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141.
This paper is concerned with the following systems of Kirchhoff‐type equations: Under more relaxed assumptions on V(x) and F(x,u,v), we first prove the existence of at least two nontrivial solutions for the aforementioned system by using Morse theory in combination with local linking arguments. Then by using the Clark theorem, the existence results of at least 2k distinct pairs of solutions are obtained. Some recent results from the literature are extended. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
142.
The heat transfer process occurring in a condensing heat exchanger where noncondensible gases are dominant in volume is different from the condensation heat transfer of the water vapor containing small amount of noncondensible gases. In the process the mass transfer due to the vapor condensation contributes an important part to the total heat transfer. In this paper, the Colburn-Hougen method is introduced to analyze the heat and mass transfer process when the water vapor entrained in a gas stream condenses into water on the tube wall. The major influential factors of the convective-condensation heat transfer coefficient are found as follows: the partial pressure of the vapor p
v
, the temperature of the outer tube wall T
w
, the mixture temperature T
g
, Re and Pr. A new dimensionless number Ch, which is defined as condensation factor, has been proposed by dimensional analysis. In order to determine the relevant constants and investigate the convection-condensation heat and mass transfer characteristics of the condensing heat exchanger of a gas fired condensing boiler, a single row plain tube heat exchanger is designed, and experiments have been conducted with vapor-air mixture used to simulate flue gases. The experimental results show that the convection-condensation heat transfer coefficient is 1.52 times higher than that of the forced convection without condensation. Based on the experimental data, the normalized formula for convention-condensation heat transfer coefficient is obtained.
A
heat transfer area m2
-
Ch
condensation factor
-
c
p
specific heat at constant pressure, J/(kg·K)
-
G
mass flux Kg/(m2·s)
-
h
heat transfer coefficient W/(m2·K)
-
J
J-factor
-
Nu
Nusselt number
-
pa
pressure
- Pr
Prandtl number
-
Q
heat transfer rate
-
q
heat flux W/m2
-
r
latent heat, kJ/kg
- Re
Reynolds number
-
Sc
Schmidt number
-
T
temperature, C or K
-
heat conductivity m W/(m·K)
-
density, kg·m3
-
g
gas
-
h
moistened hot air
-
i
interface
-
v
vapor
-
w
water 相似文献
143.
The near-wall transport characteristics, inclusive of mass transfer coefficient and wall shear stress, which have a great
effect on gas–liquid two-phase flow induced internal corrosion of low alloy pipelines in vertical upward oil and gas mixing
transport, have been both mechanistically and experimentally investigated in this paper. Based on the analyses on the hydrodynamic
characteristics of an upward slug unit, the mass transfer in the near wall can be divided into four zones, Taylor bubble nose
zone, falling liquid film zone, Taylor bubble wake zone and the remaining liquid slug zone; the wall shear stress can be divided
into two zones, the positive wall shear stress zone associated with the falling liquid film and the negative wall shear stress
zone associated with the liquid slug. Based on the conventional mass transfer and wall shear stress characteristics formulas
of single phase liquid full-pipe turbulent flow, corrected normalized mass transfer coefficient formula and wall shear stress
formula are proposed. The
calculated results are in good agreement with the experimental data. The shear stress and the mass transfer coefficient in
the near wall zone are increased with the increase of superficial gas velocity and decreased with the increase of superficial
liquid velocity. The mass transfer coefficients in the falling liquid film zone and the wake zone of leading Taylor bubble
are lager than those in the Taylor bubble nose zone and the remaining liquid slug zone, and the wall shear stress associated
falling liquid film is larger than that associated the liquid slug. The mass transfer coefficient is within 10−3 m/s, and the wall shear stress below 103 Pa. It can be concluded that the alternate wall shear stress due to upward gas–liquid slug flow is considered to be the major
cause of the corrosion production film fatigue cracking. 相似文献
144.
The forced convection heat transfer with water vapor condensation is studied both theoretically and experimentally when wet
flue gas passes downwards through a bank of horizontal tubes. Extraordinarily, discussions are concentrated on the effect
of water vapor condensation on forced convection heat transfer. In the experiments, the air–steam mixture is used to simulate
the flue gas of a natural gas fired boiler, and the vapor mass fraction ranges from 3.2 to 12.8%. By theoretical analysis,
a new dimensionless number defined as augmentation factor is derived to account for the effect of condensation of relatively
small amount of water vapor on convection heat transfer, and a consequent correlation is proposed based on the experimental
data to describe the combined convection–condensation heat transfer. Good agreement can be found between the values of the
Nusselt number obtained from the experiments and calculated by the correlation. The maximum deviation is within ±6%. The experimental
results also shows that the convection–condensation heat transfer coefficient increases with Reynolds number and bulk vapor
mass fraction, and is 1∼3.5 times that of the forced convection without condensation. 相似文献
145.
Krzysztof Chełmiński Patrizio Neff Sebastian Owczarek 《Journal of Mathematical Analysis and Applications》2015
The purpose of this article is to prove the Hölder continuity up to the boundary of the displacement vector and the microrotation matrix for the quasistatic, rate-independent Armstrong–Frederick cyclic hardening plasticity model with Cosserat effects. This model is of non-monotone and non-associated type. In the case of two space dimensions we use the hole-filling technique of Widman and Morrey's Dirichlet growth theorem. 相似文献
146.
Zal U��yun Wan Mahmood Che Abd Rahim Mohamed Zaharudin Ahmad Abdul Kadir Ishak 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(1):255-260
A total of eight sediment cores with 50 cm length were taken in the Sabah and Sarawak coastal waters using a gravity corer in 2004 to estimate sedimentation rates using four mathematical models of CIC, Shukla-CIC, CRS and ADE. The average of sedimentation rate ranged from 0.24 to 0.48 cm year?1, which is calculated based on the vertical profile of 210Pbex in sediment core. The finding also showed that the sedimentation rates derived from four models were generally shown in good agreement with similar or comparable value at some stations. However, based on statistical analysis of paired sample t-test indicated that CIC model was the most accurate, reliable and suitable technique to determine the sedimentation rate in the coastal area. 相似文献
147.
Fabrication of chiral materials and revealing the mechanisms involved in their formation are crucial issues in scientific research. The combination of cooperative self-assembly routes and the chiral templating process favors the formation of inorganic chiral materials with highly ordered mesostructures. This tutorial review highlights the recent research on chiral mesoporous silica (CMS) of hierarchical helical constructions transcribed from organic templates. The rules and mechanisms involved in the synthesis of CMS and related materials, especially the novel expression of chirality and imprinting of helical micellar superstructure by the functional groups immobilized on the mesopore surface, provide us with a deeper insight into the chiral self-assembly process and new strategies for the design and application of chiral materials. This review is addressed to researchers and students interested in chiral chemistry, supramolecular chemistry and mesoporous materials (53 references). 相似文献
148.
149.
Anionic-cationic switchable monodisperse mesoporous silica nanoparticles were synthesized by one-pot amino and carboxylic acid bifunctionalization based on the self-assembly of the surfactant, two types of co-structure-directing agents containing amino and carboxylic groups, and silica sources. These nanoparticles revealed properties of dispersity and reversibility, with the advantage of the pH-responsive anionic-cationic/acid-base switchability. It was demonstrated that the extracted materials achieved reutilization and controllable dispersity in aqueous solution by adjusting the static electric power among the particles during the switching process. 相似文献
150.
Che L Gardenghi DJ Szilagyi RK Minton TK 《Langmuir : the ACS journal of surfaces and colloids》2011,27(11):6814-6821
Molecular beam surface scattering and X-ray absorption spectroscopic experiments were employed to study the reaction of deuterium atoms with a pyrite, FeS(2) (100), surface and to investigate the electronic and geometric structures of the resulting Fe-S phases. Incident D atoms, produced by a radiofrequency plasma and expanded in an effusive beam, were directed at a pyrite surface held at various temperatures from ambient up to 200 °C. During exposure to the D-atom beam, D(2)S products were released with a thermal distribution of molecular speeds, indicating that the D atoms likely reacted in thermal equilibrium with the surface. The yield of D(2)S from the surface decreased approximately exponentially with exposure duration, suggesting that the surface accessible sulfur atoms were depleted, thus leaving an iron-rich surface. This conclusion is consistent with X-ray absorption measurements of the exposed surfaces, which indicated the formation of a layered structure, with elemental iron as the outermost layer on top of a formally Fe((I))-S phase as an intermediate layer and a formally Fe((II))-S(2) bulk pyrite layer at lower depths. The reduced Fe((I))-S phase is particularly remarkable because of its similarity to the catalytically active sites of small molecule metalloenzymes, such as FeFe-hydrogenases and MoFe-nitrogenases. 相似文献