| LNG(liquefied natural gas)as a clean and efficient energy,due to its environmental friendly,high energy efficiency aspects of the significant advantages,has become the development and utilization of the main energy at this stage.LNG in the transport and unloading process,will produce a lot of flash steam,BOG compressor as an important part of the treatment of these flash gas,has become the focus of this study.Because of the BOG compressor inlet temperature is low,the cylinder wall temperature field and stress field compared with the normal temperature will vary greatly,Access to the coolant has a separated cooling effect,to prevent the low temperature pass to the other parts of the cylinder.BOG compressor inlet temperature is 110 K,and this temperature is in the ultra-low temperature state,so it is difficult to carry out field testing,this essay through the CFD simulation,the BOG compressor cylinder wall can be analysised,change the different parameters of the conditions,such as the coolant flow,the temperature,as well as adding the twin cylinder model,to observe its stress field and temperature field,For the development of BOG compressor to provide a certain numerical basis.In this article,BOG compressor cylinder block as the main research object,through Solidworks models the cylinder block by 1: 1,import different boundary conditions,calculated in Fluent,Fluent derived temperature field interpolation to the cylinder model,The temperature field and the stress field are combined in the Workbench to analyze the magnitude of the deformation and thermal stress.Using the standard k-? turbulence model,the process of compressed gas(mainly methane)is analyzed by dynamic grid simulation.The primary cylinder exhaust temperature is about 152 K,the secondary cylinder exhaust temperature is 181 K.Observe the temperature of each cylinder from the top to the bottom,the temperature's difference is less than 1K,so with a fixed temperature value to simplify the replacement.Compressed into a periodic motion,we can use an integral formula to calculate the average temperature.The temperature field and stress field of the cylinder were studied by the method of fluid-solid coupling and temperature difference.Single-stage cylinder simulation found that the access to coolant for the cylinder is very effective,compared to the absence of access to the coolant,the bottom of the cylinder temperature field found that single-stage cylinder temperature generally rose 110K-140 K.By changing the flow rate of the coolant,it is found that the stress and deformation of the cylinder decrease with the increase of the flow rate of the coolant.When the flow rate of the separated coolant bigger than 1.5m / s,the temperature hardly changed.In contrast,increasing the flow rate of the coolant will increase the flow resistance.Therefore,when the flow rate of the separator is stabilized at 1.5 m / s,the thermal stress of the cylinder wall is smaller and the stability of the compressor is better.It is foundthat the thermal stress of the cylinder wall is decreasing by increasing the temperature of the coolant.So increase the temperature of the coolant is another way to reduce thermal stress.During the process of the temperature rise from 263 K to 293 K,the thermal stress decreased from 11.42 MPa to 9.74 MPa.For the two-stage cylinder simulation,we can use the same method as the single-stage cylinder,Access to the coolant on the two-stage cylinder cooling is also a great effect.Compared with the bottom surface temperature when the intercooler is not introduced,two-stage cylinder's temperature generally rose by 70-90 K.As a result of the existence of a temperature transition zone at the junction of the two cylinders,there is a large amount of deformation in the transition zone.The simulation results show that the deformation is about1.41 mm.In order to prevent the occurrence of brittle fracture,we should focus on the design and observation of this part of the changes in the actual experiment. |
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