FANS
barbs and on their trailing edge created by adjoining feathers. These in combination contribute to the reduced noise emissions which are characteristic of owls in fl ight. The introduction of serrated leading and serrated trailing edges on both axial and centrifugal fan blades, mimicking the wings of owls, realises both effi ciency and acoustic benefi ts.
Winglets on Soaring Birds’ Wings: – Birds such as vultures, eagles and raptors have feathers at their wingtips which can move independently so as to manipulate air fl ow in that area, instinctively altering the turbulence patterns of the air passing over their wings. In doing so, the vortices which are created at the wingtips are actively managed by the bird to minimise drag and improve airfl ow over the wing. The adoption of winglets on axial fan blade tips, inspired by the wings of the soaring birds referred to above, results in enhanced impeller effi ciency and reduced noise, both contributing to reduced power required to drive the fan.
Humpback Whales’ Fin Tubercles:– Evolution has resulted in the leading edges of humpback whales’ fi ns having golf-ball sized raised nodules, known as tubercles. The ‘tubercle eff ect’ is a phenomenon whereby these leading-edge nodules increase hydrodynamic performance in the case of the whale, enabling surprising agility from such a large creature. Research on this subject was performed by Frank E. Fish et al in the early noughties and the introduction of tubercles in industrial applications followed in the form of nodules or a rippled surface on the leading edges of wind turbine sails and fan blades. The eff ect is not dissimilar to that of the serrations on owls’ wings referred to previously.
Tree Biomechanics:– Professor Claus Mattheck, a German scientist, is a recognised authority on tree biomechanics. His work in this fi eld has inspired fan impeller designers to adopt the complex curvatures observed in trees’ structures when developing impellers whereby optimum strength with minimum use of material is achieved.
The evolution in the design of electric motors and fan impellers means that, fans installed years ago in machines of many types, may have
Ziehl-Abegg ZAbluefi n ECblue centrifugal fans and ZAplus ECblue axial fans incorporate IE5 class EC motors and their impeller designs feature biomimicry concepts; both types are ideal for cost-eff ective retrofi t projects.
been cutting-edge designs at the time they were installed, but have since been superseded by fans which aff ord improved effi ciency and superior acoustic performance. The opportunity then exists to replace existing, older fans with current state-of-the- art fans, whereby the improved effi ciency of current fans can have the eff ect of signifi cantly reducing the power requirement to drive the fans, reducing the equipment operator’s expenditure on electricity. The saving in power consumption will depend upon multiple factors, including the operating point of the fan, the application within which the fan is installed, and the effi ciency of the fan to be replaced. One example of a fan retrofi t project
resulting in a potentially signifi cant reduction in expenditure on electricity is the replacement of a belt-drive, forward curved fan driven by an AC induction motor, with a backward curved free- running plug fan driven by an EC (electronically commutated) motor. In this example, factors which contribute to the increased effi ciency and resultant reduced input power requirement are: the effi ciency increase in replacing the older technology AC induction motor with the IE5 class EC motor.
the step change improvement in effi ciency by
changing from a forward curved impeller to an inherently more effi cient backward curved impeller.
the change from a belt-drive arrangement to a direct-drive arrangement, removing the losses associated with belt slippage and the airstream pressure losses resulting from the positioning of the belts and the protective structures around the belt-drive in the airstream.
Aside from the savings arising from the improved effi ciency and reduced energy costs, the equipment operator also benefi ts from reduced maintenance costs, there being no belts to re-tension and no residue from worn belts to clean. Downstream air fi lters may even be further optimised due to the absence of drive- belt residue.
Similar projects with state-of-the-art EC motor-driven axial fans, typically on existing air-cooled refrigeration condensers and dry coolers provide energy-saving opportunities. The payback period achievable will vary from project to project, depending among other factors, upon the specifi cation of the fans to be replaced and the application and fan operating point, but in many cases this has been found to be under two years, in some cases signifi cantly less.
www.acr-news.com
January 2020
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