HTTA 2022 07 08 Solutions

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Heat Transfer and Thermal Analysis - A.A. 2021/22 - Date 08/07/2022 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. NOTES: ˆ Students of the Nuclear Engineering programme (attending the 052603 - 5 CFU course) have some different questions in part A. ˆ Students having right to a test reduction should answer only to: all part A questions, the first 2 (two) part B questions, the first 2 (two) queries of the first part B exercise, the first 3 (three) queries of the second part B exercise. Part A 1) In which of the following answers are the substances correctly ordered according to increasingthermal conductivity? A Air - water - iron - stainless steel - diamond - copper B* Air - water - stainless steel - iron - copper - diamond C Water - air - copper - stainless steel - iron - diamond D Diamond - iron - copper - stainless steel - air - water 2) Concerning capillary phenomena, 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 3) The radiosity for a diffuse, gray, opaque surface can be calculated as: A radiosity=α· irradiation+εσT 4surface B* radiosity=ρ· irradiation+εσT 4surface C radiosity=ρ· irradiation+ασAsurfaceT4surface D radiosity=ρAsurface· irradiation+εσT 4surface 4) A full sphereS1 having radiusR1 = 50 mm is concentric with a spherical shellS2 having radius R2 = 100 mm. The view factorFS1→S2 from sphereS1 towards spherical shellS2 is: A* 1 B 0 C 0.5 D 0.25 5) The Grashof dimensionless group is defined as: A Gr = kP|Tf−Tw|D3C ν2f B Gr = g|Tf−Tw|D3C ρ2f C Gr = gkP|Tf−Tw|D3C µ2f D* Gr = gkP|Tf−Tw|D3C ν2f 6) Active sites for nucleation are of importance: A During film condensation to avoid the…