scholarly journals Numerical Investigation of Thermally Developing and Fully Developed Electro-Osmotic Flow in Channels with Rounded Corners

Fluids ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 22
Author(s):  
Nicola Suzzi ◽  
Marco Lorenzini
Keyword(s):  
Cross Sections ◽  
Joule Heating ◽  
Rectangular Cross Section ◽  
Entry Length ◽  
Osmotic Flow ◽  
Uniform Wall Temperature ◽  
Nusselt Numbers ◽  
Developing Flow ◽  
Uniform Wall ◽  
Electro Osmotic Flow

Electro-osmotic flow, that is, the motion of a polar fluid in microducts induced by an external electric field, is one micro-effect which allows fluid circulation without the use of mechanical pumping. This is of interest in the thermal management of electronic devices, as microchannels with cross sections of almost arbitrary shape can easily be integrated on the chips. It is therefore important to assess how the geometry of the channel influences the heat transfer performance. In this paper, the thermal entry region and the fully developed electro-osmotic flow in a microchannel of rectangular cross section with smoothed corners is investigated for uniform wall temperature. For the fully developed region, correlations for the Poiseuille and Nusselt numbers considering the aspect ratio and nondimensional smoothing radius are given, which can be used for practical design purposes. For thermally developing flow, it is highlighted how smoothing the corners increases the value of the local Nusselt number, with increases up to 18% over sharp corners, but that it also shortens the thermal entry length. It is also found that Joule heating in the fluid may cause a reversal of the heat flux, and that the thermal entry length has a linear dependence on the Reynolds number and the hydraulic diameter and on the logarithm of the nondimensional Joule heating.

Combined Forced and Free Convection in the Entrance Region of an Isothermally Heated Horizontal Pipe

1982 ◽  
Vol 104 (1) ◽  
pp. 153-159 ◽  
Author(s):  
Mikio Hishida ◽  
Yasutaka Nagano ◽  
M. S. Montesclaros
Keyword(s):  
Numerical Solutions ◽  
Entrance Region ◽  
Temperature Fields ◽  
Horizontal Pipe ◽  
Uniform Wall Temperature ◽  
Nusselt Numbers ◽  
Developing Flow ◽  
Uniform Wall ◽  
Secondary Velocity ◽  
Laminar Convection

Numerical solutions are given without the aid of a large Prandtl number assumption for combined forced and free laminar convection in the entrance region of a horizontal pipe with uniform wall temperature. The steady-state solutions have been obtained from the asymptotic time solutions of the time-dependent equations of momentum and energy with the Poisson equation for pressure. Results are presented for the developing primary and secondary velocity profiles, developing temperature fields, local wall shear stress, and local and average Nusselt numbers, which reveal how the developing flow and heat transfer in the entrance region are affected by the secondary flow due to buoyancy forces.

scholarly journals Flow control in microfluidics devices: electro-osmotic Couette flow with joule heating effect

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
C. Ahamed Saleel ◽  
Saad Ayed Alshahrani ◽  
Asif Afzal ◽  
Maughal Ahmed Ali Baig ◽  
Sarfaraz Kamangar ◽  
...  
Keyword(s):  
Flow Control ◽  
Couette Flow ◽  
Joule Heating ◽  
Dynamic Viscosity ◽  
Microfluidic Devices ◽  
Heating Effect ◽  
Content Type ◽  
Osmotic Flow ◽  
Joule Heating Effect ◽  
Electro Osmotic Flow

PurposeJoule heating effect is a pervasive phenomenon in electro-osmotic flow because of the applied electric field and fluid electrical resistivity across the microchannels. Its effect in electro-osmotic flow field is an important mechanism to control the flow inside the microchannels and it includes numerous applications.Design/methodology/approachThis research article details the numerical investigation on alterations in the profile of stream wise velocity of simple Couette-electroosmotic flow and pressure driven electro-osmotic Couette flow by the dynamic viscosity variations happened due to the Joule heating effect throughout the dielectric fluid usually observed in various microfluidic devices.FindingsThe advantages of the Joule heating effect are not only to control the velocity in microchannels but also to act as an active method to enhance the mixing efficiency. The results of numerical investigations reveal that the thermal field due to Joule heating effect causes considerable variation of dynamic viscosity across the microchannel to initiate a shear flow when EDL (Electrical Double Layer) thickness is increased and is being varied across the channel.Originality/valueThis research work suggest how joule heating can be used as en effective mechanism for flow control in microfluidic devices.

Laminar Heat Transfer in Tubes Under Slip-Flow Conditions

1962 ◽  
Vol 84 (4) ◽  
pp. 363-369 ◽  
Author(s):  
E. M. Sparrow ◽  
S. H. Lin
Keyword(s):  
Heat Transfer ◽  
Wall Temperature ◽  
Slip Flow ◽  
Mean Free Path ◽  
Uniform Wall Temperature ◽  
Nusselt Numbers ◽  
Temperature Jumps ◽  
Uniform Wall ◽  
Moving Fluid ◽  
Uniform Wall Heat Flux

The effects of low-density phenomena on the fully developed heat-transfer characteristics for laminar flow in tubes has been studied analytically. Consideration is given to the slip-flow regime wherein the major rarefaction effects are manifested as velocity and temperature jumps at the tube wall. The analysis is carried out for both uniform wall temperature and uniform wall heat flux. In both cases, the slip-flow Nusselt numbers are lower than those for continuum flow and decrease with increasing mean free path. Extension of the results is made to include the effects of shear work at the wall, temperature jump modifications for a moving fluid, and thermal creep.

Lubrication theory for electro-osmotic flow in a slit microchannel with the Phan-Thien and Tanner model

2013 ◽  
Vol 722 ◽  
pp. 496-532 ◽  
Author(s):  
O. Bautista ◽  
S. Sánchez ◽  
J. C. Arcos ◽  
F. Méndez
Keyword(s):  
Joule Heating ◽  
Dimensionless Temperature ◽  
Dimensionless Parameters ◽  
Osmotic Flow ◽  
Numerical Predictions ◽  
Pressure Profiles ◽  
Heating Effects ◽  
Viscosity Function ◽  
Fluid Properties ◽  
Electro Osmotic Flow

AbstractIn this work the purely electro-osmotic flow of a viscoelastic liquid, which obeys the simplified Phan-Thien–Tanner (sPTT) constitutive equation, is solved numerically and asymptotically by using the lubrication approximation. The analysis includes Joule heating effects caused by an imposed electric field, where the viscosity function, relaxation time and electrical conductivity of the liquid are assumed to be temperature-dependent. Owing to Joule heating effects, temperature gradients in the liquid make the fluid properties change within the microchannel, altering the electric potential and flow fields. A consequence of the above is the appearance of an induced pressure gradient along the microchannel, which in turn modifies the normal plug-like electro-osmotic velocity profiles. In addition, it is pointed out that, depending on the fluid rheology and the used values of the dimensionless parameters, the velocity, temperature and pressure profiles in the fluid are substantially modified. Also, the finite thermal conductivity of the microchannel wall was considered in the analysis. The dimensionless temperature profiles in the fluid and the microchannel wall are obtained as function of the dimensionless parameters involved in the analysis, and the interactions between the coupled momentum, thermal energy and potential electric equations are examined in detail. A comparison between the numerical predictions and the asymptotic solutions was made, and reasonable agreement was found.

Heat Transfer to Water in Downward Flow in a Uniform Wall Temperature Vertical Tube at Low Graetz Numbers

1977 ◽  
Vol 99 (4) ◽  
pp. 586-589 ◽  
Author(s):  
T. E. Mullin ◽  
E. R. Gerhard
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Experimental Error ◽  
Vertical Tube ◽  
Tube Flow ◽  
Uniform Wall Temperature ◽  
Nusselt Numbers ◽  
A Value ◽  
Uniform Wall ◽  
Convection Parameter

This paper presents an experimental investigation of heat transfer to water in vertical tube flow. Results from both Heating in Upflow and Heating in Downflow with the Natural Convection Parameter (Gr Pr D/L)w held constant at a value of 5.5 × 105 are compared with the expression developed by Martinelli and Boelter. The Nusselt numbers for Heating in Downflow were slightly higher but, within experimental error, equivalent to those values obtained for Heating in Upflow. A description of the flowfield is presented for one set of conditions for Heating in Downflow.

Three-Dimensional Laminar Heat Transfer and Fluid Flow Characteristics in the Entrance Region of a Rhombic Duct

1988 ◽  
Vol 110 (4a) ◽  
pp. 855-861 ◽  
Author(s):  
Y. Asako ◽  
M. Faghri
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Entrance Region ◽  
Perfect Agreement ◽  
Entry Length ◽  
Uniform Wall Temperature ◽  
Uniform Wall ◽  
Fluid Flow Characteristics

A solution methodology is developed to obtain three-dimensional fluid flow and heat transfer characteristics in the entrance region of a rhombic duct. Owing to the complexity of the geometry, the literature results are limited to the fully developed values. The numerical methodology is based on an algebraic coordinate transformation technique, which maps the complex cross section onto a rectangle, coupled with a calculation procedure for three-dimensional parabolic flows, which reduces the problem to a series of two-dimensional problems. The Nusselt number and friction factor results are obtained for boundary conditions of uniform wall heat flux and uniform wall temperature. The asymptotic values of the Nusselt numbers and friction factors approach the available fully developed results. The entry length results for the limiting case of φ = 90 deg are in perfect agreement with the available experimental and numerical results for a rectangular duct.

Laminar Flow Heat Transfer and Pressure Drop Characteristics of Power-Law Fluids Inside Tubes With Varying Width Twisted Tape Inserts

1999 ◽  
Vol 122 (1) ◽  
pp. 143-149 ◽  
Author(s):  
A. G. Patil
Keyword(s):  
Heat Transfer ◽  
Wall Temperature ◽  
Swirl Flow ◽  
Twisted Tape ◽  
Full Width ◽  
Uniform Wall Temperature ◽  
Nusselt Numbers ◽  
Twisted Tapes ◽  
Friction Factors ◽  
Uniform Wall

Results of an experimental investigation of heat transfer and flow friction of a generalized power-law fluid in tape generated swirl flow inside a 25.0 mm i.d. circular tube, are presented. In order to reduce excessive pressure drops associated with full width twisted tapes, with less corresponding reduction in heat transfer coefficients, reduced width twisted tapes of widths ranging from 11.0 to 23.8 mm, which are lower than the tube inside diameter are used. Reduced width twisted tape inserts give 18 percent–56 percent lower isothermal friction factors than the full width tapes. Uniform wall temperature Nusselt numbers decrease only slightly by 5 percent–25 percent, for tape widths of 19.7 and 11.0 mm, respectively. Based on the constant pumping power criterion, the tapes of width 19.7 mm perform more or less like full width tapes. Correlations are presented for isothermal and heating friction factors and Nusselt numbers (under uniform wall temperature condition) for a fully developed laminar swirl flow, which are applicable to full width as well as reduced width twisted tapes, using a modified twist ratio as pitch to width ratio of the tape. The reduced width tapes offer 20 percent–50 percent savings in the tape material as compared to the full width tapes. [S0022-1481(00)01401-8]

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