High Pressure Drop Rates Research Articles

High-pressure drop rates in solid-state batch one-step scCO2 foaming of acrylic polymers: A way to stabilize the structure of micro-nano foams

One-step solid-state batch scCO2 foaming is used with the target of achieving acrylic polymer micro-nano foams. Foaming is triggered by an average pressure drop (APDR), covering two decades, from 0.3 to 30 MPa.s−1. This study principally addresses the combined beneficial effects of block copolymer addition (BCP, here denoted as MAM) and high APDR. Numerous subtle kinetic parameters actually interplay and compete in the production of the final foams. In particular, the material effective temperature, the effective glass transition temperature of the plasticized system and the instantaneous PDR are physical quantities each having their own kinetics during foaming. The resulting foam morphologies are quantified by SEM microscopy and image analysis. A high APDR and the presence of BCP are shown to play a key role in the final structure of the foams. Over the scrutinized range of saturation temperature (40 °C to 60 °C i.e. rather ‘low’ temperatures in the CO2 supercritical state), the APDR is the main factor for significantly reducing cell size and increasing nuclei density in foams from neat PMMA. In the block copolymer approach, increasing the APDR is of secondary importance as the targeted reduction of the porosity dimensions and augmentation of nuclei density are mostly the consequence of MAM presence. In this latter case, increasing the APDR still promotes the ‘efficiency’ of the BCP nucleants. A real efficient nucleation activity of MAM additive is observed at a very high APDR (30 MPa.s−1), leading to monomodal homogeneous distribution of tiny pores in nearly nanosized foams. At lower APDR, an interesting reproducible double porosity (foams containing intra-wall and inter-wall pores) is detected in PMMA/MAM systems. In such double porosity foams, benefits from the Knudsen effect achieved within well expanded local domains (showing micron-sized pores) may remain meaningful thanks to a locally poorly expanded nanoporous thick solid skeleton encapsulating these local domains. Thereby, the radiative thermal conduction can be minimized and does not override the conductive component at the sample scale. This work provides further insight on acrylic polymer BCP foams influenced by different kinetics.

Influence of High Pressure Drop Rates on Fatigue Crack Growth

AbstractHydraulic components in mobile machines are subjected to varying conditions and loads, which limit their lifetime. In particular, high pressure drop rates are suspected to increase fatigue crack growth rates. Existing studies on the fluid‐structure interaction inside fatigue cracks during fast pressure drops do not explain increased crack growth in hydraulic systems. A laminar flow model was developed to simulate the fluid flow inside a crack under periodic pressure loads. The viscosity restrained the oil inside the crack, and the mechanical resistance of the closing crack led to a high pressure increase. Knowledge of the pressure profiles inside fatigue cracks helps to estimate the effective fatigue damage during transient loads.

Tuning High and Low Temperature Foaming Behavior of Linear and Long-Chain Branched Polypropylene via Partial and Complete Melting.

While existing foam studies have identified processing parameters, such as high-pressure drop rate, and engineering measures, such as high melt strength, as key factors for improving foamability, there is a conspicuous absence of studies that directly relate foamability to material properties obtained from fundamental characterization. To bridge this gap, this work presents batch foaming studies on one linear and two long-chain branched polypropylene (PP) resins to investigate how foamability is affected by partial melting (Method 1) and complete melting followed by undercooling (Method 2). At temperatures above the melting point, similar expansion was obtained using both foaming procedures within each resin, while the PP with the highest strain hardening ratio (13) exhibited the highest expansion ratio (45 ± 3). At low temperatures, the foamability of all resins was dramatically improved using Method 2 compared to Method 1, due to access to lower foaming temperatures (<150 °C) near the crystallization onset. Furthermore, Method 2 resulted in a more uniform cellular structure over a wider temperature range (120–170 °C compared to 155–175 °C). Overall, strong extensional hardening and low onset of crystallization were shown to give rise to foamability at high and low temperatures, respectively, suggesting that both characteristics can be appropriately used to tune the foamability of PP in industrial foaming applications.

Vacuum Freezing of Coffee Extract Under Different Process Conditions

This research work was focused on evaluating the vacuum freezing (VF) of coffee extract under different process conditions as well as on its comparison with air freezing (AF) and contact freezing (CF). Regarding VF, extract concentration (10 to 40 oBrix) did not affect freezing time (for sufficiently high pressure drop rates), whereas extract layer thickness had significant impact, with 50% higher process times for samples arranged in 6-mm-thick layers in comparison with 4-mm-thick arrangements. Moreover, reduction of pressure drop rate (from 0.57 to 0.37 kPa s−1) caused an increase of up to 5 times of VF time. In comparison with AF and CF, VF led to significantly smaller freezing times along with higher mass losses (of 26–43% contrasting with 1–2% losses for AF and CF). This fact, allied to the extremely porous structure formed during VF, makes this method particularly interesting for soluble coffee production by freeze drying.

Current status and key factors for coalbed methane development with multibranched horizontal wells in the southern Qinshui basin of China

AbstractThe Qinshui basin is the most successful area for coalbed methane (CBM) development in China. Since 2008, 45 multibranched horizontal wells (MBHWs) have been put into production in the Fanzhuang block, of which 10 wells have an average daily gas rate (DGR) of &gt;10 000 m3/d. Well 4‐5 with the total gas production of 1.054 × 108 m3achieved the China's highestDGRof 63 744 m3/d. Compared with vertical wells,MBHWis an effective way to developCBMin low permeability reservoirs in China. However, there are still 23 wells have an averageDGRof &lt;3000 m3/d, of which 18 wells are below 1000 m3/d. The results show that shallow depth (&lt;600 m), high gas content (&gt;16 m3/t) and saturation (&gt;80%), long coal seam interval (&gt;3000 m), reasonable branch spread, and stable wellbore are the basis for achieving high production. The encountered faults connected to the aquifer will cause a high water production and an extremely low gas rate (&lt;1000 m3/d). In the inclined coal seam, the up‐dipMBHWis more favorable for the formation water drainage and the pressure drop funnel expansion than the down‐dipMBHW, and the horizontal well should be drilled perpendicular to the high‐permeability direction to achieve a higher recovery ratio.MBHWis more sensitivity to drainage rate due to the coal fine migration in the horizontal segments, and the high pressure drop rate will lead to high frequency of stunk pump and eventually affect the gas production. Currently, the biggest challenge forCBMdevelopment withMBHWis wellbore stability. 57% of inefficient wells are caused by wellbore collapse during drilling and production processes. Here, a new type of “Roof Drilling‐Tree Shaped” horizontal well structure was presented in this work. The first “Roof Drilling‐Tree Shaped” horizontal well with a total length of 12 288 m and a coal seam interval of 9408 m was successfully applied without drilling accidents.

Characterization of Foamy Oil and Gas/Oil Two-Phase Flow in Porous Media for a Heavy Oil/Methane System

In our previous study, a series of experiments had been conducted by applying different pressure depletion rates in a 1 m long sand-pack. In this study, numerical simulation models are built to simulate the lab tests, for both gas/oil production data and pressure distribution along the sand-pack in heavy oil/methane system. Two different simulation models are used: (1) equilibrium black oil model with two sets of gas/oil relative permeability curves; (2) a four-component nonequilibrium kinetic model. Good matching results on production data are obtained by applying black oil model. However, this black oil model cannot be used to match pressure distribution along the sand-pack. This result suggests the description of foamy oil behavior by applying equilibrium black oil model is incomplete. For better characterization, a four-component nonequilibrium kinetic model is developed aiming to match production data and pressure distribution simultaneously. Two reactions are applied in the simulation to capture gas bubbles status. Good matching results for production data and pressure distribution are simultaneously obtained by considering low gas relative permeability and kinetic reactions. Simulation studies indicate that higher pressure drop rate would cause stronger foamy oil flow, but the exceed pressure drop rate could shorten lifetime of foamy oil flow. This work is the first study to match production data and pressure distribution and provides a methodology to characterize foamy oil flow behavior in porous media for a heavy oil/methane system.

Effect of the melt compressibility and the pressure drop rate on the cell-nucleation behavior in foam injection molding with mold opening

We investigated the cell-nucleation mechanisms in high-pressure foam injection molding for high expansion using the mold-opening technology. A polystyrene/carbon dioxide was used as the foam system. The cellular structure’s entire formation process was monitored using an in-situ mold visualization technique. Although mold opening was used to increase the void fraction, the cell density was also significantly increased by inducing a rapid pressure drop with proper setting of the processing parameters. As in the case of high-pressure foam injection molding without mold opening, we applied a melt-packing pressure to remove the earlier nucleated cells before mold opening. Consequently, a high pressure drop rate was obtained through the decreased melt compressibility. This dramatically increased the cell density and enhanced the structural uniformity within the foamed samples. We investigated the effect of the melt-packing pressure, as well as the dwelling time of the melt/gas mixture. The packing time required to remove the cells had increased as the packing pressure had decreased. However, too lengthy a dwelling time activated another cell nucleation step through melt shrinkage before mold opening, and it deteriorated the final cell structure.

Insight into bubble nucleation at high-pressure drop rate

This paper presents insight in bubble nucleation in polymer foaming with physical blowing agent using a batch foaming technique. In our experiments the bubble nucleation is triggered by a sudden pressure drop that causes the supersaturation in the polymer gas solution. In fact, the pressure drop rate is an important process variable since it plays a role in both bubble nucleation and growth. Herein, we investigated very high pressure drop rates, and confirmed the great importance of the pressure drop rate as foaming process variable. The results show that the number of nucleated bubbles increases of one order of magnitude and the foam density is reduced if the pressure drop rate is increased from 50 to 500 MPa/s. Interestingly, the number of nucleated bubble increases linearly in a bi-logarithmic scale as function of pressure drop rate at all the investigated temperatures. Moreover, in the current paper, it is discussed how talc used as nucleating agent plays a role in cooperation with pressure drop rate on bubble nucleation at different foaming temperatures.

A novel lab-scale batch foaming equipment: The mini-batch

In this paper, we report the design of a new experimental apparatus for the study of the foaming process of thermoplastic polymers with physical blowing agents. The novel lab-scale batch foaming equipment is capable of achieving accurate control of the processing variables, namely, the temperature, the saturation pressure and the pressure drop rate and, furthermore, of allowing the achievement of very high pressure drop rates, the observation of the sample while foaming and the very fast extraction of the foamed sample. By recalling the considerations discussed by Muratani et al. ( J Cell Plast 2005; 24: 15), the design converged into a simple, cheap, and very small pressure vessel, thereby denoted as mini-batch. We herein describe the overall design path of the mini-batch, its characteristics, configurations, together with some examples of use with polystyrene and CO2 as the blowing agent.

A method to calculate the annular liquid volume of an immobile string

Immobile string technology is often used to develop the production of multi-layer and thin low-permeability gas reservoirs. This type of reservoir is characterized by low productivities and high pressure drop rates. Simplified ground facilities and control choke technologies are often adopted to effectively reduce the investment. Because gas wells in low permeability gas reservoirs often have low productivities (for instance, the individual well production rates in the Sulige Gas Field range from only 3000 m3/d to 5000 m3/d), a large number of adopted down-hole sensors will result in gas fields that are unable to run properly. The water production data and the bottom pressure become difficult to measure. The casing pressure is controlled by both reservoir pressure and liquid accumulation. To predict liquid volume correctly, the superposed effects of the reservoir pressure and liquid accumulation should be stripped as a priority. Taking the dynamic reserve, production proration and production rate into consideration, we analyzed the casing pressures of dry gas wells. In addition, we quoted a parameter (the production rate in the unit casing pressure drop) to remove the influence of reservoir pressure drop and the output fluctuation “noise” on casing pressure. To strip out the effects of liquid accumulation, we discussed the casing pressure under different liquid accumulation rates. Through the above research, we created a method to calculate the annular liquid volume of an immobile string. This method applied to the Sulige Gas Field very well, and it can also be introduced to other similar gas reservoirs.

Polystyrene Foaming at High Pressure Drop Rates

We studied the foaming of polystyrene with CO2 as the physical blowing agent at large pressure drop rates (PDRs) and at different foaming temperatures, with a novel batch foaming apparatus, capable of reaching PDRs as high as 500 MPa/s (in the underlying literature, the maximum so far achieved is 100 MPa/s). Results show that, at each foaming temperature, the number of nucleated bubbles per unit initial volume (N) linearly increases with PDR in a bilogarithmic scale, with slopes increasing with the temperature. The effect of talc as the nucleating agent was also investigated. Furthermore, a phenomenological model was developed and utilized to predict N at PDRs not experimentally accessible. The approach was validated and a good agreement with the experimental data was obtained.

Development of an extrusion die with rollers for foaming polymers

Ideas concerning the use of a flat slot die with rollers in the technology of extrusion foaming of polymers are developed. Based on the experimental study of low-density polyethylene foaming with isobutane, dependences of the cell density and foam density on the polymer solution viscosity, gap width between rollers, die temperature, and talc concentration have been analyzed. A model is formulated for estimating the intensity of coalescence of supercritical bubbles in an inhomogeneous field of flow velocities. The number density of supercritical nuclei formed in a polymer–gas solution in the limiting case of high pressure drop rate is estimated. The obtained simple estimations allow the results of experiments to be justified on a qualitative level. POLYM. ENG. SCI., 2015. © 2015 Society of Plastics Engineers

A New Promising Nucleating Agent for Polymer Foaming: Applications of Ordered Mesoporous Silica Particles in Polymethyl Methacrylate Supercritical Carbon Dioxide Microcellular Foaming

The introduction of inorganic particles to improve the cell morphology of polymeric foams has been studied for decades. To this end, identifying an ideal nucleating agent and understanding the methodology to control nucleation have always been the focus of this field. In this study, spherical ordered mesoporous silica (OMS) particles were synthesized and applied as a potential nucleating agent in polymethyl methacrylate (PMMA) supercritical carbon dioxide (scCO2) microcellular foaming. These particles were modified with a silane containing fluorine to enhance their affinity with scCO2. For comparison, solid silica (SS) particles with almost similar particle size and surface treatment have also been studied. It was found that both of them could be well dispersed in the PMMA matrix, and exhibited excellent heterogeneous nucleation performance during the foaming process. The addition of a nucleating agent greatly increased the cell density and decreased the average cell diameter, and more importantly, there was no increase in the bulk density. Compared to SS particles, OMS particles showed higher nucleation efficiency. The addition of 5.0 wt % of OMS particles reduced the average cell diameter of PMMA foam from 1.62 to 0.66 μm and increased the cell density from 2.3 × 1011 cells/cm3 to 3.7 × 1012 cells/cm3, while for the composite foams with a similar content of SS particles, the cell diameter and cell density are 1.19 μm and 6.12 × 1011 cells/cm3, respectively. We speculated that the mesoporous structure of OMS particles might trap the CO2 forming gas cavities. The pre-existing gas cavities resulted in a lower nucleation energy barrier. The superior nucleation effect of the OMS particles became more significant when the foaming process was conducted at low foaming temperature, low saturation pressure, and/or high pressure drop rate.

A Microcellular Foaming Simulation System with a High Pressure-Drop Rate

In this paper, we undertook an experimental and theoretical analysis of the pressure-drop behaviors of a batch foaming system with a visualization window that was designed for microcellular foaming simulation. A polystyrene (PS)−CO2 system was used in the experiment and analysis. The maximum pressure-drop rate achievable was 2.5 GPa/s from the designed system. Some experimental simulation results at high pressure-drop rates and at low pressure-drop rates are also discussed. We observed that the application of a higher pressure-drop rate results in a higher cell density (and, thereby, a smaller cell size) for plastic foams. This confirms that the pressure-drop rate is one of the most important parameters to control the cell density of plastic foams. In addition, the results show that the content of the blowing agent (CO2) dissolved into a given polymer has a significant effect on bubble nucleation and growth.

Strategies for Enhancing Expansion in Starch-Based Microcellular Foams Produced by Supercritical Fluid Extrusion

Supercritical fluid extrusion (SCFX) is a recent technological development for production of expanded starch-based foams in which formation of a microcellular structure is achieved by injection of supercritical CO2 into the melt. The high effective diffusivity of CO2 in the porous matrix favors escape of the gas to the environment, reducing the amount available for diffusion into the bubbles, thus posing an important challenge. This study utilized two approaches to address this problem: (a) increasing the nucleation rate and thus the final bubble density in the foam, and (b) reducing the melt temperature. The former was achieved by decreasing the nozzle diameter in order to achieve a higher pressure drop rate as the starch-CO2 melt flows through the nozzle. The second approach was evaluated by introducing a cooling zone prior to the entry of the melt into the nozzle. Bubble density increased more than fourfold when the nozzle radius was decreased from 3.00 to 1.50 mm. A higher bubble density led to a greater barrier or resistance to diffusion of CO2 to the environment, and increased expansion ratio by as much as 160%. Cooling of the melt resulted in a decrease in diffusion coefficient of CO2 in the starch melt, and thus reduced CO2 loss to the environment. The expansion ratio increased by 34% as the melt temperature decreased from 60 to 40°C. The above-mentioned strategies can be useful in controlling and enhancing expansion, which ultimately determines the textural attributes of the expanded food product.

Challenge to Extrusion of Low-Density Microcellular Polycarbonate Foams Using Supercritical Carbon Dioxide

This research investigated the expansion behavior of extruded polycarbonate (PC) foams blown with supercritical (sc) CO2 to achieve low-density microcellular foams. The expansion behavior of PC foam was interpreted by the amount of gas retained in the cell structure in consideration of cell opening, cell-to-cell diffusion, and melt stiffening. The expansion ratio curve plotted against the die temperature showed a typical mountain shape, confirming our previous results. In addition, because the expansion behaviors and foam properties are strongly dependent on the cell density, the cell nucleation behaviors were also thoroughly investigated. Three filamentary dies were designed to investigate the effects of the die geometry. The pressure-drop rate had some effect on the cell density of PC foams as expected, i.e., a higher pressure-drop rate resulted in a higher cell density of PC foams. A high pressure-drop rate was also favorable for a high expansion ratio. By controlling all of these parameters, an expans...

Effect of Filler Size on Cell Nucleation during Foaming Process

This work concerns the effects of the filler size on cell nucleation during the foaming process. The cell density of foams with fillers of two different sizes has been investigated using the foaming process simulator developed previously. It was found that the cell density is strongly affected by the filler size. Foams with a fine filler show a higher cell density at a high saturation pressure but give a lower cell density at a low saturation pressure. At a certain value of the saturation pressure, cell density becomes similar with both fillers. This transition pressure changes with the foaming condition. It goes down with a higher pressure drop rate. The experimental results have been explained with an analysis off iller particle size distribution. The analysis also recommended a way to select filler size if a high cell density is desired in the foaming process.