Maximum Work Rate Extractable from Energy Fluxes

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Viorel Badescu
Keyword(s):  
Solar Radiation ◽  
Performance Indicators ◽  
Work Rate ◽  
Total Loss ◽  
Energy Fluxes ◽  
Work Content ◽  
Energy Conversion Systems ◽  
Maximum Work ◽  
Solar Energy Flux ◽  
Content Factor

Abstract A general formalism is developed to evaluate the amount of work extractable from energy fluxes. It covers nonequilibrium cases when the concept of exergy is not relevant. The rate of work deficiency, which has been previously introduced as the total loss of exergy, is defined here as the total loss of work, which would have resulted if all the work were lost to the environment. New performance indicators are proposed. First, the work content factor gives the proportion of extractable work in a given amount of energy. Second, the work deficiency factor is a measure of the potential of improvement for the operation of energy conversion systems. Previous results reported in literature are particular cases of the general results obtained here. The formalism is used to evaluate the work rate extractable from the solar energy flux. Results are shown in cases where solar radiation interacts with materials without energy bandgap (metals) and with energy bandgaps (semiconductors), respectively.

The Role of Airmass Types and Surface Energy Fluxes in Snow Cover Ablation in the Central Appalachians

2004 ◽  
Vol 43 (12) ◽  
pp. 1887-1899 ◽  
Author(s):  
Daniel J. Leathers ◽  
Daniel Graybeal ◽  
Thomas Mote ◽  
Andrew Grundstein ◽  
David Robinson
Keyword(s):  
Solar Radiation ◽  
Snow Cover ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Energy Fluxes ◽  
Synoptic Classification ◽  
One Dimensional ◽  
Central Appalachians ◽  
Synoptic Conditions ◽  
Meteorological Influences

Abstract A one-dimensional snowpack model, a unique airmass identification scheme, and surface weather observations are used to investigate large ablation events in the central Appalachian Mountains of North America. Data from cooperative observing stations are used to identify large ablation events within a 1° latitude × 1° longitude grid box that covers the majority of the Lycoming Creek basin in northern Pennsylvania. All 1-day ablation events greater than or equal to 7.6 cm (3 in.) are identified for the period of 1950 through 2001. Seventy-one events are identified, and these days are matched with a daily airmass type derived using the Spatial Synoptic Classification technique. Average meteorological characteristics on ablation days of each airmass type are calculated in an effort to understand the diverse meteorological influences that led to the large ablation events. A one-dimensional mass and energy balance snowpack model (“SNTHERM”) is used to calculate surface/atmosphere energy fluxes responsible for ablation under each airmass type. Results indicate that large ablation events take place under diverse airmass/synoptic conditions in the central Appalachians. Five airmass types account for the 71 large ablation events over the 52-yr period. Forty-three of the events occurred under “moist” airmass types and 28 under “dry” airmass conditions. Large ablation events under dry airmass types are driven primarily by daytime net radiation receipt, especially net solar radiation. These events tend to occur early and late in the snow cover season when solar radiation receipt is highest and are characterized by relatively clear skies, warm daytime temperatures, and low dewpoint temperatures. Moist airmass types are characterized by cloudy, windy conditions with higher dewpoint temperatures and often with liquid precipitation. During these events sensible heat flux is most often the dominant energy flux to the snowpack during ablation episodes. However, in many cases there is also a significant input of energy to the snowpack associated with condensation. Combinations of high sensible and latent heat fluxes often result in extreme ablation episodes, similar to those witnessed in this area in January 1996.

scholarly journals A stochastic model for the hourly solar radiation process for application in renewable resources management

2018 ◽  
Vol 45 ◽  
pp. 139-145 ◽  
Author(s):  
Giannis Koudouris ◽  
Panayiotis Dimitriadis ◽  
Theano Iliopoulou ◽  
Nikos Mamassis ◽  
Demetris Koutsoyiannis
Keyword(s):  
Solar Radiation ◽  
Stochastic Model ◽  
Renewable Resources ◽  
Renewable Energy Sources ◽  
Dependence Structure ◽  
Clearness Index ◽  
Radiation Process ◽  
Resources Management ◽  
Daily Data ◽  
Energy Conversion Systems

Abstract. Since the beginning of the 21st century, the scientific community has made huge leaps to exploit renewable energy sources, with solar radiation being one of the most important. However, the variability of solar radiation has a significant impact on solar energy conversion systems, such as in photovoltaic systems, characterized by a fast and non-linear response to incident solar radiation. The performance prediction of these systems is typically based on hourly or daily data because those are usually available at these time scales. The aim of this work is to investigate the stochastic nature and time evolution of the solar radiation process for daily and hourly scale, with the ultimate goal of creating a new cyclostationary stochastic model capable of reproducing the dependence structure and the marginal distribution of hourly solar radiation via the clearness index KT.

Effect of a precooling maneuver on body temperature and exercise performance

1981 ◽  
Vol 50 (4) ◽  
pp. 772-778 ◽  
Author(s):  
V. Schmidt ◽  
K. Bruck
Keyword(s):  
Heart Rate ◽  
Body Temperature ◽  
Peak Oxygen Uptake ◽  
Work Rate ◽  
Time To Exhaustion ◽  
Total Work ◽  
Mean Body Temperature ◽  
Deep Body Temperature ◽  
Sweat Secretion ◽  
Maximum Work

Twelve subjects exercised to exhaustion at an ambient temperature of 18 degrees C on a bicycle ergometer with the load being stepwise increased. On one day, exercise was preceded by a precooling maneuver. In the precooling tests, deep body temperature attained values of about 1 degree C lower than in the control tests. There was no indication of metabolic cold defense reactions being evoked throughout the exercise period. In the precooling tests, heart rate was significantly lower than in the controls, but the mean maximum work rate, peak oxygen uptake (VO2), time to exhaustion, and total work were not reduced, i.e., work rate and VO2 were increased for a given heart rate. In the three subjects with the lowest maximum work rates, total work and exhaustion time and, in two cases, maximum work rate were increased after precooling. The onset of sweating occurred at higher work rates but at lower core, mean skin, and mean body temperature after precooling. However, the accumulated sweat secretion was considerably smaller after precooling, indicating less thermoregulatory effort.

scholarly journals Testing the heat dissipation limit theory in a breeding passerine

2018 ◽  
Vol 285 (1878) ◽  
pp. 20180652 ◽  
Author(s):  
Jan-Åke Nilsson ◽  
Andreas Nord
Keyword(s):  
Heat Dissipation ◽  
Work Rate ◽  
Body Temperatures ◽  
Limit Theory ◽  
Ambient Temperatures ◽  
Metabolic Heat ◽  
Thermal Window ◽  
Future Reproduction ◽  
Maximum Work ◽  
Males And Females

The maximum work rate of animals has recently been suggested to be determined by the rate at which excess metabolic heat generated during work can be dissipated (heat dissipation limitation (HDL) theory). As a first step towards testing this theory in wild animals, we experimentally manipulated brood size in breeding marsh tits ( Poecile palustris ) to change their work rate. Parents feeding nestlings generally operated at above-normal body temperatures. Body temperature in both males and females increased with maximum ambient temperature and with manipulated work rate, sometimes even exceeding 45°C, which is close to suggested lethal levels for birds. Such high body temperatures have previously only been described for birds living in hot and arid regions. Thus, reproductive effort in marsh tits may potentially be limited by the rate of heat dissipation. Females had lower body temperatures, a possible consequence of their brood patch serving as a thermal window facilitating heat dissipation. Because increasing body temperatures are connected to somatic costs, we suggest that the HDL theory may constitute a possible mediator of the trade-off between current and future reproduction. It follows that globally increasing, more stochastic, ambient temperatures may restrict the capacity for sustained work of animals in the future.

scholarly journals Comparative study of the radiative and turbulent energy fluxes during summer and winter at the edge of the Antarctic ice sheet in Dronning Maud Land - East Antarctica

MAUSAM ◽  
2021 ◽  
Vol 62 (4) ◽  
pp. 557-566
Author(s):  
H.S. GUSAIN ◽  
V.D. MISHRA ◽  
AVINASH NEGI
Keyword(s):  
Heat Flux ◽  
Solar Radiation ◽  
Heat Source ◽  
Meteorological Parameters ◽  
Turbulent Energy ◽  
East Antarctica ◽  
Energy Fluxes ◽  
Glacier Surface ◽  
Dronning Maud Land ◽  
The Antarctic

Present study compares the estimated radiative and turbulent energy fluxes at the edge of the Antarctic ice sheet during summer and winter in Dronning Maud land, East Antarctica. Hourly snow meteorological parameters were recorded and analysed during winter months (May, June, July and August) of the year 2007 and summer months (November, December, January and February) of the year 2007-08 using Automatic Weather Station (AWS) on the glacier surface. Snow-meteorological parameters air temperature, relative humidity, wind speed, wind direction, incoming solar radiation, outgoing solar radiation, atmospheric pressure and glacier surface temperature were recorded by the AWS. An energy balance model was used to evaluate the surface energy fluxes from measured meteorological quantities for the summer and winter. Net radiative flux was observed the main heat source during summer with seasonal average of 98Wm-2 while sensible heat flux was observed main heat source during winter with seasonal average of 30 Wm-2. Latent heat flux was observed the main heat sink during both the season with seasonal average values of -86.7 Wm-2 for summer and -65.4 Wm-2 during winter. Sublimation was observed high during summer compare to winter.

Core temperature "null zone"

1991 ◽  
Vol 71 (4) ◽  
pp. 1289-1295 ◽  
Author(s):  
I. B. Mekjavic ◽  
C. J. Sundberg ◽  
D. Linnarsson
Keyword(s):  
Core Temperature ◽  
Recovery Period ◽  
Rest Period ◽  
Cycle Ergometer ◽  
Work Rate ◽  
The Core ◽  
Maximum Work ◽  
Male Subjects ◽  
Shivering Thermogenesis ◽  
Peak Value

An experimental protocol was designed to investigate whether human core temperature is regulated at a “set point” or whether there is a neutral zone between the core thresholds for shivering thermogenesis and sweating. Nine male subjects exercised on an underwater cycle ergometer at a work rate equivalent to 50% of their maximum work rate. Throughout an initial 2-min rest period, the 20-min exercise protocol, and the 100-min recovery period, subjects remained immersed to the chin in water maintained at 28 degrees C. On completion of the exercise, the rate of forehead sweating (Esw) decayed from a mean peak value of 7.7 +/- 4.2 (SD) to 0.6 +/- 0.3 g.m-2.min-1, which corresponds to the rate of passive transpiration, at core temperatures of 37.42 +/- 0.29 and 37.39 +/- 0.48 degrees C, as measured in the esophagus (Tes) and rectum (Tre), respectively. Oxygen uptake (VO2) decreased rapidly from an exercising level of 2.11 +/- 0.25 to 0.46 +/- 0.09 l/min within 4 min of the recovery period. Thereafter, VO2 remained stable for approximately 20 min, eventually increased with progressive cooling of the core region, and was elevated above the median resting values determined between 15 and 20 min at Tes = 36.84 +/- 0.38 degrees C and Tre = 36.80 +/- 0.39 degrees C. These results indicate that the core temperatures at which sweating ceases and shivering commences are significantly different (P less than 0.001) regardless of whether core temperature is measured within the esophagus or rectum.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Choice of ideal sunshine hour based model to predict global solar radiation in India

MAUSAM ◽  
2021 ◽  
Vol 71 (3) ◽  
pp. 451-466
Author(s):  
SAMANTA SUMAN ◽  
BANERJEE SAON ◽  
PATRA PULAK KUMAR ◽  
MAITI SUDHANSU SEKHAR ◽  
CHATTOPADHYAY NABANSU
Keyword(s):  
Energy Source ◽  
Solar Radiation ◽  
Energy Demand ◽  
Global Solar Radiation ◽  
Exponential Model ◽  
Mean Bias Error ◽  
Percentage Error ◽  
Bias Error ◽  
Energy Conversion Systems ◽  
Sunshine Hour

Solar radiation is the key energy source for most of the energy conversion systems, whether it is biological or mechanical. It is also the most fundamental energy source for future energy demand. Like most of the developing countries, India also lacks sufficient instrument facilities to measure global solar radiation (GSR) at recommended spatial interval and alternative approaches must be used to generate GSR data. In the present study, six well known empirical models were tested to estimate the GSR over twelve major cities of India using long-term global solar radiation and bright sunshine hour data. The empirical coefficients have been calculated for all the models and each location using regression analysis method. Daily GSR are then calculated using those regression constants along with statistical analysis. Results reveal that all the models shows close estimation with low mean bias error (MBE), root mean square error (RMSE) and mean percentage error (MPE) values. Among all models, linear exponential and linear logarithmic models are highly recommended for prediction of GSR throughout the country, except Shillong, where Bakircilinear exponential model is recommended. Significance tests i.e., t-test also confirms that this two model produce most significant results than others.

scholarly journals The Solar Block Generator: an additive parametric method for solar driven urban block design

2021 ◽  
Vol 2042 (1) ◽  
pp. 012049
Author(s):  
Jonathan Natanian ◽  
Francesco De Luca ◽  
Thomas Wortmann ◽  
Guedi Capeluto
Keyword(s):  
Solar Radiation ◽  
Urban Design ◽  
Performance Indicators ◽  
Block Design ◽  
Parametric Method ◽  
Urban Redevelopment ◽  
Holistic Approach ◽  
Tel Aviv ◽  
Trade Offs

Abstract This paper addresses the limitations of existing Solar Envelope (SE) methods to explore the trade-offs of solar radiation and urban shading, and to simultaneously account for several different Key Performance Indicators (KPIs). It offers an alternative parametric workflow - the Solar Block Generator (SBG) - which is based on an additive voxelization method by which multiple solar-driven massing alternatives are generated and evaluated for a given site, corresponding to a set of user-defined environmental KPIs. This method is tested here on an urban redevelopment case study in the Mediterranean (Tel Aviv). The results help achieve a more holistic approach for solar driven urban design.

scholarly journals The Study of Terrestrial Solar Radiation in Awka Using Measured Meteorological Data

2019 ◽  
pp. 1-6
Author(s):  
Chinelo U. Ikeh ◽  
Chukwunwike C. Okeke
Keyword(s):  
Relative Humidity ◽  
Solar Radiation ◽  
Meteorological Parameters ◽  
Meteorological Data ◽  
Ground Surface ◽  
Weather Station ◽  
Wet Season ◽  
Integrated Sensor ◽  
Useful Knowledge ◽  
Energy Conversion Systems

This work investigated the terrestrial solar radiation over Awka, South Eastern Nigeria using meteorological parameters of terrestrial temperature and relative humidity collected during 2013- 2014 respectively, using Davis weather station vantage pros2 (with Integrated Sensor Suite, ISS) positioned close to the ground surface. The data were logged at 30 minutes interval continuously for each day during the period. Hourly, daily and monthly averages of terrestrial radiation during dry and wet seasons were calculated from the data obtained. The result indicated that the terrestrial radiation during dry season is generally higher than during the wet season. The month of March has the highest value of terrestrial solar radiation of 410 Wm-2 , while the least terrestrial radiation of about 381 Wm-2 occurred in August. The result also showed that terrestrial solar radiation correlates positively with water vapour and more positively with temperature at 0.57 and 0.81 coefficients respectively. The results obtained from this work provide useful knowledge that is necessary to enhance the deployment of solar energy conversion systems.

Physics Considerations of Solar Energy Conversion

1984 ◽  
Vol 106 (1) ◽  
pp. 3-15 ◽  
Author(s):  
A. F. Haught
Keyword(s):  
Solar Radiation ◽  
Solar Energy ◽  
Energy Conversion ◽  
Conversion Efficiency ◽  
Radiant Energy ◽  
Solar Energy Conversion ◽  
Quantum Processes ◽  
Maximum Conversion ◽  
Energy Conversion Systems ◽  
Maximum Conversion Efficiency

A comparative analysis is presented of the conversion of radiant energy to useful work by thermal and quantum processes. The operation of thermal and quantum converters and the thermodynamic conversion efficiency of each are developed in terms of the mechanism of radiation-matter interaction in thermal and quantum systems. From the analysis the maximum conversion efficiency of a single-collector thermal converter with unconcentrated solar radiation and an ambient (reservoir) temperature of 300 K is 0.540; for the same conditions the maximum conversion efficiency of a single-collector quantum system is 0.309. The analysis is extended to consider the effects on the conversion efficiency of heat reject temperature, cascaded operation, in which the reject heat of the quantum converter is used as the input to a thermal bottoming cycle, and of concentration of the solar radiation. The results obtained represent the thermodynamic limits for radiant energy conversion by thermal and quantum processes, and calculations with solar input serve as a reference against which to judge the performance and capabilities of prospective solar energy conversion systems.

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