2025 01 21 ENG

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Exam of Multiphase Systems and Technologies – a.y. 2024-25 1st call of the Winter session – January 21st, 2025 – Test Energy Surname Name Person code Correct answers Score Mark the correct answer(s) in the dedicated space Question 1 In a drift-flux model, the distribution parameter is defined as Answer a 1 − 𝜀̅ 𝜀̅ ∫ 𝑈𝑔𝜀𝑑ΩΩ ∫ 𝑈𝑙(1 − 𝜀)𝑑ΩΩ b ∫ 𝑗𝜀𝑑ΩΩ 1 Ω∫ 𝜀𝑑ΩΩ ∫ 𝑗𝑑ΩΩ X c 𝑓𝑙 𝑓𝑔 (1 − 𝑥̅ 𝑥̅ ) 2 𝜚𝑔 𝜚𝑙 d 𝐾 (1 − 𝑥̅ 𝑥̅ ) 𝑎 (𝜚𝑔 𝜚𝑙 ) 𝑏 (𝜇𝑙 𝜇𝑔 ) 𝑏 Question 2 You would adopt the following expression for the two-phase gas-liquid multiplier Answer a In case of homogeneous flow b In case of horizontal flow c In case of confined flow (mini channels) X d In case of laminar flow in both the phases Question 3 The pool boiling model reported below takes into account the following parametric effects: λ, thermal conductivity η, dynamic viscosity Answer a Heater shape, system pressure, buoyancy forces, heat flux b Heater shape, fluid properties, heat flux c Heater size, system pressure, surface finish, heat flux d Heater size, type of fluid, system pressure, heat flux X Question 4 The critical radius of a bubble nucleated at a surface is Answer a The maximum bubble radius b The radius associated with the minimum bubble curvature c The radius associated with the maximum wall superheat required to activate a cavity d The radius associated with the minimum wall superheat required to activate a cavity X Question 5 The term departure from nucleate boiling (DNB): Answer a Refers generically to the onset of film boiling X b In flow boiling typically occurs at small qualities or even in subcooled boiling X c Is the same as dryout d Indicates the suppression of nucleate boiling as the thermodynamic quality increases Question 6 The term liquid holdup refers to: Answer a The reciprocal of the void…