Showing papers on "Pressure drop published in 2016"

Review on nanofluids characterization, heat transfer characteristics and applications

Abstract: Nanofluids are attracting many researchers for their superior thermo-physical properties with no or low penalty in pressure drop. The review is made by considering different parameters which govern the nanofluids characteristics, heat transfer performance and its application. Maximum effort is taken to account the contributions of different researchers available in open literature on different aspects of nanofluids such as thermal conductivity, viscosity, experimental, numerical studies on heat transfer performances and applications of nanofluids. The intention of this review is to provide an overview of the most recent studies on nanofluid in the literatures. It will be very useful for the scientific community working on nanofluid to update their knowhow about the nanofluid.

Enhancing Mass Transport in Redox Flow Batteries by Tailoring Flow Field and Electrode Design

Abstract: In this study, we investigate the mass transport effects of various flow field designs paired with raw and laser perforated carbon paper electrodes in redox flow batteries (RFBs). Previously, we observed significant increases in peak power density and limiting current density when perforated electrodes were used in conjunction with the serpentine flow field. In this work, we expand on our earlier findings by investigating various flow field designs (e.g., serpentine, parallel, interdigitated, and spiral), and continuously measuring pressure drop in each configuration. In all cases, these perforated electrodes are found to be associated with a reduction in pressure drop from 4% to 18%. Flow field designs with a continuous path from inlet to outlet (i.e., serpentine, parallel, spiral) are observed to exhibit improved performance (up to 31%) when paired with perforated electrodes, as a result of more facile reactant delivery and resulting greater utilization of the available surface area. Conversely, flow fields with discontinuous paths which force electrolyte to travel through the electrode (e.g. interdigitated), are adversely affected by the creation of perforations due to the high permeability 'channels' in the electrode. These results demonstrate that mass transport can significantly limit the performance of RFBs with carbon paper electrodes. (C) 2015 The Electrochemical Society. All rights reserved.

Review on hydrodynamics and mass transfer in minichannel wall reactors with gas-liquid Taylor flow

Abstract: Over the past decades, Taylor flow has got an increasing interest due to its potential to intensify reaction processes with fast kinetics which are usually controlled by mass transfer processes. Besides high mass transfer rates, the segmented flow regime offers a sharp residence time distribution of the liquid phase and a low pressure drop. Taylor flow appears in micro and minichannels whereas the terms have not always been used with a clear distinction. Minichannels are channels with characteristic diameters between 400 μm and about 1 mm, which will be in the centre of this work. These channel dimensions appear in monolithic reactors also known as reactors with honeycomb catalyst packings, in concepts using bundles of capillary tubes, as well as in microchannel plate reactors. This article presents a comprehensive overview of hydrodynamics and mass transfer in the minichannels of an open flow structure, i.e. in channels without internals, operated in the Taylor flow regime. The review summarises available correlations to predict Taylor flow characteristics, as well as mass transfer coefficients between all involved phases (gas–liquid, liquid–solid, gas–solid). Within this scope, the impact of operational and design parameters is critically discussed and limits of application for the individual correlations are defined. Special attention is given to the interaction of these mass transfer steps in heterogeneously catalysed chemical reactions.

Electroosmosis-modulated peristaltic transport in microfluidic channels

Abstract: We analyze the peristaltic motion of aqueous electrolytes altered by means of applied electric fields. Handling electrolytes in typical peristaltic channel material such as polyvinyl chloride and Teflon leads to the generation of a net surface charge on the channel walls, which attracts counter-ions and repels co-ions from the aqueous solution, thus leading to the formation of an electrical double layer—a region of net charges near the wall. We analyze the spatial distribution of pressure and wall shear stress for a continuous wave train and single pulse peristaltic wave in the presence of an electrical (electroosmotic) body force, which acts on the net charges in the electrical double layer. We then analyze the effect of the electroosmotic body force on the particle reflux as elucidated through the net displacement of neutrally buoyant particles in the flow as the peristaltic waves progress. The impact of combined electroosmosis and peristalsis on trapping of a fluid volume (e.g., bolus) inside the travelling wave is also discussed. The present analysis goes beyond the traditional analysis, which neglects the possibility of coupling the net pumping of fluids due to peristalsis and allows us to derive general expressions for the pressure drop and flow rate in order to set up a general framework for incorporating flow control and actuation by simultaneous peristalsis and application of electric fields to aqueous solutions. It is envisaged that the results presented here may act as a model for the design of lab-on-a-chip devices.

Flow boiling and frictional pressure gradients in plate heat exchangers. Part 2: Comparison of literature methods to database and new prediction methods

Abstract: In the second part of this study a sensitivity analysis on the prediction methods is performed to consider the effect of plate geometry on thermal–hydraulic performance and an extensive comparison of all the two-phase pressure drop and flow boiling heat transfer prediction methods available in the open literature are also provided versus the large diversified database presented in Part 1. The experimental databank, from numerous independent research studies, is then utilized to develop the new prediction methods to evaluate local heat transfer coefficients and pressure drops. These new methods were developed from 1903 heat transfer and 1513 frictional pressure drop data points (3416 total), respectively, and were proved to work better over a very wide range of operating conditions, plate designs and fluids (including ammonia). The prediction for flow boiling heat transfer coefficients was broken down into separate macro- and micro-scale methods.

Scaling Roughness Effects on Pressure Loss and Heat Transfer of Additively Manufactured Channels

Abstract: Additive manufacturing (AM) with metal powder has made possible the fabrication of gas turbine components with small and complex flow paths that cannot be achieved with any other manufacturing technology presently available. The increased design space of AM allows turbine designers to develop advanced cooling schemes in high-temperature components to increase cooling efficiency. Inherent in AM with metals is the large surface roughness that cannot be removed from small internal geometries. Such roughness has been shown in previous studies to significantly augment pressure loss and heat transfer of small channels. However, the roughness on these channels or other surfaces made from AM with metal powder has not been thoroughly characterized for scaling pressure loss and heat transfer data. This study examines the roughness of the surfaces of channels of various hydraulic length scales made with direct metal laser sintering (DMLS). Statistical roughness parameters are presented along with other parameters that others have found to correlate with flow and heat transfer. The pressure loss and heat transfer previously reported for the DMLS channels studied in this work are compared to the physical roughness measurements. Results show that the relative arithmetic mean roughness correlates well with the relative equivalent sand grain roughness. A correlation is presented to predict the Nusselt number of flow through AM channels, which gives better predictions of heat transfer than correlations currently available. [DOI: 10.1115/1.4034555]