三分螺旋折流板电加热器流动和传热性能研究

发布时间：2017-12-27 20:11

本文关键词：三分螺旋折流板电加热器流动和传热性能研究　出处：《东南大学》2016年硕士论文　论文类型：学位论文

【摘要】：三分螺旋折流板电加热器是针对工业工程中常用的多圈环形分层布管方式弓形折流板电加热器优化改进而来的新型方案,采用“斜日字”单元环形布管方案解决了多圈环形布管方案因管间距不统一导致在保持最小管间距时壳体尺寸较大,且对流动和传热不利的问题；以周向重叠三分螺旋折流板取代弓形折流板强化电加热器流动和传热性能,在继承螺旋折流板高效低阻特性的同时,避免了弓形折流板方案存在有流动死区、传热系数偏低、流动阻力较大,易诱导振动、易结垢等缺点,极大地改善了加热管表面温度均匀性问题。在此基础上,为改善三分螺旋折流板加工、安装及固定不便的问题,设计了折耳三分螺旋折流板,将原有扇形三分螺旋折流板两端靠近拉杆孔位折弯形成,折耳折流板方案进一步改善了三角区漏流,同时取消了原三分方案中环形端板,并消除了其阻碍流体的负面影响,优化了流场及温度场,延长了电加热器使用寿命,且结构紧凑,加工方便,定位和安装简单,因每套拉杆套管组可紧固两组相邻折流板,拉杆套管组的数目亦是最少,对电加热器的节能优化设计具有良好的效果。本文首先针对电加热器流动与传热特性,建立了“斜日字”单元环形布管的弓形折流板、三分螺旋折流板、折耳三分螺旋折流板3种折流板电加热器的物理及数学模型,采用数值模拟软件FLUENT和可视化分析软件TECPLOT等手段,深入研究了上述三种电加热器内的流动与传热及表面温度均匀性特性。其次,在数值对比研究三种电加热器方案各项性能参数指标的基础上,为深入研究各方案流动换热特性,采用可视化分析软件结合数据分析对比考察了各方案的速度场、压力场、温度场,加热管表面换热系数及壁面温度分布,重点分析了换热系数、综合指标、加热管表面平均温度及最高温度等指标,揭示了“斜日字”布管、周向重叠搭接方式下,折流板结构形式对三分螺旋折流板电加热器加热性能的影响。综合研究了折流板倾斜角对折耳三分螺旋折流板电加热器流动与传热性能影响,设计了折流板倾斜角为20°、25°、300及300双螺旋等方案,寻找出在此设计条件下流动与传热综合指标及电加热管表面温度均匀性指标最高下最佳倾斜角为25°。第三,在此基础上数值模拟研究了三分螺旋折流板电加热器在不同结构形式下加热性能。为进一步揭示所改进的折耳方案流动特性,对比研究了等倾斜角与等螺距的无折耳与折耳三分螺旋折流板方案的流场与压力场；为探究三分螺旋折流板方案换热潜力,设计了2种管长缩短方案并进行了表面温度均匀性分析；为改善大倾斜角下换热性能下降的问题,进行了双螺旋与单螺旋方案流动换热性能的对比研究；研究了电加热器管束方位与入口接管的相对位置对加热性能的影响；从强化传热的目的出发,探索了允许压降下换热系数最优方案。数值结果表明,折耳三分螺旋折流板方案高效低阻特性明显,既继承了三分螺旋折流板优异的流动换热性能,又简化了电加热器结构,并极大改善了电加热管表面温度均匀性,相比于相同工况下弓形方案可将换热系数及综合指标分别提升7%-20%,24%-32%,同时加热管表面平均温度及最高温度分别下降15K-50K,130K-151K。折耳三分螺旋折流板方案可在保持三分方案优异的换热性能基础上,优化流场及温度场,并改善三分螺旋折流板不易加工及安装定位等问题。对管长缩短方案的研究结果表明,三分螺旋折流板方案可减小加热面积30%以上；而允许压降下最佳方案的研究表明相同压降下,三分螺旋折流板对电加热器换热性能提升明显,同时能大幅降低加热管表面最高温度,减少局部高温区,增加运行安全性。第四,针对流体介质为液体的导热油电加热器在变工况下的加热性能进行了数值模拟研究,结果表明倾斜角为15°周向重叠折耳三分螺旋折流板导热油电加热器与板间距为100mm的弓形折流板方案相比,换热系数及综合指标分别提升18%、17%,同时加热管表面平均温度及最高温度分别下降14K、94K,几乎消除了弓形方案中所普遍存在的局部高温区。
[Abstract]:Three spiral baffle plate electric heater is a new scheme for multi ring ring bow cloth tube commonly used methods in industrial engineering baffle electric heater optimization to improve, the cable on the word "unit ring cloth tube solves the multi circle pipe for pipe spacing a result in keeping the minimum shell when the tube spacing is large in size, and the flow and heat transfer problem of circumferential overlap three points; with helical baffles instead of segmental baffles to strengthen the electric heater flow and heat transfer performance of plate flow, in the succession of spiral baffle plate with high efficiency and low resistance characteristics at the same time, to avoid the baffle scheme there is a dead flow zone the heat transfer coefficient, low flow resistance, large, easily induced vibration, easy fouling and other shortcomings, greatly improving the heating tube surface temperature uniformity. On this basis, for the baffle plate processing, installation and fixation of three spiral inconvenience to improve the problem of designing three fold helical baffles, the original fan three helical baffle rod holes near the ends of bending forming, fold the baffle plan to further improve the triangle leakage current, at the same time cancel the original ring three scheme in the end plate, and to eliminate the negative influence of blocking fluid, optimization of the flow field and temperature field, prolong the service life of the electric heater, and has the advantages of compact structure, convenient processing, simple installation and positioning, because each rod casing group fastening two adjacent baffle plates, the number of rod sleeve the group is also the least, the electric heater has a good effect of energy saving optimization design. In this paper, the electric heater flow and heat transfer characteristics, established a "slant on the word" unit annular tube baffle, three helical baffles, fold three spiral baffle 3 models of physics and mathematics baffled the electric heater, using the software of FLUENT and visual analysis software TECPLOT the numerical simulation method, in-depth study of the above three kinds of electric heater in the flow and heat transfer characteristics and surface temperature uniformity. Secondly, based on the comparison of three numerical electric heater performance parameters, to further study the scheme of flow and heat transfer characteristics, using visual analysis software combined with data analysis and contrast the effects of the scheme of velocity field and pressure field and temperature field, heating tube surface heat transfer coefficient and wall temperature distribution, key analysis of the heat transfer coefficient, comprehensive index, heating surface average temperature and maximum temperature index, reveals the "slant on the word" cloth tube, circumferential overlap mode, the baffle plate structure affect the form of the three points spiral baffle plate electric heater heating performance. A comprehensive study of the baffle angle fold ear three spiral baffle plate electric heater effect of flow and heat transfer performance, design of the baffle angle is 20 degrees, 25 degrees, 300 and 300 double helix scheme, to find out the design under the condition of flow and heat transfer in comprehensive index and the electric heating tube surface temperature the uniformity of the highest index under the optimum tilt angle of 25 degrees. Third, on the basis of the numerical simulation, the heating performance of the three - point spiral baffle electric heater in different structure forms is studied. For the fold scheme further reveal the improved flow characteristics, we studied the flow field and pressure field with three fold fold helical baffle scheme etc. tilt angle and pitch; the baffle plan for heat potential of three spiral inquiry, 2 design scheme and the length of shortening analysis of surface temperature uniformity; to improve the heat transfer performance of a large tilt angle decreased, compared with the scheme of double helix single spiral flow and heat transfer performance; influence of the relative position of the electric heater tubes and take over the entrance range on the heating performance; starting from the purpose of heat transfer enhancement, explore the heat under the optimum allowable pressure drop coefficient. The numerical results show that the three fold helical baffle scheme of high efficiency and low resistance characteristics is obvious, not only inherited the three helical baffles excellent flow and heat transfer performance, but also simplifies the structure of the electric heater, and greatly improve the electric heating tube surface temperature uniformity, compared to the same condition can be changed T. the heat transfer coefficient and comprehensive index were increased 7%-20%, 24%-32%, and the surface of the heating pipe average temperature and maximum temperature decrease of 15K-50K, 130K-151K. The three fold helix baffle scheme can optimize the flow field and temperature field on the basis of keeping the excellent heat transfer performance of the three points, and improve the problem of three point spiral baffle plate's hard processing and installation location. Study on the length of shortening scheme. The results show that the three spiral baffle scheme can reduce the heating area of more than 30%; and allows the pressure drop of best scheme shows that the same pressure drop, three spiral baffle plate for electric heater heat transfer performance significantly, and can significantly reduce the heating surface of the tube maximum temperature, reduce local the high temperature zone, increase operation safety. Fourth, the fluid medium for conducting oil liquid electric heater in the heating performance condition is studied by numerical simulation. The results show that the tilt angle of 15 degrees to three week overlap fold helical baffle heat conduction oil heater and plate spacing of 100mm baffle scheme compared to heat transfer coefficient and the comprehensive index were increased by 18% and 17%, while the average surface temperature of heating pipe and the highest temperature decreased 14K and 94K respectively, virtually eliminates the local high temperature zone exists in the bow.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK172

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