2024 12 16 A

Page 1

Exam of Multiphase Systems and Technologies – a.y. 2024-25 Pre-call of the winter session – December 16th, 2024 – Test A Surname Name Person code Correct answers Score Mark the correct answer in the dedicated space Question 1 The cross-section averaged void fraction in a gas-liquid flow is Answer a The ratio of gas to the liquid volume flow rates b The ratio of gas to the mixture volume flow rate c The ratio of the actual to superficial velocity of the gas d The ratio of the actual velocity of the gas to the superficial velocity of the mixture NONE OF THEM Question 2 With reference to the nucleate boiling region in the following figure Answer a The white dots refer to the smoothest copper surface b The roughness of the surface decreases from right to left c The white squares correspond to the highest values of the heat transfer coefficient at constant heat flux d The white squares refer to the smoothest copper surface X Question 3 The critical radius of a bubble nucleated at a conical cavity is Answer a The radius at the bubble departure b The radius of the mouth of the cavity X c The radius corresponding to the height of the cavity d The radius corresponding to the RMS roughness Question 4 The reversible components of the pressure gradient in a gas-liquid flow are Answer a Accelerative, gravitational, frictional b Accelerative, gravitational X c Accelerative, frictional d Gravitational, frictional Question 5 The gravitational component of the pressure gradient in a gas-liquid flow Answer a Decreases with the inclination angle b Decreases with increasing the actual density of the mixture c Is maximum for vertical layouts X d Lowers with the system pressure Question 6 The following void fraction correlation is based on Answer a The slip ratio model b The drift-flux…