Adiabatic Expansion Process Research Articles

A novel electrochemical system with adiabatic pre-charging and pre-discharging processes for efficient refrigeration

The extraordinary thermal-to-electricity conversion efficiency of thermally regenerative electrochemical cycle triggers interest in its reverse counterpart, namely thermally regenerative electrochemical refrigerator (TRER), a promising alternative to conventional cooling devices. Nevertheless, due to three fundamental obstacles, the practically feasible TRER model is still absent, which hinders the development of follow-up research. To break this bottleneck, heating by discharging and cooling by charging effects are innovatively utilized to construct TRER models where the electrochemical counterparts of traditional adiabatic compression and expansion processes, namely adiabatic pre-charging and pre-discharging processes, are proposed and introduced. Significantly, the maximum coefficient of performance (COP) and the COP at maximum cooling power are predicted to achieve up to 40% and 5% of Carnot COP, respectively for the given values of parameters. Moreover, the great potential for efficient refrigeration is highlighted by comparing the obtained results with various refrigeration systems. This work lays the foundation for further experimental investigations and opens a new avenue for constructing other novel electrochemical cycles.

Processing, characteristics and applications of expanded grains

The popping and puffing are adiabatic expansion process in which the grains are exposed to high temperature for short time. The heat increases vapour pressure inside the grain leading to rupture of outer shell with expansion of starchy endosperm to several folds creating a crispy and aerated puffed snack. Conventional puffing methods use hot air, oil and sand as medium of puffing, whereas non-conventional puffing methods make use of microwave, fluidized air and pressure differential in system. Although it is commonly believed that processing conditions solely influence the quality of expanded grains, many other variables such as physical, chemical and genetic characteristics of grain, post-harvest handling practices, storage conditions and pre-treatments can also largely affect quality indices of expanded grains. As exposed to heat for only short time, expanded grains retain majority of nutrients and even improved digestibility and nutrient bioavailability traits. Flour obtained by milling of expanded grains exhibit desired functional properties expected in bakery products. This paper briefly discussed the factors influencing puffing quality and effects of puffing on physicochemical and morphological characteristics of grain along with its applications.

Disquisitions Relating to Principles of Thermodynamic Equilibrium in Climate Modelling.

We revisit the fundamental principles of thermodynamic equilibrium in relation to heat transfer processes within the Earth’s atmosphere. A knowledge of equilibrium states at ambient temperatures (T) and pressures (p) and deviations for these p-T states due to various transport ‘forces’ and flux events give rise to gradients (dT/dz) and (dp/dz) of height z throughout the atmosphere. Fluctuations about these troposphere averages determine weather and climates. Concentric and time-span average values <T> (z, Δt)) and its gradients known as the lapse rate = d < T(z) >/dz have hitherto been assumed in climate models to be determined by a closed, reversible, and adiabatic expansion process against the constant gravitational force of acceleration (g). Thermodynamics tells us nothing about the process mechanisms, but adiabatic-expansion hypothesis is deemed in climate computer models to be convection rather than conduction or radiation. This prevailing climate modelling hypothesis violates the 2nd law of thermodynamics. This idealized hypothetical process cannot be the causal explanation of the experimentally observed mean lapse rate (approx.−6.5 K/km) in the troposphere. Rather, the troposphere lapse rate is primarily determined by the radiation heat-transfer processes between black-body or IR emissivity and IR and sunlight absorption. When the effect of transducer gases (H2O and CO2) is added to the Earth’s emission radiation balance in a 1D-2level primitive model, a linear lapse rate is obtained. This rigorous result for a perturbing cooling effect of transducer (‘greenhouse’) gases on an otherwise sunlight-transducer gas-free troposphere has profound implications. One corollary is the conclusion that increasing the concentration of an existing weak transducer, i.e., CO2, could only have a net cooling effect, if any, on the concentric average <T> (z = 0) at sea level and lower troposphere (z < 1 km). A more plausible explanation of global warming is the enthalpy emission ’footprint’ of all fuels, including nuclear.

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.

Thermal-mechanical coefficient analysis of adiabatic compressor and expander in compressed air energy storage systems

Compressed air energy storage (CAES) technology can play an important role in large-scale utilization of renewable energy, the peak shaving and valley filling of power system, and distributed energy system development. Multi-stage compression and expansion units are key components in CAES systems, while the two key processes exist insufficient study, such as a lack of considering the coordination of temperature and pressure, ignoring coupling relationship between compressor and expander when typically being analyzed independently. To cope with the above critical issues, the new concept of thermal-mechanical coefficient is put forward based on the coupling relationship between temperature and pressure in adiabatic compression and expansion processes, and a C–P diagram (C is thermal-mechanical coefficient, and P is a function of pressure) is established to illustrate the thermodynamic processes concentrating on their work transfer. Besides, the expression of change rate of exergy to enthalpy for adiabatic compression and expansion processes is revealed. By depicting the C–P diagram of single-stage CAES system, it highlights that the thermal-mechanical coefficient of expander is higher compared with that of compressor, but with shorter change in the x-coordinate representing P that results in smaller work output for expander. In addition, it is found that the change of thermal-mechanical coefficient is generally accompanied with thermal-work conversion or heating/cooling effect. When drawing the C–P diagram of a multi-stage CAES system, the influence of heat exchanger's heat/pressure loss and the reduction of expander stage number on system's work transfer process is clearly shown. Significantly, results show that increasing the inlet temperature of expander is beneficial to enhance thermal-mechanical coefficient, which enables the thermal-work conversion ratio to be improved especially at higher inlet pressure and lower outlet pressure.

Theoretical study of the critical dynamic behaviors for pore collapse in explosive

The shock loading process of porous explosive is simulated by molecular dynamics for different pore diameters and piston velocities. We find that the defect evolution consists of three steps: pore collapse, stress relaxation and hot spot evolution. The critical dynamic behaviors for each step are investigated. First, at the pore collapse process, the shock wave reflected at pore face induces rarefaction waves. Two reflection types are considered: downside face reflection and upside face reflection. The wave reflection equations are derived. Second, at the stress relaxation process, a spherical rebounding wave is obtained. For low spherical radius, the rebounding wave is supersonic; and for high spherical radius, the rebounding wave is sonic. The propagation of rebounding wave is an adiabatic expansion process for hot spot, therefore, the hot spot temperature decreases quickly at this stage. Third, by considering the thermal diffusion and thermal decomposition effects, the hot spot ignition equation is derived, and the critical temperature for ignition is evaluated. A complete physical picture of defect evolution is obtained.

Dark-state sideband cooling in an atomic ensemble

We utilize the dark state in a {\Lambda}-type three-level system to cool an ensemble of 85Rb atoms in an optical lattice [Morigi et al., Phys. Rev. Lett. 85, 4458 (2000)]. The common suppression of the carrier transition of atoms with different vibrational frequencies allows them to reach a subrecoil temperature of 100 nK after being released from the optical lattice. A nearly zero vibrational quantum number is determined from the time-of-flight measurements and adiabatic expansion process. The features of sideband cooling are examined in various parameter spaces. Our results show that dark-state sideband cooling is a simple and compelling method for preparing a large ensemble of atoms into their vibrational ground state of a harmonic potential and can be generalized to different species of atoms and molecules for studying ultracold physics that demands recoil temperature and below.

Analysis of the adiabatic process by using the thermodynamic property diagram of water vapor

In the steam power plant, the working medium used for energy transformation is water vapor. The thermodynamic properties of water vapor are usually obtained by using water vapor tables and charts. Adiabatic process of water vapor is widespread in engineering applications. The adiabatic process is realized without heat addition or rejection and the entropy of the working medium during a reversible adiabatic process remains constant. During an adiabatic expansion process, superheated steam turns into saturated vapor , and further into wet vapor, the pressure and the temperature of the steam decreases. The entropy during a irreversible adiabatic process increases. In general, when analyzing the thermodynamic process of water vapor, we first determine the state parameters by using charts and tables, and then make relevant calculations according to the first law of thermodynamics.

Experimental investigation of spray-sublimation cooling system with CO2 dry-ice particles

Thermal management system (TMS) is becoming a major factor to restrict the development of electronic devices, thus an advanced cooling approach is urgently needed for satisfying the increasing requirement on heat dissipation capacity. In the current study, a carbon dioxide (CO2) dry ice spray cooling system is presented to explore the heat dissipation capacity using the sublimation as the two-phase-change cooling process integrated with the designed multi-orifice spray nozzle (MOSN). The dry ice particles can be converted from liquid CO2 through a sudden adiabatic expansion process by the Joule-Thomson effect. Heat transfer experiments were organized to investigate the effects of nozzle orifice diameters (NOD) and spray mass flow rate (SMFR) since there is a lack of study on the dry ice spray cooling performance. The relatively optimal NOD of 1.2 mm was obtained under a certain SMFR of 6.2 g/s and a fixed spray height of 7 mm according to the cooling performance. The highest heat flux performed was 221.1 W/cm2 with a best surface temperature of only 64.1 °C which justifies its future application of TMS.

Work done on a single-particle gas during an adiabatic compression and expansion process.

We compute the average work done by an external agent, driving a piston at constant speed, over a single-particle gas going through an adiabatic compression and expansion process. To do so, we get the analytical expression relating the number of collisions between the piston and the particle with the position of the piston during the process. The ergodicity breaking of the system during the process is identified as the source of its irreversibility. In addition, we observe that by using particular initial distributions for the state of the particle, it is possible to preclude the possibility of a net energy transfer from the agent to the particle during the process.

Estimation of Residual Exhaust Gas of Homogeneous Charge Compression Ignition Gasoline Engine Operating Under Negative Valve Overlap Strategy

To meet the requirements of the homogeneous charge compression ignition gasoline engine’s rapid cylinder exhaust gas rate and accurate control of combustion phasing, a residual exhaust gas rate model was proposed. A heat dissipation model for gas flow in the exhaust passage and exhaust pipe was established, and the exhaust gas was established. Flow through the exhaust valve was considered as an adiabatic expansion process, the exhaust temperature was used to estimate the temperature in the cylinder at the time that the valve was closed, and the cylinder exhaust gas rate was calculated. To meet the requirements of transient operating conditions, a first-order inertial link was used to correct the thermocouple temperature measurement. Addressing this delay problem and modification of the exhaust wall temperature according to different conditions effectively improved the accuracy of the model. The relative error between the calculated results of this model and the simulation results determined using GT-POWER software was within 3.5%.

Various Ways of Adiabatic Expansion in Organic Rankine Cycle (ORC) and in Trilateral Flash Cycle (TFC)

Abstract For energy production and conversion, the use of thermodynamic cycles is still the most common way. To find the optimal solution is a multiparametric optimization problem, where some parameters are related to thermodynamic and physical chemistry, while others are associated with costs, safety, or even environmental issues. Concerning the thermodynamic aspects of the design, the selection of the working fluid is one of the crucial points. Here, we are going to show different types of adiabatic expansion processes in various pure working fluids, pointing out the ones preferred in Organic Rankine Cycles or in Trilateral Flash Cycles. The effect of these expansions on the layout of the cycles will also be presented. Finally, we are giving a few thumb-rules, derived from thermodynamic studies, useful for energy engineers to select the proper working fluid for a given thermal system.

Limit of Relativistic Quantum Brayton Engine of Massless Boson Trapped 1 Dimensional Potential Well

A quantum Brayton engine using a massless Boson trapped in a one-dimensional potential well as a working substance has been constructed to be studied. We used a modified analogical model by the first law of thermodynamics for a quantum system implementation. The system was built with Klein Gordon equation, relativistic quantum mechanics Hamiltonian, without the mass term of the Hamiltonian and it was trapped in a one-dimensional potential well. Then, it underwent the quantum ideal Brayton cycle process. The quantum Brayton process consisted of adiabatic compression, isobaric expansion, adiabatic expansion, and isobaric compression processes. This relativistic quantum mechanics Brayton engine has found that the efficiency formulation was similar to the classical one. This study obtained the conformity results between the quantum relativistic and classical Brayton engines. By this cycle process, we also invented that the ratio of heat capacity under constant pressure and volume of the system was 2. It could indicate that the efficiency of quantum relativistic Brayton engine is higher than the classical one.

A near-isothermal expander for isothermal compressed air energy storage system

Compressed air energy storage technology is considered as a promising method to improve the reliability and efficiency of the electricity transmission and distribution, especially with high penetration of renewable energy. Being a vital component, the expander takes an important role in compressed air energy storage operation. The specific work of an expander can be improved through an isothermal expansion compared with the adiabatic expansion process due to a nearly constant temperature which enables the expander to operate with a high pressure ratio. In this study, a specific reciprocating expander with a high pressure ratio was developed and its adiabatic expansion characteristics were measured. Numerical modelling was performed to simulate adiabatic expansion. This model was also validated by experimental results. Based on these findings, we propose a quasi-isothermal expansion process using water injection into the expander cylinder. Modelling was also extended to simulate the quasi-isothermal process by introducing water–air direct heat transfer equations. Simulation results showed that when spraying tiny water droplets into the cylinder, the specific work generated was improved by 15.7% compared with that of the adiabatic expansion under the same air mass flowrate, whilst the temperature difference was only about 10% of that of the adiabatic process, and cylinder height was decreased by 8.7%. The influence of water/air mass flowrate ratio and the inlet temperature on the expander performance was also studied.

Numerical Study of a Quasi-isothermal Expander by Spraying Water

Compressed air energy storage (CAES) technology is considered as a promising method to improve the reliability and efficiency of the electricity transmission and distribution, especially with high penetration of renewable energy. The expander is a vital component of CAES system. The specific work generation through an expander can be improved through an isothermal expander compared with an adiabatic expansion process. And the temperature is almost constant, which enables the expander operate with high pressure ratio. A specific reciprocating expander with high pressure ratio is developed and its adiabatic expansion process is measured. A numerical modelling is constructed to mimic the adiabatic expansion, and it is validated by the experimental results. Furthermore, a quasi-isothermal expansion is proposed by using water injection into the cylinder based on the studied expander. The modelling is further developed by introducing water-air direct heat change equations to simulate the quasi-isothermal process. The simulated results of the quasi-isothermal expander when spraying tiny water droplets into the cylinder indicate that the specific work generation is improved by 11.57% compared with that of the adiabatic expansion under the same air inlet condition. The temperature difference is only about 10% of that of the adiabatic process.

Measurement of transient heat transfer in vicinity of gas–liquid interface using high-speed phase-shifting interferometer

The heat transfer process and initial stage of coupled convection at a gas–liquid interface are observed with high temporal and spatial resolutions in view of understanding phase transition dynamics such as evaporation or condensation for energy technologies. A high-speed phase-shifting interferometer is used to precisely measure the transient heat conduction and convection processes near the gas–liquid interface of a small water droplet. In the present study, the transient heat conduction around a water droplet interface during the adiabatic expansion process before the appearance of convection is visualized and examined. In the visualization experiment, transient density variations due to heat conduction in the vicinity of the gas–liquid interface are observed with temporal and spatial resolutions of 1ms and 8.83μm/pixel, respectively. It is determined that convection appears at approximately t=0.25s in a fast depressurization process, while transitions in both temperature and pressure are observed. In addition, the transient density variations and distributions of the gas phase before convection are compared with numerical simulations as an optical path length difference, and there is good agreement between the simulations and experimental results. The measurement methods developed in this study can be applied in the measurement of interfacial heat and mass transfers with high temporal and spatial resolutions.

Thermodynamic Mechanism of Self-Heat Recuperative and Self-heat Recovery Heat Circulation System for a Continuous Heating and Cooling Gas Cycle Process

The thermodynamic mechanism of self-heat recuperative and self-heat recovery heat circulation system for a continuous isobaric heating and cooling gas cycle process without chemical reaction has been studied in terms of the exergy analysis by using energy conversion and temperature-entropy diagrams. The modularization of the thermal gas cycle process which is decomposed into four thermodynamic elementary process modules, isobaric heating and cooling process modules (HR and HT) and adiabatic compression and expansion process modules (WR and WT), and a heat exchange process module (HX) indicates that in four thermodynamic elementary process modules (HR, HT, WR, and WT) both exergy and anergy are conserved except for HX in which the exergy is transformed into the anergy because of the exergy destruction due to the heat transfer. In the self-heat recuperative heat circulation system for the heating and cooling gas cycle process, providing the minimum work required for the heat circulation to compensate for the exergy destruction in HX the process heat is recuperated with increasing temperature of process fluid from T to T+ΔT and then recirculated through HX. The minimum work required for heat circulation, or work input, is converted to heat output, or the thermal energy of which anergy and exergy are the exergy destruction due to heat transfer in HX and the exergy to discard the anergy transformed by the exergy destruction, respectively. For the conventional self-heat recovery heat circulation system by providing heat instead of work the additional exergy to discard the anergy of heat input into the environment is needed with the minimum work required for heat circulation to compensate for the exergy destruction due to the heat transfer in HX, increasing the energy requirement for heat circulation by self-heat recovery.

GLOBAL ENERGETICS OF SOLAR FLARES. IV. CORONAL MASS EJECTION ENERGETICS

ABSTRACT This study entails the fourth part of a global flare energetics project, in which the mass m cme, kinetic energy E kin, and the gravitational potential energy E grav of coronal mass ejections (CMEs) is measured in 399 M and X-class flare events observed during the first 3.5 years of the Solar Dynamics Observatory (SDO) mission, using a new method based on the EUV dimming effect. EUV dimming is modeled in terms of a radial adiabatic expansion process, which is fitted to the observed evolution of the total emission measure of the CME source region. The model derives the evolution of the mean electron density, the emission measure, the bulk plasma expansion velocity, the mass, and the energy in the CME source region. The EUV dimming method is truly complementary to the Thomson scattering method in white light, which probes the CME evolution in the heliosphere at r ≳ 2 R ⊙, while the EUV dimming method tracks the CME launch in the corona. We compare the CME parameters obtained in white light with the LASCO/C2 coronagraph with those obtained from EUV dimming with the Atmospheric Imaging Assembly onboard the SDO for all identical events in both data sets. We investigate correlations between CME parameters, the relative timing with flare parameters, frequency occurrence distributions, and the energy partition between magnetic, thermal, nonthermal, and CME energies. CME energies are found to be systematically lower than the dissipated magnetic energies, which is consistent with a magnetic origin of CMEs.

Steam explosion technology based for oil extraction from sesame (Sesamum indicum L.) seed

Steam explosion, an adiabatic expansion and conversion process of thermal energy into mechanical energy, was employed to extract oil from sesame seed. Steam explosion was performed with different pressure levels and retention time periods (2.0 MPa 10 s and 1.0 MPa 30 s). After pretreatment, petroleum ether as the solvent, oil yield was generally improved with the severity factor increased. Steam explosion resulted in micropores on the seed surface and made it rough. The kinetics of oil extraction from sesame seed showed when the severity factor raised, the oil yield increased and mass transfer coefficient decreased. In addition, GC–MS was used to analyze the change of fatty acid composition, and a few changes were observed. Our study suggests that steam explosion improved the oil extraction yield of sesame seed, and the quality of oil was slightly changed.

Performance analysis and optimization of irreversible Dual–Atkinson cycle engine (DACE) with heat transfer effects under maximum power and maximum power density conditions

This study presents an analysis considering the effects of heat transfer loss and internal irreversibility due to adiabatic compression and expansion processes on the performance of an irreversible Dual–Atkinson cycle engine (DACE) under non-dimensional maximum power (MP), non-dimensional maximum power density (MPD) and maximum thermal efficiency (MEF) conditions. The effects of the inlet temperature, combustion constant and heat transfer constant on the engine performance are investigated. The results could be used by engine designers to optimize the performance of the internal combustion engines (ICEs).