查看更多>>摘要：In this work, experimental measurements of the heat conduction transfer function (HCTF) within the limit cycle of thermoacoustic instabilities were conducted associated with a feedback controller. The responses of the heat conduction from the heater to the air in the vicinity to the oncoming flow disturbance can be described as the HCTF. When self-excited thermoacoustic instability occurs, it is not possible to measure the HCTF. The measurement experiment is twofold. Firstly, the active feedback control is applied to suppress the self-excited thermoacoustic oscillation in the Rijke tube. Secondly, the two-microphone method is applied to achieve the measurement of the HCTF at different working conditions. Experimental results show that the mean air flow velocity has an effect on the attenuation time of the thermoacoustic oscillation. Both of the mean air flow velocity and the electric-heating power have a significant effect on HCTFs.
查看更多>>摘要：Based on effective heat dissipation in electronic devices, the current study deals with heat transfer characteristics of oriented square shaped pin fin heat sink having a fin angle of 22.5°. It has been investigated experimentally employing graphene oxide (GO) nanofluid under laminar flow regime. The performance of graphene oxide (GO) nanofluid having concentrations of 0.004%, 0.0065%, and 0.009 vol% is compared with a mixture of EG-water (50:50) as base fluid under three different heating powers of 20 W, 35 W, and 50 W. The experimental results revealed better thermal performance for all used concentrations of (GO) nanofluid compared to the base fluid due to the heat transfer augmentation and reduction in thermal resistance as a result of enhanced thermal conductivity of nanofluid. It was observed that the thermal performance of heat sink improved with increasing Reynolds number and heating power. Minimum wall temperature and maximum enhancement in Nusselt number of 30.75 °C and 19.68% respectively is associated with graphene oxide nanofluid having a concentration of 0.009 vol%. According to the results, nanofluid exhibited better trends of thermal enhancement in comparison of EG/water base fluid with an increase in nanoparticle concentration usually at low Reynolds number. Thus, graphene oxide nanofluid has proven to be the potential candidate for improving the thermal performance of heat sink.
查看更多>>摘要：Despite the desirable perks offered by solar thermoelectric generators (TEGs), their efficiencies are nowhere close to those of solar photovoltaic systems. This has limited their large-scale reliance for power generation and competitive market advantage. It has been established that the use of variable area pins (VAPs), and nanomaterials, in place of traditional bulk semiconductor materials, have improved the performance of TEGs. However, more work is still needed to further improve the efficiency of TEGs. Therefore, we model a full nano-enhanced VAP TEG module with 127 thermoelectric pairs in three-dimensions using ANSYS 2020 R2. The shortcomings of the previous studies on VAP TEGs are also discussed and addressed. Results indicate that the power density and efficiency of the nano VAP TEG are 12x and 6x higher than that of the traditional bulk semiconductor VAP TEG, respectively.
查看更多>>摘要：Moving-bed heat exchangers with a horizontal tube arrangement offer a promising solution to exchange high-temperature heat with a particle stream. However, in order to guide the design of such heat exchangers, accurate and time-efficient simulation tools capable of capturing the complex heat transfer characteristics still need to be improved. In this article we present experimental results of the local heat transfer coefficients around the tube circumference of a heat exchanger mockup. To this end, specially prepared measuring probes were developed and a test campaign was conducted. A comprehensive thermal model was applied to the setup under consideration. This model takes into account the temperature-dependent thermophysical properties of the bulk, variable temperature boundary conditions, and the increased thermal resistance caused by the stagnation and void zones. To validate the model, calculated and experimental results were compared. It turns out that the predicted heat transfer coefficients well match the experimental data, albeit with slight deviations at the stagnation and void zones of the tubes. The prediction of a tube's area-weighted heat transfer coefficient, which constitutes the most important factor for design purposes, yields results with errors of less than 3%. Therefore, it is concluded that the proposed thermal model is able to well predicts the heat transfer in shell-and-tube moving-bed heat exchangers.
查看更多>>摘要：In this investigation, the thermal performance of single-stage absorption refrigeration systems (ARSs) utilizing different MWCNT nanoparticle-enhanced 1-hexyl-3-methylimidazolium (HMIM) cation-based ionic liquids with R1234yf refrigerant were analyzed. The specific heats of the various MWCNT nanoparticle-enhanced [HMIM] cation-based ionic liquids were obtained experimentally at a temperature and a concentration of 303–383 K and 0–1 wt%, respectively, and were subsequently used for modeling the solubility and absorption refrigeration cycle. As a result, the maximum specific heats of all considered ionic liquids were examined at the highest temperature of 383 K. The solubility order of R1234yf refrigerant from highest to lowest was [HMIM][Bf4], [HMIM][Pf6], [HMIM][TfO], and [HMIM][Tf2N] RTILs. In addition, the maximum COPs of the ARSs were achieved at the temperature and concentration of 363 K and 1 wt%, respectively, which were 0.205, 0.242, 0.286, and 0.259 for the [HMIM][Bf4], [HMIM][TfO], [HMIM][Pf6], and [HMIM][Tf2N] MWCNT NEILs, respectively. By applying the proposed system could be simplified at high-temperature applications and prevent undesirable side effects of conventional working pairs such as metal incompatibility, toxicity, and chemical instability.
查看更多>>摘要：The capacitive mixing method generates energy through spontaneous ionic mixing caused by the salinity gradient between sea and river waters. We introduce a continuous thermal regenerative system to combine an intermittent cycle with electrode flow capacitors using flowable slurries as electrodes to improve the efficiency of the existing capacitive mixing method by adding low-grade heat as another energy source. A continuous harvesting system was constructed to utilize the capacitive Donnan potential effect by switching the temperature and salt concentration with four separate reactors and two flow-electrode slurries. Experiments were conducted for continuous cycle operations by varying the active carbon and salt concentrations of the slurry as well as a single electrode flow capacitor test to evaluate the contributions of two different energy sources, i.e., concentration and temperature differences. The continuous cycle operation was further optimized, resulting in a maximum power density of 3.84 mW/m2. Based on the exergy analysis, the theoretical thermal efficiency of the thermally–assisted continuous system was calculated at 10.8%. Waste-heat energy was successfully used for continuous power production using an electrode flow capacitor, and a continuous power generation cycle was implemented by combining the concentration and temperature differences without supplying external power.
查看更多>>摘要：For the current thermal performance of the concentrating solar power (CSP) plants, the thermocline storage approach in a packed bed is recommended to be a favorable thermal energy storage (TES) system because of its cost effectiveness. Based on this, several parametric studies were performed to examine the thermal efficiency of various configurations of packed bed thermocline TES schemes. However, the impact of inlet temperature fluctuations on the storage tank's thermal performance has not been studied. The main objective of this research is to analyze, examine and evaluate the charge and discharge control strategies under different meteorological conditions using different storage configurations. A two-phase dispersion-concentric approach is formulated and verified to analyze the system's periodic thermal characteristics. The results indicate that the hybrid sensible-latent heat storage (HSLHS) case has the highest capacity ratio, utilization ratio, recovered energy, and overall efficiency over the changing inlet temperature, which is equal to 85.2%, 82.5%, 150.7 MWh, 95.2%, respectively, at Tin = 565 °C. In addition, the findings proved that the overall efficiency improved by 19.2% using the HSLHS configuration at low temperature while it improved by 34.4% at a higher temperature.
查看更多>>摘要：In recent years, research on high-performance battery thermal management systems (BTMSs) has increased to improve the safety and reliability of electric vehicle (EV) batteries. However, some underlying concepts have not been clearly explained. For example, which conditions are considered safe, and what about not？ This study focuses on the prediction and prevention of battery over-temperature risk using the finite element method. The critical heat transfer coefficient (hcr) is proposed as a quantitative criterion for risk prediction since it provides sufficient information on the battery operation, such as the dynamic operating parameters and the battery's safety temperature. The intervention time is specified, and intervention methods are suggested to prevent risky conditions. Three parameters were found to have a substantial impact on risk prevention, namely, the equivalent heat transfer coefficient (h), representing the maximum heat transfer capacity of the heat dissipation system, the ambient temperature (Tab), representing the coolant temperature of the heat dissipation system, and the discharge current rate (Crate), representing the current level during discharge. A response surface analysis was performed using the maximum operating temperature of the battery (Tmax) as the response variable and three influencing factors as the input variables. The results show that safety zones can be found for each of the three influencing factors. For example, for the case considered in this work, the optimum Tab is around 281.15 K and should not exceed 305.15 K; the Crate should be below under 5C and should never exceed 8C; h should be greater than 50 W·m?2·K?1. Suggestions are provided for choosing risk prevention methods according to the response characteristics of Tmax. The proposed method provides a novel approach for the research and design of intelligent BTMSs.
查看更多>>摘要：A novel tower solar aided coal-fired power generation (TSACPG) system with thermal energy storage is proposed in this paper. Based on the principle of energy grade matching and cascade utilization, the high-temperature solar energy is used to heat the first and second reheat steam extracted from the boiler and the low-temperature solar energy is used to heat the boiler feed water. The maximum steam extraction mass flow rates of the boiler under different load rates are obtained and the thermal performances are also analyzed. The results show that the maximum steam extraction mass flow rates from the first and second reheat part of boiler are 69.7 kg/s and 37 kg/s in 100 %THA (Turbine Heat Acceptance), 78.7 kg/s and 37 kg/s in 90 %THA, 81 kg/s and 31.4 kg/s in 75 %THA, 76.3 kg/s and 31 kg/s in 60 %THA, 68.2 kg/s and 31.2 kg/s in 50 %THA load, respectively. And the standard coal consumption rates can be reduced by 39.85 g/kWh, 39.47 g/kWh, 38.08 g/kWh, 35.50 g/kWh and 35.25 g/kWh, respectively. Both the boiler thermal efficiency and overall thermal efficiency of the TSACPG system descend sightly and the boiler exergy efficiency ascends. With the decline of the load, the solar-to-electricity efficiency, the power output and the proportion of solar power generation descend gradually. And they can reach up to 28.62%, 120.90 MW and 18.32% in 100 %THA load, respectively. The economic performance analysis of the TSACPG system is carried out. The system configuration and investment corresponding to different typical days, different thermal energy storage hours and capacities are considered. The payback times and the levelized costs of electricity of the solar field in different DNI level regions are analyzed. The results show that these two evaluation indices are the lowest in high level DNI region and they are on the contrary in low level DNI region. As for the environmental protection, the CO2 emission rates are reduced by 69.26 g/kWh in 100 %THA, 68.61 g/kWh in 90 %THA, 66.19 g/kWh in 75 %THA, 61.69 g/kWh in 60 %THA and 61.26 g/kWh in 50 %THA load, respectively. The maximum annual CO2 emission can be reduced about 526739.55 tons. The renewable energy and traditional fossil energy are integrated organically in this study and the low-carbon transformation of coal-fired power generation system is further promoted. The study also contributes to the realization of both the carbon peak and the carbon neutralization.
查看更多>>摘要：A unique, solar-driven hydrogen energy system is developed for data centers in this study by specifically developed Arctic Regions and addressing three of the key sustainable development targets of the United Nations, namely affordable and clean energy, industry-innovation-infrastructure and climate action. A bifacial photovoltaic (PV) plant is integrated with an ammonia trilateral Rankine cycle heat recovery system, a proton-exchange membrane (PEM) electrolyzer, and a PEM fuel cell system with the additional cooling stream. A case study is carried out for a data center with 11.2 MW electrical capacity in the Arctic Region, Norilsk. A time-dependent analysis is performed with hourly meteorologic and simulation data by considering commercially available solar components and actual meteorological measurements. Both energy and exergy approaches are used in order to conduct thermodynamic analysis and assessment. The overall energy and exergy efficiencies are found to be 23.42% and 24.33% for the average ambient conditions, respectively. An average of 2920.7 tons of hydrogen is produced annually, while 2728.7 tons of it are consumed. The data center consumes 92.2 GWh electricity with 172.3 GWh total annual energy demand, which is 100% met by the 175 MWp bifacial PV plant, 11.6 MW fuel cell, 109.1 MW electrolyzer and 375 kWp heat recovery systems. 100% self-sufficiency is reached by exploiting the arctic environment's unique conditions, low temperature, and high albedo with a uniquely designed integrated system by producing 17.6 GWh more electricity just from the bifacial gains and heat recovery. The LCOE for the grid-connected scenario is found between $0.0275/kWh and $0.0395/kWh, and for the stand-alone scenario is found between $0.0945/kWh and $0.1361/kWh.
NSTL
Elsevier