With the in-depth study of the air supply principle of the fabric air duct system, the design method of fabric air duct becomes maturer and maturer, including the study and calculation of the on-way resistance inside the fabric air duct.
There are also pressure losses due to the frictional resistance and local resistance along the length direction of the fabric air duct system. Because the pressure loss is proportional to the wind speed, when the wind speed along the length direction becomes smaller and smaller, the resistance loss also decreases continuously. At the same time, there are also local resistance losses at the standard parts of the air duct and at the air outlets.
The main part is the straight duct in fabric air duct system, and there are a few tee-junctions, elbows and reducings in the system. Generally, the on-way resistance loss is the main resistance loss form. The frictional on-way resistance of the air flow in the duct with the unchanged air cross-section shape is calculated as follows:
The frictional resistance coefficient; the average velocity of the air in the duct, m/s; the air density, kg/m3; the duct length, m; the diameter (inside diameter) of the round air duct, m. The frictional resistance coefficient is a variable value, which is related to the flow condition of air in the air duct and the roughness of the duct wall. The frictional resistance coefficient obtained is no more than 0.024 (about 0.019 for iron air duct) according to the comprehensive study on the fiber material and the fabric air duct system. The average wind speed in the air duct is 1/2 of the speed at the inlet of the air duct, because there are air supply holes in the extension direction of the fabric air duct. It can be seen that the on-way resistance loss of fiber air duct is much smaller than that of traditional iron air duct.
In order to reduce the local resistance loss of the fabric air duct system, we usually carry out certain optimization designs:
1. Take various factors into consideration when choosing the duct diameter, and try to reduce the wind speed in the duct as much as possible.
2. Optimize the design of special-shaped parts to avoid too rapid change of flow direction and too fast change of section.
It can be seen that the on-way resistance loss of fabric air duct system, especially the straight duct system, is very small and generally it will not exceed the static pressure regain value, so the resistance loss can be basically ignored in rough calculation!