Numerical Investigation on the Impact of Exergy Analysis and Structural Improvement in Power Plant Boiler through Co-Simulation

© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/)In current power station boilers, fuel burns at a low temperature, which results in low exergy efficiency. This research combined the second law of t with the boiler structure to maximize the efficiency of a 350 MW power plant boiler. A three-dimensional simulation of the combustion process at the power plant boiler is performed. A one-dimensional simulation model of the boiler is then constructed to calculate the combustion exergy loss, heat transfer exergy loss, and boiler exergy efficiency. Under the principle of high-temperature air combustion technologies, this paper also proposes a new structure and improved operating parameters to improve the exergy efficiency of boilers by reducing the heat exchange area of the economizer and increasing the heat exchange area of the air preheater. Simulation results show that the exergy efficiency of the boiler increased from 47.29% to 48.35% through the modified model. The simulation outcomes can instruct future optimal boiler design and controls.Peer reviewe

Comprehensive thermal energy storage analysis of ceramic foam-enhanced molten salt in a shell-and-tube unit

Ceramic foam can be used to enhance the energy storage efficiency of molten salt for high-temperature solar thermal applications. However, its performance in a shell-and-tube unit is not fully understood. In this study, the energy storage performance of ceramic foam-enhanced molten salt in a shell-and-tube unit is investigated. The effects of ceramic foam configurations such as the filling height, porosity and outer diameter are studied. The results show that when the ceramic foam reaches the inner tube, the enhancement performance is remarkable, while it is insignificant in the case of below the inner tube. Although the total stored energy of the full foam-filled case is decreased by 13.6% compared to the no foam-filled case, the energy storage rate is improved by 54.9%. The variation of energy storage rate with porosity is generally regular. Ceramic foam with a small outer diameter has great enhancement performance; as the outer diameter increases, the difference in the enhancement gets less remarkable. The three factors are compared through a normalised effective porosity and the ceramic foam with varying outer diameters shows the best performance including the shortest melting time, the largest total stored energy and the highest energy storage rate. It is attributed that the ceramic foam surrounds the tube completely and concentrates around the tube, so its performance of conducting the heat of the tube is the best. The corrosion resistance of ceramic foams and the cost advantage make it a suitable thermal enhancer for molten salt in high-temperature solar thermal energy storage applications

A review of phase change heat transfer in shape-stabilized phase change materials (ss-PCMs) based on porous supports for thermal energy storage

Latent heat thermal energy storage (LHTES) uses phase change materials (PCMs) to store and release heat, and can effectively address the mismatch between energy supply and demand. However, it suffers from low thermal conductivity and the leakage problem. One of the solutions is integrating porous supports and PCMs to fabricate shape-stabilized phase change materials (ss-PCMs). The phase change heat transfer in porous ss-PCMs is of fundamental importance for determining thermal-fluidic behaviours and evaluating LHTES system performance. This paper reviews the recent experimental and numerical investigations on phase change heat transfer in porous ss-PCMs. Materials, methods, apparatuses and significant outcomes are included in the section of experimental studies and it is found that paraffin and metal foam are the most used PCM and porous support respectively in the current researches. Numerical advances are reviewed from the aspect of different simulation methods. Compared to representative elementary volume (REV)-scale simulation, the pore-scale simulation can provide extra flow and heat transfer characteristics in pores, exhibiting great potential for the simulation of mesoporous, microporous and hierarchical porous materials. Moreover, there exists a research gap between phase change heat transfer and material preparation. Finally, this review outlooks the future research topics of phase change heat transfer in porous ss-PCMs

Depression of melting point and latent heat of molten salts as inorganic phase change material: size effect and mechanism

The depression of melting point and latent heat is a common phenomenon for nanoporous shape-stabilised phase change materials (ss-PCMs), however, the underlying mechanism is not well understood, especially from the microscopic perspective. As PCMs are embedded in nanopores, the depression of thermal properties may be due to the size effect, interaction effect or both. In this paper, the size effect on thermal properties was studied using a molecular dynamics simulation and the underlying mechanism was explored. NaCl was selected as PCM and the size of the nanoparticle is from 2 nm to 9 nm. Bulk molten salt was also simulated to validate the correctness of the simulation results. It is found that atoms in smaller nanoparticles vibrate more intensely so the crystal structure of smaller nanoparticle is easier to be destroyed, leading to a lower melting point. The lower coordination number indicates the more loosely packed structure. Thus, less energy is required to destroy the crystalline lattice and the latent heat is decreased. This paper reveals the underlying mechanism of the depression of melting point and latent heat from the atomic point of view and paves the way for further studying the depression of thermal properties of PCMs embedded in nanopores

Research on Air Distribution Control Strategy of Supercritical Boiler

Supercritical boilers have become a major development trend in coal-fired power plants, and the air distribution strategy is a key factor in the design and operation of making it fully combustible. In this paper, the mathematical and physical models of a 350 MW supercritical boiler is established, and the optimal air distribution mode of the boiler at different load is determined based on the furnace outlet temperature, NOx concentration, and O2 content. The air distribution control strategies were derived and the corresponding procedures were established. 160 MW and 280 MW were selected for positive pagoda and 180 MW and 230 MW for waist reduced. At 290–350 MW load, the effect of adjusting the combustion damper opening on the outlet oxygen is weak, so preferentially adjusting the SOFA damper opening can achieve better results. The results show good thermal efficiency and emission performance and are applicable to adjust the air distribution mode to achieve fuller combustion of supercritical boilers

Efeito do procedimento FOCUS-PDCA na melhoria da capacidade de autocuidado de pacientes submetidos a colostomia por câncer retal

Objetivo: Investigar el efecto del procedimiento FOCUS-PDCA sobre la capacidad de autocuidado de pacientes sometidos a colostomia por cáncer de recto. Método: Un ensayo controlado no aleatorizado de 160 pacientes con cáncer de recto sometidos a colostomia. El grupo de control recibió una intervención de enfermería de rutina y el grupo de observación recibió el procedimiento FOCUS-PDCA. La capacidad de autocuidado de los dos grupos se investigó 1 semana y 1 mes después de la cirugía, y se realizó un análisis comparativo entre los grupos. Resultados: En una semana después de la cirugía la capacidad de autocuidado de los pacientes con cáncer de recto con colostomía aumentó de 39,09 puntos antes de la implementación del procedimiento FOCUS-PDCA a 60,15 puntos después de la implementación; un aumento del 21,06%. En un mes después de la cirugía, la capacidad de autocuidado aumentó de 61,50 puntos a 83,13 puntos después de la implementación del procedimiento FOCUS-PDCA; un aumento del 21,63%. Conclusión: La aplicación del procedimiento FOCUS-PDCA mejoró la capacidad de autocuidado de los pacientes con cáncer de recto sometidos a colostomía, mejoró su salud física y mental, redujo las complicaciones de la colostomía y mejoró su calidad de vida. Los resultados sugieren que vale la pena aplicar FOCUS-PDCA de manera más amplia.Objetivo: Investigar o efeito do procedimento FOCUS-PDCA na habilidade de autocuidado de pacientes submetidos a colostomia por câncer retal. Método: Um ensaio clínico não randomizado com 160 pacientes com câncer retal submetidos a colostomia. O grupo controle recebeu intervenção de enfermagem de rotina, e o grupo observação recebeu o procedimento FOCUS-PDCA. A capacidade de autocuidado dos dois grupos foi investigada por 1 semana e 1 mês após a cirurgia, e foi feita uma análise comparativa entre os grupos. Resultados: Em uma semana após a cirurgia a capacidade de autocuidado de pacientes com câncer retal com colostomia aumentou de 39,09 pontos antes da implementação do procedimento FOCUS-PDCA para 60,15 pontos após a implementação; um aumento de 21,06%. Em um mês após a cirurgia, a capacidade de autocuidado aumentou de 61,50 pontos para 83,13 pontos após a implantação do procedimento FOCUS-PDCA; um aumento de 21,63%. Conclusão: A aplicação do procedimento FOCUS-PDCA melhorou a capacidade de autocuidado de pacientes com câncer retal submetidos a colostomia, melhorou sua saúde física e mental, reduziu as complicações da colostomia e melhorou sua qualidade de vida. Os resultados sugerem que vale a pena aplicar o FOCUS-PDCA de forma mais ampla.Objective: To investigate the effect of the FOCUS-PDCA procedure on the self-care ability of patients undergoing colostomy for rectal cancer. Method: A nonrandomized controlled trial of 160 patients with rectal cancer undergoing colostomy. The control group received routine nursing intervention, and the observation group received the FOCUS-PDCA procedure. The self-care ability of the two groups was investigated 1 week and 1 month after surgery, and a comparative analysis was made between the groups. Results: One week after surgery, the self-care ability of rectal cancer patients with colostomy increased from 39.09 points before implementation of the FOCUS-PDCA procedure to 60.15 points after implementation; an increase of 21.06%. One month after surgery, the self-care ability increased from 61.50 points to 83.13 points after implementation of the FOCUS-PDCA procedure; an increase of 21.63%. Conclusion: Application of the FOCUS-PDCA procedure improved the self-care ability of rectal cancer patients undergoing colostomy, improved their physical and mental health, reduced colostomy complications, and improved their quality of life. The results suggest that it is worth applying FOCUS-PDCA more widely

Heat transfer characteristics of ceramic foam/molten salt composite phase change material (CPCM) for medium-temperature thermal energy storage

Molten salts have been widely used as energy storage materials in medium- and high-temperature thermal energy storage. However, pure salt commonly suffers from low thermal conductivity and many conventional methods of heat transfer enhancement do not apply due to the serious corrosion and the extremely high temperature. In the current study, the open-cell SiC ceramic foam was integrated with solar salt (60wt% NaNO3 + 40wt% KNO3) to enhance the heat transfer of salt and avoid severe corrosion issues. A visualised experiment was for the first time conducted to investigate the melting phase change heat transfer in the ceramic foam/molten salt composite phase change material (CPCM). A representative elementary volume (REV)-scale simulation was simultaneously performed and the computational results were compared with experimental data. It is found that the conduction-friendly ceramic skeleton remarkably enhances the heat transfer in molten salt, especially in the region far away from the heat source. The spatial temperature difference across the composite is decreased in both horizontal and vertical directions and the local superheating is mitigated. The enhancement of heat conduction is greater than the suppression of natural convection; as a result, the melting rate of the CPCM is increased by 41.3%. This study provides crucial benchmark data of phase change heat transfer for medium-temperature thermal energy storage and paves the way for system design and optimization

Advanced Study of Spray Cooling: From Theories to Applications

With the continuous integration and miniaturization of electronic devices, the heat transfer of the electronic devices continues to surge. This means that thermal management equipment with higher heat flux cooling capacity is required to maintain its normal operation. This paper systematically reviews the progress of spray cooling. In the first part, the thermal dissipation mechanism of spray cooling in the non-boiling regime and boiling regime are summarized, and the correlation formula of heat transfer is summarized. In the second part, the influencing factors of various parameters of the nozzle are summarized, the experimental research and numerical simulation research are summarized separately, and some means and methods to strengthen heat transfer are listed. In the third part, we summarize the current application research of spray cooling in some hot new fields, including electronic technology, aerospace, biomedicine, battery safety, etc. The research prospects and challenges in these fields are highlighted. This research provides a timely and necessary study of spray cooling