FC Fan Airflow Measurement Using Single Pressure Sensor
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Solution Overview
Problem
Determining the volume airflow rate through a centrifugal fan is challenging due to varying air velocity and the need for multiple pressure taps, which can disrupt the flow and create undesirable restrictions.
Innovation Solution
A single pressure sensor is used to measure the static gage pressure at a specific point on a curved inlet cone, allowing for accurate airflow volume determination without creating a pressure drop or obstruction, and this method is applicable to forward-curved centrifugal fans.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple pressure taps are used to integrate air velocity profile, then measurement precision is improved, but device complexity and flow restriction increase
Solution Approach 1:
The patent extracts the pressure measurement function from multiple distributed taps and concentrates it into a single tap location on the inlet cone. By taking out the essential measurement capability and removing unnecessary multiple taps, the system achieves simplified design while maintaining measurement accuracy through the specific strategic placement of one pressure tap at the cone's minimum diameter section.
Solution Approach 2:
The inlet cone itself serves as an intermediary structure that facilitates the measurement. The cone's geometry, particularly its minimum diameter section, acts as a natural flow restrictor that creates a measurable pressure differential. This intermediary structure allows a single pressure tap to capture flow information that would otherwise require multiple taps distributed across the flow path.
2Measurement precision
If pressure taps are inserted across the flow path, then airflow measurement is enabled, but flow restriction and disruption occur
Solution Approach 1:
The patent applies local quality by concentrating the pressure measurement function at a specific localized position on the inlet cone rather than distributing taps across the entire flow path. The single pressure tap is strategically placed at the minimum diameter section of the cone where it can accurately reflect the flow characteristics without requiring multiple invasive taps that would disrupt the airflow pattern.
3Ease of operation
If a flow restriction with known pressure drop relationship is used, then airflow rate determination is simplified, but undesirable flow restriction is created
Solution Approach 1:
Instead of creating an artificial flow restriction device and measuring pressure drop across it (the conventional approach), the patent inverts the approach by using the inlet cone's minimum diameter section as a passive flow feature. The cone's geometry naturally creates a measurable pressure differential without requiring additional flow restriction elements, thereby simplifying airflow measurement while avoiding the harmful effects of artificial restrictions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise airflow measurement, unaffected by changes in fan speed, geometry, or other variables, using a single pressure gage and protecting the pressure sensor within a discharge air chamber.
Implementation Method 1
measuring a static gage pressure of the air entering the fan at a single point on an inlet cone of the fan
Implementation Method 2
sensing the minimum static pressure of the air entering the fan, whereby the reading is more accurate due to a relatively large or maximum pressure differential between the sensed minimum subatmospheric static pressure and the ambient barometric pressure
Data Source
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AI summary
An airflow volume sensing means for determining the flow rate through a fan includes a curved inlet cone with a pressure sensor at the minimum diameter of the cone, wherein the flow volume sensing means is particularly suited for FC centrifugal fans (centrifugal fans with forward curved fan blades). With an FC fan, the minimum diameter of the inlet cone's interior surface is adjacent the fan wheel, and the static pressure there is at a minimum value. A predetermined relationship between the static gage pressure at that point and the volume flow rate through the fan is applied regardless of variables such as fan speed, fan housing geometry, supply air duct configurations, return air duct configurations, location of various heat exchangers or filters, etc. In some embodiments, a single pressure sensor senses an average of a plurality of pressure taps, wherein each tap is at approximately the same minimum pressure.