No abstract

An experimental investigation of heat transfer from a small heated patch to a subcooled, fully developed turbulent flow is conducted. The test patch, approximately 0.25 mm long and 2.0 mm wide, is located on the floor of a small rectangular channel through which a coolant (R-113 or FC-72) is circulated. A thin film of Nichrome deposited on a quartz substrate serves as an integrated heater element and resistance thermometer. The maximum achievable heat flux with R-113, limited by the thermal decomposition temperature of the fluid, is 2.04 MW/m2 at a bulk velocity of 1.8 m/s and a high wall superheat of 80° C. The results obtained with FC-72 show large temperature excursions at the onset of nucleate boiling and a boiling hysteresis near the onset of nucleate boiling. These effects decrease with increasing velocity and/or subcooling. The heat flux at departure from nucleate boiling increases with increasing velocity and/or subcooling. A maximum heat flux of 4.26 MW/m2 at departure from nucleate boiling is observed.

A new technique using nickel-chromium wire, called the NiCr (Nichrome R ) wire technique, has been presented in a rst paper describing the technique [1]. This second paper focuses on the results obtained when this new technique is applied to ballistic fabrics. Strain distributions on the layer impacted, as well as in dierent layers, are presented. An energy balance based on the strains is shown to provide reasonable values for the elastic energy stored by the yarns. Failure times of the rst layer as a function of impact velocity are discussed and a simple momentum balance is shown to predict well the deection history of the fabric. Ultra-high-speed photography and high-speed videos allowed recording of fabric deection vs. time.The combination of the four diagnostic techniques, including X-rays, delivers a very complete picture of the impact mechanics in fabrics, both for early-time and latetime phenomena.