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基于对换热器换热特点的认识,引入了反映换热器经济性能的物理量-温差有效度,其定义为流体对数平均温差与入口温差的比值.温差有效度体现了换热器流体入口温差的利用程度,其值越大,每单位传热单元数承担的换热量就越大,换热器的经济性就越好.传热有效度和温差有效度实际上共同组成了一个平衡的换热器评价体系.具体地,借助于传热有效度和温差有效度,构建了评价换热器综合性能的目标函数.分析表明,同时考虑换热器的收益和经济性时,存在最佳的传热单元数使目标函数取得最大值,即换热器达到最佳综合性能.“,”Based on understanding of heat transfer characteristics of heat exchanger,a new concept-'temperature difference effectiveness' is introduced that reflects economic performance of heat exchanger.It is defined as a ratio of LMTD (logarithmic mean temperature difference) to inlet temperature difference.Temperature difference effectiveness describes the utilization degree of inlet temperature difference.The greater temperature difference effectiveness implies the greater heat transfer rate undertaken by per unit number of transfer units.Therefore,the economic performance of heat exchanger is better.Heat transfer effectiveness and temperature difference effectiveness form a balanced performance evaluation system of heat exchanger.Concretely,the objective function evaluating comprehensive performance of heat exchanger is established by means of heat transfer effectiveness and temperature difference effectiveness.Analysis shows that considering both the benefit and economic performance of heat exchanger,there is optimal number of heat transfer units where the objective function reaches the global maximum and heat exchanger has the optimal comprehensive performance.