传热学第五版第14章习题解答

1、传热学（第五版）第0章-第3 章习题解答第0章 绪论0-4、0-6、0-7解答题略。0-13：解：(m2k)/w w/(m2k) w/m2 又 =385.73 w0-14：解： k/w (面积为a2的平板表面上的热阻) (m2k)/w （单位面积热阻） w/m2 w0-15：解： 0-17：解：（1） (m2k)/w w/(m2k) w（2） w 误差（3）可以忽略，因为厚度很小，金属的导热系数较大，则导热热阻很小。故可以忽略。第一章 导热理论基础1-4：前提是假定所研究的物体是各向同性的连续介质，其导热系数比热容c，和密度均为已知，并假定物体内具有内热源。1-5 （1） k/m w/m2 （

2、2） k/m w/m2 温度分布图略。1-6：解：（1） w/m2平板一侧：平板另一侧： w/m2(2)根据式（1-20），导热微分方程应为：即： w/m3 则平壁有内热源，其强度为 w/m3 1-9 解：由于对称受热，在球坐标系中为常物性一维无内热源非稳态导热问题，分析厚度为的微元球的导热：忽略高阶小量得微元球净导热：微元球内能增量由能量守恒定律 于是得导热微分方程 ： （1）边界条件：（中心无热流，绝热）（2） （第三类边界条件）（3）注意：本题的导热微分方程也可由教材p19页：式（1-25）化简得出。第二章 稳态导热2-9 解：未加贴硬泡沫塑料时： w/(m2k)加贴硬泡沫塑料时： 根据

3、题意：即： 或:0.091m91mm2-13 解： (m2.k)/w w/(m2k) w2-14解： (m2.k)/w w/(m2.k) =29.94（250-60）=5689 w/m2 w/m2 w/(m2.k) w/(m2.k)=30.03（250-60）=5706 w/m2 w/m2 w/(m2.k) w/(m2.k)=36.10（250-60）= 6859 w/m2 w/m2答：三种方案的传热量分别增加了1，17，1171 w/m2 ，第三种方案最有效。2-17 mm mm mm mm mm 单位管长圆筒壁的导热热阻：管道： (m.k/w)第一层： (m.k/w)第二层： (m.k/w

4、)（2） w/m2-18 解： mm mm w/m 即所产生的热量必须小于导线能承受的热量。 a2-19： 即： mm2-24 解：已知： , (1) 1/m (2)th(ml)=th(18.90.025)=th(0.4725)=0.4402 w/m2第三章 非稳态导热3-8 解：因为钢板的高度和宽度远大于厚度，所以是无限大平板。 所以定型尺寸为 mm可以采用集总参数法。即：解得： s 3-14 3-8 解：因为钢板的高度和宽度远大于厚度，所以属于无限大平板的导热问题。 所以定型尺寸为 mm可以采用集总参数法。即：解得： s =0.5 h3-19 解： (本题中115应改为11.5)常热流密度

5、条件下半无限大物体内温度场的表达式为：当时，其中 即： （1）当m 时 即 （2）由（1）、（2）求得： m2/s w/(m.k)3-23 解：砖墙显波层厚度：解得： m木墙的显波层厚度：解得： m3-24 解： 当 m 时， 根据波动振幅的定义知： 滞后时间 s =2.1h当 m 时， 根据波动振幅的定义知： 滞后时间 h“第四章 导热数值解法基础”的习题解答略。acknowledgements my deepest gratitude goes first and foremost to professor aaa , my supervisor, for her constant enc

6、ouragement and guidance. she has walked me through all the stages of the writing of this thesis. without her consistent and illuminating instruction, this thesis could not havereached its present form. second, i would like to express my heartfelt gratitude to professor aaa, who led me into the world

7、 of translation. i am also greatly indebted to the professors and teachers at the department of english: professor dddd, professor ssss, who have instructed and helped me a lot in the past two years. last my thanks would go to my beloved family for their loving considerations and great confidence in

8、 me all through these years. i also owe my sincere gratitude to my friends and my fellow classmates who gave me their help and time in listening to me and helping me work out my problems during the difficult course of the thesis. my deepest gratitude goes first and foremost to professor aaa , my sup

9、ervisor, for her constant encouragement and guidance. she has walked me through all the stages of the writing of this thesis. without her consistent and illuminating instruction, this thesis could not havereached its present form. second, i would like to express my heartfelt gratitude to professor a

10、aa, who led me into the world of translation. i am also greatly indebted to the professors and teachers at the department of english: professor dddd, professor ssss, who have instructed and helped me a lot in the past two years. last my thanks would go to my beloved family for their loving considerations and great confidence in me all through these years. i also owe my sincere gratitude to my