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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: 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]