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Four‐kilowatt homogeneous microwave heating system using a power‐controlled phase‐shifting mode for improved heating uniformity

2019; Institution of Engineering and Technology; Volume: 55; Issue: 8 Linguagem: Inglês

10.1049/el.2019.0060

1350-911X

C.‐H. Jeong, Sung‐Hoon Ahn, Wang‐Sang Lee,

Induction Heating and Inverter Technology

Electronics LettersVolume 55, Issue 8 p. 465-467 Microwave technologyFree Access Four-kilowatt homogeneous microwave heating system using a power-controlled phase-shifting mode for improved heating uniformity C.-H. Jeong, C.-H. Jeong Department of Electronic Engineering/Engineering Research Institute (ERI), Gyeongsang National University (GNU), 501, Jinju-daero, Jinju, Gyeongnam, 52828 Republic of KoreaSearch for more papers by this authorS.-H. Ahn, S.-H. Ahn Department of Electronic Engineering/Engineering Research Institute (ERI), Gyeongsang National University (GNU), 501, Jinju-daero, Jinju, Gyeongnam, 52828 Republic of KoreaSearch for more papers by this authorW.-S. Lee, Corresponding Author W.-S. Lee wsang@gnu.ac.kr orcid.org/0000-0002-6414-2150 Department of Electronic Engineering/Engineering Research Institute (ERI), Gyeongsang National University (GNU), 501, Jinju-daero, Jinju, Gyeongnam, 52828 Republic of KoreaSearch for more papers by this author C.-H. Jeong, C.-H. Jeong Department of Electronic Engineering/Engineering Research Institute (ERI), Gyeongsang National University (GNU), 501, Jinju-daero, Jinju, Gyeongnam, 52828 Republic of KoreaSearch for more papers by this authorS.-H. Ahn, S.-H. Ahn Department of Electronic Engineering/Engineering Research Institute (ERI), Gyeongsang National University (GNU), 501, Jinju-daero, Jinju, Gyeongnam, 52828 Republic of KoreaSearch for more papers by this authorW.-S. Lee, Corresponding Author W.-S. Lee wsang@gnu.ac.kr orcid.org/0000-0002-6414-2150 Department of Electronic Engineering/Engineering Research Institute (ERI), Gyeongsang National University (GNU), 501, Jinju-daero, Jinju, Gyeongnam, 52828 Republic of KoreaSearch for more papers by this author First published: 01 April 2019 https://doi.org/10.1049/el.2019.0060Citations: 5AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract For homogeneous microwave heating in a microwave cavity with multiple 2.45 GHz microwave generators, power-controlled phase-shifting mode is proposed in this Letter. The proposed microwave heating system consists of a multimode microwave cavity in which dielectric materials are placed to be heated, four phase-shifting WR-340 waveguides for different phase excitation, four 1 kW magnetrons that produce microwave power at 2.45 GHz, and a power supply with a system controller for the magnetron output power controls. Using the proposed power-controlled phase-shifting mode, uniform heating distribution is achieved by reducing the hot and cold spots in the microwave cavity. The proposed experiments demonstrated that in comparison to a conventional mode with simultaneous multiple inputs, the proposed mode can achieve an improved heating uniformity of 64.4. Introduction Microwave (MW) ovens are commonly used as a cost-effective and convenient solution for heating, drying, curing, cooking, pasteurising, and sterilising for ceramics, agricultural products, polymer raw materials, electronic materials, and so on [1, 2]. A MW oven is adapted to radiate MWs generated by means of MW supply (commonly, magnetrons) to the inside of a metal heating applicator, thereby causing a material to be heated within the heating applicator (MW cavity) where it is subjected to heating by radiated MWs [3]. In conventional MW ovens, the non-uniformity of the electromagnetic-field distribution within the MW cavity is the primary drawback in that homogeneous MW heating of an object (heated material) cannot be achieved. This can produce improper heating due to hot and cold spots within the MW cavity. To address this problem and achieve uniformity in MW heating, several approaches have been employed [4-12]. These approaches include the adoption of various structures, such as a turntable upon which the heated material is placed and rotated within the MW cavity, a mode stirrer [5], or a structure designed to allow the use of MW sources with different frequencies [6]. The introduction of extra moving parts, such as a turntable with a motor, a mode stirrer, and MW sources with different frequencies, increases the risk of malfunction and also makes MW ovens more complicated to manufacture. Proposed system configuration Fig. 1a shows the configuration of the proposed 4 kW MW drier system. It consists of a MW cavity ( mm, mm, mm) in which dielectric materials are plated to be heated, four phase-shifting WR-340 waveguides with 90 rotated positions for different phase excitation, four 1 kW magnetrons that produce MW power at 2.45 GHz, and a power supply with a system controller for magnetron output power controls. The proposed system has four MW inputs located at various positions on the top of the MW cavity, as shown in Fig. 1b. Basically, increased temperature caused by MW heating can be represented by (1)where f, , , , , , and are the frequency (Hz), the free-space dielectric constant, the relative dielectric constant related to the amount of energy that can be stored in a material, the internal electric field intensity (V/m) at MW frequency, the temperature rise time (s), the density of the material to be heated (kg/m), and the specific heat of the material to be heated (J/kgC), respectively [2]. For uniform heating, even electric field distribution on the surface upon which the heated material is placed is required. From Helmholtz equation (), the radiated electric field from waveguides can be calculated by . Fig. 2 shows the deployment of the four MW waveguides (EIA Standard, WR-340 in Fig. 2a) with the magnetron inputs. Fig. 2b presents a conventional mode () with the same input length ( mm), which is approximately 1.4 at 2.45 GHz. Fig. 2c shows a phase-shifting mode () with a length of 90 phase difference ( mm at P1, mm at P2, mm at P3, and mm at P4) which is approximately 30 mm (1/4) at 2.45 GHz. In this case, the maximum phase difference between adjacent inputs is 270 at P3 and P4. In Fig. 2d, the proposed mode () has a minimum phase difference of 180 between adjacent inputs by changing the inputs of P3 and P4 in Fig. 2c. In Figs. 2b and c, the radiated electric fields ( or ) at x- or y-axis direction in the conventional and phase-shifting modes can be cancelled or doubled due to the input phase conditions (P1 and P3 or P2 and P4). However, the proposed mode achieves the improved heating uniformity due to 90 phase difference between P1 and P3 or P2 and P4 in Fig. 2d. Fig 1Open in figure viewerPowerPoint Configuration of the 4 kW MW drier with four 2.45 GHz MW sources through four phase-shifting waveguides (WR-340) a Simplified configuration of the MW drier b Perspective view of the MW cavity Fig 2Open in figure viewerPowerPoint Multiple waveguide deployment a Configuration of a waveguide (WR-340) b Conventional mode with the same length c Phase-shifting mode with a length of 90 phase difference d Proposed mode with minimum phase difference between adjacent inputs Using a commercial full-wave electromagnetic simulation tool (Microwave Studio 2018 by CST), the electric field distributions (Figs. 3a–c) and temperature variations(Figs. 3d–f) in the heated material (water sheet with 5 mm thickness, , S/m) in the MW cavity with regard to the various operating modes(conventional, phase-shifting, and proposed modes) are described, respectively. Incomparison to the conventional mode, the phase-shifting mode reduces hot and coldspots in the heated material. With continuous control of the incident power of eachwaveguide from P1 to P4, Fig. 4 represents the comparison of electric field intensityand temperature distributions in the MW cavity in the conventional, phase-shifting, andproposed modes, respectively. The power-controlled mode provides a uniformtemperature distribution as a whole, but hot spots occur in the phase-shifting mode inwhich the phase difference is large, as seen in Fig. 4e. However, the proposed modecan obtain improved heating uniformity without peak spots in the heated material in Fig. 4f. Fig 3Open in figure viewerPowerPoint Comparison of electric field intensity and temperature distributions in a water sheet for various operating modes under steady-state condition in the MW cavity a–c Electric field distributions d–f Temperature variations for conventional, phase-shifting, and proposed modes, respectively Fig 4Open in figure viewerPowerPoint Comparison of electric field intensity and temperature distributions in the MW cavity when the incident power of each waveguide was controlled a–c Electric field distributions d–f Temperature variations for conventional, phase-shifting, and proposed modes, respectively Results and discussions To experimentally verify the homogeneous heating performance of the proposed MW system with a power-controlled phased-shifting mode, we designed and implemented a MW drier including four waveguides and four 1 kW magnetrons (2M246 Model) made by LG Electronics Inc., Seoul, Korea. Figs. 5a–d show the experimental setup for the uniform heating verification of the proposed power-controlled phase-shifting mode with multiple MW generators. To verify the uniform drying performance for a heated material (water), 49 small paper cups filled with 20 g of water were placed on the bottom of the MW cavity. In the case of the conventional mode, a 200 W power level was applied to the four rectangular waveguides for 25 min simultaneously. Alternatively, an 800 W power level (6 min and 15 s) was divided evenly and applied to each input (P1–P4), respectively. The induced total power of the conventional and proposed modes was equal to 800 W for the heating time. Figs. 5e–g describe the remaining residues from an initial amount (20 g) of heated material (water) in the MW cavity after the application of simultaneous inputs in the conventional, phase-shifting, and proposed modes, respectively. The remaining residues for the power-controlled modes with conventional, phase-shifting, and proposed modes, respectively, are shown in Figs. 5h–j. In comparison to the conventional simultaneous multiple-input method, the power-controlled method achieved a heating uniformity improvement of 44.1 (see Figs. 5e and h), while the proposed power-controlled phased-shifting method achieved a heating uniformity improvement of 64.4 (see Figs. 5e and j). Table 1 describes the comparison between simulated and measured results. Fig 5Open in figure viewerPowerPoint Experimental setup of the proposed mode with multiple MW generators and the remaining residues from an initial amount (20g) of heated material (water) in the MW cavitya MW cavity with door open b Designed waveguides with various lengths c Top view of magnetron-equipped waveguides d 49 Small paper cups filled with water e–g Remaining residues with simultaneous inputs h–j Remaining residues with power-controlled modes in conventional, phase-shifting, and proposed modes, respectively Table 1. Comparison between simulated and measured results Simulated Temp. Min. (C) Max. (C) Ratio Comp. (%) W/O conventional 63.4 298.7 4.7 N/A power phase-shift. 38.2 159.3 4.2 11.5 control prop. 33.9 132.8 3.9 16.9 W conventional 57.9 186.1 3.2 31.8 power phase-shift. 63.4 221.2 3.5 25.9 control prop. 62.3 127.4 2.0 56.6% Measured residues Min. (g) Max. (g) Comp. (%) W/O conventional 6.4 17.6 1.88 N/A power phase-shift. 11.1 17.8 1.36 27.7 control prop. 13.8 18.0 1.11 41.5 W conventional 14.5 18.9 1.05 44.1 power phase-shift. 15.6 19.2 0.86 54.3 control prop. 16.1 18.9 0.67 64.4 Conclusion For improved heating uniformity, the proposed 4 kW homogeneous MW heating system with the power-controlled phase-shifting mode was optimised using state-of-the-art full-wave electromagnetic simulations prior to experimental verification of the MW system. It provides a cost-effective and efficient solution that overcomes the problem of the non-uniform heating in conventional MW systems. Acknowledgments This work was supported in part by the Industrial Technology Innovation Program and in part by of the Human Resources Program in Energy Technology of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry Energy, under grant 20172010106020 and grant 20174030201440, respectively. 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