Market trends for equipment where cooling is required demand high-density and miniaturisation in design, observes Dynetics, requiring a re-think on fan design
Dynetics at PCIM Europe 2017: Stand 9-144
Today’s equipment requires quality fans with high static pressure capabilities, which are optimised to raise the cooling efficiency. The criteria for differentiation of fans includes a list beginning with motor design, the slot-pole combination for efficiency and power saving. Material selection calls for long life, the use of magnets and plastics, and a strong housing. An efficient design method is also needed for low acoustic noise.
Dynetics assists engineers across Europe in selecting the most suitable motor according to application requirements. It represents motor manufacturers and offers a range of small motors, based on various technologies and can customise many motors to meet specifications. The company also supplies cooling equipment, axial instrument ventilators and radial blowers from manufacturers. One of which, Nidec Servo illustrates the company’s fan design technology.
Nidec Servo selected a three-phase brushless motor and immediately saw a 10 per cent increase in efficiency, compared to a single-phase motor. Further improvements were realised by increasing the diameter, making the motor more powerful.
By using SmFeN instead of ferrite as magnet material, the magnetic flux increased by a factor of 1.4, and the higher HFe (high ferrite) magnet material prevents demagnetisation, reports the company.
The G-series fans are cUL/TUV-approved and offered in plastic or aluminium housings
The fan blades are made of polyphenylene sulfide (PPS), preventing the deformation at high speed at high temperature.
For high static pressure applications, diagonal flow fans, (which expel air in a centrifugal direction) or two axial fans mounted in series, are usually considered. However, these offer disadvantages due to the direction of air-flow, physical size and cost.
Keeping up with market trends and demands using traditional design methods, can be time-consuming, involving manufacturing and testing many trial samples.
New techniques, such as computational fluid dynamics (CFD), have been introduced to assist in the design process. However, when using CFD, it is necessary to understand the complexities of axial fan design which have been refined over many years. Therefore, the important point is how CFD is mastered. In recognition of this fact, Nidec Servo has developed the fan optimisation design system, which combines all the strengths of CFD with an optimisation technique to model a new design offering the desired characteristics.
By understanding the pressure distribution, it is possible to arrive at the best design to reduce noise occurrence, according to the effectiveness of the blade shape. By numerical simulations, the CFD analysis detects the large-scale, unsteady states of the blade tip, as well as the mechanisms of aerodynamic noise generation in the fan for industrial or home use.
In addition, innovative design techniques for fan’s blades using CFD can be applied to the design of rotor cascades for low-noise fans. The special shape of the fan blade, shows not only in better result in airflow, but also in a low noise level.
Using this system, Nidec Servo has developed its G-series axial fan range (Figure 1) to meet both high level performance requirements and specific application demands.
One of the objectives of fan optimisation design is to allow ease of use, the CFD function has been incorporated into all levels of the design system.
As an integral part of the optimisation process, CFD calculates the static pressure efficiency from the brake shaft power, static pressure and air-flow. The maximum calculated value of the static pressure efficiency is used to determine the optimised form required. Nidec Servo combined CFD and the optimization technique to produce a fully automatic modeling tool which continually repeats this calculation, selecting the next most suitable data range until the optimum form with highest static pressure efficiency is simulated.
There is a trade-off, however, between calculation time and accuracy. The higher the number of lattices analysed, the greater the accuracy, but this requires more time for the calculations. The first important criteria is to balance the calculation time and accuracy, aiming to achieve the optimised result in the shortest time.
The general procedure for CFD is to firstly create the model and define the form. Next, an analysis lattice, or mesh, is created and performance and physical parameters are set. The final stage is analysis execution.
The contours of an impeller are complicated, three-dimensional forms. To use the optimisation technique, these three-dimensional forms are translated into numerical parameters.
Using the performance data and dimensional analysis of conventional fans and then translating this information into numerical parameters, Nidec Servo has been able to construct a comprehensive data file. This allows a total of 23 individual parameters, which are key factors in the fan performance, to be addressed during the design process.
The inputs of 23 individual numerical parameters, derived from the form definition, are used to create a direct analysis lattice. The number of lattices, their size and surface finish can be adjusted as required. The creation of a lattice for a single impeller takes less than 60 seconds.
CFD software analyses the required parameters for fluid analysis. During analysis, the system rewrites the macro code automatically from the specified design points, e.g. required air-flow, static pressure. The results are stored as part of the optimisation technique for future use.
The simulated annealing (SA) method has been adopted for the optimisation technique. Combined with Nidec Servo's broad knowledge of applications, highly reliable and accurate analysis can now be rapidly conducted.
By using the fan optimisation design system, Nidec Servo claims to have developed a new version of axial fans, which offers high static pressure performance and more airflow without compromising in size and noise level.
The cUL/TUV-approved, high performance, ball-bearing fans are suitable for use in the industrial and the IT markets. The new models come in a choice of popular frame sizes, namely 80 x 80 x 38mm (GO838X54BAYP-00, GO838X54BBZP-00, GO838X54BXYP-00) 92 x 92 x 38mm (GO938C12BAYP-00, GO938V48BDYP-00), 120 x 120 x 38mm (G1238V48BHZP-00, G1238V48BFZP), and 134 x 134 x 38mm (G1438X54BMZP-00). They are offered in a range of DC voltage (12, 48 and 54V) options, depending on the model. The fans’ housings are available in plastic or aluminum.
The fans also have a brake system, securing that the rotor will stop within 2seconds, when the motor power is disconnected, for maintenance and safety.
The DC fans and blowers from Nidec Servo can also have functions that send an alarm signal when the fan motor revolutions slow down (i.e. lock detection, pulse output, speed detection). These fans offer standard a pulse width modulation (PWM) speed control and speed sensor. The variable speed operation is possible by means of a PWM input signal, resulting in further reduction of the power consumption and noise, as requested during idling.
Dynetics at PCIM Europe 2017: Stand 9-144