Fan Wiki

What are the main differences between radial and axial fans?

Fans are generally divided into two types: axial and radial. Axial fans are used wherever high volume flows in combination with low pressures are required. Their design is similar to that of a propeller. They draw in air axially (across the motor axis) and blow it out again axially.

Centrifugal fans are used at higher pressures and are comparable to a drum. The air is sucked in parallel or axially to the drive axis of the centrifugal fan and deflected by 90° by the rotation of the radial impeller and blown out radially. Centrifugal fans can achieve significantly higher pressures than axial fans with the same outer impeller diameter and speed.

P.S: We are all about centrifugal fans.

What types of drive are available?

We differentiate between motor machines (directly mounted on the motor shaft), belt drives, and clutch drives, with clutch drives offering the highest performance.

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What is meant by operating point?

The characteristic curve of a fan depends on the speed (revolutions per minute) and describes the pressure increase over the volume flow.

The operating point of the fan is the intersection between the fan characteristic curve and the system characteristic curve (resistance parabola). This results in the actual volume flow and the actual pressure difference to be overcome by the fan.

How is pressure defined?

In general, local pressures occurring in fluid flow machines are always measured, calculated, and considered as pressure differences relative to the atmosphere. The generally accepted designation is “p.” Absolute pressures are used exclusively in the equation of state of gases and in pressure ratios. A distinction is made between static pressure, dynamic pressure, total pressure, and pressure difference.

What is the difference between pressure-resistant and pressure-shock-resistant?

Strict guidelines apply in industrial environments. Pressure-resistant fans are subject to the Pressure Equipment Directive and are designed to withstand high system pressures.

Pressure-shock-resistant fans can withstand a brief, defined increase in pressure, e.g., due to explosions.

1. Pressure-resistant design:

In pressure-resistant designs, the pressure-bearing components (housing, inlet pipe, flanges and screw connections, seal) must be able to withstand the working pressure completely without noticeable deformation.

The housing is designed in accordance with DIN EN 13445-3:2016-12. The material is used with a 1.5-fold safety factor against the yield strength.

The standard wall thicknesses for housings are designed so that an overpressure of at least 25,000 Pa (= 0.25 bar) can be transmitted at room temperature.

Only a floating labyrinth seal with the appropriate number of rings is used as the shaft seal.

2. Pressure shock-resistant design:

In pressure shock-resistant designs, the components must withstand the pressure wave once in the event of an explosion. Deformations of the components are permissible; however, the component must not burst.

The housing is also designed in accordance with DIN EN 13445-3:2016-12 in conjunction with VDI 2263. The material is used with a safety factor of 1.0 against the yield strength.

The standard wall thicknesses for housings are designed so that a pressure surge of at least 40,000 Pa (= 0.40 bar) can be transmitted at room temperature.

According to VDI 2263-3, a water pressure test with 90% of the pressure surge is also required here.

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What types of pressure loss are there?

Different types of pressure loss can occur in systems. Calculating them depends on fluid dynamics laws. A distinction is made between:

a) Velocity-independent pressure losses: This type of pressure loss only occurs in technical applications when liquids or bulk materials flow through a system.

b) Velocity-dependent pressure losses: All other types of pressure loss in plant components are velocity-dependent. These include elbows, filters, and pipes.

What units are used for pressure values?

The standard unit is the “Pascal” – [Pa]. Other units include:

• 1 bar = 100,000 Pa
• 1 mbar = 100 Pa
• 1 mmWS = 9.81 Pa
• 1 mmHG = 1 Torr = 133 Pa
• 1 inWC = 249 Pa
• 1 psi = 1 lb / in² = 6894.76 Pa

What is the ErP Directive?

The ErP Directive (Energy-related Products) or Ecodesign Directive implements the Integrated Product Policy (IPP) in the European Union. With a few exceptions, it applies to almost all energy-related products. The aim of the directive is to save energy and other resources in the manufacture, operation, and disposal of energy-related products.

The ErP Directive defines specific minimum efficiency levels for fans sold within the EU with an electric input power of 0.125 kW to 500 kW. There are numerous exceptions, such as for fans that comply with ATEX directives, for certain operating and ambient temperatures, for use with toxic, corrosive, or abrasive media, or for fans for non-gaseous media.

What is calculated using Euler's equations?

Euler's equations (or Euler equations) in fluid mechanics are a mathematical model developed by Leonhard Euler to describe the flow of frictionless elastic fluids. With radial wheels, a theoretical characteristic curve can be easily calculated using Euler's equation.

What guidelines are used to manufacture explosion-proof fans?

Our explosion-proof fans are manufactured and designed in accordance with ATEX guidelines and comply with standard EN 14986:2017, category II G or D (G only explosion protection group II A, II B and hydrogen) and III G or D.

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What casing positions are available?

Our PDF shows you all possible casing positions as viewed from the drive side.

Click here for the document POLLRICH – Casing positions.pdf

What are the most important parameters?

In fan design, dimensionless parameters are used that are derived from the physical variables involved in the working process. They serve as distinguishing features for the different designs and their operating behavior, and as a basis for new designs. The most important parameters are:

• Specific diameter
• Specific speed
• Pressure number
• Delivery number
• Performance number
• Efficiency

What does the fan characteristic curve indicate?

The fan generates positive pressure (pressure increase) to counteract flow resistance. The fan characteristic curve shows this interdependence between volume flow and pressure increase.

What is convection?

Convection (flow transport) is the transfer of heat by a flowing fluid. In fan design, a distinction is made between free convection (occurs due to density differences as a result of temperature differences) and forced convection (flow is generated by external influences such as wind or air flow).

What types of bearings are there?

We distinguish between block bearings, plain bearings, and spindle bearings.

What does the bearing temperature depend on?

The bearing temperature depends on the friction torque of the bearing, the housing surface, convection, and the amount of oil (if present).

What is pneumatic conveying?

The principle of pneumatic conveying is based on the physical principle that flowing air is capable of carrying and transporting heavier solids under certain conditions.

Pneumatic conveying makes technical use of this principle, with transport taking place through pipes. The material to be conveyed is carried along by the air due to its own flow resistance. The conveying medium is the air flow generated by a fan. Depending on the type of material feed, a distinction is made between suction conveying and pressure conveying, as well as a combination of both types.

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What options are available for reducing noise?

Good sound insulation is important for ensuring the health of employees. This can be achieved through the following measures: insulation and encapsulation, installation of silencers and/or prevention of structure-borne noise transmission.

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What blade shapes are available?

The impeller blades can be shaped as follows: backward curved (circular arc), backward curved (logarithmic), backward inclined, straight blade, radial ending, or forward curved.

What types of wear protection are available?

Depending on the area of application and requirements, there are different types of protection against wear. These can be, for example, special materials, special coatings or – in the high-end sector of fan technology – high-strength carbide coatings.

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What causes vibrations?

Vibrations on the fan can be caused by:

• Imbalance due to contamination or wear on the impeller
• Incorrect alignment of the coupling or belt drive
• Loose or slack components
• Bearing wear
• Resonance effects due to operation near the critical speed of individual components or the entire fan
• External vibration excitation
• Aeromechanical vibration excitation due to flow separation or gas column vibration

The permissible vibrations and the required balance quality for fans are specified in ISO 14694. We recommend regular vibration checks.

What is meant by temperature increase?

When the medium being conveyed is compressed in the fan, it heats up, and this is further increased by internal losses. The actual temperature increase is calculated according to the laws of thermodynamics

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What are volume flow and mass flow?

Volume flow (or, less precisely, flow rate) is a physical quantity in fluid mechanics. It indicates how much volume of a medium is transported through a fixed cross-section per unit of time.

The basic unit is [v] = 1 m³/sec.

Other units of volume flow include: 1 m³/s = 60 m³/min, 1 m³/s = 3600 m³/h

Other units of mass flow include: 1 kg/s = 3600 kg/h

How is the volume flow regulated?

The volume flow of a fan often needs to be adjusted to different operating conditions. Three systems are available for this purpose:

a) Throttle valves. Throttle valves are a simple, inexpensive method of reducing the air flow. However, they also have the lowest energy efficiency and a significantly lower degree of efficiency.

b) Swirl regulators. Swirl regulators, which are used for mechanical control of the air flow, are suitable for systems in which electronic control is not possible or not desired.

c) Speed control using frequency converters. Frequency converters offer the highest energy efficiency because they optimally adjust the circumferential speed to the given conditions. This achieves the best ratio between speed, volume flow, and energy consumption.

What waveforms are available?

For rotors mounted on both sides, we differentiate between solid shafts, hollow shafts, and tapered shafts.

What is efficiency?

Several individual efficiencies can be defined for a fan: internal efficiency (housing and impeller), mechanical efficiency (bearings, seals, etc.) and the efficiency of additional components (cooling disc, etc.).

The overall efficiency is calculated using a physical equation.

Where are shredding fans used?

Shredding fans are mainly used in the paper and fiber industry. They are used, for example, for edge strip extraction.

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