In the present work a two-dimensional steady state convective heat transfer problem in a channel aluminum foam partially filled with an external thermos-electrical generator (TEG) component is numerically solved. The channel is characterized by a length equal to 272 mm and by a height of 60mm; instead, the TEG has a length equal to 65 mm and a thickness of 8.5 mm. The metal foam is modelled assuming the local thermal equilibrium (LTE) hypothesis. The TEG is analyzed as a solid with an internal energy generation. Thermophysical properties of the exhaust gas are assumed equal to the ones of the air. The governing equations are considered with temperature independent thermophysical properties. The governing equations for gas, porous media and TEG are solved by finite volume method using the Ansys-Fluent code. The foam is characterized by a porosity of 0.92 and number of pores per inch equal to 5, 20, 40. Results are carried out for several mass flow rates of gas and different thicknesses of metal foam. Results are given in terms of temperature distributions, pressure drop, thermoelectric efficiency and power density for TEG for different exhaust gas flow rates and aluminum foam thicknesses.

Gas to Liquid (GTL), an alternative synthetic jet fuel derived from natural gas has gained significant attention recently due to its cleaner combustion characteristics when compared to conventional counterparts. The effect of chemical composition on key performance aspects such as ignition delay time, laminar burning speed, and emission characteristics have been experimentally studied. However, the development of chemical kinetics mechanism to predict those parameters for GTL fuel is still in its early stage. In this work, a detailed kinetics model (DKM) has been developed based on the chemical kinetics reported for GTL surrogate fuels. The DKM is applied to the chemical kinetic mechanism of 597 species and 3853 reactions. The DKM is employed in a constant internal energy and constant volume reactor to predict the ignition delay times for GTL and its three surrogates over a wide range of initial temperature, pressure and equivalence ratio. The ignition delay times predicted using DKM are validated with those reported in the literature. Furthermore, the CANTERA freely propagating 1D flame code is used in conjunction with the chemical kinetic mechanism to predict the laminar burning speeds for GTL fuel over a wide range of operating conditions.

The nano-scale interaction between polymer molecules and nanoparticle is a key factor in determining the macro-scale strength of the composite. In recent years numerous efforts have been directed towards modeling nanocomposites in order to better understand the reasons behind the enhancement of mechanical properties, even by the slight addition (a few weight percent) of nano-materials. In order to better understand the local influence of nano-particle on the mechanical properties of the composite, it is required to perform nano-scale analysis. In this context, modeling of fracture and damage in nano-graphene reinforced EPON 862 has been discussed in the current paper. Regarding fracture in polymers, the critical value of the J-integral (J I ), where the subscript I denotes the fracture mode (I=1, 2, 3), at crack initiation could be used as a suitable metric for estimating the crack driving force as well as fracture toughness of the material as the crack begins to initiate. However, for the conventional macroscale definition of the J-integral to be valid at the nanoscale, in terms of the continuum stress and displacement fields and their spatial derivatives — requires the construction of local continuum fields from discrete atomistic data, and using these data in the conventional contour integral expression for atomistic J-integral. One such methodology is proposed by Hardy that allows for the local averaging necessary to obtain the definition of free energy, deformation gradient, and Piola-Kirchoff stress as fields (and divergence of fields) and not just as total system averages. Further, the atomistic J-integral takes into account the effect of reduction in J from continuum estimates due to the fact that the free energy available for crack propagation is less than the internal energy at sufficiently high temperatures when entropic contributions become significant. In this paper, the proposed methodology is used to compute J-integral using atomistic data obtained from LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator). As a case study, the feasibility of computing the dynamic atomistic J-integral over the MD domain is evaluated for a graphene nano-platelet with a central crack using OPLS (Optimized Potentials for Liquid Simulations) potential. For model verification, the values of atomistic J-integral are compared with results from linear elastic fracture mechanics (LEFM) for isothermal crack initiation at 0 K and 300 K. Computational results related to the path-independence of the atomistic J-Integral are also presented. Further, a novel approach that circumvents the complexities of direct computation of entropic contributions is also discussed. Preliminary results obtained from the bond-order based ReaxFF potential for 0.1 K and 300 K are presented, and show good agreement with the predictions.

The effect of turbulent natural convection in vertical storage tubes containing a supercritical fluid is investigated computationally. In a supercritical thermal storage system, thermal energy is transferred to the storage fluid and is stored as the internal energy of the fluid in supercritical state. The heat is conducted from the heat transfer fluid to the storage fluid through the storage tube wall. Unlike phase-change systems, the heat transfer mechanism within the storage tubes of supercritical thermal storage system is dominantly affected by rigorous turbulent natural convection. The natural convection enhances the heat transfer and compensates for the low thermal conductivity of the storage fluid. The turbulent buoyancy-driven flow field in vertical storage tubes with different aspect ratios is investigated in this paper and the effect of vertical orientation of storage tubes on the characteristics of the flow field is explored. A standard k-epsilon method is utilized to model the Reynolds stresses in turbulent natural convection flow. The results of this study show that the turbulent buoyancy-driven flow and natural convection play an important role in charge and discharge of the supercritical thermal storage system. The charge time of the system is a function of Rayleigh number and aspect ratio of the storage tube.

The present study presents CFD simulations of a liquid-piston compressor with metal foam inserts. The term “liquid-piston” implies that the compression of the gas is done with a rising liquid-gas interface created by pumping liquid into the lower section of the compression chamber. The liquid-piston compressor is an essential part of a Compressed Air Energy Storage (CAES) system. The reason for inserting metal foam in the compressor is to reduce the temperature rise of the gas during compression, since a higher temperature rise leads to more input work being converted into internal energy, which is wasted during the storage period as the compressed gas cools. Liquid, gas, and solid coexist in the compression chamber. The two-energy equation model is used; the energy equations of the fluid mixture and the solid are coupled through an interfacial heat transfer term. The fluid mixture, which includes both the gas phase and the liquid phase, is modeled using the Volume of Fluid (VOF) method. Commercial CFD software, ANSYS FLUENT, is used, by applying its default VOF code, with user-defined functions to incorporate the two-energy equation formulation for porous media. The CFD simulation requires modeling of a negative momentum source term (drag), and an interfacial heat transfer term. The first one is the pressure drop due to the metal foam, which is obtained from experimental measurements. To obtain the interfacial heat transfer term, a compression experiment is done, which provides instantaneous pressure and volume data. These data are compared to solutions of a zero-dimensional compression model based on different heat transfer correlations from published references. By this comparison, a heat transfer correlation which is most suitable for the present study is chosen for use in the CFD simulation. The CFD simulations investigate two types of metal foam inserts, two different layouts of the insert (partial vs. full), and two different liquid piston speeds. The results show the influence of the metal foam inserts on secondary flows and temperature distributions.

Vortex methods for simulating natural convection of an ideal gas in unbounded two-dimensional domains are presented. In particular, the redistribution method for diffusion is extended to enable simulation of nonlinear diffusion of an ideal gas in isobaric conditions encountered in unbounded low-Mach number flows. We also address the problem of handling source terms in grid-free vortex methods and propose a fast, accurate, and physically motivated method for solving the associated inverse problems. Examples include generation of baroclinic vorticity in non-reacting buoyancy driven flows, and in addition, generation of internal energy and species in buoyant reacting flows. Accuracy and speed of the proposed algorithms for nonlinear diffusion and vorticity generation are investigated separately. Simulations of natural convection of a “thermal patch” for Grashof number ranging from to 1562.5 to 25000 are presented.

It is a common practice to approximate the thermodynamics properties of fluids in the compressed liquid regions from their saturation properties. Most thermodynamics textbooks state that the specific volume, specific internal energy, and specific entropy in the compressed liquid region are functions of temperature only and are independent of pressure. Therefore, compressed liquid property tables are not provided for any substance, except for water, and compressed liquid properties are approximated by their saturated liquid properties at a given temperature. Recent examination of current practice in approximating compressed liquid properties has shown that the internal energy of fluids exhibits growing dependency on pressure with increases in temperature. This paper compares the behavior of internal energy and enthalpy four compressed fluids along isotherms with those behaviors along isentropic lines. Water, ammonia, methane, and propane are examined in this study. It is shown that effects of pressure on the internal energy and enthalpy of compressed liquids are much lower along isentropic lines than those along isotherms.

Experimental evidence is presented and compared with theoretical predictions from Quantum Thermodynamics, (QT) to examine whether or not the claims of QT are consistent with the existence and generation of entropy at atomistic scales. QT makes the assertion that entropy is an intrinsic property of matter in the same way that inertial mass, energy, and momentum are and must, thus, exist even for single particles. Entropy as defined by QT is a measure of the distribution of a system’s internal energy at any given instant of time amongst the available internal degrees of freedom, i.e., the energy eigenlevels of the system. In this paper, it is shown that QT predicts the internal relaxation of a 5-level rubidium system that is consistent with the experimental data and not explained by current theory, i.e. by Quantum Mechanics. In addition, it is demonstrated that the decay of so-called “cat states” for single ions that are contained in Paul traps and that interact with a heat reservoir is also consistent with the idea of the existence of entropy and entropy generation at atomistic scales. This is accomplished by comparing experimental data with the predictions made using an extension of the equation of motion of QT that allows for heat interactions.

Most thermodynamic textbooks state that the specific volume, specific internal energy, and the entropy of fluids in the compressed liquid region are independent of pressure and vary only with temperatures. Therefore in the compressed liquid region, these properties at given pressures and temperatures are approximated by their saturated liquid properties at the given temperatures. Examination of property values in the compressed liquid region verifies that these assumptions are valid at low temperatures close to the triple point of the fluids. However, the data show that, with increasing temperature, the internal energy and entropy of fluids exhibit higher dependencies on pressure in the compressed liquid region. In a similar fashion, in most applications, it is assumed that the values of constant pressure specific heat (c p ) and constant volume specific heat (c v ) are approximately the same in the compressed liquid region. Again, examination of these properties in the compressed liquid region validates this assumption for water at low temperatures. However, with increasing temperatures away from the triple point, the deviations between the two specific heat values increase. For fluids other than water the values of c p and c v in the compressed liquid region are not very close, even at temperatures close the triple point. Thermodynamic property behavior of several common fluids in the compressed liquid region is examined in this paper. The paper presents data on the behavior of v, u, h, c p and c v in the compressed liquid region and establishes the range of pressures and temperatures in this region where it is valid to assume that the v, u, h, and s are functions of temperature only and the ranges for which the values of c p and c v can be assumed to be nearly the same.

High Temperature exposure and the corresponding thermo-mechanical behavior of cylindrical polymer composite pipe using CFD simulation has been investigated in this study. The software FLUENT was employed for the analysis of heat transfer, by coupling equations of energy and motion. Analysis was done based on applied external boundary temperature profile, change in internal energy, the total surface heat flux and surface heat transfer rate in order to evaluate the extent of thermal damage. FLUENT compatible program written in C++ language in the form of user define functions (UDF) has been developed and used to specify the time dependent heat flux generated temperature as well as temperature dependent thermal properties of density, thermal conductivity and specific heat. Available furnace test experimental data from (ASTM 1173-95) database were used as outer surface boundary condition in the model setup by developing it into UDF correlation equations. The outputs of the FLUENT simulations are predictions of transient temperature distribution through the thickness of the pipe wall that were then used in evaluating the thermal stresses of the composite pipe. Validation of the simulation results is done with existing data available in the literature. Using the wall generated temperatures, internal energy, the rate of change of the temperature dependent properties and the heat transfer rate, the thermal endurance of each of the coatings materials has been predicted in this work. At the same time knowledge of the thermal performance of these materials is essential for the optimum design of protection based on the composite application.

In order to accurately capture crash behavior during high-speed impact, a large amount of detailed finite element modeling features are needed in the dynamic analysis. An important feature in crash simulation is the amount of detail included in modeling spot weld connections. Traditionally for efficiency, simple node-to-node rigid (MPC) connections for modeling spot weld connections between different components are used in crash models, especially when many components are connected in a fully assembled vehicle crash model. In this work, different levels of complexity in spot weld modeling are examined: (a) simple node-to-node rigid connection, (b) rigid mesh independent spot welds, (c) elastic mesh independent spot welds, and (d) elastic mesh independent spot welds with failure. Mesh-independent spot-weld models define the location of the center point of the spot weld and define the spot weld radius on adjacent surfaces of connected components. A distributed coupling to nodes within the radius specified is automatically created which approximates the behavior of a spot weld of finite size. In order to study the fundamental behavior of different mesh-independent spot weld models, pullout and peal tests between two thin ductile steel plates are performed which isolate different failure modes. Comparisons of reaction force versus displacement curves and internal energy versus displacement for different spot weld models are examined. A case study of a front longitudinal rail for an automobile is presented to illustrate the behavior of the spot-weld models for crash analysis on a realistic and important automotive component which exhibits complex crushing modes with combined axial and bending and designed for strength and energy absorption.

Currently it is a common practice to use saturated liquid properties to approximate thermodynamics properties of fluids in the compressed liquid region. In this practice it is assumed that specific volume, internal energy, and entropy of fluids in the compressed liquid region are functions of temperature only and pressure practically has very little or no effect on these properties. Therefore, these properties at a given temperature and pressure are approximated by the saturated liquid properties at the given temperature. In the current literature the approximation formula given for enthalpy in the compressed liquid region is expressed as h(T, p) = h f (T) + v f (T) [p – p sat (T)], where the aim of the second term on the right hand side of the equation is to improve the accuracy of the approximation, when pressure is much greater than the saturation pressure. However, in a recent study of thermodynamic properties of water, Kostic has shown that the second term in the equation improves the accuracy of the approximation of the enthalpy only at temperatures below 100 °C. In fact, he has shown that the second term increases the error when the formula is used to approximate the enthalpy of water in the compressed liquid region at intermediate and high temperatures. Kostic’s investigation is expanded in this paper to include substances other than water. The study shows that in many situations pressure has a bigger influence on the internal energy than it does on enthalpy of fluids in the compressed liquids. This paper demonstrates that the current practice of approximating properties of fluids in the compressed liquid region is not accurate at all range of temperatures and pressures. It establishes the range of pressures and temperatures for which the current approximation method could be used with reasonable accuracies. It also proposes a new scheme for the approximation of thermodynamic properties in the compressed liquid region.

The generation and propagation of thermally induced acoustic waves in a confined layer of supercritical carbon dioxide are investigated by solving the fully compressible unsteady Navier-Stokes equations. These waves are generated by rapidly heating/cooling a sidewall. Due to the high compressibility, thermally induced acoustic waves are generated along any heated/cooled surface. The acoustic wave reflects from the opposing sidewall and continues to reverberate between the opposing walls. Even though supercritical fluids have high thermal conductivity, heat diffusion is slow. However, the temperature of the layer of the supercritical carbon dioxide is found to increase due to the dissipation of the acoustic energy. Ideal-gas law does not apply to supercritical fluids. Furthermore the internal energy is also not a function of temperature only. The above property variation effects are considered in the present paper.

In this paper, we use a full-scale finite element vehicle model of a 1996 Dodge Neon in simulating two types of vehicle crashes, offset-frontal and side impacts. Based on an analysis of the vehicle’s histories of internal energy absorption under both impacts, we select twenty components as design variables in the optimization of the vehicle’s weight without decreasing the vehicle’s energy absorption capacity and energy absorption rate. We use the second-order polynomials in creating the metamodels for the response functions of energy absorption under both impacts. The optimization result shows a significant reduction on the total weight of the selected components. The LS-DYNA MPP v970 and a full-scale finite element vehicle model of 320,872 nodes and 577,524 elements are used in the simulations. A simulation of 100 ms offset-frontal impact takes approximately 17 hours with 36 processors on the IBM Linux SuperCluster, which has a total of 1038 Intel Pentium III 1.266 GHz processors and 607.5 GB RAM. A simulation of 100 ms side impact takes approximately 29 hours with the same condition as the offset-frontal simulation.

A new method is proposed to predict the life of pressure components operating within the creep range. The method is based on exhaustion of the internal energy in the critical zones of the material. It is shown that the proposed method alleviates some of the major shortcomings of the existing methods yet it is simple enough to be readily applicable to industrial cases. Its predictions compared with a set of experimental data shows that the proposed approach may be used to predict the creep life with an accuracy of better than 2%.

The entropy content of electromagnetic ("black-body") radiation at equilibrium in an enclosure is represented, on a per unit volume basis, by s = [4/3] aT 3 and the internal energy content by u = aT 4 , so s = [4/3] u/T . The entropy transfer rate S τ associated with emission from the radiation is related to the internal energy trans-fer rate Q by S τ = Q/T . In both cases, content and flux, the entropy is proportional to energy divided by temperature. But, in one case the proportionality factor is [4/3] and in the other it is unity. The question has been raised, "Why, this difference?" The following develop-ment explains the source of the difference.