The head losses generated by the blade tip angles (inlet and outlet) define a fan's 'air' efficiencies. Mechanical/electrical efficiency must be dealt with by the designer when selecting suitable materials and drive systems. The fan calculator addresses only the blade angles. Therefore, having achieved the design requirements, the designer should then proceed to optimise operational efficiency.Ī fan's operational efficiencies are primarily dependent upon two factors blade tip angles and mechnical/electrical equipment. Whilst a fan's efficiency is not the only consideration for a designer, performance being his/her primary concern, it should not be ignored. Please bear in mind that the backward-straight-forward relationship refers to the inlet tip of the impeller blade (0° 110°) as it would disrupt airflow and give unreliable results. The following table summarises the characteristics you can expect from your fan dependent upon the shape of its blades ( Fig 3). v₁ᵢ and v₁ₒ: the inlet and outlet velocities of the air through the blades will be the same for axial fans and different for centrifugal fans v₂ᵢ and v₂ₒ: the circular speed of the inlet and outlet edges of the blade will be the same for axial fans and different for centrifugal fans v₃ᵢ and v₃ₒ: the speed of the air over the surface of the blade will vary from inlet to outlet for both axial and centrifugal fans v₄ᵢ and v₄ₒ: the centrifugal velocity component of the air will be zero for the inlet edge of an axial fan blade and will vary from inlet to outlet for both axial and centrifugal fans vᵢ and vₒ: the absolute velocity of the air at the inlet and outlet edges of the blade and will vary from inlet to outlet for both axial and centrifugal fans Fig 3 shows the velocity diagram for the air flowing into the fan (inlet) and out of it (outlet). The shape of your blades and the direction they travel will define the performance characteristics of your fan. Pressure Head is the head generated by the discharge pressure at the outlet side of the fan Fan Blade Design (Axial and Centrifugal) Static Pressure is the maximum of the inlet and outlet pressures Velocity Pressure is the pressure generated by the gas moving through the fanĭischarge Pressure is the sum of the velocity pressure and the difference between the outlet pressure and the inlet pressure ( Fig 2) You can include this effect if you wish by using the following formula:
This should also include the velocity pressure on the inlet side (if known) that is constant and in-line with the fan. Inlet Pressure is the static pressure on the inlet side of the fan. Generic FansĬalQlata has tried to keep the operation of this calculation option as simple as possible, given that it is recommended for general purpose calculations only and not for actual purchase specifications (see Fan Calculator – Technical Help below).įig 2 shows the pressures through a fan, each of which is described below: A high-efficiency, multi-stage (series of fans) turbo-blower can achieve pressures more than a hundred times greater. One normal axial fan operating at maximum efficiency can achieve a velocity pressure (pᵥ) of up to 0.5psi (≈3,500N/m²). each fan in the sequence increases pressure over the previous fan until you have achieved the pressure required. Multi-stage fans are used where a very high outlet pressure is required. the lower the air resistance, the faster the rotation and the greater the flow. All fans of a given power rating will rotate at a speed commensurate with the air resistance, i.e.
Multi-stage fans are normally used to increase outlet pressure, but are comparatively expensive.Īirflow through the impeller is generated by rotating profiled blades ( Fig 1) in a cowling that cut into the air at their inlet tip pushing the air back along the blade and, in the case of centrifugal fans, also from centrifugal forces generating a partial vacuum on the inlet side of the fan due to the entrained air being thrown outwards according the relationship a = v²/rĪpart from the electrical and mechanical components, the efficiency of a fan is to a large extent dependent upon the shape and orientation of the blades. For example, an impeller fan has a higher efficiency when transporting clean (light air) at high flow rates (high speed), whereas a straight-bladed Sirocco fan is more efficient when propelling heavy gases (vapours and particulates) because centrifugal force is the dominant driver.
Differences such as efficiency or flow rate occur in the type of fan due to particular design advantages that favour one characteristic over another. all of which have individual benefits (volume, pressure, speed, power, efficiency, etc.) but all of them will shift gases at the same rate based upon the input power. There are a number of fan types: impeller, axial, centrifugal, Sirocco, etc.
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