Supercritical Methane Research Articles

Thermal oscillation behavior profiling of supercritical methane in cooling rocket engines

Regenerative cooling is widely used in rocket engines as an efficient cooling method, and nowadays spacecraft shows faster flight speed and greater acceleration. Therefore, the fuel is subjected to large inertial force during flight acceleration or deceleration process. Hence, since it is novel, it is necessary to analyze the thermal performance with large acceleration. To reveal the effect of acceleration on the heat transfer of supercritical methane fuel in the cooling channel, the three-dimensional numerical simulation has been performed with structured mesh. Specifically, the effects of acceleration, mass flux, pressure and ratio of heat flux to mass flux on the flow and heat transfer in the cooling channel have been studied, and the buoyancy parameter (Bo*) and thermal acceleration factor (Kv) have been also employed to analyze the buoyancy effect and thermal acceleration. The results show that at the conditions of low supercritical pressure, low mass flux and large ratio of heat flux to mass flux, the buoyancy effect increases significantly when the acceleration increases from 0 g to 6 g. As a result, the heat transfer is deteriorated gradually, and the average heat transfer coefficient decreases from 3800 to 3000. On the other hand, when the acceleration and heat flux exceed a range, the unstable phenomenon of thermal oscillation will occur with the period of oscillation about 90 s. The thermophysical properties of the fluid near-wall will change rapidly when approaching the pseudo-critical region, which leads to the continuous change of the thickness of the viscous boundary layer.

Molecular insights into supercritical methane sorption and self-diffusion in monospecific and composite nanopores of deep shale

• Montmorillonite, kerogen and MMT-kerogen composite slit nanopores with desirable pore sizes are constructed; • GCMC and EMD simulations are conducted to study the sorption and self-diffusion behaviors of methane in various nanopores; • Pore surface roughness can impede the diffusion of gases, especially in smaller pores. Up to now, a large number of studies have utilized various representative materials to approximate the replacement of shale and investigate the gas adsorption and diffusion behavior in various shapes of nanopores by means of molecular simulations. However, the study of methane sorption and self-diffusion behavior under high temperature and pressure reservoir conditions in deep shale is not clear. In this study, we first established montmorillonite (MMT), kerogen and MMT-kerogen composite slit nanopores using representative shale components of MMT and kerogen. On this basis, we investigated the methane sorption and self-diffusion characteristics employing the grand canonical Monte Carlo (GCMC) and equilibrium molecular dynamics (EMD) simulations. The results show that the differences in the molecular composition and structure of MMT and kerogen surfaces lead to stronger adsorption performance of MMT surface than kerogen in a single nanopore for the same conditions, which results in the inhomogeneity of spatial distribution of methane molecules in the pores. While the sorption capacity of the kerogen matrix is more potent than MMT due to its larger specific surface area (SSA). The smaller pores have stronger adsorption capacity compared to the larger pores. At the same time, the methane density profiles indicate that the adsorption of the MMT and kerogen in smaller pores is less differentiated. The methane sorption energy distribution and isosteric heat of sorption also mutually corroborate the more stable methane sorption at a higher pressure and smaller pores. The self-diffusion coefficient of methane in nanopores gradually decreases with increasing pressure, with a more pronounced variation at lower pressure. Pore surface roughness will hinder the diffusion of gas, and the closer the distance is, the more noticeable the effect will be. This study sheds light on the sorption and self-diffusion phenomena and difference of gas in monospecific and composite nanopores, which provides insights into the reserve evaluation and development of the deep shale gas reservoirs, and is further expected to furnish ideas for exploring the occurrence and transport characteristics of supercritical fluids on other composite nanomaterials.

Thermal performance investigation of supercritical methane in minichannel heat sink on flight vehicle actuator under geometry effect of cross section

With rapid development of high-power electromechanical actuator, the conventional cooling technologies become hard to meet the requirement of heat dissipation, the minichannel heat sink using supercritical cryogenic propellant methane is proposed for high power electromechanical actuator’s thermal control in flight vehicles, withstanding the extreme ambient of flight vehicles like gravity acceleration and replacing the air-cooled method under the rarefied atmosphere. However, the optimal working patterns especially considering both the factors of geometric and operation conditions need to be investigated thoroughly due to the complicated heat transfer mechanism of supercritical methane in minichannel of heat sink. Therefore, in the present article, based on the actual configuration of IGBT power module in flight vehicle actuator, the numerical models of minichannel heat sink under various cross sections with the same aspect ratio and hydraulic diameter, namely triangle, trapezoid, and rectangle, are established with the overall region of 50 mm × 100mm. The hydraulic diameter of fluid region in single channel is 1.5 mm, the size of solid region for computational domain is 3 mm × 5 mm (width × height) and the material is silicon. The overall channel number is 17, the inlet Reynolds number covers from 500 to 1500 and the operation pressure ranges 5 MPa to 7 MPa, while the ratio of mass flux to heat flux keeps constant. On this basis, the thermal performance, in especial the local heat transfer features of supercritical methane in minichannel heat sinks under three different geometric configurations of cross section is researched.

Flow capacity characterization of unconventional natural gas bearing rocks using digital rock physics: A comparison between advection and diffusion

Experimental flow capacity characterization of unconventional rocks is a nontrivial task, and the relative contribution of advective vs. diffusive flow mechanisms remains illusive. Herein we apply a digital rock physics workflow to systematically compare the advection and diffusion behavior of supercritical methane in two 3D reconstructed unconventional shale and coal core samples. Nitrogen sorption experiments and scanning electron microscope observations are combined to inform the construction of representative pore network models. For advection modeling, we consider the nanometer-scale confinement effect and pore shape effect, while for diffusion modeling the contributions of Fick diffusion, transitional diffusion, and Knudsen diffusion are considered separately based on the Knudsen number. The effect of pore size, shape, pressure, and temperature on methane flow capacity in a single nanopore is first studied. Then the apparent permeability and effective diffusivity of the two reconstructed nanoporous media are calculated and compared. We demonstrate that at reservoir pressure and temperature conditions, diffusion contributes to mass flux (above 10%) only in micropores and small mesopores (< 10 nm). For most realistic unconventional rocks, the contribution of bulk diffusion can be neglected when estimating the flow capacity.

Numerical investigation on heat transfer and flow characteristics of supercritical methane in a horizontal tube

The main component of liquefied natural gas (LNG) is methane. The regasification process of LNG is usually under a supercritical condition. In this paper, a three-dimensional model is established to study the heat transfer and flow mechanism of supercritical methane in a heating process. The special physical properties of supercritical methane are compiled and imported through user-defined database. The standard k–ε model with the standard wall function is selected for simulation. The results show that deterioration of heat transfer occurs on the upper surface of the channel, which is most evident when the bulk temperature approaches the pseudocritical temperature. And the heat transfer coefficient increases first and then decreases along the channel with the bulk temperature rising. The peak value appears near the pseudocritical temperature. The pressure also has a great influence on heat transfer and flow. Besides, the buoyancy effect is strong near the pseudocritical point, leading to nonuniform distribution of temperature and density on the cross section, and causing significant radial circulation. The heat transfer deterioration can be effectively reduced by using special structures such as fins to hinder the buoyancy.

Thermal Analysis of Cooling Channels on Electromechanical Actuator During Actual Flight

Liquid methane is regarded as a potential cryogenic propellant that can be used as coolant for regenerative cooling channels of high-power electrical devices, in addition to the oxygen/methane thrust chamber, owing to its moderate working temperature. This study examines the thermal performance of supercritical methane in cooling channels of the electromechanical actuator of a flight vehicle at varying angles of inclination and flight acceleration overloads. The main effects of overload and attitude at various angles of inclination on heat transfer are shown as variation in buoyancy force, which can be classified into gravitational and centrifugal buoyancy forces. Both forces can disturb the turbulent structure and complicate heat transfer under the influence of the drastically variable properties of the supercritical fluid. The authors also discuss conjugate impacts of the two kinds of buoyancy forces on the thermal performance of the cooling channel at various angles of inclination and flight acceleration overloads. The physical model was constructed as a helically coiled tube with angles of inclination varying from 0 to 90 deg, and flight overload was implemented as and (where is the gravitational acceleration). The analysis shows that both the flight attitude and overload played an essential part in the thermal performance of supercritical methane in the cooling channel. Some novel findings were obtained; an enhancement and a deterioration in local heat transfer could occur at large overloads with inclined orientations. The gravitational buoyancy force leading to secondary flow was an essential factor in the deterioration of local heat transfer but was inconspicuous under the gravity of Earth. Moreover, the trends of development of and were consistent, implying that the buoyancy force generated by gravity and centrifugal forces was not isolated.

Large-Eddy Simulation on the Aerodynamic and Thermal Characteristics in a Micropipe of the Hypersonic Engine Precooler.

The precooling air-breathing technique has become a study focus in the aerospace field. Research on the internal flow and heat-transfer mechanism of the precooler is important for design and optimization. A large-eddy simulation was used to study the aerodynamic and thermal characteristics in a micropipe of the hypersonic engine precooler with supercritical methane as coolant and fuel. Under the effect of buoyancy, the high-temperature and low-density fluid near the wall in the circumferential direction gradually accumulate to the top wall. The accumulation of low-density fluid enhances the thermal acceleration effect at the top wall, which intensifies the local turbulent relaminarization and forms an M-shaped velocity distribution, resulting in the weakening of the heat transfer. On the other hand, the high-density fluid gathers to the bottom wall under the influence of gravity, the local thermal acceleration effect is weakened, and the flow heat transfer is enhanced. The influence of the relationship between the turbulent burst and the turbulent heat transfer under the effect of buoyancy is analyzed. It is found that the low-speed ejection events and high-speed sweep events are strengthened at the bottom wall, especially the low-speed ejection. However, the occurrence of these events at the top wall is restrained to a certain extent.

Fluid phase equilibria in asymmetric model systems. Part I: CO2+ diphenylmethane

Asymmetric reservoir fluids with high gas-to-oil ratios and heavy oils could present complex phase behaviors at reservoir or production conditions, as observed in Brazilian Pre-Salt reservoirs. To better understand the phase behaviors of these types of reservoir fluids with high carbon dioxide and methane contents, we initiated a study in our laboratory on the fluid phase equilibria of systems containing supercritical CO2 and/or methane plus a heavy hydrocarbon. In the initial phase of this program, which forms this article, the choice was made to experimentally determine the phase diagram of the binary system: carbon dioxide + diphenylmethane within the temperature range 293.15–378.15 K. In addition, the data were compared with those modeled using a predictive version of the Peng-Robinson equation of state (PPR78).

Study on supercritical methane flow and heat transfer performance in a 180-degree curved duct

ABSTRACT In this paper, an investigation into flow and heat transfer performance of supercritical methane (S-CH4) in a 180-degree curved circular duct has been numerically carried out. The mathematical description of energy equation induced by the Dean vortices under the Cartesian-coordinate is first deduced. After validating the dynamic computational fluid dynamics model and method against the public experimental data, the effect of mass flux on the thermodynamics properties of S-CH4 is revealed. The calculation results show that due to the centrifugal force, the low temperature of S-CH4 gathers near the outer wall generatrix. Meanwhile, owing to the existence of multiple Dean vortices, all thermophysical parameters on the 90° cross-section are symmetrically concave along the vertical axis. The core position of multiple Dean vortices inside the curved duct is closer to the inner wall generatrix, which makes the velocity fluctuation greater. The maximum value of circumferential heat transfer coefficient on different cross-sections differs, and the non-uniform flow development process occurs inside the curved duct. Compared to the straight duct, when the mass fluxes are respectively 300 kg/m2 · s and 600 kg/m2 · s, the magnitude of increase in heat transfer coefficient of curved duct presents 18.8% and 23.5%. In addition, the forced convection caused by the secondary flow inside curved duct is so strong that the natural convection by the gravity could be neglected. The research outcome is of vital importance for the optimization design of liquefied natural gas vaporizer.

Diffusion, viscosity, and Stokes-Einstein relation in dense supercritical methane

The new results on the diffusion in dense supercritical methane reported by Ranieri et al. [Nature Communications 12, 1958 (2021)] are examined from the freezing density scaling perspective. It is demonstrated that the high pressure behaviour of the self-diffusion coefficient is consistent with the freezing density scaling of dense Lennard-Jones and hard sphere fluids. It is also observed that the Stokes–Einstein relation of the form Dη(Δ/kBT)=αSE holds in a wide pressure and density regime, where it is expected to hold (here D and η are the diffusion and shear viscosity coefficients, Δ is the intermolecular separation and kBT is the temperature). Unexpected violation occurs at highest densities in the vicinity of the freezing point, where the coefficient αSE reaches values ≃10% higher than the upper theoretically expected limit.

Heat Transfer Analysis of Supercritical Methane in Microchannels With Different Geometric Configurations on High Power Electromechanical Actuator

Abstract The issue of regenerative cooling is one of the most important key technologies of flight vehicles, which is applied into both the engine and high-power electrical equipment. One pattern of regenerative cooling channels is the microchannel heat sinks, which are thought as a prospective means of improving heat removal capacities on electrical equipment of smaller sizes. In this paper, three numerical models with different geometric configurations, namely, straight, zigzag, and sinusoid, respectively, are built to probe into the thermal hydraulic performance while heat transfer mechanism of supercritical methane in microchannel heat sinks for the heat removal of high-power electromechanical actuator is also explored. In addition, some crucial influence factors on heat transfer such as inlet Reynolds number, operating pressure, and heating power are investigated. The calculation results imply the positive effect of wavy configurations on heat transfer and confirm the important effect of buoyancy force of supercritical methane in channels. The heat sinks with wavy channel show obvious advantages on comprehensive thermal performance including overall thermal performance parameter η and thermal resistance R compared with that of the straight one. The highest Nu and average heat transfer coefficient αm appear in the heat sink with zigzag channels, but the pumping power of the heat sink with sinusoidal channels is lower due to the smaller flow loss.

Effect of rolling motion with large radius on flow and heat transfer characteristics of supercritical methane in a mini channel

• Rolling results in the violent fluctuation of flow and heat transfer in supercritical methane. • Additional force along the flow direction is the key to affect the flow and heat transfer. • Hysteresis exists in the coupling of rolling, flow fluctuation and temperature fluctuation. • Rolling produces greater fluctuation in the near-wall area than that in the inner center area. The offshore floating storage and regasification unit (FSRU) is developing rapidly as a new type of storage and gasification system for liquefied natural gas (LNG), and the heat transfer and system stability of offshore LNG vaporizers are greatly affected by ocean rolling. To reveal the regular pattern and mechanism of supercritical methane heat transfer performance under ocean motion, this research numerically studied the flow and heat transfer characteristics of supercritical methane in a 1 × 1 × 100 mm mini channel under the additional inertial force by large radius rolling. Based on the non-inertial coordinate system, the normal inertial acceleration, radial inertial acceleration and Coriolis inertial acceleration were considered. Moreover, Nusselt number, degree of fluctuation and friction factor were investigated. The ranges of Reynolds number and Nusselt numbers are 15,000 to 45,000 and 35 to 130 respectively. The results show that the Nusselt number and friction factor violently fluctuate under rolling motion, and the fluctuation period is similar to the rolling period. Besides, the fluctuation degree of Nusselt number is greater than that of friction factor, and the largest fluctuation degree of Nusselt number is 27.9%. The effect of the fluctuation increases with the decrease of the rolling period and the increase of the rolling amplitude. Hysteresis exists in the coupling of rolling, flow fluctuation and temperature fluctuation. In addition, the degree of fluctuation is reduced with the increase of fluid temperature and mass flux. For the effect of rolling, the additional force in the mainstream direction plays a leading role. Besides, the influence of radial force is greater than that of normal force for horizontal flow condition.

Absolute adsorption and adsorbed volume modeling for supercritical methane adsorption on shale

Adsorbed methane significantly affects shale gas reservoir estimates and shale gas transport in shale formations. Hence, a practical model for accurately representing methane adsorption behavior at high-pressure and high-temperature in shale is imperative. In this study, a reliable mathematical framework that estimates the absolute adsorption directly from low-pressure excess adsorption data is applied to describe the excess methane adsorption data in literature. This method provides detailed information on the volume and density of adsorbed methane. The obtained results indicate that the extensively used supercritical Dubinin-Radushkevich model with constant adsorbed phase density underestimates absolute adsorption at high pressure. The adsorbed methane volume increases both the pressure and expands with the temperature. The adsorbed methane density reduces above 10 MPa, and approaches a steady value at high pressure. This study provides a novel method for estimating adsorbed shale gas, which is expected improve the prediction of shale gas in place and gas production.

Characteristics and Influencing Factors of Supercritical Methane Adsorption in Deep Gas Shale: A Case Study of Marine Wufeng and Longmaxi Formations from the Dongxi Area, Southeastern Sichuan Basin (China)

Characteristics and Influencing Factors of Supercritical Methane Adsorption in Deep Gas Shale: A Case Study of Marine Wufeng and Longmaxi Formations from the Dongxi Area, Southeastern Sichuan Basin (China)

Numerical investigation on flow and heat transfer characteristics of supercritical methane–ethane mixture in a straight channel

Printed Circuit Heat Exchanger (PCHE) is considered as a promising heat exchanger for offshore Liquefied Natural Gas (LNG) production due to its compactness and high efficiency. To reveal the flow and heat transfer performance of real component nature gas mixture in PCHE, numerical study was conducted to obtain flow and heat transfer characteristics of supercritical methane–ethane mixture in a straight channel of PCHE. The influence of operating parameters including inlet temperature, mass flux and outlet pressure are investigated. The simulation results show that heat transfer coefficient and pressure drop increase with the increase of inlet temperature and mass flux, and decrease with the increase of outlet pressure. The overall variation tendency of heat transfer coefficient and pressure drop in supercritical methane–ethane mixture flow was similar to those in supercritical methane flow, but there still exists some difference due to their different physical properties. For the value of heat transfer coefficient, supercritical methane flow is about 7% larger than that of supercritical methane–ethane mixture flow. And for frictional pressure drop, supercritical methane flow is much larger by about 12%. Finally, new correlations were proposed for supercritical methane–ethane mixture flow, which are helpful for a more accurate flow and heat transfer calculation in PCHE designing for natural gas.

Numerical Investigation on Pseudo-Critical Flow and Heat Transfer Characteristics of Supercritical Methane in Zigzag Printed Circuit Heat Exchanger

Numerical Investigation on Pseudo-Critical Flow and Heat Transfer Characteristics of Supercritical Methane in Zigzag Printed Circuit Heat Exchanger

Experimental study on solubility of lubricating oils in a supercritical methane gas

In a boil-off gas (BOG) compressor, there could be a carryover phenomenon of lubricants oil which flows with a solvent gas. To protect process system downstream of the compressor, it is necessary to select low solubility lubricants at supercritical state. In this study, the experiment of solubility measurement was conducted at 300 bar of methane with six different types of lubricating oils using supercritical fluid extracting devices operated at different temperature conditions. The solubility measurement results were analyzed according to the density of methane in the supercritical states and the vapor pressure of the lubricants. This indicates that there is a possibility of developing the criteria to choose the proper lubricant oil used by the equipment operating in the supercritical state.

Supercritical methane adsorption measurement on shale using the isotherm modelling aspect.

In shale gas reservoirs, adsorbed gas accounts for 85% of the total shale gas in place (GIP). The adsorption isotherms of shale samples are significant for understanding the mechanisms of shale gas storage, primarily for assessing the GIP and developing an accurate gas flow behaviour. Isothermal adsorption experiments primarily determine the adsorption capacity of methane in shale gas reservoirs. However, experimental data is limited due to the heterogeneous properties of shale and extreme reservoir conditions at high pressures and temperatures. This work discusses the effect of total carbon (TOC), pore size distributions, and mineralogical properties on adsorption capacity. In this study, the gravimetric adsorption isotherm measurement method was applied to obtain the adsorption isotherms of methane on four shale core samples from Eagle Ford reservoirs. Four shale core samples with TOC of 9.67% to 14.4% were used. Adsorption experiments were conducted at a temperature of 120 °C and to a maximum pressure of 10 MPa. The data obtained experimentally were compared with adsorption isotherm models to assess each model's applicability in describing the shale adsorption behaviour. A comparison of these models was performed using fitting and error analysis. It was observed that the calculated absolute adsorption of supercritical methane is higher than the excess adsorption. The percentage of differences between the absolute and excess adsorption is more significant at a pressure higher than the critical methane pressure of 9.6%. Sample EF C has the highest adsorption capacity of 1.308 mg g−1, followed by EF D 1.194 mg g−1, EF B 0.546 mg g−1, and EF A 0.455 mg g−1. Three statistical error analyses, average relative error (ARE), the Pearson chi-square (χ2) test and root mean square error (RMSE) deviation were used to assess the applicability of each model in describing the adsorption behaviour of shale samples. The order of adsorption isotherm fitting with experimental data is Toth > D–R = Freundlich > Langmuir. Error analysis shows that the Toth model has the lowest values compared to other models, 0.6% for EF B, 2.5% for EF C, and 2.2% for EF A and EF D, respectively.

EFFECT OF MULTIPLE FACTORS ON FLOW AND HEAT TRANSFER OF SUPERCRITICAL METHANE IN A MINICHANNEL WITH DIMPLED STRUCTURE

EFFECT OF MULTIPLE FACTORS ON FLOW AND HEAT TRANSFER OF SUPERCRITICAL METHANE IN A MINICHANNEL WITH DIMPLED STRUCTURE

Optimization of a Zigzag-channel printed circuit heat exchanger for supercritical methane flow

Printed circuit heat exchanger (PCHE) is a compact plate heat exchanger that etches microchannels on plates by chemical etching method and exploits bonding force between the atoms to achieve diffusion bonding. It has the promising applications in the fields of floating liquefied natural gas, nuclear reactor, hydrogen energy, etc. The influence of structural parameters on flow and heat transfer characteristics in a Zigzag-channel PCHE was investigated using supercritical methane as flow media. Three-dimensional turbulent steady numerical method was determined and verified through the SST k-ω turbulent model in FLUENT platform. The influence mechanism of structural parameters on flow and heat transfer characteristics was analyzed from temperature distribution, turbulent dissipation rate, vortex vector, turbulent intensity and helicity. The results indicated that the worse flow and better heat transfer performance exhibited under the condition with small channel diameter, small pitch and large bending angle. Meanwhile, the optimization analysis was also conducted though the coupling consideration of flow and heat transfer performances of PCHE using thermal performance factor (TPF). The optimum channel was obtained with the diameter, channel pitch, and bending angle of 1.427 mm, 24.6 mm, and 15° respectively, in scope of this study. The optimum structure parameters obtained herein will be instructive in the design of PCHE.