HTTA 2022 02 04

Pagina 1

Heat Transfer and Thermal Analysis - A.A. 2020/21 - Date 04/02/2022 VERY IMPORTANT: the answers must be written on the “Results” paper sheet, not on this text. Only the “Results” paper sheet must be uploaded and will be evaluated! Part A In which of the following answers are the temperature and heat flow profiles correctly drawn, for a flat wall in steady-state conditions consisting of two layers, the one on the left with power generation and the other without, knowing that the left face of the wall is adiabatic while the face on the right exchanges by convection with a fluid? A B C D In steady-state conditions, the general heat flux profile ˙Q ′′ (r) in a homogeneous, hollow sphere in which a heat source˙U ′′′ is present reads as (C1>0): A ˙Q ′′ (r) =−˙U ′′′ /(3λ)r +C1/r2 B none of the other answers is correct C ˙Q ′′ (r) = ˙U ′′′ /3r−C1λ/r2 D ˙Q ′′ (r) = ˙U ′′′ /3r The most general form of the conduction equation for homogeneous, isotropic media with conductivity varying with temperature is: A λ∇2T + ˙U ′′′ =ρc∂T/∂τ B∇2T + ˙U ′′′ /(ρc) =−λ∂T/∂τ C∇(λ∇T) + ˙U ′′′ =ρc∂T/∂τ D∇2T = 0 Comparing Rayleigh and Mie scattering: A Rayleigh scattering is due to larger particles and is less isotropic B Rayleigh scattering is due to smaller particles and is less isotropic C Rayleigh scattering is due to larger particles and is more isotropic D Rayleigh scattering is due to smaller particles and is more isotropic A gray emitter hasε = 0.6,ρ = 0.4,τ = 0. If it is atT = 25° C and its total irradiation isEi = 100 W, what is its total radiosity? A 309 W B 269 W C 40 W D 60 W During pool boiling, the maximum heat flux is: A at the onset of nucleate boiling B just before the onset of nucleate boiling C just before the dryout D just after the dryout The temperature profileT (τ) of a small, very…