Isothermal Expansion Processes Research Articles

Modeling of a Zero CO2 and Zero Heat Pollution Compressed Air Engine for the Urban Transport Sector

Zero CO2 and Zero heat pollution compressed air engine for the urban transport sector is an engine design that is powered and lubricated solely by compressed air. In other to guarantee these functionalities for the engine design, its modeling was done following the mechanical engineering design method. This article highlights the creation of a mathematical model of the engine. This work covers the design synthesis and the analysis of the kinematics of the engine. For the design synthesis; FAST, GRAFCET and later one realization of conceptual sketches all deductions from the problem definition. With the sketches considered, the kinematics and dynamic formulations where later on realized. The design chosen highlight’s the external forces to come principally from an isothermal expansion process of the compressed air what is termed the expansion chamber of the engine. The analysis was done on the kinematics of the engine with considerations of some assumptions. This article ends with remarkable results as it concerns the engine’s simplicity and guaranteed high efficiency. These conclusions were drawn from the compact nature of the design, the low part count and the reduced displaceable masses which give little of no conflicting movements in the engine design.

Study on quasi-isothermal expansion process of compressed air based on spray heat transfer

The piston expander with compressed air as working medium has been widely studied for its advantages of cleanliness, reliability and safety, but its application is limited by low exhaust temperature and low output power/efficiency. Theoretically the isothermal expansion process is the best method to solve the above problems. Spraying into the cylinder can greatly improve the heat transfer rate, which is an effective way to realize the isothermal expansion process. In order to realize the isothermal expansion process of piston expander,we propose a method to inject micron water mist at high temperature into the cylinder. Firstly, the nonlinear transient mathematical model of the adiabatic expansion process is established by using energy equation, gas state equation and Lagrange dynamics equation. The experimental results verify the effectiveness of the model. Secondly,based on the adiabatic expansion model, the heat transfer equation of small water droplet and air in the cylinder is introduced, and the model is extended to the nonlinear transient mathematical model of quasi-isothermal expansion process. Simulation results showed that under the given boundary conditions, compared with the adiabatic expansion model, the quasi isothermal expansion model significantly higher temperature of the air inside the cylinder, the average air temperature in cylinder increased by 24.7%, because the pressure increase in the inlet and expansion stages of the quasi-isothermal expansion model is less than that in the exhaust stage, the output power/ efficiency of the quasi isothermal expansion model is reduced by 7.7%/12.3%. Based on the analysis of the above results and the calculation of the air power in the exhaust stage of the two expansion models, a new type of two-stage piston expander is proposed. This study will provide theoretical support for the experimental study of quasi-isothermal expansion process of spray heat transfer.

Thermodynamic and exergy analysis of a combined pumped hydro and compressed air energy storage system

The Pumped-Hydro and Compressed-Air (PHCA) is a new energy storage system which can be coordinated with renewable energy sources such as wind and solar. In this paper, a comprehensive thermodynamic and exergy model is developed to study the thermal characteristics of a combined Pumped-Hydro and Compressed-Air (PHCA) energy storage system. The effect of key parameters, including storage pressure, pre-set pressure, air-compression mode and pump/hydroturbine efficiency on system performance is investigated. The results showed that an optimum pre-set pressure existed to maximize energy storage level for a specific storage pressure. The storage pressure also showed a large effect on the energy storage level and work output. As the storage pressure increased from 4 to 16 MPa, the energy storage level and work output increased remarkably. Furthermore, the performance of a PHCA system was largely influenced by the air compression/expansion mode in the energy storage vessel. The PHCA system stored 10% more energy through an isothermal compression process than that through an isentropic air compression process. It generated 14% more work output through an isothermal expansion process than that through an isentropic air expansion process. The exergy analyses showed that exergy destruction in pump was about 15% higher than that in hydroturbine.

Research and application of plasma recoil pressure physical model for pulsed laser ablation material

In this paper, the physical properties of plasma in the isothermal expansion process when material is ablated by pulsed laser is analyzed. It is shown that the recoil pressure distribution of the plasma near the material surface indicates an exponential decrease as the distance from the material surface increases and the recoil pressure distribution exhibits the characteristics of a Poisson distribution in the X direction; the recoil pressure distribution is in accordance with Maxwell's velocity distribution law in the Y direction; the recoil pressure distribution conforms to a Gaussian distribution in the Z direction. A three-dimensional plasma recoil pressure equation and the plasma kinetic equation for laser-ablation materials are studied. These equations only require parameters to relate to plasma temperature, laser parameters and material properties, thus having a certain diversity. The equations are used for numerically analyzing the pulsed laser ablation of a bronze-bonded diamond grinding wheel. The numerical analysis shows that in the X and Y direction the plasma expansion dimension shows linear growth. After the pulse is ended, the plasma expansion dimension values reach their maxima. The plasma expansion velocity shows nonlinear growth. After the pulse is ended, the expansion velocity first increases and then decreases along the X direction and Y direction. Based on the analyses of the plasma expansion dimension and the plasma expansion velocity, the maximum plasma recoil pressure appears at a location approximately 0.05 mm away from the surface of the grinding wheel after approximately 25 ns. Through calculating the Saha equation, the degree of ionization is 0.0012 at 7506 K, and the maximum plasma recoil pressure value is approximately 870 Pa. The experiments on the pulsed laser ablation of a bronze-bonded diamond grinding wheel under the corresponding conditions are conducted. A high-speed camera is used to observe splash phenomenon in the laser ablation process. A grating spectrometer is used to measure the plasma emission spectrum. According to the Boltzmann plot method, the electron temperature value is calculated to be 7506 K; according to the Stark broadening method, the electron density values range from 7.6451015 to 1.16081016 cm-3 and the recoil pressure values from 792 to 1203 Pa. The experiments show that the recoil pressure during the pulsed laser ablation of bronze-bonded diamond grinding wheel process can be ignored, and the correctness and feasibility of the plasma recoil pressure equation are also verified, which has heuristic significance for optimizing the laser ablation process.

Simulation and measurements of volumetric and phase behavior of carbon dioxide + higher alkanes at high pressure: CO2 + n-decane at temperatures (313–410) K and pressures up to 76 MPa

Injection of CO2 in hydrocarbon rock formation is one of the proven technologies for both enhanced oil recovery and carbon sequestration. Accurate knowledge of thermodynamic properties of CO2 and reservoir fluid mixtures are required for successful design and operation. In this work, new ρTp and bubble pressure pb measurements are reported for the binary system of carbon dioxide (1)+n-decane (2). Compressed liquid density was determined from the complex resonance frequency of a vibrating U-tube driven by a lock-in amplifier and bubble points were visually detected and also calculated from the discontinuity of a p-V plot of a constant composition isothermal expansion process (CCE). The measurements were made along three isotherms at temperatures T=(313, 363, and 410) K at pressures up to 76MPa for three concentrations of carbon dioxide mole fraction x1=(0.207, 0.471, and 0.730). The experimental results are compared with previous experimental data in literature, and with predictions from four types of equations of state (EOS), commonly used in petroleum and chemical industry: (1) cubic, Peng-Robinson (PR); (2) virial, Benedict−Webb−Rubin−Starling (BWRS); multi-parameters, Groupe European de Recherche Gaziere (GERG-2008); and (4) Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT). Analysis of all experimental data, in previous literature and this work, show a systematic increase in deviations from both BWRS and PC-SAFT from 1% to about 10% with increasing carbon dioxide mole fraction which is a clear evidence of the need for adjusting the equation’s parameters, especially at pressures close to bubble points. Best prediction for density was obtained with GERG-2008 EOS, with deviations of about 1%, for all CO2 mole fractions from (0.05 to 0.87), and best prediction for phase behavior was obtained by PR EOS. Earlier experimental data are only limited to 40MPa, while this work extends the measurements to a higher range, of 76MPa and 410K, commonly encountered in gas reservoirs and supercritical CO2 injection processes, and not studied before.

An Isothermal Steam Expander for an Industrial Steam Supplying System

Steam is an essential medium used in the industrial process. To ensure steam quality, small and middle scale boilers are often adopted. However, because a higher steam pressure (compared to the necessary steam pressure) is generated, the boiler’s steam pressure will be reduced via a pressure regulator before the steam is directed through the process. Unfortunately, pressure is somewhat wasted during the reducing process. Therefore, in order to promote energy efficiency, a pressure regulator is replaced by a steam expander. With this steam expander, the pressure will be transformed into mechanical energy and extracted during the expansion process. A new type of isothermal steam expander for an industrial steam supplying system will be presented in the paper. The isothermal steam expander will improve the energy efficiency of a traditional steam expander by replacing the isentropic process with an isothermal expansion process. With this, steam condensation will decrease, energy will increase, and steam quality will be improved. Moreover, the mathematical model of the isothermal steam expander will be established by using the Schmidt theory, the same principle used to analyze Stirling engines. Consequently, by verifying the correctness of the theoretical model for the isothermal steam expander using experimental data, a prototype of 100 c.c. isothermal steam expander is constructed.

Geological storage of carbon dioxide by residual gas and solubility trapping

A CO 2 geological storage technology based on residual gas and solubility trapping is proposed. First, we experimentally evaluated the maximum trapped CO 2 saturation for typical conditions of aquifers at depths from 750 to 1000 m. To avoid the experimental difficulty due to the dissolution of CO 2 in water and the compressibility of CO 2, the trapped gas saturations were estimated from the relationship between pressure and volume under an isothermal expansion process. The trapped gas saturation is in the range from 24.8 to 28.2% despite the variation of CO 2 density, viscosity and interfacial tension. Therefore, at least 38.8% of CO 2 would be stored by residual gas and solubility trapping per unit volume as compared to physical trapping with cap rock. The storage potential of Japan by the proposed scheme is evaluated to be 71.6 Gt CO 2, which corresponds to the emission in Japan for 53.6 years. The storage by residual gas and solubility trapping not only augments the storage capacity but also provides the sites that are located close to the large emission sources.

エクセルギー再生燃焼によるガスタービンの高性能化

Exergy regenerating combustion is aimed at direct extraction of high-quality energy, such as electric power, light, mechanical work from combustion. In an isothermal expansion process, all energy released by combustion is converted to external work. If the internal heating is utilized in the compression process, we can obtain a higher pressure ratio as well as high temperatures at the same compression ratio. A new gas turbine cycle based on isothermal expansion combustion and polytropic compression are proposed. Different from conventional views, the feature of this cycle indicates that the target of gas turbine is a high pressure ratio rather than a higher peaking temperature. In comparison to the case of a conventional gas turbine, higher efficiency is expected due to the high pressure ratio. Inasmuch as the temperature of exhaust gas is identical with maximum, it is plausible for combined cycle. In addition, related combustion schemes are briefly discussed.

Thermodynamic analysis of the two-component, two-phase Stirling cycle.

A theoretical analysis has been carried out of the two-component, two-phase regenerative Stirling cycle using a mixture of condensable and incondensable gases as a working fluid. When the condensable component always remains in its wet region throughout the entire cycle, the thermal efficiency is smaller, while the specific work is remarkably larger, if compared with those of an ordinary one-component Stirling cycle working under the same temperature conditions. In the case where the condensable component is superheated during the isothermal expansion process, the rate of increase of the specific work with the cycle compression ratio becomes somewhat smaller than that of the cycle working in the wet region, but considerably higher thermal efficiency can be obtained. Generally, the cycle characteristics are mainly dependent on the thermophysical properties of the condensable component.

A Note on Anomalous Adiabatic Cooling Rates in Clouds

During the brief period of extremely rapid condensation accompanying the activation phase of cloud-droplet growth, latent-heat release produces adiabatic cooling rates well below the conventional saturated adiabatic value. Using results of drop-growth calculations made by Mordy, the main features of this anomalous thermodynamic process are examined quantitatively. For a convective updraft of the not excessive speed of 1 m sec−1, it is found that an isothermal expansion process prevails throughout a depth of approximately 10 m just above cloud-base. It seems almost certain that the even more extreme case of expansion in which the parcel temperature actually rises slightly during ascent will be found to occur when computer studies are extended to models with updraft speeds closer to the maximum observed cumulus-base up-draft speeds.

A Comparison of Adiabatic and Isothermal Expansion Processes in Rocket Nozzles

An analysis has been made of the expansion of gases through a de Laval nozzle under isothermal condit ions. It is shown that for ideal gases, the increase in kinetic energy of the gases is equal to the heat transferred into the gas to mainta in constant temperature. The initial energy, or temperature, enters only in the design of the nozzle and determination of the pressure ratio required for the transference of the fixed quanti ty of heat . Unlike the adiabatic case, the jet velocity is not l imited by the initial energy content of the gas but only by the pressure ratio or energy content of the reservoir transferring the heat . Formulas are derived for isothermal exhaust velocity, mass flow, and thrust coefficient which are analogous to those for adiabatic flow.