HTTA 2023 07 10 Solutions

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Heat Transfer and Thermal Analysis - A.A. 2022/23 - Date 10/07/2023 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 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 and 3 of the second part B exercise. Part A 1) When integrating the Poisson equation in cylindrical coordinates for a full cylinder, the value of the first integration constantC1 appearing in the heat flux and temperature profiles ˙Q ′′ (r) andT (r): A is equal to the temperature on the cylinder axis B* is always zero C is equal to the temperature on the cylinder external surface D depends on the type of boundary condition applied on the external surface 2) In which of the following answers is the Kirchhoff law correctly written? A ρλ,T +αλ,T +τλ,T = 1 B λmax emission·T = const C* ελ,T,↗ = αλ,T,↗ D ˙E ′′ T =εTσT 4 3) The net energy flux by radiation between two diffuse, gray, opaque facing planes with temperaturesT1 andT2 can be expressed as: A ˙E ′′ 1,2 =−σ (T24−T14) 1 ε1 − 1 ε2 B ˙E ′′ 1,2 =−ε1ε2σ (T24−T14) C* ˙E ′′ 1,2 =− σ (T24−T14) 1 ε1 + 1 ε2 − 1 D ˙E ′′ 1,2 =−σ (T24−T14) ε2 +ε1− 1 4) The Young equation reads: A ∆P = σ/ (1/RI + 1/RII) B ∆P = σ (1/RI + 1/RII) C* cosθ = σSA−σSL σLA D cosθ = σLA σSA−σSL 5) The Grashof dimensionless group is defined as: A Gr = kP|Tf−Tw|D3 C ν2 f B Gr = g|Tf−Tw|D3 C ρ2 f C Gr =…