2025 02 10 NUC

Pagina 1

Exam of Multiphase Systems and Technologies – a.y. 2024-25 1st call of the Winter session – February 10th, 2025 – Test Nuclear Surname Name Person code Correct answers Score Mark the correct answer(s) in the dedicated space Question 1 Which one is not a two-phase multiplier? Answer a (𝑑𝑝𝑓 𝑑𝑧⁄ ) (𝑑𝑝𝑓 𝑑𝑧⁄ )𝑔 b (𝑑𝑝𝑓 𝑑𝑧⁄ ) (𝑑𝑝𝑓 𝑑𝑧⁄ )𝑔𝑜 c (𝑑𝑝𝑓 𝑑𝑧⁄ )𝑙 (𝑑𝑝𝑓 𝑑𝑧⁄ )𝑔 X d 𝑓𝑇𝑃 𝑓𝑙𝑜 (1 + 𝑥 𝑣𝑙𝑔 𝑣𝑙 ) Question 2 The slip ratio is equal to 1 if: Answer a The local velocity of the phases is the same b The cross-section average velocity of the phases is the same X c The superficial velocity of the phases is the same d The void fraction is equal to the mass quality Question 3 What is not verified in case of homogenous flow? Answer a The liquid holdup is equal to the ratio of the liquid volume flow rate to the total volume flow rate of the mixture b The bulk density is equal to the actual density c The bulk specific volume is equal to the momentum averaged specific volume d The ratio of the superficial velocities is equal to one X Question 4 Which are not typical correlations for nucleate boiling? Answer a 𝛼~𝑞"𝑠0.67 b 𝛼~∆𝑇𝑠,𝑆𝐴𝑇 2 c 𝛼~∆𝑇𝑠,𝑆𝐴𝑇 0.25 X d 𝛼~∆𝑇𝑠,𝑆𝐴𝑇 0.33 X Question 5 In the frame of the drift-flux model by Zuber and Findlay, the drift-velocity: Answer a Is equal to 1 in case of homogeneous flow b Is equal to 0 if the slip ratio is 1 X c Is the difference between the gas and the liquid velocities d Is negligible at low mixture velocities Question 6 The term “heterogeneous nucleation” generally refers to: Answer a Molecular clusters with vapour-like energy b Boiling in multicomponent mixtures c Boiling at rough surfaces d Pre-existing vapour nuclei X Question 7 Referring to the Heat Atlas pool boiling model (Gorenflo et al.), the following parameter is used to: 𝑃𝑓 = (𝑑𝑝 𝑑𝑇) 𝑉𝑃𝐶 𝜎…