Computational analysis of the flow of pseudoplastic power-law fluids in a microchannel plate

The flow of pseudoplastic power-law fluids with different flow indexes at a microchannel plate was studied using computational fluid dynamic simulation.The velocity distribution along the microchannel plate and especially in the microchannel slits,flow pattern along the outlet arc and the pressure drop through the whole of microchannel plate were investigated at different power-law flow indexes.The results showed that the velocity profile in the microchannel slits for low flow index fluids was similar to the plug flow and had uniform pattern.Also the power-law fluids with lower flow indexes had lower stagnation zones near the outlet of the microchannel plate.The pressure drop through the microchannel plate showed huge differences between the fluids.The most interesting result was that the pressure drops for power-law fluids were very smaller than that of Newtonian fluids.In addition,the heat transfer of the fluids through the microchannel with different channel numbers in a wide range of Reynolds number was investigated.For power-law fluid with flow index(n=0.4),the Nusselt number increases continuously as the number of channels increases.The results highlight the potential use of using pseudoplastic fluids in the microheat exchangers which can lower the pressure drop and increase the heat transfer efficiency.

ERRATUM TO “CHARACTERISTICS OF PRESSURE DROP AND CORRELATION OF FRICTION FACTORS FOR SINGLE-PHASE FLOW IN ROLLING HORIZONTAL PIPE”

This is the erratum to the article [zhang Jin-hong, Yan Chang-qi, Gao Pu-zhen, Journal of Hydrodynamics, 2009, 21(5)]. The Fig.5 is corrected.

Effect of polymer and fiber additives on pressure drop in a rectangular channel

The influence of minute amounts of additives on pressure drop is an interesting fundamental phenomenon, potentially with important practical applications. Change of the pressure drop in a quasi-two-dimensional channel flow using various additives is experimentally investigated. Tests were conducted for a wide range of concentrations（100 ppm-500 ppm） and Reynolds numbers（16 000-36 000） with two polymers and four rigid fibers used as additive. Maximum drag reduction of 22% was observed for xanthan gum. However, xanthan gum loses its drag-reducing property rapidly. It was also seen that drag reduction percentage of xanthan gum remains almost constant for different Reynolds numbers. Guar flour demonstrated good drag reduction property at high Reynolds numbers. Drag reduction of 17.5% at Re= 33 200 using 300 ppm solution was observed. However, at low Reynolds numbers guar flour will cause an increase in pressure drop. Fiber fillers（aspect ratio=21） have been tested as well. In contrast to polymers, they increased the drag for the range of examined concentrations and Reynolds numbers. Polyacrylonitrile fiber with three different aspect ratios（106, 200, 400） was also used, which showed an increase in pressure drop at low aspect ratios. Polyacrylonitrile fibers of larger lengths（6 mm） demonstrated minor drag-reducing effects（up to 3%）.

Design aspect of a novel L-shaped pulsed column for liquid–liquid extraction applications: Energy consumption and the characteristics velocity concept

This article deals with the evaluation of the consumption of energy for a steady state solvent extraction in a novel L-shaped pulsed sieve-plate column, which is highly required for design and optimization of the periodic flow processes for industrial applications. In this regard, a comprehensive evaluation on the energy consumption in case of a pulsed flow for three different chemical systems is conducted and besides the influence of pulsation intensity, the effect of geometrical parameters including the plate spacing and the plate free area is investigated as well. Moreover, the concept of characteristic velocity models at flooding points is evaluated with respect to the variation of pressure drop along the column at different operational conditions.

Study on Characteristics of Steady Flow Condensation Heat Transfer in a Tube under Zero－Gravitation

In this paper, the annular flow. model for in tube completed condensation is employed to predict the steady flow condensation heat transfer characteristics in a tube under zero-gravitation. In this easel it is proposed that vapor condenses on the liquid film surface. Due to the effect of surface tension, the liquid exists in the form of liquid film ring contacting wall; when the velocity of vapor core decreases to zerol the condensation process ends. Putting forward the physical and mathematical models, the problem is solved and the multi-order equation of the thickness of liquid film is obtained, which includes terms of the pressure gradient along axial direction, the friction force between vapor and liquid on interface. By computational calculation, this model can be used not only to predict the thickness of liquid film, the condensation pressure gradient along the axial direction, but also to determine the Nusselt number, the condensation length and the total flow pressure drop of condensation etc. At the end, the calculation results of the necessary condensation length are compared approximately with those from the experiments, which are obtained on the test set-up placed horizontally in gravitation field, and the deviation is analyzed.

Flow-regime transitions in fluidized beds of non-spherical particles

Fluidized beds frequently involve non-spherical particles, especially if biomass is present. For spheri- cal particles, numerous experimental investigations have been reported in the literature. In contrast, complex-shaped particles have received much less attention. There is a lack of understanding of how par- ticle shape influences flow-regime transitions. In this study, differently shaped Geldart group D particles are experimentally examined. Bed height, pressure drop, and their respective fluctuations are analyzed. With increasing deviation of particle shape from spheres, differences in flow-regime transitions occur with a tendency for the bed to form channels instead of undergoing smooth fluidization. The correlations available in the literature for spherical particles are limited in their applicability when used to predict regime changes for complex-shaped particles. Hence, based on existing correlations, improvements are derived.

Two-phase flow distributors for fuel cell flow channels

All existing proton exchange membrane （PEM） fuel cell gas flow fields have been designed on the basis of single-phase gas flow distribution. The presence of liquid water in the flow causes non-uniform gas distribution, leading to poor cell performance. This paper demonstrates that a gas flow restrictor/distributor, as is commonly used in two-phase flow to stabilize multiphase transport lines and multiphase reactors, can improve the gas flow distribution by significantly reducing gas real-distribution caused by either non-uniform water formation in parallel flow channels or flow instability associated with negative-slope pressure drop characteristic of two-phase horizontal flow systems.