Bush Induction Heating

UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 1 of 20 Bush Induction Heating Maximum excitation current, Imax: 50 A Frequency, f: 75 kHz Carlo Ferri Apr 2024 UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 2 of 20 Revision history Revision Date Comment 0.3 2024-04-30 Final revision. 0.2 2023-11-22 WED Add 6 turn coil for small bush, flat spiral 2 turns, core iron co-axial 0.1 2023-11-17 FRI Initial revision. Contents Revision history ....................................................................................................................................... 2 Contents .................................................................................................................................................. 2 Acronyms ................................................................................................................................................ 2 1. Introduction .................................................................................................................................... 2 2. Bush temperature ........................................................................................................................... 4 3. Volumetric Electric power density losses ....................................................................................... 7 4. Field of the Magnetic flux density norm ||𝐁|| ................................................................................ 9 5. Doubling the numbers of turns for the small bush ....................................................................... 10 6. Two-turn flat spiral and small bush .............................................................................................. 12 7. Using an iron core to transfer the magnetic flux density to the bush .......................................... 14 8. Coil concatenated with the small bush ......................................................................................... 15 References ............................................................................................................................................ 20 Acronyms Not relevant in this report so far. 1. Introduction The bush being considered have dimension and designation as in in Table 1. The dimensions are displayed in the schema of Figure 1. UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 3 of 20 Table 1 Size of the bushes considered in this study. designation 10--f-km 12--f-km 13-____fakm A_max_OD 14.029 16.029 30.035 B_Min_OD 14.018 16.018 30.022 G_Max_ID 10.027 12.033 25.04 H_Min_ID 10.005 12.006 25.007 A_width_incl_flange 12 12 24.75 C_Flange_width_stem 1.5 1.5 1.4375 E_OD_Flange 16 22 34.875 D_Bore_ID 11.027 13.033 27.024 E C A_width A D Figure 1 Schema of the bush dimensions. UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 4 of 20 2. Bush temperature The temperature filed in stationary regime is considered for the bushes of three sizes: small size, i.e., 10--f-km, medium size, i.e., 12--f-km, large size, i.e., 13-____fakm. It is noticed that the hottest Figure 2 3D figure of the temperature field small bush in stationary regime. Figure 3 Temperature field in a cross section of the small bush in stationary regime. UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 5 of 20 region is in flange area for each of the three bush sizes, see Figure 2, Figure 4 and Figure 6. Cross sections of the bushes allows a better appreciation of the temperature gradients for each of the three bush sizes, see Figure 3, Figure 5 and Figure 7. When the size of the bush is smaller, the air gap to the coil is larger. The effect of this larger gap is increasing the maximum temperature that the bush reaches, which ranges from 135.93 C to 152.29 C to 176,27 C for the small, medium, and large sizes respectively. The range of the temperatures is 135.86 – 135.93 C for the small bush, 152.04 – 152.29 C for the medium size bush and 175.42 – 176.26 C for the large bush. The Study of the temperature increment during the first 240 second from the activation of the excitation current in the coils is provided in three separate video. The temperature shown here are in stationary regime, i.e., when an equilibrium is reached in the balance of power the heat the bush and the power that is radiate by the bush hot surfaces. Because of this equilibrium of power, the temperature remain constant. Figure 4 3D figure of the temperature field medium size bush in stationary regime. UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 6 of 20 Figure 5 Temperature field of the medium size bush in stationary regime. Figure 6 3D figure of the temperature field for the large size bush in stationary regime. UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 7 of 20 3. Volumetric Electric power density losses As it is observed in Figure 8, Figure 9 and Figure 10 the maximum of the volumetric power loss in W/ is increasing from 56.7 to 85.7 to 288 when considering bushes of larger size in the same coil size. Figure 8 Power loss density Qrh for the small bush. Figure 7 Temperature field in stationary regime for the large size bush. UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 8 of 20 Although the maximum is increasing, the figures do not show a noticeable change of the Power density losses on average. That means that the power loss that is translated into heating power in the bush might be larger in some areas of the bush the thicker the air gap coil-bush is. Yet, on average this is scarcely visible in a bush cross section. The frequency of 75 kHz used focuses the losses, hence the heating power generation in a very thin layer around the surfaces of the bush. Figure 9 Power loss density Qrh the medium size bush. . Figure 10 Power loss density Qrh for the large size bush. UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 9 of 20 4. Field of the Magnetic flux density norm ||𝐁|| Figure 11 Magnetic flux density Norm ||B|| for the small size bush. Figure 12 Magnetic flux density Norm ||B|| for the medium size bush. UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 16 of 20 S/m, as suggested in the COMSOL video tutorial Modeling Transformers and Inductors in COMSOL Multiphysics® . A second coil geometry was then tested where a three-turn winding close to the bush is examined. The Figure 23 shows that the bush still remains at 20 C, the coil reaches 49.7 C. The COMSOL video tutorial Modeling Inductive Heating in a Coil Using COMSOL Multiphysics® suggests using a spherical air domain with a layer that is assigned an “Infinite Element domain” definition. Conductivity of the air domain is kept at its default 0 S/m value. Following these suggestions, a second analysis was conducted. In Figure 24, the resulting bush and coil temperatures are inferred by the colour scale. The bush remains cools at 20 C, whereas the coil reaches 46.6 C. These values appear in good agreement with those obtained with slightly conductive box-shaped air domain, considered earlier. Figure 20 Geometry of the concatenated coil. UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 17 of 20 Figure 21 Concatenated coil, small bush, 50 A, 75 kHz, one turn, , box air domain with conductivity 1 S/m. Figure 22 Concatenated coil, Small bush, 50 A, 75 kHz, two turn, box air domain with conductivity 1 S/m. UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 18 of 20 Figure 23 Concatenated coil, small bush, 50 A, 75 kHz, narrow winding box air domain 1 S/m. UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 19 of 20 Figure 24 Concatenated coil, narrow winding, but air domain 0 S/m, spherical, with 'infinite domain layer'. UNIVERSITY OF WARWICK COVENTRY CV4 7AL UK T +44 (0)24 7657 5453 WWW.WMG.WARWICK.AC.UK page 20 of 20 9. Matrix of design performance Bush size Small Medium Large Conc-1: coil parallel to bush axis, 2D X X X Conc-2: coil orthogonal to bush axis Conc-4: coil with turns inside bush X References [1] NASA, “Pluto: The ’other’ red planet,” https://www.nasa.gov/nh/pluto-the-other-red-planet, 2015, accessed: 2018-12-06.