The Investigation On Gas-liquid Two-phase Flow Of Pulsating Heat Pipe And Heat Transfer Application

As the key equipment of one million tons ethylene project,twin-screw extruder has a high requirement for barrel temperature uniformity.As a heat transfer element with high heat transfer efficiency,pulsating heat pipe has the advantages of simple structure,strong environmental adaptability and good heat transfer effect.It is of great significance to study the laws of boiling,condensing and gas-liquid two-phase flow in pulsating heat pipe and to explore its application in twin-screw extruder.Based on the phase field theory and coupled with the phase field module and heat transfer module in Comsol Multiphysics,a numerical simulation model of pulsating heat pipe was established in this paper.A visual experimental platform of pulsating heat pipe was built to verify the model.On this basis,the laws of boiling,condensing and gas-liquid two-phase flow of pulsating heat pipes were studied,and the gas-liquid two-phase flow rules and heat transfer characteristics of pulsating heat pipes with different diameters were compared.For large heat transfer,the evaporating section and the adiabatic section of the pulsating heat pipe were changed into the evaporating chamber and the condensing section into the variable-diameter pulsating condenser tube,and the boiling heat transfer in the evaporating chamber and the gas-liquid two-phase flow in the variable-diameter pulsating condenser tube were studied.The results showed that the pulsating heat pipe had gone through three phases: initial phase transition,boiling and condensing,and gas-liquid oscillation from the initial moment.Compared with the thick inner diameter,the thin inner diameter promoted the gas-liquid two-phase flow inside the pulsating heat pipe,and improved the oscillation frequency and gas-liquid two-phase flow speed.For the pulsating heat pipe with a changed structure,there was more liquid in the evaporation chamber at the bottom,so there was no drying phenomenon when boiling.The pulsating condensing pipe with a variable diameter at the top had a circulatory oscillation between condensate and steam,which promoted the internal gas-liquid two-phase circulation.According to the actual structure and working condition of the extruder,the heat transfer model with an evaporating chamber around the barrel and a variable-diameter pulsating condenser tube at the top of the evaporating chamber was established in this paper.The condensation,boiling,gas-liquid two-phase velocity,heat transfer,and temperature distribution uniformity of each part inside were analyzed.The results showed that the condensation startup time of the model was 1s,and the boiling startup time was 0.5s.There was velocity fluctuation inside the variable-diameter pulsating condenser tube,and the velocity fluctuation was different with different pipe diameters.Within the longitudinal thickness of unit millimeter,the average heat release power of steam condensation in the variable-diameter pulsating condenser tube was 352.85 W,and the average heat absorption power of liquid evaporation at the bottom of the evaporation chamber was 345.20 W.The maximum temperature difference between the cylinder wall surface in contact with the evaporation chamber was 1.08 K,and the maximum temperature difference between the five rings evenly distributed in the cylinder wall was 1.40 K.The results showed that the barrel has good temperature uniformity.