Enhanced convective heat transfer using graphene dispersed nanofluids

Nanofluids are having wide area of application in electronic and cooling industry. In the present work, hydrogen exfoliated graphene (HEG) dispersed deionized (DI) water, and ethylene glycol (EG) based nanofluids were developed. Further, thermal conductivity and heat transfer properties of these nanofluids were systematically investigated. HEG was synthesized by exfoliating graphite oxide in H2 atmosphere at 200°C. The nanofluids were prepared by dispersing functionalized HEG (f-HEG) in DI water and EG without the use of any surfactant. HEG and f-HEG were characterized by powder X-ray diffractometry, electron microscopy, Raman and FTIR spectroscopy. Thermal and electrical conductivities of f-HEG dispersed DI water and EG based nanofluids were measured for different volume fractions and at different temperatures. A 0.05% volume fraction of f-HEG dispersed DI water based nanofluid shows an enhancement in thermal conductivity of about 16% at 25°C and 75% at 50°C. The enhancement in Nusselts number for these nanofluids is more than that of thermal conductivity

Ultrasonic Assessment of Microcrack Damage in Ceramics

The inherent brittleness of ceramics often results in catastrophic failure due to microcrack damage caused by thermal treatment or mechanical loading. Extensive theoretical and experimental studies have been performed to analyze microcrack damage in ceramics caused by thermal shock [1–7]. Hasselman [1,2] proposed a simple model describing the strength behavior of ceramic materials as a function of thermal shock temperature difference ΔT. The important characteristic parameter in this model is the critical temperature difference, ΔT c . For thermal shock temperature differences less than ΔT c (stage I, Fig. 1) ceramics retain their strength. Thermal shocks with temperature differences equal to ΔT c (stage II) are characterized by unstable crack propagation and instantaneous decreases in strength. Above ΔT c is a plateau of constant strength (stage III), where cracks are subcritical and gradual decrease in strength is observed at higher thermal shock temperatures (stage IV). As shown experimentally [3,6], the actual behavior depends on the composition and the microstructure of the material