Advanced computational methods for modelling ventilation and heat transfer

Influence of metal foam thickness on the conduction and convective heat transfer for a flat plate with metal foam impinged by a rectangular slot jet

In order to predict and manage the thermal behavior of microelectronic packages cooled principally by natural convection, a two-way coupling method was developed between a accurate conduction model and a computational fluid dynamics (CFD) simulation. An iterative solution loop was performed by applying as a boundary condition the local convection coefficients obtained from the CFD to the conduction model, and the temperature field at the solid-fluid interface obtained from the solid conduction model to CFD simulation. For the first iteration, the conduction heat transfer was solved by considering an initial guess of a uniform convection coefficient (e.g. from empirical formulas) for each solid-fluid interface. The procedure was repeated until the convergence of the solution was reached. The comparison between the total convection coefficients including the radiation obtained with the CFD iterative procedure and those from the conventional empirical methods showed important differences, thus demonstrating the usefulness of the CFD approach to obtain accurate thermal results. The numerical results were compared to measurements from a test vehicle, carried out under the natural convection Jedec JESD51 standards in a still air chamber. Radiation plays an important role in heat transfer in this setting because of the large temperature difference between the walls of the box and the test vehicle. The junction temperatures obtained with the numerical simulation for different operating powers were in good agreement with the experimental measurements, with an error of less than 1°C, showing that the proposed methodology allows the accurate simulation of the natural heat transfer for microelectronic packages mounted on PCB in the horizontal orientation.

An application of the finite volume method (FVM) in the field of strip rolling mills will be presented. The aim of the simulation is to predict the development of temperature distribution in a work roll and to determine the thermal camber accordingly. The FVM is used for treatment of heat conduction in the work roll with the consideration of different boundary conditions like heat transfer by contact with the strip and bearings, spray water cooling, convection and radiation to air, etc. The first part shows the treatments of the volume elements used in the FVM. A quasi 3-D model is applied. The roll is divided in two regions in radial direction to consider the typical compound roll structure. Part two gives the view of treatments of the different boundary conditions involved on the roll surface. A sub-model coupled with strip and work roll is used for the region of roll gap. The quantification of conduction heat with the consideration of the deformation energy and friction heat is a main point of the sub-model. Another sub-model is used to treat the region, where the coolant is applied via spraying nozzles. The sub-model calculates the water flow rate distribution with specified conditions like nozzle positions, nozzle characteristic data, reference and actual pressure and then determines the distribution of heat transfer coefficients correspondingly. The rest of wet and dry surface is treated separately. Finally an example is presented, which shows the usability and range of applications of the implemented computer program. The model is suitable for simulation of complicated real rolling processes and has been calibrated with measured data. The results of this model are essential for the improvement of product quality and for the layout of new rolling mills. Advanced Computational Methods in Heat Transfer VI, C.A. Brebbia & B. Sunden (Editors) © 2000 WIT Press, www.witpress.com, ISBN 1-85312-818-X 520 Advanced Computational Methods in Heat Transfer V

The bending of large pipes due to temperature differentials between the bottom and top of the pipe is a very serious problem. The temperature differentials can either be caused by extremely cold liquids (such as methane or ethylene flowing from a lateral into a flare header) or hot liquids flowing at the bottom of a piping system (such as in a Vacuum transfer line) while the top is exposed to atmospheric conditions. In some cases liquids may be produced by Joule-Thompson cooling of high pressure cold gas as it expands through a safety-relief or emergency depressurization valve. The liquid so formed can accumulate, for example, on the dead leg side of a flare header. The differential expansion can deform the pipe so that it lifts off its supports. It takes a finite amount of time for the heat transfer by conduction to equilibrate the temperature to a more benign level. The initial stresses induced due to large thermal differential may even cause the pipe to crack in the region of the supports and T-joints to the laterals. This phenomenon has been observed in several industries, most predominantly in the petrochemical industry. This paper recounts the use of Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) to study this important phenomenon. The liquid flowing from the lateral into the main header pipe is multiphase in the dispersed, stratified, slug or annular flow re´gime. Multiphase flows with heat transfer are analyzed using CFD. The temperatures on the walls of the pipe system are then transferred to the FEA and analyzed for heat transfer and thermal stresses. These stresses are compared to ASME standards to see if they are within allowable limits. This paper also recounts efforts to reduce the bending effect by preventing liquid accumulation on the dead leg side. Other methods that provide better supports for bent piping are studied. Further, methods of equilibrating the temperature faster to prevent the bowing of the pipe are also studied. It is hoped that this presentation will benefit people designing piping networks with varying liquid and vapor traffic by providing a safe environment free of cracks and spills.

The objective of this paper is to investigate the self-cooling performance of a novel integrated flux-switching PM (FSPM) machine with the airfoil-shaped rotor. The rotor of the proposed integrated machine is functioning as both a rotor of the motor as well as an axial fan. It rotates to draw air from the ambient into the rotor and accelerate the flow through the rotor stage. The high-speed flow provides forced convection to the rotor, stator, windings, and magnets. Therefore, self-cooling is achieved. Accounting for manufacturing challenges of the airfoil blades, 3-D printed blade caps are designed and assembled over the laminated rotor poles for the airfoil-shaped rotor. In this work, electromagnetic performance is verified by 3-D finite element analysis (FEA). The convective heat transfer coefficients are calculated by analytical methods using Taylor-Couette flow and numerical simulations by 3-D computational fluid dynamics (CFD). The effect of encapsulations on the windings will also be investigated accounting for effective thermal conductivity and in-slot heat transfer from the winding to the stator.

The optimization of heat transfer between fluid and metal plays a crucial role in gas turbine design. An accurate prediction of temperature for each metal component can help to minimize the coolant flow requirement, with a direct reduction of the corresponding loss in the thermodynamic cycle. Traditionally, in industry fluid and solid simulations are conducted separately. The prediction of metal stresses and temperatures, generally based on finite element analysis, requires the definition of a thermal model whose reliability is largely dependent on the validity of the boundary conditions prescribed on the solid surface. These boundary conditions are obtained from empirical correlations expressing local conditions as a function of working parameters of the entire system, with validation being supplied by engine testing. However, recent studies have demonstrated the benefits of employing coupling techniques, whereby computational fluid dynamics (CFD) is used to predict the heat flux from the air to the metal, and this is coupled to the thermal analysis predicting metal temperatures. This paper describes an extension of this coupling process, accounting for the thermo-mechanical distortion of the metal through the engine cycle. Two distinct codes, a finite element analysis (FEA) solver for thermo-mechanical analysis and a finite volume solver for CFD, are iteratively coupled to produce temperatures and deformations of the solid part through an engine cycle. At each time step, the CFD mesh is automatically adapted to the FEA prediction of the metal position using efficient spring analogy methods, ensuring the continuity of the coupled process. As an example of this methodology, the cavity flow in a turbine stator well is investigated. In this test case, there is a strong link between the thermo-mechanical distortion, governing the labyrinth seal clearance, and the amount of flow through the stator well, which determines the resulting heat transfer in the stator well. This feedback loop can only be resolved by including the thermo-mechanical distortion within the coupling process.

Cathodic protection (CP) anode bed grounding resistance calculating formulae, given by CP standards, are reviewed firstly. Underground assumptions and limitations of these grounding calculating formulae are analyzed, which means formula method may encounter problems when designing anode beds in high soil resistivity area. Based on finite element analysis (FEA) method, a new grounding resistance calculation method is suggested, which is can be treated as more suitable and flexible for anode bed grounding resistance calculation in high soil resistivity condition. The main steps of FEA method, geometric model building, meshing, boundary condition and solver setting, and grounding resistance calculating according to Ohmic law, are clearly presented. In order to introduce the FEA method in detail, a realistic anode bed design program for Northwestern China area, where soil resistivity is always very high, is demonstrated. Based field soil resistivity survey data by Wenner 4-pin method, the candidate anode bed site, named Station A, is regarded as optimal site, and Barnes’ soil layer analysis method is used to predict soil resistivity distribution in depth direction. Both formula method and FEA method are used to calculate grounding resistance. The following comparison results show that formulae from COR-GS-023, GB21448-2008, РД 153-39.4-039-99 standards and FEA method give out almost the same grounding resistance results under the assumption of uniform soil resistivity, which also, from another angle, verifies the correctness of FEA method. But for FEA method, designers can include realistic soil resistivity distribution function and any anode rod layout plan in calculation model. So, FEA method can be treated as a more flexible tool to calculate CP anode bed grounding resistance.

An investigation into the solution dependence of a conjugate heat transfer computational fluid dynamics (CFD) model of a synchronous generator, with respect to meshing, has been carried out. Utilising CFD as a tool for investigating the airflow and thermal performance of electrical machines is increasing. Meshing is a vital part of the CFD process, but its importance is often misunderstood or overlooked in the context of electrical machine analyses; partly due to the relative mesh independency of the finite element analysis (FEA) numerical method. This paper demonstrates how a relatively complex, air-cooled generator CFD model can be considerably influenced by changes in the mesh. Flow rate, velocity and windage effects are assessed as a function of the mesh adopted. Mesh changes have been shown to affect the mass flow rate through a single vent by up to 55% and the associated heat transfer coefficient by 128%.

This paper deal with structural deformation of one rectangular, closed, thin walled, steel made, thermally loaded channel and influence of this deformation on the air flow through the channel, recognised as coupled fluid-structure interaction problem. The geometrically non-linear deformation of thermally loaded channel was solved using commercial finite-element analysis software ANSYS. The unsteady Navier-Stokes equations in their conservation form defining fluid flow are solved using commercial computer fluid dynamics software ANSYS CFX. A fuzzy logic-based expert system has been developed to predict some results of structural and fluid flow numerical simulation instead of directly evaluating it by a time-consuming software coupling of finite-element and computer fluid dynamics numerical analysis. Three input parameters, namely temperature of channel inner walls, difference in temperature of inner and outer surface of channel wall, and factor of mesh size, are varied while solving the fluid-structure interaction problem. A pressure drop downstream the flow was considered as a computer fluid dynamics output parameter of importance, while Von Misses maximum stresses were an finite-element analysis output parameter observed. The developed FLES can predict the results of finite-element and computer fluid dynamics analysis, a pressure drop and Von Misses maximum stresses respectively, within a reasonable accuracy limit and at lower computation cost compared to the finite-element, and CFD computer fluid dynamics packages combined into series of multi-physics analyses.

Freeze-Drying in Novel Container System: Characterization of Heat and Mass Transfer in Glass Syringes

Heat transfer in BCC lattice materials: Conduction, convection, and radiation

A three-dimensional conjugate heat transfer model for thermal protective clothing

A new method is introduced to calculate radiative heat transfer between two grey end plates with an arbitrary number of thin grey films in between. With this method it is also possible to do an almost exact analysis for coupled radiative and conductive heat transfer through one film between two grey end plates. It is almost exact for an arbitrary position of the film because the maximum deviation from the true heat flux can be evaluated exactly. There is one position of the film between the plates where the new method for coupled heat transfer is absolutely exact. This is where the heat flux is a minimum. This is a most interesting result for all heat insulating applications. The position for the minimum heat flow through more than one film can be determined exactly as well as the value of the heat flow itself. It has been shown by experiment that the method for radiative heat transfer can be applied not only to multifilm layers but also to PMMA foam or capillary structures. First experiments were in excellent agreement with theory.

The anti-scuffing bearing capacity of gears is a significant issue for their service lives, especially for the cases with heavy loads or high speeds. Generally, the anti-scuffing bearing capacity is evaluated according to the surface contact temperature that can be calculated with either analytical methods or finite element analysis (FEA) methods. The analytical methods usually apply the theory of Blok to efficiently obtain the results by simplifying some actual physical conditions, which are well considered in the FEA methods with accurate results but more computation time. Conversely, a new efficient and accurate analytical method is proposed by introducing the actual lubricant film thickness and continuous heat transfer for the theory of Blok. These two physical conditions are the key issues for the calculation of the two parts of surface contact temperature, flash temperature and bulk temperature, respectively. For the calculation of flash temperature, elastohydrodynamic lubrication (EHL) is introduced to consider the lubricant film thickness for the theory of Blok, and the result is obtained by solving the Reynolds equation efficiently with the finite difference method. For the bulk temperature, the result for a contacting point on the gear tooth surface is directly obtained according the theory of Blok, and the continuous heat transfer among the adjacent contacting points is considered with Gaussian heat morphology, which can accurately construct the bulk temperature field distribution in the contact region. The proposed method is validated as in good agreement with the FEA method and with less computation time.

This paper discusses a one-quarter long Heat Transfer course for Mechanical Engineering curriculum. The primary objective of this course is to provide the fundamental knowledge necessary to understand the behavior of different thermal systems. This course provides a detailed calculus-based analysis, including the applications of differential equations, of heat transfer through different media. Conduction, convection, and radiation heat transfer in one- and two- dimensional steady and unsteady systems are examined. Covering all of these topics in a one quarter long course is very challenging to complete in a satisfactory manner. Therefore, we use a combination of analytical, numerical and experimental studies to strengthen the students’ conceptual understanding beyond the classroom lectures. The learning process starts with a one-dimensional heat transfer problem using a straight fin. First, students learn how to solve for the temperature distribution using the standard differential equations. Then, students solve the same problem numerically using the finite element analysis (FEA). In this case, students solve the problem using both matrix algebra and the FEA package, ANSYS. Finally, students perform the experiment and compare the experimental outcomes with analytical and numerical results. Similar learning strategies are used to analyze the heat transfer from 3D objects made of different materials. Problems are solved for temperature distribution using the lumped capacitance model. Then the analytical solutions are compared with numerical and/or experimental results. Finally, several parametric analyses, using ANSYS, are conducted to extend the students’ understanding for more complex systems. The teaching methodologies using these approaches offer a great experience for students to learn numerous heat transfer concepts in the limited time. The purpose of this paper is to explain the details of this teaching methodology in our heat transfer curriculum.