No abstract

No abstract

I. Introduction Due to their high torque density and an excellent efficiency, axial flux PM machines are favorable for vehicle propulsion and wind energy conversion. Although many effort was already done to simulate the electromagnetic properties of the machine using full 3D or multilayer-2D simulations, the work towards modelling of the thermal behavior is still very limited. As the disc-shaped rotors will operate as a fan during rotation, convective heat transfer in the air gap will have a major influence on the thermal design of the machine. Rather than performing full 3D combined fluid and thermal analysis, empiric analytical expressions based on CFD are used in this work to define the convective heat coefficient in different parts of the machine. The final thermal simulations are carried out for the stator and rotor individually, where only a segment needs to be modelled due to thermal periodicity. As a result, the use of this coupled modelling technique results in a significant decrease of the overall simulation time. The coupled electromagnetic and thermal modelling techniques are illustrated on a 4kW axial flux PM machine having the yokeless and segmented armature (YASA) topology. Finally, both the electromagnetic and thermal simulation results were validated on a preliminary prototype. II. Coupled Electromagnetic and Thermal Modelling In the first step of the analysis, the electromagnetic behavior of the machine is modelled. The results from the electromagnetic field computations are used to calculate the corresponding losses in post-processing. In a second step, these losses are used as the heat sources for the thermal simulations. As the axial flux PM machine has an inherent 3D structure, multilayer-2D simulations [1] are used to obtain the electromagnetic properties such as flux-linkage, back-emf and (cogging) torque. In postprocessing, the magnetic flux density pattern of the different layers in the core is used to calculated the core losses. The solutions for the air gap magnetic flux density pattern of each layer are combined and used for a time harmonic calculation of the eddy current losses in the permanent magnets [1]. Together with the Joule losses in the machine winding, the iron losses in the stator cores and eddy current losses in the PM's are used as the source terms in the thermal simulations. As the thermal process is particularly slow with respect to the electromagnetic one, the time average values of the losses are chosen as a source in the thermal model. Instead of using full 3D combined fluid and thermal analysis, empirical equations derived in [2] are used to model the convective heat transfer from each of the surfaces near the air gap region. Next to an empirical formula for the convective heat coefficients of each surface, an expression for the reference temperatures is also derived using dimensionless numbers. The reference temperature is the bulk fluid temperature of the domain near each surface which can be expressed as a function of the average stator, rotor and ambient temper...

No abstract

If you would like to write for this, or any other Emerald publication, then please use our Emerald for Authors service information about how to choose which publication to write for and submission guidelines are available for all. Please visit www.emeraldinsight.com/authors for more information. About Emerald www.emeraldinsight.comEmerald is a global publisher linking research and practice to the benefit of society. The company manages a portfolio of more than 290 journals and over 2,350 books and book series volumes, as well as providing an extensive range of online products and additional customer resources and services.Emerald is both COUNTER 4 and TRANSFER compliant. The organization is a partner of the Committee on Publication Ethics (COPE) and also works with Portico and the LOCKSS initiative for digital archive preservation. AbstractPurpose -This work aims to focus on the study of natural convection heat transfer characteristics in a vertical wall embedded in a non-Darcy porous medium filled with nanofluids. Design/methodology/approach -The governed partial differential equations are transformed into ordinary differential equations which are obtained by similarity solution and then have been solved through homotopy analysis method. Findings -The results show that Cu-water as nanofluid enhances the local Nusselt number more than other nanofluids. Originality/value -Nanoparticles and nanofluid enhance the local Nusselt number.