Ideal Thermodynamic Model Research Articles

An approach of studying the full-spectrum conversion potential for solar photovoltaic and thermal processes

Cascading solar energy utilization could provide access to ample supplies of clean energy and has thus attracted widespread attention. However, there are urgent challenges that need to be overcome. For example, where is the solar energy conversion potential, and how to reduce the spectral irreversibility? The mature and reliable study approach on the first law of thermodynamics has its limitations. For this reason, this paper develops a new study approach based on the second law of thermodynamics. Firstly, an ideal thermodynamic model is presented and validated, including solar photovoltaic and thermal (or thermochemical) processes. Furthermore, a description of an isolated system is provided. The incident solar radiation is reflected and concentrated by the mirror. When the concentration ratio is 30, the electricity and solar heat at 300 °C are co-produced. Correspondingly the optimal spectrum distribution could be determined for least entropy generation. As a result, an energy quality conversion potential of about 0.46 and an optimal product ratio of about 1 are disclosed. Finally, an evaluation coefficient is developed to explore the decrease of extropy generation while adopting a methanol-reforming reaction. In detail, the maximum value of the evaluation coefficient is about 0.15, correspondingly, the minimum entropy generation decreases by 13.1 W·m2·K−1 by enhancing solar heat quality. In addition, the optimal input energy ratio of fossil fuel to solar heat is determined at about 4.8, the solar energy quality conversion efficiency has been further enhanced by about 0.1 and surpasses 0.55. The results can be extended to consider non-idealities to explore the tremendous potential of the full spectrum of sunlight.

Use of multiple inter-reboilers to achieve energy savings and improve thermodynamic efficiency of the distillation of N,N-dimethylformamide wastewater

The purification of N,N-dimethylformamide wastewater involves an energy intensive distillation process. We propose a novel energy-saving process scheme involving multiple inter-reboilers sed. In this scheme, ideal thermodynamic model non-random two liquid (NRTL) model was used to calculate the phase equilibrium using Aspen Plus platform. While the relationship between important process parameters and energy consumption by the distillation process was studied, several parameters such as the most suitable positions for the inter-reboilers and the most reasonable steam extraction rates were obtained. The feasibility was detected under the same separation duties and main technological structure. For 10wt% DMF wastewater, the inter-reboilers were installed on the 37th, 38th and 39th plates, while the corresponding heat transferred values were 3,038 kW, 91 kW and 179kW, respectively. In comparison to the conventional distillation process, an energy consumption of 77.43% and thermodynamic efficiency of 65.69% were obtained. For 20 wt% DMF wastewater, the inter-reboilers were installed on the 21st and 25th plate, while the corresponding values for the heat transferred were 1,632kW, and 1,450kW, respectively. In comparison to the conventional distillation process, the energy consumption can be reduced by 71.31%, while the thermodynamic efficiency can be improved by 47.10%.

Утилизация конвертерных газов с целью получения водорода

Ways of reducing the consumption of natural gas for the existing methods of producing hydrogen by subjecting natural gas to steam-water conversion are analyzed. The basic process flow scheme for producing hydrogen according to the above-mentioned method is developed and analyzed under the conditions of an ideal thermodynamic model adopted proceeding from the intensive energy conservation theory. It is shown that the specific consumption of natural gas for producing hydrogen under the conditions of a thermodynamically ideal model is 0.327 m3/m3 H2 that is 29 % lower than that achieved in the best methods for producing hydrogen from natural gas. A way to reduce the consumption of natural gas is proposed which involves the use of high-temperature secondary resources, specifically, converter gases of steelmaking production. Good prospects expected from using converter gases for these purposes are stemming from the fact that these gases are reclaimed to a poor degree, and that there is a need to increase hydrogen production at metallurgical plants. A hydrogen production method involving utilization of the thermal and chemical potential of converter gases is proposed. According to the proposed method converter gases are subjected to energy-chemical accumulation by natural gas which gives rise to a larger amount of carbon monoxide along with generation of hydrogen. After finishing the energy-chemical accumulation stage the obtained gas is mixed with steam and forwarded to the reactor in which carbon monoxide is subjected to steam-water conversion, which contributes to increasing the content of hydrogen in the gas mixture. After that the gas mixture is cooled again, the process condensate is separated and hydrogen is extracted by using the short-cycle adsorption method. The proposed technology allows a continuous hydrogen production process to be organized. When there is no yield of converter gases, hydrogen-containing gas produced by steam-water conversion of natural gas is used. An analysis of the proposed hydrogen production method shows that the consumption of natural gas can be reduced down to 0.148 m3/m3 H2 that is 68 % lower than in the best methods for producing hydrogen from natural gas.

Effect of ethanol on the solubility of ampicillin and phenylglycine in aqueous media

Ampicillin is one of the most consumed antibiotics. Due to environmental issues the production of ampicillin has been forbidden by the conventional chemical route. An alternative is the enzymatic route followed by crystallization of the antibiotic. Therefore, this work aims the determination of a series of ampicillin and phenylglycine solubility data in aqueous media using an analytical method. The measurements were carried out at 283.15 and 298.15 K, varying the pH between 3 and 8, and ethanol composition up to 70 wt%. Dissociation constants (pKa's) have also been measured at the studied temperatures and ethanol compositions. It is demonstrated that ideal thermodynamic model with the predetermined pKa's is able to describe satisfactorily solubility profiles. Solubility measurements of ampicillin and phenylglycine have been determined at different conditions of industrial interest. These data may be applied for the evaluation of the crystallization step of ampicillin in the enzymatic synthesis.

A high efficiency oxyfuel internal combustion engine cycle with water direct injection for waste heat recovery

This paper presents a novel concept of combining water injection process with an oxyfuel internal combustion engine cycle to enhance thermal efficiency. Since the emission of NOx is eliminated by using oxygen instead of air as oxidant, the exhaust gas is CO2–water vapor mixture, and CO2 is recovered through condensation of the exhaust gas at low cost. In this way, an ultra-low emission working cycle is achieved. The evaporation of injected water not only moderates the peak in-cylinder temperature, but also increases the mass of working gas inside the cylinder, therefore improves the thermal efficiency of the cycle. An ideal thermodynamic model combining an oxyfuel Otto cycle with water injection process was established to investigate the potential of the cycle thermal efficiency. Calculation results show that thermal efficiency reaches 53% when water injection temperature is 120 °C and 67% when water injection temperature reaches 200 °C. Moreover, bench tests were carried out on prototype engine based on this working cycle. Experimental results show that the thermal efficiency improves with the increase of both engine load and water injection mass, and indicated thermal efficiency increases from 32.1% to 41.5% under appropriate test condition.

Thermodynamic Modeling of Cl−, NO3− and SO42− Removal by an Anion Exchange Resin and Comparison with Dubinin−Astakhov Isotherms

The removal of chloride, nitrate, and sulfate ions from wastewaters by a macroporous ion-exchange resin is studied through the experimental results obtained for six ion exchange systems, OH(-)/Cl(-), OH(-)/NO3(-), OH(-)/SO4(2-), and HCO3(-)/Cl(-), Cl(-)/NO3(-), Cl(-)/SO4(2-). The results are described through thermodynamic modeling, considering either an ideal or a nonideal behavior of the ionic species in the liquid and solid phases. The nonidealities are determined by the Davies equation and Wilson equations in the liquid and solid phases, respectively. The results show that the resin has a strong affinity for all the target ions, and the order of affinity obtained is OH(-) < HCO3(-) < Cl(-) < NO3(-) < SO4(2-). The calculation of the changes in standard Gibbs free energies (ΔG(0)) shows that even though HCO3(-) has a lower affinity to the resin, it may affect the removal of Cl(-), and in the same way that Cl(-) may affect the removal of NO3(-) and SO4(2-). The application of nonidealities in the thermodynamic model leads to an improved fit of the model to the experimental data with average relative deviations below 1.5% except for the OH(-)/SO4(2-) system. On the other hand, considering ideal or nonideal behaviors has no significant impact on the determination of the selectivity coefficients. The thermodynamic modeling is also compared with the Dubinin-Astakhov adsorption isotherms obtained for the same ion exchange systems. Surprisingly, the latter performs significantly better than the ideal thermodynamic model and nearly as well as the nonideal thermodynamic model.

New development of one-dimensional Si/SiO 2 photonic crystals filter for thermophotovoltaic applications

One-dimensional (1D) Si/SiO 2 photonic crystals (PhCs) are regarded as the most promising candidates for thermophotovoltaic (TPV) optical filters. The performance of TPV devices can be significant improved with the designed 1D ten-layer Si/SiO 2 PhC of excellent stop-band characteristic. However, large oscillations around 1.45–1.75 μm in the pass band of this PhC filter would reduce the above band-gap power transmitted to the cells, leading to discounts of the system efficiency and power density. This work focused on the pass-band characteristics of the 1D Si/SiO 2 PhCs. The mechanism of the large oscillations mentioned above was discussed and a modified 1D five-unit Si/SiO 2 PhC in which the first and fifth units serve as refractive index match units to smooth the large oscillations in the pass band was presented. The simulation indicated that the modified 1D PhC exhibited much flatter and lower pass band around 1.45–1.75 μm than that of the original 1D PhC, even for large incident angle of 45° for both TM and TE polarizations. Both PhCs in the modified and original structures were prepared through a magnetron sputtering process and the measured optical characteristics showed good coherence with the simulation results. An ideal thermodynamic model was then applied to predict the improvement of the TPV system performance by utilizing the modified 1D PhC filter. The results indicated that the modified 1D PhC would lead to 21.0–5.9% increase of the spectral efficiency and 14.8–5.3% increase of the power density at 1200–1800 K radiator temperature.

Thermodynamic analysis of the heat regenerative cycle in porous medium engine

The advantages of homogeneous combustion in internal combustion engines are well known all over the world. Recent years, porous medium (PM) engine has been proposed as a new type engine based on the technique of combustion in porous medium, which can fulfils all requirements to perform homogeneous combustion. In this paper, working processes of a PM engine are briefly introduced and an ideal thermodynamic model of the PM heat regeneration cycle in PM engine is developed. An expression for the relation between net work output and thermal efficiency is derived for the cycle. In order to evaluate of the cycle, the influences of the expansion ratio, initial temperature and limited temperature on the net work and efficiency are discussed, and the availability terms of the cycle are analyzed. Comparing the PM heat regenerative cycle of the PM engine against Otto cycle and Diesel cycle shows that PM heat regenerative cycle can improve net work output greatly with little drop of efficiency. The aim of this paper is to predict the thermodynamic performance of PM heat regeneration cycle and provide a guide to further investigations of the PM engine.

Optical characteristics of one-dimensional Si∕SiO2 photonic crystals for thermophotovoltaic applications

This article presents a detailed exploration of the optical characteristics of various one-dimensional photonic crystal structures designed for use as a means of improving the efficiency and power density of thermophotovoltaic (TPV) devices. The crystals being investigated have a ten-layer quarter-wave periodic structure, and are based on Si∕SiO2 and Si∕SiON material systems. For TPV applications the crystals are designed to act as filters, transmitting photons with wavelengths below 1.78μm to a GaSb photodiode, while reflecting photons of longer wavelengths back to the source of thermal radiation. In the case of the Si∕SiO2 structure, the Si and SiO2 layers were designed to be 170 and 390nm thick, respectively. This structure was fabricated using low-pressure chemical vapor deposition. Reflectance and transmittance measurements of the fabricated Si∕SiO2 photonic crystals were taken from 0.8to3.3μm for both polarizations and for a range of incident angles. Measurement results were found to correlate well with simulation results for the ideal structure. Measurement results were used to predict the TPV system efficiency, power density and spectral efficiency using an ideal thermodynamic model of a TPV system.

Optimal Synthesis of Multicomponent Zeotropic Distillation Processes. 1. Preprocessing Phase and Rigorous Optimization for a Single Unit

Separations performed by distillation involve large operation costs due to either large heat loads or large amounts of solvent used in azeotropic mixtures. Thermodynamic aspects helpfully lead the process synthesis to energetically efficient designs. The reversible distillation sequence model (RDSM) is employed in this work as a theoretical and ideal thermodynamic model. The aim of the paper is to present an automatic methodology for the synthesis of simple distillation columns that approximate reversible conditions. A preprocessing phase is considered where proper values to initialize and bound the variables involved in the rigorous model are calculated by successively solving auxiliary optimization models. In all cases studied, the solutions obtained are very similar to those in the so-called reversible separation. This fact is used as a test criterion for global optimality of the solutions.