Radiation Exergy Research Articles

Deterministic matrix-based radiative design using a new general formulation of exergy and exergy efficiency for hybrid solar collectors

This paper provides two main contributions: a new general formulation of radiation exergy and exergy efficiency of photovoltaic (PV) panels as grey surface absorbers; the development of an analytic method of radiative design of hybrid solar collectors by using matrix formalism.The new proposed GS (Gray Surface) model of exergy efficiency applicable for gray surfaces is proposed and compared with the classical models (in the first case study) and with its value of 0.939 reveals a difference of up to 1% compared with Petela-Landsberg-Press model (0.932) or Jeter-Carnot model (0.949).The new methodology is able to determine the thermal radiation losses through the lateral walls. The second case study includes an estimation of these losses at 2.63% for the analyzed design. A sensitivity analysis of thickness vs. exergy efficiency is performed, showing that each increase of the thickness of the collector by 10 mm determines a decrease of the extracted power (work) by 1.6% while the radiative exergy efficiency decreases by 0.75%.By including, in future research, the effect of the convection heat transfer, the proposed methodology could stand as a theoretical reference that can be compared with other two paths of research: numerical (CFD) and empirical.

A more realistic performance evaluation of solar convertors: the need for exergic spectral analysis of radiative heat transfer

Solar energy harvesting devices have got considerable attention and significant efforts have been made to optimise their performance recently. Exergy analysis is a useful approach to evaluate the thermodynamic behaviour of the related system. However, the exergy theory of radiation is not well developed, yet. The conventional theory of Petela for radiation exergy, is not well applied for solar energy convertors which are working in a certain spectrum bandwidth such as photovoltaic (PV) panels. More specifically, the inlet exergy of PVs are generally assumed to be the full spectrum exergy, which is not the case for the available panels. In the present study, the exergy fraction functions are presented. As an application, the second law efficiency of various PV panel types are estimated based on the proposed method. It is shown that up to 55% error for exergic efficiency of PV panels might occur by using the conventional relation.

Human body exergy consumption models’ evaluation and their sensitivities towards different environmental conditions

We can use the concept of exergy to analyze a human body as a heat emitter: while generating heat continuously, the body remains at roughly the same temperature through physiological responses such as shivering, sweating, breathing thus raising/decreasing the core and/or skin temperature to maintain effective heat dissipation. Existing literature provides an estimated exergy consumption rate of the human body ranging from 2 to 5W/m2, while nearly unanimously agreeing on a local exergy consumption minima points to potential individual thermal comfort. To clarify the underlying assumptions used in the existing human body exergy models, we analytically and numerically reviewed the terms used for assessing metabolism, radiation, evaporation, and convection exergy changes of the human body in this paper. We observed overestimations of exergy from metabolism, underestimations of exergy change through radiation, and some caveats in the signage of convective exergy losses in the results we obtained. We were also able to propose an improved expression to estimate human body radiation exergy exchanges as well as selecting reference temperatures that are more process-specific. Future studies that provide experimental verification of these models were also deemed necessary.

Second Law Analysis of Spectral Radiative Transfer and Calculation in One-Dimensional Furnace Cases.

This study combines the radiation transfer process with the thermodynamic second law to achieve more accurate results for the energy quality and its variability in the spectral radiation transfer process. First, the core ideas of the monochromatic photon exergy theory based on the equivalent temperature and the infinite-staged Carnot model are reviewed and discussed. Next, this theory is combined with the radiation transfer equation and thus the spectral radiative entropy and the radiative exergy transfer equations are established and verified based on the second law of thermodynamics. Finally, one-dimensional furnace case calculations are performed to determine the applicability to engineering applications. It is found that the distribution and variability of the spectral radiative exergy flux in the radiation transfer process can be obtained using numerical calculations and the scatter media could slightly improve the proportion of short-wavelength radiative exergy during the radiation transfer process. This has application value for research on flame energy spectrum-splitting conversion systems.

Development of empirical models for estimation of global solar radiation exergy in India

In this work, exergy of incoming solar radiation is estimated using empirical models. Long-term meteorological data (1986–2000) consisting of monthly mean diffuse and global solar radiation on a horizontal plane, ambient temperature and sunshine hours for 23 selected stations were available from Indian Meteorological Department (Pune), India. Exergy of direct and diffuse radiations was calculated using Petela model and summed to obtain exergy of global solar radiation. Beam and diffuse exergy efficiencies were in the range of 0.9286–0.9365 and 0.7189–0.7499 respectively. Estimated global exergy efficiencies were found in the range of 0.7700–0.8912. Empirical models were developed by correlating global solar exergy (in the form of global exergy efficiency and global exergy efficiency factor) in terms of clearness index and relative sunshine period. Four categories of single predictor models were defined with each consisting of eight models. Statistical analysis was used to compare and evaluate the accuracy of the models. Further, Global Performance Indicator was calculated and used to rank the models within the individual categories of models as well as the overall group of the 32 developed models. Overall assessment proved that power model with the clearness index is the best one for estimation of global exergy efficiency factor.

Thermodynamic evaluation of irreversibility and optimum performance of a concentrated PV-TEG cogenerated hybrid system

In this paper, the thermodynamics evaluation of an irreversible CPV-TEG cogenerating system, having Siemens SP75 PV module and commercially available Bi2Te3 TE module, has been investigated for wide solar spectrum to encompass the winter and summer solar radiation. Modeling and simulation of the hybrid system has been carried out to understand the feasibility of the system and to determine the irreversibilities present in the hybrid system. The irreversibilities or exergy destruction caused by the irreversible conversion process of solar energy into electricity are calculated using exergy analysis based on second law of thermodynamics. The various exergy losses occurring in the hybrid system have been calculated using exergy analysis. The effects of the incident solar irradiance varying in a wide range from 100 W/m2 to 1000 W/m2, TEG junction temperature ratio, concentration ratio, TEG current, Thomson coefficient, irreversibilities or exergy destruction and the incoming solar radiation exergy have been studied. The results showed that the Thomson effect has adverse effect on the performance of the hybrid system and the irreversibilities increase with increase in concentration ratio, C. Further, the power output of hybrid system increases by 86% as C increases from 1 to optimum value of 3 and the exergy efficiency is higher than the energy efficiency by 8%. The higher values of the irreversibilities make the system less inefficient and therefore, significant improvements are required because the elevated temperature could result in hot spots formation. The results of this analysis may be helpful in designing of practical CPV-TEG hybrid system.

Research Results of Bioenergetics Factors Influence on Crop Production Yields Increase

The results of a fundamental research is presented confirming two hypotheses concerning the process of a crop harvest forming and transpiration as the two main bio-energetic factors of fertility. Transpiration is a thermodynamic process in an open self-organizing system, which has a dissipative random character. Transpiration consumes about 95 percent of the water consumed by the plant. (Purpose of research) The research objective is to obtain results confirming two hypotheses, according to which the efficiency of the process of crop formation is due to transpiration as a bio-energy factor of fertility and its components: photosynthetic exergy and thermal exergy. (Methods and materials) The basic principles of thermodynamic systems self-organization, as well as methods of experimental studies of the principle of subordination to the parameter of the order in which the system control variable is dependent on parameter of the order. The relation of the order parameter (thermal exergy of solar radiation (SR)) and the variable control (transpiration) was determined. The values of the correlation coefficients of these two processes have a value close to one. This confirms that transpiration is a dissipative self-organizing process underlying the transpiration irrigation mechanism. It is revealed that a fractal dimension of a time series of transpiration of cucumber with natural light, a potato is artificial, and their probability haracteristics: the mathematical expectation, standard deviation and variance. (Results and discussion) We received confirmation of the scientific hypothesis about the influence of limiting climatic factors on the theoretical limit of plant productivity and fractal dimension of transpiration as an indicator of production processes in crop production. (Conclusions) We put forward supplemental scientific hypothesis about the influence of limiting climatic factors on the theoretical limit of plant productivity. It was showed that under artificial light intensity of shoots of potatoes fractal dimension is equal to 1.1, and the variance of the temporary random number of transpiration series decreased more than 6 times compared to the same time series under natural light of SR

Radiative energy and exergy analyses of spectrally-selective surfaces for CSP systems

This work presents a new methodology for calculations of spectral radiative energy and radiative exergy to evaluate the performances of concentrated solar power (CSP) systems. Spectral radiative properties and the operating temperature of selective surfaces, along with the temperature of the environment, are taken into account in analyses. The fundamental expressions needed for the spectral radiative energy and exergy analyses are introduced first. Then, the two approaches are used to assess the spectral performance of five selective coatings. The spectral analysis is performed in the wavelength range of 250 nm to 20,000 nm, while thermal analysis is carried out for the temperature range of 325 K to 800 K. NREL 6A coating was found to result in the highest radiative energy and radiative exergy for both efficiencies and gains, and for the best thermal stability compared to the other coatings.

Radiative energy and exergy analyses of spectrally-selective surfaces for CSP systems

This work presents a new methodology for calculations of spectral radiative energy and radiative exergy to evaluate the performances of concentrated solar power (CSP) systems. Spectral radiative properties and the operating temperature of selective surfaces, along with the temperature of the environment, are taken into account in analyses. The fundamental expressions needed for the spectral radiative energy and exergy analyses are introduced first. Then, the two approaches are used to assess the spectral performance of five selective coatings. The spectral analysis is performed in the wavelength range of 250 nm to 20,000 nm, while thermal analysis is carried out for the temperature range of 325 K to 800 K. NREL 6A coating was found to result in the highest radiative energy and radiative exergy for both efficiencies and gains, and for the best thermal stability compared to the other coatings.

Solar radiation exergy and quality performance for Iraq and Turkey

The present study is conducted with two primary objectives: First, a new formulation for the maximum efficiency of the solar radiation conversion is developed by considering the radiative energy transfer between two surfaces at different temperatures for a constant volume system. Second, a new methodology is introduced for estimating the exergy value of the monthly average daily horizontal global radiation, including many parameters, such as monthly average daily value of the horizontal extraterrestrial radiation, the number of sunny hours, the day length, the mean temperature and the mean wind velocity. Seven statistical parameters are used to validate the accuracy of all models. The results of the two new models are found to be more reliable than the results obtained from other models. This study, which was conducted for four locations in Iraq and Turkey. The findings would help in predicting the maximum availability of solar radiation based on weather parameters.

Solar radiation exergy and quality performance for Iraq and Turkey

Solar radiation exergy and quality performance for Iraq and Turkey

Computing the Exergy of Solar Radiation From Real Radiation Data

The decrease of fossil fuels availability and the consequent increase of their price have led to a rapid evolution of renewable market and policy frameworks in recent years. Renewable resources include solar radiation, which is of considerable interest as it is inexhaustible, free, and clean. In order to calculate how much work can be obtained from solar radiation, several methods have been proposed in the literature and are here reviewed. In this paper, a single exergy factor to be applied to the total radiation measured on horizontal surface in a given place is proposed. The factor is estimated from both direct and diffuse radiation.

Exergy of Blackbody Radiation and Monochromatic Photon

The study of radiation exergy has important significance for solar energy and high-temperature engineering. In this paper, several exergy expressions of blackbody radiation were discussed and the differences between Petela’s expression of exergy and two other expressions were analyzed. Considering that radiant energy and thermal energy are different, the radiation machine model was established; furthermore, the validity of Petela’s formula was indicated by this model. Based on the concept of radiation equivalent temperature, the integral form expression of monochromatic photon exergy was put forward by establishing the infinite-staged Carnot heat engine model. At the same time, an approximate relation between equivalent temperature and radiation wavelength was given. The error of this relation is negligible when calculating the exergy of blackbody radiation within the temperature range of the engineering field. Finally, the monochromatic photon entropy was discussed by considering the infinite-staged Carnot heat engine model, and an expression of photon entropy with integral form was given. The monochromatic photon entropy and exergy proposed in our paper satisfy the thermodynamic relation and can reflect the differences between radiant energy and thermal energy.

Composite indicator for monitoring of Norway spruce stand decline

ABSTRACTThe study is aimed to explore the potential of time-series airborne hyperspectral and satellite multispectral data to track the changes in spruce forest decline expressed by a composite spruce decline indicator. Vegetation indices and exergy of solar radiation extracted from remote sensing data are used to predict the development of the composite spruce health indicator. The canopy-level spectral reflectance properties of spruce stands are investigated to identify categories of spruce stand decline: healthy, initial decline, and initial to moderate decline. The sensitivity peaks for initial decline and initial to moderate decline of spruce are shown. The highest potential for the estimation of the composite spruce health indicator is demonstrated by vegetation indices WBI and NDVIred_edge from airborne hyperspectral data, and by PSRI, NDII and exergy of solar radiation from Landsat and Sentinel-2 satellite multispectral data. MODIS data show only a poor correlation between the composite spruce stand health indicator and NDII index. The proposed methodology to obtain the distribution of the composite spruce decline indicator using remote sensing (RS) data promisingly suggests its applicability over a large forest area with potential time and economic benefits, since foliar spectral measurements, canopy chemistry, and laboratory analysis are not required.

Solar radiation exergy and enviroeconomic analysis for Turkey

The knowledge of useful solar energy amount is important for designing solar energy systems. In this study, solar radiation exergy (SRE) values are calculated for the 81 cities in Turkey. The data are obtained from the General Directorate of Renewable Energy and the General Directorate of Meteorology. The approaches of Petela, Spanner and Jeter are used to calculate the exergy-to-energy ratios for determining the maximum utilisable solar radiation energy. The exergy-to-energy ratios, the SRE values, the locations having the highest solar exergy potential and the monthly, seasonal and annual total SRE maps are presented for Turkey. Finally, enviroeconomic analysis is performed and its results are presented. The available results are visualised via maps with colourbars.

Model of Plant Productivity and a Computer System for Optimization of Agro-Technology Using the Method of Exergic Analysis

A model of a potentially effective type energy-resource-saving of optimization of agro-technologies, based on the principle subordination of synergetics, was established. There was developed computer system energy-resource-saving optimization of agricultural technologies. The main feature of crop production is provided by the plants which themselves are self-organizing organisms. This allows us to adopt the principle of subordination of synergetics as the basis of the model. The value of free energy at the input into plants, estimated by the process of photosynthesis, is equal to the value of “radiation exergy for plant growth”. Assessment of the use of radiation energy is carried out based on the energy-converting characteristics of plants, which were obtained in climate chambers under controlled conditions. We used the model based on the principle of subordination of synergetics to develop common quantitative mutually agreed definitions of the main agroecological variables: Agroclimatic and Meliorative potentials of lands, their fertility, and potential (maximum) productivity of plants under different environment conditions.

Solar radiation exergy and enviroeconomic analysis for Turkey

Solar radiation exergy and enviroeconomic analysis for Turkey

Exergy analysis of a solar-powered vacuum membrane distillation unit using two models

A detailed exergy analysis of a solar powered VMD unit was performed using two models: the ideal mixture model and the model using the thermodynamics properties of seawater. The exergy flow rates of process steam, given by the two models differed of about 18%, on average. Despite these differences, the two models agree that during the step of condensation, the most important fraction of exergy was destroyed. Moreover, in this work, two forms of exergy efficiency are calculated. The overall exergy efficiency of the unit with reference to the exergy collected by the solar collector was 3.25% and 2.30% according to Cerci and Sharqawy models, respectively. But, it was 0.182% and 0.128%, when referenced to the exergy of solar radiation, according to Cerci and Sharqawy models, respectively. Besides, the utilitarian exergy efficiency was 9.96%. Since the heat exchanger, the hollow-fiber module and the condenser have a very high exergy performance, then it can be concluded that the enhancement or reduction of exergy losses will be mainly by recovering heat lost in brine discharges and in the rejection of the cooling water. In addition, the influence of the rejection rate on exergy efficiencies was studied.

Assessing the Exergy Costs of a 332-MW Pulverized Coal-Fired Boiler

In this paper, we analyze the exergy costs of a real large industrial boiler with the aim of improving efficiency. Specifically, the 350-MW front-fired, natural circulation, single reheat and balanced draft coal-fired boiler forms part of a 1050-MW conventional power plant located in Spain. We start with a diagram of the power plant, followed by a formulation of the exergy cost allocation problem to determine the exergy cost of the product of the boiler as a whole and the expenses of the individual components and energy streams. We also define a productive structure of the system. Furthermore, a proposal for including the exergy of radiation is provided in this study. Our results show that the unit exergy cost of the product of the boiler goes from 2.352 to 2.5, and that the maximum values are located in the ancillary electrical devices, such as induced-draft fans and coil heaters. Finally, radiation does not have an effect on the electricity cost, but affects at least 30% of the unit exergy cost of the boiler’s product.

Empirical modeling of solar radiation exergy for Turkey

In this study, three different empirical models are developed to predict the monthly average daily global solar radiation exergy on a horizontal surface for some provinces in different regions of Turkey by using meteorological data from Turkish State Meteorological Services. To indicate the performance of the models, the following statistical test methods are used: the coefficient of determination (R2), mean bias error (MBE), mean absolute bias error (MABE), mean percent error (MPE), mean absolute percent error (MAPE), root mean square error (RMSE) and the t-statistic method (tsta). By the improved empirical models in this paper do not need exergy-to-energy ratio (ψ) and monthly average daily global solar radiation to calculate solar radiation exergy. Consequently, the average exergy-to-energy ratio (ψ) for all provinces are found to be 0.93 for Turkey. The highest and lowest monthly average daily values of solar radiation exergy are obtained at 23.4MJ/m2day in June and 4MJ/m2day in December, respectively. The empirical models providing the best results here can be reliably used to predict solar radiation exergy in Turkey and in other locations with similar climatic conditions in the world. The predictions of solar radiation exergy from regression models could enable the scientists to design the solar-energy systems precisely.