Showing papers by "Bao Yang published in 2008"

Synthesis and thermal characterization of phase-changeable indium/polyalphaolefin nanofluids

Abstract: Previous research on nanofluids has primarily focused on how to increase thermal conductivity of the fluids. Here, the use of phase change materials as nanoparticles in nanofluids has been proposed to simultaneously enhance the effective thermal conductivity and specific heat of the fluids. As an example, a suspension of indium nanoparticles (melting temperature, 157°C) in polyalphaolefin has been synthesized using a one-step, nanoemulsification method. The fluid’s thermophysical properties, i.e., thermal conductivity, viscosity, and specific heat, and their temperature dependence have been investigated experimentally. The observed melting-freezing phase transition of the indium nanoparticles would considerably augment the fluid’s effective specific heat.

Thermal Conductivity Equations Based on Brownian Motion in Suspensions of Nanoparticles (Nanofluids)

Abstract: Thermal conductivity equations for the suspension of nanoparticles (nanofluids) have been derived from the kinetic theory of particles under relaxation time approximations. These equations, which take into account the microconvection caused by the particle Brownian motion, can be used to evaluate the contribution of particle Brownian motion to thermal transport in nanofluids. The relaxation time of the particle Brownian motion is found to be significantly affected by the long-time tail in Brownian motion, which indicates a surprising persistence of particle velocity. The long-time tail in Brownian motion could play a significant role in the enhanced thermal conductivity in nanofluids, as suggested by the comparison between the theoretical results and the experimental data for the Al 2 O 3 -in-water nanofluids.

Review Article: Thermoelectric Technology Assessment: Application to Air Conditioning and Refrigeration

Abstract: A combination of factors—notably environmental concerns about global warming and ozone depletion due to refrigerants and the increasing demand for electronics and optoelectronic cooling—led to renewed activity in alternative cooling technologies. Currently, thermoelectric cooling is considered a popular cooling technology. This paper provides a critical review of thermoelectric technology and assesses its potential applications in air conditioning and refrigeration. The first part of this paper is devoted to the basic concept of thermoelectrics, with an overview of current thermoelectric materials and devices. The second part is a general overview of the applications of thermoelectric technology, with an emphasis on those related to air conditioning and refrigeration.

A Numerical Method for Solving Nonlinear Heat Transfer Equations

Abstract: Heat transfer problems are usually governed by nonlinear differential equations, which, after discretization, result in a set of algebraic and transcendental equations with the nonlinearity retained. In the present study, a numerical method for solving such equations is proposed. The primary interest of the present study focuses on situations where the traditional Newton-Raphson method fails to converge. The proposed method combines (1) the Newton-Raphson method, (2) the continuation method, and (3) perturbations of diagonal elements in the Jacobian matrices. When (3) is needed, it is possible to examine the magnitudes of diagonal elements, or those of eigenvalues of Jacobian matrices, for some guidance toward the choice of perturbations. The Burgers' transient flow problem and a problem of transient two-dimensional heat conduction with nonlinear heat generation are solved to illustrate the proposed method. Some initial guesses led to situations in which a combination of all three methods must be used joi...

Damage behaviors of fiber Bragg grating sensor in fabrication

Abstract: It is has been noted that for fiber Bragg grating sensor (FBGS), the tensile strengths of fiber Bragg grating sensors (FBGSs) were decreased after the gratings were written, which may reduce the sensor's measurement range obviously. In this paper, we focused on the damage behaviours of FBGS after fabrication experimentally. Firstly, the tensile tests were carried to measure the tensile strengths of naked optical fiber, decoated optical fiber and optical fiber with Bragg gratings to learn deduction of the tensile strength of optical fiber in the cases respectively. Further, the microscope photography was used to observe the surfaces of optical fiber with or without exposure of excimer laser. The main conclusion is that the UV pulse is the main contribution to reduce the strength remarkably, and the mechanical decoating method also can induce the surface damage on the optical fiber.