Temperature modeling and measurement of an electrokinetic separation chip

Abstract

This work presents experimental [infrared (IR) thermography] and computational (finite element model) results of temperature distributions of an electrokinetic separation chip. Thermal characteristics of both the electrolyte solution and the polymer chip (SU-8) are taken into account in modeling temperature distributions during electrokinetic flow. Multiphysics and multiscale simulation couples electrostatics, heat transfer, and fluid dynamics. The accompanying IR thermography is a non-contact method, which can measure fractional temperature differences with sub-second time resolution. Any structures or temperature marker molecules interfering with the experiment are not needed. Nominal spot size in the IR measurements is 30 lm with a field of view of several millimeters enabling both local and chip-scale temperature monitoring simultaneously. As a result, we present a computer model for electrokinetic chips, which enables simulation of fractional temperature changes during electrophoresis under real operating conditions. The accuracy of the model is within ±1°C when the deviation in electrochemical processes is taken into account. The simulation results also suggest that the temperature on the chip surface qualitatively reflects the temperature inside the microchannel with an average offset of 1-2°C.

Infrared temperature measurements in micro-channels and micro-fluid systems

“…The problems include accurate characterization of IR system performance and its calibration; the use optics to increase the spatial resolution; the choice of the most appropriate heat flux sensor and its characterization especially with regard to the lateral thermal conduction effects etc. (Astarita et al [7]; Carlomagno and de Luca [8]; Sikanen et al [14]). Here, we consider effects of the radiation losses, the body surface emissivity and the correct geometrical identification of the measured points.…”

“…Temperature monitoring can be a way of detecting chemical and biochemical reactions inducing heat and for controlling thermal conditions in chemical analyses such as the micro-polymerase chain reaction (PSR), nebulizer chips (Franssila et al [25]), and electrophoretic separation chips (Sikanen et al [14]). Temperature monitoring of small amounts of liquid in micro-chemical chips or micro-fluidic chips is being needed in expanding applications of micro-total analysis systems (m-TAS) (Dittrich et al [35]).…”

“…Numerical modeling in combination with a non-contact temperature monitoring method, IR thermography, was used by Sikanen et al [14] to examine electrolyte heating as well as heat transfer properties of a polymer chip under real electrophoresis conditions.…”

“…In his review of single-and two-phase micro-channel flows, Palm [9] suggested that heat transfer results of various single-phase flow studies were contradictory, with both high and low Nusselt numbers, Nu, reported for laminar flows. Sikanen et al [14] presented experimental IR and computational (finite element model) results of temperature distributions of an electrokinetic separation chip. Discrepancies between measurements were attributed to the difficulties in measuring fluid and surface temperatures in micro-channels.…”

Joule heating effects and the experimental determination of temperature during CE

“…Recently Sikanen et al [80] employed this technique (see Fig. 7) to measure electrolyte temperature and the temperature distribution on the surface of a microfluidic chip used for electrophoresis at an acquisition rate of 50 Hz.…”