2025 07 14 ENG

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Exam of Multiphase Systems and Technologies – a.y. 2024-25 – ENG 2nd call of the Summer session – July 14th, 2025 Surname Name Person code Correct answers Score Mark the correct answer(s), if any, in the dedicated space Question 1 An annular flow is likely to show Answer a A slip ratio larger than 0 b A slip ratio larger than 1 X c A negative slip ratio d A negative drift velocity Question 2 The concept of two-phase multiplier Answer a Only refers to the homogeneous flow model b Refers to both the homogeneous and the separated flow model X c Is related to the frictional component of the pressure gradient X d Is related to the total pressure gradient Question 3 The simple thermal stability of a boiling state on the Nukiyama’s curve Answer a Is only associated with the value of the heat flux b Is only associated with the value of the wall temperature c Depends on the surface roughness d Depends on the heating mode X Question 4 The confinement number may be used as a criterion to Answer a Assess whether a tube is small compared to the characteristic length of a gas-liquid mixture X b Assess whether boiling is convection or boiling dominated c Choose between a smoke tube and a water tube boiler d Predict the flow pattern Question 5 A smoke tube boiler is typically suited to Answer a Produce superheated steam b Produce high pressure steam for power generation c Produce low pressure steam for heating purposes X d Produce superheated liquid Question 6 The following heat transfer model 𝛼𝑇𝑃 𝛼𝑙 = 𝐶 𝑋𝑡𝑡 𝑛 Answer a Is suitable for subcooled boiling b Is suitable for nucleate boiling c Is suitable for film boiling d Is suitable for convective evaporation X Question 7 In subcooled boiling, the thermodynamic quality is Answer a The same as the void fraction b The same as the mass…