Heat Transfer Computational Fluid Dynamics Research Articles

Comparison of Single-Phase Convection in Additive Manufactured Versus Traditional Metal Foams

Abstract Metal foams have been often used for thermal management due to their favorable characteristics including high specific surface area (SSA), high thermal conductivity, and low relative density. However, they are accompanied by shortcomings including the significant contact resistances due to attachment method, as well as the need for characterization of foam parameters such as pore diameter and SSA. Additive manufactured (AM) metal foams would eliminate the substrate/foam thermal resistance, decrease the need for pre-usage characterization, and allow for tailoring structures, while also taking advantage of the characteristics of traditionally manufactured foams. A commercial, aluminum foam (nominally 5 pores per inch (PPI), 86.5% porosity) was analyzed using X-ray microcomputed tomography, and a custom-designed metal foam based on the cell diameter and porosity of the commercial sample was subsequently manufactured. Reduced domain computational fluid dynamics/heat transfer (CFD-HT) models were compared against experimental data. Postvalidation, the flow behavior, effect of varying attachment thermal conductivities, and thermal performance were numerically investigated, demonstrating the usefulness of validated pore-scale models, as well as the potential for improved performance using AM metal foams over traditionally manufactured foams.

Single-Phase Microfluidic Cooling of 2.5D-SICs for Heterogeneous Integration

A parametric study of a nonuniform pin–fin-enhanced single-phase microfluidic cooling design for 2.5D stacked integrated circuits (2.5D-SICs) heterogeneous integration is presented. A thin (0.6 mm) coolant manifold has been investigated via full-scale computational fluid dynamics/heat transfer (CFD/HT) simulations. In order to provide thermal management to this heterogeneous chip system, microfin bridges and micropins have been implemented in the manifold. Dielectric coolant polyalphaolefin (PAO) has been investigated, which provides high heat-removal capability, along with thermal isolation between dies. Microfin bridges and wings can provide enhanced thermal performance but with higher pressure drop. Desired maximum temperature limits for high-powered dies are achieved with this 2.5D-SICs liquid cooling design. The effects of chip placement, dimensions of microfin bridges and micropins, and dielectric coolant supply and removal locations within the ultrathin manifold on pressure drop and HT have also been parametrically studied.

Vandal Glass Heat Distribution and the Effect of Glass Gap Adjustments in Outdoor Digital Display Components

Abstract The use of computational fluid dynamics/heat transfer (CFD/HT) software has become common in exploring the thermal and hydrodynamic behavior of many electronic products. Well-designed CFD/HT models are very valuable for driving the product design, but accurate models can be difficult to develop in some cases for a practical use. In CFD/HT modeling of outdoor digital displays, both the surrounding ambient temperature and solar irradiance are the major contributors to temperature rise, but most software packages are limited in simulating solar irradiance through semitransparent materials and multiple surfaces. In this study, a methodology to replace the solar irradiance with a power that should be imposed on the sun-exposed exterior glass (vandal glass) is described. As outdoor digital displays face harsher thermal challenges compared to the displays that are deployed indoors, it is necessary to come up with a display design that can best benefit from the cooling effect. There are numerous parameters that can be adjusted to optimize the display in terms of its thermal performance but in particular, this study explores the effect of adjusting the gap distance between the vandal glass and the liquid crystal display (LCD) to see how the maximum LCD temperature and fan performance are influenced.

Determination of a Safe Distance for Atomic Hydrogen Depositions in Hot-Wire Chemical Vapour Deposition by Means of CFD Heat Transfer Simulations

A heat transfer study was conducted, in the framework of Computational Fluid Dynamics (CFD), on a Hot-Wire Chemical Vapour Deposition (HWCVD) reactor chamber to determine a safe deposition distance for atomic hydrogen produ... | Find, read and cite all the research you need on Tech Science Press

Numerical Predictions of Impingement Heat Transfer with Obstacles as Turbulators: Conjugate Heat Transfer Computational Fluid Dynamics Procedures

Numerical Predictions of Impingement Heat Transfer with Obstacles as Turbulators: Conjugate Heat Transfer Computational Fluid Dynamics Procedures

Development and Performance of Tungsten-Coated Graphitic Foam for Plasma-Facing Components

High-density graphitic foam is an ideal low-Z plasma-facing material for deuterium-deuterium plasma experiments where tritium codeposition is not an issue. However, like all carbon, graphitic foam suffers from a precipitous drop in thermal conductivity at high temperatures, >600°C. To mitigate these problems, functionally graded layers of tungsten can be deposited to a thickness of 2 to 4 mm onto the plasma side of the foam using chemical vapor deposition. The graphitic foam then acts as a high-conductivity heat sink at temperatures below 600°C for the thin high-Z armor coating. The overall component weighs 18 times less than a comparable volume of tungsten and lacks the coefficient of thermal expansion joining issues between the CuCrZr tubing and the tungsten. This paper discusses the coating development and characterization and presents the results of recent plasma exposures in W7-X. It also reports on computational fluid dynamics heat transfer modeling and preparations for high heat flux testing of mock-ups. This hybrid plasma-facing component (PFC) consisting of innovative engineered materials may be a cost-effective, actively cooled solution for the divertors and other PFCs in long-pulse machines like W7-X and WEST.

Thermal Performance of Microelectronic Substrates With Submillimeter Integrated Vapor Chamber

We develop a vapor chamber integrated with a microelectronic packaging substrate and characterize its heat transfer performance. A prototype of vapor chamber integrated printed circuit board (PCB) is fabricated through successful completion of the following tasks: patterning copper micropillar wick structures on PCB, mechanical design and fabrication of condenser, device sealing, and device vacuuming and charging with working fluid. Two prototype vapor chambers with distinct micropillar array designs are fabricated, and their thermal performance tested under various heat inputs supplied from a 2 mm × 2 mm heat source. Thermal performance of the device improves with heat inputs, with the maximum performance of ∼20% over copper plated PCB with the same thickness. A three-dimensional computational fluid dynamics/heat transfer (CFD/HT) numerical model of the vapor chamber, coupled with the conduction model of the packaging substrate is developed, and the results are compared with test data.

Comparison of data driven modeling approaches for temperature prediction in data centers

Energy-efficient thermal management of data centers based on dynamic optimization and provisioning of cooling resources requires rapid (nearly real-time) predictions of temperatures within data centers. This work for the first time compares multiple Data-Driven Models (DDMs) to achieve such rapid temperature predictions. DDM typically employs statistical or machine learning-based tools, in combination with physics-based modeling and/or experimental data to predict system behavior. In general, DDM approaches are well-suited to systems that have multiple operational states based on interactions between the many electrical, mechanical and control parameters typical of data centers.This study compares the performance of three different DDM methods, namely Artificial Neural Networks (ANN), Support Vector Regression (SVR), Gaussian Process Regression (GPR) in predicting both steady-state and transient rack inlet air temperature distributions in data centers. Additionally, Proper Orthogonal Decomposition (POD) was considered for transient modeling. The data used for training and analysis were obtained by performing 300 offline numerical simulations with a room-level, experimentally validated computational fluid dynamics/heat transfer (CFD/HT) model.The performance of the four data-driven models was evaluated based on the absolute mean error for interpolation and extrapolation, and the adaptability of the models to changes in physical domain (data center room) configuration. Additionally, the impact of the size of the training data set on prediction accuracy is also compared for the four models.For the steady-state case study, the predictions for ANN, SVR and GPR models are in good agreement with CFD/HT simulations, with the GPR model having the smallest overall average prediction error of 0.6 °C in rack inlet air temperature, corresponding to a relative error of 2.7% with respect to rack inlet temperature measured in °C. It was found that for all the frameworks the prediction error increases when the size of training data set was less than 300 samples. The GPR model had the best accuracy for smaller training data sets compared with the other models, with an average prediction error for rack inlet temperatures <1 °C when trained on only 50 simulations. For the transient case study, the interpolative prediction error for all the models is very low (<0.3 °C); however, the extrapolative prediction errors are much greater, and appear to be directly proportional to the (here, temporal) “distance” from the interrogation point to the input parameter space.

Multi-Disciplinary Design Optimisation of the Cooled Squealer Tip for High Pressure Turbines

The turbine tip geometry can significantly alter the performance of the turbine stage; its design represents a challenge for a variety of reasons. Multiple disciplines are involved in its design and their requirements limit the creativity of the designer. Multi-Disciplinary Design Optimisation (MDO) offers the capability to improve the performance whilst satisfying all the design constraints. This paper presents a novel design of a turbine tip achieved via MDO techniques. A fully parametrised Computer-Aided Design (CAD) model of the turbine rotor is used to create the squealer geometry and to control the location of the cooling and dust holes. A Conjugate Heat Transfer Computational Fluid Dynamics (CFD) analysis is performed for evaluating the aerothermal performance of the component and the temperature the turbine operates at. A Finite Element (FE) analysis is then performed to find the stress level that the turbine has to withstand. A bi-objective optimisation reduces simultaneously the aerodynamic loss and the stress level. The Multipoint Approximation Method (MAM) recently enhanced for multi-objective problems is chosen to solve this optimisation problem. The paper presents its logic in detail. The novel geometry offers a significant improvement in the aerodynamic performance whilst reducing the maximum stress. The flow associated with the new geometry is analysed in detail to understand the source of the improvement.

Modeling of the slab heating process in a walking beam reheating furnace for process optimization

A new methodology involving the integration of a three-dimensional (3D) Computational Fluid Dynamics (CFD) model and a two-dimensional (2D) heat transfer model for the study of the slab reheating process in a walking beam reheating furnace has been proposed. A comprehensive 3D CFD model has been developed to simulate the flow characteristics, combustion process and multi-mode heat transfer phenomena inside an industrial slab reheating furnace. A customized 2D heat transfer model for the slab reheating process has also been developed based on the finite difference method. The simulation results from the 3D CFD model provide detailed heat transfer boundary conditions for the 2D heat transfer model. Instrumented slab trials were conducted under typical operating conditions of the furnace and the results were used to calibrate the 2D model. By comparing the slab temperatures measured from the instrumented slab trials and those predicted using the models, it was demonstrated that the 3D CFD and 2D heat transfer models predict the reheating process reasonably well. The proposed methodology is fairly easy to be used by mill engineers for trouble shooting and optimizing of the slab reheating process.

Simulating Spawning and Juvenile Rainbow Trout (Oncorhynchus mykiss) Habitat in Colorado River Based on High-Flow Effects

High flow generates significant alterations in downstream river reaches, resulting in physical condition changes in the downstream regions of the river such as water depth, flow velocity, water temperature and river bed. These alterations will lead to change in fish habitat configuration in the river. This paper proposes a model system to evaluate the high flow effects on river velocity, water depth, substrates changes, temperature distribution and consequently assess the change in spawning and juvenile rainbow trout (Oncorhynchus mykiss) habitats in the downstream region of the Glen Canyon Dam. Firstly, based on the 2 dimensional (2D) depth-averaged CFD (Computational Fluid Dynamics) model and heat transfer equation applied for simulation, three indices were simulated, namely depth, flow velocity and temperature distribution. Then, the spawning and juvenile fish preference curves were obtained based on these three indices and substrates distribution. After that, the habitat model was proposed and used to simulate the high flow effects on juvenile and spawning rainbow trout habitat structure. Finally, the weighted usable area (WUA) and overall suitability index (OSI) of the spawning and juvenile fish species were quantitatively simulated to estimate the habitat sensitivity. The results illustrate that the high flow effect (HFE) increased the juvenile rainbow trout habitat quality but decreased the spawning rainbow trout habitat quality. The juvenile trout were mainly affected by the water depth while the spawning rainbow trout were dominated by the bed elevation.

Semi-Inverse Design Optimization Method for Film-Cooling Arrangement of High-Pressure Turbine Vanes

A semi-inverse design optimization method for the film-cooling arrangement of high-pressure turbine first-stage vanes is initiated based on a combinatorial optimization algorithm, a one-dimensional heat conduction model, and computational fluid dynamics methods, in which inlet temperature distortion, radiation, and inlet swirl are all considered simultaneously. This semi-inverse design optimization method can optimize the total coolant amount of the film-cooling structure while ensuring an acceptable metal temperature distribution, which finally provides a scattered and nonuniform arrangement of the film-cooling holes and a minimal coolant amount. The optimization methodology is tested on the General Electric energy-efficient engine first-stage vane under a high thermal load, and the optimization result is verified by the conjugate heat transfer computational fluid dynamics simulations. As for the optimized cooling structure, a significant improvement of cooling performance is observed while the total coolant amount is slightly reduced compared with the prototype. It is also found that neglecting each of the three factors (inlet temperature distortion, radiation, and inlet swirl) could result in a significantly different film-cooling arrangement while maintaining the overall cooling performance, which highlights the capability of the semi-inverse design optimization method at various design conditions.

Thermal protective performance evaluation of fire proof garment eliminating air gaps effect based on computational fluid dynamics simulation

To evaluate thermal protective performance of fire proof garment under flash fire exposures, it is important to discuss garment heat transfer characteristics eliminating the effect of air gaps between garment and body. In this study, a test of flame manikin clothed with close-fitting garment was designed. And a three-dimensional transient heat transfer computational fluid dynamics simulation of the test was achieved to gain the garment surface temperature. By means of three-dimensional body scanner, Geomagic and Gambit software, we developed a method of three-dimensional geometrical modeling of the full-scale close-fitting clothed manikin. The accuracy of the computational fluid dynamics simulation was validated by actual experiments. It was found that the average incident heat flux to the exterior of the Nomex® IIIA garment is not 84 kW/m2, the value measured in nude manikin tests, but the value is 11% lower than it. This will help to set more accurate boundary conditions on garment surface in further simulations.

A novel computational approach to combine the optical and thermal modelling of Linear Fresnel Collectors using the finite volume method

A computational approach is presented, which uses the finite volume (FV) method in the Computational Fluid Dynamics (CFD) solver ANSYS Fluent to conduct the ray tracing required to quantify the optical performance of a line concentration Concentrated Solar Power (CSP) receiver, as well as the conjugate heat transfer modelling required to estimate the thermal efficiency of such a receiver. A Linear Fresnel Collector (LFC) implementation is used to illustrate the approach. It is shown that the Discrete Ordinates method can provide an accurate solution to the Radiative Transfer Equation (RTE) if the shortcomings of its solution are resolved appropriately in the FV CFD solver. The shortcomings are due to false scattering and the so-called ray effect inherent in the FV solution. The approach is first evaluated for a 2-D test case involving oblique collimated radiation and then for a more complex 2-D LFC optical domain based on the FRESDEMO project. For the latter, results are compared with and validated against those obtained with the Monte Carlo ray tracer, SolTrace. The outcome of the FV ray tracing in the LFC optical domain is mapped as a non-uniform heat flux distribution in the 3-D cavity receiver domain and this distribution is included in the FV conjugate heat transfer CFD model as a volumetric source. The result of this latter model is the determination of the heat transferred to the heat transfer fluid running in the collector tubes, thereby providing an estimation of the overall thermal efficiency. To evaluate the effectiveness of the phased approach in terms of accuracy and computational cost, the novel 2-D:3-D phased approach is compared with results of a fully integrated, but expensive 3-D optical and thermal model. It is shown that the less expensive model provides similar results and hence a large cost saving. The novel approach also provides the benefit of working in one simulation environment, i.e. ANSYS Workbench, where optimisation studies can be carried out to maximise the performance of linear CSP reflector layout and receiver configurations.

CFD simulations of the effect of evaporative cooling from water bodies in a micro-scale urban environment: Validation and application studies

Computational fluid dynamics (CFD) simulations of the evaporative cooling effect from water surfaces in a micro-scale urban environment were evaluated via validation and application studies with various configurations. First, the basic ability of CFD simulations to reproduce the evaporative cooling on a simplified small-scale water surface in a boundary layer was investigated. Next, the prediction accuracy of the vapor transport mechanism from a water surface within an array of building was evaluated. It was confirmed that the vapor transport mechanism influenced by the complex wind flow around buildings could be reproduced by the current CFD code within a given accuracy. Finally, a numerical analysis that combined CFD and radiative heat transfer analysis was conducted for predicting the thermal environment around an actual residential neighborhood with a pond. The results were compared to experimental data. The experimental air temperature distribution around the pond was qualitatively reproduced via CFD. The maximum temperature decrease induced by the water surface was approximately 2°C at the pedestrian level. For a wind velocity of approximately 3m/s at a height of 10m, the effect of the evaporative cooling propagates downwind over an unobstructed distance of 100m.

Compact Model-Based Microfluidic Controller for Energy Efficient Thermal Management Using Single Tier and Three-Dimensional Stacked Pin-Fin Enhanced Microgap

Overcooling of electronic devices and systems results in excess energy consumption, which can be reduced by closely linking cooling requirements with actual power dissipation. A thermal model-based flow rate controller for single phase liquid cooled single tier and three-dimensional (3D) stacked chips, using pin-fin enhanced microgap was studied in this paper. Thermal compact models of a planar and 3D stacked two-layer pin-fin enhanced microgap were developed, which ran 104-105 times faster than using full-field computational fluid dynamics/heat transfer (CFD/HT) method, with reasonable accuracy and spatial details. Compact model was used in conjunction with a flow rate control strategy to provide the needed amount of liquid to cool the heat sources to the desired temperature range. Example case studies show that the estimated energy savings in pump power is about 25% compared with pumping fluid at a constant flow rate.

Multi-objective optimization of nanofluid flow in flat tubes using CFD, Artificial Neural Networks and genetic algorithms

In this article, multi-objective optimization of Al2O3-water nanofluid parameters in flat tubes is performed using Computational Fluid Dynamics (CFD) techniques, Artificial Neural Networks (ANN) and Non-dominated Sorting Genetic Algorithms (NSGA II). At first, nanofluid flow is solved numerically in various flat tubes using CFD techniques and heat transfer coefficient (h¯) and pressure drop (ΔP) in tubes are calculated. In this step, two phase mixture model is applied for nanofluid flow analysis and the flow regime is also laminar. In the next step, numerical data of the previous step will be applied for modeling h¯ and ΔP using Grouped Method of Data Handling (GMDH) type ANN. Finally, the modeling achieved by GMDH will be used for Pareto based multi-objective optimization of nanofluid parameters in horizontal flat tubes using NSGA II algorithm. It is shown that the achieved Pareto solution includes important design information on nanofluid parameters in flat tubes.

Experimental and CFD Heat Transfer Studies of Al2O3-Water Nanofluid in a Coiled Agitated Vessel Equipped with Propeller

This paper presents the heat transfer characteristics of Al2O3-water nanofluid in a coiled agitated vessel with propeller agitator. The experimental study was conducted using 0.10%, 0.20% and 0.30% volume concentration of Al2O3-water nanofluids. The results showed considerable enhancement of convective heat transfer using the nanofluids. The empirical correlations developed for Nusselt number in terms of Reynolds number, Prandtl number, viscosity ratio and volume concentration fit with the experimental data within ±10%. The heat transfer characteristics were also simulated using computational fluid dynamics using FLUENT software with the standard k-ɛ model and multiple reference frame were adopted. The computational fluid dynamics (CFD) predicted Nusselt number agrees well with the experimental value and the discrepancy is found to be less than ±8%.

Imbalance wall functions with density and material property variation effects applied to engine heat transfer computational fluid dynamics simulations

Heat transfer is a significant factor affecting internal combustion engine efficiency, emissions and performance. This study concentrates on model development for convective heat transfer and near-wall turbulent flow. The solution of complete fluid dynamics equations within the very thin-wall boundary layers is, and will be in the near future, very impractical in engineering scale flows with any present day method. An advanced numerical near-wall treatment method within the Reynolds averaged Navier–Stokes framework has been developed. The method solves simplified boundary layer equations for enthalpy, momentum, turbulent kinetic energy and dissipation in wall adjacent cells on cellwise high-resolution subgrids, adaptive to local conditions. The boundary layer equations include temperature gradient–induced density/multicomponent material property variations and complete imbalance contributions, for example, convection, transients, pressure gradient and external sources, in compact forms. The resulting numerical wall functions are valid with near-wall grid resolution ranging from the viscous sublayer to the fully turbulent region, thus avoiding the conflicting near wall resolution requirements of common low–Reynolds and high–Reynolds number turbulence models. The advanced near wall treatment method, comprising the numerical imbalance wall functions and accordingly modified low–Reynolds number turbulence model, is implemented in STAR-CD 4.12, extensively utilized in engine simulations. The near wall treatment method is validated against available measurements and direct numerical simulation data of strongly heated pipe flow. Performance of the near-wall treatment method in engine conjugate heat transfer simulations is also demonstrated. Local and average effects of variable properties and imbalance contributions on piston surface heat transfer, friction and turbulent sources are elaborated and contrasted to the standard high–Reynolds number near-wall treatment.

Coupled EnergyPlus and computational fluid dynamics simulation for natural ventilation

Energy modeling approaches have continued to advance to cater for emerging new design concepts toward “greener” solutions that optimize energy consumption in buildings while maintaining thermal comfort as well as healthy environment. Increasing attention is given to passive and mix-mode systems in building. Computational Fluid Dynamics (CFD) model has been widely adopted as effective tool for natural ventilation simulations. However, CFD become unstable for conjugate heat transfer model, which is the transient heat transfer between solid and fluid. Solid and fluid has different respond times to thermal energy. Typically walls respond in hours, and air responds in seconds, causing the system to become stiff. In addressing the issue, a coupled lumped heat transfer model (EnergyPlus) and CFD model (Fluent) was implemented, and 8 days of simulation was conducted. The airflow rates of openings and heat transfer coefficients from the airflow network module in EnergyPlus and those from CFD model were compared. Results show that airflow network model generally predict smaller airflow rates for the openings. Airflow network model generates better results for openings on the south and east facade and internal openings, where there is no immediate adjacent building. Among the heat transfer coefficients calculation methods in EnergyPlus, the TARP algorithm generated closest HTC values to the coupled CFD results. The overall heat transfer coefficients of all the enclosure surfaces are calculated and it is found that the overall thermal resistances generated from the three convective HTC algorithms are almost the same, yet with observable difference from coupled CFD simulations.