工质比热匹配对有机朗肯循环不可逆损失的影响  

Influence of Heat Capacity Match Between Heat Transfer Fluids on Irreversibility of Organic Rankine Cycle

作　　者：于超[1] 徐进良[1] 王华荣[1] 

机构地区：[1]华北电力大学低品位能源多相流与传热北京市重点实验室,北京102206

出　　处：《华北电力大学学报（自然科学版）》2016年第3期69-75,共7页Journal of North China Electric Power University：Natural Science Edition

基　　金：国家自然科学基金国际合作与交流资助项目(51210011);中央高校基本科研业务费专项资金资助项目(JB2015203)

摘　　要：有机朗肯循环可以将低品位热能转化为有用功。为了提高能量利用率应尽可能减小系统中的不可逆损失。蒸发器是主要的火用损部件,对其进行优化可以显著提高系统性能。为改善热源与热机系统耦合、减小蒸发器内火用损以提高热功转换效率,提出利用工质比热变化改善换热过程温度匹配的模型。固定换热器两侧流体出入口温度,定义变量k为流体在高温端与低温端比热的比值,其变化范围0.5～3.5,假设比热随温度线性变化。为分析不可逆损失与温差的关系提出＂积分温差＂,证明了积分温差与不可逆损失之间的拟线性关系。列出可能的九种温度匹配情况,得到理论上最大和最小的不可逆损失。通过计算废热气体驱动有机朗肯循环的算例,证明了利用比热变化改善换热匹配的有效性。Organic Rankine Cycle（ ORC） can convert heat to power in heat recovery processes driven by low or medium temperature heat source. The irreversibility should be reduced as much as possible to elevate the heat recovery efficiency. Evaporator is a component which contributes much（ sometimes the most） to the total irreversibility of an ORC system. Thermal performance of the system can be elevated by design optimization of the evaporator. Focused on the coupling between external heat source and isolated ORC system,a heat transfer modal was established to reduce the irreversibility in evaporator and to elevate the heat recovery efficiency. In this model heat transfer process between hot and cold fluid can be modulated through the variation of heat capacity. The inlet and outlet temperature of the heat transfer fluids were fixed,then a variable k was defined as the ratio of heat capacity of high temperature end and heat capacity of low temperature end. Assuming that k varied from 0. 5 to 3. 5,and heat capacity of fluid was linear function of its temperature. An item called＂integrated temperature difference＂was proposed to investigate the relation between heat transfer and irreversibility quantitatively. The liner relationship between integrated temperature difference and irreversibility was discovered. Nine potential heat transfer match possibilities between two fluids were exhibited,as well as the maximum and minimum value of irreversibility. Thermal performance of an ORC driven by 423. 15 K waste heat flue gas was calculated to show the validity of the proposed modulating method.

关 键 词：有机朗肯循环 换热匹配 积分温差 不可逆损失 变比热 

分 类 号：TK123[动力工程及工程热物理—工程热物理]