HTTA 2019 06 21 Solutions

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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. 2018/19 - Date 21/06/2019 Surname: Name: ID number: Signature: (“matricola” or person code) Part A 1. Draw (qualitatively but with physical accuracy) the 1D, steady-state T (r) profile in a domain constituted by: 1) a two-layer full cylinder, in which a heat source is present in the internal core, while the external layer is passive; 2) a surrounding fluid that exchanges by convection with the cylinder. 2. Write the espressions of three dimensionless groups used to estimate the convective coefficient and state their physical meaning. 3. Write the general conduction equation for a solid with conductivity variable with temperature. 4. Sketch a second surface mirror, evidencing the difference with respect to a first-surface one, and stating why it is better than the latter as a thermal control device. 5. Write the equations to calculate the apparent contact angle using the Wenzel model and the Cassie-Baxter model. 6. A cavity is formed by three surfaces. Neglecting the external exchanges, write the radiosity balance at surface 1. 7. Write the definitions of the void fraction for a two-phase flow in local, section-averaged and volume-averaged terms. Heat T ransfer and Thermal Analysis - A.Y. 2018/19 - Date 21/06/2019 - 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 suggestion is to devote to part A no more than 35’. • you must fill in all the fields (surname, name, student ID…