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issue: October 2004 APPLIANCE Magazine Part 2: Motors & Air-Moving Devices

Part 2: Motors and Air-Moving Devices
Hybrid Blower Technology


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Using its Hybrid Blower Technology (HG), Punker GmbH has been able to examine the characteristic curves of a blower.

Such examination has revealed the device’s working characteristics, which are especially valuable for low NOx blue burners. In addition to burners, applications include vacuum cleaners and low-pressure compressors.

High requirements due to the steep incline of the pressure-volume-curve at the working point are claimed by the market at a high static pressure, including a compact, low-cost construction. For innovative burner blowers, special demands are not only made on the absolute size of the static blower pressure and the volume flow, but also on the path of the curves and their stability, as well as the flow profile at the outlet cross-section. The steep incline of the characteristic curve—pressure against volume flow—is the most important component to consider for current low NOx blue burners. The steeper the curve, the less the combustion air volume changes when the counter-pressure in the combustion chamber varies. The increase of the counter-pressure at the starting explosion of the burner should not cause any temporary air deficiency during the combustion, as this would generate toxic carbon monoxide and soot particles.

 

Figure 1. Hybrid blowers act as a centrifugal fan, cross-flow fan, and regenerative blower due to a separating wall, suction plate with an opening, and the application specific flow islands.

HG Principle of Activity and Arrangement

The hybrid blower is a special design that simultaneously incorporates the principle activity of a conventional centrifugal fan and cross-flow fan. It also is a regenerative blower by means of a centrifugal fan wheel with forward-curved blades and a specially designed inlet air duct.

Apart from the fan wheel and the housing, the most important components of a hybrid blower are composed of a separating wall, a suction plate with an opening, and the application specific flow islands (see Figure 1). In the development phase, the construction of the inlet air duct is preferably of a movable design that allows a variable adjustment of the separating wall.

Through the inlet’s implemented separating wall, the suction area of the fan wheel is divided in two areas, with the function of a centrifugal fan representing area 1 and a cross-flow fan representing area 2. The suction air of area 1 is accelerated by the fan wheel and then thrown out to the outside. As Figure 2 shows, a part of the exhaust flow from area 1 then flows through the wheel into area 2, forming a second working current, which results in a flow circulation. Thus, the hybrid blower practically works as a multistage blower.

 


Figure 2. Flow circulation is achieved as exhaust flow is pushed through the wheel into a second working current. This technology achieves the function of a multistage blower in addition to a fan.

Construction Parameters

A development study revealed that there are a great number of geometric parameters affecting the blower characteristic curve to different extents. The main components and geometric parameters are:

  • housing with a variable spiral outline
  • blower wheel
  • inlet opening (size, shape, position)
  • separating wall (shape, inclination, position)
  • 3-D discontinuous step (the inside of the inlet)
  • flow islands

It is possible to achieve a steep characteristic curve with an unusually high pressure number up to more than 15 in the completely throttled flow by reasonably combining the above parameters.

Comparison Against the Technology

Due to the unique performance and the special arrangement, a blower characteristic has achieved an equal curve to that of a multistage regenerative blower. Figure 3 shows four blower curves for the same fan wheel, however, in a housing of a conventional design (B6, 7-degree housing) and a HG version with two different positions of the separating wall.

The hybrid blower technology stands out against conventional centrifugal blowers because of the following technical features:

  • an increased incline of the blower curve
  • a high specific performance density
  • compact design
  • distinctly lower sound emission due to the lower operating speed
  • high-pressure control comfort

To date, the HG technology has been approved by burner manufacturers and is currently being applied in several cooking and home appliances.

 


Figure 3. The graph depicts four blower curves results for the same fan wheel. The fan wheels, however, were equipped in a conventional design housing, (B6, 7-degree housing), while the two hybrid blowers were equipped with two different positions of the separating wall.

This information is provided by Ernst Clausen and Dr. Yingan Xia, PUNKER GmbH & Co.

 

issue: October 2004 APPLIANCE Magazine
Part 2: Motors and Air-Moving Devices

Click for the online Part 2 Table of Contents.

 

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