scholarly journals Extreme Foaming Modes for SCF-Plasticized Polylactides: Quasi-Adiabatic and Quasi-Isothermal Foam Expansion

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1055 ◽  
Author(s):  
Dmitry Zimnyakov ◽  
Roman Zdrajevsky ◽  
Nikita Minaev ◽  
Evgeniy Epifanov ◽  
Vladimir Popov ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Bubble Radius ◽  
Initial Pressure ◽  
Critical Value ◽  
Expansion Ratio ◽  
External Pressure ◽  
Pressure Derivative ◽  
Specific Internal Energy ◽  
Foam Expansion ◽  
Foam Volume

The experimental evidence on depressurization foaming of the amorphous D,L-polylactide, which is plasticized by subcritical (initial pressures below the critical value) or supercritical (initial pressures above the critical value) carbon dioxide at a temperature above the critical value, relates to two extreme cases: a slow quasi-isothermal foam expansion, and a rapid quasi-adiabatic expansion. Under certain conditions, the quasi-isothermal mode is characterized by the non-monotonic dependencies of the foam volume on the external pressure that are associated with the expansion-to-shrinkage transition. The quasi-adiabatic and quasi-isothermal expansions are characterized by a significant increase in the degree of foam expansion under conditions where the CO2 initial pressure approaches the critical value. The observed features are interpreted in terms of the energy balance in the foam volume and the phenomenological model based on the equation of the foam state. The expansion-to-shrinkage condition is based on the relationship between the average bubble radius and the pressure derivative of the surface tension for the plasticized polylactide. The maximum expansion ratio of the rapidly foamed polylactide in the vicinity of the critical point is interpreted in terms of the maximum decrement of the specific internal energy of the foaming agent (carbon dioxide) in the course of depressurization.

scholarly journals Depressurization-Induced Nucleation in the “Polylactide-Carbon Dioxide” System: Self-Similarity of the Bubble Embryos Expansion

Polymers ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1115
Author(s):  
Dmitry Zimnyakov ◽  
Marina Alonova ◽  
Ekaterina Ushakova
Keyword(s):  
Initial Rate ◽  
Initial Pressure ◽  
External Pressure ◽  
Self Similarity ◽  
Embryo Formation ◽  
Linear Behavior ◽  
Joint Influence ◽  
External Pressures ◽  
Adiabatic Cooling ◽  
Self Similar

Self-similar expansion of bubble embryos in a plasticized polymer under quasi-isothermal depressurization is examined using the experimental data on expansion rates of embryos in the CO2-plasticized d,l-polylactide and modeling the results. The CO2 initial pressure varied from 5 to 14 MPa, and the depressurization rate was 5 × 10−3 MPa/s. The constant temperature in experiments was in a range from 310 to 338 K. The initial rate of embryos expansion varied from ≈0.1 to ≈10 µm/s, with a decrease in the current external pressure. While modeling, a non-linear behavior of CO2 isotherms near the critical point was taken into account. The modeled data agree satisfactorily with the experimental results. The effect of a remarkable increase in the expansion rate at a decreasing external pressure is interpreted in terms of competing effects, including a decrease in the internal pressure, an increase in the polymer viscosity, and an increase in the embryo radius at the time of embryo formation. The vanishing probability of finding the steadily expanding embryos for external pressures around the CO2 critical pressure is interpreted in terms of a joint influence of the quasi-adiabatic cooling and high compressibility of CO2 in the embryos.

THERMAL CHARACTERISTICS OF FOAMS AND DISCHARGE FROM FIRE-EXTINGUISHMENT FOAM SPRAY NOZZLE

2009 ◽  
Vol 23 (03) ◽  
pp. 381-384
Author(s):  
YOUN-JEA KIM ◽  
JIN-SOO PYO
Keyword(s):  
Heat Flux ◽  
Temperature Gradient ◽  
Thermal Characteristics ◽  
Expansion Ratio ◽  
Experimental Results ◽  
Orifice Diameter ◽  
Spray Nozzle ◽  
Foam Expansion ◽  
Fire Extinguishment ◽  
Air Hole

To evaluate the performance of discharged foam agents used to protect structures from heat and fire damages, the thermal characteristics of fire-extinguishment foams were experimentally investigated. Especially, two different parameters of a spray nozzle, that is, the number of air holes and the orifice diameter, were considered. A simple repeatable test for fire-extinguishment foams subjected to fire radiation was performed. Experimental results showed that the expansion ratio of the discharged foam with the small orifice throat ( d 0= 9.5 mm ) and opened air hole ( N h =9) was large. Results also showed that although the temperature gradient in the foam increased as the foam expansion ratio is increased, it remained constant as the intensity of heat flux increased.

scholarly journals Polysulfone foam with high expansion ratio prepared by supercritical carbon dioxide assisted molding foaming method

RSC Advances ◽  
2018 ◽  
Vol 8 (6) ◽  
pp. 2880-2886 ◽  
Author(s):  
Zhengkun Li ◽  
Yingbin Jia ◽  
Shibing Bai
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
High Performance ◽  
Expansion Ratio ◽  
Supercritical Carbon

Polysulfone foam with high expansion ratio and high performance was prepared by new foaming method using CO2 and press vulcanizer.

scholarly journals Mechanism Analysis of Liquid Carbon Dioxide Phase Transition for Fracturing Rock Masses

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2909 ◽  
Author(s):  
Feng Gao ◽  
Leihu Tang ◽  
Keping Zhou ◽  
Yanan Zhang ◽  
Bo Ke
Keyword(s):  
Phase Transition ◽  
Carbon Dioxide ◽  
High Pressure ◽  
Initial Stress ◽  
Initial Pressure ◽  
Initial Crack ◽  
Stress Waves ◽  
Mechanism Analysis ◽  
Liquid Carbon ◽  
Liquid Carbon Dioxide

The technique of breaking rocks using carbon dioxide phase transition technology is being widely applied in current research. This article combines theoretical and practical methods to analyze the mechanism by which high-pressure gas breaks rock at different stages. Using the observation that liquid carbon dioxide forms a high-pressure jet from release holes at the moment of release, a formula for calculating the initial pressure on the wall in the direction of release was obtained, and the pattern of initial crack formation on the borehole wall under different initial stress conditions was examined. An experiment using carbon dioxide phase transition technology to fracture rock without an initial stress field was conducted. The mechanism of generation and expansion of subsequent cracks under stress waves and high-pressure gas was analyzed, and the formula for calculating crack propagation radius under stress waves was obtained. The results suggested that under the quasi-static action of high-pressure gas, cracks begin to develop when the stress intensity factor KI at the crack tip is equal to or greater than the fracture toughness KIC of the rock.

The Cooling of Methane with Vortex Tubes

1971 ◽  
Vol 13 (6) ◽  
pp. 369-375 ◽  
Author(s):  
A. Williams
Keyword(s):  
Carbon Dioxide ◽  
Natural Gas ◽  
Vortex Tube ◽  
Expansion Ratio ◽  
Methane Content ◽  
Thomson Effect ◽  
Vortex Effect ◽  
Temperature And Pressure ◽  
Vortex Tubes ◽  
Gas Supply

Measurements have been made of the amounts of cold and heat produced by a vortex tube operated with methane containing some carbon dioxide, and with Algerian natural gas, which has a high methane content. The effects of gas supply temperature and pressure have been investigated. The contribution of the Joule–Thomson effect to the total cooling has been calculated and allowed for. Vortex effect cooling decreases with lowering of the supply temperature and probably disappears at the gas liquefaction point. It is dependent on the pressure expansion ratio across the tube. The findings are compared with those of other workers and those predicted by vortex tube theories.

scholarly journals The dissociation of carbon dioxide at high temperatures

1927 ◽  
Vol 115 (771) ◽  
pp. 318-333 ◽  
Keyword(s):  
Carbon Dioxide ◽  
High Temperatures ◽  
Combustion Engine ◽  
Initial Pressure ◽  
Simple Relation ◽  
Maximum Temperature ◽  
Maximum Pressure ◽  
Complete Combustion ◽  
Explosion Pressure ◽  
Rich Mixture

The power of an internal combustion engine is greatest when operating with a “rich” mixture, that is to say, with a mixture which contains more fuel than is necessary for complete combustion. Similarly, it is found that if mixtures of carbon monoxide and air in varying proportions are exploded in a closed bomb at constant initial temperature and pressure, the explosion pressure is greatest when the ratio CO/O 2 is greater than 2. These phenomena are known to be connected with the dissociation of carbon dioxide at high temperatures, for if there were no dissociation we should expect the explosion pressure to be greatest when CO/O 2 = 2. No attention appears, however, to have been paid to the position of the maximum. It can be shown in the following way that there is a very simple relation between the composition of the mixture giving maximum pressure on explosion, and the dissociation of carbon dioxide at the maximum explosion temperature. Let the initial composition be represented by the expression 2 (1 + a ) CO + O 2 + b N 2 (Total mols = 3 + 2 a + b ), and let P i , T i represent the initial pressure and temperature; P e the maximum pressure observed after explosion, and T e the corresponding maximum temperature.

Effects of Substituent and External Pressure on Spin Trapping Rates of Carbon Dioxide Anion, Sulfur Trioxide Anion, Hydroxyl, and Ethyl Radicals with Various PBN- and DMPO-Type Spin Traps

2014 ◽  
Vol 228 (9) ◽  
Author(s):  
Yoshimi Sueishi ◽  
Keitaro Miyazono ◽  
Kazuki Kozai
Keyword(s):  
Carbon Dioxide ◽  
Sulfur Trioxide ◽  
External Pressure ◽  
Spin Trapping ◽  
Spin Traps ◽  
Trapping Method ◽  
Ethyl Radicals

AbstractUsing a competitive trapping method employing two different traps, the trapping rates of anionic radicals (CO

scholarly journals Study of the thermal stability of foam of different expansion ratio

2020 ◽  
Vol 29 (3) ◽  
pp. 103-110
Author(s):  
A. V. Koksharov ◽  
S. I. Osipenko ◽  
E. V. Gaynullina
Keyword(s):  
Thermal Stability ◽  
Thermal Exposure ◽  
Expansion Ratio ◽  
Heat Fluxes ◽  
Foam Layer ◽  
Destructive Effect ◽  
Foam Expansion ◽  
Destruction Rate ◽  
Wide Range ◽  
Thermal Stability Of

Introduction. Currently, the industry produces a wide range of foam generators to produce fire-extinguishing foams, and the foams they produce differ significantly in their expansion ratio and, consequently, fire resistance. Since heat fluxes have the main destructive effect on the foam, the purpose of this paper is to establish the patterns of destruction of foam of different expansion ratio when heated.Methods of research. The foam with expansion ratio from 7.5 to 80 was used for the tests. It was obtained by mechanical beating of 6 % solution of foaming agent PO-6RZ. The thermal stability of the foam was studied when the heat flow from the gas burner flame affects the foam layer. During the experiment, the change in the height of the foam column in time was recorded.Results and Discussion. The results of measurements, presented in the form of dependence of foam layer destruction rate on time, quantity of released liquid phase on 1 m2·s, dependence of foam layer destruction rate on its density allowed revealing a number of patterns. The destruction rate of foam with an expansion ratio of up to 30 remains constant throughout the entire duration of thermal exposure. As the foam expansion ratio increases, the rate of destruction at the initial stage of heat flux exposure increases. With a foam expansion ratio of more than 50, there is initially a sharp increase in the rate of destruction, which subsequently decreases as the foam column decreases. In the conditions of the experiment, the best characteristics were shown by the foam with an expansion ratio of 50, because in the foam with a smaller expansion ratio the syneresis makes a significant contribution to its destruction, and the foams with a larger expansion ratio are destroyed by the mechanical effect of convective flame flows.Conclusion. The study of the foam destruction patterns under thermal impact allowed establishing the fact that its destruction is limited by the rate of impoverishment of the upper layers with liquid.

Carbon particulate and controlled-hydrolysis assisted extrusion foaming of semi-crystalline polyethylene terephthalate for the enhanced thermal insulation property

2020 ◽  
pp. 0021955X2095275
Author(s):  
Junjie Pan ◽  
Feng Chen ◽  
Eusebio Duarte Cabrera ◽  
Zhiyu Min ◽  
Shilun Ruan ◽  
...  
Keyword(s):  
Moisture Content ◽  
Thermal Insulation ◽  
Expansion Ratio ◽  
Insulation Property ◽  
Melt Flow Rate ◽  
Foam Expansion ◽  
Chemically Modified ◽  
Twin Screw ◽  
Thermal Insulation Property ◽  
Controlled Hydrolysis

This work presents a facile method to produce low-density PET foams using pristine semi-crystalline resin by moisture-induced controlled-hydrolysis in a tight processing window (moisture content ∼ 0.12 wt.%). We investigated the effect of moisture and moisture containing activated carbon (AC) on the foam expansion ratio, cell morphology, and PET resin degradation and crystallization properties. Controlled-hydrolysis increased the melt-flow rate of PET resin (intrinsic viscosity: 0.52 to 0.54 dL/g) without losing crystallinity, and thus the PET foams possess better tensile properties (∼2 MPa stress and ∼100% strain) and higher thermal stability (>200°C) than chemically modified PET foams. The foam density could be made as low as ∼ 0.15 g/cm3 using a lab scale twin-screw extruder. A strand array die was also designed to produce plate-shaped foam samples. AC allowed easier control of the moisture content and delayed resin degradation in extrusion. Both AC and micrographite (mGr) could stabilize the PET foam morphology in extrusion and serve as good infrared attenuation agents (IAAs) in a simulated housing thermal insulation experiment.

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