The Finite Element Study Of Non-compensated Elbow Of The Directly-burying Heating

Throughout the development history of domestic and overseas centralized heat supply network laying,non-compensated directly-burying is one of the most economical and efficient way.Non-compensated directly-burying heating technology has been available on the long straight pipeline implementation,but partial component elbow inevitably arise in buried pipe heating system.Elbow is often analyzed as a free component and domestic and overseas scholars have studied a lot about the stress of this elbow.However the results of majority studies only get the maximum equivalent stress of elbow,stress distribution and fitting engineering calculation algorithm of stress under different load conditions.There is few analysis and research about the strength of elbow itself.Simultaneously,elbow is also designed as compensation component in the majority of design and scientific research institute,which is an important factor in restricting non-compensated directly-burying heating technology.In this dissertation,this new non-compensated elbow aim to slove how to effectively limit the displacement of elbow which will no longer be used as compensation elements.The design concept of elbow will change fundamentally and the stress between new elbow and ordinary pre-insulated bonded elbow are essential difference.Therefore,this research has important value.In this dissertation,the finite element software ANSYS established ordinary pre-insulated bonded elbow model and new elbow model.The study shows that simply changing thickness or the block thickness of the ordinary pre-insulated bonded elbow cannot limit the displacement of elbow.Therefore,the new elbow model regarded the stress and axial displacement as the emphasis of optimization.This dissertation put forward five different forms of new elbow model.The advantages and disadvantages of each new elbow model were compared and analysed,which were regarded as the direction of further optimization.The numerical simulations indicated that:(1)It can be found from the comparison of new elbow model 1,model 2 and model 3 that the model 2 and model 3 were two different optimization based on model 1 through improving allowable stress to increase the intensity of the inner elbow and changing the surface structure of the steel pipeline to reduce the inner elbow stress.However,these three new elbow are not well limit the axial displacement.The further optimization is needed.(2)The new elbow model 4(arm length is 15m,8m),the new elbow model 5 and ordinary pre-insulated bonded elbow model were compared at the same diameter and load conditions.From the perspective of stress,the new elbow model 4 which arm length is 15m is the largest percentage decline in stress.From the perspective of displacement,the axial displacement of the inner elbow of the new elbow model 4 which arm length is 8m is more than the new elbow model 5,while the new elbow model 4 which arm length is 15m is less than new elbow model 5.Therefore,a comprehensive analysis of the elbow can draw a conclusion that the new elbow model 4 which arm length is 15m is an optimal structure.The new elbow model 4 and model 5 are better than the new elbow model 1,model 2 and model 3 in two aspects of stress and displacement.As a consequence,the new elbow model 4 and model 5 can be well restrict the displacement of elbow,which is the foundation of non-compensated elbow for productization.