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Gaseous slip flow of a rectangular microchannel with non-uniform slip boundary conditions

MICROFLUIDICS AND NANOFLUIDICS 2010年第2-3期9卷 513-522页

作者： Jang, Jaesung Kim, Yong-Hwan UNIST Sch Mech & Adv Mat Engn Ulsan 689798 South Korea Daewoo Engn Co Power & Energy Tech Grp Songnam 463825 South Korea

This article presents analytical expressions of velocity and mass flow rate in terms of Fourier series for gaseous slip flows in long, straight, and uniform rectangular microchannels in the case of different first-order slip boundary conditions on each wall of the microchannels. The derived velocity expressions were in good agreement with those presented by Ebert and Sparrow (J Basic Eng 87:1018, 1965), when the slip boundary conditions on each wall of the microchannels were identical. The computed first-order dimensionless mass flow rate was also in very good agreement with the dimensionless mass flow rate for the planar channel reported by Arkilic et al. (J Microelectromec Syst 6:167, 1997) as the channel aspect ratio approached zero. Using the derived first-order dimensionless mass flow expression and the previously reported mass flow data, we found the unknown tangential momentum accommodation coefficient (TMAC) of nitrogen on a glass surface in a rectangular microchannel made by anodic bonding. The effects of the channel aspect ratio and Knudsen number on the velocity fields were discussed. The uncertainty level of the estimation of TMAC from mass flow rate measurements was also discussed, along with the effects of the channel aspect ratio and Knudsen number on the uncertainty level.

关键词： Gaseous slip flow Slip boundary conditions rectangular microchannel Tangential momentum accommodation coefficient (TMAC)

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Startup electroosmotic flow of a viscoelastic fluid characterized by Oldroyd-B model in a rectangular microchannel with symmetric and asymmetric wall zeta potentials

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JOURNAL OF NON-NEWTONIAN FLUID MECHANICS 2017年 247卷 41-52页

作者： Kaushik, P. Chakraborty, Suman Indian Inst Technol Dept Mech Engn Kharagpur 721302 W Bengal India

We study the startup flow of a viscoelastic fluid in a microfluidic channel, by considering the Oldroyd-B constitutive model. In particular, we aim to capture the confluence of the interfacial charge and the combined viscous and elastic properties of the fluid toward dictating the resulting startup flow characteristics. We further highlight the implications in the asymmetric nature of the wall zeta potentials on the flow behavior. We observe an increase in flow rate with increase in elastic nature of the fluid for studies with symmetric wall zeta potentials. For cases with asymmetric zeta potentials, we observe large movement of the velocity peaks, creating crests and troughs. Results from the present study may turn out to be useful in designing lab on a chip based microfluidic devices transporting bio-fluids such as blood, saliva and mucus by means of electroosmotic mechanisms. (C) 2017 Elsevier B.V. All rights reserved.

关键词： Viscoelastic fluid rectangular microchannel Startup flow Transient analysis Oldroyd-B model

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Effects of Heat Flux, Mass Flux, Inlet Fluid Subcooling, and Channel Orientation on Subcooled Flow Boiling in a High-Aspect-Ratio rectangular microchannel

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JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME 2020年第8期142卷 1-13页

作者： Li, Wei Chen, Zengchao Li, Junye Zhou, Kan Feng, Zhaozan Zhejiang Univ Dept Energy Engn Hangzhou 310027 Peoples R China CRRC Zhuzhou Inst Co Ltd Zhuzhou 412000 Hunan Peoples R China

An experimental investigation of subcooled flow boiling in a high-aspect-ratio, one-sided heating, silicon-based rectangular microchannel was conducted utilizing de-ionized water as the working fluid. The microchannel was 5.01 mm wide and 0.52 mm high, having a hydraulic diameter of 0.94 mm and an aspect ratio (AR) of 10. The heat flux, mass flux, and inlet fluid subcooling were in the ranges of 0-30 W/cm(2), 200-500 kg/m(2)s, and 5-20 degrees C, respectively, while the orientations were vertical and horizontal. Parametric study on heat transfer characteristics including the onset of nucleate boiling (ONB), heat transfer coefficient (HTC), and critical heat flux (CHF) was carried out combined with flow visualization. Significant appearance of ONB without boiling hysteresis was observed in the boiling curve, accompanied with bubble nucleation. Nucleate boiling occurred first near the exit, where the HTC increased more sharply, while easier bubble nucleation was found near the sides. Unique time-dependent flow pattern consisting of isolated bubbly flow, elongated bubbly flow, partial dry-out, and rewetting process was observed. More nucleation sites were activated at higher heat flux, while higher initial heat flux and wall superheat for ONB as well as higher CHF value were obtained at higher mass flux and inlet subcooling. Compared to the vertical channel, higher wall temperature and pressure drop with larger oscillation amplitudes were found for the horizontal counterpart, where the merged bubbles agglomerated in the heating section, resulting in earlier dry-out which deteriorated heat transfer.

关键词： subcooled flow boiling heat transfer characteristics rectangular microchannel high aspect ratio flow visualization

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Heat transfer characteristics of magnetohydrodynamic electroosmotic flow in a rectangular microchannel

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EUROPEAN JOURNAL OF MECHANICS B-FLUIDS 2019年 74卷 180-190页

作者： Yang, Chunhong Jian, Yongjun Xie, Zhiyong Li, Fengqin Inner Mongolia Univ Sch Math Sci Hohhot 010021 Inner Mongolia Peoples R China

The heat transfer characteristics of incomprehensible magnetohydrodynamic electroosmotic flow through a two-dimensional rectangular microchannel are studied theoretically, and we consider electromagnetic effect under the combined electrokinetic effect by applying a lateral electric field and a vertical magnetic field to existing axial electric field. To maintain the flow, pressure gradient is also provided. The effect of viscous dissipation combined with Joule heating and electromagnetic coupling heat is also taken into consideration under the boundary assumption of uniform wall heat flux. The analytical expression of non-dimensional velocity in rectangular microchannel is obtained, from which non-dimensional temperature and Nusselt number are derived. Through theoretical analysis and numerical calculation, these dimensionless physical quantities are graphically discussed by different parameter values, such as Hartmann number Ha, Brinkman number Br and parameter S (denoting the intensity of the lateral electric field). The results show that the lateral electric field has obvious effect in controlling the flow. Without the applied lateral electric field, the normal velocity gradually decreases with Ha. In the presence of imposed lateral electric field, with the increase of Hartmann number Ha, both the variation profiles of velocity and temperature fields show increasing-decreasing trend, the threshold value is determined by a so-called critical Hartmann number, whereas Nu profile has the adverse trend. Finally, we also discuss the impacts of the viscous dissipation on the thermal transport processes. (C) 2018 Elsevier Masson SAS. All rights reserved.

关键词： Heat transfer Electroosmotic flow (EOF) Magnetohydrodynamic (MHD) rectangular microchannel

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Numerical investigation of ammonia boiling heat transfer in rectangular microchannel under high pressure

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INTERNATIONAL JOURNAL OF REFRIGERATION 2024年 168卷 607-619页

作者： Yang, Chenbing Pang, Liping Guo, Yuandong Ma, Desheng Beihang Univ Sch Aeronaut Sci & Engn Lab Fundamental Sci Ergon & Environm Control Beijing 100191 Peoples R China

Ammonia boilers are commonly used as expendable radiators during the return phase of spacecraft. The aim of this study is to investigate the bubble behavior and heat transfer characteristics within a vertical rectangular microchannel of a plate-fin ammonia boiler under gravity at an absolute pressure of 354-615 kPa. In order to achieve this, a single rectangular microchannel unit was intercepted from the ammonia boiler structure to construct a simulation model, and the high-pressure boiling process of ammonia in the rectangular microchannel was numerically investigated using the VOF model. Good agreement was obtained by comparing the numerical results with the experimental data with the error within 8 %. The results show that the wake flow at the lower end of the primary bubbles has an enhanced effect on the heat transfer, which is about 50-60 %. The maximum horizontal dimension of primary bubbles increases with increasing superheat, and significant bubble coalescence occurs when 45 % of the rectangular microchannel spacing is exceeded. In addition, the effect of different saturation temperatures on the heat transfer performance on the hot high temperature wall was investigated. Significant heat transfer deterioration was found to occur at saturation temperatures below 4 degrees C (superheat above 15 degrees C). The reason found in this study was that bubble coalescence significantly increases the percentage of gas-phase contact area on the high-temperature wall (from 25 % to 54 %) and weakens the wake enhancement effect.

关键词： Ammonia boiler Boiling heat transfer Numerical simulation rectangular microchannel

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A note on "Start-up electroosmotic flow of Maxwell fluids in a rectangular microchannel with high zeta potentials" [J. Non-Newton Fluid Mech. 227 (2016) 17-29]

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JOURNAL OF NON-NEWTONIAN FLUID MECHANICS 2016年 234卷 114-117页

作者： Jimenez, E. Escandon, J. Bautista, O. Mendez, F. Inst Politecn Nacl ESIME Azcapotzalco Av Granjas 682 Mexico City 02250 DF Mexico UNAM Mexico Fac Ingn Dept Termofluidos Mexico City 04510 DF Mexico

This work is an extension of the research carried out by Jimenez et al. [1] entitled "Start-up electroosmotic flow of Maxwell fluids in a rectangular microchannel with high zeta potentials". They conducted a semi-analytical study of an electroosmotic flow (EOF) with a Maxwell fluid in a rectangular microchannel considering high and asymmetric zeta potentials at the walls of the microchannel. In their solution of the EOF, the separation-of-variables method is used, and derived from the transient-state solution they determined that the limit values of the dimensionless relaxation time are (lambda) over bar (1) = 0 for Newtonian fluids, while for Maxwell fluids values greater than (lambda) over bar (1) > 1/8 pi(2) correspond to square microchannels and (lambda) over bar (1) H*W-2*(2) [4 pi(2) (H*(2) + W*(2))](-1) to rectangular microchannels. This extension provides a general solution for all values of X1 and shows results for 0 <= (lambda) over bar (1) <= H*W-2*(2)[4 pi(2) (H*(2) + W*(2))](-1) that in the above work were not presented. (C) 2016 Elsevier B.V. All rights reserved.

关键词： Transient electroosmotic flow Maxwell fluids rectangular microchannel Field effects

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Start-up electroosmotic flow of Maxwell fluids in a rectangular microchannel with high zeta potentials

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JOURNAL OF NON-NEWTONIAN FLUID MECHANICS 2016年 227卷 17-29页

作者： Jimenez, E. Escandon, J. Bautista, O. Mendez, F. Inst Politecn Nacl ESIME Azcapotzalco Ave Granjas 682 Mexico City 02250 DF Mexico Univ Nacl Autonoma Mexico Fac Ingn Dept Termofluidos Mexico City 04510 DF Mexico

In this paper, the start-up from rest of the electroosmotic flow of Maxwell fluids in a rectangular microchannel with asymmetric high zeta potentials at the walls is studied. By appropriately combining the momentum equation with the rheological Maxwell model, a hyperbolic partial differential equation to determine the flow field is obtained. The dimensionless mathematical model is solved using Green's functions and the separation-of-variables method. Because the high zeta potentials at the walls of the microchannel are taken into account, the electrical potential distribution is numerically solved. We show that the flow is characterized by two relevant parameters that control the electroosmotic flow: the dimensionless relaxation time of the viscoelastic fluid, (lambda) over bar (1), and the dimensionless zeta potentials of the walls, (zeta) over bar (i). The most important results of this paperare that the required time to reach the steady state depends on the assumed values of the relaxation time and that the velocity profiles exhibit a singular transient oscillatory behavior because of the competition between viscous, elastic and electroosmotic forces. For asserting the correctness of the semi-analytical solution of the electroosmotic flow, an analytical solution was determined by considering low zeta potential, and a very good agreement between them was found. (c) 2015 Elsevier B.V. All rights reserved.

关键词： Transient electroosmotic flow Maxwell fluids rectangular microchannel Field effects

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HEAT AND MASS TRANSFER RESEARCH ON FLOW CONDENSATION OF BINARY ZEOTROPIC MIXTURES IN A rectangular microchannel

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HEAT TRANSFER RESEARCH 2021年第6期52卷 75-95页

作者： Zhang, Yongxin Jia, Li Dang, Chao Yin, Liaofei Beijing Jiaotong Univ Inst Thermal Engn Sch Mech Elect & Control Engn Beijing 100044 Peoples R China Beijing Key Lab Flow & Heat Transfer Phase Changi Beijing 100044 Peoples R China

An annular flow condensation model for binary zeotropic mixtures in the horizontal rectangular microchannel was developed, and it was validated with the experimental data for R134a/R245fa mixtures in the same conditions. The prediction error of heat transfer coefficients was within an acceptable range. The influences of mass fraction, mass flux, wall subcooling temperature, and inlet pressure were considered with parametric analysis. The sensible heat gradient, diffusion flux fraction, meniscus curvature radius, and heat transfer coefficient were analyzed. A comparative model study was also performed in a rectangular channel and a circular channel. Heat transfer characteristics and degradation were analyzed for R134a/R245fa in two channels. The parameters had different influence on heat and mass transfer resistance and meniscus curvature radius, which affected the heat transfer coefficient. Higher condensation heat transfer performance existed in the rectangular channel;however, stronger heat transfer coefficient degradation also appeared.

关键词： zeotropic mixture flow condensation model rectangular microchannel

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Numerical Simulation of Heat Transfer in rectangular microchannel

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Advances in Applied Mathematics and Mechanics 2009年第2期1卷 231-241页

作者： Jun Yao Yufeng Yao Peter J.Mason Mayur K.Patel Faculty of Engineering Kingston University104 Friars AvenueRoehampton ValeLondon SW153DWUnited Kingdom School of Computing and Mathematical Sciences University of Greenwich30 Park RowGreenwichLondon SE109LSUnited Kingdom

Numerical simulation of heat transfer in a high aspect ratio rectangular microchannel with heat sinks has been conducted,similar to an experimental *** channel heights measuring 0.3 mm,0.6 mm and 1 mm are considered and the Reynolds number varies from 300 to 2360,based on the hydraulic ***ulation starts with the validation study on the Nusselt number and the Poiseuille number variations along the channel streamwise *** is found that the predicted Nusselt number has shown very good agreement with the theoretical estimation,but some discrepancies are noted in the Poiseuille number *** observation however is in consistent with conclusions made by other researchers for the same flow *** continues on the evaluation of heat transfer characteristics,namely the friction factor and the thermal *** is found that noticeable scaling effect happens at small channel height of 0.3 mm and the predicted friction factor agrees fairly well with an experimental based *** simulation further reveals that the thermal resistance is low at small channel height,indicating that the heat transfer performance can be enhanced with the decrease of the channel height.

关键词： Computational fluid dynamics rectangular microchannel scaling effect thermal resistance

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NUMERICAL SIMULATIONS OF TURBULENT AIRFLOW PHENOMENA AND CHARACTERISTICS OF HEAT TRANSFER THROUGH A rectangular microchannel WITH MIXED-TYPE BAFFLES

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INTERNATIONAL JOURNAL OF FLUID MECHANICS RESEARCH 2021年第3期48卷 1-16页

作者： Saha, Sandip Biswas, Pankaj Raut, Santanu Das, Apurba Narayan NIT Silchar Dept Math Silchar 788010 Assam India Mathabhanga Coll Dept Math Cooch Behar 736146 W Bengal India Alipurduar Univ Dept Math Alipurduar 736121 W Bengal India

Considering four various forms of baffle (plane, trapezoidal, triangular, and isosceles) with sixteen baffle configurations, numerical simulations of steady, incompressible turbulent air hydrothermal phenomena have been studied in a rectangular microchannel, which has a key role in modeling heat exchangers. The governing equations have been solved using the finite volume method and employing the SIMPLE algorithm. To study the turbulence phenomenon, the SST k-omega turbulence model has been used. All the forms of channel, flow structure, normalized velocity profile, normalized skin friction coefficient, normalized friction factor, local, average Nusselt number, and thermal enhancement factor have also been studied at different Reynolds numbers. Among all the baffles, it has been found that trapezoidal-triangular baffles provide the highest Nusselt number, and triangular-isosceles baffles provide the lowest thermal enhancement factor.

关键词： rectangular microchannel SST k-omega turbulence model average Nusselt number thermal enhancement factor

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