No abstract

No abstract

No abstract

Flow in the cavity with heat generating body finds wide domestic and industrial applications. The heat transfer characteristics and the irreversibility generated in the cavity depend on mainly the cavity size, aspect ratio of the heat generating body, and inlet/exit port locations. In the present study, effect of exit port locations on the heat transfer characteristics and irreversibility generation in a square cavity with heat generating body is investigated. A numerical simulation is carried out to predict the velocity and temperature fields in the cavity. To examine the effect of solid body aspect ratio on the heat transfer characteristics two extreme aspect ratios (0.25 and 4.0) are considered in the analysis. Fifteen different locations of exit port are introduced while air is used as an environment in the cavity. It is found that non-uniform cooling of the solid body occurs for exit port location numbers of 13 and beyond. In this case, heat transfer reduces while irreversibility increases in the cavity. These findings are valid for both aspect ratios of the solid body. Nomenclature A = cross-sectional area of solid body (m 2 ) a = aspect ratio b = length of protruding body (m) c = height of protruding body (m) h = heat transfer coefficient (W/m 2 K) I = irreversibility (W/m 3 ) k = thermal conductivity (W/mK) l = hydraulic radius of the solid body (m) Nu = Nuselt number P = pressure (Pa) P T = wetted perimeter of solid body (m) Ra = Rayleigh number HHH = volumetric entropy generation (W/ m 3 K) T = temperature (K) u = velocity in x-axis (m) v = velocity in y-axis (m) x = distance in x-axis (m) y = distance in y-axis (m) Greek symbols = thermal diffusivity (m 2 /s) = expansion coefficient (K ±1 ) " = viscosity (N.s/m 3 ) ) = kinematic viscosity (m 2 /s) & = density (kg/m 3 ) Subscripts F = fluid s = solid w = wall o = reference IntroductionMixed convection in a cavity receives considerable attention due to its importance in many engineering applications. Some of these include energy transfer in rooms and units, and cooling of industrial machines and electronic

No abstract

No abstract

No abstract

The Fourier theory of heating is not applicable to the short-pulse type of laser heating due to the assumptions made in the theory. On the other hand, two-equation and kinetic theory models offer an improved solution to the problem. Consequently, the present study compares the predictions of one-equation (Fourier heating model), two-equation, and kinetic theory models for the laser heating pulses of 10 −9 , 10 −10 and 10 −11 s lengths. The physical significance of the predictions are described and the discrepancies among the findings are discussed. It is found that all the models employed in the present study predict similar temperature profiles in the substrate for a nanosecond laser heating pulse. As the pulse length shortens such as to 10 −10 and 10 −11 s, the one-equation model predicts excessive temperature rise in the surface vicinity; however, two-equation and kinetic theory models predict similar temperature profiles. In this case, electron temperature rises rapidly while the lattice temperature increase slows down. Nomenclature ABS Absolute C eElectron heat capacity (J kg 1− K −1 ) C l Lattice site heat capacity (J kg 1− K −1 ) C p Specific heat (J kg 1− K −1 ) E Energy change of lattice site atoms (J) f Fraction of excess energy exchange G Electron-phonon coupling factor I 0 Laser peak power intensity (W m −2 ) k Thermal conductivity k B Boltzmann's constant (1.38 × 10 −23 J K −1 ) m e Electron mass (kg) N Electron number density (m −3 ) φ(x, t) Phonon temperature (K) V Electron mean velocity (m s −1 ) x Spatial coordinate along the x-axis for phonon (m) s Spatial coordinate along the x-axis for electron movement (m) α Thermal diffusivity (m 2 s −1 ) δ Absorption coefficient (m −1 ) t Time increment (s) x Time increment (m) λ Mean free path of electrons (m) θ(s, t) Electron temperature (K) ρ Density (kg m −3 ) τ Electron mean free time