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Numerical simulation on thermal performance of helical baffled electric heaters with oneplustwo Utube units |
1.School of Energy and Environment, Southeast University, Nanjing, Jiangsu 210096, China;
2.School of Mechanical and Automotive Engineering, Zhejiang University of Science and Technology, Hangzhou, Zhejiang 310023, China |
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Abstract To overcome the defects of low heat transfer coefficient and nonuniform tube spacing in conventional multiringannular Utube layouts of segment baffled electric heaters, the novel helical baffled electric heaters with oneplustwo Utube units were designed with equilateral triangle tube layouts. Numerical simulation and comparison of the flow and heat transfer performance and the surface temperature uniformity were performed for five helical baffled electric heaters and two segment baffled ones. Each helical baffled scheme comprises of nine oneplustwo Utube units with altogether 27 16 mm Utubes supported by trisection helical baffles with 15° or 20° inclined angle, and each segment baffled scheme comprises of 30 16 mm Utubes of tworing annular layout supported by segment baffle plates spanned either 200 mm or 300 mm. The calculation results with fluid of compressed nitrogen show that the average temperature and the highest temperature of heating surface of 15° trisection helical baffles are reduced respectively by 31.7 K and 50.7 K, and the average heat transfer coefficient and the comprehensive index h·Δp-1/3 are increased respectively by 68.2% and 34.3% than those of segment baffle plate scheme. The effective heating area of 15° inclined angled trisection helical baffle electric heater is only 68.5% of that of segment baffled one with baffle plate span of 200 mm.
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Received: 15 June 2015
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