High Pressure Side Research Articles

Analysis of a Dual Recuperated Dual Expansion Supercritical CO2 Cycle for Waste Heat Recovery Applications

Superior performance and compactness of supercritical CO2 power cycles are encouraging researchers to explore them for waste heat recovery (WHR) applications. This paper presents a comprehensive thermodynamic analysis of a dual recuperated dual expansion cycle utilizing industrial waste heat. The proposed cycle incorporates two recuperators and two turbines with a single compressor. The influence of operating parameters concerning cycle performance in the context of a WHR cycle is discussed. The low side, high side pressures, and the split ratio between the high-temperature and low-temperature turbines are optimized for maximum power rather than thermodynamic cycle efficiency. The cycle performance is evaluated with air as the primary heat transfer fluid in the waste heat recovery heat exchanger operating at a maximum source temperature of 500 °C. The sink temperature is assumed to be 40 °C to enable operation in tropical conditions like India. The paper also compares the performance of the proposed WHR cycle with the baseline single recuperated sCO2 cycle operating under similar conditions. The analysis shows that the proposed cycle is able to extract 60% more heat and produce 37% more power than the single recuperated sCO2 cycle. The maximum heat recovery factor for the analyzed WHR cycle is 17.4%, compared to 12.7% for the single recuperated sCO2 cycle.

Numerical Study of the Flow Uniformity Inside the High-Pressure Side Manifolds of a Cooled Cooling Air Heat Exchanger

To maintain efficiency in advanced aero-engines, it is crucial to set high limits for the Operating Pressure Ratio (OPR) and Turbine Entry temperature (TET). This can be achieved using a Cooled Cooling Air (CCA) heat exchanger, which precools the compressed air with the bypass stream before the compressed air enters the turbine to cool the blades. The aim of the present study was to improve the aero-thermal performance of CCA heat exchangers by enhancing the uniformity of flow through its high-pressure (HP) side manifolds. The development of the new manifolds was constrained by their manufacturability, as well as the pressure drop across the heat exchanger. The inlet and outlet manifold geometries are parameterised, and Computational Fluid Dynamic (CFD) simulations are carried out for Maximum Take-Off (MTO) conditions. Shape changes were performed using the mesh morphing tool, which enabled the intermediate remeshing steps to be skipped. By means of regression analysis, it was possible to find inlet and exit manifolds with improved flow uniformity; the heat transfer, structural integrity, and weight of the baseline and new manifolds were then evaluated. The new manifolds were structurally sound, and showed an 18.8% improvement in uniformity, a 10.6% reduction in pressure drop, a 0.4% increase in heat transfer rate, and a 22.5% decrease in weight.

Studying the arrangement of submerged vanes group in a straight alluvial channel using numerical modeling of flow and bed topography around a single vane

Submerged vanes are installed in waterways bed. These structures are usually used in groups and their main performance is to create an eddy current which leads to change in stream flow pattern and the bed topography in waterways. Performance of submerged vanes group depends on their arrangement and size. In this study using SSIIM numerical model, hydrodynamic analysis of flow pattern and bed topography around a single submerged vane in a straight channel was done and tried to estimate proper arrangement of submerged vanes group. The geometry of arrangement consisted of longitudinal distance between consecutive vanes, transverse distance of two adjacent vanes, and transverse distance of submerged vanes from the outer wall. Therefore, after verification of the results of numerical model with experimental data, flow pattern and topography of the bed around a vane with different dimensions and angles (in suggested domain) were investigated and analyzed. In this order, values of transverse and longitudinal distances of scouring hole at high-pressure and low-pressure sides of the vane from center of the vane were measured. Also values of transverse and longitudinal locations of the maximum scouring hole and maximum sedimentation downstream of the vane were determined. The results of these parameters were used to estimate the location of adjacent vanes. To reduce number of modes, the Taguchi method is used in design of simulations. Finally, mathematical relations are derived for geometry of arrangement versus vanes dimensions and angles. Comparison of the results of this research with the results of previous researchers, who have studied submerged vanes groups, showed that accuracy of the method used in this study is acceptable. The numerical results showed that the values obtained for the transverse and longitudinal distances of vanes are almost in the same range of previous laboratory studies.

Performance of a Flat-Tube Louvered-Fin Automotive Condenser with R1234yf

Numerical simulation of a mini-channel, flat-tube, louvered fin, automotive condenser is performed to study the heat rejection rate, pressure drop and performance of the heat exchanger. The simulation study is carried out for the refrigerant R1234yf. The properties of R1234y are obtained from REFPROP software. The moist air properties are calculated from those of dry air and water vapor using suitable correlations. To select the input data, the cycle performance is carried out for a standard vapor compression refrigeration system working with R1234yf between the temperature limits of [Formula: see text]C on the low-pressure side and [Formula: see text]C on the high-pressure side. The condensation process is taken into account in three sections, namely, the superheated, two-phase and the subcooled regions. A custom code is prepared in MATLAB to solve the simultaneous equations of heat transfer from refrigerant to inside tube wall, inside tube wall to outside tube wall and outside tube wall to moist air. The simulation results show the sensible heat transfer during desuper heating to be very small compared to the condensing region. Results are reported for the pressure variation along the refrigerant flow passage in the desuper heating, two-phase and subcooling regions. The heat-transfer coefficient is found to be the highest in the two-phase region for higher dryness fractions. The effect of inlet air velocity is less compared to that of the inlet air temperature on the heat rejection rate.

Low global warming potential (GWP) refrigerant supermarket refrigeration system modeling and its application

• A high fidelity model for a low -GWP refrigerant supermarket refrigeration system was developed. • The model was validated by manufacture and lab testing data with accuracy within ±4%. • A near-optimal high side pressure was obtained through extensive simulation running of the model. • The model was also used to generate battery equivalent model for using in grid interactive controls. As an environmentally friendly low global warming potential (GWP) refrigerant, Carbon dioxide (CO 2 ) has continuously gained popularity and research attention as alternative refrigerant for supermarket refrigeration system. In this paper, to fulfill the increasing need of accurate Low-GWP supermarket refrigeration models for development of supervisory level control and optimization strategies, a high fidelity model is developed for CO 2 transcritical supermarket refrigeration system which includes compressor rack of low temperature (LT) compressors and medium temperature (MT) compressors, air-cooled gas cooler, evaporator, expansion valves and other auxiliary equipment. A resistance-capacity model structure is proposed to simulate the display cases. Semi-thermodynamic models are proposed to estimate reciprocating compressors volumetric efficiency and power consumption. The zone modeling approach is used for evaporator simulation, and air-cooled gas cooler is modeled with distributed modeling method. The expansion valve simulation is based on orifice flow model. To calibrate these models, both manufacture performance data and experimental data are used. The experiments are conducted with a full instrumental CO 2 supermarket refrigeration system installed in Oak Ridge National Lab Flexible Research Platform (FRP). The simulation model can predict the system performance, including power consumption, cooling capacity, mass flow rate, temperature, and pressure, with high accuracy (within ±4%) compared to experimental data. In addition, this developed model has been used to create the system optimum high side pressure for high side expansion valve control, and to generate wide operating range simulation data for developing the batter-equivalent commercial refrigeration system model which can be used in grid interactive control development.

An experimental investigation of performance and instabilities of the R744 vapour compression rack equipped with a two-phase ejector based on short-term, long-term and unsteady operations

In the case of R744 refrigeration technology, the system equipped with a two-phase ejector is one of the most efficient refrigeration systems, allowing utilisation of an R744-based unit in hot and tropical climates. However, the experimental analyses of the ejector-based system have only been performed for system performance evaluation, mapping the performance of ejectors or validation of the ejector numerical simulation. Therefore, the main goal/scope of this paper is to enhance the experimental knowledge of the state-of-the-art R744 vapour compression rack equipped with an efficient two-phase ejector, the relationship between the ejector and other components, and the influence of unsteady system work on the ejector performance and cooling demand. The test campaign was carried out on the R744 ejector-based test rig with a cooling capacity of 50 kW, high-side pressures from 60 bar to 100 bar and temperatures from 15 °C to 40 °C. The experimental analysis was conducted for three different system operating conditions, namely, short-term, long-term, and unsteady-state conditions, for refrigeration and air-conditioning applications. Utilisation of the ejector influenced the system instability, especially at the internal heat exchanger control. In addition, the low-pressure lift below 4 bar allowed the most efficient control strategy of the cooling demand for the operation below the critical point. For the transcritical unsteady operation, the most efficient operation was obtained for the defined pressure lift of 6 bar.

Steady-state off-design modeling of the supercritical carbon dioxide recompression cycle for concentrating solar power applications with two-tank sensible-heat storage

Concentrating solar power researchers are evaluating the potential of the supercritical carbon dioxide recompression cycle to improve the thermal efficiency and decrease the capital costs of next-generation systems. This analysis investigates the steady-state off-design performance of a recompression cycle integrated with two-tank sensible-heat thermal energy storage as the ambient temperature and heat-transfer fluid (HTF) inlet conditions to the cycle change. This paper presents off-design component models and then cycle convergence and control models to maximize net cycle power output while constraining the high-side pressure and air-cooler fan power to their respective design values and fixing the cycle HTF outlet temperature to its design value. Results show that inventory control and air-cooler fan power are important control parameters that can be optimized to maximize off-design power output as the ambient temperature and HTF mass flow rate diverge from design. The high-side pressure and fan power constraints cause the cycle net power to degrade when the ambient temperature is warmer than the design value, and this study calculates a maximum mass flow rate for hot days above which the cycle cannot achieve the design HTF outlet temperature. Finally, the analysis shows that optimizing compressor shaft speeds can improve cold-day performance by around 1.5 percentage points and part-load performance by up to 2.5 percentage points versus a baseline case with no active compressor control.

Simulation of Full-bore Tube Ruptures in Shell&tube Heat-exchanger

Shell & Tube heat exchanger is the most often used equipment for heat transfer between fluids in chemical plants, refineries, power generation stations and many other industries. The fluid cooled and the fluid heated are often operated at very different pressures: in this case design standards require an analysis to verify the maximum pressure surge that could be generated by an accidental fluid leak from the high-pressure side of the heat-exchanger into the other. The analysis of such accident is very complex due to a number of interacting phenomena such as vapor-liquid equilibrium, large enthalpy effects, large changes of fluid density and the formation two-phases (vapor and liquid) fluid flows. With reference to a real project case, this article presents the simulation of the pressure increase due to the full-bore rupture of a tube. This evaluation is required to assess if a rupture disk must be installed on the shell side to protect both the equipment and the operating personnel. The analysis is performed using a state-of-the-art dynamic simulation tool.

Structure and phase behavior of high-density ice from molecular-dynamics simulations with the ReaxFF potential.

We report a molecular dynamics simulation study of dense ice modeled by the reactive force field (ReaxFF) potential, focusing on the possibility of phase changes between crystalline and plastic phases as observed in earlier simulation studies with rigid water models. It is demonstrated that the present model system exhibits phase transitions, or crossovers, among ice VII and two plastic ices with face-centered cubic (fcc) and body-centered cubic (bcc) lattice structures. The phase diagram derived from the ReaxFF potential is different from those of the rigid water models in that the bcc plastic phase lies on the high-pressure side of ice VII and does the fcc plastic phase on the low-pressure side of ice VII. The phase boundary between the fcc and bcc plastic phases on the pressure, temperature plane extends to the high-temperature region from the triple point of ice VII, fcc plastic, and bcc plastic phases. Proton hopping, i.e., delocalization of a proton, along between two neighboring oxygen atoms in dense ice is observed for the ReaxFF potential but only at pressures and temperatures both much higher than those at which ice VII-plastic ice transitions are observed.

Comparative Study on Two-Stage Absorption Refrigeration Systems with Different Working Pairs

The objective of this paper is to present simulation study on a two-stage absorption refrigeration system of 2.5 kW capacity using LiBr-H2O, NH3-H2O or R124-DMAC (2-chloro-1,1,1,2-tetrafluoroethane/N′,N′-dimethylacetamide) as working pair, separately. Under the design condition that the generating, absorbing, evaporating and condensing temperatures are 75 °C, 45 °C, 5 °Cand 40 °C, respectively, the high and low pressure side solution circulation ratios and the coefficient of performance (COP) for the systems are calculated. Then the influences of medium, generating, absorbing, evaporating and condensing temperatures on system performances are analyzed. The results show that under the design condition, the COP of the LiBr-H2 O system can reach 0.49, superior to those of the NH3-H2O and R124-DMAC systems, which are 0.32 and 0.31, respectively. Furthermore, the medium temperature for higher COP lies in an interval of 64–67 °Cfor the LiBr-H2O, NH3-H2O and R124–DMAC systems. High generating temperature and low absorbing temperature can decrease the high and low pressure side solution circulation ratios, and can also increase the COP. High evaporating temperature can decrease the low pressure side solution circulation ratio and increase the COP. Low condensing temperature can decrease the high pressure side solution circulation ratio and increase the COP.

Investigation of performance improvement of a household freezer by using natural circulation loop

Growing number of household refrigerators and freezers also increase the overall energy consumption and number of household refrigerators have grown nearly 3% per year. On the other hand, investigations showed that household refrigerators have a significant technical energy saving potential of up to 30–40%. In this study, a single-phase natural circulation loop is considered as a suction line heat exchanger between the high and low pressure sides of conventional refrigeration cycle of a household chest freezer. The potential heat transfer by the single-phase natural circulation loop is studied by a CFD analysis, considering the possible temperature range for refrigeration cycle and geometrical parameters that affect the loop performance. The performance map of this refrigeration cycle is presented for different compressor suction and discharge pressures (LP/HP), discharge temperatures (T2) and different compressor speeds. The results indicate that the highest amount of heat transfer is obtained for the single-phase natural circulation loop with aspect ratio of 0.8 and pipe diameter of 6.53 mm. Moreover, the single-phase natural circulation loop provides 11.5% efficiency improvement for the household freezer for maximum compressor speed at lowest T2 and LP/HP. Considering reduction in required compressor work, SPNCmL assisted refrigeration system has a wider operating range.

A Study on Performance Characteristics of a Heat Pump System with High-Pressure Side Chiller for Light-Duty Commercial Electric Vehicles

One of barriers for the present heat pump system’s application in an electric vehicle was decreased performance under cold ambient conditions due to the lack of evaporating heat source. In order to improve the heat pump’s performance, a high-pressure side chiller was additionally installed, and the tested heat pump system was modified with respect to refrigerant flow direction along with operating modes. In the present work, the performance characteristics of the heat pump system with a high-pressure side chiller for light-duty commercial electric vehicles were studied experimentally under hot and cold ambient conditions, reflecting real road driving. The high-pressure side chiller was located after the electric compressor so that the highest refrigerant temperature transferred the heat to the coolant. The controlled coolant with discharged refrigerant from the electric compressor was used to heat up the cabin, transferring heat to the inlet air like the internal combustion engine vehicle’s heating system, except with unused engine waste heat. In the cooling mode, for the exterior air temperature of 35 °C and interior air temperature of 25 °C, cooling performance along with the compressor speed showed that the system efficiency decreased by 16.4% on average, the cooling capacity increased by 8.0% on average and the compressor work increased by 27% on average. In heating mode, at the exterior and interior air temperature of −6.7 °C, compressor speed and coolant temperature variation with steady conditions were tested with respect to heating performance. In transient mode, to increase coolant temperature with a closed loop from −6.7 °C, tested system characteristics were studied along the compressor speed with respect to heating up the cabin. As the inlet air of the HVAC was maintained at −6.7 °C, even though the heat-up rate of the cabin room was a little slow, the cabin temperature reached 20 °C within 50 min and the temperature difference with the ambient air attained 28.7 °C.

Proektnye resheniya skhemy kholodil'noy mashiny s utilizatsiey teploty kondensatsii

Refrigerating units are widely used in various sectors for artificial cold generation. While maintaining low temperatures, refrigerating machines produce a large amount of heat at cooling and condensation of a refrigerant on the high pressure side. The heat produced is not used in any way and is emitted into the environment. The article offers a circuit of a refrigerating machine that makes it possible to utilize the condensation heat and to transfer it to various consumers of heat energy at the facilities, thereby reducing the heat emission into the atmosphere and increasing technological capabilities of cooling. The methods for selection of heat exchange apparatuses, included in the circuit, which make it possible to utilize the condensation heat, are described. This methodology can be used when designing refrigeration circuits for new facilities as well as for modernization of circuits of already operating refrigeration factories.

Experimental and numerical study of effect of secondary surfaces fixed over rectangular vortex generator with an overview of dynamic mode decomposition

Addition of a vortex generator (VG) to the heated surface creates longitudinal vortices in the flow; however, it induces drag. Surface modification of the VG may play a role in the thermal performance of the system. Therefore, flow and thermal behavior are studied for a secondary surface (SS) attached to the primary surface of a rectangular VG, which is placed inside a rectangular channel using air at Re = 5000. The VG with the SS is compared with a conventional rectangular VG having volume constant. With the addition of SS, the flow behind the VG greatly shears the produced primary vortex (P), which results in stretching. Stretching increases the angular momentum of the vortex with the decrease in the span of the produced vortices. The interaction between the co-rotating vortices P and high pressure side horse-shoe vortex (Hp) shows that the higher strain field induced by the vortex P shears away the vortex Hp. The vortex P developed under the influence of SS induces a higher degree of tilting toward the heated surface with low propagation speed. Finally, the dynamic decomposition of the vortices in the channel reveals that the vortex P appears to be dominant.

Data-driven Adaptive Thresholding Model for Real-time Valve Delay Estimation in Digital Pump/Motors

Valve characteristics are an essential part of digital hydraulics. The on/off solenoid valves utilized on many of these systems can significantly affect the performance. Various factors can affect the speed of the valves causing them to experience various delays, which impact the overall performance of hydraulic systems. This work presents the development of an adaptive statistical based thresholding real-time valve delay model for digital Pump/Motors. The proposed method actively measures the valve delays in real-time and adapts the threshold of the system with the goal of improving the overall efficiency and performance of the system. This work builds on previous work by evaluating an alternative method used to detect valve delays in real-time. The method used here is a shift detection method for the pressure signals that utilizes domain knowledge and the system’s historical statistical behavior. This allows the model to be used over a large range of operating conditions, since the model can learn patterns and adapt to various operating conditions using domain knowledge and statistical behavior. A hydraulic circuit was built to measure the delay time experienced from the time the signal is sent to the valve to the time that the valve opens. Experiments were conducted on a three piston in-line digital pump/motor with 2 valves per cylinder, at low and high pressure ports, for a total of six valves. Two high frequency pressure transducers were used in this circuit to measure and analyze the differential pressure on the low and high pressure side of the on/off valves, as well as three in-cylinder pressure transducers. Data over 60 cycles was acquired to analyze the model against real time valve delays. The results show that the algorithm was successful in adapting the threshold for real time valve delays and accurately measuring the valve delays.

Response of a direct-drive large marine two-stroke engine coupled to a selective catalytic reduction exhaust aftertreatment system when operating in waves

Large two-stroke marine diesel engines are used as the prime mover in the majority of ocean going commercial vessels and are currently facing new stringent NOx emission reductions. Selective catalytic reduction is an aftertreatment technology which is able to reduce emitted NOx at allowable levels. In most marine applications, the selective catalytic reduction system is placed on the high pressure side of the turbine, due to limitations at the exhaust gas temperature at the inlet of selective catalytic reduction system. In this article, the operation of a large two-stroke marine diesel with a selective catalytic reduction aftertreatment system, is investigated in heavy weather conditions. Operation of a vessel in heavy weather results in increased ship resistance, wave-induced ship motions, and a highly varying flow field in the propeller due to ship motions. This results in a fluctuation of propeller demanded torque and hence a fluctuation in engine load and exhaust gas temperature which may affect engine and selective catalytic reduction performance significantly. To investigate this phenomenon and taking into account the engine–propeller interaction, the entire propulsion system was modeled, namely the propulsion engine, the high pressure selective catalytic reduction system, the directly driven propeller, and the ship’s hull. A propeller model was employed to simulate the transient propeller torque demand and torque fluctuations due to ship motions. A three-dimensional six degrees of freedom panel code was used to calculate ship motions and wave added resistance in regular waves. The coupled model of the marine propulsion plant was validated against available measured data from a ship-board propulsion system on good weather conditions. The model was then used to simulate the behavior of the system during transient loading conditions in the presence of regular waves.

Design of A Dual-rotor Engine Driving by the Elliptic Gear

Aiming at the shortcomings of the crank-connecting rod mechanism engine, such as low transmission efficiency and high side pressure between the piston and the cylinder, the paper proposes a kind of dual-rotor engine driving by the elliptic gear. The left and right rotors are driven by the gas pressure in the cylinder, and then the elliptic gears on the output shaft are driven by the circular gears and the elliptic gears on the intermediate shaft. When the gears rotate, the output shaft connected outputs power again and again. The rotor rotates one circle, the four “cylinders” separated by the rotor work one time respectively, and the output shaft rotates two circles. The results of the calculation and the simulation test show that the serialization design can be carried out by setting different parameters of the long half-axis and the eccentricity. When the value of the long half-axis (100mm in this design) is fixed and the eccentricity is 0.4, 0.6 or 0.8, the rotation angle and the speed of the left and right rotors change obviously. The greater the eccentricity, the greater the difference of the rotation angle and the speed of the left and right rotors. The higher the compression ratio of engine, the higher the transmission efficiency.

A case report: Trans-Anal mucosal trapezoid flap for repair of Ano-vaginal fistula

Ano vaginal fistula is a rare clinical entity with incidence <5%. It causes significant physical discomfort and psychological distress to patients as also in our case having complaints of passing flatus per vaginally and fecal staining in vagina. Repair is challenging in view of high recurrence rate. Repair from the anal side with a mucosal flap was done, this being the high-pressure side of the fistula. The ease of performance with less recurrence of this less commonly used approach is being reported.

Sediment erosion in low specific speed francis turbines: A case study on effects and causes

Hydraulic turbines experience severe operational and maintenance challenges when operated in sediment-laden water. The combined effect of erosive and abrasive wear in turbine components deteriorates their life and efficiency. The quantity and pattern of sediment erosion depends on the nature of the flow and the amount of hard minerals contained in water. Localized erosion patterns are observed mostly in guide vanes, runner blades and facing plates of Francis turbines due to different natures of fluid flow in those regions. Accelerating flow around the guide vanes and its shaft causes abrasive and erosive wear in its surface, which causes increase in the size of the clearance gap between the facing plates and the guide vanes. Flow leaving the clearance gap forms a vortex filament due to the leakage from high pressure side to the low-pressure side of the guide vane, which eventually strikes the rotating runner blades. This paper presents a case study of a power plant in India with low specific speed Francis turbines, which is severely affected by sediment erosion problems. A numerical analysis of the flow is conducted inside the turbine to study causes of various erosion patterns in the turbine components. The results from CFD are compared with the actual erosion in turbines. Erosion in guide vanes and runner blades are taken into consideration in this paper, due to the complex flow phenomena around these regions. It is found that the leakage flow through clearance gaps of guide vanes is the primary cause of erosion at the inlet of the runner blades. Furthermore, the effects of size and shape of quartz particles are studied which shows that erosion is directly proportional to these parameters.

Static compression of Fe4N to 77 GPa and its implications for nitrogen storage in the deep Earth

AbstractCompression and decompression experiments on face-centered cubic (fcc) γ′-Fe4N to 77 GPa at room temperature were conducted in a diamond-anvil cell with in situ X-ray diffraction (XRD) to examine its stability under high pressure. In the investigated pressure range, γ′-Fe4N did not show any structural transitions. However, a peak broadening was observed in the XRD patterns above 60 GPa. The obtained pressure-volume data to 60 GPa were fitted to the third-order Birch-Murnaghan equation of state (EoS), which yielded the following elastic parameters: K0 = 169 (6) GPa, K′ = 4.1 (4), with a fixed V0 = 54.95 Å at 1 bar. A quantitative Schreinemakers' web was obtained at 15–60 GPa and 300–1600 K by combining the EoS for γ′-Fe4N with reported phase stability data at low pressures. The web indicates the existence of an invariant point at 41 GPa and 1000 K where γ′-Fe4N, hexagonal closed-packed (hcp) ε-Fe7N3, double hexagonal closed-packed β-Fe7N3, and hcp Fe phases are stable. From the invariant point, a reaction γ′-Fe4N = β-Fe7N3 + hcp Fe originates toward the high-pressure side, which determines the high-pressure stability of γ′-Fe4N at 56 GPa and 300 K. Therefore, the γ′-Fe4N phase observed in the experiments beyond this pressure must be metastable. The obtained results support the existing idea that β-Fe7N3 would be the most nitrogen-rich iron compound under core conditions. An iron carbonitride Fe7(C,N)3 found as a mantle-derived diamond inclusion implies that β-Fe7N3 and Fe7C3 may form a continuous solid solution in the mantle deeper than 1000 km depth. Diamond formation may be related to the presence of fluids in the mantle, and dehydration reactions of high-pressure hydrous phase D might have supplied free fluids in the mantle at depths greater than 1000 km. As such, the existence of Fe7(C,N)3 in diamond can be an indicator of water transportation to the deep mantle.