Numerical modeling of Joule heating‐induced temperature gradient focusing in microfluidic channels

Abstract

Temperature gradient focusing (TGF) is a recently developed technique for spatially focusing and separating ionic analytes in microchannels. The temperature gradient required for TGF can be generated either by an imposed temperature gradient or by Joule heating resulting from an applied electric field that also drives the flow. In this study, a comprehensive numerical model describing the Joule heating induced temperature development and TGF is developed. The model consists of a set of governing equations including the Poisson-Boltzmann equation, the Laplace equation, the Navier-Stokes equations, the energy equations and the mass transport equation. As the thermophysical and electrical properties including the liquid dielectric constant, viscosity, and electric conductivity are temperature-dependent, these governing equations are coupled, and therefore the coupled governing equations are solved numerically by using a CFD-based numerical method. The numerical simulations agree well with the experimental results, suggesting the valid mathematical model presented in this study.

Recent developments in electrophoretic separations on microfluidic devices

“…In these articles, the separation channel had a change in width at one location. Tang and Yang numerically demonstrated this phenomenon in a PDMS microfluidic device [6]. When the channel narrowed, the heat density increased in the presence of applied potential, which caused an increase in the temperature in the narrow part of the channel.…”

“…Although TGF commonly utilizes external physical heating or cooling of the capillary, there have also been reports of using Joule heating to induce a temperature gradient [6,7]. In these articles, the separation channel had a change in width at one location.…”

“…Various processes, such as FFE, are well known on the preparative-scale, whereas others, such as IEF, have been well characterized for analytical-scale separations. There have been many innovative areas of development on the smaller scale, including taking advantage of hydrodynamic counterflow [6,7], different channel designs [8], and applying electric fields perpendicular to the flow of the sample [9][10][11][12][13].…”

Bioanalytical separations using electric field gradient techniques

“…Joule heating as a means of generating a temperature gradient, as opposed to an external source, was modeled by various groups [87,89]. Joule heating occurs when an electric field is applied along the length of a conducting medium [97].…”

Microchip isoelectric focusing with monolithic immobilized pH gradient materials for proteins separation

“…Therefore, the establishment of stable pH gradient without mobile CAs in the running buffer has been paid much attention. Several methods, such as diffusion of OH À and H 1 between anode and cathode [16][17], Joule heat-induced temperature gradient [18][19][20] and spatially varied surface electric field [21], have been developed. However, the stability of formed pH gradient should be further improved.…”