Liang X.,Changzhou University
Current Nanoscience | Year: 2016
In this review paper, the background and applications of thermoelectrics are first provided. The fundamentals of thermoelectrics which involve a few central physical parameters characterizing the electrical and thermal transport properties are described. The complicit among electrical and thermal conductivity as well as Seebeck coefficient in achieving large thermoelectric figure of merit is then discussed, which suggests nanostructure engineering as an effective approach to lower the lattice thermal conductivity for improved thermoelectric properties. The concept and approach are also demonstrated and discussed with selected examples. ZnO based thermoelectric materials are emphasized, due to the merits of inexpensiveness, earth abundance, chemical and high temperature stability as well as nontoxicity. A few examples of ZnO related oxide systems are briefly reviewed and proposed as useful model systems to investigate and understand the correlations between chemical compositions, phase equilibria, microstructure and thermoelectric properties. The outlook for designing and developing thermoelectric oxides with complex nanostructure is also provided at the end. © 2016 Bentham Science Publishers.
Zhang Y.,Changzhou University
Theoretical and Computational Fluid Dynamics | Year: 2012
A line contact inlet zone analysis is carried out for the hydrodynamic lubrication in a fully plastic asperity contact. A governing equation of the central film thickness i.e. the film thickness in the fully plastic contact area is derived. An equation predicting this film thickness is also derived. It is found that for the fully plastic contact, under relatively light loads the prediction accuracy for the central film thickness is good, while at the load heavy enough the prediction equation greatly overestimates the central film thickness and the central film thickness solved from the analytical governing equation is significantly low showing the asperity in boundary layer lubrication. For the fully plastic contact, the central film thickness is nearly half of that obtained based on the elastic contact assumption for relatively light loads or even lower for heavier loads. The hydrodynamic lubrication is found difficult to form in the fully plastic asperity contact for the carried load heavy enough or the significantly low sliding speed between the asperities. To achieve a high hydrodynamic lubrication film thickness in the fully plastic asperity contact it is recommended to employ a high sliding speed or a high fluid viscosity. However, in the fully plastic asperity contact, the potential hydrodynamic load-carrying capacity is limited and much smaller than that based on the elastic contact assumption or predicted by conventional line contact elasto-hydrodynamic lubrication theory. © Springer-Verlag 2011.
Zhang Y.,Changzhou University
Meccanica | Year: 2014
The present paper proposes three types of the boundary slippage augmentations in hydrodynamic lubricated line contacts for improving the load-carrying capacity but reducing the friction coefficient. One augmentation is at the slower moving contact surface, the second augmentation is at the faster moving contact surface, and the third is at both of the contact surfaces. They are respectively suitable for different operating conditions. The analysis was respectively carried out for the load-carrying capacity and the friction coefficient of hydrodynamic lubricated line contacts augmented with these three types of boundary slippage. The obtained results were compared with those for conventional hydrodynamic lubricated line contacts (without artificial introduction of the boundary slippage) for the same operating conditions. It was shown that in certain operating conditions these three types of the boundary slippage augmentations can respectively significantly increase the load-carrying capacity but reduce the friction coefficient of the contact. The potential application values of the proposed boundary slippage augmentations are evident for reducing the energy loss and the temperature rise as well as for improving the anti-scuffing ability of the contact. © 2013 Springer Science+Business Media Dordrecht.
Zhang Y.,Changzhou University
International Journal of Heat and Mass Transfer | Year: 2016
The flow equation for a fluid confined in a nano channel proposed previously was re-examined by comparison with the molecular dynamics simulation (MDS) results. In themselves, this equation as well as the flow factor for the confined nano fluid flow were finely proven. The comparisons showed good agreements between the calculation results from this equation and the MDS results for both the Couette and Poiseuille flows. © 2015 Elsevier Ltd. All rights reserved.
He Y.,Changzhou University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015
We theoretically investigate a two-cavity optomechanical system in which a cavity (cavity a) couples to a mechanical resonator via radiation pressure and to another cavity (cavity c) via a common waveguide. In the excitation of a strong pump filed to cavity a, the steady-state entanglement between cavity a and c, as a quantum channel, can be generated, which provides an indirect optical pathway to excite cavity c by means of the pump filed. Quantum interference between the direct and indirect optical pathways gives rise to an optomechanically induced transparency appearing in the probe transmission of cavity c. Unlike in a typical optomechanically induced transparency effect, the electromagnetical control of the transmission is implemented by resorting to the quantum channel. Furthermore, the coupling strength of the two cavities is an important factor of the quantum channel, which can influence the width of the transparency window and the bistable behavior of the mean photon number in cavity a. We also illustrate that the electromagnetical control via quantum channel can be exploited to implement the optical switch and the slow light. © 2015 American Physical Society.