The experiment was carried out inside the laboratory to set uniform initial parameters and the simulation using computational fluid dynamics software. The drying cabinet was modeled in 3D. The experiment result showed DC II had a higher air temperature and lowered relative air humidity for two hours than DC I. The simulation result showed air temperature differences and backflow in the air streamline in the DC II.

Crystal plasticity model of residual stress in additive manufacturing using the element elimination and reactivation method

Selective laser melting is receiving increasing interest as an additive manufacturing technique. Residual stresses induced by the large temperature gradients and inhomogeneous cooling process can favour the generation of cracks. In this work, a crystal plasticity finite element model is developed to simulate the formation of residual stresses and to understand the correlation between plastic deformation, grain orientation and residual stresses in the additive manufacturing process. The temperature profile and grain structure from thermal-fluid flow and grain growth simulations are implemented into the crystal plasticity model. An element elimination and reactivation method is proposed to model the melting and solidification and to reinitialize state variables, such as the plastic deformation, in the reactivated elements. The accuracy of this method is judged against previous method based on the stiffness degradation of liquid regions by comparing the plastic deformation as a function of time induced by thermal stresses. The method is used to investigate residual stresses parallel and perpendicular to the laser scan direction, and the correlation with the maximum Schmid factor of the grains along those directions. The magnitude of the residual stress can be predicted as a function of the depth, grain orientation and position with respect to the molten pool. The simulation results are directly comparable to X-ray diffraction experiments and stress–strain curves.

3D Numerical Simulation of Turbulent Mixed Convection in a Cubical Cavity Containing a Hot Block

The considerable quantities of heat transfer are dissipated during the operating electronic/electrical systems and have harmful effects on the operating time. So; to keep these systems in good working condition, the location of efficient mechanical cooling systems is essential. The heat transfer rate in an enclosure intensely depends on the combination of geometrical and physical parameters. For this purpose, a 3D Numerical simulation of turbulent mixed convection in a cubical cavity containing an internal heat source in its middle was carried out. The cavity has an inlet port at the lower left face area and an outlet port located in the upper right face area. The analyses are performed for air at ambient circumstances (Pr = 0.71) and the variation of interval for Richardson number (Ri) is chosen between 0.01 and 30 to investigate three situations: dominated forced convection, natural convection, and mixed convection for a fixed dimension of the enclosure in turbulent regimes (Gr = 109). The effects of the variation of Ri, the dimensionless time, and the dynamic parameters on the thermal flow and fluid flow phenomena are presented and discussed. The obtained results show an exchange between the forces of pressure and of buoyancy in the studied interval and a strong dependence between the geometrical parameters and the heat transfer rate, and then the correlations of the combination of the parameters were proposed.

Additive manufacturability of superalloys: Process-induced porosity, cooling rate and metal vapour

Digital technology such as metal additive manufacturing (AM) provides flexible process design freedom to fabricate intricate three-dimensional structures layer-by-layer. However, its manufacturability relies on the fundamental understanding of melt pool physics and fluid (metal) dynamics. The effect of metal vapour and porosity induced during the laser-materials interaction can influence the additive manufacturability. In this work, composition-process relationship of laser-based powder-bed fusion (L-PBF) AM is studied via computational fluid dynamics modelling to rationalise solid-liquid-vapour transformation where empirical-based approach is used to generate thermo-physical property of about 100 nickel-based superalloys at the liquid state. It is found that with larger vapor mass loss, the porosity tends to be higher. However, the higher vapour mass loss means faster cooling rate. This is indicated that the thermal-fluid flow process, which is also governed by the thermo-physical property, strongly affects the additive manufacturability. Additive manufacturability map based upon porosity, cooling rate from liquid to solid, volatile mass loss criteria has been established to link the composition in nickel-based superalloys with their thermo-physical property. This offers a thermal-fluid science based tool in designing compositions of novel superalloys for AM applications.

Interpretation of TRT data in the presence of natural convection and groundwater flow in saturated ground

Ground thermal properties play important roles in the design of geothermal heat exchangers (GHEs). Constant ground thermal properties, as often considered in analysis and design of GHEs, often do not account for the coupled effect of thermal and pore fluid flow in saturated ground. This paper presents a series of advanced finite element analyses (FEAs) of thermal response test (TRT) on a geothermal borehole heat exchanger (BHE) installed in uniform and multi-layered saturated soil deposits. Considering coupled thermo-hydro flow in saturated ground, FEAs explore the effects of ground hydraulic characteristics (e.g., groundwater flow, soil permeability), power injection rate, and duration of thermal response test on the value of effective ground thermal conductivity keff. Results show that the value of keff, in the presence of coupled thermo-hydro flow condition, can be multiple times of the thermal conductivity value estimated considering only conductive heat transport in coarse grained soil. Example calculations following two available BHE design standards confirm that consideration of soil permeability and selection of appropriate duration of TRT may lead to significant reduction in the design length of BHEs.

Multiphysics simulation of single pulse laser powder bed fusion: comparison of front capturing and front tracking methods

PurposeDuring thermal laser processes, heat transfer and fluid flow in the melt pool are primary driven by complex physical phenomena that take place at liquid/vapor interface. Hence, the choice and setting of front description methods must be done carefully. Therefore, the purpose of this paper is to investigate to what extent front description methods may bias physical representativeness of numerical models of laser powder bed fusion (LPBF) process at melt pool scale.Design/methodology/approachTwo multiphysical LPBF models are confronted: a Level-Set (LS) front capturing model based on a C++ code and a front tracking model, developed with COMSOL Multiphysics® and based on Arbitrary Lagrangian–Eulerian (ALE) method. To do so, two minimal test cases of increasing complexity are defined. They are simplified to the largest degree, but they integrate multiphysics phenomena that are still relevant to LPBF process.FindingsLS and ALE methods provide very similar descriptions of thermo-hydrodynamic phenomena that occur during LPBF, providing LS interface thickness is correctly calibrated and laser heat source is implemented with a modified continuum surface force formulation. With these calibrations, thermal predictions are identical. However, the velocity field in the LS model is systematically underestimated compared to the ALE approach, but the consequences on the predicted melt pool dimensions are minor.Originality/valueThis study fulfils the need for comprehensive methodology bases for modeling and calibrating multiphysical models of LPBF at melt pool scale. This paper also provides with reference data that may be used by any researcher willing to verify their own numerical method.

Numerical study of supercritical octane flows with multicomponent effects by pyrolysis

This study focuses on supercritical octane flow simulation with pyrolysis reactions in a heated circular pipe to determine the multicomponent effects of changes in thermophysical properties. The reaction rate of n-octane for pyrolysis was estimated by a zeroth-dimensional simulation of hydrocarbon pyrolysis. The resulting mole fractions of the decomposed components were compared with the experimental data. The mole fraction results were then used to develop three thermophysical property models for the mixture of unreacted n-octane and decomposed hydrocarbons, i.e., 1-, 4-, and 12-component models. In the supercritical octane flow simulations, the multicomponent thermophysical properties of each component model were determined using the polynomial equations in the Reference Fluid Thermodynamic and Transport Properties Database. The conventional k−ω SST model and k−ωSST+Mτ model served as the Reynolds-averaged Navier–Stokes turbulence models. In cases with a low wall temperature, the outlet temperatures in all component models were consistent with the experimental data, in which pyrolysis did not occur. In cases with a high wall temperature above 973 K, the density change and production of kinetic energy affected the turbulent thermal diffusivity in the heated pipe. In cases where the multicomponent effects of thermophysical properties and turbulence were considered, the numerical method reproduced a reasonable outlet temperature and conversion rate, whereas the experimental results were underestimated in all the other cases. These numerical results indicate that the accurate prediction of density changes and the production of turbulent kinetic energy are the key issues in reproducing thermal fluid flows of supercritical hydrocarbons with pyrolysis reactions in uniform wall temperature cases.

Propagation of Input Uncertainties in Numerical Simulations of Laser Powder Bed Fusion

Laser powder bed fusion has the potential of redefining state-of-the-art processing and production methods, but defect formation and inconsistent build quality have limited the implementation of this process. Numerical models are widely used to study this process and predict the formation of these defects. Presently, the uncertainties of model input parameters and thermophysical properties used by these numerical simulations have not been investigated. In the present study, the uncertainty in these input parameters and material properties are quantified for laser powder bed fusion, with and without a simulated powder bed, to determine their influence on the predictive accuracy of an experimentally validated numerical model. Accounting for all possible sources of uncertainty quickly becomes computationally expensive on account of the curse of dimensionality. Uncertainty in laser absorption, solid, and liquid specific heat of the metal were found to have the largest effect on model prediction reliability with or without the use of a powder bed. Results also illustrate that accounting for these three uncertain parameters still captures the majority of model prediction uncertainty. Furthermore, the methodology of this study may be used to understand the uncertainty in as-built microstructure through propagation to microstructure prediction models, or applied under processing conditions where high Péclet numbers are observed and the thermal convection and fluid flow within the molten pool are substantial.

Thermoelectric Magnetohydrodynamic Model for Laser-Based Metal Additive Manufacturing

Magnetic fields are recently being applied to metal additive manufacturing to control the molten pool dynamics and dendritic morphology. To study the molten pool dynamics under an external magnetic field, a thermoelectric magnetohydrodynamic (TEMHD) model is developed by incorporating the electrodynamic model with the Seebeck effect into the multiphysics thermal-fluid flow model. The Seebeck effect in the molten pool is analyzed with the simulation of stationary laser melting on a bare plate. Furthermore, different external magnetic fields are assigned in the TEMHD simulations with the stationary laser melting and the results show that the Lorentz force can damp the keyhole fluctuations. Finally, the laser scanning simulations on a bare plate under external magnetic fields indicate that the Lorentz force can smooth the fluid flow fields in the molten pool and increase the ratio of equiaxed grains in the solidification front.

A study of thermal distribution and fluid flow by natural convection inside a building enclosure with a centrally placed hot channel section using CFD

The thermal distribution and fluid flow by natural convection inside a closed cool enclosure is studied. A channel section is placed at the center of the compartment and its temperature is hot. Buoyancy flow is induced inside the enclosure due to the thermal variation. Air is considered as the fluid inside the enclosure and its Prandtl number is 0.71. The fluid is expected to obey Boussinesq approximation. To evaluate the flow, the streamline, isotherms, horizontal and vertical centerline velocity and Nusselt numbers were calculated. The flow is modified by changing the Rayleigh number from 103 to 106. The results show the influence of Rayleigh number on the flow pattern, velocity of fluid flow, and heat transfer rate. Computational fluid dynamics is used as the tool for this study.

CFD Comparative Study Between Different Forms of Solar Greenhouses and Orientation Effect

Only scarce studies that were adopted have considered two properties, the structure safety and energy, where the aero-dynamic and energetic phenomena were taken into account simultaneously in the agricultural greenhouses area. In fact, in this numerical study, the response of the greenhouse has been investigated in outside climate conditions, by considering the orientation relatively to the wind direction velocity and solar trajectory. A resolution of the physical problem combined between the thermal and dynamical fluid flow equations have been based on the Ansys Fluent software. The results showed that the difference between inside and outside air temperature of greenhouse has been strongly affected by the reorientation of the tunnel greenhouse structure, or by the design of the tunnel structure that was adopted in the dome and chapel shape. Moreover, the safety properties of greenhouse structure linked to the drag stress can be developed when based on the interaction fluid-structure analysis. In this view, a temperature profile evolution versus different heights inside greenhouse was highlighted. As well as like continues of our previous study of the drag evolution over tunnel design body proved by the results found in the literature will be compared with chapel and dome designs.

Phase-field modeling of grain evolutions in additive manufacturing from nucleation, growth, to coarsening

A three-dimensional phase-field model is developed to simulate grain evolutions during powder-bed-fusion (PBF) additive manufacturing, while the physically-informed temperature profile is implemented from a thermal-fluid flow model. The phase-field model incorporates a nucleation model based on classical nucleation theory, as well as the initial grain structures of powder particles and substrate. The grain evolutions during the three-layer three-track PBF process are comprehensively reproduced, including grain nucleation and growth in molten pools, epitaxial growth from powder particles, substrate and previous tracks, grain re-melting and re-growth in overlapping zones, and grain coarsening in heat-affected zones. A validation experiment has been carried out, showing that the simulation results are consistent with the experimental results in the molten pool and grain morphologies. Furthermore, the grain refinement by adding nanoparticles is preliminarily reproduced and compared against the experimental result in literature.

3D numerical simulation of a novel ventilated roof: thermal performance analysis and fluid flow behavior

This paper presents a numerical simulation of a ventilated roof based on a novel plastic support especially designed to reduce the solar heat gains by improving the airflow distribution as compared to a traditional one. In order to evaluate the benefits of the new configuration, a 3 D numerical model was developed allowing for a deep understanding of the airflow distribution inside the ventilated roof channels. The simulations were performed by varying the solar irradiance from 600 to 1000 W m−2 assuming buoyancy-driven airflow. The investigation was conducted by comparing the new proposed ventilated roof assembly to the traditional layouts. In particular, two roof types were considered as benchmarks: an insulated roof and a non-insulated one. When compared to the traditional ones, the results revealed that the innovative ventilated roof led to a great reduction (up to 70%) of the total amount of solar heat gains for all the simulated scenarios.

Digital materials design by thermal-fluid science for multi-metal additive manufacturing

Metal additive manufacturing is promising for designing advanced metallic parts of complex geometries. The challenge lies in process control on melt flow dynamics, alloy mixing and vapour mass loss, which is significantly vital for the final quality. A high-fidelity thermal-solutal-fluid modelling approach including accurate tracking of surface shape, thermo-capillary dynamics and vaporisation has been developed. Multi-species formulations are also included for multi-metal simulation. Using this method, the physical link between metal vapour mass loss and melt flow process for 21 transition metals and 3 binary alloys is investigated. The mass loss rate is governed by a fluid dynamic parameter of Reynolds number with a simple proportional correlation linked with thermal-fluid behavior of the melt pool, and convective mixing further complicates the behaviour in in-situ binary alloying. The digital materials approach is effective in understanding complex interdependent thermal-fluid flow dynamics and can advance process-based materials design.

Digital Materials Design by Thermal-Fluid Science for Multi-Metals Additive Manufacturing

Metal additive manufacturing is promising for designing advanced metallic parts of complex geometries. The challenge lies in process control on melt flow dynamics, alloy mixing and vapour mass loss, which is significantly vital for the final quality. A high-fidelity thermal-solutal-fluid modelling approach including accurate tracking of surface shape, thermo-capillary dynamics and vaporisation has been developed. Multi-species formulations are also included for multi-metals simulation. Using this method, the physical link between metal vapour mass loss and melt flow process for 21 transition metals and 3 binary alloys is investigated. The mass loss rate is governed by a fluid dynamic parameter of Reynolds number with a simple proportional correlation linked with thermal-fluid behaviour of the melt pool, and convective mixing further complicates the behaviour in in-situ binary alloying. The digital materials approach is effective in understanding complex interdependent thermal-fluid flow dynamics and can advance process-based materials design.

CFD Investigation of transfer of the heat and turbulent flow in circular copper tube with perforated conical rings of aluminum material

Today industries, societies surrounded by hybrid devices like hybrid solar collector, hybrid micro solar collectors, CNC machines etc, and these devices requires effective heat relocation systems for boosting up the life span efficiency, effectiveness and reliability of such devices. Present work based on comparative and simulation study of thermal attributes and fluid flow attributes for conical perforated ring placed inside copper tune of heat exchanger. Experimentation carried out for acknowledging the effect of diverse Pitch Ratio having range 4, 6, 12 and number of holes range 2, 3, 4 with diverse range of Reynolds number (Re number) 4000, 8000, 12000, 16000, 20,000 on thermal attributes and fluid flow attributes for conical perforated rings placed inside copper tube. Results predicted that the copper tube with different conical perforated-rings have excellent results as compared to corresponding smooth tube. So, this research offers an improved conical perforated-rings design for internal fluid flow for enhancing the heat relocation rate. The highest values of Nusselt number (Nu number) is obtain at PR = 4, conical holes N = 2 for Re number Re = 20000.

Comparative analysis of thermal and fluid flow behaviour of diverse nano fluid using Al2O3, ZnO, CuO nano materials in concentric spiral tube heat exchanger

Present paper based on computational and experimental study, in which diverse parameters have been investigated for observing the fluid flow, thermal and performance attributes like thermal performance factor, NTU, effectiveness and fluid flow attributes like Reynolds number, Nusselt number, Friction factor, HTR etc of diverse composition of nanofluids in spiral tube having insert, CTHE with insert diameter and pitch distance 2 mm and 20 mm. During present investigation water used as the base fluid associated with diverse additives or nano particles in single and combined form like Zinc Oxide, Aluminium Oxide and Cupric Oxide to form diverse composition of nano fluids with 10 nm particle size and 0.08% volume fraction like Zinc Oxide with water, Aluminium Oxide with Zinc Oxide with water, Aluminium Oxide with water and Aluminium Oxide with Cupric Oxide with water to improve the thermal conductivity. Experimentation has been performed for diverse nanofluids at 31 OC with flow range 0.721 to 2.941 L/min, which flows in the spiral tube whereas, the hot fluids as water flows at 4.02 L/min across the shell side of test set up at 50 OC. Here comparative investigation has been drawn for diverse nanofluids for observing its fluid flow, thermal and performance attributes at diverse flow rate with turbulent flow under counter flow condition with Reynolds Number 4236 to 18540. The result predicted that out of four diverse nano fluids Aluminium Oxide and Cupric Oxide with water as base fluid shows best results for fluid flow, thermal and performance attributes, for flow rate range 0.721 to 2.941 L/min and Reynolds Number 4236 to 18540. It has been evaluated that from minimum to maximum Reynolds Number, HTR, Nusselt number, Friction factor and effectiveness and NTU varies from 1228.3 to 3316.4, 88.28–160, 0.0438–0.0306, 0.84–0.55, 4.66–1.96 for Aluminium Oxide and Cupric Oxide nano fluid.