查看更多>>摘要：With the development of science and technology, the operating power of equipment is getting higher and higher, and the demand for heat dissipation is also increasing. Therefore, thermal management has become a hot topic in recent years. Boiling heat transfer has been considered as a effective solution for heat dissipation. The effect of boiling heat transfer can be enhanced by increasing the surface microstructure and nanocoating. This is the so-called surface modification technology. This paper divides the coating modification methods into two types: physical methods and chemical methods, for sorting and evaluation. For example, common physical methods include spin coating, magnetron sputtering, and chemical methods include chemical vapor deposition, electrochemical cathode and anode methods. In addition, in order to better predict the heat transfer effects of different structures at different stages, this review summarizes the common boiling strengthening mechanisms, evaluates the surface modification methods applied to pool boiling. Finally, critical heat flux (CHF) prediction models that can be used for nanostructured coatings are summarized.
Nicola BiancoAndrea FragnitoMarcello IasielloGerardo Maria Mauro...
20页
查看更多>>摘要：In recent years, significantly increasing demand for air conditioning systems has led to higher power consumption during on-peak hours. If optimized, latent heat thermal storage for chiller systems - thanks to its high storage density and compact structure - can reduce installed cooling capacity and allow the chiller to operate more continuously. Starting from the existing design, this work presents a multi-objective optimization framework to improve the storage performance of a phase change material (PCM)-based shell-and-tube heat exchanger. To address this issue - based on experimental data - a 2D axial-symmetric transient numerical model is first developed. To investigate the overall performance of the system - depending on geometrical features and chiller operating conditions - a parametric analysis is performed. Then, by coupling the numerical model developed in COMSOL Multiphysics environment with MATLAB, the system performance is optimized through the genetic algorithm (GA), i.e., minimizing PCM charging/discharging time, by varying the chiller operating conditions. The optimal solution is achieved under a water mass flow rate of 0.095 kg/s, implying a reduction in the inlet temperature of 1.25℃ with respect to the reference case. Results are further validated through experimental tests and discussed looking at the PCM melting and solidification processes for better exploitation of this storage technique. As the main outcome of the model optimization on user's demand, the maximum amount of PCM that can be fully exploited is equal to 40% of the initial one. Therefore, based on this value, a further optimization step by GA is performed to define the minimum heat transfer area, resulting in a shell diameter reduction of 12 cm to exploit 72% of the PCM potential.
查看更多>>摘要：Grid energy storage is key to the development of renewable energies for addressing the global warming challenge. Although coal-fired power plant has been coupled with thermal energy storage to enhance their operational flexibility, studies on retrofitting coal-fired power plants for grid energy storage is lacking. In this work, molten salt thermal energy storage is integrated with supercritical coal-fired power plant by replacing the boiler. Electric resistive heating is applied for the charging process using curtailed electricity or during periods with low grid demand. During discharging, the heat stored in the molten salt is exchanged to steam for electricity generation. A techno-economical analysis is performed on the coupled system and compared with other grid energy storage technologies. Results show that the integrated plant has higher thermal efficiency than the original coal-fired power plant, especially at low load for peak shaving purpose, which is due to the less exergy loss by avoiding the exhausted flue gas and the large temperature difference of heat transfer in boiler of the original plant. At full load, the round-trip efficiency of the integrated plant is ～ 41.8%. Although this efficiency is lower than other energy storage technologies, the levelized cost of electricity of the integrated plant is generally lower due to the reduction in initial investment utilizing existing infrastructures of coal-fired power plants. With longer discharging duration (≥10 h), the integrated system shows a similar levelized cost of electricity as that of compressed air energy storage. Replacing the boiler with thermal energy storage would also greatly reduce the CO_2 emission and various pollutants from coal combustion.
Shaker AlaqelEldwin DjajadiwinataRageh S. SaeedNader S. Saleh...
17页
查看更多>>摘要：The world's first integrated gas turbine-solar particle heating hybrid system has been realized on the campus of King Saud University (KSU), Saudi Arabia. The system was built and tested as a proof-of-concept, such that, upon successful completion of the test, a larger, commercial-scale system can be built with confidence. The successful execution of this project has yielded the following important observations: (1) the particle's central receiver system can heat the falling particles to 720℃; (2) the hybrid system can store solar thermal energy in particles and transfer this energy (via a particle-to-working-fluid heat exchanger) to the compressed air before entering the microturbine.; (3) the microturbine can still operate using the stored thermal energy even after the solar field was shut down; (4) although the temperature rise of the compressed air across the heat exchanger was not high, it was adequate to prove the system's ability to use the particles' stored energy as a heat source.
NSTL
Elsevier