Melt Velocity Research Articles

A scale-coupled numerical method for transient close-contact melting

We introduce a numerical workflow to model and simulate transient close-contact melting processes based on the space-time finite element method. That is, we aim at computing the velocity at which a forced heat source melts through a phase-change material. Existing approaches found in the literature consider a thermo-mechanical equilibrium in the contact melt film, which results in a constant melting velocity of the heat source. This classical approach, however, cannot account for transient effects in which the melting velocity adjusts itself to equilibrium conditions. With our contribution, we derive a model for the transient melting process of a planar heat source. We iteratively cycle between solving for the heat equation in the solid material and updating the melting velocity. The latter is computed based on the heat flux in the vicinity of the heat source. The motion of the heated body is simulated via the moving mesh strategy referred to as the Virtual Region Shear-Slip Mesh Update Method, which avoids remeshing and is particularly efficient in representing unidirectional movement. We show numerical examples to validate our methodology and present two application scenarios, a 2D planar thermal melting probe and a 2D hot-wire cutting machine.

Analysis of Factor Effects in Process of Vertical Centrifugal Casting

ABSTRACT The effects of mold rotation speed, pouring temperature, preheating mold temperature, pouring rate and coating thickness on the solidification time, shrinkage porosity and melt velocity in vertical centrifugal casting were investigated. To minimize computation time and obtain adequate estimate of the effects, a Fractional Two – Level Factorial Design 2(5–1) was applied. The results were obtained by numerical simulations using ProCAST software. The regression model was developed using Design Expert software. The analysis of variance revealed that the coating thickness had the most pronounced effect on the solidification time and shrinkage porosity. Finally, the procedure for selecting the optimal factors was carried out by application of multi objective optimization. The shortest solidification time was 20.68 s, while the shrinkage porosity was negligible, and it was achieved with the highest value of mold rotation speed and the lowest values of pouring temperature, preheating mold temperature, pouring rate and coating thickness.

Effect of phase change heat storage tank with gradient fin structure on solar energy storage: A numerical study

In this paper, the heat storage process of a latent heat thermal energy storage (LHTES) tank is studied numerically. A new type of gradient fin is added to the heat storage process in a latent heat storage tank to improve the heat transfer performance of the internal phase change material (PCM). The numerical model is verified by the experimental data. The influences of different structures on the melting rate, temperature distribution, velocity distribution, and maximum melting rate of PCM in LHTES tank are investigated, and the influence of natural convection on the energy storage system is further quantified. The results show that the melting time can be significantly reduced by 16.9% by using the four straight fins with gradient shape, and the melting time can be further reduced by 41.1% by reconstruction of the gradient fin position. The deformation in the opposite direction will slow down the melting speed and extend the melting time by more than 4.66 times. The convection criterion for judging the buoyancy convection of the melt in this paper shows that natural convection is dominant in both the upper and lower part of the melt. The closer the convection coefficient is to the overall heat transfer coefficient, the better the melting efficiency and energy efficiency will be.

Flow Disturbance Characterization of Highly Filled Thermoset Injection Molding Compounds behind an Obstacle and in a Spiral Flow Part.

In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. The position, length, and angle of weld lines are dependent on the gate location, injection speed, injection pressure, mold temperature, and, especially, the direction and degree of the polymer melt velocity in the mold-filling process. However, the wall surface velocity of the thermoset melt in the mold-filling process is not zero, which is not found for thermoplastic injection molding. The main reason leading to this difference is the slip phenomenon in the filling phase between the thermoset melt and the wall surface, which is directly affected by the filler content. In this study, commercial thermoset phenolic injection molding compounds with different amounts of filler were employed to investigate not only the mechanism of weld line formation and development behind an obstacle in the injection molding process but also the flow disturbance of the thermoset melt in the spiral flow part. In addition, the effect of the wall slip phenomenon on the flow disturbance characterization and the mechanism of weld lines of selected thermoset materials was carefully considered in this research. Furthermore, the generated material data sheet with the optimal developed reactive viscosity and curing kinetics model was imported into a commercial injection molding tool to predict the weld line formation as well as the mold-filling behavior of selected thermoset injection molding compounds, such as the flow length, cavity pressure profile, temperature distribution, and viscosity variation. The results obtained in this paper provide important academic knowledge about the flow disturbance behavior as well as its influence on the mechanism of weld line formation in the process of thermoset injection molding. Furthermore, the simulated results were compared with the experimental results, which helps provide an overview of the ability of computer simulation in the field of the reactive injection molding process.

Research on improved gas‐assisted extrusion of plastic sheets based on time–temperature equivalence principle

AbstractBased on the time–temperature equivalence principle, the relationship between the melt relaxation time (MRT) and melt heating temperature (MHT) in an improved gas‐assisted extrusion (GAE) of a polypropylene (PP) sheet was investigated by numerical simulations. In the simulations, the MRT was varied and the inherent properties of the MHT were controlled using experimental methods. With an increase in MRT, the velocity in all directions, pressure drop, and shear rate of the melt increased; however, increasing the MRT does not always yield a positive effect on the GAE process of the melt. For instance, the melt velocity increased vertically at the die exit with MRT, resulting in an outward extrudate swell. In addition, the extruded product was intact when the melt was heated to 220°C, which verified the principle of time–temperature equivalence.

Macroscopic and mesoscopic simulation of polystyrene melt in the filling process of injection molding

AbstractIn this article, a fluid flow and heat transfer model which consist of the mass, momentum, and energy conservation equations together with the level set equation and Rolie‐Poly constitution equation is proposed and applied to simulate the rheological behaviors of viscoelastic polystyrene melt in the filling process of injection molding. The macroscopic velocity, pressure, temperature, stress, and mesoscopic molecular conformation of polystyrene melt are shown and analyzed detailedly during the mold filling process. The single‐mode Rolie‐Poly model is employed to describe the stress–strain relationship of polystyrene melt, and the level set method is used to capture the evolution of melt front interface. The governing equations for polymer melt are discretized by the finite volume method on collocated mesh, and solved by the SIMPLE algorithm. Numerical simulations have been implemented based on rectangular cavities with different gate locations, and rectangular and circular inserts. Numerical results indicate that the gate locations, gate numbers, insert size and shape are major factors that affect the rheological behaviors of polystyrene melt in the filling stage of injection molding, and polymer chains experienced higher shear and extension effects in the regions near to mold walls and obstacle. In addition, the length and position of weld lines are discussed in the current study.

Defrosting Characteristics of the Cockpit Windshield of Manned Airships

Frost covering of the cockpit windshield will seriously obstruct the driver’s vision and even affect flight safety of the low-altitude manned airship. To solve the problem, this paper proposes a rapid defrosting strategy using hot gas injection method. The influences of the air inlet type, air temperature, air velocity and air angle on the defrosting characteristics of the transparent windshield are investigated and the defrost characteristics of the manned airship are obtained by fluid dynamics simulation. The result shows: (1) Defrosting effect of single inlet is not as good as double inlets. The defrosting area of the double inlet is relatively large, mainly concentrated at both ends of the windshield. (2) The effect of air supply temperature on defrosting effect of windshield surface is more significant when double air supply inlets are used. But when the air supply temperature reaches a certain value and continues to rise, the defrosting time does not change much, so there is an optimal air supply temperature range. (3) The higher the air supply velocity is, the shorter the phase transformation time of frost layer is and the faster the melting velocity is. Considering energy consumption and defrosting characteristics, the optimal air supply velocity is about 6 m/s. (4) When the angle between the air supply direction and the horizontal plane of the bridge near the windshield is 100°, the frost layer has the shortest melting time.

Melting behavior of an organic phase change material in a square thermal energy storage capsule with an array of wire electrodes

A numerical analysis of melting of an organic phase change material (PCM) in a square thermal energy storage (TES) capsule with an array of high voltage wire electrodes has been performed. Fully coupled set of governing equations for fluid flow, heat transfer, phase change, electric field and charge transport are solved using the opensource finite-volume framework of OpenFOAM. The melt interface is tracked using a fixed grid approach based on enthalpy-porosity method. The main objective of the study is to investigate the effect of direction of electric field on the melting process under different configurations of grounded walls. The transient evolution of the melting process in the presence of electric field is mapped in terms of liquid fraction, mean velocity and mean Coulomb force. The melt flow morphology, temperature field, velocity and electric field distribution at different grounded electrode configurations are visualized. Electric field leads to generation and coalescence of small vortices that influence the melt interface, velocity distribution and the total melting performance. 12 cases with different grounded wall configurations that lead to different electric field directions are considered, herein. Grounding the left and right walls of the square TES capsule notably influence the melting performance. Case 4 with grounded left wall led to the shortest melting time of 2.68 h with 97 % reduction, as compared to the case without electric field (5.28 h). Case 5 with grounded right wall has a negative impact on the total melting time (5.55 h), which is 4.86 % higher than the case without electric field (5.28 h). In general, application of electric field led to an increase in total achievable melt fraction for a given period of 6 h. Case 2 with all the four walls grounded led to a maximum melt fraction of 0.97 which is 9.39 % higher than the case without electric field (0.88). Case 4 with grounded left wall showed the maximum power storage capacity of 17.2 kW which is 49.3 % higher than the case without electric field (8.7 kW). Results presented in this study provide deeper insights on the mechanisms of electric field on melting process and will serve as a reference for design of a TES module assisted with electrohydrodynamic (EHD) flow induced by an array of wire electrodes.

Temperature-induced densification in compressed basaltic glass revealed by in-situ ultrasonic measurements

Abstract Acoustic velocities of a model basalt glass (64 mol% CaMgSi2O6 + 36 mol% CaAl2Si2O8) were measured along different pressure-temperature (P-T) paths. One set of experiments involved isothermal compression-decompression cycles, performed at temperatures of 300, 641, 823, and 1006 K and pressures up to 12.2 GPa. The other set of experiments involved constant-load heating-cooling cycles at temperatures up to 823 K and pressures up to 7.5 GPa. Both sets of experiments were performed in a multi-anvil apparatus using a synchrotron-based ultrasonic technique. Our results show that the glass compressed isothermally at 300 K (cold-compression) displays anomalously decreasing compressional (VP) and shear (VS) wave velocities with increasing pressure until ~8 GPa. Beyond 8 GPa, both VP and VS start to increase sharply with pressure and irreversible densification of the glass occurred, producing large hysteresis loops of velocities upon decompression. However, for the glass compressed isothermally at increasingly higher temperatures (hot-compression), the velocity minima gradually shift to lower pressures. At temperature close to the glass transition temperature Tg, the velocity minima disappear completely, displaying a monotonic increase of velocities during compression and higher VP and VS during decompression. In addition, constant-load heating-cooling experiments show that velocities generally decrease slightly with increasing temperature, but start to increase once heated above a threshold temperature (~650 K). During cooling the velocities increase almost linearly with decreasing temperature, resulting in higher velocities (~1.5–2.5% higher) when returned to 300 K. This implies that a temperature-induced densification may have occurred in the glass at high pressures. Raman spectra on recovered samples show that the hot-compressed and high-P heated glasses contain distinctly densified and depolymerized structural signatures compared to the initial glass and the cold-compressed glass below the velocity transition pressure PT (~8 GPa). Such densification may be attributed to the breaking of bridging oxygen bonds and compaction in the intermediate-range structure. Our results demonstrate that temperature can facilitate glass densification at high pressures and point out the importance of P-T history in understanding the elastic properties of silicate glasses. Comparison with melt velocity suggests that hot-compressed glasses may better resemble the pressure dependence of velocity of silicate melts than cold-compressed glasses, but still show significantly higher velocities than melts. If the abnormal acoustic behaviors of cold-compressed glasses were used to constrain melt fractions in the mantle low-velocity regions, the melt fractions needed to explain a given velocity reduction would be significantly underestimated at high pressures.

Effect of twisted fins on the melting performance of PCM in a latent heat thermal energy storage system in vertical and horizontal orientations: Energy and exergy analysis

• Performance of a LHTES unit in the presence of twisted fins is studied. • Different number of fins in vertical and horizontal orientations were considered. • Paraffin wax was used as PCM. • Triple fin and double fin outperformed other cases in vertical and horizontal cases. • The best case is a trade-off between the fin number and length of fins. Solar energy and other renewable energy resources are of great importance to solve the energy crisis in the 21th century. In this regard, the energy storage systems play a vital role as a means of harnessing solar energy. In this study, performance enhancement of a shell and tube latent heat thermal energy storage (LHTES) system in terms of energy and exergy has been assessed by implementing twisted fins in a PCM enclosure with both vertical and horizontal orientations by using Finite Volume Method and the Enthalpy-Porosity method has been used for simulating the melting process. The fins have constant heat transfer surface with different configurations including single, double, triple and quadruple fins along with a case study about effect of penetrating the fin inside the tube. Paraffin wax was used as PCM. The results have been presented in terms of melt fraction, temperature and velocity magnitude contours, melt fraction and temperature curves, average Nusselt number and total melting time for both horizontal and vertical orientations. In order to better evaluate the optimizations made, exergy analysis has also been performed and the exergetic efficiency has also been presented. It was revealed that the triple fin in vertical orientation and double fin in horizontal orientation have the best effect on melting enhancement of PCM with 11.2% and 10.7% of enhancement in melting time in comparison with the worst finned case, and 37.4% and 30.5% enhancement in comparison with the base case. It was also shown demonstrated that the triple fin in vertical orientation and double fin in horizontal orientation have the best exergy efficiency.

Oxidické vrstvy a bifilmy v odliatkoch hliníkových zliatin

Surface of aluminium alloy melt is covered by an oxide layer when it is in contact with the surrounding atmosphere. When the oxide layer is retained on the surface of the melt it prevents the melt by hydrogen saturation. The oxide layer is harmful when it is submerged into the melt. The work focuses on the influence of the melt velocity on the bifilm formation, morphology of oxide layers and their influence on the porosity and filling the mold cavity.

Effect of the nozzle diameter and melt velocity at the tundish outlet on solidification along microstructural and mechanical properties of the cooling slope casted AZ91 Mg alloy

ABSTRACT Experiments were carried out for investigating the effect of the nozzle diameter and melt velocity on solidification along microstructural and mechanical properties of the cooling slope casted AZ91 Mg alloy. Investigations involved five different nozzle diameters (4, 6, 8, 10, and 12 mm) with five different melt velocities (0.1, 0.2, 0.3, 0.4, and 0.5 m/s). Finally, a moderate nozzle diameter of 8 mm with a melt velocity of 0.3 m/s rendered reasonably moderate solidification. Additionally, the favoured microstructure was observed with particle size, a shape factor, α-phase fraction and particle densities of 62 μm, 0.75, 0.80 and 195. Correspondingly, better mechanical properties were observed with tensile strength, ductility, yield strength and hardness of 265 MPa, 7.5%, 200 MPa and 80 HV, respectively. The nozzle diameter/melt velocity produces poorer castings. Furthermore, the retaining/escaping of alloy elements along gases occurs throughout processing; in this case, the escape of alloy elements lessens strength whereas the escape of gases boosts strength. Moderate control of casting parameters rendered superior properties.

Cross electromagnetic nanofluid flow examination with infinite shear rate viscosity and melting heat through Skan-Falkner wedge

Abstract This demonstration of study focalizes the melting transport and inclined magnetizing effect of cross fluid with infinite shear rate viscosity along the Skan-Falkner wedge. Transport of energy analysis is brought through the melting process and velocity distribution is numerically achieved under the influence of the inclined magnetic dipole effect. Moreover, this study brings out the numerical effect of the process of thermophoresis diffusion and Brownian motion. The infinite shear rate of viscosity model of cross fluid reveals the set of partial differential equations (PDEs). Similarity transformation of variables converts the PDEs system into nonlinear ordinary differential equations (ODEs). Furthermore, a numerical bvp4c process is imposed on these resultant ODEs for the pursuit of a numerical solution. From the debate, it is concluded that melting process cases boost the velocity of fluid and velocity ratio parameter. The augmentation of the minimum value of energy needed to activate or energize the molecules or atoms to activate the chemical reaction boosts the concentricity.

A study on weld morphology and periodic characteristics evolution of circular oscillating laser beam welding of SUS301L-HT stainless steel

Many studies have identified the periodicity of oscillating laser beam welding (OLBW), but they do not provide a deep perspective to show the periodic changes of molten pool and keyhole characteristics. In the process of circular OLBW, the spatters were easily formed due to the unstable melt generated by rapid change in keyhole velocity, and its number was prone to decrease with the increase of frequency. The computational fluid dynamics (CFD) method successfully predicted the cross-section morphology of the weld, and the prediction deviation was small. In a single cycle, the fusion state between the newly generated melt and the existing molten pool determined the morphology of molten pool boundary, showing a ‘W-U-W’ shape change. The keyhole first destabilized and then stabilized again, and its depth exhibited a ‘V’ shape. The average flow velocity of the melt in the longitudinal section of the weld or keyhole center presented a ‘W’ shape. The keyhole depth or the average melt velocity period was equal to the oscillation period of circular OLBW.

Optimization on a novel irregular snowflake fin for thermal energy storage using response surface method

In this study, the horizontal sleeve phase change heat storage unit filled with RT55 is taken as the research object. Providing at the low thermal conductivity of phase change materials (PCM), this work proposes using an irregular snowflake-shaped longitudinal fin structure to improve the melting performance of horizontal latent heat storage sleeves (LHTES) under natural convection and to numerically simulate the phase change heat transfer process. Here, Thermal assessments on the melting fraction, temperature field, velocity distribution, and heat storage for melting are made. Results demonstrate that the snowflake fin structure significantly shortens the full melting time of LHTES, saving 45.92% time compared to the traditional fin structure. This study reveals that moderate changes of fin length, width, shape, and distribution angle could shorten the heat filling time. As a result of aggregated evaluation of the heating time, heat storage capacity, and heat storage temperature, the study determined the optimal fin distribution angle α to be 40°. This work further optimized the geometric parameters using the response surface method (RSM) and proved that the optimal solution to be the fin end length at 13mm, the width at 0.58mm, and the bifurcation angle at 40°.

No fins attached? Numerical analysis of internal–external fins coupled PCM melting for solar applications

Thermal energy storage/sink is imperative for any type of solar energy harnessing system/technology. However, the inevitable challenge remains in developing and optimizing a thermal energy storage (TES) system suitable for long cyclic operation. This work numerically analyses the melting characteristics of phase change material (PCM; RT42)-based latent thermal energy storage (LTES) as a two-dimensional rectangular enclosure. The consequence of utilizing internal–external extended surfaces (fins) with realistic convective boundary condition is studied for photovoltaic thermal (PVT) applications. The application of internal–external fins is intended for enhancing the charging (melting) duration according to the long cyclic solar operation and better dissipation of heat after complete melting. Three kind of fins-rectangular, triangular, and Y-type- are investigated for two orientations of storage/sink enclosures-upright ( θ = 90°) and inclined ( θ = 35°). Moreover, three fin configurations are analyzed-equal, decreasing and increasing-stepped-based on the arrangement of fins along the enclosure height. Two-dimensional, transient numerical simulations are conducted for governing PCM melting, contemplating the consequences of natural convection. The performance assessment of each storage unit (orientation/fin-type/fin-arrangement) is made based on parameters such as time enhancement ratio, suppression ratio, liquid fraction, temperature distribution, melt velocity magnitude, storage capacity/rate, and enhancement in Nusselt number. The melting is delayed for triangular and Y-fins enclosures as compared to that for rectangular fins. Equal and increasing-stepped Y-fin arrangements yielded the largest time enhancement ratios of 42.38% and 29.86% for inclined and upright enclosures, respectively. Moreover, Y-fins-based enclosure produced a larger average suppression ratio as compared to other types of fins. A 2.56, 2.67, and 2.64 times enhancement in Nusselt number is observed for increasing-stepped fin arrangement of rectangular, triangular, and Y-finned upright enclosures, respectively. However, for the inclined enclosure, a 2.32 times enhancement in Nusselt number is reported for increasing-stepped Y-fin. • Internal–external fin-coupled thermal storage for cyclic solar PVT applications. • Utilization of rectangular, triangular, and Y-fins in augmenting PCM melting. • Assessment of 3 configurations/fin-immersions for intensifying convection currents. • Effect of cavity inclination on melting characteristics for long duty operation. • Maximum 2.67 times Nusselt number enhancement for increasing triangular fin.

Effect of Pressure Difference between Inner and Outer Gas Layer on Micro-Tube Deformation during Gas-Assisted Extrusion.

In the process of double-layer gas-assiste extrusion of a plastic micro-tube, the tugging effect caused by the pressure difference of the gas cushion layer inside the die has a great influence on the external dimensions of the micro-tube. Therefore, this study establishes a two-phase extrusion model based on compressible gas and incompressible melt. Ansys Polyflow finite element software was used to numerically simulate the extrusion process of the melt to analyze the effect of the gas cushion layer pressure difference on the micro-tube deformation. The research shows that the shrinkage rate of the micro-tube increases with increasing pressure of the outer cushion layer, and the degree of tube wall migration increases, too. In the process of extrusion, the first normal stress difference at the entrance of the gas cushion layer shows a significant effect on the melt velocity field distribution and the extruded micro-tube cross-sectional deformation.

Effect of Al2O3 on Sound Velocity of MgSiO3 Glass at High Pressure

Silicate glass has been used as an analog for silicate melts to understand the nature of dense magmas in the Earth’s mantle. To understand the effect of Al2O3 on the sound velocity and structure of MgSiO3 glass, in this study, combined with Brillouin scattering and diamond anvil cells (DACs), the acoustic velocity of MgSiO3∙5 mol%Al2O3 (MA1) and MgSiO3∙24.5 mol%Al2O3 (MA2) glass were measured up to 20 and 42 GPa, respectively. Our studies show that the incorporation of Al2O3 could increase the sound velocity of MgSiO3 glass. Using the obtained velocities, the bulk and shear moduli (KS, G), density (ρ) and Poisson’s ratio (ν) are calculated at high pressures, and the results indicate that Al2O3 could induce the stiffness of MgSiO3 glass. However, the effect of Al2O3 content on the stiffness of MgSiO3 glass is non-linear, and MA1 and MA2 exhibit similar KS and G at high pressures. With the increase of pressure, the transverse acoustic mode (VS) of MA1 and MA2 shows abnormal changes at 17.8 GPa and 31.8 GPa, which are related to the transition of coordination number (CN) for Si-O in Al-bearing MgSiO3 glass. Compared with previous studies on sound velocity of MgSiO3 glass, the incorporation of Al2O3 delays the transition pressure of Si-O coordination to a higher pressure. Our study has profound implications for understanding the density and sound velocity of Al-bearing MgSiO3 melt in the Earth’s interior.

Numerical modeling of the effect of nozzle diameter and heat flux on the polymer flow in fused filament fabrication

A numerical model that fully account for the velocity of the traveling filament (push velocity) in the liquefier is presented in the current work to predict the pressure, temperature, outlet melt viscosity, strain rate, and velocity in the hot-end of a FFF system for printing tough-poly(lactic acid) (TPLA). The numerical model was thoroughly validated by comparing the model predictions with experimentally measured feeding force data. The predicted numerical results closely approximated the experimentally measured feeding force. Then the model was also validated with extrudate temperature, measured with a thermal imaging camera, and the results obtained are in good agreement. Outlet capillary diameter, feeding rate, and heat flux (quantified in terms of Nusselt number) were varied to determine the response of pressure field, temperature, velocity, viscosity, and strain rate in the liquefier. The results show that an increase in the nozzle outlet diameter decreases the extrusion pressure in the hot-end. The maximum pressure predicted for TPLA is 3.34, 2.91, and 2.04 MPa for the 0.4, 0.6, and 0.8 mm outlet diameters nozzles, respectively. Also, an increase in the nozzle outlet diameter decreases the central velocity at the outlet and decreases the shear rate with an increase in the viscosity of TPLA at the exit during material extrusion. The area-weighted averaged outlet temperature for TPLA decreases as the feeding rate increases for all three nozzle diameters. Elucidated from the simulation results, significant variation of the normalized velocity at the center of the nozzle outlet suggests that different printing speeds for TPLA material extrusion should be set for different nozzle diameters. Otherwise, the accuracy and precision of the gantry motion during layer deposition on the print will be compromised. The simulation results indicate that based on the 90% core melting temperature requirement, at a liquefier set temperature of 503 K, the TPLA should be printed below 80mm/min for all outlet diameters considered. A Nusselt number of 49.61 was observed to be the upper limit where an increase in the heat flux in the liquefier has no significant effect on the area-weighted averaged outlet temperature of TPLA.

Effects of gas-assisted technology on polymer micro coextrusion

Abstract In this paper, a three-dimensional viscoelastic flow model of double-layer micro coextrusion with circular cross-section was established. The simulations were carried out by the finite element method and the influence of wall slip coefficient on micro coextrusion was studied. The results show that gas-assisted technology is suitable for polymer micro coextrusion forming. The differences between the gas-assisted and conventional micro coextrusion process were compared by analyzing the distribution of melts velocity, pressure, shear rate and first normal stress difference. The research results show that in the conventional micro coextrusion process there are pressure drop, shear rate, first normal stress difference and secondary flow. And there is a gradient distribution of melts velocity. The die swell and deformation vary with the forming process parameters, and it is difficult to control the product quality. But in the gas-assisted micro coextrusion process, there is no pressure drop, shear rate, first normal stress difference and secondary flow. The velocity of polymer melts is evenly distributed and the melts are extruded in a plunger shape. The melts do not swell and deform and it is independent of forming process parameters. It is easy to ensure the products quality and the inherent problems of polymer conventional micro coextrusion are well solved.