Energy Storage Rate Research Articles

Global energy cycle between land and ocean in the simulated 20th century climate systems

[1] The global energy cycle between the land and the ocean has been studied with simulations of the 20th century performed with coupled ocean-atmosphere climate models. The energy cycle consists of the net energy fluxes at the top-of-the-atmosphere (TOA) and the surface, the atmospheric energy storage rates over the global land and ocean, and the atmospheric energy transport between the land and ocean. The energy cycle was investigated using a multi-model ensemble for its centennial mean, climatological annual variation and long-term trend. Some distinctive features of the cycle were revealed: (1) the ocean-to-land atmospheric energy transport plays a key role in partitioning the global net TOA flux between the ocean and land, (2) the annual variation of the global net TOA flux is primarily attributed by the ocean surface flux, and (3) it is ascertained that the planetary energy imbalance on the long-term period is induced by the ocean's heat uptake.

Effect of Cell Geometry on the Freezing and Melting Processes inside a Thermal Energy Storage Cell

This paper presents an analysis of the charge and discharge processes in a latent thermal energy storage cell. An individual cell is analyzed to study how its behavior affects the performance of a thermal energy storage system. The analysis considers the exchange of thermal energy between a thermal energy storage cell and a source or sink of thermal energy. Two cases are considered, (i) a process in which the phase change material melts and freezes when a constant and uniform temperature is imposed at the lower surface of the cell, and (ii) a process in which the phase change material melts and freezes when a fluid with a constant inlet temperature flows under the cell. The effect of the aspect ratio of the energy storage cell is analyzed in detail as a possible method to enhance heat transfer and improve performance of the thermal energy storage system. The results include, for different aspect ratios of the storage cell, the evolution of the solid-liquid interface, the rates of melting and solidification, the rate of energy storage and the total amount of energy storage.

Experimental and numerical investigation of thermal energy storage with a finned tube

A latent heat thermal energy storage system using a phase change material (PCM) is an efficient way of storing or releasing a large amount of heat during melting or solidification. It has been determined that the shell-and-tube type heat exchanger is the most promising device as a latent heat system that requires high efficiency for a minimum volume. In this type of heat exchanger, the PCM fills the annular shell space around the finned tube while the heat transfer fluid flows within the tube. One of the methods used for increasing the rate of energy storage is to increase the heat transfer surface area by employing finned surfaces. In this study, energy storage by phase change around a radially finned tube is investigated numerically and experimentally. The solution of the system consists of the solving governing equations for the heat transfer fluid (HTF), pipe wall and phase change material. Numerical simulations are performed to investigate the effect of several fin parameters (fin spacing and fin diameter) and flow parameter (Re number and inlet temperature of HTF) and compare with experimental results. The effect of each variable on energy storage and amount of solidification are presented graphically. Copyright © 2005 John Wiley & Sons, Ltd.

Numerical study for enhancing the thermal conductivity of phase change material (PCM) storage using high thermal conductivity porous matrix

In this paper, the melting process inside an irregular geometry filled with high thermal conductivity porous matrix saturated with phase change material PCM is investigated numerically. The numerical model is resting on solving the volume averaged conservation equations for mass, momentum and energy with phase change (melting) in the porous medium. The convection motion of the liquid phase inside the porous matrix is solved considering the Darcy, Brinkman and Forchiemer effects. A local thermal non-equilibrium assumption is considered due to the large difference in thermal properties between the solid matrix and PCM by applying a two energy equation model. The numerical code shows good agreement for pure PCM melting with another published numerical work. Through this study it is found that the presence of the porous matrix has a great effect on the heat transfer and melting rate of the PCM energy storage. Decreasing the porosity of the matrix increases the melting rate, but it also damps the convection motion. It is also found that the best technique to enhance the response of the PCM storage is to use a solid matrix with high porosity and high thermal conductivity.

Effect of pre-strain direction on energy storage process during tensile deformation of polycrystal

Abstract The energy storage process is characterised by the energy storage rate d e s /d w p as a function of plastic work w p or of plastic strain e P ( e s is stored energy). At the initial stage of plastic deformation the dependence of d e s /d w p on e P has a maximum. The present work is devoted to the experimental verification of a hypothesis that the maximum of d e s /d w p can be related to the internal micro-stresses caused by incompatible slip in grains of different orientation. The verification needed two groups of specimens in which the influence of internal micro-stresses on the energy storage rate is different. This requirement was achieved using specimens pre-strained in different directions. Experiments that make it possible to estimate the influence of internal micro-stresses on the rate of energy storage are presented. The obtained results confirm the hypothesis.

Experimental analysis of energy storage rate components during tensile deformation of polycrystals

Abstract The energy storage rate d e s /d w p ( e s is the stored energy, w p the work of plastic deformation) is a macroscopic quantity that is influenced by many microscopic mechanisms. At the initial stage of plastic deformation the dependence of d e s /d w p on the plastic strain e p has a maximum. It has been suggested that the maximum of d e s /d w p is connected with long-range stresses caused by the polycrystalline nature of the material. A polycrystalline specimen deforms plastically, non-uniformly on a micro-scale, each grain in a polycrystal deforms by a different amount depending on its orientation and the constraints imposed thereon by its neighbours. In order to verify the hypothesis, two groups of specimens were prepared in which the impact of long-range internal micro-stresses on the energy storage rate differs. This requirement was achieved using specimens pre-strained in different directions. The dependence of the energy storage rate on the plastic strain for the pre-strained specimens was experimentally found. The results obtained seem to confirm the hypothesis.

Energy balance and macroscopic strain localization during plastic deformation of polycrystalline metals

The energy balance during uniaxial test of the annealed FeSi sheet and the rolled one has been studied. The method of estimation of the energy storage rate in the stage of macroscopic strain localization has been presented. Heterogeneous temperature distribution on the surface of the loaded sample as an experimental indicator of the macroscopic localization of strain was used. The experimental evidence for the existence of recovery process during a development of the localized plastic deformation has been provided.

Physiology of pregnancy and nutrient metabolism

Pregnancy consists of a series of small, continuous physiologic adjustments that affect the metabolism of all nutrients. The adjustments undoubtedly vary widely from woman to woman depending on her prepregnancy nutrition, genetic determinants of fetal size, and maternal lifestyle behavior. Studies of protein and energy metabolism illustrate the potential of adjusting the use of those nutrients to conserve a fetal supply. Adjustments in the metabolism of nitrogenous compounds are in place by the second quarter of pregnancy. During the last quarter of pregnancy, when fetal demands are greatest, those adjustments allow a positive nitrogen retention. The energy requirement of basal metabolism is influenced by maternal prepregnant nutrition and by fetal size. If maternal energy reserves are low at conception, the basal metabolic rate is down-regulated to conserve energy. Also, women having larger babies tend to have greater increases in their basal metabolic rate and lower rates of maternal energy storage. Changes in maternal food and physical activity behaviors during gestation may augment the physiologic adjustments. However, the substantial variability in food intakes and physical activity makes it difficult to show those changes. Thresholds in the capacity to adjust nutrient use to the amount supplied exist for all nutrients. When intakes fall below the threshold, fetal growth and development is affected more than is maternal health. Efforts to achieve good maternal nutritional status preconception as well as throughout gestation best assure a good milieu for fetal growth and development.

2714 下向き強制流中に置かれた加熱球まわりの伝熱特性とその促進 : 潜熱蓄・放熱促進を目的として

2714 下向き強制流中に置かれた加熱球まわりの伝熱特性とその促進 : 潜熱蓄・放熱促進を目的として

Passive Enhancement Technique for Free Convection-Dominated Melting of Phase Change Material in Horizontal Cylindrical Annulus.

Knowledge of heat transfer during melting and freezing in enclosures is important in the design of heat exchangers using phase change materials (PCMs) for thermal energy storage. While freezing heat transfer is governed mainly by conduction, melting of a PCM generally invokes free convective currents in the melt phase depending on the orientation and geometry of the heat transfer surfaces. In this paper, a finite element simulation is carried out to predict the flow and temperature fields as well as the rate of heat storage during melting of a PCM in a horizontal cylindrical annulus heated from an isothermal inside surface. A novel yet simple method is suggested and validated numerically to enhance the heat storage rate in a PCM. The technique involves simply “flipping” the horizontal cylinder, i.e., turning it through 180° about its own axis, at an optimum time during the melting process. It is found that up to 18% enhancement in the energy storage rate can be achieved with this simple technique.

LIFE-HISTORY RESPONSES TO VARIABLE ENVIRONMENTS: STARVATION AND REPRODUCTION IN PLANKTONIC ROTIFERS

Zooplankton live in environments where resource abundance and quality can vary drastically over time. Success in nonequilibrium environments depends in part on the ability to store energy and control its allocation during periods of extreme food limitation or outright starvation. Starvation resistance is one measure of the ability of a species to persist when energy intake is less than energy expenditure. The life-history responses of nine species of planktonic rotifers to food deprivation were compared using cohort life- table experiments. Allometric patterns of energy storage and respiration rate lead to the prediction that larger species should have greater starvation resistance than smaller species. Contrary to this prediction, when rotifers were acclimated to high resource levels and starved as young adults, body mass did not predict starvation time. Rather, there was a trade-off between survival and reproduction during starvation. Some species did not reproduce during starvation and had high starvation times (up to 5.0 d). Other species maintained or increased fecundity relative to fed controls and had low starvation times (as low as 0.4 d). Species with more rapid senescence when fed tended to have shorter starvation times. However, the interspecific-trade-off between survival and reproduction remained after removing the effect of control survivorship. Differences in life-history responses to starvation may be critical in determining competitive outcome and community structure in variable environ- ments. When acclimated to low food levels prior to food deprivation, simulating conditions of declining resource abundance in nature, rotifer starvation time decreased. Juveniles had longer starvation times than adults, further supporting the idea that allocating energy to reproduction decreases starvation resistance.

Mode of deformation and the rate of energy storage during uniaxial tensile deformation of austenitic steel

The mechanism of slip and its consequence in the process of energy storage during uniaxial tension of austenitic steel was studied. The interpretation of the energy storage process in terms of the slip development and microscopic shear band formation is presented.

Effect of temporary reductions in feeding on protein synthesis and energy storage of juvenile Atlantic salmon

Biochemical and tissue‐composition indices were used to determine the impacts of temporary feeding reductions on juvenile Atlantic salmon (4.2g initial weight). Three levels of food reduction (fasting, 20% of control, 50% of control) lasting for 2, 4 or 8 days were compared to a control group (constant feeding at 2.75% of body weight day−1). Ornithine decarboxylase (ODC) activity and RNA concentrations were used to measure changes in protein synthesis; condition factor (K), liver‐somatic index (LSI), visceral‐somatic index (VSI), and gut index (GI)were used to provide information on stored energy levels. Results showed that physiological adjustments to decreases or increases in feeding occur very quickly. The most rapid responses were changes in ODC activity (within 2 days) and LSI (2–4 days). Changes in RNA concentrations and K required 4–8 days. There was no apparent effect of the treatments on VSI or GI. Temporary reductions of feeding lasting 2 days or less would not be detected by any index except ODC activity. Changes in the indices are discussed with respect to short‐term changes in rates of protein synthesis and energy storage.

The use of solar-based CO 2/CH 4 reforming for reducing greenhouse gas emissions during the generation of electricity and process heat

CSIRO/Pacific Power research on using the reversible CO 2/CH 4 reforming reaction for solar energy storage and transport is described. Catalysts have been developed and used to conduct the forward and reverse reactions in fluidised-bed reactors under practical conditions without carbon formation. Thermochemical energy storage rates up to 30 MW th/tonne of catalyst were obtained. Closed and open loop thermochemical heat-pipes based on CO 2/CH 4 reforming have a range of applications in Australia. They have considerable potential in reducing the emissions of Greenhouse gases associated with the production of electricity and process heat. Results of a techno-economic evaluation of selected concepts are presented. Concepts for linking solar energy to the reformer have been identified and future work must focus on reactor scale-up and linking the reformer with solar energy.

Effect of the grain size on the rate of energy storage during the tensile deformation of an austenitic steel

The effect of the grain size on the energy storage process in a low carbon austenitic steel deformed in tension is studied. The energy conversion at each instant of the deformation process is characterized by the instantaneous rate of energy storage, de s de w , where e s is the stored energy and e w is the mechanical energy expended on the plastic deformation. It has been shown experimentally that, in the initial stage of plastic deformation in this austenitic steel, the dependence of the rate de s de w on e w exhibits a maximum. The location of the maximum depends on the grain size of the material. In fine-grained samples, the maximum appears at smaller strains. After reaching a certain degree of deformation, plots of de s de w vs. the strain for the samples of both groups are practically the same. These results are interpreted in terms of the microstructural evolution during deformation. It has been shown that the grain boundaries favour the formation and affect the evolution of low energy dislocation structures.

A differential photomicrocalorimetric method for investigating the rate of energy storage in plants

Abstract This paper describes the equipment and method for the direct measurement of the quantity and rate of light-induced changes in plants. The photomicrocalorimetric method can be used for the investigation of energetics in photosynthesis and other photobiological processes in higher plants, algae and microorganisms. The rate of energy storage of Chlorella cells and a number of agricultural plants under optimal and extreme conditions have been determined.

Pigment-dependent light influence on the energetics of Serratia marcescens

This paper describes a direct determination of the light energy accumulation by pigmented Serratia marcescens using a photomicrocalorimetric method. At 5400 lux the rate of energy storage by the pigmented strain 9986 was 1.5 J h −1 (g dry wt) −1 . The stored energy accumulation by pigmented strain 33 and by its non-pigmented equivalent, and also by strain 24-5 (control), was in the range 0.4–0.77 J h −1 (g dry wt) −1 . Growing cultures contain monomer and dimer forms of the photosensitive pigment, prodigiosin. The visible light directly affected the pigment itself and provoked its phototransformation.

Nutrient reserve storage, energetics, and food consumption during the prebreeding and premoulting foraging periods of king penguins

Nutrient reserve storage during the prefasting foraging trips of king penguins Aptenodytes patagonicus was investigated by measuring body composition at the beginning and the end of the prebreeding and premoulting periods at sea. Both periods were marked by a 45–47% increase in body mass (4.6 and 5.6 kg during the prebreeding and premoulting trips, respectively) including body water (31% and 55% of the total increase in body mass), protein (13% and 16%) and lipid (46% and 23%), but not ash. Fat accretion accounted for most of the energy stored (86% and 71% versus 14% and 29% for protein) and it was mainly located in the subdermal depot, the larger increase in body protein occurring in pectoral muscles. Daily mass gain was lower during the prebreeding foraging trip than during the premoulting one (195 versus 328 g/day), while there was no difference in the rate of energy storage (4,097 and 4,155 kJ/day). The total energy costs of the foraging periods were calculated to be 381 and 315 MJ during the prebreeding and premoulting trips respectively, which corresponded to a 70-kg and a 58-kg food intake. The consumption of marine resources by the king penguin population from Crozet Islands was estimated to be 166,000 tons in spring/summer during the two foraging periods preceding long-term fasts.

The effect of nucleation models on dynamic recrystallization I. Homogeneous stored energy distribution

Abstract A Monte Carlo simulation technique, in which the microstructure is mapped onto a discReve, two-dimensional lattice with the use of the Q-state Potts model, is applied to the problem of dynamic recrystallization in a polycrystalline matrix. The response of the material to hot deformation is simulated by adding recrystallization nuclei and stored energy continuously with time. The simulations use an energy storage rate Schedule that models both work hardening and dynamic recovery of metals by way of a parabolic work hardening law. Recrystallization nuclei, having zero stored energy, were added at a rate which is related to the level of work hardening. Departing from a previously applied scheme, the nucleation rate is chosen to be proportional to the strain rate. Also considered is a more intuitive, local model in which the creation of a nucleus oceurs with a probability proportional to exp (−δE), where δE is the energy change associated with the introduction of an embryo into the matrix. The evolution of the stress and the mean grain size is similar to those obtained with use of the constant nucleation rate. It was found, however, that the relations between steady-state parameters are different from the results obtained earlier but are more consistent with the experimental literature. Careful numerical analysis of data obtained for the exponential nucleation model yield new power-law relations between steady-state parameters and nucleation attempt rate. The kinetics of dynamic recrystallization are analysed with use of the Johnson-Mehl-Avrami-Kolmogorov (JMAK) eauation which is shown to be sensitive to the rate of deformation. Higher than expected values of the JMAK kinetic exponent were obtained that are attributed to the use of the parabolic work hardening model in the simulations.

Rate of energy storage and microstructure evolution during the tensile deformation of austenitic steel

The results of investigations of the energy storage process in austenitic stainless steel deformed in tension are reported. Conclusive evidence is presented for the existence at the initial stage of deformation of the maximum in the instantaneous rate of energy storage defined as d e s/d e w, where e s is the stored energy and e w is the mechanical energy expended in plastic deformation. Its occurrence is interpreted in terms of the evolution of the microstructure during deformation.