Discharge Pressure Research Articles

Computational study of a novel microwave electrothermal thruster using dielectric resonators (DRs)

This paper presents the study of a novel microwave electrothermal thruster with a dielectric resonator based approach for the plasma localization and propellant gas heating. The study is purely computational in a two-dimensional planar geometry and establishes the concept and demonstrates feasibility as an electric propulsion device. The resonant structure consists of a two cylindrical high dielectric constant (ɛr = 172.5) resonator enclosed within a plasma chamber that terminates at a convergent-divergent nozzle. The plasma chamber is irradiated by an incoming microwave that experiences a large wave electric field amplification of about 25 000 at a resonant frequency of 18.5 GHz. The field amplification results in breakdown and establishment of a steady plasma in a helium propellant in close vicinity to the nozzle. With a microwave power input of 40 W mm−1 (depth) at 1 atm. discharge pressure, the peak gas temperature is about 1300 K, with an electron number density of approximately 1020 m−3, resulting in a peak specific impulse of 245 s. The corresponding cold gas specific impulse is 150. The high specific impulse is attributed to the plasma hot zone being located in close vicinity of the nozzle, which effectively increases thrust. However, the thrust increase is accompanied by significant heat conduction losses, particularly as the dielectric gap size increases, underscoring the importance of thermal management in the system.

Performance study of oil-injection hermetic CO2 scroll compressor for automotive air conditioning system.

An oil-injection CO2 scroll compressor prototype and relative simulation model are developed for automotive Air Conditioning. The effects of oil to refrigerant mass ratio on the compressor performance are studied theoretically and experimentally. The results show that oil-injection is an effective way to improve the volumetric and indicated efficiencies, and reduce discharge temperature. The optimal oil-injection quantity varies at different conditions, and it decreases from 7.9% to 6.3% at fixed discharge pressure 10MPa when the suction pressure increases from 4.5MPa to 5MPa. Similar linear relationships are found and the different slopes of the line are exhibited at fixed suction and discharge pressure separately. Numerical results show that oil-injection has little influence on pressure in working chamber during suction and discharge process, but it can slow up the rising of pressure in compression process and reduce the salient of pressure at the end of compression process.

Experimental study on the transcritical cycle performance of a closed-loop heat pump drying system based on R744/R290/R32 ternary refrigerant

Given the issue of high operating pressure in CO2 transcritical cycles, this paper proposes a novel non-combustible and low-GWP R744/R290/R32 ternary refrigerant used for heat pump drying systems. Six different mass ratios of the R744/R290/R32 are determined based on the limits posed by non-flammability and low GWP, and the transcritical cycle performance of these mixed refrigerants and pure CO2 applied to a closed-loop heat pump drying system (HPDS) at various drying air supply temperatures (DAST) is studied and compared experimentally. The analytic hierarchy process is used to assess the weights of the evaluation indices. Based on the experimental data, comprehensive scores for seven refrigerants are calculated, leading to the determination of the optimal mass ratio. The results show that at the same DAST, compared to pure CO2, the discharge pressure of the HPDS using the six mixed refrigerants decreases, and the COP increases. The optimal R744/R290/R32 mass ratio is 0.741/0.06/0.199. When the HPDS uses this, the compressor discharge pressure, heating capacity, moisture extraction rate (MER), and specific moisture extraction rate (SMER) decrease by an average of 14.8 %, 7.7 %, 17.6 %, and 0.06 %, respectively, while the COP increases by 4.9 % to 12.4 %. These research results can provide a reference for the development of new environmentally friendly refrigerants and their systems in the heat pump drying field.

Influence of gravity density on discharge flow pattern and pressure distribution along silo walls

Influence of gravity density on discharge flow pattern and pressure distribution along silo walls

Performance characteristics of rotary lobe pumps for high viscosity food medium

Abstract This paper analyses the effects of food media with high viscosity on the performance of rotary lobe pumps. Rotary lobe pumps have long been used in the food industry for pumping highly viscous media and are designed to operate for long periods of time without replacement of any parts. The study utilised publicly available data from factory tests of the PLP 3-4 pump for pumping food media of various viscosities μ (μ above 10,000 cP). The paper presents the results of processing these data, which allow us to draw some conclusions. It is established that the power input of the pump PLP 3-4, due to the viscosity of the food medium, is directly proportional to the rotor speed and increases with its increase. Thus the power spent on overcoming back pressure depends on rotor speed nonlinearly. At the same rotor speed the increase in pressure drop and dynamic viscosity coefficient do not affect the productivity, but lead to a significant increase in power consumption. The obtained results allow to draw a conclusion that it is not necessary to connect the increase of hydraulic efficiency of rotary lobe pump with improvement of energy efficiency of unit utilisation and to take into account the reason of increase of discharge pressure.

Two-phase radial ejector for transcritical CO2 refrigeration

Transcritical refrigeration systems using natural refrigerants like CO2 operate on the ejector–expansion cycle to achieve high operating efficiency. The variability of ejector geometry dictates the adjustability of refrigerating capacity in such systems. Traditional spindle-controlled axial-flow ejectors significantly obstruct the high-pressure motive flow to regulate mass flow rate by controlling flow area. This study introduces the first radial-flow ejector geometry for transcritical CO2 refrigeration systems, designed to operate at high mass flow rates and entrainment ratios with minimal obstruction to motive flow. The study numerically investigates the performance of a radial-flow two-phase ejector for CO2, comparing it with an axial-flow ejector of similar dimensions under the same conditions. It explores the impact of applied compression ratio, motive nozzle throat spacing, and other geometries on radial ejector performance. An increase in the motive throat spacing improves the range of operable discharge pressures and achievable compression ratios, with a slight reduction in the secondary flow entrainment. A nozzle throat spacing of 0.6 mm allows a wider range of operable discharge pressures, and beyond this, the operable discharge pressure range drops. The addition of a diffuser section of sufficient length also improves the flow entrainment in the radial ejector. The radial ejector allows substantially high mass flow rates of even 15 times that of the axial ejector. This high mass flow capacity in the radial configuration can significantly compact ejector designs for large-capacity transcritical CO2 refrigeration and air-conditioning systems.

Optimization of Electron Beams for Ion Bombardment Secondary Emission Electron Gun

Abstract Electron beam fluorescence technology is an advanced non-contact measurement in rarefied flow fields, the fluorescence signal intensity is positively correlated with the electron beam current. The ion bombardment secondary emission electron gun is suitable for the technology. To enhance the beam current, COMSOL simulations and analyses were con-ducted to examine plasma density distribution in the discharge chamber under the effects of various conditions and the electric field distribution between the cathode and the spacer gap. The anode shape and discharge pressure conditions were optimized to increase plasma density. Additionally, an improved spacer structure was designed with the dual purpose of enhancing the electric field distribution between the cathode-spacer gap and improving vacuum dif-ferential effects. This design modification aims to increase the pass rate of secondary elec-trons. Both simulation and experimental results demonstrated that the performance of the optimized electron gun was effectively enhanced. When the electrode voltage remains con-stant and the discharge gas pressure is adjusted to around 8 Pa, the maximum beam current was increased from 0.9mA to 1.6 mA.

Optimization of Centrifugal Pump Properties to Improve the Accuracy of Water Discharge and Pump Head Measurements

Centrifugal pumps are extensively used in industries and water management systems, where accurate measurements of water flow rate and pump head are essential for evaluating performance. However, inaccuracies arising from suboptimal designs of training kits present challenges in educational environments. This study aimed to optimize a centrifugal pump training kit to enhance measurement accuracy and reliability. The research was conducted over four months, involving modifications to the impeller, casing, and pressure measurement systems, along with rigorous calibration to minimize errors. Measurements of suction pressure, discharge pressure, water flow rate, and pump head were repeated under standardized conditions to ensure data consistency. The results demonstrated significant improvements, with consistent measurements of suction pressure (21 inHg), discharge pressure (15 PSI), water flow rate (0.5 L/s), and pump head (1.38 mH₂O). These optimizations reduced system inefficiencies, such as backflow and turbulence, and enhanced the kit’s ability to replicate real-world operating conditions. The improved training kit provides students with a reliable tool for practical learning, bridging theoretical concepts with real-world applications in fluid mechanics. This study underscores the importance of continual enhancement of laboratory teaching tools to support effective education and industrial relevance.

Optimizing Vanadium Redox Flow Battery Performance with Embroidered Porous Electrodes and Corrugated Bipolar Plates

Vanadium Redox Flow Batteries (VFBs) occupy a critical position in the quest for sustainable energy solutions, offering an attractive option for large-scale energy storage due to their operational simplicity, longevity, and exceptional efficiency.[1] However, the broader deployment of VFBs is hindered by significant energy losses, primarily due to pressure drops across porous electrodes and suboptimal electrolyte utilization at high current densities, which limit their discharge capacity and overall energy efficiency.[2] This research introduces a comprehensive strategy that employs embroidered porous electrodes for substantial pressure drop reduction and corrugated bipolar plates to improve mass transport and electrolyte distribution, thus addressing concentration polarization and mass transport limitations that significantly impact performance at high current densities. Embroidered porous electrodes: Through an innovative embroidery technique, the study engineered carbon electrodes with distinct patterns—diamond, parallel, and perpendicular—to optimize flow dynamics and decrease resistance. This method, reinforced by hydraulic modeling, achieved remarkable pressure drop reductions of 36%, 39%, and 12% for diamond, parallel, and perpendicular patterns, respectively, when compared to unmodified electrodes. The diamond pattern, in particular, demonstrated a notable increase in energy efficiency of 5.5%, including pumping losses, across various current densities. The hydraulic model provides further insight into the ideal channel width and spacing for these patterns, leading to pressure drop reductions of up to 73.5%, marking a significant breakthrough in electrode design. This research not only highlights the potential of embroidered porous electrodes in addressing VFBs' pressure drop challenges but also broadens the application horizon for these technologies across different energy storage systems. Corrugated bipolar plates: The study also investigated the role of corrugated bipolar plates, manufactured via a hot-pressing technique. These plates, in comparison to flat counterparts, offer a fresh approach to refining the VRFBs' flow field. By adjusting the thickness of these corrugated plates (1.0, 1.5, and 2.0 mm), battery performances were methodically assessed across a range of current densities. The corrugation promotes electrolyte flow turbulence and distribution, effectively minimizing ohmic losses and facilitating higher ion transport rates—essential for high-current-density operations. The results demonstrate that the synergistic application of embroidered porous electrodes and corrugated bipolar plates significantly bolsters VRFB performance. Specifically, an uplift in energy efficiency from 62.3% to 72.3% and an enhancement in voltage efficiency from 64.1% to 74.5% were observed at a current density of 200 mA cm-2. Additionally, discharge capacity increased from 1.46 Wh to 1.89 Wh under these conditions, underscoring the efficacy of the design modifications in surmounting VRFBs' intrinsic high-current-density limitations.This holistic approach, merging innovations in both electrode and bipolar plate designs, signifies a shift in VRFB development and optimization. It addresses critical challenges of pressure drop and electrolyte utilization while laying groundwork for future enhancements in flow battery technologies. By improving pressure drop and discharge capacity, this study furthers the objective of integrating renewable energy into the grid, leading the way to more sustainable and reliable energy storage solutions. Keywords: Vanadium Redox Flow Batteries, Embroidered Porous Electrodes, Corrugated Bipolar Plate, Pressure Drop, Discharge Capacity.[1] H. Jiang, J. Sun, L. Wei, M. Wu, W. Shyy, T. Zhao, A high power density and long cycle life vanadium redox flow battery, Energy Stor. Mater. 24 (2020) 529-540.[2] T. Li, F. Xing, T. Liu, J. Sun, D. Shi, H. Zhang, X. Li, Cost, performance prediction and optimization of a vanadium flow battery by machine-learning, Energ. Environ. Sci. 13(11) (2020) 4353-4361. Figure 1

Optimizing discharge pressure control in carbon dioxide heat pumps using particle swarm optimization

The provision of hot water constitutes a substantial fraction in the composition of household energy consumption. The deployment of carbon dioxide (CO2) heat pump technology for water heating shows notable benefits, which are critical for enhancing the energy performance of buildings. An effective control strategy for CO2 heat pump systems is indispensable for stable operation, system safety, user comfort, and optimal energy conservation. However, the majority of existing control strategies primarily investigate system performance under steady-state conditions, thus limiting their practical applicability. Consequently, this study conducts a dynamic experiment of a circulating heating heat pump water heater system. The findings indicate that maintaining a discharge pressure of 8.5 MPa during the heating stage can sustain the system’s coefficient of performance (COP) close to 3. Conversely, increasing the discharge pressure beyond 9.0 MPa during the frequency reduction stage mitigates the COP’s decline. During the start-up stage, the compressor speed is increased from 50 to 60 rps to expedite the start-up process in the shortest possible time (120 s), while ensuring system safety. Based on the experimental results, a proportional–integral–derivative (PID) control strategy is introduced, integrating both electronic expansion valve and compressor regulation. This strategy enhances total heating capacity by 20 % and the overall COP by 12 %. Subsequently, the PID parameters are optimized using the Particle Swarm Optimization (PSO) algorithm to achieve precise control and minimize overshoot of target parameters. Experiments evidence the superiority of the optimized PSO-PID control strategy, with a stable stage deviation of less than 0.1 MPa.

Trade-off between surface area and tap density when selecting carbon adsorbents for hydrogen compression

While high-surface-area activated carbons (ACs) are widely recognized as essential for maximizing H2 adsorption, this study emphasizes the importance of tap density and explores the potential of using more cost-effective ACs with lower surface areas for H2 compression by adsorption. We thus critically evaluated the performance of an adsorption compressor using six commercial ACs with BET areas ranging from 1000 to 3300 m2/g and tap densities from 270 to 560 kg m−3. Experimental and numerical analyses revealed the impact of these parameters on compression efficiency. Our results suggest that optimizing both surface area and tap density is essential for improving the viability of porous materials in the hydrogen economy. Specifically, the ACs tested here can achieve outlet pressures up to 70 MPa, but with minimal H2 discharge. Therefore, lower discharge pressures (<30 MPa) are required to maintain a stable H2 flow rate, which can be further improved at temperatures above ambient (298 K).

Theoretical analysis and experimental validation of optimal vapor injection conditions for a low-pressure ratio scroll compressor

This study investigates the impact of vapor injection parameters and positions on the performance of a low-pressure ratio scroll compressor in electric vehicle thermal management systems under extremely low temperatures. The research combines experimental and simulation methods to analyze five injection ports designed at different positions. Key performance metrics, including mass flow rate, discharge temperature (Tdis), coefficient of performance (COP), compression work, and heating capacity (Qh) were evaluated under various conditions. A low-pressure ratio (scroll number N = 2) vapor injection scroll compressor was designed with an optimized injection port configuration. This design was rigorously validated through experimental results, confirming its efficacy. Notably, the findings reveal that the enhancement in Qh and COP is more pronounced in extremely low-temperature working conditions compared to non-injection conditions, with improvements of 10.7 % and 4.6 %, respectively. Compressor performance increases with increasing vapor injection pressure, and compressor speed and performance increment are more significant under low-temperature working conditions. Finally, an injection coefficient, denoted as k, is proposed to determine the optimal injection pressure for diverse discharge and suction pressures in cold climates. According to the experimental results, the value of k associated with the best heating COP ranges between 0.65 and 0.85.

Influence of cyclic loading on physical and mechanical properties of thin-film membrane structures

The principle of modification of mechanical properties of thin-film membrane structures of arbitrary shape by non-contact method was proposed, realized and explained for the first time. The idea was tested on an aluminum thin-film membrane formed by magnetron method on a silicon substrate. The external influence was realized by means of cyclic loading in the form of discharge and supply of excess air pressure to the membrane. As a result of repeated impacts, physical properties of materials (grain size and roughness) and mechanical properties (internal mechanical stresses and critical overpressure) are changed. Changing the magnitude of residual mechanical stresses in the membrane material allows the formation of a surface with a desired curvature value. In this work, after cyclic loading with pressure equal to half of the critical pressure, the following effects were revealed: the deflection of the membrane in the absence of external influence increased by more than an order of magnitude, the structure shifted to the plastic type of deformation, the critical rupture pressure decreased by several tens of percent. Application of this methodology allows to create new materials with unique mechanical properties.

ATMOSPHERIC PRESSURE DIELECTRIC BARRIER DISCHARGE IN HMDS VAPOR AS A COATING DEPOSITION INSTRUMENT

The paper demonstrates the possibility of using a dielectric barrier discharge for the deposition of polymer organosilicate films on the surface of glass substrates. A planar barrier discharge of atmospheric pressure was excited in a flow reactor in an atmosphere of (Bis(trimethylsilyl)amine at a fixed flow rate. Helium as the carrier gas was used. The carrier gas and working fluid flow rates were fixed at 45 ml/s and 0.2 ml/s, respectively. The frequency of the dielectric barrier discharge was 50 Hz, the average discharge current was 3 mA at a total power put into the discharge of 24 VA. The deposition time varied in the range of 30–1200 s. It was shown that under the conditions studied, the discharge has a filamentous form. The study of the surface morphology and elemental composition of the deposited film was carried out using scanning electron microscopy and energy-dispersive spectroscopy. Surface wettability was determined by the contact angle method and the method of photofixation of drops. The elemental composition of the deposited coatings indicates the formation of an organosilicon film. The contact angle method for polar (distilled water) and non-polar (diiodomethane, glycerol) liquids showed that the wettability of the deposited coatings is higher than that of the original substrate. Additionally, the effect of storage time of deposited coatings (under normal conditions) on their properties was studied. It was found that the storage effect does not have a significant effect on the wettability of the films. For citation: Shutov D.A., Ivanov A.N., Sungurova A.V., Ignatiev A.A., Morozova Yu.N., Rybkin V.V. Atmospheric pressure dielectric barrier discharge in hmds vapor as a coating deposition instrument. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 12. P. 80-85. DOI: 10.6060/ivkkt.20246712.7148.

Optimal Intermediate Pressure Investigation in a CO₂ Transcritical Distributed Compression Refrigeration Cycle

The CO2 transcritical distributed compression cycle proposal provides a novel approach for refrigerant cooling in traditional transcritical cycles. This paper employed an exhaustive search method to derive the correlation formula for the optimal intermediate pressure. From the perspectives of thermodynamic performance and economics, a comparative analysis was conducted between the cycle established under the optimal intermediate pressure obtained in this study, the cycle based on equal compression ratios in traditional two-stage compression cycles, and the cycle established using the optimal secondary compression ratio method based on low-pressure stage discharge pressure mentioned in previous literature study. The research results indicate that the system's COP calculated using the obtained optimal intermediate pressure correlation method can be improved by up to 7.26% and 5.32%, respectively, compared to the traditional and literature-based methods. The exergy loss with the optimal intermediate pressure method is less than with the other two methods. The entransy dissipation rate of the system obtained using the optimal intermediate pressure correlation method is 24.61% and 50.14% lower than that of the traditional and literature-based methods, respectively. The investment cost of the main components using the optimal intermediate pressure correlation method is about 5% higher than that of the traditional method and about 1% higher than that of the optimal pressure ratio method. However, the total annual cost rate of the system is the lowest. The research enriches and improves the theory of the CO₂ transcritical distributed compression cycle, thereby facilitating the advancement of practical applications based on this cycle theory.

Application of radio frequency capacitively coupled Ar+H2 plasma on rapid annealing of Cu-based photovoltaic grid line

With the continuous thinning of photovoltaic silicon wafers for cost reduction, copper based photovoltaic grid lines (Cu-PGL) require annealing and softening treatment. However, for the commonly used short circuit annealing method in industry, some issues exist such as air surface oxidation and environmental pollution, which need to be addressed for large-scale development of high-performance Cu-PGL. In this study, we propose a medium-pressure capacitively coupled plasma driven by radio frequency (RF) for plasma rapid annealing of Cu-PGL to meet solar cell performance requirements. The experimental results show that the yield strength of Cu-PGL decreases from 336.5 MPa to 59 MPa after plasma rapid annealing while electrical conductivity increases from 87 %IACS (International Annealed Copper Standard) to 116 %IACS at the optimal condition of discharge pressure of 1.0 kPa, and input power of 150 W with wire speed of 50 m/min. The plasma annealing mechanism of Cu wire was disclosed by combining spectral diagnosis of the plasma and Cu wire performance characterization.

Energy, exergy, and economic analysis of a novel solar-assisted ejector subcooling CO2 transcritical refrigeration systemt

To further enhance the performance of transcritical CO2 refrigeration cycle (base cycle), a solar-assisted ejector subcooling transcritical CO2 refrigeration cycle (SESRS) is proposed. The base cycle is subcooled utilizing a solar-assisted ejector refrigeration cycle. This research performed energy, exergy, and economic evaluations of SESRS utilizing the eco-friendly refrigerant R152a in the ejector cycle based on the established model. The thermodynamic analysis results demonstrate that SESRS outperform the base cycle. At typical working conditions, the COPm of the SESRS demonstrates a 22.96 % increase compared to that of the base cycle. Although the total cost of the SESRS is 7.98 %–17.9 % higher than that of the base cycle when subcooling degree is 5 °C, the enhancement of COPm is larger and is increased by approximately 18.34 %–26.22 %. The impact of subcooling degree and other parameters on system performance are also investigated. Overall, this study confirms the potential of the SESRS system for utilization in the refrigeration and air-conditioning fields. Considering both the system’s performance and economy, further optimized analysis should be done on key operational parameters, such as subcooling degree and discharge pressure.

Adaptive fuzzy PI control for the dynamic operation of the transcritical CO2 thermal system in electric vehicles

Process control is essential for ensuring the stable and efficient operation of EVs’ transcritical CO2 thermal management systems. Traditional PI control generally shows an insufficient dynamic response for the variable and complex operating conditions and then causes fluctuant process control. This study proposed an adaptive fuzzy PI control strategy to provide real-time varying PI gains for fast-tracking response and fluctuation suppression, considering the compressor discharge pressure, coolant, and air outlet temperature. A high-fidelity transcritical CO2 thermal model in EVs was first built in the Amesim platform to simulate real-time operation, and the adaptive fuzzy PI control algorithm was then developed to optimize the process control. The co-simulation is conducted to validate the effectiveness and adaptability of the proposed control methodology by comparing it with a benchmark traditional PI control strategy. The results indicated that the proposed adaptive fuzzy PI could provide a 9.22 % overshoot suppression for discharge pressure, a maximal 22.29 % overshoot inhibition and 86 s settling time reduction for the air outlet temperature, and a 25 % settling time reduction for the coolant temperature control. In addition, the fuzzy PI improved the start-up characteristics by avoiding excessive response. Such findings demonstrate that the proposed fuzzy PI control algorithm can effectively optimize the dynamic operation of the transcritical CO2 thermal system in EVs.

Simulation of a system to simultaneously recover CO2 and sweet carbon-neutral natural gas from wet natural gas: A delve into process inputs and units performances

The growing need for carbon-neutral energy solutions necessitates the development of efficient systems for carbon dioxide (CO2) recovery and the production of sweet carbon-neutral natural gas (CNNG) from wet natural gas. Despite existing approaches, limitations in process optimization, solvent efficiency, and output purity persist. This study aims to address these gaps by simulating a system for simultaneous recovery of CO2 and CNNG using an integrated three-stage process, modeled in Aspen Plus V8.8. The unique aspect of this work lies in employing the ENRTL-RK base model, coupled with sensitivity analyses to optimize input parameters across 13 interconnected process units, including compressors, heat exchangers, and extraction columns. Key innovations include the novel configuration of units, yielding a recovery efficiency of 95.94% for CNNG and a CO2 purity of 93.185% at optimal conditions, surpassing conventional methods. The performance of the monoethanolamine (MEA) solvent was enhanced by careful adjustment of input parameters, improving its absorption efficiency by 12% compared to standard operational settings. Sensitivity analysis revealed critical parameters such as feed pressure and solvent flow rate as primary drivers for maximizing output efficiency. This study also provides a detailed quantitative assessment of power requirements, with a compressor brake horsepower (BHP) of 18,2605 watts at 110 bar discharge pressure. It addresses the existing research gap by introducing a systematic approach to process optimization, significantly improving the purity and recovery of CNNG and CO2 while minimizing energy consumption. The results not only demonstrate the viability of this process but also provide a foundation for further refinement in sustainable gas processing technologies.

Single-screw extrusion performance for LLDPE resin as a function of compression ratio

High-quality polyethylene film and sheet must be free of solid polymer fragments and degraded resin. Moreover, the products must be produced at high rates to minimize conversion costs. Thus, the extruder must produce a homogenous extrudate at the proper discharge temperature and pressure. The screw design and process operating parameters are key. A key screw design parameter is the compression ratio. This paper experimentally studies how the compression ratio affects a linear low-density polyethylene (LLDPE) resin extrusion process. A 2.8 compression ratio screw was optimal for LLDPE resin. Significant solid polymer fragments were observed in the extrudate for 2.8 to 3.6 compression ratio screws at 110 rpm and higher. For 2.0 and 2.4 compression ratio screws at less than 50 rpm, the internal pressures in the extruder were relatively low. At screw speeds 50 rpm and higher, the specific rates for all screws were higher than the calculated specific rotational rate, creating negative axial pressure gradients in the metering sections.