| 1 | 管内对流换热系数的瞬态测量方法显示文摘1前言 直接测定对流换热系数的方法分稳态法和瞬态法,前者对实验条件要求苛刻.近年来,瞬态法倍受人们关注”-”.Hausen和Kast’‘·”相继阐述了利用周期变化的流体温度在固体壁内的传播特性确定对流换热系数的原理,即根据流体与固体温度变化之间的相位角滞后(或振幅衰减)确定对流换热系数.Roetzel‘”提出了一套适用于任意形式周期振荡流体温度的瞬态测量方法. 对实测的流体温度波Tf(t),利用傅里叶级数分析方法把Tf*)展开为傅里叶级数,其一次谐波正弦和余弦函数项的系数表述为 u。——一Ill(t)Slnwtdt.u。——一11’()cosnddt(l)则一次谐波可表达为 01。“fslflO此十贝)(2)式(2)中,振幅u;一 Vu: + ug,相位角9一 arc ig(uc/us),一次谐波的周期 P—Zt。,角速度。一。八。2 测量基础2.1 模型A——霉壁面导热热阻 忽略管壁导热热阻,管壁的能量方程为 厂dL川t一。S叮f一几)一兄凡(几一瓦)(3)若求得的管壁周期振荡温度的一次谐波为Tw(t)一u。sinnd,则流体温度超前相位角9和振幅U;分别为 .y.,o\ It【._o\“工_P_\“ 9”sfCtg WN .Ut=U。。l---- W l e -- (4)一旦实际测得相位角差贝或振幅比ff八。,即可确定对流换热系数。;.显然,当ac《a时,管外对流换热的影响甚小. | 宣益民 W.Roetzel | 1994 | 化工学报1994，45，6： | 4 |
| 4 | Synthesis of Flexible Heat Exchanger Networks with Stream Splits Based on Rangers of Stream Supply Temperatures and Heat Capacity Flowrates显示文摘A new superstructure model of heat exchanger networks (HEN) with stream splits based on rangers of streams supply temperatures and heat capacity flow rates is presented. The simultaneous optimal mathematical model of flexible HEN synthesis is established too. Firstly, the streams with rangers of supply temperatures and/or the streams with the rangers of heat capacity flow rates are pretreated; Secondly, several rules are proposed to establish the superstructure model of HEN with splits and the simultaneous optimal mathematical model of flexible HEN; Thirdly, the improving genetic algorithm is applied to solve the mathematical model established at the second step effectively, and the original optimal structure of HEN based on the maximum operation limiting condition can be obtained easily; Finally, the rules of heat exchange unit merged and the heat load of heat exchanger relaxed are presented, the flexible configuration of HEN satisfied the operation condition between the upper and down bounds of supply temperature and heat capacity flow rates can be obtained based on the original optimal structure of HEN by means of these rules. A case study demonstrates the method presented in this paper is | 李志红 罗行 华贲 W.Roetzel | 2004 | Chinese Journal of Chemical Engineering2004，12，2： | 0 |
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