2025 06 24 ENG

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Exam of Multiphase Systems and Technologies – a.y. 2024-25 1st call of the Summer session – June 24th, 2025 Surname Name Person code Correct answers Score Mark the correct answer(s), if any, in the dedicated space Question 1 The gravitational component in the pressure gradient for a gas-liquid flow is Answer a Zero for descending flows b Zero for ascending flows c Zero for horizontal flows X d Always positive Question 2 In a steady-state, adiabatic gas-liquid flow, without phase change, the accelerative pressure gradient Answer a Is null X b Increases with the quality c Decreases with the quality d Strongly depends on the flow pattern Question 3 Which of the following is not a definition of the cross-section averaged void fraction Answer a The ratio of the gas cross section to the liquid cross section X b The ratio of the superficial velocity to the actual velocity of the gas c The complement to 1 of the liquid holdup d The ratio of the gas cross section to the pipe cross section Question 4 The sequence of heat transfer regimes in case of saturated pool boiling on a temperature-controlled heater is Answer a Natural convection, nucleate boiling, film boiling b Natural convection, nucleate boiling, partial film boiling, film boiling X c Natural convection, subcooled boiling, nucleate boiling, partial film boiling, film boiling d Natural convection, subcooled boiling, nucleate boiling, film boiling Question 5 Which factor is not described through mechanistic assumptions in the Rohsenow’s pool boiling model? Answer a The effect of buoyancy forces b The effect of capillary forces c The effect of the wall heat flux d The effect of surface finish X Question 6 The concept of critical radius of a bubble Answer a Is significant only for homogeneous nucleation b Is significant…