Dear experts, I would like to ask for your insights on the analysis of changes in the fan outlet pressure
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My current understanding is as follows; is that correct? The pressure at the fan outlet is divided into dynamic pressure and static pressure. 1. Dynamic pressure: Dynamic pressure refers to the kinetic energy of the airflow; if the flow rate remains constant and the cross-sectional area of the pipeline is the same, then the flow velocity remains constant, and thus the dynamic pressure also remains constant. 2. Static pressure: A pressure transmitter is installed on the wall of the fan’s outlet pipe; this transmitter measures the static pressure at the fan’s outlet, and this pressure is used to counteract the resistance in the pipeline. Therefore, the static pressure is highest at the fan outlet; as the flow moves along the pipeline, the static pressure decreases gradually until it reaches 0. At this point, the fan is no longer able to maintain the current flow rate, and thus its flow rate drops.
It is recommended to get a copy of \"Principles of Chemical Engineering\" to read; for theoretical issues, it’s best to refer to books as a guide.
This post was last edited by wanlirn on 2022-4-3 at 14:45. To ensure proper ventilation, there is a need for static pressure to overcome the resistance in the piping system, as well as dynamic pressure to propel the gas flow outward. When fans operate within an actual piping system, both static pressure and dynamic pressure are necessary. (1) The static pressure of the fan exists only in the inlet and outlet piping systems of the fan, and it is necessarily equal to the resistance of those piping systems; at the outlets at both ends of the piping systems, the fan’s relative static pressure is equal to “zero”. (2) The dynamic pressure of the fan experiences no loss in the pipelines at the fan’s inlet and outlet; when the cross-sectional areas of these pipelines are equal, the dynamic pressures at the fan’s inlet and outlet are also equal. If the cross-sectional area of the pipeline network varies, the dynamic pressure within the network also changes. The dynamic pressure changes with the variation in the cross-sectional area of the inlet and outlet piping networks. In other words, in order to maintain a constant flow rate, when the cross-sectional area is large, the flow velocity is low, the dynamic pressure decreases while the static pressure increases; conversely, when the flow velocity is high, the dynamic pressure is high and the static pressure decreases ； In short, it’s the Poynting equation: pressure changes back and forth while keeping the total energy constant. You can look for a professional book like \"Hydraulics: Pumps and Fans\" to read
Regarding the dynamic pressure part, it’s the same as what I understand. Regarding the hydrostatic part, do you think I understand it correctly? If the fan outlet is a section of pipeline with constant cross-section and constant flow rate, then the static pressure at the fan outlet is the highest, and this static pressure value equals the total resistance of the outlet pipeline. Then, the static pressure at various points along the fan’s outlet duct is measured sequentially; the static pressure values decrease as the duct moves further away from the fan’s outlet, until it reaches the outlet of the duct, where the static pressure is 0.