Due to tight thermal integration and the requirement for large volumetric flow rates, air ducting of a power plant is boxy in structure and contains abrupt changes in flow direction and cross-section, flow splits and mergers. Achieving a desired flow distribution among several possible paths is therefore a difficult task. In recent years, computational fluid dynamics (CFD) has emerged as a useful tool for flow analysis in a number of industrial applications. In the present study, a flow control algorithm is developed for optimally locating guide vanes in header manifolds to achieve a desired flow distribution. It is based on evaluating approximately the sensitivity of flow distribution at a flow split to the orientation of guide vanes. A simple gradient-based method has been developed which enables a robust, automated procedure for finding the optimal orientation of guide vanes in a small number of CFD computations. Its application to a typical industrial flow situation containing sharp bends and flow splits has been illustrated through a case study and verified experimentally. © 2015 Elsevier Ltd. All rights reserved.

Sreenivas Jayanti

Department Of Chemical Engineering

Ramesh Avvari

Algorithms

Flow control

Flow of fluids

FLUID DYNAMICS

Optimization

AUTOMATED PROCEDURES

DUCTING

FLOW APPORTIONMENT

GRADIENT-BASED METHOD

GUIDE VANE

OPTIMAL ORIENTATION

THERMAL INTEGRATION

Volumetric flow rate

Computational fluid dynamics

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Applied Thermal Engineering

Flow splits and manifolds are encountered in many industrial processes such as heat recovery systems to feed reactant streams and take out product streams. Depending on the application, the flow distribution among the several outlets may be equal or unequal. In this paper we describe a computational method for achieving desired flow distribution in a flow manifold using optimally positioned guide plates. For multiple outlet streams, determining the orientation of the guide plates is a non-trivial problem. The positioning of one guide plate will have an effect on the flow rate through the other outlets. This effect cannot be estimated from simple models but can be calculated using computational fluid dynamics (CFD) simulation of the corresponding flow problem. However, a conventional CFD simulation cannot predict the optimal location of the guide plates. In view of this, we pose the flow distribution problem as a constrained optimization problem and use a well-established algorithm coupled to a computational fluid dynamics (CFD)-based flow solver to develop an automated procedure for the optimal positioning of the guide plates. The robustness of the procedure is illustrated for both equal and unequal flow distributions in a one-inlet, four-outlet manifold with guide plates of fixed and variable lengths. © 2014 Elsevier Ltd. All rights reserved.

An automated procedure for the optimal positioning of guide plates in a flow manifold using Box complex method

Sudden changes in the flow direction are quite common but are inevitable in the lay-out in gas ducting in process and power plants. While it is well known that such changes lead to high pressure drops and flow separation, the scope for optimization is limited by constraints such as on-site fabrication and lay-out limitations. In the present paper, we present an efficient, computational fluid dynamics (CFD)-based shape optimization method which results in lesser pressure drop and more streamlined flow while adhering to site-specific constraints in terms of the extent of changes that can be made. The method is based on velocity defect in the plane of the bend: if, at a particular streamwise location, the average velocity in one half of cross section is above (or below) the cross sectional average velocity by, say, 10% or more, then the width of the duct locally is increased (or decreased), if it is possible to do so within the lay-out restrictions. An iterative application of this criterion using a commercial CFD code is shown to lead to better design of the bend. The optimized solution is validated with experimental results. © 2013 The Institution of Chemical Engineers.

Chemical Engineering Research and Design

Heuristic shape optimization of gas ducting in process and power plants

A proper thermal management strategy is needed to maintain uniform temperature distribution and derive optimal performance in high temperature proton exchange membrane fuel cells (HT-PEMFC). In HT-PEMFCs, more than half of the chemical energy is converted into thermal energy during the electrochemical generation of electrical power. We investigate the viability of three heat removal strategies: (a) using cooling plates through which cathode air is passed in excess of stoichiometric requirement for the purpose of heat removal, (b) using forced convection partly in conjunction with cooling plates, and (c) using forced convection alone for heat removal. Calculations, partly done using computational fluid dynamics simulations, for a 1 kWe HT-PEMFC stack, which is suitable for scooter type of transport applications, show that a combination of excess stoichiometric factor and forced draft appears to provide the optimal strategy for thermal management of high temperature PEM fuel cells. With proper cooling strategy, the temperature variations within the cell may be reduced to about 20 K over most of the cell and to about 50 K in isolated spots. © 2012 Elsevier Ltd. All rights reserved.

Thermal management strategies for a 1 kWe stack of a high temperature proton exchange membrane fuel cell

A numerical study of the interaction between flow, reactions and thermal effects in a planar two dimensional model of a catalytic convertor is presented. A typical catalytic convertor consists of an inlet manifold, a catalytic monolith and an outlet manifold. The catalytic monolith is modeled as a multi-channel structure. Two different planar 2D geometries are compared: a full-scale geometry with 85 channels and a reduced-scale model with 21 channels. The diverging diffuser section of the inlet manifold, which lies immediately upstream the catalytic monolith, induces flow non-uniformity along the transverse direction. The flow immediately upstream of the multi-channel monolith is highly non-uniform. However, the frictional pressure drop in the individual channels tends to reduce this non-uniformity within individual channels. A "flow distribution index" - ratio of actual flow-rate in a channel to the ideal expected flow-rate if the flow was uniform - is defined to numerically characterize the flow mal-distribution across the various channels in the monolith. The velocity and scale effects are analyzed. Higher inlet velocities induce more flow non-uniformity. Catalytic oxidation of CO represented by power-law kinetics is employed to study the role of flow distribution. The flow distribution affects the conversion in the catalytic convertor, with different conversions in central and peripheral channels of the monolith. The net conversion from the device is marginally lower than what is predicted by single channel simulations with an assumption of uniform flow distribution. The thermal effects due to heat losses and reactions also in turn affect flow distribution. The flow tends to be more uniform when heat losses are included in the non-adiabatic simulations for the geometric parameters and kinetics considered in this work. © 2011 Elsevier Ltd.

Chemical Engineering Science

Modeling the effect of flow mal-distribution on the performance of a catalytic converter

Power plant ducting generally designed with simple shapes has to undergo many changes of shape to accommodate interfacing equipment associated with plant operation leading to higher pressure drop, higher power consumption and flow maldistribution zones having higher or lower velocities. To redress this situation, baffles, guide vanes and other internals are used to streamline the flow through ducts, especially in bends. A basic disadvantage in coal fired plants of using baffles is that they get punctured/eroded due to impact of high velocity ash particles in flue gas ducting, and the effectiveness of baffles is lost in short duration. To overcome the above disadvantages, a new method is developed to change the shape of the duct in such a way that a more streamlined flow is maintained across any cross section. The velocity profile, obtained using computational fluid dynamics (CFD) calculations, across the cross-section is examined at several locations along the duct. Wherever high velocity compared to average velocity is found, the cross-section is increased and where the velocity is low. the cross-section is reduced. A new grid is created through the revised cross-section and a fresh CFD analysis is made to identify zones of flow maldistribution. The flow simulation is done in an iterative manner, alternately calculating the flow domain and modifying the local cross-section based on the local velocity distribution. The method has been found to be more robust and led, after a few iterations, to a shape of the duct which resulted in a significant reduction in the pressure drop without using any baffles or inserts. Copyright © 2008 by ASME.

ASME International Mechanical Engineering Congress and Exposition, Proceedings

Shape optimization of power plant ducting using CFD

Flow apportionment algorithm for optimization of power plant ducting

Journal	Data powered by TypesetApplied Thermal Engineering
Publisher	Data powered by TypesetElsevier Ltd
ISSN	13594311
Open Access	No