A nozzle converts the chemical energy of the propellant to kinetic energy without any moving parts. Rocket nozzle channelize and accelerate the combustion products produced by the burning propellant inside the rocket, in such a way that it maximizes the velocity of the exhaust at the exit to the supersonic velocity. Generally, nozzles are used to control the flow rate, direction, mass, speed, shape, and pressure of the exhaust stream.

The following are the assumptions considered for the conceptualizing of Ideal Rocket for expressing basic thermodynamics equations in terms of simple mathematical expressions.

• The working substance is homogeneous.

• All the species of the working fluid are in the gaseous state, any other phases are negligible when compared with the total mass.

• The working substance obeys the perfect gas law.

• There is no heat transfer across the rocket walls, therefore the flow is adiabatic.

• There is no appreciable friction and all the boundary layer effects are neglected.

• There are no shock waves or discontinuities in the nozzle flow.

• The propellant flow is steady and constant.

• The expansion of the working fluid is uniform and steady, without vibration.

• Transient effects (i.e. the start and shutdown) are of very short duration and may be neglected.

• All exhaust gases leaving the rocket have an axially directed velocity.

• The gas velocity, pressure, temperature, and density are all uniform across any section normal to the nozzle axis.

• Chemical equilibrium is established within the rocket chamber and the gas composition does not change in the nozzle.

Ref: Biblarz, O., Sutton, G. P. (2016). Rocket Propulsion Elements. United Kingdom: Wiley.