通过实验,对传热过程和间壁式换热器有哪些认识?

2025-03-17 15:11:08
推荐回答(1个)
回答1:

一、间壁式换热器及其传热过程

简化假设:

1. 冷热流体主体内扰动程度剧烈,主体温度T、t恒定;

2. 传热热阻主要集中在厚度δt1和δt2的有效膜内;

3. 固体间壁符合单层理想薄壁假设。

流体的流向:

1. 并流;冷热同流;

2. 逆流;冷热相反;

3. 错流;冷热交叉;

4. 折流。U型转折流动;

二、换热器的热负荷及热量衡算方程式:

热负荷:

定义:单位时间冷热流体间交换的热量,单位W、kW。

计算:比热法、热焓法。

热量衡算方程式:

当冷热流体均不发生相变时:

三、总传热系数K

综合反映传热设备性能、流动状况和流体物性的影响。

物理意义:K=Q/A*△tm

表征间壁两侧流体传热过程的强弱程度。

K=f(流体物性、操作条件、换热器本身特性等)

传热系数K的确定方法:

1. 选用经验数据;

2. 实验测定;

3. 由对流传热系数计算得到。

污垢热阻:

流体中的可沉积物在换热表面上生成的垢层,或换热面被流体腐蚀而形成的垢层。

垢层产生附加热阻,使K减少,传热速率显著下降。

因垢层λ很小,即使厚度不大,热阻也很大,往往会成为主要热阻,必须给予足够重视。

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