2025 02 10 ENG

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Exam of Multiphase Systems and Technologies – a.y. 2024-25 1st call of the Winter session – February 10th, 2025 – Test Energy 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 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 3 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 4 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 5 Referring to the Heat Atlas pool boiling model (Gorenflo et al.), the following parameter is used to: 𝑃𝑓 = (𝑑𝑝 𝑑𝑇) 𝑉𝑃𝐶 𝜎 Answer a Consider the effect of the pressure b Consider the effect of the saturation temperature c Consider the effect of the heater wettability d Consider the variation in the properties of different fluids at the same reduced pressure X Question 6 Referring to the cavities (b) to (e) in the figure reported below: Answer a Only cavity (b) may act as a nucleation site b Only cavity (c) may act as a…