1,721,082 research outputs found
A Conjugate Heat Transfer Procedure for Gas Turbine Blades
No full textA conjugate heat transfer procedure, allowing for the use of different solvers on the solid and fluid domain(s), is presented. Information exchange between solid and fluid solution is limited to boundary condition values, and this exchange is carried out at any pseudo-time step. Global convergence rate of the procedure is, thus, of the same order of magnitude of stand-alone computations
Numerical investigation of the effect of boundary conditions for a highly rarefied gas flow using the GPU accelerated Boltzmann solver
No full textThe effect of the gas-surface interaction model on the rarefied gas flow between parallel plates is investigated on the basis of the Boltzmann kinetic equation. The Cercignani-Lampis model for diffuse scattering with incomplete energy accommodation is provided as the boundary condition on plates. The numerical analysis of the heat transfer problem between parallel plates with uniform and sinusoidal temperature distributions is carried out. The computational algorithm is adapted for solving the Boltzmann equation onto Graphics Processing Units (GPUs). The speedup of the GPU-accelerated computation is up to 50 times as compared to the CPU one. It was found that a non-uniform temperature distribution on plates induced a steady flow. In addition, the flow field strongly depends on the value of accommodation coefficients imposed in the Cercignani-Lampis model and this effect is more visible for high Knudsen numbers. Presented results are in good agreement with open literature ones obtained by means of the direct simulation Monte Carlo method. (C) 2014 Elsevier Ltd. All rights reserved
Empirical equation for the prediction of viscosity for some common nanofluids
No full textA new model is proposed for calculating the relative viscosity of some common nanofluids. Based both on the available literature data and some theoretical considerations it was proposed that the relative viscosity can be calculated using only the values of densities of the particles and of the base fluid. The comparison of our results with existing empirical models using various concentrations and temperatures demonstrated that the proposed equation predicts satisfactory the experiments with an average error of about 4%. The model confirms the already published dependence of the relative viscosity on the variation of volume concentration, temperature and of the particle characteristics reported in some experimental studies. One can use the proposed model to predict the behavior of the system in the case of missing of contradicting experimental data and to develop innovative nanofluids
Compressibility and rarefaction effect on heat transfer in rough microchannels
No full textHigh pressure drop and high length to hydraulic diameter ratios yield significant compressibility effects in microchannel flows, which compete with rarefaction phenomena at the smaller scale. In such regimes, flow field and temperature field are no longer decoupled. In presence of significant heat transfer, and combined with the effect of viscous dissipation, this yields to a quite complex thermo-fluid dynamic problem. A finite volume compressible solver, including generalized Maxwell slip flow and temperature jump boundary conditions suitable for arbitrary geometries, is adopted. Roughness geometry is modeled as a series of triangular shaped obstructions, and relative roughness from 0% to 2.65% were considered. The chosen geometry allows for direct comparison with pressure drop computations carried out, in a previous paper, under adiabatic conditions. A wide range of Mach number is considered, from nearly incompressible to chocked flow conditions. Flow conditions with Reynolds number up to around 300 were computed. The outlet Knudsen number corresponding to the chosen range of Mach and Reynolds number ranges from very low value to around 0.05, and the competing effects of rarefaction, compressibility and roughness are investigated in detail. Compressibility is found to be the most dominant effect at high Mach number, yielding even inversion of heat flux, while roughness has a strong effect in the case of rarefied flow. Furthermore, the mutual interaction between heat transfer and pressure drop is highlighted, comparing Poiseuille number values for both cooled and heated flows with previous adiabatic computation
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