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This paper deals with an analysis of two-dimensional temperature distribution within a rectangular fin assembly under wet conditions and subject to convective condition at the primary inner wall. An analytical method based upon the separation of variables was suggested to determine the two-dimensional temperature field. A modified one-dimensional model was used to more closely approximate the results of the two-dimensional model; a one-dimensional classical model was also elaborated to provide a basis for comparison, allowing the two-dimensional effect to be established in the case of wet fins. Next, wet fin efficiency was determined. To establish the merit of the present work in considering the two-dimensional effect in wet fins, the results of the two-dimensional model were compared with those obtained from the one-dimensional classical models, demonstrating a considerable difference in their results for various design and psychrometric conditions. The wet-fin analysis presented herein is equall...

In this study, the Gaussian Diffusion Sphere Model (GDSM) and the Statistical Lagrangian Particle Tracking (SLPT) approach were employed and adjusted to calculate the local deposition velocity onto a flat plate in horizontal airflow. The GDSM and the SLPT approach were validated by comparing the predicted local deposition velocities with those determined by solving the equation of convective diffusion. Both the GDSM and the SLPT approach were found to be accurate in calculating the local deposition velocity onto a flat plate in horizontal airflow. In addition, the GDSM was much more efficient than the SLPT approach in terms of the calculation time. Finally, a parametric study on the local deposition velocity onto a flat plate exposed to horizontal airflow was performed using the GDSM with the consideration of the effects of the gravity, convection, diffusion, and thermophoresis.Copyright 2015 American Association for Aerosol Research

Polymer electrolyte membranes (PEMs) play a crucial role for use in major polymer-based fuel cell applications. Key PEM properties such as ion conductivity, reactant permeability, and chemical/physical stability are strongly influenced by the chemical structure and processing conditions of PEMs. This paper presents the property measurement techniques of PEMs using stand-alone membranes and membrane electrode assembly (MEA) configurations. PEM properties such as ion exchange capacity, water uptake, ion conductivity, gas/liquid permeability, and chemical/physical stability are discussed with emphasis on measurement techniques. In addition, the measurement techniques for polymer electrolyte in the catalyst layer are briefly discussed. This review may give some insight to polymer scientists when novel PEM materials are designed, prepared, screened, or fine-tuned for advanced fuel cell systems.

The heat transport and fluid flow with forced convection across a locally heated square cylinder near a wall were investigated using numerical simulations. A uniform heat flux was applied to half of the square cylinder to simulate local heating. The parameters that were varied in this study were the Reynolds number and the distance between the wall and the square cylinder. Critical points were identified at which the system exhibited a transition between oscillatory flow and steady flow. Each of these flow regimes was investigated, and the effects of the fluid flow on the heat transport were examined.

A novel and efficient method for the conversion of carboxylic acids to primary amides using N,N′-carbonyldiimidazole in combination with ammonium acetate/triethyl amine system in [BMIM]BF4 is developed.

A prototype spray freeze dryer was constructed to produce microsized porous particles for pulmonary inhalable drugs by incorporating a spray freezing module into a commercial batch-type freeze drye...

This paper describes the development of a mathematical model and application of the numerical results to predict the adhesion forces between wheels and rails. The adhesion force is realized on a small area of a wheel–rail contact. Many factors have an influence on the adhesion process for these surfaces (e.g., environment, pollution, parameters and conditions of railway vehicle service, track, etc.). The paper focuses on different modelling aspects. Experimental investigation on the process of friction in the contact zone was performed. The data obtained were used to create a mathematical model. The adhesion, which is dependent on load from the wheel to the rail, temperature, friction conditions in the contact zone and wheel slip, was calculated. Finally, a quick method to determine the adhesion force between the wheels (wheel pair) of a railway vehicle and rails (rail track) is presented.

The design optimization of a 7 × 7 pin-fin heat sink is performed numerically. To achieve higher thermal performance of the heat sink, the thermal resistance at the junction of the chip and the heat sink and the overall pressure drop in the heat sink have to be minimized simultaneously. The fin height (h), fin width (w), and fan-to-heat sink distance (c) are chosen as the design variables, and the pressure drop (ΔP) and thermal resistance (θ ja ) are adopted as the objective functions. To obtain the optimum design values, we used the finite-volume method for calculating the objective functions, the Broydon-Fletcher-Goldfarb-Shanno method for solving the unconstrained nonlinear optimization problem, and the weighting method for predicting the multiobjective problem. The results show that the optimum design variables for the weighting coefficient of 0.5 are as follows: w = 4.653 mm, h = 59.215 mm, and c = 2.669 mm. The objective functions corresponding to the optimal design are calculated as ΔP = 6.82 Pa an...

The optimization of the plate heat exchanger with staggered pin arrays for a fixed volume is performed numerically. The flow and thermal fields are assumed to be periodic fully developed flow and heat transfer with constant wall temperature and they are solved using the finite-volume method. The optimization is carried out by using the sequential linear programming (SLP) method, and the weighting method is adopted for solving the multiobjective problem. The results show that the optimal design variables for the weighting coefficient of 0.5 are as follows: S = 6.497 mm, P = 5.496 mm, D 1 = 0.689 mm, and D 2 = 2.396 mm. The Pareto optimal solutions are presented also.

The modeling for turbulent flow through a porous medium has not been confirmed because of an undetermined constant which appears in the governing equations. In the present study, turbulent porous modeling based on one energy equation has been extended to turbulent clear flow. An undetermined constant is also suggested by performing microscopic analysis in the flat tube geometry. The undetermined constant is found to be 0.99 by comparing the results of macroscopic and microscopic analysis. It is shown that the results of the macroscopic analysis using the constant agree well with those of the microscopic analysis, with a maximum error of 3.5%.

The characteristics of moisture ventilation in a dry room are studied numerically. The effects of three important parameters: the positions of outlets, the aspect ratio (β) of horizontal section and the air exchange rate (N), are analyzed in terms of the scales of ventilation efficiency. Ventilation performance is evaluated by varying the aspect ratio and the air exchange rate for the four different outlet arrangements. It is found that the ventilation performance is improved when the aspect ratio in the transverse arrangement of outlets is decreased. Ventilation efficiency reaches its highest value when β is set to be 4 in the longitudinal arrangement of outlets. Regardless of the aspect ratio, the upper arrangement of the outlets shows a better ventilation performance than the lower arrangement. For all geometrical models and aspect ratios investigated in this study, the increase of the air exchange rate for improving the ventilation performance is only valid up to 60 h−1.

In this paper, the characteristics of moisture ventilation in a lithium ion battery manufacturing dry room are studied numerically using the standard k–ϵ turbulence model. Both the steady-state and the unsteady behavior of moisture ventilation are analyzed by considering two different cases; i.e., local moisture generation and uniformly distributed moisture generation in the room. In order to evaluate the characteristics of moisture ventilation, three scales of ventilation efficiency and characteristic ventilation time are presented from the numerical results. It is shown that moisture distribution is dependent strongly on the flow field. The characteristics of moisture ventilation are improved by 20% and 40% in terms of the 1st scale of ventilation efficiency (SVE1) and the 2nd scale of ventilation efficiency (SVE2), respectively, through the modifications of design variables such as the addition of inlets, outlets and partition. A significant improvement in the characteristic ventilation time and the mo...

The transition from steady laminar to chaotic convection in a glass-melting furnace specified by upper surface temperature distribution has been studied by direct numerical analysis of two- and three-dimensional time dependent Navier-Stokes equations. Thermal instability of the convection roll may take place when the modified Rayleigh number Ram is larger than 9.71 x 10 4. It is shown that the basic flow patterns in a glass-melting furnace are steady laminar, unsteady periodic, quasi-periodic, and chaotic flow. The instabilities have the characteristic (viscous diffusion, tau d = H2/upsilon 0) timescales observed in the typical transitions. Through primary (2-D) and secondary (3-D) instability analyses, the fundamental unsteady feature in a glass-melting furnace is well defined as an unsteady periodic or a weak chaotic flow with typical periods of 1 - 3 times tau d. The results strongly imply the possibility of unsteady or chaotic flow in glass melters.

An experimental and numerical study of three-dimensional natural convection-radiation conjugate heat transfer in an enclosure adjacent to a heat-generating chip has been performed. A three-dimensional simulation model is developed by considering heat transfer phenomena by conduction, convection, and radiation. Radiative transfer is analyzed with the discrete ordinates method. Experiments were conducted to validate the numerical model. Comparisons with experimental data show that good agreement is obtained when the radiation effect is considered. The effects of thermal conductivity of the substrate and power level of the chip on heat transfer are investigated. It is shown that radiation is the dominant heat transfer mode and that the thermal conductivity of the substrate has important effects on heat transfer in the enclosure.