HTTA 2024 06 11 text with solutions

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Heat Transfer and Thermal Analysis - A.A. 2023/24 - Date 11/06/2024 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 of the Nuclear Engineering programme (attending the 052603 - 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) Which of the following correlations can be for forced convection around a sphere? A NuL = C1ReC2 D BiC3 D B* NuD = C1ReC2 D PrC3 C NuD = C1GrC2 D PrC3 D NuL = C1ReC2 L PeC3 2) In which of the following answers is the Wien law correctly written: A* λmax emissionT = const B λmax emissionT2 = const C λmax emissionT3 = const D λmax emissionT4 = const 3) 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 ′′′ r/(3λ) +C1/r2 B* none of the other answers is correct C ˙Q ′′ (r) =− ˙U ′′′ /3r−C1r2/λ D ˙Q ′′ (r) = ˙U ′′′ /3r 4) 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 + ˙Q ′′ /(ρc) =−λ∂T/∂τ C* ∇(λ∇T) + ˙U ′′′ = ρc∂T/∂τ D ∇2T + ˙Q ′′ = ρc∂T/∂τ 5) Which of the following is true for two surfaces that exchange heat by…