Fig 1 - uploaded by Rong-Jie Wang
Content may be subject to copyright.
Exploded view of an AFPM machine, 1: rotor discs, 2: stator winding, 3: permanent magnets, 4: epoxy core, 5: radial channels, and 6: air-inlet holes.
Source publication
A thermofluid model combining a lumped parameter heat transfer model and an air-flow model of a typical axial-field permanent-magnet (AFPM) machine is developed. The accuracy and consistency of the derived model are assessed by comparing the calculated flow rate and temperature values of a prototype machine with the measured ones. The developed the...
Contexts in source publication
Context 1
... of electrical machines with advantageous features such as high efficiency and power/weight ratio. An axial flux permanent magnet (AFPM) machine, with an axially directed magnetic field crossing the air gap, has a remarkably short axial length and can find applications in power generation, light trac- tion drives, electric pump, and fan drives. Fig. 1 shows the layout and active components of a typical AFPM ...
Context 2
... examination of the machine structure shown in Fig. 1 reveals that an air stream will be drawn through the air inlet holes into the machine and then forced outwards into the radial channel as the rotor discs rotate. The PMs act as impeller blades. The fluid behavior of the AFPM machine is much like that of a centrifugal ...
Context 3
... ness from a Moody diagram [10]. To facilitate numeric calcula- tions, the Moody diagram may be represented by [8] (12) where . 4) Characteristics: It is now possible to relate the theoret- ical prediction obtained from the ideal flow model to the actual characteristic by accounting for the various losses discussed above. Since the AFPM machine (Fig. 1) has two identical coaxial rotating discs operating on the same stator, it may be treated as two identical fans in parallel. The characteristic curve presented in this section represents only half of the AFPM machine. The characteristic curve of the whole machine may be obtained by adding flow rate at the same ...
Context 4
... function of volumetric flow rate for different motor speeds varying from 200 to 1400 r/min. The results are plotted in Fig. 7. Note that the pressure losses occurring in the discharge duct have been subtracted from the measured values. 6) Volumetric Flow Rate: Fig. 8 shows both the computed and measured volumetric flow rate of the AFPM machine ( Fig. 1) at different operating speeds. Predicted results correlate well with the measured ones. This confirms that shock and leakage losses, as previously assumed, become less significant as the operating point is ...
Context 6
... is instructive to compare the heat-transfer capabilities be- tween a rotation disc and a stationary disc. Considering the AFPM machine depicted in Fig. 1, which has a diameter of 0.4 m and rotates at 1260 r/min, the convection heat-transfer coeffi- cient may be calculated by using (14) and (16) as 41 W/m K, which is about ten times that of the same disc at standstill. Al- ternatively, one can say that the effective heat dissipation area of the same disc can be increased by a factor of ...
Context 7
... Rotor-Stator System: As seen in Fig. 1, the main heat- transfer region consists of surface-mounted PMs with radial channels between the PMs. Due to centrifugal effects, there is a forced flow through the PM channels, which increases the local heat-transfer rate compared to that of a free disc. The relative increase will depend on the gap ratio , the mass flow rate, and the ...
Context 8
... thermofluid model for calculating thermal behavior of AFPM machines has been developed and experimentally vali- dated. To further verify the developed models, relevant thermal tests were carried out on a 250-kW power AFPM generator. This generator is shown in Fig. 11 together with an inlet duct to measure the air-flow ...
Citations
... Although the PM machines have certain superiorities over the asynchronous ones for their high electromagnetic energy densities and low manufacturing cost, the losses should be minimized. [6][7][8][9][10][11][12][13][14] There exist various factors to affect the efficiency of such machines: Mechanical losses, electrical losses and magnetic losses are main issues in this respect. Especially, the mechanical losses and related aerodynamic aspects are worth exploring. ...
... They achieved good agreement calculated and the measured results. 12 Wrobel and his colleagues explored mechanical losses for components of axial flux permanent magnet motors with high power density, high speed and compact design. They analyzed air gap and aerodynamic affect for losses and heat transfer. ...
Heat transfer problem is explored for a new-designed low power generator. A self-cooling mechanism of the generator is designed and implemented for the forced convection via a fan being on the generator rotor. In addition, air is naturally directed towards the lateral parts of the machine in air gaps between stator and rotors. The designed fan has 16 blades with 65 degrees. The CFD and experimental self-cooling analyses are performed to focus on the flow velocities and temperature measurements. In this study, it has been aimed to compare heat transfers by the natural convection and by the forced convection. For this reason, besides Rayleigh (Ra), Nusselt (Nu), Grashof (Gr) and Reynolds (Re) numbers, heat transfer terms on the small winding coil, which is important heat source for the generator, are calculated for natural and forced convection. They are also clarified experimentally and theoretically. The heat transfer at 300 rpm varies between 0.04 W and 0.30 W by time for forced convection and varies between 0.21 W and 0.30 W by time for natural convection, whereas, it increases up at 1000 rpm from 0.50 W to 1.49 W by time for forced convection and from 0.02 W to 0.45 W by time for natural convection. It is proven that the proposed cooling system operates efficiently and the proposed self-cooling method can be used for other axial flux machines, too.
... the external area, the convection coefficient for the horizontal and vertical surfaces of the rotating and stationary components are different. The Nusselt number for the radial surface of a cylinder (cover) and axial surface of a disk (end-cap) are expressed as[25]: ...
... In this regard, extensive researches have been performed in the thermal modelling of stator-PM FSPM machines [10][11][12][13][14][15][16][17][18][19]. However, there is a lack of contribution in excited rotor FSPM machines. ...
... For the EOR-FSPM, convection is classified into the external area and internal regions such as air-gap and inner lateral surfaces. The convection heat transfer coefficients for the radial surfaces of rotating parts are calculated using the following formulas [16]. ...
... 0.166 (+0.671Pr -0.5625 ) -0.296 ) 2 (13) where Gr, , g (m 2 /s), R (m), ∆T (℃), and Ra are Grashof number, coefficient of thermal expansion, Gravity acceleration, radius, temperature difference between the component and the surrounding air, and Rayleigh number, respectively. As the end-cap is a rotating disk, Nusselt numbers for axial surfaces in the laminar flow are calculated as follows [16]: ...
In this paper, precise thermal analysis is investigated for an excited outer rotor flux-switching permanent magnet (EOR-FSPM) machine. To fulfil this aim, a Three-Dimensional (3D) Finite Element Analysis (FEA) is established to accurately calculate PM and rotor holder eddy current loss as well as iron losses in rotor segments and stator core. Through electromagnetic-thermal coupling, all loss sources are injected into the detailed thermal analysis in order to determine both transient and steady-state component temperatures. In addition to the temperature investigation of components, temperature distribution, heat flow path, and heat generation density specifications are analyzed. To achieve a realistic analysis, critical parameters in thermal modelling such as the convection heat transfer in the air gap, end regions and external surfaces, and contact thermal resistances are all considered. The results ensure temperature-sensitive components such as PM and winding will not exceed critical temperature due to appropriate heat dissipation of the proposed topology.
... Because the calculation of the stator convection coefficient in the air-gap is not investigated well and due to the short air-gap length, the stator convection coefficient in the air-gap can be considered equal to that of the rotor [41]. ...
... Local Reynolds number, Nusselt number, and convection coefficient for heat transfer in the radial peripheral edge of the rotor set, the shaft, and the internal radial surface of the frame are presented as follows [41]. ...
... As the frame end cover is a rotating disk, Grashof and Nusselt numbers for a free rotating disk in the laminar flow are calculated, respectively, as follows [41]:. Table 4 Interface gap [28]. ...
In this paper, a three-dimensional (3-D) lumped parameter thermal network (LPTN) model is presented for the first time for a rotor-excited axial-field flux-switching permanent magnet (RE-AFFSPM) machine. The 3-D LPTN predicts the steady-state temperature of different parts in various operating conditions. To enhance the LPTN accuracy and comprehensiveness, (i) the convection heat transfer in the internal and external areas, as well as radiation from the end-windings, (ii) core material anisotropic thermal conductivity, (iii) the equal thermal conductivity of the winding in the slot, and (iv) contact thermal resistances are all considered. Heat transfer coefficients are obtained mathematically to be applicable for the RE-AFFSPM machines with different parameters. A 3-D finite element method (FEM) is established to calculate the electromagnetic losses and thermal analysis with high accuracy. Eddy current losses in the stator core, rotor core, permanent magnets (PMs), and carriers, along with hysteresis losses in the stator and rotor cores, are calculated by 3-D FEM then coupled to the thermal analysis to predict the temperature distribution. By comparing the temperature results of the 3-D LPTN and 3-D FEM at various speeds, air-gap lengths, loading levels, and simultaneous variation of the current density and speed, the performance of the proposed 3-D LPTN is further investigated and verified. Results indicate that by the proposed 3-D LPTN, components temperature can be approximated with high accuracy in a lesser time than the 3-D FEM.
... The most challenging part of the thermal analysis is computing the heat transfer coefficients. Governing equations, including continuity, momentum and energy equations [12][13][14][15][16][17] need to be solved. In [13], the stator body is considered as the main overheating part of the machine and numerical simulation is performed to find the convection heat transfer coefficients in the stator disk of an AF-PMSM. ...
... It is found that there is a certain gap size ratio at which the stator heat transfer shows a maximum. Rong-Jie et al. [14] have developed a thermo-fluid model combining a lumped parameter heat transfer and an air-flow model of a typical AF-PMSM. They also presented two empirical correlations to compute the Nusselt number of the air gap clearance in both laminar and turbulent regimes. ...
A new method for computing convection heat transfer coefficients in axial flux permanent magnet synchronous machines (AF‐PMSMs) is introduced. The method is based on a two‐step finite element analysis (FEA). In the first step, a simple 2D model is introduced and fluid flow and temperature fields are studied using computational fluid dynamic (CFD) technique. Convective heat transfer coefficients for all heat transfer surfaces of the model are extracted from CFD analysis and are then used as inputs to a 3D thermal finite element model. Two case studies are considered to check the accuracy of the abovementioned two‐step method. One of the case studies is an air‐cooled AF‐PMSM that has air inlet and outlet on its enclosure and the other case is a totally enclosed AF‐PMSM. The correctness of the mentioned method is verified by practical measurements on the second case. In addition, an experimental set‐up is conducted to measure the temperature of different parts of the second case. It is observed that the results of the two‐step CFD‐FEA model are in good agreement with the experimental data. In the other case, the effect of inlet air velocity on heat transfer coefficients, as well as the thermal behaviour of the machine are explored.
... In Ref. [11], Scowby et al., discussed a special machine with a 300 kW power at 2300 rpm and they thermally modelled their structure for different conditions. In a different thermal analysis study, the flow rate and temperature values of a prototype machine have been measured [12]. In another paper, the methods to calculate rotor eddy current losses have been discussed and harmonic methods are applied to the machine [13]. ...
In this study, flow phenomena through the axial fan and the rotor dynamic performance analysis of a permanent magnet generator with three phases has been explored for a wide velocity range by using an Ansys-Fluent computational fluid dynamics package. In this respect, velocities of dependence angle for a flat blade have been analyzed, numerically. The self-sustained air cooling performance has been optimized in order to provide more efficient machine, namely the number of blades and blade angles have been considered as different input parameters in the simulations. As a result of simulations, the optimum flat angle of the blade is determined after having the highest velocity value from the outlet of the simulation. Besides, the rotor fan power is obtained from the pressure differences between the inlet and outlet. According to the results, the highest velocity has been predicted as 1.86 m/s and power has been calculated as 0.48 W at 65 degrees of blade. In addition, the optimum number of blade has been ascertained as 40 and the velocity for this blade geometry has been found as 1.39 m/s. Consequently, the optimum rotor blade angle and number have been determined as 65 degrees and 40, respectively.
... In [7], the authors point out that the thermal parameters method can reduce the computation, but this method cannot determine the actual temperature distribution of the IWM well. In [8], the equivalent thermal circuit method is adopted to calculate the temperature field of the IWM. In [9], the finite element method is used to calculate the temperature field of the IWM, and the influence of stator yoke height, the heat transfer coefficient of air gap on the temperature is analyzed quantitatively. ...
The driving conditions of vehicles, such as rapid acceleration, lasting downhill and so on, which the demand for drive power is rapidly increased. For an electric vehicle driven by in-wheel motor (IWM), it means that the IWM needs to provide greater power to maintain the normal operation of the vehicle. At present, the pursuit of high power density for IWM reduces the volume of motor under the same power. But the loss density is increased correspondingly, which will lead to overheating of IWM. In this paper, a 15kW IWM drive system is taken as the research object. Based on the establishment of the temperature analysis model, instantaneous thermal characteristics of the IWM drive system are analyzed under the long climbing condition with low-speed and rapid acceleration driving cycles. The results show that the temperature of the stator winding and stator core is relatively high under the two driving cycles. The temperature of the stator winding is always in the highest level, and the maximum all appears on the end winding. The highest temperature of the end winding can reach 229.49°C under the rapid acceleration driving cycles, which significantly exceeds the limitation for the insulation (155°C) and will seriously affect the normal operation of the IWM and the vehicle. Therefore, in the follow-up design of cooling system, spray cooling with good local cooling effect can be adopted to focus on the cooling for the end winding. This study can provide theory for the design of the feasibility thermal cooling solution.
... The lumped-circuit thermal network is commonly used to perform thermal analysis of electrical machines because of its good accuracy and solutions (steady state and also transient) can be done in seconds. The integration of equivalent thermal network and flow network has been demonstrated for open self-ventilated induction machine [1], axial flux permanent magnet (AFPM) machines [2,3], dual mechanical port machine [4], water-hydrogen-hydrogen-cooled turbogenerator [5] and synchronous machine [6]. ...
... However, it is necessary to discard those dimensionless groups that are irrelevant to the entrance loss to reduce the number of terms in Eq. (12) and to simplify the investigation. As the cooling medium used for the rotor-stator gap and ducts in rotor is mostly air [1][2][3][4]14], so air is only the focus in the present study, the Prandtl number can be discarded from Eq. (12). Both Re ω and Re can be integrated into a single parameter as follows: ...
The annular gap between rotor and stator is an inevitable flow path of a throughflow ventilated electrical machine, but the flow entering the rotor-stator gap is subjected to the effects of rotation. The pressure loss and volumetric flow rate across the rotor-stator gap were measured and compared between rotating and stationary conditions. The experimental measurements found that the flow entering the rotor-stator gap is affected by an additional pressure loss. In the present study, the rotational pressure loss at the entrance of rotor-stator gap is characterised. Based upon dimensional analysis, the coefficient of entrance loss can be correlated with a dimensionless parameter, i.e. rotation ratio. The investigation leads to an original correlation for the entrance loss coefficient of rotor-stator gap arisen from the Coriolis and centrifugal effects in rotating reference frame.
... Extensive research on the electromagnetic analysis of AFPM machines has been undertaken, yet limited research using Computational Fluid Dynamics (CFD) on the thermal aspect has been carried out [11], particularly compared to radial flux permanent magnet counterparts. Conventionally, Lumped Parameter (LM) networks of one-dimensional [12], and two-dimensional [13] approaches have been used in predicting the thermal behaviour of AFPM by compiling both solid and fluid domains. This method is favourable to AFPM machine designers because it gives a fast solution over a broad range of machine speeds. ...
The thermal management of an Axial Flux Permanent Magnet (AFPM) machine is essential because it determines the machine’s continuous power output and reliability. In this paper, a secondary cooling method is proposed using rotor cooling which allows better thermal management on the permanent magnets that are attached to the rotor. This will reduce the potential of the machine failing due to magnet demagnetization and degradation. Thermal analysis via Lumped Parameter (LM) networks is usually sufficient in predicting the motor’s thermal behaviour. However, the accuracy of the prediction can be increased especially for devices with complex flow regions by Computational Fluid Dynamics (CFD). In this study, the fan blade was attached to the rotor of a Yokeless and Segmented Armature (YASA) machine for flow validation and then three different fan blade designs from other engineering applications were tested. The evaluation includes the flow characteristic, power requirement and thermal characteristic for the AFPM’s rotor cooling applications. Additionally, the Rotor Cooling Performance Index (RCPI) is introduced to assess each fan design performance.
... For this reason, the number of experiments on the thermal performance assessment of the AFPMSMs are very limited. Nevertheless, Wang et al. [47,48] constructed a prototype of an AF-PMSM. The machine was set up with a discharge duct. ...
