Numerical Study of Thin Film Condensation in Forced Convection on an Inclined Wall Covered with a Porous Material

The present work presents a study of forced convection condensation of a laminar film of a pure and saturated vapor on a porous plate inclined to the vertical. The Darcy-Brinkman-Forchheimer model is used to write the flow in the porous medium, while the classical boundary layer equations have been exploited in the pure liquid and in the porous medium taking into account inertia and enthalpy convection terms. The problem has been solved numerically. The results are mainly presented in the form of velocity and temperature profiles. The obtained results have been compared with the numerical results of Chaynane et al. [1]. The effects of different influential parameters such as: inclination (ϕ), effective viscosity (ReK), and dimensionless thermal conductivity λ* on the flow and heat transfers are outlined.

Influence of Prandtl Number on Thin Film Condensation in Forced Convection in an Inclined Wall Covered with a Porous Material

The numerical study of thin film type condensation in forced convection of a saturated pure vapor in an inclined wall covered with a porous material is presented. The generalized Darcy-Brinkman-Forchheimer (DBF) model is used to describe the flow in the porous medium while the classical boundary layer equations have been exploited in the case of a pure liquid. The dimensionless equations are solved by an implicit finite difference method and the iterative Gauss-Seidel method. The objective of this study is to examine the influence of the Prandtl number on the hydrodynamic and thermal fields but also on the local Nusselt number and on the boundary layer thickness. For Pr ≤ 0.7 (low) the velocity and the longitudinal temperature increase with the Prandtl number. On the other hand, when Pr ≥ 2 (high) the Prandtl number no longer influences the velocity and the longitudinal temperature. The local Nusselt number increases as the Prandtl number increases and the thickness of the hydrodynamic boundary layer increases as the Prandtl number decreases.

Effect of Bogie Cavity End Wall Inclination on Flow Field and Aerodynamic Noise in the Bogie Region of High-Speed Trains

Combining the detached eddy simulation(DES)method and Ffowcs Williams-Hawkings(FW-H)equation,the effect of bogie cavity end wall inclination on the flow field and aerodynamic noise in the bogie region is numerically studied.First,the simulation is conducted based on a simplified cavity-bogie model,including five cases with different inclination angles of the front and rear walls of the cavity.By comparing and analyzing the flow field and acoustic results of the five cases,the influence of the regularity and mechanism of the bogie cavity end wall inclination on the flow field and the aerodynamic noise of the bogie region are revealed.Then,the noise reduction strategy determined by the results of the simplified cavity-bogie model is applied to a three-car marshaling train model to verify its effectiveness when applied to the real train.The results reveal that the forward inclination of the cavity front wall enlarges the influence area of shear vortex structures formed at the leading edge of the cavity and intensifies the interaction between the vortex structures and the front wheelset,frontmotor,and front gearbox,resulting in the increase of the aerodynamic noise generated by the bogie itself.The backward inclination of the cavity rear wall is conducive to guiding the vortex structures flow out of the cavity and weakening the interaction between the shear vortex structures and the cavity rear wall,leading to the reduction of the aerodynamic noise generated by the bogie cavity.Inclining the rear end wall of the foremost bogie cavity of the head car is a feasible aerodynamic noise reduction measure for high-speed trains.

Lattice Boltzmann simulation of natural convection in open end cavity with inclined hot wall

Natural convection in an open end cavity with a hot inclined wall is simulated based on the lattice Boltzmann method （LBM）. The physics of flow and energy transfer in open end cavities are addressed when the hot wall is inclined. The combination of the two topics （open cavity and inclined walls） is the main novelty of the present study. The effects of the angle of the hot inclined wall on the flow field and heat transfer are thoroughly investigated. The Prandtl number is fixed to 0.71 （air）. The Rayleigh number and the angle of the hot inclined wall are varied in the range of 10^4 to 10^6 and 60° to 85°, respectively. The results are presented for two different aspect ratios, i.e., A = 1 and 2. The results obtained with the LBM are also compared with those of the finite volume method （FVM）. The predicted results of the LBM conform to those of the FVM. The results show that by increasing the angle of the hot inclined wall and the aspect ratio of the cavity, the average Nusselt number decreases. The trend of the local Nusselt number on the inclined wall is also discussed.

Study on attached ventilation based on inclined walls

In practical engineering,inclined building walls are often presented due to their functional and aesthetic needs.A reasonable air distribution design is essential for creating a satisfactory indoor environment in such buildings.In the present study,inclined walls with a variable inclination angle β were used as the research object to explore a novel air supply mode.Visualization experiments and numerical simulations were conducted to investigate the induced airflow,such as the airflow pattern,the airflow characteristics(maximum jet velocity decay and jet spreading rate)and the ventilation effect(vertical air temperature difference,draft rate,air diffusion performance index).The results show that the"air lake"phenomena occurred over the floor,which resembles the displacement ventilation to some extent.The proposed air supply mode has a good ventilation effect and could be applied to building spaces with inclined walls.The current study can be used as a reference for ventilation design in buildings with inclined walls.

Settlement patterns of mountainous half-filled and half-cut widened subgrade with retaining wall

The settlement of widened highway subgrade in mountainous area is not only affected by the interaction between new and existing subgrade, but also seriously restricted by the external retaining wall. Based on the practical engineering of half-filled and half-cut widened mountainous highway subgrade with external balance weight retaining wall(BWRW), a sophisticated finite element numerical model is established. The evolution law of subgrade settlement is revealed during the whole process of new subgrade filling and BWRW inclination after construction. The settlement component of subgrade is clarified considering whether the existing pavement continues to be used. The results show that the additional settlement caused by the BWRW inclination after construction cannot be ignored in the widening and reconstruction of mountainous highway subgrade. In addition, pursuant to the comprehensive design of subgrade and pavement, the component of subgrade settlement should be determined according to whether the existing pavement continues to be used, while considering the influence of BWRW inclination after construction. When the existing pavement continues to be used, the settlement of the existing subgrade is caused by the new subgrade filling and the BWRW inclination after construction. On the contrary, the settlement is only caused by the BWRW inclination after construction.

Fabrication of micro pin fins on inclined V-shaped microchannel walls via laser micromilling

A laser-micromilling process was developed for fabricating micro pin fins on inclined V-shaped microchannel walls for enhanced microchannel heat sinks.A pulsed nanosecond fiber laser was utilized.The feasibility and mechanism of the formation of micro pin fins on inclined microchannel walls were investigated for a wide range of processing parameters.The effects of the laser output power,scanning speed,and line spacing on the surface morphologies and geometric sizes of the micro-pin fins were comprehensively examined,together with the material removal mechanisms.Micro pin fins with acute cone tips were readily formed on the V-shaped microchannel walls via the piling of recast layers and the downflow of re-solidified materials in the laser-ablation process.The pin-fin height exhibited an increasing trend when the scanning speed increased from 100mm/s to 300 mm/s,and it decreased continuously when the line spacing increased from 5μm to 20μm.The optimal processing parameters for preparing micro pin fins on V-shaped microchannels were found to be a laser output power of 21 W,scanning speed of 100-300 mm/s,and line spacing of 2-5μm.Moreover,the V-shaped microchannels with micro pin fins induced a 7%-538%boiling heat-transfer enhancement over their counterpart without micro pin fins.