ABSTRACT
This study introduces a new class of heat transfer fluids by dispersing functionalised graphene oxide nanoparticles (GNPs) in ammonium and phosphonium-based deep eutectic solvents (DESs) without the aid of a surfactant. Different molar ratios of salts and hydrogen bond donors (HBD) were used to synthesise DESs for the preparation of different concentrations of graphene nanofluids (GNFs). The concentrations of GNPs were 0.01 wt%, 0.02 wt% and 0.05 wt %. Homogeneous and stable suspensions of nanofluids were obtained by high speed homogenisation and an ultrasonication process. The stability of the GNFs was determined through visual observation for 4 weeks followed by a centrifugal process (5000-20,000 rpm) for 30 min in addition to zeta potential studies. Dispersion of the GNPs in DES was observed using an optical microscope. The synthesised DES-based GNFs showed no particle agglomeration and formation of sediments in the nanofluids. Thermo-physical properties such as thermal conductivity and specific heat of the nanofluids were also investigated in this research. The highest thermal conductivity enhancement of 177% was observed. The findings of this research provide a new class of engineered fluid for heat transfer applications as a function of temperature, type and composition DESs as well as the GNPs concentration.
ABSTRACT
Pressure-induced amorphous-to-amorphous configuration changes in Ca-Al metallic glasses (MGs) were studied by performing in-situ room-temperature high-pressure x-ray diffraction up to about 40â GPa. Changes in compressibility at about 18â GPa, 15.5â GPa and 7.5â GPa during compression are detected in Ca(80)Al(20), Ca(72.7)Al(27.3), and Ca(66.4)Al(33.6) MGs, respectively, whereas no clear change has been detected in the Ca(50)Al(50) MG. The transfer of s electrons into d orbitals under pressure, reported for the pressure-induced phase transformations in pure polycrystalline Ca, is suggested to explain the observation of an amorphous-to-amorphous configuration change in this Ca-Al MG system. Results presented here show that the pressure induced amorphous-to-amorphous configuration is not limited to f electron-containing MGs.
ABSTRACT
A thin PbTiO(3)-n-p(+) silicon switch diode has been developed, in which the switching voltage (the turned-on voltage) changes in proportion to the infrared light power. The diode has a rapid response time of 0.65 mus compared with other conventional infrared sensors. It is attributed to the rapid switching device structure and the smaller pyroelectric layer thickness, 50 nm. In this paper, we have analyzed the rapid switching transient response by using heat conduction and switching theory successfully. The experimental results are in agreement with the theoretical analysis.
ABSTRACT
Wavelength and temperature-dependent characteristics of silicon P-I-N laser detectors are studied using the modified Baraff theory. Both the electron or hole injection effect and photogeneration effect are considered in the calculation of the power spectral density of multiplication noise and efficiencies. The results thus obtained are compared with previous papers where the photogeneration effect was neglected.
