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Heat transfer simulation in thermoplastics processing is crucial to predict the quality of parts in terms of geometry and mechanical properties. The results accuracy depends on the knowledge of thermo-physical properties, crystallization kinetics and boundary conditions, which have to be determined in representative process conditions. In this work, we focus on the impact of high cooling rate on heat transfer and crystallization at the surface of a thermoplastic part. For this purpose, a home-made device named “Lagardère apparatus” is presented. It can reproduce cooling rate encountered in injection moulding by the sudden contact between a cold surface and a molten polymer. The first objective of this paper is the direct measurement of the thermal contact resistance used to model the imperfect contact between the polymer and the mould. The mould surface temperature and the heat flux at the interface were provided by a heat flux sensor. The specificity of this methodology was to obtain the polymer surface temperature with an optical fibre associated with a photodetector. A particular attention was made to avoid the invasiveness of the sensors on heat transfer. The second objective of the paper is the crystallization study at the surface of the polypropylene part. The experimental heat flux was compared with computed ones for which crystallization kinetics comes from Fast Scanning Calorimetry measurement and a standard model commonly used in the literature. It seemed that a very fast crystallization occurred at the surface of the part with a lower released enthalpy compared to the bulk. [ABSTRACT FROM AUTHOR]

Abstract: This paper computes the thermal delay in multilayer systems. The heat transfer by conduction across multilayer systems under unsteady boundary conditions is simulated using analytical solutions. The solutions, obtained as Green''s functions, are established by imposing temperature and heat flux continuity at the media interfaces of the various layers. The unsteady state conditions are dealt with by first computing the solution in the frequency domain and then applying (fast) inverse Fourier transforms into space-time. After validating the analytical formulation by comparing these results with those obtained experimentally, the thermal delay is computed for different multilayer systems. It is computed as the difference between the time the thermal variation is recorded in one of the system''s surfaces and the time it appears at the opposite surface. The paper calculates the computed thermal delay for construction walls made of cork, mineral wood and extruded polystyrene panels. The thermal properties of these materials have been previously defined experimentally. In the simulations, the systems are subjected to temperature changes that vary according a sine function, with the aim of defining the environmental exterior temperature variation over a period of several days. [Copyright &y& Elsevier]

Abstract: This paper focuses on discussing four myths and concerned conventional practices of film cooling research guided by a series of computational simulations. The issues that have been discussed include: (a) the film cooling effectiveness (φ) is given a constant (0.6) to calculate the heat flux ratio between film-cooled and no-film cases; (b) the adiabatic wall temperature is the driving temperature of film cooling; (c) the adiabatic film heat transfer coefficient can be obtained from an isoenergetic film experiment (T j = T g); (d) using a heated surface can provide a simplified approach to simulate the film-cooling condition. The result shows that the adiabatic wall temperature is not always the driving temperature (i.e. T aw is not always larger than T w), but T aw does act well as the reference temperature in correctly predicting the heat flux direction and giving an always positive adiabatic film heat transfer coefficient. Using a constant value for φ is questionable and may lead to un-realistic or false HFR. The conventional equation of HFR was not theoretically exact and can lead to an error of up to 20%. A revised HFR equation is provided in this paper. The dominant energy passage in turbine airfoil film cooling is always from hot combustion gas flows into the airfoil; therefore, employing a heated wall as a boundary condition with hotter main stream flow and cold film injection to simulate the actual film cooling condition is found to be fundamentally questionable. A conjugate simulation that includes wall heat transfer and internal flow cooling shows that reversed heat transfer from blade to gas that gives a negative HFR is possible, due to the heat conduction from the downstream hotter region into the near film hole cooler region. [Copyright &y& Elsevier]

Abstract: Natural convection in an open ended cavity is simulated using Lattice Boltzmann Method (LBM). The paper is intended to address the physics of flow and heat transfer in open end cavities and close end slots. The flow is induced into the cavity by buoyancy force due to a heated vertical wall. Also, the paper demonstrated that open boundary conditions used at the opening of the cavity is reliable, where the predicted results are similar to conventional CFD method (finite volume method, FVM) predictions. Prandtl number (Pr) is fixed to 0.71 (air) while Rayleigh number (Ra) and aspect ratio (A) of the cavity are changed in the range of 104–106 and of 0.5–10, respectively. It is found that the rate of heat transfer deceases asymptotically as the aspect ratio increases and may reach conduction limit for large aspect ratio. The flow evaluation in the cavity starts with recirculation inside the cavity, as the time proceeds the flow inside the cavity communicates with the ambient. [Copyright &y& Elsevier]

In this paper we describe the implementation of a ghost-cell immersed boundary method for compressible flow with Dirichlet, Neumann and Robin boundary conditions. A general second-order reconstruction scheme is proposed to enforce the boundary conditions via ghost points. The convergence test shows that the present method has a second-order accuracy for three types of boundary conditions. Laminar flow heat transfer problems are used to test the capability of the present method to handle different boundary conditions with stationary and moving boundaries. The compressible effect on the heat transfer process is then studied to illustrate the advantage and necessity of combining IB methods with a compressible flow solver. [ABSTRACT FROM AUTHOR]

Abstract: Nanofluids are a novel strategy to improve heat transfer characteristics of fluids by the addition of solid particles with diameters below 100nm. Experimental measurements have shown that this approach can greatly increase heat conductivity, even above that predicted by Maxwell’s theory. However, it is still not clear what mechanism accounts for this increase, mainly in thermal conductivity, thus great effort is being put into investigating the different phenomena occurring inside the fluid. This paper shows a direct numerical simulation of the flow and thermal behaviour of a nanofluid loaded with alumina nanoparticles which considers the effects of particle–particle and particle–fluid interactions. The boundary element method is used given its capabilities to deal with moving boundary problems. This formulation was employed to simulate the behaviour and time evolution of a 30nm alumina/water nanofluid at six different particle concentrations, looking to observe flow fields, temperature distributions and total heat flow through the domain. Results showed strong convective currents caused by the presence of the nanoparticles, which in time increased total heat flow in the cavity. As expected, particle concentration increased the total heat flow affecting not only the conductive part of heat transfer, but the convective part as well. [Copyright &y& Elsevier]

Abstract: This paper investigates the numerical simulation of non-Fourier transient heat transfer in a two-dimensional sub-100nm metal-oxide-semiconductor field-effect transistor (MOSFET). The dual-phase-lag (DPL) model with a specific normalization procedure is introduced for the modeling of nanoscale heat transport. The boundary conditions are selected similar to what existed in a real MOSFET device, both uniform and non-uniform heat generations within the transistor are applied, and the end parts of the top boundary which are in contact with the metallic material are left open. A temperature-jump boundary condition is used on all boundaries in order to consider the boundary phonon scattering at micro and nanoscale. A three-level finite difference scheme has been employed to generate the numerical results which are illustrated for a silicon sub-100nm MOSFET corresponding to the Knudsen number of 10. The results are presented at real times less than 50ps to avoid the three-dimensional effects. It is concluded that the combination of the DPL model with mixed-type temperature boundary condition is able to predict the heat flux and temperature distribution obtained from the Boltzmann transport equation (BTE) more accurate than the ballistic-diffusive equations (BDE). After verification of our results, the thermal field and the hotspot temperature within the bulk silicon are presented and the effect of adding a layer of silicon-dioxide to the transistor on its thermal behavior has been investigated. [Copyright &y& Elsevier]

Abstract: The purpose of this paper is to present heat transfer measurements of gas in a tube under rarefied condition. The measurements are made in a circular tube of inner diameter 25mm for approximately constant wall temperature boundary conditions, with nitrogen, oxygen, argon, and helium as the working fluids. The range of Knudsen and Reynolds numbers covered in this study are 0.0022–0.032 and 0.13–14.7, respectively. Whereas the continuum values are correctly reproduced in our setup, the measured values for Nusselt numbers are very small in the slip regime. The measured values are two-five orders of magnitude smaller than the corresponding values in the continuum regime, and suggest that the Nusselt number is a strong function of Reynolds, Knudsen and Brinkmann numbers in the slip flow regime. These are among the first heat transfer measurements in the slip flow regime and the current theoretical and simulation models are inadequate to explain such low values of Nusselt number. [ABSTRACT FROM AUTHOR]

Abstract: This paper focuses on the investigation of the 3D mathematical model to simulate the coupled heat and liquid moisture transfer in hygroscopic porous fibrous media. The flow of the liquid moisture, the water vapor sorption/desorption by fibers and the diffusion of the water vapor are taken into account in this 3D model. Prediction-corrector method is used to solve the 3D governing equations. A series of computational results of the coupled heat and moisture transfer are obtained with the specific initial conditions and boundary conditions. The distribution of the water vapor concentration in the void spaces, the volume fraction of the liquid water in the void spaces, the distribution of the water content in fibers and the changes of the temperature in porous fibrous media are computed. It is shown that the effects of the gravity and capillary actions are significant in hygroscopic porous fibrous media. The comparison with the experimental measurements shows the reasonable agreement between the two. The results illustrate that the 3D model of the coupled heat and liquid moisture transfer in hygroscopic porous fibrous media is satisfactory. [Copyright &y& Elsevier]