# Fabrication and calibration of micro temperature sensors on silicon for measurement of surface temperature during nucleate pool boiling in dielectric liquid

#### Abstract

The objective of this new experimental investigation was to measure surface temperature variation and bubble departure frequency during boiling heat transfer in a dielectric liquid. The research consisted of two parts: fabrication of micro temperature sensors, and utilization of these instruments to measure temporal and spatial surface temperature during pool boiling. Using semiconductor fabrication technologies, a high density of micro temperature sensors was fabricated directly on silicon heat transfer surfaces. The 1.27cm square silicon surfaces were instrumented with eighty-one micro sensors, each 12$\mu$m x 24$\mu$m in size. These micro sensors were the smallest, and the number density on the surfaces was the largest ever fabricated in the known literature. A large number of square based inverted pyramids, 10$\mu$m across and 7.1$\mu$m deep, were etched into the $<$100$>$ silicon surfaces, to serve as potential nucleation sites. The number of inverted pyramids ranged from 0 to 41,616 per surface. Micro sensors were successfully fabricated on the non-planar walls of these inverted pyramids. Two sensor types were fabricated, a silicon resistance thermometer detector and a silicon diode. These micro sensors were capable of measuring a constant temperature to within 0.05$\sp\circ$C and had a measured transient time constant of less than 1 msec.^ Using these micro sensors, new heat transfer measurements are presented. Local surface temperature measurements were made during saturated pool boiling from vertical silicon surfaces in FC-72, a dielectric liquid. Vertical spatial variation in surface temperature was measured, from high temperature at the leading edge to low temperature at the trailing edge. The difference in surface superheat between the leading and trailing edges was up to 50% of the average wall superheat. This significant result indicates that rising bubbles cool the trailing edge. Although vertical boiling surfaces have been used extensively in research and industry, this trailing edge cooling effect had never been measured.^ Surface temperature measurements at an active nucleation site indicate that bubble growth and departure caused only a small periodic temperature perturbation on the average value. The local surface temperature fluctuated only 0.5 to 1.5$\sp\circ$C as bubbles grew and departed from silicon substrates. Using spectral techniques to analyze the surface temperature data, bubble departure frequencies were measured, ranging from 23 to 35Hz. The bubble departure frequencies were insensitive to heat flux in the measured range of 3.6 to 9.5 W/cm$\sp2.$ Cross correlation between neighboring sensors indicated periodic components of bubble growth were detected predominantly in the vertical bubble flow direction. ^

#### Subject Area

Engineering, Electronics and Electrical|Physics, Condensed Matter

#### Recommended Citation

William John Miller, "Fabrication and calibration of micro temperature sensors on silicon for measurement of surface temperature during nucleate pool boiling in dielectric liquid" (January 1, 1996). Dissertations available from ProQuest. Paper AAI9627966.
http://repository.upenn.edu/dissertations/AAI9627966

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