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DIFFUSER AXITOPFriction lossesInternal lossesand gap lossesExit losses PudFigure 1 (left): Power flow of an axialfan with unimpeded airflowFigure 3 (right): The AxiTop diffuserallows part of the dynamic pressureto be converted into useful staticpressure by retarding the flow.PressureConversionof dynamicpressure intoheatAir performance PuDrivepower PoLEGENDCustomer benefi tStaticoutput Pusp fp fsStart of diffuserEnd of diffuserp fd_cgesp fd_caxp fd_cuAxis of rotationFigure 2: The AxiTop diffuser from ebm-papstprovides for a significant improvement ofefficiency and noise. Its pressure-boostingeffect minimises exit losses and makesit easier to adapt the fan to commerciallyavailable heat exchangers.is often no longer technically utilised. With theAxiTop diffuser, much of the dynamic kineticenergy is converted into static pressure (p fs ) byway of retardation. Physically, this is easy to explain:The total pressure generated (p f ) by a fanis the sum of the static pressure pfs and the dynamicpressure p fd_cges . In turn, taking the densityr into account, the dynamic pressure can be splitinto three speed components (cylinder coordinates),the axial component p fd_cax = /2*c ax² , thecircumferential component p fd_cu = /2*c u² andthe radial component p fd_cr = /2*c r² .In the diffuser, the axial and circumferentialcomponents of dynamic pressure (/2*c ges² ) arereduced due to the air slowing in the expandingcross section and, due to the conservation of energy(Bernoulli´s principle), the usable static pressurecomponent increases (see Fig. 3). Efficiencycan be significantly increased in this way if allcomponents are co-ordinated to be aerodynamicallyoptimised.In practice, the use of the AxiTop diffuserdoes not just mean lower energy consumption;it also means greater degrees of freedom for theuser and for the development engineer. The diffuserconfiguration can be optimised for differentcharacteristics, depending on the application concerned.Either a greater blower output is possiblewith unchanged energy input, or unchanged airperformance is possible with lower energy consumption.A diffuser can also greatly improve thenoise behaviour. This acoustic improvement isespecially interesting when fans are working is anoise-sensitive environment, for example in overnightoperation in ventilation and climate controlsystems in residential buildings or in rooms wherepeople meet and where there are also noise protectionregulations to be fulfilled.Significant potential to be exploited The potentialof the possible energy savings, increasedefficiency and noise reduction provided by an optimaldiffuser is substantial for common heat exchangerson the market. This has been confirmedin extensive test series. Figures 4a and 4b illustratea specific example. Replacing a normal fanwith a guard grille with the same fan with a supportbracket, guard grille and diffuser allows savingsof 27 % for energy consumption while enablingan operating noise level 7.2 dB(A) lower withthe same air flow (see Fig. 4a).Alternatively, if the greater efficiency of thefan with differ is exploited, it will deliver about 9 %more air flow with the same input power, and atthe same time noise emissions will be reduced by4.9 dB(A) (see fig. 4b). This value has been determinedon an exemplary customer application.Depending on the individual configuration, the optimisedefficiency can be used either to reducepower input or to increase air performance. So10techmag 01°2013
DIFFUSER AXITOPEnergy consumptionin kW2.521.51Outputin m 3 /h25,00024,00023,00022,00021,00020,00019,00018,000-27 %+9 %Noise development (LwA)in dB(A)90858075709085807570-7.2 dB(A)Noise development (LwA)in dB(A)-4.9 dB(A)Figure 4a (left, up): Energyconsumption and noise developmentare significantly lower withunchanged air performance.Figure 4b (left, down): Bloweroutput is increased and noisereduced with unchanged powerinput. Details from an exampleapplication.Figure 5 (right): The thrust range isnot affected by the AxiTop diffuser.The illustration shows the axial flowrate with diffuser on the left andwithout diffuser on the right.not only does the user save energy during operation;the design engineer for a climate controlsystem can get by with smaller heat exchangersurface areas. The space needed for the coolingunit can be reduced with unchanged or even improvednoise behavior and constant refrigerationcapacity. The reduction in the space needed isan argument which cannot be neglected, aboveall for larger heat exchangers. A diffuser is evenworthwhile if it subsequently turns out that thesystem does not have a sufficient refrigerationcapacity, e.g. in the case of a design error. It enhancesthe air performance without increasingnoise. In such cases, the installation of an additionalheat exchanger (and the associated costs)can often be avoided.Can be retrofitted and used in existing wallrings Equipping existing heat exchangers with adiffuser is easy and only requires a few changesto ventilation and air-conditioning units. The diffuseris fitted in place of the guard grille. Existingwall rings can still be used. The AxiTop diffuserfrom ebm-papst is just 250 mm high so it needsvery little space.With these dimensions, the developmentengineers have succeeded in achieving a verygood compromise. Physically, a diffuser cannotbe large enough in order to increase staticpressure. But dimensions which are as compactas possible are required in practice. CFD simulationscombined with parametric optimisationshave produced an excellent aerodynamic result.The change in the outflow profile causes the flowto split slightly, enabling the thrust range of thefan to be maintained. Figure 5 shows the differentcharacteristics of the exit speed cax, which is ofrelevance for the thrust range, with and withouta diffuser.The new AxiTop diffuser is designed for fansof the sizes 800 and 910. Versions for 500 whichare frequently employed with heat exchangerswill follow in the near future. It doesn´t matterwhether the fan works with GreenTech EC or withan AC drive. However, in the interest of energy efficiency,the combination with GreenTech EC fansin certainly preferable.Authors are Dipl.-Ing. (FH) Oliver Haaf, head of Product Development, Aerodynamicsgroup (left) and Dipl.-Ing (FH) Markus Engert, Predevelopment,Aerodynamics (right) at ebm-papst MulfingenYou would like more information on this topic? Please address your questionto: Oliver.Haaf@de.ebmpapst.com or Markus.Engert@de.ebmpapst.comtechmag 01°201311
Page 1 and 2: 01 ° 2013Technology by ebm-papst°
Page 4 and 5: ACTIONBRAKEFans with a wear-freerun
Page 6 and 7: ACTIONBRAKEFigure 2 (left): Clearly
Page 8 and 9: DIFFUSER AXITOPAxiTop - Less noise
Page 12 and 13: INTEGRATED DIAGNOSTIC SYSTEMIntegra
Page 14 and 15: INTEGRATED DIAGNOSTIC SYSTEMFigure
Page 16 and 17: GREENTECH EC MOTORSExternal rotor m
Page 18 and 19: GREENTECH EC MOTORSFigure 1: Explod
Page 20 and 21: CONDENSING BOILER SYSTEM NRV 77The
Page 22 and 23: CONDENSING BOILER SYSTEM NRV 77Figu
Page 24: Listen to the difference.40038-7-88

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