Influence Of Flow Characteristics Research Articles

Influence of Flow Characteristics on Logarithmic Velocity Profile

Influence of Flow Characteristics on Logarithmic Velocity Profile

A reduced-order electrochemical model for analyzing temperature distributions in a tubular solid oxide fuel cell stack

It is challenging to improve the computational efficiency of temperature predictions in tubular solid oxide fuel cell (SOFC) stacks, since the complex flow field usually leads to non-uniform heat generations and heat dissipations. In this study, we have developed a reduced-order electrochemical model for fast predicting the temperature distributions in a kilowatt-class tubular solid oxide fuel cell stack. This model can explicitly express the current density as a function of operating potential, concentration, and temperature, which can significantly reduce the computational cost of stack level simulations. The influence of flow characteristics on temperature distributions in the tubular SOFC stack is examined and analyzed. We show that the vortices formed by flow separations could affect temperature uniformity among all cells. At a low inlet air velocity, few vortices are formed, and the convective heat transfer is too weak to dissipate the heat generations from electrochemical reactions. As the air velocity is increased, the number and strength of vortices are both increased. These vortices enable the air stream to flow spirally and enhance the local convective heat transfer. We also demonstrate that as the air inlet velocity is increased from 1 m/s to 4 m/s, the temperature uniformity among tubular solid oxide fuel cells first decreases and then increases, but the output power is reduced from 2.19 kW to 1.78 kW due to the decrease in operating temperatures. The inlet air velocity should be carefully selected to balance the electrical and thermal performance of the SOFC stack.

自動車エンジン排気系流動場を想定した脈動気流における矩形管壁面熱伝達の研究

The airflow in the exhaust pipe of an automobile engine fluctuates periodically in terms of flow velocity and gas temperature, and understanding the complex flow and heat transfer characteristics is extremely important for improving the performance of exhaust systems. In this study, using a horizontal rectangular pipe with a rectangular cross section, we experimentally obtained the time-averaged temperature in the cross section measured by thermocouples and the wall temperature by thermography on the outer wall of the pipe under the pulsation conditions assumed in the actual system, and investigated the effects on the heat transfer characteristics. The influence of flow characteristics on heat transfer characteristics was also investigated by using PIV. The results showed that the heat transfer coefficient peaked at a pulsation frequency of 25 Hz. At higher frequencies, the decrease in velocity amplitude was considered to be responsible for the decrease in heat transfer coefficient. At lower frequencies, the decrease in turbulent energy in the area close to the inner wall was considered to be the cause.

Analysis of Efficiency of Use of the Longitudinal-Flow Hydropower Plant Unit of a Micro Hydropower Station without a Dam for Small Rivers

In the research of alternative sources of energy much attention is paid to hydro energy, in particular, micro hydropower stations, which use rivers’ kinetic energy. This issue is relevant for research. The target of this paper is to analyze the efficiency of longitudinal-flow hydropower plant of a micro hydropower station without a dam for small rivers. The operational efficiency of hydraulic power plants is mainly determined by the interaction of working elements with the hydraulic flow and the utilization level of its characteristics. The features of its usage and the influence of flow characteristics of the hydropower stations efficiency are examined in this paper. Besides, the interaction between the flow and working elements is assessed. The possibility of improving efficiency level by using working elements with changing weight is tested. Moreover, empirical data is used for calculations.

An Experimental Study on Heat/Mass Transfer From a Rectangular Cylinder

Abstract Local and average mass transfer rates from a rectangular cylinder having various width to height ratios are measured using naphthalene sublimation technique, and influence of flow characteristics on mass transfer is investigated. The experimental apparatus comprises a wind tunnel, a naphthalene casting facility and a sublimation depth measurement system. Mass transfer data are compared with those of heat transfer which are obtained using thermocouples in the constant heat flux boundary condition, and analogy between heat and mass transfer is examined. The reasons for discrepancy in both transport values are explained in detail.

A study of sample withdrawal for lubricated systems. Part 1: influence of flow characteristics, sampling techniques and locations

The wear of a machine element, whether it is due to fatigue or abrasive wear, will add contaminants in the form of particulates to the system. If a machine element is starting to wear out it will produce a large amount of particles and it will finally break down. Since this can be very costly, one can establish the need to monitor the system so that one can foresee failure. There are many different ways to monitor a system, e.g. measurements of the temperature, pressure, vibrations and the degree of contamination. The purpose of contamination control is to extend the life of a component and thereby save money. When monitoring a system it is very important that the monitoring control instrument should give the right output. One important factor in achieving this is the withdrawal of a representative oil sample. In this paper an investigation of where and how to take a representative sample is performed using Stokes’ law and the migration of spheres in a channel. A generalised sedimentation chart for different oils and particles is introduced. Sampling routines for proper sample withdrawal are also presented.

Steady and oscillatory transnasal pressure-flow relationships in healthy adults

The influence of flow characteristics and gas physical properties on nasal resistance (NR) is difficult to ascertain with traditional rhinomanometric methods because the respiratory airflows used in these methods are largely uncontrolled. As an alternative, we used a novel method of rhinomanometry in which an externally generated flow is passed through the nasal passage via a mouthpiece. The transnasal pressure-flow relationships for both quasi-steady and oscillating flows and with different gases were obtained in five healthy adults with this method. For quasi-steady nasal flows the dimensionless pressure losses were largely independent of physical properties of the gas and a function of the Reynolds number (Re) of the flow. Values of NR for quasi-steady flows were largely independent of flow direction for Re up to roughly 3,000 in all five subjects and for Re up to roughly 19,000 in two of the five subjects. Airway collapse occurred in two subjects at Re greater than 3,000, suggesting that the nonrigid segments of the nasal passage contribute to the intersubject variations in NR at high flow rates. Pressure losses associated with oscillating flows measured at frequencies between 1 and 16 Hz were similar to steady flow losses provided that Re was less than roughly 3,000. For Re greater than 3,000 the oscillating flow resistances were affected by the phasic redistribution of flow into compliant segments of the nasal passage. These results indicate that, for flow rates and harmonic frequencies associated with breathing at rest, the nasal passage behaves as a rigid rough-walled pipe in which pressure losses are largely determined by forces relating to viscous friction and convective accelerations.

Experimental Study of a Reacting Mixing Zone Generated by High Wall Injection in a Duct Flow

Abstract In this work we develop an experimental approach to determine the influence of flow characteristics on the burning of solids (auto-extinguishable propellants) inside a hybrid rocket motor. An experimental device utilizing gaseous mixtures which simulates real conditions as closely as possible (high blowing mass transport at the wall) was used to characterize the main flow as a function of geometric and aerodynamic parameters. At first the isothermal case was studied to explore the mixing zone. In a second step a diffusion flame was stabilized to separate the influence of aerodynamics from that of combustion. These results underline the parameters having a preponderant influence on the burning and stabilization of a flame in such a combustion chamber.