Spatially resolved temperature measurement in microchannels

Abstract

Non-intrusive local temperature measurement in convective microchannel flows using infrared (IR) thermography is presented. This technique can be used to determine local temperatures of the visualized channel wall or liquid temperature near this wall in IRtransparent heat sinks. The technique is demonstrated on water flow through a silicon (Si) microchannel. A high value of a combined liquid emissivity and substrate overall transmittance coupled with a low uncertainty in estimating this factor is important for quantitative temperature measurement using IR thermography. The test section design, and experimental and data analysis procedures that provide increased sensitivity of the detected intensity to the desired temperature are discussed. Experiments are performed on a 13-mm long, 50 lm wide by 135 lm deep Si microchannel at a constant heat input to the heat sink surface for flow rates between 0.6 and 1.2 g min À1 . Uncertainty in fluid temperature varies from a minimum of 0.60°C for a Reynolds number (Re) of 297 to a maximum of 1.33°C for a Re of 251. Keywords Microchannels AE Microscale heat transfer AE Infrared thermography AE Spatially resolved AE Temperature measurement AE Single-phase flows List of symbols a absorption coefficient (cm À1 ) D h channel hydraulic diameter (m) e radiant energy flux (W m À2 ) G radiant flux incident on the heat sink (W m À2 ) H height of the channel (m) h local heat transfer coefficient (W m À2 K À1 ) i location index in channel direction (x direction) j location index in a cross-direction to channel (y direction) i¢ location index in detector array corresponding to i j¢ location index in detector array corresponding to j _ m mass flow rate (kg s À1 ) n refractive index Nu Nusselt number ðNu ¼ h D h =kÞ (dimensionless) q¢¢ heat flux to the heat sink (W m À2 ) Re Reynolds number ðRe ¼ V D h =mÞ (dimensionless) " R total reflectance S radiation path length (m) t thickness of the medium (cm) T f fluid temperature (°C) V channel mean velocity (m s À1 ) W width of the channel (m) x i distance of position i from the channel entrance (m) Greek symbols D incremental value e emissivity k wavelength l dynamic viscosity of fluid (Pa s) m kinematic viscosity of fluid (m 2 s À1 ) q surface reflectivity s f transmittance of water Superscripts and subscripts b blackbody cal calibration det detector e emission f fluid hsb heat sink background lens camera lens sens sensed Si Silicon

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

“…Non-intrusive local temperature measurement in convective micro-channel flows using IR thermography is presented by Patil and Narayanan [21].…”

“…The paper by Patil and Narayanan [21] discusses the theory and procedure of the measurement of the liquid temperature of an Table 4.…”

“…They explained a low rate of oscillations by the slow processes of the periodic wetting and dryout. Patil and Narayanan [21] presented an uncertainty analysis of a temperature measurement in convective micro-channel flows using IR. This technique was used to determine both the local temperatures of the visualized channel wall and the liquid temperature near this wall in IR partially transparent heat sinks.…”

“…Uncertainties in measured and estimated variables (Patil and Narayanan[21]). Based on deviation from a 50  135 lm rectangular geometry Channel cross-section 2.0% Based on deviation from a 50  135 lm rectangular geometry D h (mm) 135 mm 2 (2.0%) Based on wetted perimeter and channel cross-section Camera spatial resolution (mm) Mass flow rate-_ m (g s À1 ) Water radiation flux leaving the heat sink-C3 f T Si Surface temperature-T sur ( C) 10 2.3% (Re ¼ 297) to 4.0% (Re ¼ 204) 0.26% 0.15 Calibrated using a set flow rate from a syringe pump; data averaged over 20 min Includes bias and precision errors in intensity and calibration error in thermocouple used for fluid temperature measurement Calibration error of thermocouple Estimated variable T f ( C) 0.91 (Re ¼ 204) Based on measurements 1.33 (Re ¼ 251) 1.04 (Re ¼ 285) 0.60 (Re ¼ 297) Re 3.3% (Re ¼ 297) to 4.7% (Re ¼ 204) Includes uncertainty in geometry and flow rate opaque fluid near the channel wall for transparent channel walls.…”

Joule heating effects and the experimental determination of temperature during CE

“…The fluorescent probe (fluorescein) was Figure 7. Experimental set-up for infrared thermography on a microfluidic electrophoresis device [81]. With kind permission from Springer Science1Business Media, Fig.…”