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1.
In this article, we study a contact problem between a one-dimensional porous thermoelastic layer and a rigid obstacle. The mechanical problem consists of a coupled system of two hyperbolic partial differential equations and a parabolic one. By defining penalized problems, an energy decay property is obtained. Then, fully discrete algorithms are introduced to approximate both penalized and Signorini problems using the finite element method and the implicit Euler scheme. Stability properties are shown for both problems and a priori error estimates are proved for the penalized problem, from which the linear convergence of the algorithm is derived. Finally, some numerical simulations are performed to demonstrate the accuracy of the approximation and the behavior of the solution.  相似文献   

2.
An analysis of the effective thermal contact resistance between two semi-infinite solids in the presence of a periodic array of rough zones at the interface is carried out on the basis of a solution of the corresponding thermoelastic contact problem. The effect of the roughness is modeled by localized thermal contact resistances varying inversely with the contact pressure. The contact problem is reduced to a nonlinear singular integrodifferential equation, and an iterative procedure is proposed for its solving. The results demonstrate that the periodic array of rough zones between two semi-infinite solids exhibits thermal rectification. It is also found that the effective temperature jump and the effective thermal contact resistance are nonlinear functions of a far field heat flux.  相似文献   

3.
The present article deals with the investigation of the propagation of thermoelastic plane harmonic waves in a nonlocal thermoelastic medium. The Green and Naghdi theory II (without energy dissipation) of generalized thermoelasticity with elastic nonlocal effect is adopted to address this problem. The problem of reflection of thermoelastic waves due to an incident coupled longitudinal elastic wave from the rigid and thermally insulated boundary of a homogeneous, isotropic nonlocal thermoelastic half-space is also studied. The amplitude ratios of the reflected waves and their respective energy ratios are determined analytically. For a particular model, the effect of elastic nonlocality parameter on the variations of phase speeds, attenuation coefficients, amplitude ratios and corresponding energy ratios of the reflected waves is presented graphically and analysis of these results is given.  相似文献   

4.
This paper is focused on the film cooling performance of combustor-turbine leakage flow at off-design condition. The influence of incidence angle on film cooling effectiveness on first-stage vane endwall with combustor-turbine interface slot is studied. A baseline slot configuration is tested in a low speed four-blade cascade comprising a large-scale model of the GE-E3Nozzle Guide Vane (NGV). The slot has a forward expansion angle of 30 deg. to the endwall surface. The Reynolds number based on the axial chord and inlet velocity of the free-stream flow is 3.5 × 105 and the testing is done in a four-blade cascade with low Mach number condition (0.1 at the inlet). The blowing ratio of the coolant through the interface gap varies from M = 0.1 to M = 0.3, while the blowing ratio varies from M = 0.7 to M = 1.3 for the endwall film cooling holes. The film-cooling effectiveness distributions are obtained using the pressure sensitive paint (PSP) technique. The results show that with an increasing blowing ratio the film-cooling effectiveness increases on the endwall. As the incidence angle varies from i = +10 deg. to i = ?10 deg., at low blowing ratio, the averaged film-cooling effectiveness changes slightly near the leading edge suction side area. The case of i = +10 deg. has better film-cooling performance at the downstream part of this region where the axial chord is between 0.15 and 0.25. However, the disadvantage of positive incidence appears when the blowing ratio increases, especially at the upstream part of near suction side region where the axial chord is between 0 and 0.15. On the main passage endwall surface, as the incidence angle changes from i = +10 deg. to i = ?10 deg., the averaged film-cooling effectiveness changes slightly and the negative incidence appears to be more effective for the downstream part film cooling of the endwall surface where the axial chord is between 0.6 and 0.8.  相似文献   

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7.
A model is presented for p–n hetero-junction solar cells in which interface recombination is the dominant diode current transport mechanism. The model explains the large diode ideality factor (n>2) and the increased saturation current density in terms of increased density of interface states Nir. Furthermore, the model allows us to explain the non-translation between illuminated and dark JV characteristics. The explanation is based on the assumption that, for high interface state density values, both the depletion layer width and the diffusion voltage in the p- and n-side of the junction are functions of Nir. The interface recombination leads to lower values of the open-circuit voltage, short-circuit current density, and fill factor. These results are illustrated by numerical calculations of solar cell parameters and compared with experimental data achieved for ZnO/CdS/CuGaSe2 single-crystal solar cells.  相似文献   

8.
The effect of surface wettability on evaporation of a water drop has been examined experimentally using surfaces with various contact angles. To greatly change the surface wettability, TiO2 superhydrophilicity, plasma irradiation, and super‐water‐repellent surface are adopted as the heating surface. The range in contact angle achieved by these methods was between 0° and 170°. The relationship between the contact angle and the wetting limit temperature was obtained and it was found that the lifetime of a water drop dramatically decreases with contact angle in the lower temperature region, and that the wetting limit temperature increases with the contact angle. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(7): 513–526, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20128  相似文献   

9.
Effect of air gap on the performance of building-integrated photovoltaics   总被引:1,自引:0,他引:1  
Ventilation of photovoltaic (PV) modules installed over or beside a building envelope can reduce the module temperature and increase the electrical conversion efficiency. A computational fluid dynamics (CFD) method has been used to assess the effect of the size of air gap between PV modules and the building envelope on the PV performance in terms of cell temperature for a range of roof pitches and panel lengths and to determine the minimum air gap that is required to minimise PV overheating. It has been found that the mean PV temperature and the maximum PV temperature associated with hot spots decrease with the increase in pitch angle and air gap. The mean PV temperature also decreases with increasing panel length for air gaps greater than or equal to 0.08 m whereas the maximum PV temperature generally increases with panel length. To reduce possible overheating of PV modules and hot spots near the top of modules requires a minimum air gap of 0.12–0.15 m for multiple module installation and 0.14–0.16 m for single module installation depending on roof pitches.  相似文献   

10.
Compound-honeycomb solar collectors employ a honeycomb to suppress natural convection and air gaps between the honeycomb and the absorber plate or the glazing to reduce conductive and radiative heat losses. Results of an experimental study on the effect of the thickness of these gaps on the total heat transfer across a compound honeycomb confined between two isothermal and low emissivity boundaries are presented. The honeycomb consists of rectangular cells with elevation aspect ratio 6.3 and plan aspect ratio 82 (15.8 mm thick, 206 mm wide and 2.5 mm deep), constructed from parallel glass strips. Plots of Nusselt number versus Rayleigh number are given for compound honeycombs with air gaps of thickness 1.6 mm, 3.3 mm, 6.4 mm and 9.6 mm above and below the honeycomb and for a compound-honeycomb layer with an air gap of thickness 6.4 mm below the honeycomb. Measurements are reported for tilt angles of 0°, 30° and 60° where the long dimension of the rectangular cells in the honeycomb is horizontal. As the air gaps' thickness increase, coupled conductive-radiative heat transfer is reduced, while the critical Rayleigh number is also reduced and convective heat transfer increases. However, even for relatively thick air gaps, the decrease in critical Rayleigh number is moderate, and the rectangular-cell compound honeycomb is found to be an effective convection suppressor. A compound honeycomb with air gaps above and below the honeycomb is shown to be superior in suppressing convection to a compound honeycomb of equal total thickness with only one air gap below the honeycomb.  相似文献   

11.
Composite Nafion-based membranes were prepared and characterized, using an organosilane derivative (sulfonated diphenylsilanediol, SDPSD) as a filler. The physico-chemical and electrochemical properties of the composite membranes were investigated using differential scanning calorimetry (DSC), field emission scanning electron microscopy (FE-SEM), water uptake (W.U.), and electrochemical impedance spectroscopy (EIS). Both conductivity values and thermal features of the composite demonstrated that the presence of SDPSD as a filler significantly modified the properties of the Nafion matrix, allowing to increase its performance in terms of proton conductivity as well as thermal stability. In particular, the interaction between Nafion and SDPSD was found to improve the mechanical stiffness of the Nafion matrix, leading to an increase in the temperature range at which the Nafion membrane maintains proper hydration requirements and hence satisfactory proton conductivity values, allowing its use as an electrolyte in Polymer Electrolyte Fuel Cells operating at intermediate temperatures.  相似文献   

12.
An experimental investigation was conducted to understand the effect of solid properties on dynamic wetting. Using a liquid tank method, the wetting behavior of silicone oil over glass, aluminum, and stainless steel surfaces was measured. For all three surfaces, the dynamic contact angles disagreed with the universal function proposed by Hoffman. However, if a dimensionless parameter is introduced to describe the nature of the solid surfaces, the experimental results can be in good agreement with the model. Furthermore, the present experiments indicated that the Hoffman–Voinov–Tanner law should be valid for a wider range of dynamic contact angles or capillary numbers. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(1): 1–12, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20099  相似文献   

13.
Thermal contact conductance (TCC) measurements are made on bare and gold plated (?0.5 μm) oxygen free high conductivity (OFHC) Cu and brass contacts in vacuum, nitrogen, and argon environments. It is observed that the TCC in gaseous environment is significantly higher than that in vacuum due to the enhanced thermal gap conductance. It is found that for a given contact load and gas pressure, the thermal gap conductance for bare OFHC Cu contacts is higher than that for gold plated contacts. It is due to the difference in the molecular weights of copper and gold, which influences the exchange of kinetic energy between the gas molecules and contact surfaces. Furthermore, the gap conductance is found to increase with increasing thickness of gold plating. Topography measurements and scanning electron microscopy (SEM) analysis of contact surfaces revealed that surfaces become smoother with increasing gold plating thickness, thus resulting in smaller gaps and consequently higher gap conductance.  相似文献   

14.
In this article, we studied the propagation of SV-waves under the effect of electromagnetic field and initial stress for three models in thermoelasticity: The couple and Green–Lindsay theories as well as the dual-phase-lag theory. The problem of reflection and transmission of thermoelastic waves at a solid–liquid interface in the presence of electromagnetic fields and initial stress we investigated subjected to certain boundary conditions. The appropriate expressions to find the amplitude ratios of the incident waves (SV-waves) were obtained. The reflection and transmission coefficients for the incident SV-waves were computed numerically. The effect of electric field, magnetic field, and initial stress were illustrated graphically. Comparisons were made with the obtained results in the presence and absence of considered variables and displayed graphically. The results indicate that the effect of electric field, magnetic field, and initial stress on SV-waves incidence at the interface between solid–liquid media are very pronounced.  相似文献   

15.
The influence of the TiO2/electrode interface was investigated on electron transport properties at the interface and in TiO2 porous film in back contact dye-sensitized solar cells. Analysis of dye-sensitized solar cells (DSCs) with Ti and TCO indicated that electron transport properties at TiO2/Ti and TiO2/TCO interfaces are similar despite the former's lack of a ‘built-in potential’. The dependence of short circuit current density on TiO2 thickness indicated that TiO2 electron transport is not affected by ‘built-in potential’ or electrode structure. Electron transport thus appears similar in back contact dye-sensitized solar cells and DSCs. A back contact dye-sensitized solar cell fabricated with a Ti electrode and optimum TiO2 porous film showed a conversion efficiency of 7.8% with a metal mask under an air mass of 1.5 sunlight.  相似文献   

16.
Existing models over-predict the thermal contact resistance of conforming rough joints at low contact pressures. However, the applicable pressure range in some applications such as microelectronics cooling is low. A new model is developed which is more suitable for low pressures. The effect of elastic deformations beneath the plastically deformed microcontacts is determined by superimposing normal deformations due to self and neighboring contact spots in an elastic half-space. A parametric study reveals that the elastic deformation effect is an important phenomenon at low contact pressures. The model is compared with data and good agreement is observed at low contact pressures.  相似文献   

17.
This paper presents the effect of interface on the equivalent thermal conductivity of the carbon nanotube composites. The element free Galerkin method has been utilized as a numerical tool to evaluate the thermal conductivity of the composites. The numerical results have been obtained using continuum mechanics approach for a model composite problem, and it was found that the interface has a major effect on the thermal conductivity of the composites. The effect of interface on the effective conductivity of the composite is small for short nanotubes as compared to long nanotubes. Interface thickness also plays an important role on the effective thermal conductivity of the composite. Nanotube anisotropy has got a small effect on effective thermal conductivity of the composites. Transverse thermal conductivity of the composite has got nearly linear variation with nanotube length.  相似文献   

18.
Thermodynamic analysis has been employed in this paper to study the effect of capillarity on the interfacial phase change of liquid without surfactant, and a modified expression of phase change rate of liquid without surfactant has been developed. The new expression demonstrates that the capillarity of the concave liquid surface will promote the interfacial vaporization if sufficient heat is exerted on liquid, and the capillarity of the convex liquid surface will be helpful for increasing the condensation rate from vapor to liquid. The analyses of this paper showed that the newly developed expression is in accordance with practical observations reported in the literature.  相似文献   

19.
Electrical contact resistance (ECR) is one of the most important factors affecting the ohmic loss in proton exchange membrane (PEM) fuel cells. Dominated by the contact pressure at the interface of two neighboring components, the ECR can be reduced by increasing the clamping force applied on fuel cell stack. However, too large a clamping force will result in excessive resistance to the transport of reactants in the gas diffusion layer (GDL) and even damage to the fuel cell components. Therefore, for a given clamping force, the minimum ECR is expected by making the pressure distribution as uniform as possible. This paper investigates two questions: (a) how to evaluate the distribution of non-uniform pressure based on the ECR, and (b) in what situation will a uniform pressure distribution reduce the ECR obviously, i.e., the sensitivity of the contact resistance to the pressure distribution.  相似文献   

20.
The resultant thermoelectric (TE) figure of merit Z, the coefficient of performance (COP), the heat pumping capacity per unit area (Qc/S) were derived analytically as functions of l0, ρc, κc and sc for a single thermoelement (STE) by taking into account the interface layers, where l0 is a length of a TE material, ρc the electrical interface resistivity, κc the thermal interface conductivity and sc the ratio of the Seebeck coefficient of an interface layer to that of a TE material. As a result, it was first revealed that the increase in Z0T of a TE material is not necessarily reflected in the increase in ZT of an STE as long as the interface layers are present. The COP and Qc/S are lowered remarkably for sc = 0 and κc ? 104 W/m2 K. However, it was clarified that even for low values of κc, the COP and Qc/S return to the original high values (obtained for κc ? 105 W/m2 K) at sc = 0.45 and 0.90, respectively. The definite criterion of sc whether or not the boundary Seebeck coefficient has an effect on the enhancement of the cooling performance was indicated quantitatively for an STE with interface layers.  相似文献   

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