Molecular Dynamics Study of the Interfacial Thermal Conductance at the Graphene/Paraffin Interface in Solid and Liquid Phases

By utilizing molecular dynamics (MD) simulations, we study the interfacial thermal conductance at the interface of graphene and paraffin. In doing so, we conduct non-equilibrium heat source and sink simulations on systems of parallel and perpendicular configurations in which the heat flow is parallel and perpendicular to the surface of graphene, respectively. For the perpendicular configuration, graphene with different number of layers are considered. The results show that the interfacial thermal conductance decreases with the number of layers and converges to a value which is equal to the obtained conductance by using the parallel configuration. We also study the conductance for the solid phase paraffin. The results indicate that solid paraffin-graphene interfaces have higher conductance values with respect to the corresponding liquid phase systems.

Transient Thermal Analysis for the Automotive Underhood and Underbody Components

The transient thermal simulation is an important part of thermal management development for new vehicle architectures. Different techniques have been studied in the past to address this coupled conduction/convection/radiation problem. In order to fully capture the transient thermal behavior of various underhood and underbody components, it is also necessary to accurately model the thermal mass of each part and the thermal links between dissimilar materials. The paper will outline a new, efficient methodology for this type of thermal analysis that shows acceptable results for complex full vehicle thermal analysis without sacrificing accuracy. The methodology is based on approximating the transient convective field with intermittent steady state solutions. The paper will present results from this new approach and compare them with fully transient simulation results as well as experimental data. The new methodology can be optimized to significantly reduce simulation run times without sacrificing accuracy and to be more practical for application in the vehicle development cycle.

Modeling of Thermally Grown Oxide Layer Growth as a Moving Boundary Problem

Thermal efficiency of energy conversion systems such as gas turbines can be increased greatly with an increase in the turbine inlet temperature of combustion gases. However, this necessitates the use of efficient cooling techniques in addition to thermal barrier coatings (TBCs) to help significantly improve the life expectancy of gas turbine blades. The effect of TBC use is the formation of oxides, particularly alumina, at the interface of the ceramic top coat and bond coat material during in-service application. This effect is well known to cause failure of TBCs exposed to extreme high temperature environments. The objective of this paper is to present a micro-scale finite difference thermal model for the TBC-Substrate system that considers growth of the TGO layer and predicts in-situ thermal gradients. The governing equation is the transient heat diffusion equation discretized over a 1-D domain using mean value finite volume method with grid adaptation for zones involving depletion of bond coat (BC) material and TGO growth; hence, necessitating a moving interfacial boundary problem. The resulting algebraic equations are simultaneously solved in MATLAB to produce temperature distributions and BC/TGO interfacial locations. The model has utility in studying the evolution of residual stresses and hence prediction of TBC durability and failure.

Exploration of Hands-On Discovery Pedagogy in Heat Transfer

Recent research in the development of the “Thermal and Transport Concept Inventory” test (TTCI) has shown that, despite completing several related courses, students have significant misconceptions of heat transfer principles such as the differences between heat, energy and temperature. This lack of conceptual understanding limits students’ problem-solving abilities (and thus their transition to expertise) and their ability to transfer knowledge to other courses and contexts. This research demonstrates how this problem can be addressed by integrating hands-on workshops into a traditional heat transfer lecture course. The workshops are designed to actively engage students in exploration and discovery using authentic problems. Using heat flux sensors allows students to physically observe abstract phenomena that cannot be easily observed.

On Why the Flipped Classroom Model May Be the Optimum for Heat Transfer Education

Much has been made of recent news that the field of heat transfer has fewer teaching professors now than in years past. It remains a challenging field for many college students who then tend to go into other engineering applications. But this trend can be reversed by utilizing modern educational tools in a flipped class model that takes advantage of and optimizes both online delivery in concert with classroom activities. Specifically, the flipped classroom model allows for the use of graphical visualization of heat transfer (a phenomena that for the most part is outside our visual spectrum) in an online format and active learning exercises that engage students in the classroom. This paper will explain how both sides of this educational equation may be the optimal method for heat transfer content delivery.

The Outside Transport Phenomena of the Passive Containment Cooling System

Based on the outside cooling of the Passive Containment Cooling System (PCCS), a simplified containment mathematical model was built and was numerically solved. Air circulation driven by natural forces for a steady condition along with the coupled thermal-hydraulic phenomena was then obtained and analyzed. Variations of humid air temperature and velocity, water film sub-cooling and heat fluxes along the flow direction were discussed and driving forces were compared to obtain the ranked important phenomena of the PCCS outside cooling. The conclusions are significant to reasonably understand the PCCS outside transport phenomena.

A Space-Time Meshless Method for Heat Transfer Problems With High Discontinuities

The aim of this research is the development of a space-time driscretization method based on Diffuse Approximation Meshless method. This method, devoted to transient heat transfer problems presenting high temporal discontinuities, avoids any Finite-Difference time stepping procedure. The space-time discretization proposed here seems to be convenient for continuous transient heat transfer. Nevertheless, for problems including temporal discontinuities, some spurious oscillations, whose amplitudes depend on source power, appear. A new weight function respecting the principle of causality, based on a modification of the involved node’s selection and a normalisation of the distances, is developed. The use of this new weight function both improves the accuracy and vanishes the oscillations. The method is validated by a source free transient heat transfer problem presenting convective exchanges. Then problems including a constant and a discontinuous heat source are solved. Temperatures fields obtained when using the classical weight function are closer to those obtained with a backward Finite Difference scheme when the heat source is continuous. In case of discontinuous sources, when using the classical weight function, temperature fields present some spurious oscillations which disappear when choosing the new one. The proposed method associated to a grid refinement procedure will lead to adaptive grids in space and/or time, independently.

Prediction of Non-Uniform Frost Distribution on a Fin Tube Heat Exchanger

Heat exchanger experiences frost on its surface when it operates below 0°C under heating condition of the heat pump. Since frost blocks air flow through the fin tube heat exchanger, it increases air-side pressure drop and deteriorates heat transfer rate of the heat exchanger. Prediction of the frost profiles on the heat exchanger is needed to minimize the unfavorable effect on the heat exchanger by frost. The present study predicts non-uniform frost distribution on the surface of fin-tube heat exchanger and shows its accuracy by comparing with measured profiles. Fin and tube heat exchanger for heat pump was considered for the frost prediction under practical refrigerant and air conditions. Non-uniform frost pattern was predicted by using segment by segment method of the heat exchanger. Heat transfer rate and exit temperature of air and refrigerant for each segment were calculated by applying ε-NTU method. Air volume flow rate in the front of the heat exchanger was decreased as frost goes on. It was utilized for the prediction of the frost formation. Numerically predicted results were compared with measured local data. They agreed within ±10.4% under the ISO 5151 condition.

Microtomography-Based Analysis of Pressure Drop and Heat Transfer Through Open Cell Metal Foams

Their light weight, open porosity, high surface area per unit volume and thermal characteristics make metal foams a promising material for many industrial applications involving fluid flow and heat transfer. Pressure drop and heat transfer of porous media have inspired a number of experimental and numerical studies. Many models have been proposed in the literature that correlate the pressure gradient and the heat transfer coefficient with the mean cell size and porosity. However, large differences exist among results predicted by different models. Most studies are based on idealized periodic cell structures. In this study, the true 3-D micro-structure of the metal foam is obtained by employing x-ray computed microtomography (XCT). For comparison, ideal Kelvin foam structures are developed in the free-to-use software “Surface Evolver” surface energy minimization program. Pressure drop and heat transfer are then investigated using the CFD Module of COMSOL® Multiphysics code. A comparison between the numerical predictions from the real and ideal geometries is carried out.