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TECHNICAL PAPERS: Evaporation, Boiling, and Condensation

Spatially and Temporally Resolved Temperature Measurements for Slow Evaporating Sessile Drops Heated by a Microfabricated Heater Array

[+] Author and Article Information
S. W. Paik

Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843

K. D. Kihm1

Department of Mechanical, Aerospace and Biomedical Engineering, University of Tennessee, Knoxville, TN 37996kkihm@utk.edu

S. P. Lee

Department of Mechanical Engineering, Kyonggi University, Suwon, Korea

D. M. Pratt

AFRL/VAS, Wright-Patterson Air Force Base, Dayton, OH 45433

Sixteen concentric zones are used for the actual tomographic conversion calculations, whereas only eight of the zones are presented in Fig. 8 for simplicity.

In the 100-point moving average technique, the first 100 data samples are averaged to determine the first data point value. Then, the next 100 data samples (i.e., from data sample No. 2 to data sample No. 101) are averaged to determine the second data point value. This technique was used the tomographic deconvolution.

1

Corresponding author.

J. Heat Transfer 129(8), 966-976 (Oct 27, 2006) (11 pages) doi:10.1115/1.2728904 History: Received October 05, 2005; Revised October 27, 2006

The spatially and temporally resolved evaporation phenomena of a slowly evaporating water droplet are investigated using a microfabricated gold heater array consisting of 32 linear heater elements (100 μm wide and 15 mm long, each). Each of the gold microheater elements works both as a temperature sensor and as a heater. The experiment is performed under a constant voltage mode to examine the spatially resolved temperature history of the droplet contact surface for a period starting at initial contact with the heater and lasting to the point of complete dryout. The raw data obtained from the linear array have been tomographically deconvolved so that the radial temperature profile can be determined assuming a circular droplet contact surface.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Three-layered microheater design by AutoCAD

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Figure 2

Schematic illustration of the fabrication process for the three layers: the seed layer (a), (b) the heater layer (c)–(f) and the wiring layer (g)–(j) subprocesses

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Figure 3

Seed layer removal and opening layer fabrication procedure

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Figure 4

Schematic illustration of the constant-voltage supply circuit for the microheater array

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Figure 5

Sequential images of slowly evaporating water droplets on the microheater array at Th=60°C

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Figure 6

Nondimensionalized radius variation with nondimensionalized evaporation time on epoxy surface and open chamber

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Figure 7

Comparison of the measured dry-out times with the calculated dry-out times based on the Buckingham-Pi regression analysis for three different tested droplet sizes contacting three different heater surface temperatures

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Figure 8

Tomographic deconvolved temperature zones: (a) eight zone tomographic deconvolved heater area and (b) zone reconstruction for temperature calculation with electric resistance

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Figure 9

Temperature variation of droplet center on the microheater (for 10μL data, both of them are 100 data, moving average method was used)

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Figure 10

Microheater temperature drop by the water droplet evaporation with tomographically deconvolved 16 zone model at 80°C: (a) t∕τ=0.01; (b) t∕τ=0.1; (c) t∕τ=0.5; (d) t∕τ=0.9; (e) t∕τ=1.1; and (f) t∕τ=2.0 (τ=dry-out time)

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Figure 11

The center point temperature drop and recovery history: (a) 40°C; (b) 60°C; and (c) 80°C

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Figure 12

Temporal temperature variation of microheater at several positions of r∕r0 for Th=80°C, 10μL (evaporation started at 30.76s, ended at 172.99s)

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