POOL BOILING OF N-PENTANE, CFC-113, AND WATER UNDER REDUCED GRAVITY -PARABOLIC FLIGHT EXPERIMENTS WITH A TRANSPARENT HEATER

A series of pool boiling experiments have been conducted under reduced gravity condition (the order of 10(-2) times the terrestrial gravity) available in an aircraft taking parabolic flight. A transparent resis tant heater, a transparent indium oxide film plated on a glass plate, was employed so that the vapor/liquid behavior interacting with the he ater surface could be observed from the rear side of the heater simult aneously with the side view of vapor bubbles above the heater surface. The experiments were performed for three different fluids-n-pentane, CFC-113, and water-under subcooled conditions. The critical heat fluxe s for both n-pentane and CFC-113 under the reduced gravity were lowere d to about 40 percent of the corresponding terrestrial values. Althoug h the heat transfer characteristics in a low heat flux nucleate boilin g regime for both n-pentane and CFC-113 showed no more than a slight c hange with the reduction in gravity, a significant heat transfer deter ioration was noted with water in the reduced gravity boiling. The obse rvation from the rear side of the heater suggested that this particula r difference in the gravity dependency of heat transfer was ascribed t o a considerable difference, between the organic fluids and water, in the behavior of attachment to the heater surface of the bubbles grown up, while the behavior of attachment must depend on the surface tensio n of each fluid and the wettability of the heater surface with the flu id.