Energy Flow Rate Research Articles

Analysis of mass and energy flow rates in an orifice pulse-tube refrigerator

The relationship among the curves of mass flow rate, temperature and pressure as a function of time in an orifice pulse-tube refrigerator is analyzed to explain the previously measured distortion of mass flow rate and temperature oscillation curves. The mass flow rate and temperature oscillations are described in terms of fundamental oscillations and harmonics, where the frequency of the fundamental oscillation is the same as that of the sinusoidal pressure oscillation. The time-averaged enthalpy flow rate and other energy flow rates are expressed in terms of the amplitude and phase of the fundamental oscillation of the mass flow rate through the orifice.

Robust Optimal Design of Energy Supply Systems Based on Minimax Regret Criterion.

A robust optimal design method based on the minimax regret criterion is proposed to determine equipment capacities of energy supply systems so that they are robust economically against the uncertainty in energy demands. Equipment capacities and utility contract demands as well as energy flow rates are determined to minimize the maximum regret in the annual total cost while satisfying all the possible energy demands. This optimization problem is formulated as a kind of multilevel linear programming problem, and its solution is obtained by repeatedly evaluating lower and upper bounds for the maximum regret in the annual total cost. Through a numerical case study on a cogeneration system, it is shown that determining equipment capacities appropriately is more important under uncertain energy demands rather than certain ones. It is also shown that the ratio of power generating capacity to total power supply capacity decreases with an increase of the uncertainty in energy demands.

Influence of quantum energy flow and localization on molecular isomerization in gas and condensed phases

Just as collisions between a reactant and its environment affect thermal unimolecular reaction rates, as described by the Lindemann mechanism, energy flow between the reaction mode and other modes of the reactant analogously influences microcanonical rates. Conformational isomerization typically proceeds over a relatively low-energy barrier, and the influence of slow quantum energy flow or localization on the microcanonical rate can be dramatic. We briefly review a theory describing quantum energy flow in moderate-sized to large molecules and how that picture can be used to understand and predict the influence of intramolecular energy flow on unimolecular reaction rates in gas and condensed phases. This theory locates a transition to global energy flow, the quantum ergodicity transition (QET), and predicts relatively slow flow rates at energies not far above the transition. We then apply the theory to predict rates of conformational isomerization of 2-fluoroethanol and allyl fluoride, each with a barrier between 1000 and 2000 cm−1. We find the QET of each to lie at energies near or above 3000 cm−1, consistent with recent experimental findings. How the thermal rate varies with pressure or viscosity is seen to depend sensitively on the QET and the rate of quantum energy flow. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 523–531, 1999

Influence of quantum energy flow and localization on molecular isomerization in gas and condensed phases

Just as collisions between a reactant and its environment affect thermal unimolecular reaction rates, as described by the Lindemann mechanism, energy flow between the reaction mode and other modes of the reactant analogously influences microcanonical rates. Conformational isomerization typically proceeds over a relatively low-energy barrier, and the influence of slow quantum energy flow or localization on the microcanonical rate can be dramatic. We briefly review a theory describing quantum energy flow in moderate-sized to large molecules and how that picture can be used to understand and predict the influence of intramolecular energy flow on unimolecular reaction rates in gas and condensed phases. This theory locates a transition to global energy flow, the quantum ergodicity transition (QET), and predicts relatively slow flow rates at energies not far above the transition. We then apply the theory to predict rates of conformational isomerization of 2-fluoroethanol and allyl fluoride, each with a barrier between 1000 and 2000 cm−1. We find the QET of each to lie at energies near or above 3000 cm−1, consistent with recent experimental findings. How the thermal rate varies with pressure or viscosity is seen to depend sensitively on the QET and the rate of quantum energy flow. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 523–531, 1999

The Dynamic J Integral, Separated Dynamic J Integrals and Moving Finite Element Simulations, for Subsonic, Transonic and Supersonic Interfacial Crack Propagation.

First, the concepts of separated dynamic J integral and separated energy release rate were presented for dynamic interfacial fracture mechanics. The separated dynamic J integral has the physical meaning of the energy flow rate to a propagating interfacial crack tip from each material component. Next, a moving finite element method for dynamic interfacial fracture analysis was developed to make it possible to analyze transonic and supersonic interfacial crack propagation. The moving finite element simulations revealed the shock waves (Mach waves) emanated from transonically and supersonically propagating crack tips. The dynamic J integral and the separated dynamic J integrals showed excellent path independence for all crack velocity regimes even for supersonic interfacial crack propagation. It was found that, in the subsonic crack-velocity regimes, the compliant material supplies larger fracture energy than the stiff material does. From the energy flow rate to the propagating interfacial crack tip, the theoretical limit of interfacial crack velocity without macro contact zone was found to be the shear wave velocity of the compliant material.

Design of U-Column Microwave-Assisted Extraction System and Its Application to Pigment Extraction from Food

Amicrowave-assisted extraction (MAE) system for biological material was designed with a cylindrical cavity, a rectangular wave guide, a magnetron of 2450 MHz and a U-column made of two glass columns; one for heating solvent and the other for the packed bed. The central focusing, dipolar power mode in the cavity was simulated, and the actual mode when using the extraction column was verified with dummy food (agar containing 0−5% NaCl). The position and the alignment of the U-column in the cavity were examined using two design strategies. Firstly, the heating column was matched to the central focusing mode to achieve the highest heating rate of the solvent, and secondly, the packed column was positioned at a mild power mode to disrupt biological cells to increase the extraction rate. The set-up of the MAE system was applied successfully to the extraction of the edible yellow pigment from Cape Jasmine ( Gardenia Jasminoides Ellis ) and the extraction yield was 50% higher than the conventional extraction method on the basis of identical thermal energy input and flow rate. The extract from the MAE system showed a pulsating flow pattern with a nearly constant volume fraction. In spite of focused microwave irradiation to the heating column, the temperature of the extract was self-regulated in the range of 70−95°C.

Thin Film Growth and Surface Modification by keV Ion Beam

High-quality ZnO film and highly wettable polymethylmethacrylate (PMMA) are obtained by using a keV ion beam. ZnO films are grown on glass substrates by ion beam sputter deposition, changing the oxygen/argon gas ratio, ion beam energy, and substrate temperature. Physical properties of ZnO films were investigated by X-ray diffraction, Rutherford backscattering spectroscopy, and the Van der Pauw method. All the films show a strong preferred orientation along the c-axis. The electrical resistivity is varied from 10-3 to 106 Ωcm and its dependence on the deposition parameters is discussed. The PMMA surface was modified by the ion-assisted reaction technique. Ion dose, ion energy, and oxygen gas flow rate are varied from 5×1015 to 1×1017 ions/cm2, from 0.6 to1.2 kV, and from 0 to 8 ml/min, respectively. A highly wettable PMMA surface can be obtained by irradiating oxygen ions in an oxygen gas environment. X-ray photoelectron spectroscopic analysis shows that hydrophilic groups are formed on the surface of PMMA.

Biodiversity in soil ecosystems: the role of energy flow and community stability

In a series of community food webs from native and agricultural soils, we modeled energetics and stability, and evaluated the role of the various groups of organisms and their interactions in energy flow and community stability. Species were aggregated into functional groups based on their trophic position in the food webs. Energy flow rates among the groups were calculated by a model using observations on population sizes, death rates, specific feeding preferences and energy conversion efficiencies. From the energetic organization of the communities we derived the strengths of the mutual effects among the populations. These interaction strengths were found to be patterned in a way that is important to community stability. The patterning consisted of the simultaneous occurrence of strong top down effects at lower trophic levels and strong bottom up effects at higher trophic levels. These patterns resulted directly from the empirical data we used to parameterize the model, as we found no stabilizing patterns with random but plausible parameter values. Also, the impact of each individual interaction on community stability was established. This analysis showed that some interactions had a relatively strong impact on stability, whereas other interactions had only a small impact. These impacts on stability were neither correlated with energy flow nor with interaction strength. Comparison of the seven food webs showed that these impacts were sometimes connected to particular groups of organisms involved in the interaction, but sometimes they were not, which might be due to different trophic positions in the food webs. We argue that future research should be directed to answer the question which energetic properties of the organisms form the basis of the patterning of the interaction strengths, as this would improve our understanding of the interrelationships between energetics, community stability, and hence the maintenance of biological diversity.

Energy escape rate of neutrals from Io and the implications for local magnetospheric interactions

The rate at which energy is carried away by atomic oxygen and sulfur escaping from Io because of the interaction of its atmosphere with the corotating magnetospheric plasma is calculated for three different ion‐neutral collisional processes: (1) incomplete collisional cascade, (2) slow‐velocity charge exchange and direct ejection (centered ∼20 km/s), and (3) fast‐velocity charge exchange (centered ∼60 km/s). The calculations are based on information for the O and S source rates and their velocity distributions at Io as independently determined from the combined results of previous studies for the observed column density and/or brightness morphology of the satellite's neutral corona and extended neutral clouds. The calculated energy escape rates for the three processes are 7.5 × 109 W, 3.3 × 1010 W, and 6.04 × 1011 W and are ∼11%, 50%, and 900%, respectively, of the upstream ion kinetic energy flow rate of 6.7 × 1010 W determined for a Voyager corotating plasma flowing through a minimum interaction area of πRIo2, where RIo is Io's radius. A larger more physically appropriate upstream interaction area of 2πRIo2 = π(1.414 RIo)2 would reduce these percentages by a factors of 2. For incomplete collisional cascade, the calculated energy escape rate is expected to be only ∼20% of the total energy deposition rate for this process, indicating a heating rate for the atmosphere of 3.0 × 1010 W (the remaining ∼80%). This implies that 56% of the minimum upstream ion kinetic energy flow rate is supplied to the atmosphere through the collisional cascade process, a factor of 2.8 times larger than the previously adopted value, and that the effective deflection of magnetospheric plasma out of the interaction region near Io is less than previously estimated. The total estimated neutral energy rate for all three processes (including heating) is 6.75 × 1011 W and is so large that it can only be supplied by the magnetic field energy, which is partially converted near Io to kinetic energy for the neutrals by the ion pickup current created by these processes. This is possible since an ion after a collision with a neutral can rapidly regain its original local corotational and gyration energies by acceleration in the local corotational electric field and magnetic field and may undergo many collisions in the interaction region and hence transfer many times its initial kinetic energy to the atmospheric neutrals. The magnitude of the pickup current and its magnetic field reduction near Io will depend critically upon the volume of the interaction region established by the solution of the three‐dimensional magnetospheric flow problem past Io, including these complex plasma‐neutral interactions. Rough estimates given here suggest a pickup current in the range of ∼5 × 106 to 2 × 107 A and a reduction (ΔB) in the local magnetic field of ∼450 nT. This estimated reduction of the magnetic field is similar to the remaining and unexplained ΔB of ∼400 nT determined in a recent analysis [Khurana et al., 1997] of the magnetic field depression measured near Io by the Galileo magnetometer [Kivelson et al., 1996a, b] and attributed in their treatments (where pickup current was neglected) to an internal magnetic dipole field for Io. Hence the remaining and unexplained ∼400‐nT reduction of the magnetic field measured by Galileo near Io may be a direct reflection of the local charge exchange source and need not require an internal magnetic field for the satellite.

Feeding ecology of short-tailed shearwaters:breeding in Tasmania and foraging in the Antarctic?

The food, feedlng and physiological ecology of foraging were studied in the short-tailed shearwater Puffinus tenujrostris of Tasmania, to establish whether this species can rely on Antarctic food to fledge its chick. Parents were found to use a 2-fold foraging strategy, on average performing 2 successive short trips at sea of 1 to 2 d duration followed by 1 long trip of 9 to 17 d. These long foraging tnps are the longest yet recorded for any seabird. During short trips the parents tend to lose mass, feeding the chick with Australian krill and fish larvae caught in coastal and neritic waters around Tasmania. The prey are caught at maximum diving depths of 13 m on average (maximum 30 m). During long trips, adults gain mass and feed their chlcks with a very rich mixture of stomach oil and digested food composed of a high diversity of prey including myctophid fish, sub-Antarctic krill and squids. Prey are probably caught mainly in the Polar Frontal Zone, at least 1000 km south of Tasmania, at maximum depths of 58 m on average (maximum 71 m). Long foraging trips in distant southern waters gave at least twice the yield of trips in close waters but during the former, yield decreased with the time spent foraging, as indicated by the inverse relationship between time spent forag~ng and adult body condition. Decisions whether to forage in close or distant waters appear to be determined by the body condition of :he paieiits iclthei i i ~ a ~ ~ by ihdi oi ihe C ~ ~ C K . Good body condition of parents was associated with high blood prolactin levels: birds in poor body condition invested in the restoration of body reserves and went to the rich area of the Polar Frontal Zone or to Antarctic waters, whereas those in good condition continued to provision the chick with food caught in Tasmanian waters and use their body reserves. The species thus exploits 2 water masses that differ in profitability. Most of the energy budget for rearing the ch~ck 1s balanced by prey caught in rich southern waters where the birds build up their body reserves and find most of the energy needed by the chick. However, nearby shallow waters are important for the breeding strategy as they allow an increased rate of energy flow to the chick. In a species as abundant as the short-tailed shearwater, the 2-fold strategy has the advantage of limiting competition in coastal and shallow waters, as at any one time only 17 % of birds are feeding there. The influence of the manne environment and energetic constra~nts on the evolution of provisioning strategies is discussed.

Quantum energy flow during molecular isomerization

Intramolecular energy flow greatly influences molecular isomerizations, particularly when the energy barrier to reaction is low, as in catalytic and biochemical reactions. We discuss here a simple quantum mechanical theory that describes the extent and rate of vibrational energy flow in molecules, and apply it for the first time to predict rates of isomerization. We consider trans-cis photoisomerization of stilbene, which has been extensively studied experimentally. Vibrational flow in stilbene plays a crucial role in moderating isomerization; the rate both in supersonic jets and low pressure gases is well described by the theory treating quantum flow.

Retrofit of complex and energy intensive processes

Sequential structural and parameter optimization of retrofitted complex and energy intensive continuous processes has been studied. A method for sequential optimization of retrofits, combined sequential approach has been developed using pinch analysis, an improved optimization procedure and mixed integer nonlinear programming (MINLP) or nonlinear programming (NLP) algorithms. Pinch analysis gives many alternative retrofit designs for postulating a superstructure. The superstructure, material and energy flow rates have been optimized sequentially by a direct search method using ASPEN PLUS simulator with energy and material bounds. The heat exchanger network of the superstructure obtained, flashes and compressor were optimized simultaneously with the MINLP or NLP algorithms. We have realized an additional profit of 2,803 MUSD/yr with the combined sequential approach in a case study of an existing methanol plant.

Ecological Energetics of the Diara Land Ecosystem and Its Management

Ecological energetics involve energy's relationship with the ecosystem. From the standpoint of energetics, it is necessary to express biomass in terms of calories, so that the relationship between the rate of energy flow and average standing biomass can be established. Net annual energy fixation by green plants on diara land at the natural field site I (wild vegetation) was 3,408·53 Kcal m-2 y-1 and at the mixed cultivated field site II (edible vegetation with wild species) was 19,714·3 Kcal m-2 y-1. These values, measured on an area-weighted average basis, were 285·09 × 105 KJ ha-1 y-1 at site I and 5,771·16 × 105 KJ ha-1 y-1 at site II. The energy conserving efficiency was 0·13% at site I and 2·7% at site II. The ecological efficiency of the livestock community was 0·004%, and energy transfer efficiency was 0·14%. The allometric relationship between the biomass component (independent) and caloric content (dependent) was found to be highly significant with standing dead and total biomass at site I and with aboveground parts, standing dead, and total biomass at site II.

Energy exchange between seismic and ultrasonic vibrations in an elastic medium with a microstructuret

The flow rate of seismic energy under conditions of long-wave-short-wave resonance in granular geomaterials (soil or fissured mountain rock) is calculated using a continuous elastic non-linear model with microrotations.

An Optimal Operational Planning Method for Energy Supply Systems in Consideration of Equipment Startup/Shutdown Costs.

A method of determining the operational strategy for energy supply systems in consideration of equipment startup/shutdown costs is proposed. This operational planning problem is formulated as a large-scale mixed-integer linear programming problem, in which the on/off status and energy flow rates of equipment are determined so as to minimize the sum of operational and startup/shutdown costs over the period considered. By utilizing a special feature of the problem, an algorithm for solving the problem efficiently is proposed, in which dynamic programming is adopted to determine the most cost-effective path regarding on/off status, the branch and bound method is modified to enumerate multiple candidates for on/off status, and a strategy is incorporated to reduce the number of candidates by using lower and upper bounds for the objective function. Through a numerical study on the operational planning of an energy supply system for district heating and cooling, the effectiveness of the proposed algorithm is ascertained in terms of computation time, and the effect of startup/shutdown costs on the operational strategy and cost is investigated.

Vibrational couplings and energy flow in complexes of NH3 with HCN, HCCH, and HCCCCH

A tunable color-center laser and a molecular-beam electric-resonance optothermal spectrometer have been used to record the infrared spectra of the C–H stretching vibrations of HCCH–NH3, HCCD–NH3, NCH–NH3, and HCCCCH–NH3. The hydrogen-bonded C–H stretching vibrations of NCH–NH3, HCCH–NH3, and HCCCCH–NH3 are redshifted by 200.88126(30), 75.1042(38), and 127.4(1) cm−1 from the respective free monomer modes. The non-hydrogen-bonded C–H stretches are less perturbed by complexation, being blueshifted by 0.2992(3) cm−1 in HCCCCH–NH3 and redshifted by 1.179(1) cm−1 in HCCD–NH3. Consistent with the much larger perturbation of the monomer vibration for the bonded C–H stretch, the B rotational constants increase by 1%–2% for the bonded C–H stretch excited NCH–NH3 and HCCH–NH3 complexes, but change by less than 0.1% for the nonbonded C–H stretches in HCCCCH–NH3 and HCCD–NH3. The decoupling of the two C–H stretches in HCCH–NH3 is not sufficient to allow the observation of the nonbonded C–H stretch in the complex, which correlates to the Raman-active symmetric C–H stretch of acetylene. Also, no spectra were observed for the weaker N–H stretching vibrations of the complexes, consistent with the very weak intensities of these modes in the monomer. The homogeneous linewidths of the transitions, assumed to be a measure of the vibrational predissociation rate, are approximately two orders of magnitude larger for the bonded C–H stretches than for the nonbonded C–H stretches. The similarity in homogeneous widths for the nonbonded C–H stretches in HCCD–NH3 and HCCCCH–NH3, of 7–12 MHz, suggests that the rate of vibrational energy flow along acetylene chains is only weakly dependent on chain length.

Computational study of many-dimensional quantum vibrational energy redistribution. I. Statistics of the survival probability

We statistically analyze the dynamics of vibrational energy flow in a model system of anharmonic oscillators which are nonlinearly coupled, with a local topology. The spectra of many basis states of similar energy are computed, for different values of the magnitude of the coupling in the Hamiltonian between these states. From individual spectra of zero order basis states at each coupling strength the individual survival probabilities are determined, which are then used in computing statistical averages. When the average fluctuation of the survival probability is small, in the strongly coupled limit, the average survival probability closely follows a semiclassical diffusion prediction and reflects a predicted linear dependence of the rate of energy flow on coupling strength. When the average fluctuation is large, in the weakly coupled limit, the average survival probability closely follows a power law decay of t−1, in agreement with a quantum extension of the diffusion picture. In this regime, individual survival probabilities show strong quantum beats. We conclude that these large variations reflect a strong influence of quantum interference in the weakly coupled limit.

Matrix-assisted laser desorption/ionization with nitrogen lasers of different pulse widths

The effect of the laser pulse width has been investigated for matrix-assisted laser desorption/ionization (MALDI) of analyte and matrix ions as well as for (photoionized) neutral matrix molecules by comparing two nitrogen lasers (337 nm) with 0.55 and 3 ns pulse widths as commonly used for MALDI mass spectrometry. A homogeneous “flat-top” laser beam profile was used in these experiments. Neither did the threshold fluences (minimum incident laser energy per unit area for producing a spectrum) change, nor was there a difference in the increase in ion signal intensity with laser fluence between the two lasers. Also, no significant differences were found in the mass spectra. The results show that the desorption/ionization process is essentially determined by the energy supplied in the studied pulse width range, rather than by the rate of energy flow into the sample.

HERA Workshop on proton, photon and pomeron structure

HERA Workshop on proton, photon and pomeron structure

Finite Element Analysis of Thermal Behavior in Metal Machining. 2nd Report. Determination of Energy Balance and Its Application to Three-Dimensional Analysis.

An inverse analysis approach using the finite element method has been proposed to determine the energy balance or the energies flowing into a tool, workpiece and chip per unit volume of material removed in two dimensional machining. Once the energy flow rates are obtained, a three-dimensional temperature distribution for complicated tools such as an end mill can be analyzed easily and efficiently. The method proposed has been employed to clarify the effect of thermal properties on the energy balance. The energy flowing into the tool is most enhanced when a low-thermal-conductivity workpiece is machined by a high-thermal-conductivity tool with a coolant: wet turning of a titanium alloy by a diamond tool is a typical case. It is found that temperature change of a carbide square end mill in titanium machining ranges from 400 to 800°C at a cutting speed of 314 m/min because of a low energy flow rate into the tool of around 0.04 and the cooling action by a coolant. The suitability of the present method has been confirmed numerically and experimentally.