⚙️ Mechanical Eng Solved MCQs with Answers

Practice 934 approved ⚙️ Mechanical Eng questions with verified answers from the 🛠️ Engineering Essentials subject for Pakistan exams.

934 solved MCQs

The rate of discharge through the nozzle __________ when the exit pressure is gradually reduced.Answer: increases In a nozzle, whole frictional loss is assumed to occur betweenAnswer: throat and exit The critical pressure ratio for initially wet steam isAnswer: 0.582 The isentropic enthalpy drop in moving blade is two-third of the isentropic enthalpy drop in fixed blades of a turbine. The degree of reaction will beAnswer: 0.4 The impulse reaction turbine has its driving forceAnswer: partly as an impulsive force and partly as a reaction force The efficiency of reaction turbine is maximum when (where α = Angle made by the absolute velocity (V) at inlet)Answer: Vᵇ = 0.5 V cos α A regenerative steam cycle rendersAnswer: decreased work output per unit mass of steam as well as increased thermal efficiency De-Laval turbine is aAnswer: single rotor impulse turbine The turbine, in which the general direction of the steam flow is parallel to the turbine axis, is called axial flow turbinesAnswer: True The critical pressure gives the velocity of steam at the throat equal to the velocity of sound.Answer: Agree The reheat factor is the ratio of theAnswer: cumulative heat drop to the isentropic heat drop The turbine blades do not change the direction of steam issuing from the nozzle.Answer: False Thermal equilibrium means that the flow of steam isAnswer: isentropic When the back pressure of a nozzle is below the designed value of pressure at exit of nozzle, the nozzle is said to beAnswer: underdamping The ratio of the workdone on the blades to the energy supplied to the blades, is calledAnswer: blading efficiency The discharge is __________ at critical pressure.Answer: maximum The supersaturated flow of steam through a nozzle as compared to a stable flow, the available heat dropAnswer: decreases The steam leaves the nozzle at aAnswer: low pressure and a high velocity The critical pressure gives the velocity of steam at the throatAnswer: equal to the velocity of sound The Parsons' reaction turbine hasAnswer: identical fixed and moving blades The action of steam in a steam turbine isAnswer: dynamic The blade velocity coefficient is ratio of relative velocity of steam at outlet tip of the blade to the relative velocity of steam at inlet tip of the blade.Answer: True Multi-stage steam turbines are of theAnswer: all of these In reaction turbines, the axial thrust is due toAnswer: both (a) and (b) Which of the following statement is correct?Answer: All of the above A binary vapour plant consists ofAnswer: all of these In a De-Laval nozzle expanding superheated steam from 10 bar to 0.1 bar, the pressure at the minimum cross-section (i. e. pressure at throat, p2) will beAnswer: 5.46 bar The stage efficiency (ηS) is given by (where ηB = Blading efficiency, and ηN = Nozzle efficiency)Answer: ηS = ηB x ηN The critical pressure ratio for initially dry saturated steam is more as compared to initially wet steam.Answer: No In a convergent divergent nozzle, the discharge depends upon the initial conditions of steam and the area of nozzle at throat.Answer: Correct