Energy Transport Theory Research Articles

Exploring the effect of the inlet gas volume fraction on the energy-conversion features of a multiphase pump using energy-transport theory

This work sought to reveal the role of the inlet gas volume fraction (GVF) on the energy-conversion features of a multiphase pump. To this end, a self-developed single-stage multiphase pump was used as the research object, and a gas–liquid transport medium was examined based on the energy-transport theory. The role of the GVF in the pressure-gradient work, Lamb-vector divergence, and vortex pseudo-energy dissipation in the pressurization unit of the multiphase pump were analyzed, and the impact of the GVF on the energy-conversion features of the multiphase pump was also investigated. The results indicate that under various GVFs, increasing the tip clearance prevents the pressure gradient from exerting its intended function. Furthermore, as the GVF is increased, the scale of the tip-leakage vortex increases, the flow field in the pressurization unit is disturbed, and the vortex pseudo-energy dissipation in the impeller increases. As a result, the energy loss increases, the pressurization effect of the pump is weakened, and its work performance decreases. These results offer a reference for enhancing the efficiency of multiphase pumps.

Influence of tip clearance on internal energy loss characteristics of axial flow pumps under different operating conditions

Axial flow pumps possess a unique structure where there must be clearances between the impeller and the piping wall, usually not exceeding 0.1% of the impeller diameter. Despite the small size of the clearance, the internal micro-vortex structures have a non-negligible impact on the main flow field of the impeller. Under the action of the pressure difference between the suction and pressure surfaces of blades, some fluids form high-energy jets in the tip clearance area, known as tip leakage vortices (TLVs). TLV interacts with the flow of the main flow field, exerting a significant impact on the internal flow state, energy loss, and hydraulic performance of the pump. To identify the influence of TLVs on the internal flow field and energy loss of axial flow pumps, this work uses a modified partially averaged Navier–Stokes (PANS) model to perform full flow field numerical calculations for a certain axial flow pump and conducts a comparative analysis of the internal flow field energy dissipation, unsteady vortex structures, energy loss, and other characteristics under three different tip clearances: 0.2 mm (0.05%D), 0.6 mm (0.15%D), and 1.0 mm (0.25%D) based on the energy transport theory. The results indicate that at optimal operating conditions, the internal energy distribution of the fluid in each flow passage is uniform, and the energy loss is primarily caused by axial backflow in the tip area; under critical rotating stall conditions, clearance size affects the distribution state of enstrophy in the guide vane flow passage, leading to average enstrophy being highest at the rim area and the most uneven distribution of enstrophy, inducing larger energy loss in the impeller; during deep stall conditions, the unevenness of internal energy distribution is stronger than that under critical stall conditions, but the overall energy loss within the impeller flow area is lower than that under critical stall conditions, while energy unevenness is mitigated as the tip clearance size increases.

Effect of Flow on the Energy Conversion Characteristics of Multiphase Pumps Based on Energy Transport Theory

Multiphase pumps operate under different flow conditions with different work performance. In order to reveal the energy conversion regulations in multiphase pumps under different flows, this paper presents an analysis of the effects of different flows on the pressure propulsion power, Lamb vector dispersion, and vortex enstrophy dissipation in the pressurization unit of a multiphase pump based on energy transport theory. It is found that at different flows, the pressure propulsion power near the impeller inlet decreases sharply, the pressure propulsion power is mainly located in the first half of the impeller near the suction side of the blade, and with the increase in the flow, the pressure propulsion power in the pressurization unit increases gradually, as well as its energy loss, while the Lamb vector dispersion gradually increases and the area of scattering region tends to be narrow under the small impeller tip clearance, while the Lamb vector dispersion region area slowly decreases with the flow rate when the impeller tip clearance is larger. The effect of flow on the vortex enstrophy dissipation in the multiphase pump is mainly located in the middle of the impeller near the blade pressure surface, and as the flow increases, the value of the vortex enstrophy dissipation in the impeller pressurization unit increases accordingly, and the vortex enstrophy dissipation in the first half of the impeller is even more chaotic. The investigation results have significant theoretical meaning for the deep mastery of the energy conversion characteristics in multiphase pumps.

The theory of macroscopic energy and mass transport based on the synergy and dissipation analysis

The theory of macroscopic energy and mass transport based on the synergy and dissipation analysis

Establishment of a Reynolds average simulation method and study of a drag reduction mechanism for viscoelastic fluid turbulence

Reynolds average simulation governing equations are derived for viscoelastic fluid turbulence using the Reynolds time-averaged method combined with the Navier–Stokes equations, the viscoelastic fluid finitely extensible nonlinear elastic-Peterlin constitutive equation, the viscoelastic fluid molecular conformation tensor transport equation, and the k−ε−v′2¯−f turbulence model. To identify the relevant viscoelastic terms, user-defined functions and the programing language C are used to write a simulation subroutine for the Reynolds average of viscoelastic fluid turbulence; this subroutine is embedded into computational fluid dynamics software to establish a simulation method for Reynolds average of viscoelastic fluid turbulence. Then, the flow field structure of viscoelastic fluid turbulence is analyzed. Using energy transport theory, expressions for the contribution of viscous, elastic, and Reynolds shear stress to the turbulent friction factor of viscoelastic fluid in a horizontal tube are established, and the turbulent drag reduction mechanism of the viscoelastic fluid is revealed. The simulated values for pressure drop, Fanning friction factor, and the drag reduction rate of viscoelastic fluid in tests are in good agreement with experimental values, and the average relative error is less than 12.37%. In addition, elastic shear stress is produced after the dissolution of drag reduction agents in water, which increases the turbulent friction factor; however, Reynolds shear stress is greatly reduced, and viscous shear stress is weakened by inhibiting the turbulence fluctuation, so the turbulent friction factor decreases; more importantly, the increase in the friction factor of the former is much smaller than that of the latter.

Buoyancy Forcing Dominates the Cross-Equatorial Ocean Heat Transport Response to Northern Hemisphere Extratropical Cooling

Abstract Cross-equatorial ocean heat transport (OHT) changes have been found to damp meridional shifts of the intertropical convergence zone (ITCZ) induced by hemispheric asymmetries in radiative forcing. Zonal-mean energy transport theories and idealized model simulations have suggested that these OHT changes occur primarily due to wind-driven changes in the Indo-Pacific’s shallow subtropical cells (STCs) and buoyancy-driven changes in the deep Atlantic meridional overturning circulation (AMOC). In this study we explore the partitioning between buoyancy and momentum forcing in the ocean’s response. We adjust the top-of-atmosphere solar forcing to cool the Northern Hemisphere (NH) extratropics in a novel set of comprehensive climate model simulations designed to isolate buoyancy-forced and momentum-forced changes. In this case of NH high-latitude forcing, we confirm that buoyancy-driven changes in the AMOC dominate in the Atlantic. However, in contrast with prior expectations, buoyancy-driven changes in the STCs are the primary driver of the heat transport changes in the Indo-Pacific. We find that buoyancy-forced Indo-Pacific STC changes transport nearly 4 times the amount of heat across the equator as the shallower wind-driven STC changes. This buoyancy-forced STC response arises from extratropical density perturbations that are amplified by the low cloud feedback and communicated to the tropics by the ventilated thermocline. While the ocean’s specific response is dependent on the forcing scheme, our results suggest that partitioning the ocean’s total response to energy perturbations into buoyancy and momentum forcing provides basin-specific insight into key aspects of how the ocean damps ITCZ migrations that previous zonal-mean frameworks omit.

Mode vortex and turbulence in ventilated cavitation over hydrofoils

In this paper, the complex interaction of gas-vortex-turbulence in ventilated cavitation over a NACA0015 hydrofoil is investigated by using large eddy simulation. The proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) are used for analyzing the three-dimensional fluctuation modes of gas-liquid interfaces induced by turbulent coherent structures in ventilated cavitation. The results show that among the first four dominant POD modes possessing 99.5% modal kinetic energy in the ventilated cavitating flow, and the turbulent POD mode 2 contains the multi-scale coherent structures and acts as a bridge for the energy scale transition from mode 1 to mode 3 through the gas-liquid interface oscillations. The DMD modal structures are reconstructed from the roller-shaped energetic structure captured by POD mode 2, which further reveal the process of breaking down near the hydrofoil leading edge, changing into the hairpin shape and finally stretching into the horseshoe shape above the hydrofoil trailing edge for the turbulent coherent structures on the cavity interfaces. Such low-frequency wake structures are energetic but sustained by means of the high-frequency turbulent fluctuations, with the interfacial oscillation amplitude changed through the formation and transition of the multi-scale coherent structures. Further, the modal turbulent kinetic energy transport theory is introduced to describe the ventilated coherent structures. It is worth noting that the large-scale energetic structures in POD mode 2 are mainly drawing energy from mean flows through the Reynolds stress, and the modal turbulent energy stored by shedding vortex and air cavities in the ventilated wake flow is redistributed and balanced due to the turbulent and pressure diffusion effects. Besides, the uneven spatial distribution of turbulent energy caused by the vortex structures of different modal scales is proved to promote the spatial oscillation level of the ventilated cavity interfaces. This study is helpful to understand the interaction mechanism between turbulence and gas-liquid interfacial fluctuations for the ventilated wake flow.

Microscopic theory of photon-induced energy, momentum, and angular momentum transport in the nonequilibrium regime

We set up a general microscopic theory for the transfer of energy, momentum, and angular momentum mediated by photons. Using the nonequilibrium Green's function method, we propose a unified Meir-Wingreen formalism for the energy emitted, force experienced, and torque experienced by the objects due to the fluctuating electromagnetic field. Our theory does not require the local thermal equilibrium that is the central assumption of the conventional theory of fluctuational electrodynamics (FE). The obtained formulas are valid for arbitrary objects as well as the environment without the requirement of reciprocity. To show the capability of our microscopic theory, we apply the general formulas to transport problems of graphene edges in both equilibrium and nonequilibrium situations. We show the local equilibrium energy radiation of graphene obeys the well-known $T^4$ law with a converged theoretical emissivity of 2.058$\%$. In the ballistic nonequilibrium situation driven by chemical potential biases, we observe nonzero results for force and torque from the graphene edges, which go beyond the predictive ability of the FE theory. Our method is general and efficient for large systems, which paves the way for studying more complex transport phenomena in the nonequilibrium regime.

Numerical study on energy conversion characteristics of molten salt pump based on energy transport theory

Molten salt pump (MSP) used in concentrating solar power (CSP) system to circulate the molten salt. The operation of MSP needs to understand the energy conversion characteristics in the flow field. In this study, the energy conversion characteristics of MSP were investigated based on energy transport theory. A significant portion of power is consumed in the propulsion of pressure between the inlet throat to the outlet throat of the impeller passage. The increase in the energy of medium by the Lamb vector divergence mainly occurs on the rear of the impeller passage. Whereas the enstrophy dissipation area is primarily located in the suction surface area at the impeller outlet. In addition, the pressure propulsion power is critical for energy transfer in the impeller, while the contribution of Lamb vector divergence and enstrophy dissipation is limited. It was observed that the distribution of the three energy transport dynamic parameters have a high degree of coincidence irrespective of the medium density, which indicates that the density of the medium does not have a significant impact on the law of energy conversion. Therefore, when the geometrical characteristics of the impeller are determined, the energy conversion characteristics of different medium do not change significantly.

Charge Mobility in Discotic Liquid Crystals.

Discotic (disk-shaped) molecules or molecular aggregates may form, within a certain temperature range, partially ordered phases, known as discotic liquid crystals, which have been extensively studied in the recent past. On the one hand, this interest was prompted by the fact that they represent models for testing energy and charge transport theories in organic materials. However, their long-range self-assembling properties, potential low cost, ease of processability with a variety of solvents and the relative ease of tailoring their properties via chemical synthesis, drove the attention of researchers also towards the exploitation of their semiconducting properties in organic electronic devices. This review covers recent research on the charge transport properties of discotic mesophases, starting with an introduction to their phase structure, followed by an overview of the models used to describe charge mobility in organic substances in general and in these systems in particular, and by the description of the techniques most commonly used to measure their charge mobility. The reader already familiar or not interested in such details can easily skip these sections and refer to the core section of this work, focusing on the most recent and significant results regarding charge mobility in discotic liquid crystals.

Numerical Study on Energy Conversion Characteristics of Molten Salt Pump for Concentrating Solar Power Based on Energy Transport Theory

Molten salt pump (MSP) used to circulate the molten salt in concentrating solar power (CSP) system. The operation of MSP needs to understand the energy conversion characteristics in the flow field. In this study, the energy conversion characteristics of MSP were investigated based on energy transport theory. A significant portion of power is consumed in the propulsion of pressure between the inlet throat to the outlet throat of the impeller passage. The increase in the energy of medium by the Lamb vector divergence mainly occurs on the rear of the impeller passage. Whereas the enstrophy dissipation area is primarily located in the suction surface area at the impeller outlet. In addition, the pressure propulsion power is critical for energy transfer in the impeller, while the contribution of Lamb vector divergence and enstrophy dissipation is limited. It was observed that the distribution of energy transport dynamic parameters have a high degree of coincidence irrespective of the medium density, which indicates that the density of the medium does not have a significant impact on the law of energy conversion. Therefore, when the geometrical characteristics of the impeller are determined, the energy conversion characteristics of different medium do not change significantly.

Mean field theory of thermal energy transport in molecular junctions.

Mean field theory is applied to nonequilibrium thermal energy transport in a model molecular junction. An approximation to the total time-dependent heat current in the junction is constructed using an ensemble of Ehrenfest trajectories, and the average heat current in the steady state is obtained. The accuracy of this treatment is verified through benchmark comparisons with exact quantum mechanical results and various approximate quantum transport theories for the nonequilibrium spin-boson model. The performance of the multitrajectory Ehrenfest approach is found to be quite robust, displaying good accuracy in intermediate cases that remain elusive to many perturbative approximations and in the strong coupling limit where many methods break down. Thus, mean field theory and related trajectory-based approximate quantum dynamics methods emerge as a promising toolkit for the study of transport properties in nanoscale systems.

On the role of thermal expansion and compression in large-scale atmospheric energy and mass transports

Abstract. There are currently two views of how atmospheric total energy transport is accomplished. The traditional view considers total energy as a quantity that is transported in an advective-like manner by the wind. The other considers that thermal expansion and the resultant compression of the surrounding air causes a transport of total energy in a wave-like manner at the speed of sound. This latter view emerged as the result of detailed analysis of fully compressible mesoscale model simulations that demonstrated considerable transfer of internal and gravitational potential energy at the speed of sound by Lamb waves. In this study, results are presented of idealized experiments with a fully compressible model designed to examine the large-scale transfers of total energy and mass when local heat sources are prescribed. For simplicity a Cartesian grid was used, there was a horizontally homogeneous and motionless initial state, and the simulations did not include moisture. Three main experimental designs were employed. The first has a convective-storm-scale heat source and does not include the Coriolis force. The second experiment has a continent-scale heat source prescribed near the surface to represent surface heating and includes a constant Coriolis parameter. The third experiment has a cloud-cluster-scale heat source prescribed at the equator and includes a latitude-dependent Coriolis parameter. Results show considerable amounts of meridional total energy and mass transfer at the speed of sound. This suggests that the current theory of large-scale total energy transport is incomplete. It is noteworthy that comparison of simulations with and without thermally generated compression waves show that for a very large-scale heat source there are fairly small but nevertheless significant differences of the wind field. These results raise important questions related to the mass constraints when calculating meridional energy transports, the use of semi-implicit time differencing in large-scale global models, and the use of the term “heat transfer” for total energy transfer.

The properties of nonlinear excitations and verifi cation of validity of theory of energy transport in the protein molecules

The properties of nonlinear excitations and verifi cation of validity of theory of energy transport in the protein molecules

Determining Sources of Unsteady Energy Transfer in Time-Accurate Computational Fluid Dynamics

With the increase in computational resources, time-accurate reacting flow, computational fluid dynamics have improved to the point where periodic, unsteady behavior associated with hydrodynamic instability and acoustic resonance can be accurately modeled. However, computational fluid dynamics solutions, like experiments, only reveal the manifestation of unstable behavior such as pressure fluctuations or vortex generation. They do not readily divulge the sources of energy transfer leading to and sustaining instabilities. Because of this, it can be arduous to correlate design decisions with overall system stability using computational fluid dynamics alone. Combining the well-established unsteady energy transport theory and a choice of viable data analysis techniques, a rigorous approach for analyzing time-accurate computational fluid dynamics solutions is established. Through this approach, the sources of driving and damping can be visualized and quantified. Thereby, the aforementioned issue is rectified and a deeper insight into the root causes of instability and its overall effect is achieved.

A comprehensive study of thermoelectric and transport properties of β-silicon carbide nanowires

The temperature dependence of the Seebeck coefficient, the electrical and thermal conductivities of individual β-silicon carbide nanowires produced by combustion in a calorimetric bomb were studied using a suspended micro-resistance thermometry device that allows four-point probe measurements to be conducted on each nanowire. Additionally, crystal structure and growth direction for each measured nanowire was directly obtained by transmission electron microscopy analysis. The Fermi level, the carrier concentration, and mobility of each nanostructure were determined using a combination of Seebeck coefficient and electrical conductivity measurements, energy band structure and transport theory calculations. The temperature dependence of the thermal and electrical conductivities of the nanowires was explained in terms of contributions from boundary, impurity, and defect scattering.

Organic single crystals: Addressing the fundamentals of organic electronics

Abstract

Statistical Thermodynamic Theory for Non-Equilibrium, Quasi-Equilibrium, and Equilibrium Electrochemical Reactions

An electrochemical reaction as a branch of chemical reactions is one of the fundamental phenomena, but exact electrochemical reaction mechanisms have been unknown. We here propose a statistical thermodynamic theory for electrochemical reactions, which is vital to investigate electrochemical reactions for non-equilibrium, quasi-equilibrium, and equilibrium. The theory utilizes a postulate that electric potential, time, and space are independent and orthogonal variables in extended phase spaces. It is an internal Gibbs energy transport theory for electrochemical reactions leading to the unification of non-equilibrium and equilibrium reactions, a non-equilibrium generalization beyond quasi-equilibrium theories for migration and diffusion, and the integration of diffusion and convection mechanisms. It predicts that there are current density gaps and broken discrete symmetries at the activation potential, time, and displacement. It provides the Nernst equation, the rate equation, and the spatial cross section of electrochemical reactions. The electrochemical theory demonstrates relationships among electrochemical reactions, thermodynamics, and statistical physics.

Thermal conductivities of one-dimensional anharmonic/nonlinear lattices: renormalized phonons and effective phonon theory

Heat transport in low-dimensional systems has attracted enormous attention from both theoretical and experimental aspects due to its significance to the perception of fundamental energy transport theory and its potential applications in the emerging field of phononics: manipulating heat flow with electronic anologs. We consider the heat conduction of one-dimensional nonlinear lattice models. The energy carriers responsible for the heat transport have been identified as the renormalized phonons. Within the framework of renormalized phonons, a phenomenological theory, effective phonon theory, has been developed to explain the heat transport in general one-dimensional nonlinear lattices. With the help of numerical simulations, it has been verified that this effective phonon theory is able to predict the scaling exponents of temperature-dependent thermal conductivities quantitatively and consistently.

Fluorescence Spectroscopic Properties Analysed within the Extended Förster Theory with Application to Biomacromolecular Systems

The extended Förster theory (EFT) of electronic energy transport accounts for translational and rotational dynamics, which are neglected by the classical Förster theory (FT). EFT has been developed for electronic energy transfer within donor-acceptor pairs [Isaksson, et al, Phys. Chem. Chem. Phys., 9, 1941(2007)] and donor-donor pairs [Johansson, et al, J. Chem. Phys., 105, 10896 (1996); Norlin, et al, Phys. Chem. Chem. Phys., 10, 6962(2008)]. For donors that exhibit different or identical non-exponential fluorescence relaxation within a donor-donor pair, the process of reverberating energy migration is reversible to a higher or lower degree. Here the impact of the EFT has been studied with respect to its influence on fluorescence quantum yields, fluorescence lifetimes as well as depolarisation experiments. The FT predicts relative fluorescence quantum yields which usually agree with the EFT within experimental accuracy, however, substantial deviations occurs in the steady-state and in particular the time-resolved depolarisation data.