共查询到20条相似文献,搜索用时 10 毫秒
1.
《Applied Thermal Engineering》2001,21(11):1119-1135
This paper deals with an experimental and theoretical investigation of air humidification/dehumidification processes carried out in a hollow-fibre membrane contactor.The cross-flow contactor consists of a 1.2 m2 total membrane surface of hollow polypropylene capillaries arranged in a staggered array and has a mass transfer area per unit volume of 593 m2/m3.The heat and vapour mass transfer between the liquid phase (water and LiCl saturated solution) and the process air is analysed.During the humidification process, experiments were carried out using three different mass flow rates of water (19, 35, 54 kg/h), while two different mass flow rates of LiCl saturated solution (25, 41 kg/h) were used for air dehumidification. Air flow rates ranging from 30 to 80 m3/h were considered. Variations in the relative humidity of the air and in the temperatures of the air and liquid were measured. Experiments show a high mass transfer efficiency for both humidification and dehumidification.Furthermore, a numerical model to predict heat and mass transfer through the contactor has been developed. Experimental results are in good agreement with theoretical predictions. 相似文献
2.
Geyuan YIN Chaojun WANG Meng ZHOU Yajie ZHOU Erjiang HU Zuohua HUANG 《Frontiers in Energy》2022,16(2):263
The laminar flame speeds of ammonia mixed with syngas at a high pressure, temperature, and different syngas ratios were measured. The data obtained were fitted at different pressures, temperatures, syngas ratios, and equivalence ratios. Four kinetic models (the Glarborg model, Shrestha model, Mei model, and Han model) were compared and validated with experimental data. Pathway, sensitivity and radical pool analysis are conducted to find out the deep kinetic insight on ammonia oxidation and NO formation. The pathway analysis shows that H abstraction reactions and NHi combination reactions play important roles in ammonia oxidation. NO formation is closely related to H, OH, the O radical produced, and formation reactions. NO is mainly formed from reaction, HNO+ H= NO+ H2. Furthermore, both ammonia oxidation and NO formation are sensitive to small radical reactions and ammonia related reactions. 相似文献
3.
This paper has focused on the droplets behavior of kerosene RP-3 spray produced by a pressure swirl atomizers in terms of spray pattern, droplet size spatial distribution, mean droplet size, and distribution index with variations of pressure differential. The analyses have been carried out experimentally with the aid of optical diagnostic methods. The spray pattern, such as spray cone angle and fuel spatial distribution, has been measured by the technique of planar laser induced fluorescence of kerosene. A method for correction of fuel distribution measurement error induced by laser attenuation in spray is proposed and validated. The droplet size spatial distribution in central axis plane of the spray has been measured by a planar droplet sizing method which combining laser induced fluorescence and Mie scattering. The spray pattern in axial center plane and cross-sectional plane perpendicular to axis of the atomizer indicate that the droplets in spray concentrate around the outer periphery and in a narrow annular zone at the near-field of fuel injector exit, and then disperse to produce a solid spray at downstream of the spray. The analyses of droplet size spatial distribution, Sauter mean diameter, and distribution index with pressure differential clearly show the presence of droplets collision and its adverse effects on droplet size uniformity. The spray outline, droplet mass spatial distribution, and droplet size spatial distribution, droplets dispersion and collision in the process of atomization provide a great insight into the processes of atomization and spray development, which are key information for fuel injector design and quality control. The visualizations of spray pattern and droplet size spatial distribution with variations of pressure differential for pressure swirl atomizer are key issues in swirl cup or internally staged airblast fuel injectors because pressure swirl atomizer provides primary atomization or pilot spray which affects the quality of air/fuel mixing in lean-burn combustion. Moreover, a well-defined and complete database regarding the isothermal hollow cone spray is provided for validation of spray model. 相似文献
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5.
Gas absorption by droplets is an important route to reduce greenhouse gas emissions, especially for carbon dioxide. To recognize the fundamental absorption processes of greenhouse gases by single droplets, the mass transport phenomena of greenhouse gas uptake by a quiescent water droplet at atmospheric and elevated pressures are analyzed theoretically and four common greenhouse gases of CO2, N2O, CH4 and O3 are taken into consideration. On account of piecewise function encountered at the droplet surface, it is impossible to obtain a fully analytical solution for describing the mass transfer process. Instead, a semi-analytical method is developed to predict the mass diffusion between the gas phase and the liquid phase. The obtained results indicate that, by virtue of the four greenhouse gases characterized by low mass diffusion number, the entire mass transfer is controlled by the liquid phase. A unified formula has been successfully established to aid in estimating the dimensionless solute uptake process and the dimensionless aqueous diffusion time of 0.45 is sufficiently long the implement the absorption process. For the ambient temperature and pressure in the ranges of 280–350 K and 1–20 atm, respectively, it is found that increasing the two parameters will intensify the solute absorption amount significantly and the absorption process can be accelerated by increasing temperature. 相似文献
6.
Sungwoo Park 《International Journal of Hydrogen Energy》2021,46(50):25712-25725
The present study investigates freely propagating methane/hydrogen lean-premixed laminar flames at elevated pressures to understand the hydrogen addition effect of natural gas on the NO formation under the conditions of industrial gas turbine combustors. The detailed chemical kinetic model which was used in the previous study on the NO formation in high pressure methane/air premixed flames was adopted for the present study to analyze NO formation of methane/hydrogen premixed flames. The present mechanism shows good agreement with experimental data for methane/hydrogen mixtures, including ignition delay times, laminar burning velocities, and NO concentration in premixed flames. Hydrogen addition to methane/air mixtures with maintaining methane content leads to the increase of NO concentration in laminar premixed flames due to the higher flame temperature. Methane/hydrogen/argon/air premixed flames are simulated to avoid the flame temperature effect on NO formation over a pressure range of 1–20atm and equivalence ratio of 0.55. Kinetic analyses shows that the N2O mechanism is important on NO formation for lean flames between the reaction zone and postflame region, and thermal NO is dominant in the postflame zone. The hydrogen addition leads to the increase of NO formation from prompt NO and NNH mechanisms, while NO formation from thermal and N2O mechanisms are decreased. Additionally, the NO formation in the postflame zone has positive pressure dependencies for thermal NO with an exponent of 0.5. Sensitivity analysis results identify that the initiation reaction step for the thermal NO and the N2O mechanism related reactions are sensitive to NO formation near the reaction zone. 相似文献
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In this study, a test system for spray cooling, in which the heating surface temperatures were simultaneously measured by thermocouples and an infrared imager, was set up. A mathematical model of spray cooling heat transfer characteristics was presented based on the fundamentals of dynamics and heat transfer. The temperature distribution on the heating surface was investigated by the experimental and theoretical methods, the surface temperature non-uniformity and its influencing factors were analyzed. The predictions by the model coincided with the experimental results well, and a comparison was demonstrated with a deviation below 10%. It can be concluded that the surface temperature non-uniformity is influenced by the spray characteristics, nozzle-to-surface distance, inlet pressure, heat flux, spray angle and the system pressure. In the case of the same heat flux, the surface temperature non-uniformity can be reduced by the small spray angle, low system pressure, low nozzle-to-surface distance, and the high inlet pressure. 相似文献
9.
A recycle operation design using a flat-plate solar water heater with rectangle flow conduits was theoretically and experimentally investigated. Devices with differing flow-conduit geometries (i.e. aspect ratio) and external recycle were designed to create a solar heater with low heat-transfer resistance between the absorber and working fluid to increase the convective heat-transfer coefficient. Considerable solar water heater collector efficiency improvement has been obtained employing rectangle flow conduits and a recycle operation, instead of recycle solar collector constructed with circular pipes operated at the same total mass flow rate. Under a fixed absorber area and distance between the flow conduits, the collector efficiency increases with increasing flow conduit aspect ratio, total mass flow rate and recycle ratio but with decreasing inlet water temperature. The incident solar radiation, mass flow rate, recycle ratio and flow conduit aspect ratio influences on the collector efficiency and energy consumption are also discussed. 相似文献
10.
《International Journal of Hydrogen Energy》2023,48(53):20225-20237
Experimental and numerical study on ammonia-air combustion and explosion characteristics at elevated temperature and pressure was conducted. The results revealed that the ammonia-air flame of different equivalence ratios is quite smooth at elevated temperature and pressure. The laminar burning velocity (LBV) reaches the peak of 0.073 m/s at Ф = 1.1 and increases as increasing initial premix temperature and decreasing initial premix pressure. Maximum explosion overpressure (MEO) and maximum pressure rise rate (MPRR) reach the peak of 0.43 MPa and 0.13 MPa/ms respectively at Ф = 1.1. The theoretical MEO is significantly higher than the experimental results due to heat loss, and the minimum heat loss occurs at Ф = 1.1. MEO, MPRR and heat loss increase with increasing initial premix pressure, and MEO and heat loss decrease with increasing initial premix temperature, while MPRR increases. Okafor mechanism has the best LBV prediction performance among seven mechanisms. And the main elementary reactions affecting LBV are H + O2=O + OH and HNO + HH2+NO. 相似文献
11.
Liquid desiccant dehumidification was proved to be an effective method to extract the moisture from air with a relatively less energy. An experimental study was carried out to evaluate the liquid desiccant system performance during dehumidification and humidification processes using an injected air through the liquid desiccant solution (calcium chloride). A different air mass flow rates though the desiccant solution was considered during the experimental work. The desiccant system was studied at different operating conditions like different temperatures, different humidity ratios and different solution levels. The effectiveness for both the dehumidification and humidification processes was calculated through this work. It was found that, the system effectiveness reached to 0.87 in the dehumidification and about 0.92 in the humidification process. Also; the experimental results showed a mass transfer coefficient of 28 kg s−1 m2 mm Hg at an air mass flow rate of 0.022 kg s−1 in the dehumidification process. The cooling effect factor was also studied and analyzed during that work. 相似文献
12.
《能源学会志》2019,92(6):1821-1830
Freely-propagating laminar premixed n-heptane/air flames were modeled using the Lawrence Livermore National Laboratory (LLNL) v3.1 n-heptane mechanism and the PREMIX code. Numerical calculations were conducted for unburned mixture temperature range of 298–423 K, at elevated pressures 1–10 atm and equivalent ratio 0.6–1.6, and the changes of laminar burning velocity (LBV), adiabatic flame temperature (AFT), heat release rate (HRR), and concentration profiles of important intermediate species were obtained. The results show that the overall results of LBVs of n-heptane at different elevated temperatures, pressures, and equivalence ratios are in good agreement with available experimental results. However, at the initial temperature 353 K, the calculated values of LBVs at pressure 1 atm and the 10 atm deviate significantly from the experimental results. The sensitivity analysis shows that, similar to many other hydrocarbon fuels, the most sensitive reaction in the oxidation of n-heptane responsible for the rise of flame temperature promoting heat release is R1 H + O2<=>O + OH, and the reaction that has the greatest influence on heat release is R8 H2O + M<=>H + OH + M. In addition, when the initial temperature is 353, 398 and 423 K, the mole fractions of H, OH, and O increase rapidly around the flame front, while the mole fractions of C1C3 dramatically decreases, reflecting the intense consumption of the intermediate products at the reaction zone. 相似文献
13.
《International Journal of Hydrogen Energy》2019,44(30):15962-15972
Electric assisted combustion for hydrogen enriched hydrocarbons may even extend the lean burn limit and provide the further improvement on combustion stability. This study investigates the effect of hydrogen enrichment and DC electric field on lean CH4/air flame propagation. Electric field inside the chamber was generated by mesh and needle electrodes. Effect of hydrogen enrichment on the ion mole fraction in the flame was discussed based on reaction mechanism included neutral and ion reactions. The flame propagation images, flame displacement speed were used to evaluate the combined influences of hydrogen enrichment and electric field on propagating flame. Results showed that the hydrogen addition would increase positive ions mole fraction and the peak value is mainly determined by H3O+. This would be due to that CH increases with hydrogen fraction, which is the main species in the initial reaction for the ion reactions. Electric field effect about flame propagation was suppressed with hydrogen addition due to the competition between the increment in ion mole fraction and the decrement in flame time. Electric assisted combustion is more evident at leaner conditions and elevated pressure. The ratio of ionic wind velocity to flow velocity may be the determined factor to predict the electric field effect about propagating flame. The tendency based on this ratio is in accordance with the experimental results for various hydrogen fraction and equivalence ratio at elevated pressure. 相似文献
14.
Experimental and numerical study on the lean methane–hydrogen–air flames at elevated pressures and temperatures was conducted. The unstretched laminar burning velocities and Markstein lengths were obtained over a wide range of hydrogen fractions at elevated pressures and temperatures. The sensitivity analysis and flame structure were also analyzed. The results show good agreement between the computed results and experimental data. The unstretched laminar burning velocities are increased with the increase of initial temperature and hydrogen fraction, and they are decreased with the increase of initial pressure. With the increase of initial pressure and hydrogen fraction, Markstein lengths are decreased, indicating the increase of flame instability. Laminar burning velocity is depended on the competition between the main chain branching reaction and chain recombination reaction. The chain branching reaction is a temperature-sensitive reaction, while the recombination reaction is a temperature-insensitive reaction. Numerical study shows that the suppression (or enhancement) of overall chemical reaction with the increase of initial pressure (or temperature) is closely linking to the decrease (or increase) of H, O and OH mole fractions in the flames. Strong correlation is existed between burning velocity and maximum radical concentrations of H and OH radicals in the reaction zone of premixed flames. 相似文献
15.
Juan-Jorge Hermosillo Camilo A. Arancibia-Bulnes Claudio A. Estrada 《Solar Energy》2012,86(4):1070-1076
A desalination system based on the humidification and dehumidification of air is studied. The evaporator unit is based on a treated cellulose paper substratum through which water flows, and which has a large area to favor evaporation. The condenser unit is a liquid–gas heat exchanger, where water vapor is condensed and the enthalpy of condensation is recovered to preheat the water. The mathematical model and experimental results are presented and it is shown that they present a good agreement. Some operating conditions for better heat recovery are presented. 相似文献
16.
《International Journal of Hydrogen Energy》2022,47(85):36046-36057
Ammonia (NH3) is a carbon-free fuel that shows great research prospects due to its ideal production and storage systems. The experimental data of the laminar burning velocity of NH3/H2/air flame at different hydrogen ratios (XH2 = 0.1–0.5), equivalent ratios (φ = 0.8–1.3), initial pressures (P = 0.1–0.7 MPa), and initial temperatures (T = 298–493 K) were measured. The laminar burning velocity of the NH3/H2/air flame increased upon increasing the hydrogen ratios and temperature, but it decreased upon increasing the pressure. The equivalent ratio of the maximum laminar burning velocity was only affected by the proportion of reactants. The equivalence ratio value of the maximum laminar burning velocity was between 1.1 and 1.2 when XH2 = 0.3. The chemical reaction kinetics of NH3/H2/air flame under four different initial conditions was analyzed. The less NO maximum mole fraction was produced during rich combustion (φ > 1). The results provide a new reference for ammonia as an alternative fuel for internal combustion engines. 相似文献
17.
《International Journal of Hydrogen Energy》2019,44(39):21324-21335
The current work examines the excitation of thermoacoustic instability of lean premixed hydrogen-methane/air low swirl flames under both atmospheric and elevated pressure conditions (up to 0.3 MPa). Under a given pressure condition, The tests were conducted at different bulk velocities (U), hydrogen proportions (ηH), and equivalence ratios (Ф). Results show that thermoacoustic instability can be excited by increasing one of these variables while keeping others the same. It was found that pressure elevation has a minor effect on the oscillation frequency. Moreover, it was demonstrated that the current instability is induced by large coherent structures. The effect of pressure elevation on the excitation of thermoacoustic instability is found to be Φ dependent. As indicators of the flame response to impinging vortices, the curvature and local flame surface area features were calculated with images captured with the planar laser-induced fluorescence of the OH radical (OH-PLIF) method. Results demonstrate a great similarity between the flame front evolution and the instability trend, implying that the effect of the chamber pressure on the instability trend can be indicated by the change in the flame front curvature and local flame surface area. 相似文献
18.
The heat and mass transfer equations for a co-flow water spray in air were solved for different combinations of drop diameter category and velocity sub-class, and compared with experimental data. For uniform drop velocities, the number of categories was increased to 10, 50, 100 and 200, as against 5 in an earlier study. Best predictions were obtained with 100 categories. For 5 categories, 10, 20 and 40 velocity sub-classes within each category were introduced, and predictions were slightly better than with a single velocity. Results with 100 categories–1 velocity and 10 categories–10 velocity sub-classes were similar; the latter matched experiments mostly within ± 15% as against ± 30% in an earlier study. 相似文献
19.
Yuzhou Chen Chunsheng Yang Shuming Zhang Minfu Zhao Kaiwen Du Xu Cheng 《Frontiers of Energy and Power Engineering in China》2009,3(2):175-180
Experimental studies of the critical flow of water were conducted under steady-state conditions with a nozzle 1.41 mm in diameter
and 4.35 mm in length, covering the inlet pressure range of 22.1–26.8 MPa and inlet temperature range of 38–474°C. The parametric
trend of the flow rate was investigated, and the experimental data were compared with the predictions of the homogeneous equilibrium
model, the Bernoulli correlation, and the models used in the reactor safety analysis code RELAP5/MOD3.3. It is concluded that
in the near or beyond pseudo-critical region, thermal-dynamic equilibrium is dominant, and at a lower temperature, choking
does not occur. The onset of the choking condition is not predicted reasonably by the RELAP5 code. 相似文献
20.
Experimental and theoretical radiation damage studies on crystalline silicon solar cells 总被引:1,自引:0,他引:1
M. Alurralde M. J. L. Tamasi C. J. Bruno M. G. Martínez Bogado J. Pl J. Fernndez Vzquez J. Durn J. Schuff A. A. Burlon P. Stoliar A. J. Kreiner 《Solar Energy Materials & Solar Cells》2004,82(4):8
An experimental facility was developed to asses in situ the degradation of crystalline silicon solar cells, fabricated by the Solar Energy Group of the National Atomic Energy Commission (CNEA), by measuring the current–voltage characteristic curve. The cells were irradiated with 10 MeV protons and fluences between 108 and 1013 p/cm2, using an external beam of the linear tandem accelerator TANDAR, at CAC-CNEA. Furthermore, theoretical simulations were performed to establish the relation between the variation of the electrical parameters and the degradation of the lifetime of minority carriers in the base. The damage constant for 10 MeV proton irradiated silicon solar cells of n+–p–p+ structure and 1 Ω cm base resistivity was determined. Finally, a proposal of a new model of radiation damage for silicon solar cells is discussed. 相似文献