HTTA 2019 07 12 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 12/07/2019 Surname: Name: ID number: Signature: (“matricola” or person code) Part A 1. Draw (qualitatively but with physical accuracy) the velocity and temperature profiles for free convection over a vertical flat plate, with Tplate <T∞. See slides group 2 p. 12 (top-right chart) and mirror vertically both the profiles, as Tplate <T∞ 2. Calculate the capillary pressure jump for a spherical water drop in air ( σ = 72 mN/m) having radius R = 1µm. From Laplace-Young equation for a sphere (see slides group 3A p. 8): 1.44 bar 3. Draw the Nukiyama curve for pool boiling, evidencing the regions corresponding to the different boiling regimes. See slides group 3B p. 8 4. Indicate three passive and one active devices for thermal control. See slides group 6 pp. 24-26 5. Write the Beer law and the distinction between optically thick and thin media. See slides group 5 p. 8 6. Write the Fourier law for a medium with conductivity varying with position, direction and temperature. See slides group 1 p. 10 7. Put the following substances/materials in ascending order of conductivity: water - iron - copper - diamond. They are already in the correct order: water - iron - copper - diamond. Heat T ransfer and Thermal Analysis - A.Y. 2018/19 - Date 12/07/2019 - 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…