【Daily Question】Theoretical Foundation 2020.10.18
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Multiple-choice question: The question is as shown in the figure ( ). Answer: B. Hint: An additional reward will be given to those who can explain the solution process; the answer can be submitted there
The critical adiabatic diameter for B 20mm is: http://admintk.100xue*.com/UpLoadImage/2013-05-07/45c2798e-4292-452a-ab3f-bbf2b68cee60.png. When the pipe diameter is smaller than the critical thermal insulation diameter dc, the heat transfer rate of the pipe is actually greater than that without an insulating layer. It is only when it increases further to a certain critical value that the insulating layer begins to play a role in reducing heat loss. It is generally used more frequently in cables ； When the pipe diameter is greater than the critical diameter dc, a covering insulating layer is necessary to effectively provide thermal insulation. Therefore, dc=20mm.