HTTA 2023 01 10 Solutions

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Heat Transfer and Thermal Analysis - A.A. 2021/22 - Date 10/01/2023 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 Students having right to a test reduction should answer only to: all part A questions, the first 2 (two) part B questions, all the queries of the first part B exercise, query n.2 of the second part B exercise. Part A 1) The temperature profileT (τ) of a small, very conductive sphere (with uniform and constant thermophysical properties), initially atT0 and convectively heated by a constant temperature ambient atT∞: A has oscillations when a constant internal heat source is present B has oscillations if no internal heat source is present C* tends toT∞ if no internal heat source is present D tends toT∞ if an internal heat source is present 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) In which of the following answers are the substances correctly ordered according to decreasing values of the Prandtl number? A* viscous mineral oil - water - air - liquid metal B air - water - viscous mineral oil - liquid metal C liquid metal - air - water - viscous mineral oil D air - water - liquid metal - viscous mineral oil 4) For a medium with constant conductivity, the conduction equation can be written as: A* λ∇2T + ˙U ′′′ = ρc∂T/∂τ B ∇2T + ˙U ′′′ /(ρc) =−λ∂T/∂τ C ∇(λ∇T)−λ ˙U ′′′ = ρc∂T/∂τ D ∇2T =−λ 5) The Richardson dimensionless group is defined as: A* Ri = Gr Re2, where Gr and Re are the Grashof and Reynolds dimensionless groups, respectively B Ri = Re2 Bi , where Re and Bi are the Reynolds and Biot dimensionless groups, respectively C Ri =…