【作者】 栾志坚；

【导师】 潘继红；

【作者基本信息】 山东大学 ， 热能工程， 2009， 博士

【摘要】 板式换热器是近年来发展很快的热交换设备,但相对其他型式的热交换设备,由于阻力较大一直影响其在高粘性介质换热领域中的应用。在分析影响对流换热关键因素的基础上,研究了高粘性流体在一新型板式换热器内换热时的传热与阻力特性,并应用场协同的基本原则对其换热特性进行了分析。最后从热力学(Exergy)损角度分析了不同换热条件下流道形状(长宽比)对板式换热器内流动与换热过程中热力学性能的影响。通过分析Reynolds及Prandtl关于对流换热的经典假设,认识到表面传热系数取决于壁面法线方向上流体的质量输运。使用Blasius解等成熟的理论成果分析大平板上的层流对流换热,结果表明:无限大平板上的局部表面传热系数正比于当地热边界层内壁面法线方向上的平均速度。对文中得到的表面传热系数与流体在边界层内壁面法向上平均速度的正比关系,同边界层能量积分方程中得到的对流换热关系作了比较和鉴别。通过对边界层内对流换热过程热阻的分析,计算了Prandtl模型的导热层厚度。随着Pr数的增加,导热热阻逐渐减小,纯对流热阻逐渐增加。在边界层发展过程中,其导热热阻和纯对流热阻之比保持不变,该比值随着Pr数的增加逐渐减小并在Pr数＞10后基本趋于稳定。对复合波纹板式换热器进行了水水换热和水油换热实验测试,得到了复合波纹板式换热器在雷诺数范围2000＜Re＜20000和较低雷诺数范围50＜Re＜360内换热特性和阻力特性的实验关联式。并将实验结果与文献报道的研究结果进行了比较,证实在低Re数下复合波纹板式换热器的传热-阻力综合性能优于传统人字型板式换热器。选取与实验板片完全相同的波纹几何参数及对流换热条件,建立数值计算物理模型,得到的数值计算结果与实验结果一致性较好,说明在复合波纹板片形成的复杂通道内利用数值方法研究其换热和流动规律是可靠的。通过分别建立不同波纹几何参数模型的数值研究方法,分析得到了每个波纹几何参数对复合波纹板式换热器换热和流动特性的影响规律,讨论了介质粘性以及粘性受温度影响时换热和流动特性随波纹几何参数改变时的规律。归纳得到了研究Re数范围内包含波纹几何参数影响的复合波纹板片换热准则关联式和阻力关联式,可作为该板型换热器设计计算和参数优化的依据。应用场协同原理,分析了壁面法向矢量与流动速度矢量间的协同程度对表面传热系数的影响。通过在平板、人字型波纹板以及复合波纹板上壁面法向速度影响表面传热系数的趋势分析,阐述了fluent数值模拟软件取到的数据与h-v正比关系的差异及出现差异的原因。对比研究了同为波纹倾角60°的复合波纹板片和人字型波纹板片,结果表明复合波纹板片具有更显著的强化换热作用,从传热壁面法向同速度的夹角余弦场与速度场间良好匹配可以强化换热的角度阐释了上述结果。最后从热力学(火用)损角度,数值分析了不同流量下板片宽长比对传热和流动产生比(火用)损的影响。通过板片宽长比对恒热流、恒壁温及等质量逆流时比(火用)损影响的分析,发现上述三类条件下取得最小比总(火用)损时,比热(火用)损大于比流(火用)损,且占据总(火用)损中的多数份额。且随流量的增加,三类条件下取得最小比(火用)损时板片的宽长比增大;随流量的增加,恒热流换热时最小比(火用)损出现先增加而后减小的趋势,主要由于换热温度及换热温差共同作用导致。随流量的增加,恒壁温及等质量逆流时的最小比(火用)损增大,主要由于传热温差增大导致。相同流量时,恒热流,恒壁温及等质量逆流条件下,波高的增加均导致最佳宽长比γ_g减小。相同流量时,恒壁温及两侧介质等质量逆流条件下,波高的增加导致最佳宽长比时的比总(火用)损呈现增加的趋势。更多还原

【Abstract】 As a type of thermal power mechanical apparatus, plate heat exchangers are developing rapidly in recent years. Comapred with other types of thermal power apparatus, it is fewly used in heat transfer of high viscosity fluid for its disadvantage in flow resistance. The heat transfer and flow resistance properties of high viscos media in PHE are researched, which is based on the analys in critical factor of influencing heat transfer. The principles of synergism theory are applying in heat transfer properties analysis of new type PHE. Finally, thermol dynamical properties of plate heat exchangers in differential channel shape and mass flux using exergy.Heat transfer coefficient is determined on mass transport of the direction nomal to wall while tracking the idea of Reynolds and Prandtl in depicting heat convection. The heat convection can be analysis by using the ripe Blasius Resolution on unlimited plate. The result indicate that local heat transfer coefficient direct ratio to average velocity which direct upright to wall in thermal boundary layer. And compare that with the intergral energy equation in boundary layer. The synergism parameters are the velocity vector and the wall normal vector if the heat transfer coefficient is considered, and the parameters are the velocity vector and temperature field if the heat flux is considered.Thermal resistance in boundary layer is researched base on prandtl model and thickness thermal viscous layer in Prandtl Model are calculated. The propotion of conduction resistance increase and the propotion of convection resistance decrease with increase of Prandtl number. The ration between conduction ressistance and convection resistance unchanged with the development of boundary layer, and the ration decrease step with Prandtl Number increase. The ration touch a fix value after Pr>10.Heat transfer and flow resistance properties of compound corrugate PHE are tested on their experimental unit. The experimental correlated equation of heat transfer and flow resistance are achieved in the range of 2000<Re<20000 for water and 50<Re<360 for oil. The comparetion between experimental results and inclinded corrugated PHE indicated that the compound corrugated PHE better than classical PHE in compromise performance for heat transfer and flow resistance.Physical and numerical models is constructed as same as the experimental PHE. Numerical simulation result shows that it is accord with experiment almostly. That indicates it is reliable to simulating heat convection in such complex channels as compound corrugated plates. The simulation has advantages in economization for time and expense obviously, which can be used in researching new PHE for several corrugate parameters in heat transfer and flow properties. The relational discipline of each corrugate parameter is analysised in heat transfer and flow resistance properties, which including consideration of visocity and viscosity various in temperature.The relations between heat transfer /flow resistance and Reynolds number, which contains corrugate parameter, are conclude in the range of Reynolds number that researched. It can sustain the designing or optimize compound for corrugated PHE. The numerical results are analysis using synergism theory. Difference between fluent data and h-v relation is induced by thei data acquire types.The compound corrugated type is distinct advance over inclined corrugated type with the same obliquity (60°). The conclusion is interpreted with synergism performance and synergism matching performance.The Exergy dissipation of common inclined corrugation is researched from aspect of specific exergy dissipation that derivating from heat transfer and flow resistance. The relation between specific exergy dissipation and width-length-ratio /flux is analysised and summarized. The minum specific dissaption of constand heat flux are as same as that of constant wall temperature and converse flow with equal flux. The result is that the specific heat dissipation is farly larger than flow dissipation while the minimum dissapition are achieved. The width-length-ratio(WLR) are increased while minimum specific dissipation with the increase of flux. The minimum specific dissipation of constant heat flux is first increase and then decrease with the increase of flux, which are induced by temperature and temperature diffrerence. The minimum specific dissipation of constant temperature and converse flow are increase with the flux increase, which is induced by the increase of temperature difference. The optimazed WLR reduce while corrugation depth increase in same flux for constant wall temperature, constant wall heat flux and counter flow. The specific exergy dissipation on optimize WLR are increase while corrugation depth increase in same flux for constant wall temperatue and counter flow.更多还原