HTTA 2019 02 07 Solutions

Pagina 1

VER Y IMPOR T ANT Please read with great attention the instructions written at the beginning of the text of Part B. Not complying with them will result in a penalty . Heat T ransfer and Thermal Analysis - A.Y. 2017/18 - Date 07/02/2019 Surname: Name: ID number: Signature: (“matricola” or person code) Part A 1. Write the finite difference approximation of the 1D conduction equation without heat source: ρc ∂T ∂τ = λ ∂ 2T ∂x 2 using the basic centered form for the space derivative and 1) the explicit approach, 2) the implicit approach, for the time dependence. 2. Write a commonly used criterion to distinguish between forced, natural and mixed convection. 3. Write the general form of the Laplace-Young equation, stating the meaning of the involved terms. 4. Draw (qualitatively but with physical accuracy) the steady-state temperature profiles in a passive flat plate having fixed temperatures on the external surfaces and: A) constant conductivity, B) conductivity increasing with temperature, C) conductivity decreasing with temperature. 5. Write the general integrals (before application of any b.c.) giving the temperature and heat flux profiles as a function of the radius for a homogeneous sphere with heat source, in steady-state conditions. 6. Write the definitions of the void fraction for a two-phase flow in local, section-averaged and volume-averaged terms. 7. Write if and why the heat transfer during dropwise condensation is larger or lower than in film condensation. Heat T ransfer and Thermal Analysis - A.Y. 2017/18 - Date 07/02/2019 - Part B INSTRUCTIONS Read them very carefully - Not complying with them will result in a penalty from -1 point to not having some parts of the test corrected. • test duration is 1 h 45’. The text of both exam parts is given at the beginning. The…