Devices and Components for the Delivery System

Rotator flow meter and mass flow controller are usually used to measure and control the gas flow rate. 

The mass flow meter, also called mass flow controller (MFC), operates by measuring variations in the temperature of flowing gas subjected to heat flux. The temperature variation is related to the amount and the heat capacity of the gas. The transferred heat (Q) is calculated by [30] 

Compared with rotator meters, mass flow meters are more accurate, typically giving an accuracy of 2% of the full scale. Another distinct advantage is the ease of automation and programming for the CVD processes according to the requirements. 

Needle valves are used to accurately control the gas flow in the gas lines, while butterfly valves are employed to regulate the gas flow and the pressure in the CVD reaction chamber. 

It is important to generate rapid and turbulent gas movements such as turbulent flow or spiral gas flow. This helps to speed up the mass transport, hence shortening the mixing time and improving mixing efficiency. 

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