Stress calculation problem (recommended as a key issue to address; moderators are asked to give extra points to those who conduct in-depth discussions--------Benzhen Xuan)
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This post was last edited by BenbenXuan on 2010-10-10 at 11:00. The copper pipe inside the condenser has an outer diameter of 20x1, a length of 3 meters, and its temperature rises from 20 degrees to 70 degrees. If both ends of the copper pipe are fixed in place, what is the stress at those ends?
This post was last edited by jintchinssen on 2010-10-12 at 22:52. Initially, it is analyzed that the stress in the pipeline is caused by thermal expansion; the pipeline stress includes axial compressive stress and bending stress. In this analysis, only axial compressive stress is considered; the calculation of bending stress can be carried out by referring to the principles of material mechanics. Axial compression stress is generated in the axial direction; the axial linear displacement (in absolute value) is given by △l=αL△T, where α is the average linear expansion coefficient of the pipe when its temperature changes from 20°C to 70°C, expressed in mm/(mm·°C). According to relevant manuals, the average linear expansion coefficient of copper and copper alloys at these temperatures is 17.072÷1000000 mm/(mm·°C) ； L is the initial length of the pipe, in mm ； △T is the temperature change value, in °C. △l==17.072÷1000000×3000×(70-20)=2.5608 mm. Therefore, the total axial compressive stress at both ends of the pipe is: δ=Eε=110×1000×(2.5608÷3000)=93.896 MPa. The axial compressive stress at either end is: 93.896 MPa÷2=49.948 MPa
I completely agree with the moderator’s view; however, the actual stress on the pipe owner’s end should not be that high. Generally, containers connected to both ends of the pipe can undergo plastic deformation, and when the temperature is not too high, the stress is not significant, so it’s unnecessary to consider the stress at the pipe ends.
Indeed, the calculations above assume a completely rigid connection between the pipe and its end, resulting in the maximum axial stress at the pipe end; in practice, the pipe end can absorb some of this stress, or expansion mechanisms can be installed on the heat exchanger shell to handle such stress.
I still can’t calculate this stress. But the result for the 2nd floor is considered too high. 1 Is the stress unit N or MPa? Isn’t the latter a unit of pressure? The maximum thrust of the fixing frame on 2 01R413 is only 200 KN