Nozzle exit loss example

However, at the microscale, the performance of the microrocket is limited by viscous losses due to the low Reynolds number of the expanding flow. These losses are characterized by the thrust efficiency which compares the observed momentum flux to the momentum flux predicted for an ideal (zero viscosity) fluid. Computations and experiments (e.g., [1]) cOTifirmed supersonic exit flow and have found efficiencies ranging from 10 % to 80 %, depending on the Reynolds number of the system, which in turn depends directly on the size of the throat and the fluid temperature and pressure as it passes through the nozzle, prior to supersonic expansion. The performance of the system can be improved by raising the temperature of the gas. Examples include using an electrical heater in the plenum upstream of the throat [2] and using a chemical reaction, such as combustion [3]. 

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