A series of four-start spirally corrugated tubes has been subjected to heat transfer and hydrodynamic testing in a double-pipe heat exchanger. The study has been focused on the non-symmetric nature of the corrugation angles along the longitudinal direction. Both friction factors and heat transfer coefficients inside the tubes have been correlated against various process parameters. It can be shown that by altering the internal non-symmetric wavy shapes of the tubes, one is able to manipulate heat transfer and friction characteristics. The experimental results have been compared with some popular correlation models developed previously for both friction and heat transfer for corrugated tubes. Considerable differences between the experimental results and the predictions made using the existing correlations have been found and the probable causes have been discussed. Performance evaluation criteria are presented using the standard constant power criterion. A neural network modeling approach has been taken so that, based on the limited data, one can generate the contour showing the effect of corrugation angle on heat transfer coefficient for geometry optimization purposes.

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Axial field flux-switching magnetic gear composite motor (AFFSMGCM) combines the advantages of axial field flux-switching permanent magnet machine (AFFSPMM) and magnetic gear (MG). In order to reduce the time and cost of design and optimization due to the complicated structure of AFFSMGCM, the nonlinear varying-network magnetic circuit (VNMC) is researched and developed for the machine. First, the topology of AFFSMGCM is introduced in details. Then, the accurate VNMC model is established with consideration of magnetic saturation and leakage flux. Finally, multi-objective optimization of AFFSMGCM based on VNMC is carried out to obtain large torque and low torque ripple. Meanwhile, the finite element analysis (FEA) method is used to validate the VNMC model. It is shown that the calculation results based on VNMC model are similar to those of FEA. The proposed VNMC improves the efficiency and accuracy of the design and optimization of the machine.INDEX TERMS Axial field flux-switching magnetic gear composite machine (AFFSMGCM), varyingnetwork magnetic circuit (VNMC), sensitivity analysis, multi-objective optimization, finite element analysis (FEA) method.

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Numerical studies of Heat transfer enhancement of belt-type Electric-resistance Heater is reported in this paper. The effect of different kinds of belt arrangements is studied in detail. Results show that, for changing m and n, which is the spacing between adjacent belts both in vertical and horizon, the comprehensive Performance Evaluation Criterion(PEC) increases as belt spacing decreases; For the case of model adding several baffles, the PEC reaches 1.6, with Nu/Nuo and f / f0 comes to 3.38 and 9.51; For the staggered arrangement belt geometry, the PEC attains 1.18 and the flow field uniformity improves significantly compared with the aligned arrangement one.