HTTA 2025 07 08 Solutions

Pagina 1

Heat Transfer and Thermal Analysis - A.A. 2024/25 - Date 08/07/2025 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. NOTES: ˆ Students attending the 5 CFU course may have some different questions in part A. ˆ For the exercise queries, in case none of the multiple-choice answers the exercise matches the result you get, write your own result instead of marking an answer (so that in case we did a mistake and your answer is correct you can get the related points). ˆ Students having right to a test reduction should answer only to: all part A questions; part B questions 1 and 2; queries 1, 2 of the first part B exercise; queries 1, 2, 3 of the second part B exercise. Part A 1) The 1D,T =T (r), Poisson equation in cylindrical coordinates can be written as: A 1 r2 ∂ ∂r ( r2∂T ∂r ) = − ˙U ′′′ λ B* 1 r ∂ ∂r ( r∂T ∂r ) = − ˙U ′′′ λ C 1 r2 ∂ ∂r ( r2∂T ∂r ) = 0 D 1 r ∂ ∂r ( r∂T ∂r ) = 0 2) In which of the following answers is the Stefan-Boltzmann law correctly written? A ρλ,T,↗ +αλ,T,↗ +τλ,T,↗ = 1 −ελ,T,↗ B λmax emission ·T = 2897 C ελ,T,↗ ≈ αλ,T,↗ D* ˙E ′′ T =εTσT 4 3) Which of the following answers is usually true when considering temperatures or temperature ranges for thermal control? A ∆Toperating> ∆Tnon-operating> ∆Tsurvival B Toperating> Tnon-operating> Tsurvival C Toperating< Tnon-operating< Tsurvival D* ∆Toperating< ∆Tnon-operating< ∆Tsurvival 4) 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 a positive heat source and the other without, knowing that the left face of the wall is adiabatic while the face on the right exchanges by…