U型翅片管换热器传热单元数计算式

为了得到U型翅片管换热器传热单元数计算式,以U型翅片管换热器为研究对象,通过建立翅片管换热模型,推导出了逆流和顺流2种流体流动趋势的传热单元数计算式(NTU计算式)．分别采用推导出的传热单元数计算式(εNTU法)和前人推导出的平均温差关系式(LMTD法)计算U型翅片管传热系数,并进行对比分析．结果表明,当进水温度为45～60 ℃,热水流量为30～110 kg／h时,由εNTU法和LMTD法计算出来的翅片管传热系数相差很小．所推导出来的U型翅片管换热器传热单元数计算式是合理的．

Approximate formulas of number of transfer unit of U shaped fin-tube heat exchangers

To obtain the formulas of number of transfer unit(NTU) of U shaped fin-tube heat exchangers,a U shaped fin-tube heat exchanger is taked as research object.Approximate NTU formulas of number of transfer unit are derived by establishing heat transfer model of U shaped fin-tube when the trend of two flows in fin-tube heat exchanger is counter and parallel,respectively.Subsequently,the heat transfer coefficients of fin-tube are compared and analyzed by effectiveness-number of transfer unit method(ε-NTU method) and logarithm mean temperature difference method(LMTD method) when inlet water temperature is from 45 ℃ to 60 ℃ and water flow rate is from 30 kg/h to 110 kg/h.The results show that,the difference of the heat transfer coefficients respectively calculated by ε-NTU method and LMTD method is so small that these NTU formulas are valid.