Elevated Pressure Conditions Research Articles

Analysis of NOX Formation in an Axially Staged Combustion System at Elevated Pressure Conditions

The objective of this investigation was to study the effect of axially staged injection of methane in the vitiated air cross flow in a two stage combustion chamber on the formation of NOX for different momentum flux ratios. The primary cylindrical combustor equipped with a low swirl air blast nozzle operating with Jet-A liquid fuel generates vitiated air in the temperature range of 1473–1673 K at pressures of 5–8 bars. A methane injector was flush mounted to the inner surface of the secondary combustor at an angle of 30 deg. Oil cooled movable and static gas probes were used to collect the gas samples. The mole fractions of NO, NO2, CO, CO2, and O2 in the collected exhaust gas samples were measured using gas analyzers. For all the investigated operating conditions, the change in the mole fraction of NOX due to the injection of methane (ΔNOX) corrected to 15% O2 and measured in dry mode was less than 15 ppm. The mole fraction of ΔNOX increased with an increase in mass flow rate of methane and it was not affected by a change in the momentum flux ratio. The penetration depth of the methane jet was estimated from the profiles of mole fraction of O2 obtained from the samples collected using the movable gas probe. For the investigated momentum flux ratios, the penetration depth observed was 15 mm at 5 bars and 5 mm at 6.5 and 8 bars. The results obtained from the simulations of the secondary combustor using a RANS turbulence model were also presented. Reaction modeling of the jet flame present in a vitiated air cross flow posed a significant challenge as it was embedded in a high turbulent flow and burns in partial premixed mode. The applicability of two different reaction models has been investigated. The first approach employed a combination of the eddy dissipation and the finite rate chemistry models to determine the reaction rate, while the presumed JPDF model was used in the further investigations. Predictions were in closer agreement to the measurements while employing the presumed JPDF model. This model was also able to predict some key features of the flow such as the change of penetration depth with the pressure.

QUANTIFICATION OF TRANSIENT FUEL FILMS UNDER ELEVATED AMBIENT PRESSURE ENVIRONMENTS

Impingement of fuel sprays on solid surfaces is of interest in a wide range of industrial applications including automotive, gas turbines, and process and hazard analysis. Consequently, accurate quantification of fuel films is necessary for model validation. In this study, the transient liquid fuel film formed as a result of spray impingement of a direct injection spray, relevant to practical engine operation, is quantified for the first time. A non-intrusive technique utilizing total internal-reflection-laser-induced fluorescence (TIR-LIF) is utilized to quantify the spatial and temporal distribution of the film thickness. The LIF technique is based on the principle that the intensity of the fluorescent signal from a fluorescent tracer is proportional to the film thickness. Application of the technique to elevated pressure conditions is far from trivial since the fluorescence from the dopant can be adversely affected. This technique utilizes TIR to control the propagation of a laser source in order to target the liquid fuel film only and not the airborne droplets, which had been shown previously to induce significant error. A binary mixture of 10% 3-pentanone in iso-octane is used as a substitute for gasoline, and a new linear calibration function is derived for the elevated pressure considered. Observations of the transient development of the liquid fuel films include details of fine surface waves. Significant quantitative differences are found between the TIR-LIF results at 0.1 and 0.4 MPa ambient pressures, and the results are compared and discussed in relation to pre-impingement spray characteristics.

Air Flow Modulation for Refined Control of the Combustion Dynamics Using a Novel Actuator

A specific actuator able to modulate the air feed of a gas a burner at a given frequency and amplitude is presented. The Combustion Department at the Institute for Thermal Turbomachinery and Machine Dynamics at the Graz University of Technology has experience on the study of combustion instabilities in gas turbines using a flow excitor. The stability of an industrial burner is tested at elevated pressure and temperature conditions in the frame of the NEWAC project. For practical matters of operation among which the possibility to induce progressively a perturbation when the flame conditions are all set, the need was expressed to design, construct and validate a flexible actuator able to set an air flow modulation at a given frequency and at a desired amplitude level, with the possibility during operation to let these two factors vary in a given range independently from each other. This device should operate within the 0–1 kHz range and 0%–20% amplitude range at steady-state, during transients, or follow a specific time sequence. It should be robust and sustain elevated pressures. The objective is to bring a perturbation in the flow to which the combustor will respond, or not. For elevated levels of pulsation, it can simulate the presence of vortex-driven combustion instabilities. It can also act as a real-time actuator able to respond in frequency and in phase to actively damp a “natural” combustion instability. Other issues are a better and quicker mixing due to the enhanced turbulence level, and pushing forward the blow out limits at lean conditions with controlled injection dynamics. The basic construction is the one of a siren, with an elevated pressure side where the air is throttled, and a low pressure outlet where the resulting sonic jet is sheared by a rotating wheel. A mechanism allows to let vary the surface of interaction between the wheel and the jet. Two electromotors driven by Labview set both frequency and amplitude levels. This contribution describes the actuator’s principles, design, operation range and the results of the characterization campaign.

Capillary-Trapping Capacity of Sandstones and Sandpacks

This paper (SPE 120960) was accepted for presentation at the EUROPEC/EAGE Conference and Exhibition, Amsterdam, 8–11 June 2009, and revised for publication. Original manuscript received for review 23 February 2009. Revised manuscript received for review 3 December 2010. Paper peer approved 15 April 2011. Summary We quantify the influence of the initial nonwetting-phase saturation and porosity on the residual nonwetting-phase saturation using data in the literature and our own experimental results on sandpacks and consolidated sandstones. These experiments were conducted at ambient or elevated pressure and temperature (ETP) conditions. The principal application of this work is for carbon capture and storage (CCS) where capillary trapping is a rapid and effective way to render the injected CO2 immobile, guaranteeing safe storage. We introduce the concept of capillary-trapping capacity (Ctrap) which is the product of residual saturation and porosity that represents the fraction of the rock volume that can be occupied by a trapped nonwetting phase. We show that the measured trapping capacity reaches a maximum of approximately 11% for porosities of 22%, which suggests an optimal porosity for CO2 storage.

In this issue

AbstractScaling up production of plasmid DNA vaccinesLara et al., Eng. Life Sci. 2011, 11, 382–386.DNA vaccination is a propitious alternative therapeutic strategy. However, mass production of DNA vaccines for the demanding commercial market has not been fully explored. In this issue, Alvaro Lara and collaborators from the National Autonomous University of Mexico and the AVT Biochemical Engineering Department (Aachen, Germany) set out to develop scale‐up strategies for the production of high‐quality plasmid DNA. Escherichia coli expressing the S region of the hepatitis B virus was cultured at high density in fed‐batch mode at small scale (1 L) using oxygen‐enriched air, and at pilot scale (50 L) using a pressurized bioreactor. Cultivation parameters and DNA topology were similar under high oxygen or elevated pressure conditions, indicating that pressurized bioreactors can be used for scaling up DNA vaccine production……………382.http://dx.doi.org/10.1002/elsc.201000104magnified imageAutomated malaria vaccine productionMartens et al., Eng. Life Sci. 2011, 11, 429–435.Pichia pastoris tirelessly yields high protein production levels, but expression of fusion proteins with multiple units is often achieved at the expense of proteolytic cleavage. In this issue, Reiner Luttmann and his colleagues from the Hamburg University of Applied Sciences (Germany) and the Biomedical Primate Research Center (The Netherlands) describe a self‐engineered fully automated system to efficiently produce anti‐malarial composite vaccines. P. pastoris expressing a fusion of two of the Plasmodium falciparium's membrane proteins were subjected to a sequential integrated bioprocess. This strategy offers stable culturing conditions, as evidenced by constant, elevated expression of high‐quality proteins.……………429http://dx.doi.org/10.1002/elsc.201000163magnified imageA single‐use bioreactor on your benchKaiser et al., Eng. Life Sci. 2011, 11, 359–368.Disposable culture vessels are easy‐to‐handle and cost‐effective systems with no sterilization requirements. However, are these bench‐top bioreactors able to meet the performance of their conventional, reusable counterparts? In this issue, Stephan Kaiser and colleagues from the Institute of Biotechnology (Wädenswil, Switzerland) answer this question by describing the engineering features of the recently marketed Mobius® CellReady 3L. Based on computational modeling, flow patterns, and oxygen mass transfer analyses, the authors show that stirred single‐use bioreactors provide low mechanical stress conditions with adequate oxygen transfer. These findings establish single‐use bioreactors as a valid alternative to conventional bioreactors at bench‐scale.……………359http://dx.doi.org/10.1002/elsc.201000171magnified image

Surgical and histopathological effects of topical Ankaferd® hemostat on major arterial vessel injury related to elevated intra-arterial blood pressure.

The aim of this study was to assess the surgical and histopathological hemostatic effects of topical Ankaferd blood stopper (ABS) on major arterial vessel injury related to elevated intra-arterial blood pressure in an experimental rabbit model. The study included 14 New Zealand rabbits. ABS was used to treat femoral artery puncture on 1 side in each animal and the other untreated side served as the control. Likewise, for abdominal aortic puncture, only 50% of the aortic injuries received topical liquid ABS and the others did not (control). The experiment was performed under conditions of normal arterial blood pressure and was repeated with a 50% increase in blood pressure. Histopathological analysis was performed in all of the studied animals. Mean bleeding time in the control femoral arteries was 105.0±18.3 s, versus 51.4±9.8 s (p<0.05) in those treated with ABS. Mean blood loss from the punctured control femoral arteries was 5.0±1.5 mg and 1.6±0.4 mg from those treated with ABS (p<0.05). Histopathological examination of the damaged arterial structures showed that ABS induced red blood cell aggregates. ABS administered to experimental major arterial vessel injury reduced both bleeding time and blood loss under conditions of normal and elevated intra-arterial blood pressure. ABS-induced erythroid aggregation was prominent at the vascular tissue level. These findings will inform the design of future experimental and clinical studies on the anti-bleeding and vascular repairing effects of the novel hemostatic agent ABS.

Reprint of: Mechanisms of retinal ganglion cell injury and defense in glaucoma

Glaucoma is a disease in which retinal ganglion cells (RGCs) die leading ultimately to blindness. Over the past decade and a half, information has begun to emerge regarding specific molecular responses of the retina to conditions of elevated intraocular pressure (IOP). It is now clear that the state of the RGC in glaucoma depends on a balance of pro-survival and pro-death pathways in the retina and details of these responses are still being worked out. In this review, we will discuss the evidence supporting the involvement of specific apoptotic cascades as well as the insults that trigger RGC apoptosis. In addition, we will present evidence supporting the existence of endogenous protective mechanisms as well as exogenous neuroprotective strategies.

Model Verification of Mist/Steam Cooling With Jet Impingement Onto a Concave Surface and Prediction at Elevated Operating Conditions

Internal mist/steam blade cooling technology is proposed for advanced gas turbine systems that use the closed-loop steam cooling scheme. Previous experiments on mist/steam heat transfer with a 2D slot jet impingement onto a concave surface showed cooling enhancement of up to 200% at the stagnation point by injecting approximately 0.5% of mist under low temperature and pressure laboratory conditions. Realizing the difficulty in conducting experiments at elevated pressure and temperature working conditions, computational fluid dynamics (CFD) simulation becomes an opted approach to predict the potential applicability of the mist/steam cooling technique at real GT operating conditions. In this study, the CFD model is first validated within 3% and 6% deviations from experimental results for the flows of steam-only and mist/steam flow cases, respectively. The validated CFD model is then used to simulate a row of multiple holes impinging jet onto a concave surface under elevated pressure, temperature, and Reynolds number conditions. The predicted results show an off-center cooling enhancement with a local maximum of 100% at s/d=2 and an average cooling enhancement of about 50%. The mist cooling scheme is predicted to work better on a concave surface than on the flat surface. The extent of wall jet and the size of 3D recirculation zones are identified as a major influencing parameter on the curvature effect on mist cooling performance. The mist enhancement from a slot jet is more pronounced than a row of round jets. The effects of wall heat flux and mist ratio on mist cooling performance are also investigated in this study.

Deoxygenation of Methanol over ZSM‐5 in a High‐Pressure Catalytic Pyroprobe

AbstractDeoxygenation is a critical step in making hydrocarbon‐rich biofuels from biomass constituents. Although the thermal effects of oxygenate aromatization have been widely reported, the effect of pressure on this critical reaction has not yet been closely investigated, one primary reason being the unavailability of a reactor that can pyrolyze oxygenates, especially those in solid form, under pressurized conditions. Here, the first of a series of studies on how oxygenates behave when catalytically pyrolyzed under elevated pressure and temperature conditions is reported. Methanol, the simplest alcohol, was selected as the candidate to study the chemical phenomena that occur under pressurized catalytic pyrolysis. The reactions were carried out over the shape‐selective catalyst ZSM‐5 (SiO2/Al2O3 = 30) under varying pressure (0 to 2.0684 MPa (300 psi) in 0.3447 MPa (50 psi) increments) and temperature (500 to 800 °C in 50 °C increments) conditions. Benzene, toluene, ethyl benzene, and xylenes (BTEX) were analyzed as the deoxygenated products of the reaction. The results indicate that the reactor pressure significantly affects deoxygenated product composition.

Reactions of NO2 with BaO/Pt(111) model catalysts: the effects of BaO film thickness and NO2 pressure on the formation of Ba(NOx)2 species

The adsorption and reaction of NO(2) on BaO (<1, ∼3, and >20 monolayer equivalent (MLE))/Pt(111) model systems were studied with temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and infrared reflection absorption spectroscopy (IRAS) under ultra-high vacuum (UHV) as well as elevated pressure conditions. NO(2) reacts with sub-monolayer BaO (<1 MLE) to form nitrites only, whereas the reaction of NO(2) with BaO (∼3 MLE)/Pt(111) produces mainly nitrites and a small amount of nitrates under UHV conditions (P(NO(2))≈ 1.0 × 10(-9) Torr) at 300 K. In contrast, a thick BaO (>20 MLE) layer on Pt(111) reacts with NO(2) to form nitrite-nitrate ion pairs under the same conditions. At elevated NO(2) pressures (≥1.0 × 10(-5) Torr), however, BaO layers at all these three coverages convert to amorphous barium nitrates at 300 K. Upon annealing to 500 K, these amorphous barium nitrate layers transform into crystalline phases. The thermal decomposition of the thus-formed Ba(NO(x))(2) species is also influenced by the coverage of BaO on the Pt(111) substrate: at low BaO coverages, these species decompose at significantly lower temperatures in comparison with those formed on thick BaO films due to the presence of a Ba(NO(x))(2)/Pt interface where the decomposition can proceed at lower temperatures. However, the thermal decomposition of the thick Ba(NO(3))(2) films follows that of bulk nitrates. Results obtained from these BaO/Pt(111) model systems under UHV and elevated pressure conditions clearly demonstrate that both the BaO film thickness and the applied NO(2) pressure are critical in the Ba(NO(x))(2) formation and subsequent thermal decomposition processes.

Gene Profiling of Aortic Valve Interstitial Cells under Elevated Pressure Conditions: Modulation of Inflammatory Gene Networks

The study aimed to identify mechanosensitive pathways and gene networks that are stimulated by elevated cyclic pressure in aortic valve interstitial cells (VICs) and lead to detrimental tissue remodeling and/or pathogenesis. Porcine aortic valve leaflets were exposed to cyclic pressures of 80 or 120 mmHg, corresponding to diastolic transvalvular pressure in normal and hypertensive conditions, respectively. Linear, two-cycle amplification of total RNA, followed by microarray was performed for transcriptome analysis (with qRT-PCR validation). A combination of systems biology modeling and pathway analysis identified novel genes and molecular mechanisms underlying the biological response of VICs to elevated pressure. 56 gene transcripts related to inflammatory response mechanisms were differentially expressed. TNF-α, IL-1α, and IL-1β were key cytokines identified from the gene network model. Also of interest was the discovery that pentraxin 3 (PTX3) was significantly upregulated under elevated pressure conditions (41-fold change). In conclusion, a gene network model showing differentially expressed inflammatory genes and their interactions in VICs exposed to elevated pressure has been developed. This system overview has detected key molecules that could be targeted for pharmacotherapy of aortic stenosis in hypertensive patients.

Effects of Pressure on Prompt NOX Formation in CH4/Air Lean Premixed Flame

Since lean premixed combustion in gas turbine combustors undergoes in elevated pressure condition, it is important to know NOX formation characteristics under elevated pressure. Generally, effects of pressure on NOX formation characteristics are evaluated by using pressure coefficient on conventional systems. However, the value of pressure coefficient distributes widely from -0.2 to 0.5. This difference in the pressure coefficient stems from differences in experimental conditions and formation processes of NOX. As a result, effects of pressure on different NOX formation mechanisms have not been elucidated yet because of difficulties of temperature control of combustion region. In this study, to clarify the effects of pressure on the prompt NOX formation process is set as the objective. Experimental measurements and numerical simulation with detailed elementary reactions are conducted. The temperature controllable premixed flat flame burner is fabricated in the elevated pressure combustion chamber, and measurement of NOX concentration is conducted in the chamber. Both the experimental and numerical results clearly show that the pressure does not affect to the prompt NOX formation.

F121 高温高圧下におけるエタノール予混合火炎の燃焼メカニズムに関する研究(OS-9:燃焼の最近の進展(3))

Laminar burning velocities for ethanol/air premixed flames were measured in elevated pressure and elevated temperature conditions by using the local angle method which employs particle tracking velocimetry (PTV) to Bunsen flames. Experimental data of laminar burning velocities were compared with numerical results calculated using detailed chemical reaction mechanisms for ethanol oxidation, i.e., the mechanism by Marinov and the mechanism by Saxena and Williams, and the validation of the existing chemical reaction mechanisms was performed under high pressure and high temperature conditions.

Controlled cargo handling with piston fluid for pressurized liquid CO2 carrier

Abstract This study proposed a concept of the cargo handling system to load the pressurized liquid CO2 into the CO2 carrier and to offload the cargo out of the carrier with the piston fluid in a controlled way. The carrier was designed to transport a large amount of the captured CO2 in liquid phase. The cargo containment system consisted of pressure vessels to withstand the elevated pressure condition. Employment of the piston fluid enabled the pressurized liquid CO2 to enter and leave the cargo vessels without phase change or evaporation of the cargo. An increased loading and offloading rate seemed to cause generation of emulsion droplets in the interface of the piston liquid and the cargo. The droplets were separated into the cargo and the piston liquid by a conventional separator. Fresh water was considered excellent piston liquid since it was easily available and immiscible with the liquid CO2. As the cargo temperature decreased, CO2 gas was found to serve as the piston gas.

Osmotic phenomena in application for hyperbaric oxygen treatment

Hyperbaric oxygen (HBO) treatment defines the medical procedure when the patient inhales pure oxygen at elevated pressure conditions. Many diseases and all injuries are associated with a lack of oxygen in tissues, known as hypoxia. HBO provides an effective method for fast oxygen delivery in medical practice. The exact mechanism of the oxygen transport under HBO conditions is not fully identified. The objective of this article is to extend the colloid and surface science basis for the oxygen transport in HBO conditions beyond the molecular diffusion transport mechanism. At a pressure in the hyperbaric chamber of two atmospheres, the partial pressure of oxygen in the blood plasma increases 10 times. The sharp increase of oxygen concentration in the blood plasma creates a considerable concentration gradient between the oxygen dissolved in the plasma and in the tissue. The concentration gradient of oxygen as a non-electrolyte solute causes an osmotic flow of blood plasma with dissolved oxygen. In other words, the molecular diffusion transport of oxygen is supplemented by the convective diffusion raised due to the osmotic flow, accelerating the oxygen delivery from blood to tissue. A non steady state equation for non-electrolyte osmosis is solved asymptotically. The solution clearly demonstrates two modes of osmotic flow: normal osmosis, directed from lower to higher solute concentrations, and anomalous osmosis, directed from higher to lower solute concentrations. The fast delivery of oxygen from blood to tissue is explained on the basis of the strong molecular interaction between the oxygen and the tissue, causing an influx of oxygen into the tissue by convective diffusion in the anomalous osmosis process. The transport of the second gas, nitrogen, dissolved in the blood plasma, is also taken into the consideration. As the patient does not inhale nitrogen during HBO treatment, but exhales it along with oxygen and carbon dioxide, the concentration of nitrogen in blood plasma drops and the nitrogen concentration gradient becomes directed from blood to tissue. On the assumption of weak interaction between the inert nitrogen and the human tissue, normal osmosis for the nitrogen transport takes place. Thus, the directions of anomalous osmotic flow caused by the oxygen concentration gradient coincide with the directions of normal osmotic flow, caused by the nitrogen concentration gradient. This leads to the conclusion that the presence of nitrogen in the human body promotes the oxygen delivery under HBO conditions, rendering the overall success of the hyperbaric oxygen treatment procedure.

Physical state of the deep interior of the CoRoT-7b exoplanet

AbstractThe present study takes the CoRoT-7b exoplanet as an analogue for massive terrestrial planets to investigate conditions, under which intrinsic magnetic fields could be sustained in liquid cores. We examine the effect of depth-dependent transport parameters (e.g., activation volume of mantle rock) on a planet's thermal structure and the related heat flux across the core mantle boundary. For terrestrial planets more massive than the Earth, our calculations suggest that a substantial part of the lowermost mantle is in a sluggish convective regime, primarily due to pressure effects on viscosity. Hence, we find substantially higher core temperatures than previously reported from parameterized convection models. We also discuss the effect of melting point depression in the presence of impurities (e.g., sulfur) in iron-rich cores and compare corresponding melting relations to the calculated thermal structure. Since impurity effects become less important at the elevated pressure and temperature conditions prevalent in the deep interior of CoRoT-7b, iron-rich cores are likely solid, implying that a self-sustained magnetic field would be absent.

Gas Holdup in Gas−Liquid Stirred Tanks

A single-point optical probe is developed that can accurately obtain local gas holdup in a gas-liquid stirred tank across a wide range of operating pressures, temperatures, and fluids. It is found that the probe orientation to the flow in a stirred tank can cause underestimations in gas holdup if only a single probe orientation is used. The probe is also able to capture the complex flow pattern in the vessel. This allows improved understanding of optical probes and stirred tanks and generation of data at elevated pressure and temperature conditions needed for development of new fundamental models.

Ammonia combustion at elevated pressure and temperature conditions

This numerical study examines the combustion characteristics of premixed ammonia–air mixtures, with equivalence ratios around unity, at elevated pressure and temperature conditions which are encountered in SI engine operations. The laminar burning velocity, final flame temperature and species concentrations were determined using Konnov’s mechanism [18]. A flat, freely propagating flame was considered. Both equivalence and compression ratios have an important impact on both the laminar burning velocity and the adiabatic flame temperature. Furthermore, only the variation of the equivalence ratio has a major impact on the formation of nitrogen monoxide. It was found that the compression ratio and the final temperature do not have a significant impact on NO yields for equivalence ratios above unity.

Does blood pressure enhance solute transport in the bone lacunar–canalicular system?

Solute transport through bone plays an important role in tissue metabolism and cellular mechanotransduction. Due to limited diffusion within the mineralized bone matrix, both mechanical loading and vascular pressure have been proposed to drive interstitial fluid flow within the lacunar–canalicular system (LCS); thereby augmenting solute diffusion in bone. Although blood supply is critical for bone nutrition, growth, and fracture healing, whether physiological blood pressures can drive significant fluid and solute convection remains controversial within the literature. The goal of this study was to directly test the hypothesis that in vivo blood pressures enhance solute transport in the bone LCS. Using a newly developed imaging approach based on fluorescence recovery after photobleaching (FRAP), we first measured the transport rate of sodium fluorescein (M.W. 376 Da) through the tibial LCS in four anesthetized mice (in the presence of vascular pressure). These data were then compared with the tracer transport rates at the same locations/lacunae after sacrifice (in the absence of vascular pressure). Using paired FRAP experiments we did not detect differences in tracer transport rates between bones from live anesthetized animals versus those in postmortem bodies ( p > 0.05, N=18). In a separate cohort of four anesthetized mice a mean jugular pulse pressure of ∼ 10 mmHg at ∼ 10 Hz was measured. Further theoretical analysis showed that for bones from both small and large animal species the blood pressure-driven convection of either small (376 Da) or large (43,000 Da) molecules was at least one order of magnitude smaller than diffusion under either normal or elevated pressure conditions. We conclude that despite the extreme importance of vasculature in bone physiology, vascular pressure itself does not enhance acute solute transport within the bone LCS. Therefore, mechanisms other than the vascular pressure-induced fluid flow such as altered biochemical factors may account for the bone adaptation associated with altered circulation. The present study helped clarify a long-standing controversy regarding vascular pressure-induced bone fluid flow and provided a better understanding of bone adaptation in both physiological and pathological conditions.

Aqueous fluids at elevated pressure and temperature

AbstractThe general major component composition of aqueous fluids at elevated pressure and temperature conditions can be represented by H2O, different non‐polar gases like CO2 and different dissolved metal halides like NaCl or CaCl2. At high pressure, the mutual solubility of H2O and silicate melts increases and also silicates may form essential components of aqueous fluids. Given the huge range of P–T–x regimes in crust and mantle, aqueous fluids at elevated pressure and temperature are highly variable in composition and exhibit specific physicochemical properties. This paper reviews principal phase relations in one‐ and two‐component fluid systems, phase relations and properties of binary and ternary fluid systems, properties of pure H2O at elevated P–T conditions, and aqueous fluids in H2O–silicate systems at high pressure and temperature. At metamorphic conditions, even the physicochemical properties of pure water substantially differ from those at ambient conditions. Under typical mid‐ to lower‐crustal metamorphic conditions, the density of pure H2O is , the ion product Kw = 10−7.5 to approximately 10−12.5, the dielectric constant ε = 8–25, and the viscosity η = 0.0001–0.0002 Pa sec compared to , Kw = 10−14, ε = 78 and η = 0.001 Pa sec at ambient conditions. Adding dissolved metal halides and non‐polar gases to H2O significantly enlarges the pressure–temperature range, where different aqueous fluids may co‐exist and leads to potential two‐phase fluid conditions under must mid‐ to lower‐crustal P–T conditions. As a result of the increased mutual solubility between aqueous fluids and silicate melts at high pressure, the differences between fluid and melt vanishes and the distinction between fluid and melt becomes obsolete. Both are completely miscible at pressures above the respective critical curve giving rise to so‐called supercritical fluids. These supercritical fluids combine comparably low viscosity with high solute contents and are very effective metasomatising agents within the mantle wedge above subduction zones.