Non-intrusive temperature measurement using microscale visualization techniques

Pramod Chamarthy, Purdue University

Abstract

Two non-intrusive temperature measurement techniques which utilize microscale visualization techniques are developed and evaluated. A PIV-based thermometry technique is developed to simultaneously measure the temperature and velocity of the fluid for low speed flows. Laser induced fluorescence thermometry is investigated to measure the temperature of the fluid for higher speed flows. μPIV is a widely accepted tool for making accurate velocity measurements in microscale flows. The particles that are used to seed the flow, due to their small size, undergo Brownian motion which contains valuable temperature information. A PIV algorithm which detects both the location and broadening of the correlation peak can measure velocity as well as temperature simultaneously using the same set of images. The approach presented in this work eliminates the use of the calibration constant employed in the literature (Hohreiter et al. 2002), making the method system-independent, and reducing the uncertainty involved in the technique. The temperature in a stationary fluid was experimentally measured using this technique and compared to that obtained using the particle tracking thermometry method (PTT) and a novel method, low image density PIV (LID-PIV). The method of cross-correlation PIV was modified to measure the temperature of a moving fluid. A standard epi-fluorescence μPIV system was used for all the measurements. The experiments were conducted using spherical fluorescent polystyrene-latex particles suspended in water. Temperatures ranging from 20°C–80°C were measured. This method allows simultaneous non-intrusive temperature and velocity measurements for low-speed flows in lab-on-a-chip devices. Ratiometric Laser Induced Fluorescence (LIF) Thermometry is applied for temperature measurements using microscale visualization methods. Rhodamine B (RhB) and Rhodamine 110 (Rh110) are used as the temperature-dependent and temperature-independent dyes, respectively. The temperature responses of the two dyes were carefully measured for different concentrations. A novel normalization procedure which only requires a single dye is proposed to reduce the uncertainty and render the technique system-independent. The capabilities of this method are demonstrated by visualizing the mixing plane between a hot and a cold fluid stream neat a ‘T’ junction. The method is then applied to study the non-uniform temperature profiles generated due to flow maldistribution in a silicon microchannel heat sink. The experimental results illustrate the importance of proper design of inlet and outlet manifolds to maximize the performance of a microchannel heat sink. The technique is demonstrated to have a maximum uncertainty of ±1.25°C for single pixel measurements and a minimum uncertainty of ±0.6°C for measurements averaged over a large area for a temperature range of 20°C to 50°C.

Degree

Ph.D.

Advisors

Garimella, Purdue University.

Subject Area

Mechanical engineering

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