Microscale heat transfer to subcooled water: 200-6,000psia, 0-3,500W/cm2.

Abstract

Exciting heat transfer phenomena have been discovered with a micron-sized heat transfer element operating in subcooled (20 degrees C) degassed, demineralized water over a wide pressure range (200-6,000psia) at heat fluxes up to 3,500W/cm2. The platinum heat transfer element (diameter 7.5 microns, length 1.14mm) is installed within a one-cm3 stainless steel chamber. Sealed electrical terminals penetrate the chamber to effect direct current heating of the platinum element. Pressure is applied pneumatically. The adiabatic heating rate of the element is 6 degrees C per microsecond at 3,700W/cm2; response is essentially instantaneous for the procedure described herein. The direct current voltage and current are measured from which the power and the resistance (temperature) are determined. The following procedure applies: (1) Pressurize the water-filled stainless steel chamber to 6,000psia. (2) Apply power at 3,000W/cm2. (3) Maintain constant heat flux as pressure is smoothly reduced from 6,000psia to 200psia over a period of 20 seconds. Record voltage, amperage, and pressure at 0.1 second intervals. Heat transfer phenomena thus discovered: (1) Element starting temperature of 370 degrees C at 6,000psia smoothly increased to 380 degrees as pressure was reduced to 3,970psia. (2) At 3,970psia the temperature abruptly stepped upward to 590 degrees C. (3) Temperature smoothly increased to 730 degrees C as pressure was reduced to 3,230psia. (4) In the vicinity of the critical pressure, the temperature turned around and began smoothly decreasing. (5) At 2,350psia, the temperature stepped down from 520 to 350 degrees C. (6) Temperature smoothly decreased to 230 degrees C at 190psia and power was then turned off. Bulk water temperature increased less than 4 degrees C. Controlled gravity (KC-135) tests are planned.