Revue Générale de Thermique最新文献

We propose numerical solutions for a laminar jet, accounting for emission conditions at the exit of the nozzle. Two emission cases are considered in this study: velocity and temperature profiles are uniform or parabolic, respectively. A finite difference scheme is developed for the resolution of the equations governing the isothermal and non-isothermal free jet and wall jet developing tangentially along an adiabatic flat plate. The analysed results are the centerline velocity and centerline temperature for the free jet, and wall temperature and shear stress for the wall jet. The results obtained are compared to another method that is based on two constraints of integration, i) conservation of momentum and ii) conservation of energy, to replace the emission conditions at the exit of the nozzle for the resolution of equations. Our results of the velocity and temperature profiles compare well with those obtained by the latter method solely in the plume region, where buoyancy forces are responsible for flow.

This article sets out an experimental technique for the determination of the local convective heat transfer coefficients on the surface of a rotating disc. This technique is based on the use of thermally thick walls, on infrared thermography as a method of surface temperature determination, and on the numerical solution of the energy equation to evaluate the local convective exchanges. The tests were carried out on a disc with a large temperature difference between its periphery and its interior. The rotational Reynolds number varies from 2·10⁴ to 1.4·10⁶, extending from the laminar to the turbulent regime. The experimental results are compared with the ones taken from the literature and show the influence of the disc geometry and of the nature of the temperature distribution law on its surface on the convective heat transfer.

Three-dimensional non-grey gas radiation analyses were conducted using the statistical narrow-band model with updated band parameters and three implementation methods: the exact or the correlated formulation, the non-correlated expression, and the grey-band approximation with the absorption coefficient estimated using the local properties. The accuracy of the two approximate narrow-band implementation methods was evaluated for both low-resolution spectral intensity and spectrally integrated radiative source term and wall heat flux in a rectangular enclosure containing (1) isothermal pure water and (2) a CO₂/H₂O/N₂ mixture with a furnace type gas temperature distribution. For spectrally integrated quantities, results of the grey-band approximation are very close to those of the non-correlated formulation and are in qualitative agreement with the results of the correlated formulation. The two approximate methods are capable of predicting qualitatively correct and fairly accurate distributions of low-resolution spectral radiation intensities for the isothermal case. However, they predict less accurate low-resolution spectral intensities for the non-isothermal case.

The laminar natural convection in a square cavity submitted to different heating modes on its vertical walls, is investigated numerically. The temperature of the heated wall is varied sinusoidally with time while the temperature of the opposite vertical wall is either maintained constant or varied sinusoidally with time. The parameters of the study are the amplitude of the variable temperature(s) (0 ≤ a ≤ 0.8), its (their) period (0.001 ≤ τ < 1), the Rayleigh number (10⁴ ≤ Ra ≤ 10⁶) and the Prandtl number (Pr = 0.7). For adequate combinations of these parameters, the variation with time of the two imposed temperatures gives the possibility to control the heat transfer through the cold boundary of the cavity.

Recently an extension of the principle of maximum, for the variation of the entropy due to irreversibility, has been obtained for the open systems. This result is analysed and a comparision between this one and other thermodynamical variational principles of stability is developed. An application to two-phase flows is done to obtain the pressure drop.