250+ TOP MCQs on Chemical Rocket Propellant – Nozzle Expansion Processes Analysis and Answers

Rocket Propulsion Multiple Choice Questions on “Chemical Rocket Propellant – Nozzle Expansion Processes Analysis”.

1. Which of the following is not true for an ideal expansion in the nozzle?
a) Adiabatic, reversible expansion
b) Drop in static temperature and pressure
c) Drop in stagnation temperature and pressure
d) Conversion of thermal to kinetic energy
Answer: c
Clarification: Stagnation temperature remains constant for ideal expansion in the nozzle. Ideal expansion is isentropic and involves conversion of thermal to kinetic energy.

2. Which of the following effects are neglected for simple cases of nozzle expansion?
a) Heat exchange
b) Frictional effects
c) Divergence angle
d) Reversibility
Answer: d
Clarification: For simple cases of nozzle expansion, the effects of friction, heat transfer, shock waves, non-equilibrium and divergence angle are neglected. But the process is considered to be reversible none the less.

3. Assertion: The condensed phases (liquid and solid) are assumed to have zero volume.
Reason: Particles or droplets are very small in size.
a) The assertion is correct, but the reason is incorrect
b) Both assertion and reason are incorrect
c) Both are correct and the reason is the correct explanation for the assertion
d) Both are correct but the reason is not the correct explanation for the assertion
Answer: c
Clarification: The condensed phases are assumed to have zero volume. It implies that the droplets or particles are very small in size and have the same temperature as the gas at all the nozzle locations.

4. What is the typical value of penalty incurred by assuming a frozen equilibrium rocket performance?
a) 1-4%
b) 0%
c) 12-15%
d) 25-30%
Answer: a
Clarification: By assuming frozen equilibrium, we assume that the composition of the chemical products remains constant throughout the nozzle and is the same as that under the chamber conditions. In such a case, there are no phase changes or chemical reactions within the nozzle. The typical penalty on the rocket performance by assuming frozen equilibrium is about 1-4%.

5. In which of the following cases is the chemical equilibrium maintained instantaneously, even though the gas composition varies through the nozzle due to temperature and pressure variations along the nozzle?
a) Frozen equilibrium
b) Non-equilibrium
c) Shifting equilibrium
d) Isothermal equilibrium
Answer: c
Clarification: In shifting equilibrium, even though there is an instantaneous chemical equilibrium between all molecular species, under the variation of pressure and temperature along the nozzle, the chemical composition varies. The gas composition at the chamber and at the exhaust in such a case would be different.

6. In which of the following modes of analysis does the temperature, velocity or pressure at any normal cross-section of an axisymmetric nozzle remain to be the same?
a) One dimensional
b) Two dimensional
c) Three dimensional
d) N-dimensional, where N can be 1,2,3,…
Answer: a
Clarification: The simplest nozzle analysis is one-dimensional. In this case, for an axisymmetric nozzle, the flow properties across any normal cross-section will remain to be the same, or the flow properties are said to be uniform.

7. What is the average diameter of a solid particle in a nozzle flow above which there is a chance of occurrence of thermal lag?
a) 0.1 μm
b) 10 μm
c) 100 μm
d) 1 μm
Answer: a
Clarification: If the average diameter of the solid particles or the liquid droplets in a nozzle flow exceeds 0.1μm, it may lead to thermal and velocity lag. The thermal lag depends upon the convection and radiation means of losing energy and the velocity lag depends upon the drag experienced by the particles.

8. Which of the following does the nozzle boundary layer depend on?

I) Axial pressure gradient 
II) Nozzle geometry 
III) Surface roughness

a) I, II and III
b) Only II and III
c) Only I and III
d) Only III
Answer: a
Clarification: Nozzle boundary layer depends on all three factors. In addition to these, it also depends on the heat losses to the walls.