Energetic Profitability Research Articles

Design and Operation of a Cost-Effective Cooling Chamber for Testing Power Electronics at Cryogenic Temperatures

In recent decades, research in the field of cryogenic power electronics has gained increasing interest, as it promises advantages such as higher power density and higher efficiency. Particularly in the mobility sector, lower weight and smaller size are essential to advance electrification [1]. Another incentive and benefit of lower power losses is the reduction in operating costs. However, the study in [2] has shown that energetic profitability of low-temperature cooling is achieved, in particular, in applications where the necessary cooling for the power electronics is available for free and synergy effects can be realized within the overall system. Interesting areas of application are, therefore, in the field of aviation, where the cold ambient temperature of -55 °C is available, and in the mobility sector. Cryogenically stored fuels such as liquid hydrogen (LH2) or liquid natural gas (LNG) must be heated before they can be used, for example LH2 for application in a fuel cell, for which the power losses generated in a power electronic converter can be used perfectly. This saves energy for extra heaters and increases the efficiency of the power electronics [2]. One challenge when operating power electronics at temperatures below -40 °C is that most electronic components are not specified from the manufacturer for these temperatures. Therefore, a comprehensive characterization of all required electronic components for a deep temperature operation is essential, for which a suitable environment—a cryogenic cooling system—with variably adjustable ambient temperature is required.

Novel hybrid solar dryer for medicinal plants: An experimental evaluation (Tithonia diversifolia Gray)

The present study examines a hybrid solar drying (HSD) system designed to dry the medicinal plant species, Tithonia diversifolia Gray, via both natural and forced convection. The dryer was built and tested at the Polytechnic University of Chiapas, Mexico. The hybrid solar technology used in the present research comprise a flat solar collector, a solar water heater, and the paraffin wax HS-58, which was used as a phase-change material. The solar dryer was experimentally tested both with and without a thermal energy storage system. Experimental tests were carried out to evaluate the energetic profitability and the quality of the drying produced by the system proposed. Energetic profitability was evaluated based on exergy indicators, the sustainability index, and the quality of drying. The results show that, used with the flat solar collector, the solar dryer was able to operate for only 4 h, while, used with the proposed auxiliary subsystem, the system was able to continually operate for 14 h. The total autonomy of the HSD was 71.42% higher than that recorded for a simple solar dryer. The exergetic efficiency of the HSD ranged from 17.68% to 57.66%. The HSD reduced the moisture content of the T. diversifolia by 90%.

Energy analysis and life cycle assessment of a thermal energy storage unit involving conventional or recycled storage materials and devoted to industrial waste heat valorisation

Any system intending to improve the environmental performances of a process should be assessed by a Life Cycle Assessment. This work draws up the environmental profile of the heat provided by a storage system recovering industrial waste heat at high temperature (500 °C) through 5 selected indicators: Cumulative Energy Demand, Global Warming Potential, abiotic depletion potential, particle matter and freshwater eutrophication. The calculated indicators were compared to those of the fossil fuel substituted by the recovered heat, that is to say natural gas, and proved to be reduced. Then, the environmental payback times were calculated; and an energetic profitability evaluation by the Energy Returned on Investment expanded on the profile. Besides, the influence of operating conditions variations was investigated through a parametric study. An optimal number of cycles to provide the same amount of energy may be defined, as a compromise between the abiotic resource depletion potential reduction with smaller tanks performing more cycles and the energy returned on investment deteriorated with the operational energy consumption increased due to higher pressure drop with smaller tank diameter. The most rewarding environmental performances concerned the Cumulative Energy Demand, Global Warming Potential indicators of the provided heat, about 1.2 kgCO2-eq and 65 MJ-eq per kWh (payback time lower than 3 months), and the Energy Returned on Investment that doubled compared to natural gas, e.g. reached a value of 55. The positive effect of using recycled storage materials on the resource depletion indicator were enlightened, notably when the operating conditions strayed from the reference case.

Profitability of low-temperature power electronics and potential applications

This article presents an investigation of the profitability of cryogenic power electronics at different cooling and ambient temperatures. Thermodynamic fundamentals of low-temperature refrigeration processes are considered and the Carnot efficiencies of state-of-the-art refrigerators are evaluated in order to establish the necessary power loss reduction for energetic profitability of low-temperature to cryogenic power electronic systems down to 77 K. In this context, special attention is paid to two loss contributions in a power electronic system which, based on investigations on active and passive components, show the greatest potential for loss reduction at low temperatures. These are the on-state losses of Si and GaN transistors and the DC winding losses of inductors. The analysis shows that over the entire low temperature range, the loss reduction in a cryogenic converter can hardly compensate for the electrical power required to provide the necessary cooling capacity when cooling against an ambient temperature of 300 K.

Maize stubble as foraging habitat for wintering geese and swans in northern Europe

Agricultural crops have become increasingly important foraging habitats to geese and swans in northern Europe, and a recent climate-driven expansion in the area of maize fields has led to a rapid increase in the exploitation of this habitat. However, due to the novelty of maize foraging in this region, little is known about the abundance and energetic value of this resource to foraging birds. In this study we quantify food availability, intake rates and energetic profitability of the maize stubble habitat, and describe the value of this increasingly cultivated crop to wintering geese and swans in the region. Our results indicate that the maize resource varies considerably among fields and years, but also that the energetic returns from maize foraging is substantial. As such, fields with extensive spill allow foraging birds to fulfill their daily energetic demands in 4 h of active foraging. Both the area of cultivated maize fields and the importance of this habitat to foraging birds are expected to increase in years to come. This may alleviate conflicts with other more vulnerable crops such as winter cereals, and have the potential to affect migratory decisions, site use and population dynamics of geese and swans wintering in northern Europe.

Two-stage fractionation of sugarcane bagasse by autohydrolysis and glycerol organosolv delignification in a lignocellulosic biorefinery concept

Bioethanol production from lignocellulose biomass offers a solution to current environmental challenges caused by fossil fuel energy resources, while satisfying the biorefinery concept. In this study, two-stage fractionation (autohydrolysis (AH) followed by glycerol organosolv delignification (GOD)) of sugarcane bagasse (SCB) was studied as a function of temperature, time, glycerol content and liquid-to-solid (LSR) ratio using experimental designs. The effect of three different AH pretreatment severities on delignification extents (DE) of the solid fractions were also evaluated. Scanning electron microscopy was used to examine the changes in the surface of SCB pretreated by AH. Energy balances of four fractionation conditions were estimated, and the use of pure and crude glycerol in GOD was evaluated based on DE and lignin contents. A DE of ∼64% was obtained at 210.3°C, 40min, LSR of 6.5 (v/w) and 80% (v/v) pure glycerol for GOD of SCB pretreated by AH at 175.8°C, 49min and LSR of 5.3 (v/w), which resulted in an energetic profitability (EP) of 141.48MJ/kgSCB. The use of crude glycerol at 80% (v/v) under the same process conditions optimized for pure glycerol also proved to be feasible (DE of ∼64% and EP of 142.67MJ/kgSCB), widening the possibilities for its direct use in GOD of SCB pretreated by AH in a 2G bioethanol integrated plant.

Opportunity costs influence food selection and giving‐up density of dabbling ducks

The interaction of animals with their food can yield insights into habitat characteristics, such as perceived predation risk and relative quality. We deployed experimental foraging patches in wetlands used by migrating dabbling ducks Anas spp. in the central Illinois River Valley to estimate variation in seed removal and giving‐up density (GUD; i.e. density of food remaining in patches following abandonment) with respect to seed density, seed size, seed depth in the substrate, substrate firmness, perceived predation risk, and an energetic profitability threshold (i.e. critical food density). Seed depth and the density of naturally‐occurring seeds outside of experimental plots affected seed removal and GUD in experimental patches more than perceived predation risk, seed density, seed size or substrate firmness. The greatest seed removal and lowest GUDs in experimental patches occurred when food resources in alternative foraging locations outside of plots (i.e. opportunity costs) appeared to be near or below a critical food density (i.e. 119–181 kg ha–1). Giving‐up densities varied substantially from a critical food density across a range of food densities in alternative foraging locations suggesting that fixed GUDs should not be used as surrogates for critical food densities in energetic carrying capacity models. Foraging and resting rates in and near experimental foraging patches did not reflect patterns of seed removal and were poor predictors of GUD and foraging habitat quality. Our results demonstrated the usefulness of GUDs as indicators of habitat quality for subsurface, benthic foragers relative to other available foraging patches and suggested that food may be limited for dabbling ducks during spring migration in some years in the midwestern USA.

Bioenergetic calculations evaluate changes to habitat quality for salmonid fishes in streams treated with salmon carcass analog

Nutrient supplementation in oligotrophic streams is proposed as a means of mitigating losses of marine-derived subsidies from declining or extirpated populations of anadromous fishes. One of the central predictions of nutrient addition is an increased production of fish through bottom-up increases in invertebrate abundance. Such changes in food availability may increase growth and production rates for stream fishes by increasing habitat quality. In this study we apply bioenergetic calculations to estimate changes to habitat quality based on predicted increases in net energy intake. We compared invertebrate drift abundance and estimated changes in energy availability in streams treated with salmon carcass analog versus untreated controls. Our results revealed a two- to threefold increase in invertebrate drift abundance following the addition of salmon carcass analog; however, this effect appeared to be short-term. Measures of the energetic profitability of stream habitat for salmonid fishes revealed small, yet significant, increases in net energy availability in streams that received analog additions, but only after controlling for differences in physical habitat features such as temperature and stream flow.

Combining energetic profitability and cover effects to evaluate salmonid habitat quality

Recent studies have demonstrated that the energetic profitability (net energy intake potential; NEI potential) of a habitat, which is calculated as the gross energy gain from foraging minus the energy expenditure from swimming at a focal point, may be a useful tool for predicting the salmonid biomass. The effectiveness of the NEI potential should be tested in various systems. Even if the NEI potential is validated, its predictive accuracy and transferability could be limited if the cover habitat, which is known to be an important factor for determining salmonid abundance, is not considered. We tested whether the NEI potential is effective for predicting the salmonid biomass even in a stream with abundant cover and whether combining the NEI potential and cover effects can improve the predictability of fish biomass using a generalized linear model. Our results demonstrated that the NEI potential could generally predict the fish biomass (percent deviance explained = 79.9 %), and the model that incorporated both the NEI potential and the cover ratio improved the predictive accuracy (percent deviance explained = 88.5 %). These results suggest that energetic profitability can be an effective indicator for assessing habitat quality and is relatively transferable to other systems. Furthermore, when cover effects are considered, the habitat quality is more accurately represented; thus, combining the energetic profitability and the cover effects might improve the transferability of the assessment across habitats.

Priority effects among young‐of‐the‐year fish: reduced growth of bluegill sunfish (Lepomis macrochirus) caused by yellow perch (Perca flavescens)?

Summary1. When available, Daphnia spp. are often preferred by age‐0 yellow perch and bluegill sunfish because of energetic profitability. We hypothesised that predation by age‐0 yellow perch could lead to a midsummer decline (MSD) of Daphnia spp. and that priority effects may favour yellow perch because they hatch before bluegill, allowing them to capitalise on Daphnia spp. prior to bluegill emergence.2. Data were collected from 2004 to 2010 in Pelican Lake, Nebraska, U.S.A. The lake experienced a prolonged MSD in all but 1 year (2005), generally occurring within the first 2 weeks of June except in 2008 and 2010 when it occurred at the end of June. MSD timing is not solely related to seasonal patterns of age‐0 yellow perch consumption. Nevertheless, when Daphnia spp. biomass was low during 2004 and 2006–2010 (<4 mg wet weight L−1), predation by age‐0 yellow perch seems to have suppressed Daphnia spp. biomass (i.e. <1.0 mg wet weight L−1). The exception was 2005 when age‐0 yellow perch were absent.3. Growth of age‐0 bluegill was significantly faster in 2005, when Daphnia spp. were available in greater densities (>4 mg wet weight L−1) compared with the other years (<0.2 mg wet weight L−1).4. We conclude that age‐0 yellow perch are capable of reducing Daphnia biomass prior to the arrival of age‐0 bluegill, ultimately slowing bluegill growth. Thus, priority effects favour age‐0 yellow perch when competing with age‐0 bluegill for Daphnia. However, these effects may be minimised if there is a shorter time between hatching of the two species, higher Daphnia spp. densities or lower age‐0 yellow perch densities.

Energy intake, kleptoparasitism risk, and prey choice by Glaucous-winged Gulls (Larus glaucescens) foraging on sea stars

ABSTRACT. Energy gain is thought to play a central role in prey selection by most foragers, but it may conflict with food theft avoidance and be constrained by undeveloped foraging skills. We investigated predation by the Glaucous-winged Gull (Larus glaucescens) on the ecologically important Ochre Sea Star (Pisaster ochraceus). We tested the hypothesis that Pisaster size selection by gulls was based on energetic profitability, defined as energy provided per unit handling time. We then examined the degree to which profitability interacts with intraspecific kleptoparasitism risk and age-related foraging efficiency (i.e., energy intake rate, prey capture success) to produce the patterns of prey choice observed in a natural setting. Behavioral observations of free-living gulls revealed moderate to high (32.5–91.6%) occurrences of Pisaster in gull diets. We used handling time data and bomb calorimetry to determine the relationship between Pisaster size and energetic profitability, which informed prey offer exp...

Small prey size offers immunity to predation: a case study on two species of Asplanchna and three brachionid prey (Rotifera)

We tested the hypothesis that small prey can coexist with large predators. For this we confronted two predators (smaller Asplanchna brightwellii: 900 μm and larger A. sieboldi: 1400 μm) with three prey rotifers (smaller: Anuraeopsis fissa (70 μm); larger: Brachionus calyciflorus (200 μm) and intermediate: B. patulus (120 μm)) using functional response, prey preference, population growth and life table demography. Regardless of prey type, A. sieboldi was able to consume more prey than A. brightwellii and it consumed higher number of B. patulus than of B. calyciflorus or A. fissa. Prey preference experiments showed that A. brightwellii had no preference for B. calyciflorus regardless of prey density, while A. sieboldi preferred B. calyciflorus and avoided A. fissa. Data on population growth showed that A. brightwellii was always numerically more abundant than A. sieboldi. Prey type had a significant effect on peak abundances of A. sieboldi but not of A. brightwellii. Life table demography data revealed a significantly lower lifespan in A. brightwellii fed B. calyciflorus, compared to B. patulus, but not when compared to A. fissa. A. sieboldi lifespan was not affected by prey type. Depending on prey type and predator species, generation time varied from 2 to 3 days. Both lowest (0.38 d−1) and highest (0.98 d−1) population growth rates were observed in A. sieboldi. We suggest that reduced reproductive output in Asplanchna was caused by either large (B. calyciflorus) or small (A. fissa) prey. At natural densities of Anuraeopsis, it is unlikely that Asplanchna reaches abundances high enough to exterminate this prey. By its extremely small size (combining low energetic profitability with low encounter rates with predators) A. fissa may coexist with Asplanchna in nature.

A spatial energetics model of cadmium accumulation by diving ducks

Food-chain transfer of contaminants is often predictable below the level of birds, but relations between contaminant concentrations in birds and their foods are often weak and variable. Much of this variation probably results from the energetics of foraging in fluctuating, heterogeneous environments, which has not been accounted for in past models of contaminant uptake by birds. Because birds are highly mobile with varying lengths of stay in different areas, collecting birds and analyzing their tissues yields unclear information on the importance of local contaminants. Likewise, toxicity assays with captive birds ignore changes in food intake with varying activity and weather experienced by wild birds. Neither of these approaches alone can predict maximum allowable contaminant levels in foods that avoid toxic effects under different field conditions, or what body burdens accumulate during varying lengths of stay that might affect the birds' biology at other places and times. To allow such predictions, an individual-based computer model was developed to simulate the intake of contaminated foods by diving ducks for varying conditions such as weather, water depth, food dispersion, and the size and digestibility of food. Food-intake estimates are combined with laboratory data on contaminant uptake as a function of food consumption and contaminant content. As an example, cadmium uptake is estimated for Canvasback ducks (Aythya valisineria) foraging on belowground winter buds of the submerged plant Vallisneria americana. Results indicate that relations between cadmium content of food and cadmium uptake by kidneys can be quite different depending on field conditions, and that cadmium content of food can be less important than food dispersion and resulting search costs in determining cadmium uptake. Models that estimate food intake based on energetic profitability can yield very different predictions than models that assume constant daily intake, or assume that food intake simply increases as energy costs of thermoregulation or other factors go up. Such profitability effects might explain much of the confounding variation in deriving bioaccumulation factors for birds.

Learning and remembering of spatial patterns by hummingbirds

Hummingbirds' responses to the spatial distribution of their food were examined using arrays of visually identical feeders in the laboratory. Rufous hummingbirds, Selasphorus rufus, learned to visit profitable feeders in square arrays of 64 feeders on a wall in which only half contained food and the only source of information about feeder quality was location. Birds learned quickly and well if profitability was simply patterned. They learned more slowly but eventually reached high performance on complex patterns, especially if feeders were regularly distributed. Memory of pattern accounted for much more of performance on all patterns than either simple movement rules or memory of individual locations. When food distributions were switched to their mirror images after birds had reached asymptotic performance, all birds that had performed well before the switch continued for several trials to visit the feeders they had visited before the switch, lagging in redistributing effort to match the new pattern. It is suggested that in the absence of visible correlates of feeder quality, hummingbirds use coarse-grained memories of the spatial patterning of energetic profitability to guide their foraging. These memories develop with repeated experience of environments, develop more quickly in simply patterned environments and persist despite changes in food distribution. Poorer performance in complex arrays is inconsistent with a fine-grained model in which birds remember point sources of food independently. Persistence of foraging patterns at the cost of significantly reduced gross food intake and severely reduced net intake after pattern switches demonstrates that hummingbirds rely greatly on memory of profitability in guiding foraging; however, their quick recovery to previous performance shows that they quickly modify their memory of places on the basis of new information. These results are compared with some recent field studies of hummingbird foraging in which use of memory could not be reliably demonstrated, or was only one of several mechanisms underlying foraging patterns.

Colour association influences honey bee choice between sucrose concentrations

Certain colours associated with floral food resources are more quickly learned by honey bees (Apis mellifera) than are other colours. But the impact of colour, and other floral cues, on bee choice behaviour has not yet been determined. In these experiments, colour association and sugar concentration of reward were varied to assess how they interact to affect bee choice behaviour. Thirty-five bees were individually given binary choices between blue and yellow artificial flowers that contained either the same rewards or rewards of different sucrose concentrations. Honey bee choice between sucrose concentrations was affected by colour association and this effect was greatest when absolute difference between rewards was the lowest. The honey bee's ability to maximize energetic profitability during foraging is constrained by floral cue effectiveness.

Resource use, energetic profitability, and behavioral decisions in migrant rufous hummingbirds.

Migrant Rufous Hummingbirds (Selasphorus rufus) defend nectar resources at stopover sites while replenishing fat reserves needed for migratory flights. During late summer in the Sandia Mountains, central New Mexico, they defend the wasp- and bee-pollinated Scrophularia montana from other hummingbirds. Both hummingbirds and hymenopterans exploit Scrophularia nectar during the early part of its flowering period. As summer colony growth increases the densities of the eusocial hymenopterans by 100-150%, their exploitation of Scrophularia nectar lowers its mean standing crop in flowers by 200-300%. Sometime during the summer, Rufous Hummingbirds abandon and do not further use this resource for the remaining 3-4 weeks of its flowering period. The abandonment always occurs when the mean standing crop of nectar is approximately 0.2-0.3 μL/ flower. This paper describes a model of Rufous Hummingbird energetics, that shows abandonment occurred 1-3 days after they passed the threshold at which the resource could have provided their minimum daily energy requirements. I suggest that constraints imposed by a highly competitive social environment severely reduced the options available to the hummingbirds, and caused them to continue to defend a resource that could no longer meet their energetic requirements.

Locomotor impairment and defense in gravid lizards (Eumeces laticeps): behavioral shift in activity may offset costs of reproduction in an active forager

Female Eumeces laticeps experience a substantial decrease in running speed (ca. 25%) and an even greater loss of endurance (slightly over 50%) while gravid. Because some widely foraging lizards, including E. laticeps, rely primarily on running to escape predators, the decreases in speed and stamina may contribute to an increased risk of predation. However, observations suggest that gravid females become less active or conspicuous on the surface. Ambush foraging lizards rely relatively more on crypsis associated with immobility to avoid predation and thus can have greater average relative clutch mass (RCM) than active foragers. Behavioral compensation for locomotor impairment by becoming less active or conspicuous may allow some species the advantages inherent in both high relative clutch mass when gravid and the increased energetic profitability of active foraging when not gravid. As females gain weight during the breeding season, they may forage actively until the risk due to increasing locomotor impairment becomes too great and then change defensive strategy to greater reliance on crypsis. Without such a shift, widely foraging squamate reptiles may be less able than ambush foragers to exploit life-historical strategies demanding high current investment in reproduction.

Specialization by territorial hummingbirds on experimentally enriched patches of flowers: energetic profitability and learning

On unmanipulated hummingbird feeding territories, time spent foraging in patches was directly proportional to the number of flowers they contained. After we added nectar to the flowers in some patches, foraging increased in those patches, decreased in other patches, and decreased overall relative to control conditions. Specialization on enriched patches and reduction in foraging effort quantitatively reflected the energy we added, but the reduced effort had little effect on overall energy expenditure. Nevertheless, rates of net energy intake increased under enrichment, because gross intake rates increased. These experiments provide evidence that hummingbirds allocate effort among patches, using memory of relative patch quality when they initiate bouts of foraging. The strongest evidence is that individuals begin each day of foraging as if it were the previous day. On mornings after control days, birds foraged among patches as they had the day before, even though there was an (undiscovered) bonanza on their territories. On mornings after days of enrichment, however, whether or not a patch was enriched again, birds specialized on it at first. If the patch was enriched again, they continued to exploit it; if not, they reverted to normal patterns of allocation.

Effective charges of atoms and oxidative reactions

1. The concept of the effective coordination charge was discussed. It was shown that in a series of inorganic crystals, the metal atoms may possess a negative effective charge. 2. A thermodynamic analysis was made of reactions of oxidation, and the energetic profitability of increasing the valence of the metal in the case when it possesses a negative effective coordination charge was substantiated. 3. The presence of correlation between the sign and magnitude of the effective charge and temperatures of oxidation reactions was demonstrated experimentally.