Charge Pressure Research Articles

Micro-occurrence of formation water in tight sandstone gas reservoirs of low hydrocarbon generating intensity: Case study of northern Tianhuan Depression in the Ordos Basin, NW China

A series of experimental techniques which contain casting thin slice observation, field emission scanning electron microscopy, high-pressure mercury injection, constant-velocity mercury injection, and NMR(nuclear magnetic resonance) were used to study the throat microstructure and microscopic occurrence of formation water in the Upper Paleozoic tight sandstone gas reservoir in northern Tianhuan Depression, Ordos Basin. The results show that intragranular dissolution pores, intercrystalline pores, and residual intergranular pores represent 33 %, 31 %, and 16 % of the pore types in the reservoir of the He8-Shan1 members in the northern Tianhuan Depression, respectively. Pore radii range from 80 μm to 300 μm, with an average of 154.18 μm, while throat radii range from 0.01 μm to 1.60 μm, with an average of 0.55 μm. Micron pores and nano throats control the seepage ability of the reservoirs, and the throat radius serves as the controlling factor. Formation water has four microscopic occurrences: bound water, capillary water, free water, and adsorbed water. At low charging pressure, a mixture of gas and water was found in the intergranular pores and dissolution pores controlled by macro throats, with a high gas content and existent free water; a small amount of membrane adsorption water was observed at high charging pressure. However, in the intergranular pores and dissolution pores controlled by medium-small throats, the mixture of gas and water at low charging pressure presents a low gas content and a large amount of capillary water, while at high charging pressure, the mixture of gas and water or pure gas presents a high gas content and a small amount of capillary water. Pure water controlled by tiny throats, on the other hand, was found at low charging pressure in the intergranular pores, whereas gas and water mixture was found at high charging pressure, but the gas content is low and bound water appears. In the intergranular micropores, pure water, which is bound water, is the primary composition at both low and high charging pressure. The throat radius cut-offs of the four kinds of formation water are 0.10 μm, 0.26 μm, and 0.28 μm, the permeability cutoffs are 0.21 × 10−3 μm2, 0.51 × 10−3 μm2, and 0.55 × 10−3 μm2, and the porosity cutoffs are 5.86 %, 7.99 %, and 8.18 %, respectively. The starting pressure gradient and throats less than 0.10 μm are controlling factors on the micro-occurrence and residual water saturation of formation water. As the amount of gas driving water increases in the natural gas accumulation process, the percentage of formation water controlled by large throats gradually decreases. Free water makes up 50 % of the research area, capillary water makes up 18 %, bound water compensates 30 %, adsorbed water is 2 %, and residual water saturation is about 32 %.

Experimental and Dynamic Analysis of a Small-Scale Double-Acting Four-Cylinder α-Type Stirling Engine

This research studies the double-acting four-cylinder α-type Stirling engine. A numerical model is developed by combining the thermodynamic model and dynamic model to study the engine performance. The pressure values of the working zone calculated using the thermodynamic model are taken into the dynamic model to calculate the forces acting on the mechanism. Then, the dynamic model further calculates the displacement, velocity, and acceleration of the mechanism link to provide the pistons’ displacements for the thermodynamic model. The model is also validated using experimental data obtained from testing an engine prototype. Under a heating temperature of 1000 K, cooling temperature of 315 K, charged pressure of 10 bar, and loading torque of 0.33 Nm, the engine is capable of achieving a shaft power of 26.0 W at 754 rpm. In addition, the thermal properties and the transient behavior of the engine can be further simulated using the validated numerical model.

CHARACTERIZING THE HYDROGEN TRANSPORT PROPERTIES OF RUBBERY POLYMERS BY GRAVIMETRIC ANALYSIS

ABSTRACTWe develop an ex situ technique to quantitatively analyze the transport properties of hydrogen gas dissolved under high pressure in rubbery polymers, such as cylindrical and spherical samples of nitrile butadiene rubber (NBR), ethylene propylene diene monomer (EPDM), and fluoroelastomer (FKM), which are potential sealing materials for hydrogen energy infrastructures. The technique consists of real-time gravimetric measurements during the desorption of hydrogen gas from samples using an electronic balance and a self-developed analysis program to determine the total charge (CH0), diffusivity (D), solubility (S) and permeability (P) of hydrogen. Dual absorption behavior is found for all three rubbers as the charging pressure increases. CH0 follows Henry's law at low pressures of up to ∼25 MPa, whereas the Langmuir model applies at high pressures. No significant pressure, size, or shape dependences are observed for D and P. The measured P values are consistent with those from the literature within the combined uncertainty evaluated. The effect of a carbon black filler mixed into rubber is discussed with respect to S and D. This method can be applicable as a standard test for the transport properties versus the pressure of various polymers irrespective of sample shape.

Linear Dynamic Analysis of Free-Piston Stirling Engines on Operable Charge Pressure and Working Frequency along with Experimental Verifications

This paper presents a linear dynamic analysis on operable charge pressure and working frequency of free-piston Stirling engines (FPSE) along with experimental verifications. The equations of motion of the FPSE are formulated as a 2-degree-of-freedom (DOF) vibration system of the power piston (PP) and displacer piston (DP), based on the state equation of ideal gas and the isothermal Stirling cycle model. The dynamic models of FPSE we considered are the 1-DOF simple vibration model of each piston and the 2-DOF root locus model of coupled pistons. We developed a test FPSE for verification of the dynamic models and conducted a series of experiments to measure the dynamic behaviors of PP and DP under varying charge pressures for various masses and stiffnesses of the PP. As a result, both prediction models showed good agreements with experimental results. The 1-DOF vibration model was found to be simple and effective for predicting the operating frequency and charge pressure of FPSE. The root locus method showed reasonable predictions with an operation criterion of the PP–DP phase angle of 90°. In addition, the FPSE was confirmed to operate in resonant oscillations when the DP–PP phase angle is 90°, based on analysis of the force vector diagram of the two pistons.

SERBEST DİSPLEYSIRLI BİR STİRLİNG MOTORUNUN NODAL TERMODİNAMİK VE DİNAMİK ANALİZİ

In this study, the dynamic and thermodynamic features of free displacer Stirling engines were investigated by preparing a simulation program. The dynamic component of the simulation program involves the movement equations of power piston, crankshaft and displacer. The thermodynamic component is a nodal analysis based on 24 nodal volumes. The study indicates that starting these engines requires an initial speed is required as the displacer system natural frequency. While the engine is running, the displacer exhibits some secondary vibrations (named as beatings) and causes irregularities in its work and power generation however, it can be minimized by changing some working parameters such as displacer mass, working fluid mass, external loading, spring constant etc. For each value of the working fluid charging pressure, a different spring is needed. While the spring constant is the same, the displacer mass can vary in a limited range. The thermal performance of the engine increases as the displacer mass is decreasing. For an engine working between 1000 K heater temperature, 356 K cooler temperature and 18 bar charging pressure, the effective thermal efficiency ranges between 21 and 26 %. An engine with a 3.5 liter total inner volume is capable of generating about 3.9 kW effective power and 4.7 kW indicated power. A strong relation is observed between engine performance and phase angle.

Dynamic flow instabilities of hydrocarbon fuel in a horizontal heating tube

To investigate dynamic flow instabilities of hydrocarbon fuel in thermal protection structure of the scramjet, experiment was conducted at the pressure of 1.5–3.0 MPa, heat flux of 190–250 kW⋅m−2, and the charge pressure at the surge tank of 0.5–1.0 MPa. Three main types of dynamic flow instabilities, pressure drop oscillation, density wave oscillation, and thermal oscillation took place during some experimental conditions. The influence of hydraulic characteristics of the test loop on dynamic flow instabilities was discussed. It was found that dynamic flow instabilities were mainly affected by the hydraulic characteristics of the test loop rather than the heating section. Pressure drop oscillation with large fluctuation amplitude and long period occurred in the negative slope region of the pressure drop curve. Density wave oscillation appeared in the positive slope region with low flow rate. The fluctuation amplitude and period of density wave oscillation were much smaller than those of pressure drop oscillation. Dynamic flow instabilities were more intense at lower pressure and higher heat flux. The oscillation region was independent of the compressible volume. However, a large compressible volume could promote the fluctuation amplitude of both inlet mass flow rate and outlet fuel temperature.

Effects of the regenerator on engine performance of a rhombic drive beta type stirling engine

ABSTRACT Regenerative cycles have higher thermal efficiency than other closed cycles because of their heat recovery capability. In this manner, Stirling engines have advantage because regeneration can be applied easily to the cycle. In this study, effects of the regenerator on engine performance of a beta type Stirling were examined. Stainless steel wire, having 0.15 mm diameter and 15% solidity ratio, were used as regenerator material. Experiments were carried out at 800°C hot end temperature and the charge pressures for 3, 4, 5, 6 bar. Maximum power and torque of the engine were measured as 1831.09 W at 1035 rpm, and 19.74 Nm at 837 rpm for engine without regenerator while as 1940.45 W at 1046 rpm, and 20.55 Nm at 867 rpm for engine with regenerator, respectively. It was found that the use of regenerator, the engine power and engine torque increased by 5.97% and 4% respectively.

The examination of performance characteristics of a beta‐type Stirling engine with a rhombic mechanism: The influence of various working fluids and displacer piston materials

In this study, to develop a power generation system that can use renewable energy resources more efficiently, a beta-type Stirling engine with rhombic mechanism was designed and manufactured. Kinematic and thermodynamic analyses of a beta-type Stirling engine were performed numerically in the Fortran program. Volume and pressure changes depending on crankshaft angle of Stirling engine were made using the isothermal analysis. The effects of the basic parameters related to engine performance, such as working fluid mass, charge pressure, heater, and coolant temperatures, on the net work amount were investigated. Five different gases, including helium, air, nitrogen, carbon dioxide, and argon, were used as a working fluid in experimental studies. The effects of all these gases on engine performance characteristics were examined at charge pressures of 1 to 5 bar for two different displacer pistons made of stainless steel and titanium material. The performance characteristics of Stirling engine manufactured were tested using a specially designed electrical heater, at 727°C hot end and 27°C cold end temperature, depending on engine speed. In all experimental studies, maximum power output was acquired to be 215.48 W, at 4 bar and 550 rpm when a stainless steel displacer piston and helium gas as a working fluid were used, and maximum torque value was acquired to be 7.54 Nm, at 5 bar and 150 rpm. The lowest engine power output among maximum engine powers was acquired to be 34.66 W when argon gas was used as a working fluid at 3 bar and 300 rpm, using a displacer piston made of titanium material. Maximum power output acquired in the experimental studies using a stainless steel displacer piston and helium; it was determined that it is 72.12%, 73.69%, 241.49%, and 288.81% higher than the engine power acquired by nitrogen, air, carbon dioxide, and argon gases, respectively.

ПНЕВМОКОМПЕНСАТОР ДЛЯ ПЛУНЖЕРНОГО НАСОСА С ПОГРУЖНЫМ ЛИНЕЙНЫМ ПРИВОДОМ

Актуальность. Разработана конструкция и принцип работы пневмокомпенсатора для плунжерного насоса с погружным магнитоэлектрическим двигателем, позволяющего снизить амплитуду колебаний давления на выкиде насоса путем выравнивания скорости потока жидкости в лифтовых трубах. При использовании в пневмокомпенсаторах диафрагмы, выполненной из резины с армированием, она становится устойчивой к разрушению, что в целом увеличивает эффективность работы и срок эксплуатации пневмокомпенсатора. Цель: разработать пневмокомпенсатор для плунжерного насоса с погружным магнитоэлектрическим двигателем. Провести прочностной анализ и оценку эффективности применения диафрагмы с армированием в пневмокомпенсаторах, применяемых для снижения пульсаций скорости и давления потока флюида в насосно-компрессорных трубах; обосновать выбор материала диафрагмы пневмокомпенсатора. Объекты: скважинные пневмокомпенсаторы, погружной бесштанговый плунжерный насос с линейным магнитоэлектрическим двигателем, колонна насосно-компрессорных труб. Методы: имитационное моделирование диафрагмы, закрепленной на перфорированной трубе, с применением программного комплекса «Компас 3D» модуль APMFEM; задание в граничных условиях расчетной модели технологических параметров при моделировании численных значений скорости, расхода, давления, температуры аналогичными действующей скважинной установке. Результаты. Установлено, что максимальные напряжения, возникающие в диафрагме в процессе работы пневмокомпенсатора, в 4 раза меньше предельно допускаемых, что показывает работоспособность пневмокомпенсатора в скважинных условиях. Показано положительное влияние армирования диафрагмы с точки зрения снижения максимальных напряжений в эластичной оболочке. Проанализировано влияние технологических параметров пневмокомпенсаторов (суммарного газового объема, начального давления в газовой камере) на эффективность их работы. Обосновано оптимальное давление зарядки пневмокомпенсаторов, которое не должно превышать минимально давление в насосно-компрессорных трубах в течение цикла откачки, чтобы исключить негативное влияние прижатия эластичной оболочки к перфорированной трубе (внутренней стенке пневмокомпенсатора).

The investigation of an energetic and exergetic performance characteristics of a beta-type Stirling engine with a rhombic drive mechanism

In this study, effects of using helium, nitrogen, air, carbon dioxide and argon gases as working fluid in a beta-type Stirling engine with rhombic drive mechanism and swept volume of 365 cm3 on the engine performance characteristics for two different stainless steel and titanium displacer pistons at charge pressures of 1–5 bar were examined. The performance characteristics of manufactured Stirling engine were investigated at 1000 K (± 10 K) hot end and 300 K (± 5 K) cold end temperatures using a specifically designed electrical heater. Energy and exergy analyses were carried out using temperature, pressure, speed and torque values measured in performance tests. As a result of the exergy analysis, helium gas performed the best in the stainless steel displacer piston at a charge pressure of 4 bar and an engine speed of 550 rpm. Under the said conditions, 0.3726 W/K entropy generation and 195.53 W destroyed exergy were calculated in thermodynamic analysis in the helium working fluid. Furthermore, under the same conditions, helium gas achieved the highest efficiency values of 48.04% for thermal efficiency, 56.54% for exergy efficiency and 69.2% for Carnot efficiency. The lowest exergetic performance was revealed in titanium displacer piston when argon was used as working fluid.

Multi-objective optimum design of an alpha type Stirling engine using meta-models and co-simulation approach

An alpha type Stirling engine was optimized using meta-models considering uninterrupted electric power supply concurrently with natural gas combi boilers at homes during electricity interruptions. To predict and optimize the power and efficiency of the designed Stirling engine, an artificial neural network (ANN) model was trained as a meta-model. The ANN modeling method was used in solving a multi-objective Pareto optimization problem under some constraints to determine the optimum engine parameters. The design parameters were swept volume, hot and cold cylinder temperatures, gas constant, charge pressure and engine operation speed. Feed forward and Levenberg–Marquardt back propagation algorithms were evaluated to determine the best resulting network architecture that was found as 6–12–8–1. Subsequently, the fraction of variance (Rf) value was calculated close to 1 and the absolute mean error percentage (AMEP) was calculated as 6.07%. Trained ANN model was used in solving the multi-objective optimization problem. Using the optimum design parameters, the meta-model predicted the power as 73.3 W and efficiency as 32.2%. Co-simulation approach was followed to verify the optimization results, and the nominal power output and corresponding efficiency were calculated using the Schmidt theory and the calibrated 1-D model created by the GT-Suite software that yield respectively, 144.6 W and 85.8 W for the power and 35% and 35.1% for the cycle efficiency. Consequently, the use of an ANN model in solving the associated optimization problem proved itself as a fast, accurate enough and powerful method to find the optimum design parameters and predict the engine performance.

Study on flow dynamic characteristic of bladder pressure pulsation attenuator based on dynamic mesh technology

To solve the problem that the flow dynamic characteristic of the bladder pressure pulsation attenuator cannot be quantitatively analyzed, a bladder pressure pulsation attenuator was taken as the research object, and the dynamic mesh technology was combined with the User-Defined-Function (UDF) to numerically simulate the working process of the attenuator. Overcoming the divergence problem in finite-element fluid calculation and the negative volume problem in mesh updating process, the bladder pressure pulsation attenuator was dynamically simulated under different fluctuating frequencies and different inflatable pressure, the change of internal flow field was monitored in time. The results show that the resistance loss through the attenuator increases with the increase of the frequency and the increase of the charging pressure. The local resistance loss is much higher than the frictional resistance loss. The simulation results match the experimental results, that verifies the model's validity and correctness, and also provides a new method and idea to improve bladder attenuator's resistance loss and analyze the variable boundary problem.

The use of high decomposition temperature materials for chemical looping electricity storage

Using chemical looping as a large-scale electricity storage mechanism, where electricity is converted and stored as chemical energy via a thermochemical reaction, is an attractive concept. It can achieve high volumetric capacity and moderate round-trip efficiency. In early schemes, a heat pump was employed to convert electricity to heat, but its operating temperature is limited and only those solid oxides capable of releasing oxygen at low temperatures (below 900 K) were feasible. Therefore, ways of using materials with a higher decomposition temperature, i.e. the commonly used materials in chemical looping systems, are investigated. Two methods are proposed: using a vacuum pump to reduce the charging pressure or an electrical heater to increase the charging temperature. Results show using a vacuum pump to be infeasible, whereas, a simplified charging cycle only comprising of an electrical heater and a recuperator is deemed optimal. This system capacity can be as high as 600–800 kWh/m3 with round-trip efficiency in the range of 40–55%.

Influence of the charging pressure of the hydraulic pneumatic accumulator of the communal machine control device on the pressure force of the brushed working body

The article is devoted to the actual problem of increasing the efficiency of cleaning the roadway with a communal machine. To increase the cleaning efficiency, it is necessary to provide the required pressing force and thus the required area of the contact spot between the brush pile and the surface to be cleaned, which can be done by using a position control device for the brush working equipment.Research methods. In the process of research were used the following methods: analysis, synthesis, ascent from the abstract to the concrete. The results of the study of the influence of the parameters of the control device on the criterion of the efficiency of the working process of the communal machine are presented.Results. As a result of the analysis of the process of interaction of the brush working equipment with the surface being cleaned, the dependences connecting the standard deviation of the pressing force of the brush working equipment to the surface to be cleaned from the required value, taking into account the wear of the pile and the charging pressure of the hydraulic pneumatic accumulator, were revealed, their approximation was carried out, and the regression equation was obtained.Conclusions. The studies carried out made it possible to obtain regression equations which are used to determine the optimal value of the standard deviation of the pressing force from the required one for different degrees of wear of the pile, depending on the charging pressure of the hydraulic pneumatic accumulator. The research results can be applied in the design of automatic control systems for the position of the working bodies of construction and road machines.

First-principles-assisted band gap predictions of methylammonium metal formates

Identifying metal-organic frameworks that are applicable in the visible light area is significant. In this study, the band gaps of six different systems of methylammonium metal formates ([CH3NH3][M(HCOO)3] (M = Ni, Cu, Zn, Ge, Sn, and Ba)) were examined systematically. The formation energies of hypothetically designed systems of methylammonium germanium formate ([CH3NH3][Ge(HCOO)3]), methylammonium tin formate ([CH3NH3][Sn(HCOO)3]), and methylammonium barium formate ([CH3NH3][Ba(HCOO)3]) were calculated to investigate their stability. Among the compounds, methylammonium barium formate ([CH3NH3][Ba(HCOO)3]) and methylammonium copper formate ([CH3NH3][Cu(HCOO)3]) possessed the highest and lowest band gap, respectively. In addition, the effects of charge transfer and pressure on the band gaps of methylammonium nickel formate ([CH3NH3][Ni(HCOO)3]) were explored.

Investigation of thermal and fluidic losses and their effect on the performances of a Stirling refrigerator

The design of a Stirling machine requires the understanding of the processes that govern their operation to predict the optimum operating parameters of the machine. The modified simple model using the geometrical parameters of the FEMTO-ST engine model is applied in this paper to investigate the trend of losses with respect to operating frequency and charging pressure. The variation of pressure drops across the regenerator and heat exchangers have been investigated as functions of operating frequency and charging pressure in order to predict the extent of fluid friction losses. The share of different power and heat losses as well as their effects on cooling performance have been evaluated at the different operating frequencies and charging pressures. The share of fluid friction loss and loss due to regenerator imperfection increase with rotational speed and charging pressure.

Performance analysis of free piston Stirling engine based on the phasor notation method

The free piston Stirling engine (FPSE) is a couple system of dynamics and thermodynamics. Due to the complicated and interactive relationships between the dynamic parameters and thermodynamic parameters, the performance of the FPSE is always difficult to predict and evaluate. The phasor notation method is proposed based on a thermodynamic-dynamic coupled model of a beta-type FPSE in this paper. The output power and efficiency under the different heating temperature and charging pressure are analysed and compared. In addition, based on the Sage numerical model, the influences of heating temperature and charging pressure on the pistons’ displacement amplitudes, power work and efficiency are revealed. This study can provide the assistance for the performance analysis, prediction and optimization of the FPSE.

Development of a 100-Watt-Scale Beta-Type Low Temperature Difference Stirling Engine Prototype

This paper documents the ongoing design process of a Stirling engine prototype for a source temperature of 95 °C, aiming to achieve shaft power on the order of 100 Watts. The engine will serve to produce experimental data for the validation of a numerical low temperature Stirling model. The higher-level motivation is to assess the technical and economical potential of producing power from abundant sources of low temperature heat by using Stirling engines. Design decisions are governed by the goals of minimizing energy losses and maximizing the variability of operating points through variable heat exchanger geometry, compression ratio and charge pressure. The resulting design is a beta engine with a total gas volume around 100 liters. It features displacer and power pistons in a combined cylindrical working space and a mechanism using pivoting links similar to a bellcrank. The stroke of the power piston is adjustable while maintaining a constant top dead center position. A component critical for friction is the power piston seal, for which a low friction rolling seal and a conventional sliding seal were considered. As of June 2021, the development is at an advanced state and the first set of components are entering production.

A Study of Mesh Sheets of 3-kW Stirling Engine

In recent years, the interest in low-pollution and high-efficiency heat engines has been increasing due to the growing awareness of environmental protection, and power generation at relatively low temperatures, such as use of exhaust heat and sunlight, has been attracting attention. Compared with other heat engines, Stirling engine is very important because it can be driven by any heat source at low temperatures, such as exhaust heat, and it does not emit exhaust gas. In order to realize a more efficient Stirling engine, it is essential to design a heat exchange system that is suitable for each component. Performance measurement and analysis on a new mesh regenerator material at low temperature difference using a 2-piston alpha-type 3-kW Stirling engine, NS03T are carried out. Mesh sheets developed for high performance Stirling engines can be designed with CAD and CAM technologies by etching process. For this study, M5 and M7 mesh sheets which are thin sheets of stainless steel with square holes in a grid arrangement, are used. With nitrogen and helium as the working fluid, the engine performance is measured by changing the charge pressure, heating temperature, and engine speed to clarify the flow resistance and heat transfer characteristics of the M5 and M7.

A miniature Stirling cryocooler operating above 100 Hz down to liquid nitrogen temperature

Working temperature of infrared detectors increases to higher than 100 K with the breakthrough of infrared materials, and the HOT (High Operation Temperature) cryocoolers with features of low weight and volume for infrared detectors cooling are now attracting more attentions. Increasing the operating frequency of the Stirling cryocooler to ultra-high level (>100 Hz) can significantly reduce the volume and weight of it, but the complicated acoustic and mechanical coupling inside the Stirling cryocooler limits the efficiency of Stirling cryocoolers operating above 100 Hz. In this paper, a pneumatically driven split-Stirling cryocooler operating above 100 Hz is designed and fabricated based on the Acoustic-Mechanical-Electrical (AcME) coupling method, and the cryocooler achieves a no-load temperature of about 77 K and the net refrigeration power at 90.0 K is 0.28 W. The operating frequency is 105 Hz and the charging pressure is 2.50 MPa.To the knowledge of the authors, the cryocooler is the first pneumatically driven split-Stirling cryocooler operating above 100 Hz working at liquid nitrogen temperature. This study confirms the feasibility of AcME coupling method, and the optimized design of ultra-high working frequency Stirling cryocooler based on this method.