U型翅片管换热器传热单元数计算式

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

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.

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 com- pared and analyzed by effectiveness-number of transfer unit method （e-NTU method） and logarithm mean tem- perature 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 differenbe of the heat transfer coefficients respectively calculated by 6-NTU method and LMTD method is so small that these NTU formulas are valid.