1761337433 2025 01 21 NUC

Pagina 1

Exam of Multiphase Systems and Technologies – a.y. 2024-25 1st call of the Winter session – January 21st, 2025 – Test Nuclear 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 experimental data reported in the following figure likely refer to (Legend: the plot reports the actual gas velocity against the mixture velocity) Answer a A bubbly flow X b A slug flow c A stratified flow d A slip ratio lower than 1 Question 4 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 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 You would consider using the following void fraction correlation for horizontal flows because Answer a It accounts for the different shear stress of the phases…