Combined Effect Of Pressure Research Articles

Combined effect of pressure and temperature for yogurt production.

Fermentation under non-conventional conditions has gained prominence in the last years, due to the possible process improvements. Fermentation under sub-lethal pressures is one of such cases, and may bring novel characteristics and features to fermentative processes and products. In this work, the effect of both pressure (10-100 MPa) and temperature (25-50 °C) on yogurt production fermentation kinetics was studied, as a case-study. Product formation and substrate consumption were evaluated over fermentation time and the profiles were highly dependent on the fermentation conditions used. For instance, the increase of pressure slowed down yogurt fermentation, but fermentative profiles similar to atmospheric pressure (0.1 MPa) were obtained at 10 MPa at almost all temperatures tested. Regarding temperature, higher fermentative rates were achieved at 43 °C for all pressures tested. Moreover, the inhibitory effect of pressure increased when temperature decreased, with complete inhibition of fermentation occurring at 50 MPa for 25-35 °C, contrasting to 43 °C where inhibition occurred only at 100 MPa. Therefore, an antagonistic effect seems to occur, since yogurt fermentation was slowed down by pressure increasing, on one hand, and by temperature decreasing, on the other hand. Additionally, some kinetic parameters were calculated and fermentation at 43 °C presented the best results for yogurt production, with lower fermentation times and higher lactic acid productivities. Interestingly, fermentation at 10 MPa/43 °C presented the optimal conditions, with improved yield and lactic acid production efficiency, when compared to fermentation at 0.1 MPa (efficiency of 75% at 10 MPa, against 40% at 0.1 MPa). As the authors are aware, this work gives the first insights about the simultaneous effect of pressure and temperature variation on a microbial fermentation process, which can be combined to modulate the metabolic activity of microorganisms during fermentation in order to improve the fermentative yields and productivities of the desired product.

Unstable crack growth in hydraulic fracturing: The combined effects of pressure and shear stress for a power-law fluid

The underlying mechanisms of hydraulic fracturing remain elusive, and the optimization of the related processes for rocks of low permeability is challenging. There exists local crack closure induced by shear stress, which is one of the crack instabilities for a straight crack. In this study, we develop a full-stress model, which includes the combined effects of hydrodynamic pressure and shear stress on the crack surfaces. The hydrodynamic pressure is a driving force, while the shear stress is a resistance force. A novel criterion for crack propagation is derived based on the asymptotic solution of shear stress. The asymptotic solution, which is derived using perturbation analysis in the toughness-dominant regime, reveals the existence of the crack-closure phenomenon and shear-stress-dominant regime. The necessary condition for the crack closure is obtained according to numerical calculations. An energy analysis is conducted to discuss the difference between the shear-stress-dominant and the viscosity-dominant regimes. The existence of the crack closure is shown to be independent of two assumptions, lubrication theory and no-fluid-lag zone. The results presented in this study are useful for the simulation and design of hydraulic fracturing.

Single-crystal elasticity of MgAl2O4-spinel up to 10.9 GPa and 1000 K: Implication for the velocity structure of the top upper mantle

The combined effect of pressure and temperature on the single-crystal elasticity of MgAl2O4-spinel has been studied using Brillouin scattering and X-ray diffraction up to 10.9 GPa and 1000 K in externally-heated diamond anvil cells. The obtained single-crystal elastic moduli of MgAl2O4-spinel at ambient conditions are consistent with literature values and follow a linear increase with pressure at high temperatures. More importantly, the pressure dependence of the elastic moduli at high temperatures is much smaller than that at 300 K, indicating a stronger temperature effect on the elastic moduli of MgAl2O4-spinel at high pressures. Our new results were applied to model the sound velocity of MgAl2O4-spinel at relevant pressure and temperature conditions of the top upper mantle, showing that MgAl2O4-spinel has the greatest velocity and the VP/VS ratio among major mantle minerals. We further modeled the velocity of spinel-peridotite at the top upper mantle. Varying the composition of spinel-peridotite can lead to up to 2.1% variation in VP and 1.3% in VS. The top upper mantle with greater VP and VS should contain more olivine and spinel but less orthopyroxene. The velocity of the top upper mantle is thus strongly correlated with the composition of the region. Our results are thus important in understanding the composition and velocity of the top upper mantle.

Swage and hydraulic autofrettage impact on fracture endurance and fatigue life of an internally cracked smooth gun barrel Part II – The combined effect of pressure and overstraining

The distributions of KIA (the stress intensity factor (SIF) due to autofrettage) along the front of a single inner radial semi-elliptical crack emanating from the bore of an autofrettaged smooth gun barrel were calculated for a large number of crack configurations in Part I of this paper. In order to assess the combined effect of overstraining and pressurizing the barrel, values of KIP, the SIF caused by internal pressure, and those of KIN, the combined SIF, are evaluated. The 3-D analysis is performed using the finite element (FE) method employing singular elements along the crack front. The novel realistic overstrain residual stress fields, incorporating the Bauschinger effect, for the two types of autofrettage presented in Perl and Saley (2016) are applied to the barrel. Hill's (Hill, 1950) residual stress field (RSF) is also applied for comparison reasons. The RSFs for Swage and Hydraulic autofrettage as well as Hill's solution are simulated in the FE analysis using equivalent temperature fields. Values of KIP and KIN=KIP+KIA are evaluated for a typical barrel of radii ratio R0/Ri=2, a wide range of crack depth to wall-thickness ratios (a/t=0.005–0.1), various crack ellipticities (a/c=0.2–1.0), and five levels of Swage, Hydraulic and Hill's autofrettage (ε=40%, 60%, 70%, 80%, and 100%). In total, 375 different 3-D cases are analyzed. A detailed study of the influence of the above parameters on the prevailing SIF is conducted. The results clearly indicate the favorable effect of all three types of autofrettage in enhancing the fatigue life of the barrel. However, the magnitude of such life extension depends on the type of autofrettage employed. Among the two realistic overstrain processes, Swage autofrettage is found to be considerably superior to Hydraulic autofrettage in prolonging the barrel's fatigue life. Hill's autofrettage is far from being realistic, overestimating the magnitude of the RSF, and, thus, exaggerating the barrel's fatigue life. Finally, the results highlight the importance of properly accounting for the Bauschinger effect including re-yielding, as well as the significance of the three dimensional analysis herein performed.

The effects of pressure and temperature on the exchange energy of a parabolic quantum dot under a magnetic field

The combined effects of pressure and temperature on the energy levels of a parabolic GaAs quantum dot under a magnetic field have been studied. The exact diagonalization method was used to solve the two-electron quantum dot Hamiltonian and to obtain the eigenenergies. In addition, we investigated the effects of pressure and temperature on the singlet-triplet exchange energy (J=ET−Es) of the quantum dot as a function of a magnetic field. The magnetic field-parabolic confinement (ωc−ω0) phase diagram of the quantum dot was calculated. The comparisons show that our results are in very good agreement with the previously published works.

Constitutive modeling and experimental calibration of pressure effect for polyurea based on free volume concept

Abstract The combined effect of pressure and temperature on the mechanical behavior of polyurea is characterized and integrated into a constitutive model based on Williams-Landel-Ferry (WLF) equation. An increase in pressure is related to a decrease in temperature, both pressure and temperature affecting the polymer's molecular free volume and thereby introducing a pressure-dependent term into the WLF equation. The model is derived based on Fillers and Tschoegl's original work, regarding the free volume as a state variable. The model provides a closed-form expression for the time scale shift factor for equivalent temperature in terms of temperature and pressure and its three-dimensional surface representation. The prediction of the present model agrees well with pressure shift factor data obtained from confined compression tests of polyurea, reported elsewhere, confirming our constitutive model and its experimental calibration procedure. A simplified model of the pressure effect is also developed which yields good approximate results.

Optimisation of the Supercritical Fluid Extraction of Antioxidants from Broccoli Leaves

This work presents the application of supercritical fluid extraction (SFE), an environmentally friendly methodology, to obtain broccoli leaves extracts with a high antioxidant activity. The following processing variables: pressure, temperature, percentage of ethanol and dynamic extraction time were optimised by means of a central composite design, combined with response surface methodology. The optimised conditions were applied to the extraction of broccoli leaves from different cultivars (Naxos, Nubia, Marathon, Parthenon and Viola). The optimal values of the extraction variables were 150 bars, 35 °C, 20 % ethanol and 10 min of dynamic extraction time. Percentage of ethanol and the combined effect of pressure and time were the factors that affected the extraction the most. The results obtained from different cultivars showed that the Naxos variety provided the extracts with the highest antioxidant activity and total phenolic content; moreover, DPPH (EC 50) values were higher than those previously reported for water extracts. The extracts were recovered in a small quantity of ethanol that could be easily eliminated, obtaining a residue free of contaminants.

Sinterability Enhancement by Collapse of Mesoporous Structure of SBA‐15 in Fabrication of Highly Transparent Silica Glass

Highly transparent silica glass was prepared from mesoporous silica SBA‐15 powders at low temperature using Spark Plasma Sintering. It was found that the combined effect of pressure and temperature resulted in collapse of porous structure of SBA‐15 and transformation to transparent glass. A sinterability enhancement mechanism involving generation of incremental surface area from pore collapse during sintering process was proposed to interpret the fully densification at low temperature.

The combined effects of pressure and cementation on 4D seismic data

Time-lapse seismology has proven to be a useful method for monitoring reservoir fluid flow, identifying unproduced hydrocarbons and injected fluids, and improving overall reservoir management decisions. The large magnitudes of observed time-lapse seismic anomalies associated with strong pore pressure increases are sometimes not explainable by velocity-pressure relationships determined by fitting elastic theory to core data. This can lead to difficulties in interpreting time-lapse seismic data in terms of physically realizable changes in reservoir properties during injection. It is commonly assumed that certain geologic properties remain constant during fluid production/injection, including rock porosity and grain cementation. We have developed a new nonelastic method based on rock physics diagnostics to describe the pressure sensitivity of rock properties that includes changes in the grain contact cement, and we applied the method to a 4D seismic data example from offshore Australia. We found that water injection at high pore pressure may mechanically weaken the poorly consolidated reservoir sands in a nonelastic manner, allowing us to explain observed 4D seismic signals that are larger than can be predicted by elastic theory fits to the core data. A comparison of our new model with the observed 4D seismic response around a large water injector suggested a significant mechanical weakening of the reservoir rock, consistent with a decrease in the effective grain contact cement from 2.5% at the time/pressure of the preinjection baseline survey, to 0.75% at the time/pressure of the monitor survey. This approach may enable more accurate interpretations and future predictions of the 4D signal for subsequent monitor surveys and improve 4D feasibility and interpretation studies in other reservoirs with geomechanically similar rocks.

Pressure-magnetic field induced phase transformation in Ni46Mn41In13 Heusler alloy

The effect of hydrostatic pressure and magnetic field on the magnetic properties and phase transformation in Ni46Mn41In13 Heusler alloy was investigated. Pressure (P)-magnetic field (H)-temperature (T) phase diagram has been constructed from experimental results. In the P–T contour of the phase diagram, the slope of the austenite-martensite phase boundary line appears positive (dT/dP > 0), while it appears negative (dT/dH < 0) in the H–T contour. The results revealed that pressure and magnetic field have opposite effect on phase stabilization. The combined effect of pressure and magnetic field on martensitic transition has led to two important findings: (i) pressure dependent shift of austenite start temperature (As) is higher when larger field is applied, and (ii) field dependent shift of As is lowered when a higher pressure is applied. The pressure and magnetic field dependent shift observed in the martensitic transformation has been explained on the basis of thermodynamic calculations. Curie temperature of the phases was found to increase with pressure at a rate of 0.6 K/kbar.

Combined effect of pressure and geometric imperfection on buckling of stressed thin films on substrates

This paper deals with the combined effect of pressure and geometric imperfection on buckling of stressed thin films on a semi-infinite rigid substrate. Analytical approximate solutions are proposed by using the total potential energy of the system and the Rayleigh–Ritz’s method, and their stabilities are also determined. The present analytical approximate solutions agree very well with the numerical solutions obtained via the improved shooting method. The effect of pressure mismatch together with imperfection on the critical stress (above which the film buckles) and on the film-center deflection is characterized. It is found that, compared with the classical case of the Euler column buckling, the equilibrium solutions and critical stress of the film are strongly dependent on the linear combination of the pressure mismatch and imperfection amplitude.

Optical properties of parabolic quantum dots with dressed impurity: Combined effects of pressure, temperature and laser intensity

In this paper simultaneous effects of pressure, temperature and laser radiation on the optical absorption coefficient and refractive index of a spherical quantum dot with parabolic confinement and dressed impurity are studied. By means of matrix diagonalization technique, energy eigenvalues and functions are evaluated and used to find the optical properties of the system via density operator method. It is shown that linear and nonlinear optical properties strongly depend on pressure, temperature and dressing laser intensity. The interesting point is that the influence of laser radiation depends on pressure and temperature.

Estimation of the effects of longitudinal temperature gradients caused by frictional heating on the solute retention using fully porous and superficially porous sub-2 μm materials

In this study, the retention changes induced by frictional heating were evaluated for model small compounds (150–190Da) and a small protein, namely insulin (5.7kDa). For this purpose, the effect of longitudinal temperature gradient caused by frictional heating was experimentally dissociated from the combined effect of pressure and frictional heating, by working either in constant and variable inlet pressure modes. Various columns packed with core–shell and fully porous sub-2μm particles were tested. It appears that frictional heating was less pronounced on the column packed with smallest core–shell particles (1.3μm), compared to the ones packed with core–shell and fully porous particles of 1.7–1.8μm. This observation was attributed to the low permeability of this material and the fact that it can only be employed in a restricted flow rate range, thus limiting the generated heat power. In addition, the thermal conductivity of the solid silica core of superficially porous particles (1.4W/m/K) is known to be much larger than that of fully porous silica. Then, the heat dissipation is improved. However, if systems with higher pressure capability would be available and the mechanical stability of 1.3μm core–shell material was extended to e.g. 2000bar, the retention would be more severely impacted. At 2000bar, ∼4.4W heat power and +30°C increase at column outlet temperature is expected. Last but not least, when analyzing large molecules, the impact of pressure overcomes the frictional heating effects. This was demonstrated in this study with insulin (∼5.7kDa).

Determination, analysis and prediction of the volumetric behavior of milk at high pressure

High pressure preservation technologies are consolidating in the food industry as an interesting alternative to traditional thermal processes. Process modeling contributes to its progress and requires the input of food properties like density for calculations. The dependency on pressure of these properties is indispensable but it is rarely available in the literature. The sector of dairy products is an important target for the development of novel foods by high pressure treatments (both high hydrostatic pressure processing and ultra-high pressure homogenization). Thus, the main objective of this research was to characterize the volumetric properties of raw whole milk and skim milk. A variable-volume piezometer with a solid-piston volumeter was employed for this purpose. Density, specific volume, isothermal compressibility and thermal expansion coefficient were determined between 0 and 60°C under pressures up to 350MPa; at atmospheric pressure, measurements cover temperatures up to 90°C. Results show that milk solutes and fats, although present in low quantities in milk compared to water, have an influence which is worthy of consideration on milk volumetric properties. Irregularities appear from 200MPa in the dependencies on temperature of the studied milk properties. From a composition-based model, it is highlighted that milk solutes' specific volume behavior is inverted around 55°C and that milk fats' compressibility goes through a maximum around 30°C. The composition-based model is further developped for the calculation of milk properties as a function of pressure at different temperatures; prediction errors are below 2%. Useful data and equations for high pressure processing simulation are provided together with an original view on the combined effects of pressure and temperature on milk solutes and fats.

The combined effect of pressure and temperature on the impurity binding energy in a cubic quantum dot using the FEM simulation

Using the finite element method, the binding energies of a hydrogenic shallow donor impurity are investigated in a cubic GaAs/Ga1−xAlxAs quantum dot structure with realistic potential barrier height under the combined effect of hydrostatic pressure and temperature in the framework of the effective mass approximation. In the calculations, we have taken into account the electronic effective mass, dielectric constant, and conduction band offset between the dot and barriers varying with pressure and temperature. The results we have obtained show that the donor binding energy varies with the dot size, the confining potential, the position of impurity, the hydrostatic pressure and temperature. It is also found that the donor binding energy increases linearly with the pressure in direct gap regime and its variation is larger for narrower dots only and drops slightly with the temperature. A good agreement is obtained with the existing literature values.

Combined Effect of Pressure and Temperature on the Viscous Behaviour of All-Oil Drilling Fluids

The overall objective of this research was to study the combined influence of pressure and temperature on the complex viscous behaviour of two oil-based drilling fluids. The oil-based fluids were formulated by dispersing selected organobentonites in mineral oil, using a high-shear mixer, at room temperature. Drilling fluid viscous flow characterization was performed with a controlled-stress rheometer, using both conventional coaxial cylinder and non-conventional geometries for High Pressure/High Temperature (HPHT) measurements. The rheological data obtained confirm that a helical ribbon geometry is a very useful tool to characterise the complex viscous flow behaviour of these fluids under extreme conditions.The different viscous flow behaviours encountered for both all-oil drilling fluids, as a function of temperature, are related to changes in polymer-oil pair solvency and oil viscosity. Hence, the resulting structures have been principally attributed to changes in the effective volume fraction of disperse phase due to thermally induced processes. Bingham’s and Herschel-Bulkley’s models describe the rheological properties of these drilling fluids, at different pressures and temperatures, fairly well. It was found that Herschel-Bulkley’s model fits much better B34-based oil drilling fluid viscous flow behaviour under HPHT conditions.Yield stress values increase linearly with pressure in the range of temperature studied. The pressure influence on yielding behaviour has been associated with the compression effect of different resulting organoclay microstructures. A factorial WLF-Barus model fitted the combined effect of temperature and pressure on the plastic viscosity of both drilling fluids fairly well, being this effect mainly influenced by the piezo-viscous properties of the continuous phase.

Direct observation by in situ transmission electron microscopy of the behaviour of IF‐MoS2 nanoparticles during sliding tests: influence of the crystal structure

ABSTRACTDirect observation of the behaviour of individual inorganic fullerenes (IF)‐MoS2 nanoparticles in a sliding interface is essential for the understanding of the influence of the intrinsic characteristics of the nanoparticles on their lubrication mechanisms, when they are used as additives in lubricant oil. In this work, in situ transmission electron microscopy sliding tests were performed on two different types of MoS2 nanoparticles synthesised by two different methods. It is shown that the IF‐MoS2 nanoparticles having perfect structure with a high crystalline order and without defects are able to roll and to slide under the combined effect of pressure and shear stress, whereas the IF‐MoS2 nanoparticles containing many defects exfoliate immediately in the same conditions to deliver MoS2 layers covering the mating surfaces. A link between these results, the lubrication mechanisms of the nanoparticles and their tribological properties at the macro‐scale was established, proving that the lubrication mechanisms of fullerenes depend on their intrinsic characteristics. Copyright © 2013 John Wiley & Sons, Ltd.

Role of the plastic flow of the matrix on yielding and void evolution of porous solids: Comparison between the theoretical response of porous solids with Tresca and von Mises matrices

In this paper, it is shown that yielding and void evolution in a porous metallic material is strongly influenced by the particularities of the plastic flow of the matrix. This is demonstrated by comparing the effective response of porous solids for which the matrix is described by Tresca and von Mises yield criterion, respectively. The effective response of the porous solid is calculated analytically using rigorous limit analysis theorems and upscaling techniques. Analysis is conducted for both tensile and compressive axisymmetric loading scenarios and spherical void geometry. For the first time it is demonstrated that if the matrix plastic response is governed by Tresca yield criterion, the overall response is softer, the combined effects of pressure and the third-invariant on yielding being much stronger than in a porous solid with von Mises matrix. Furthermore, the rate of void growth or collapse is much faster in a porous solid with Tresca matrix.

The effect of pressure and oxygen concentration on the combustion of PMMA

An experimental study of the flammability properties of PMMA at low pressures and oxygen concentrations was performed. The work was motivated by the importance of these effects on fire safety in the aviation industry. Measurements were obtained in a mass loss calorimeter inside a large 10m3 pressure vessel capable of reaching pressures as low as 0.1atm. The PMMA flammability was characterized by measuring the burning rate and the time to ignition of small test samples. These were ignited and burned under different external heat fluxes, total pressures and oxygen concentrations. The combined effects of pressure and oxygen concentration on the burning rate, combustion flow field, and ignition were evaluated. Results showed that at low pressure, the burning rate was less intense with a decrease in the mass loss rate. However, the reduction in pressure caused a shortened ignition delay time. Experimental measurements were compared with a simple analytical model showing good agreement. The results also show how pressure and oxygen concentration contributed to the heat transfer from the flame. The model revealed that a single function in oxygen and pressure could account for both flame radiative and convective effects. As a result, a power law fit was obtained for the relation of the combined pressure and oxygen effect on the burning rate. This correlation shows a good agreement with the measurements and predicts the burning rate behavior for the full range of pressure and oxygen tests.

Anti-wear Chemistry of ZDDP and Calcium Borate Nano-additive. Coupling Experiments, Chemical Hardness Predictions, and MD Calculations

Zinc dialkyl dithiophosphate (ZDDP) is an anti-wear additive for steel surfaces currently used in engine oils. Its anti-wear performance (against abrasion) is due to tribochemical reaction of zinc polyphosphate with abrasive metal oxides nanoparticles, under the combined effect of pressure and shear. However, phosphorous and sulfur are nocuous for environmental issues. Borates are possible candidates to replace phosphates in engine oils. Friction reduction with borates is found to be better than ZDDP but the anti-wear efficiency of borates is lower. In this work, we show how chemical hardness model and computer simulation can explain these different behaviors. Also we show that molecular dynamics is able to predict accurately behavior of mixtures of phosphates and borate. Results show that mixtures of additives with a P:B ratio slightly above unity can be a good compromise to have both good tribological performance and low content of phosphorous and sulfur in the lubricant.