Issues related to fan selection
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Under actual operating conditions, the gauge pressure in the flue at the fan inlet is required to be -2500 Pa, while the gauge pressure in the flue at the fan outlet should be +2000 Pa. During the selection process, a gauge pressure of 0 Kpa at the fan inlet and a total pressure of 4500 Pa for the fan were chosen. Can this fan be used at this time? I need an expert to help solve this!
The Roots blower works fine under these conditions; I’m not sure about other types.
1. From the analysis of the fan design process, pressure has an impact, with the main factors being pressure ratio and mass flow rate. 2. The pressure ratio plays a role throughout the design process and affects the selection of both the overall structure and the impeller flow channels. However, in the description of the operating conditions, the actual pressure ratio is 1.046, while the selected pressure ratio is 1.045; the difference between these ratios is less than 1%. Therefore, for a fan that includes a design margin, this difference is sufficient to meet the requirements. 3. Due to the low pressure under actual operating conditions, the density of the medium is lower. With constant temperature conditions, the mass flow rate will be slightly lower for the same volume flow rate, and this can be calculated using the gas equation
May I ask, if the inlet negative pressure of the centrifugal fan purchased is -4500 Pa and the total pressure is 5000 Pa? Is it suitable for my current actual operating conditions?
1 From the perspective of fan principles, changes in inlet conditions still reflect on the impact of pressure ratio on the fan. The pressure ratio does not change much, and its impact on the structural parameters of the fan is also minimal. However, when analyzing the fan, the air ducts, and the medium as a single system, different operating conditions result in differences. For example: when the back pressure at the fan outlet is high, the negatively pressurized flue gas drawn in may not reach such a high pressure after being pressurized by the fan; as a result, the fan is unable to push the flue gas into the outlet pipeline. The lower pressure leads to a decrease in the density of the gas medium, thereby reducing the mass flow rate
Total pressure includes static pressure and dynamic pressure; static pressure is the resistance in the pipeline, while you haven’t provided the value for dynamic pressure, so it needs to be calculated first. The fan is then selected based on the total pressure. Generally speaking, the dynamic pressure in air ducts is relatively low, being smaller than the static pressure
The temperature of the inlet medium also needs to be taken into account, as well as the impact of altitude and the cleanliness of the medium. Such a description is incomplete, so the response may not necessarily solve the problem.