Which of the following are the effects of nozzle friction?

1. Enthalpy drop decreases

2. Exit velocity reduces

3. Decreases in the specific volume

4. Decrease in mass flow rate

Select correct code.

Explanation:

Nozzle:

• A nozzle is a device, a duct of smoothly varying cross-section area, that increases the velocity of a fluid at the expense of pressure.
• The chief use of nozzle is to produce a jet of steam (or gas) of high velocity to produce thrust for the propulsion of rocket motors and jet engines and to drive steam or gas turbines.

Friction losses in a nozzle depend upon various aspects, the effects of nozzle friction are as follows:

Reduction in enthalpy drop:

• Friction in nozzle affects its efficiency. As the efficiency of the nozzle is the ratio of actual enthalpy drop to ideal enthalpy drop in the nozzle, the friction in nozzle decreases the enthalpy drop.

Reduction in exit velocity:

• The kinetic energy of the steam increases at the expense of its pressure energy in a steam nozzle. Some kinetic energy gets lost to overcome the friction in the nozzle. Therefore, the exit velocity of steam decreases due to nozzle friction.

Increase in specific volume:

• The specific volume of steam can be defined as the volume of steam per unit weight of the steam. Specific volume increases due to nozzle friction.The specific volume of steam is increased due to frictional reheating

Decrease in mass flow rate:

• As the friction in the nozzle slows down the flow of steam in it, the mass flow rate also decreases due to nozzle friction.

Reheating of steam i.e., improving the quality of vapour at the exit: