David T.W. Lin

Natural convection heat and mass transfer in vertical annuli with film evaporation and condensation

A numerical study of natural convection heat and mass transfer with film evaporation and condensation in vertical concentric annular ducts is performed. The emphasis is focused on the eAects of the film evaporation and condensation along the wetted walls on the heat and mass transfer in vertical annuli. The numerical results, including the velocity, temperature and concentration profiles, local Nusselt and Sherwood numbers and induced volume flow rate are presented for air‐water vapor system under diAerent wall temperature T1 and ratio of radii k. The results show that tremendous enhancement in heat transfer due to the exchange of latent heat in association with film evaporation and condensation was found. In addition, the extent of augmentation of heat transfer due to mass transfer is more significant for a system with a higher wetted wall temperature T1. ” 2001 Elsevier Science Ltd. All rights reserved.

Optimization of Thermal Management by Integration of an SCGM, a Finite-Element Method, and an Experiment on a High-Power LED Array

This paper proposes an original idea to minimize heat concentrations of high-power light-emitting diode (LED) arrays. The purpose of this paper is to investigate temperature distribution with and without an optimal process of high-power LED arrays by experiment and a numerical method in order to achieve an optimal design of LED arrays for thermal management. This paper develops an effective method to design each LED position for decreasing thermal concentrations in high-power LED arrays. In this paper, temperature profiles are measured by a thermal infrared camera and a thermocouple and compared with simulated results under different power. The optimal method is adopted by a simplified conjugate gradient method combined with a finite-element method. This method proves reliability of simulated results in advance. Through this optimal method, efficiency of heat removal will be enforced as an extra cooling device is added. The important part is that this optimal design will not affect brightness through an illumination analysis.

Mixed convection heat transfer in a radially rotatingsquare duct with radiation effects

Abstract The interaction of thermal radiation with laminar mixed convection for a gray fluid ina radially rotating square duct is numerically studied. The integro-differential radiative transferequation is solved by the discrete ordinates method. The coupled momentum and energyequations are solved by the DuFort–Frankel numerical scheme. Results are presented in a radiallyrotating square duct over a wide range of the governing parameters. The effects ofrotation-induced buoyancy and thermal radiation on the developments of velocity, temperature,friction factor and Nusselt number are examined in detail. The axial variations of the fRe and Nu are characterized by a decay near the entrance due to the entrance effect, but thedecay is attenuated by the onset of the secondary flow. The predictions also demonstrate that theradiation presents significant effects on the axial distributions of the total Nusselt number Nu t and tends to reduce the centrifugal buoyancy effects. In addition, the heattransfer rate increases with the decrease in the conduction-to-radiation parameter N c .

Experimental study of unsteady thermal convection in heated rotating inclined cylinders

An experimental study through temperature measurements was conducted to investigate the thermal characteristics induced by the interaction between the thermal buoyancy and rotation-induced Coriolis force and centrifugal force in an air-filled heated inclined cylinder rotating about its axis. Results were obtained for the following ranges of the governing groups: thermal Rayleigh number Raa 2:3 10 6 and 4.6 10 6 , Taylor number 0RTaR2:2 10 10 , rotational Rayleigh number 0RRaOR5:9 10 8 and inclined angle 0RCR908: The experimental data suggested that when the cylinder is stationary, the thermal buoyancy driven flow is random oscillation at small amplitude after initial transient for inclined angle C< 608: Rotating the cylinder was found to destabilize the temperature field when the rotation speed O is less than 30 rpm and to stabilize it when the O exceeds 30 rpm. Additionally, the distributions of time-average temperature yav in the Z-direction for various inclined angles become

The Optimization of the Thermal Response on the ZnO Flexible Pyroelectric Film Temperature Sensor

In a previous study, the present group designed and fabricated ZnO thin-film pyroelectric sensors with four different upper electrode configurations, namely rectangular, criss-cross, target and web. However, the voltage response of the proposed devices was not formally analyzed. Accordingly, the present study commences by performing an experimental investigation to determine the voltage-temperature transfer function for one of the four electrode configurations (i.e., rectangular). An optimization algorithm based on the simplified conjugate gradient method (SCGM) and COMSOL finite-element analysis software is then applied to establish the optimal geometry parameters of each of the four upper electrode configurations. It is shown that the optimized electrode designs improve the temperature variation rate of the four sensors by a minimum of 15%. As a result, the responsivity of the proposed devices is significantly improved.

A Closed Form Solution for the Pull-in Voltage of the Micro Bridge with Initial Stress subjected to Electrostatic Loads

This paper derives a closed form solution with fringing filed effects for the pull-in voltages of the micro fixed-fixed beam subjected to electrostatic loads and initial stress. The closed form solution is derived based on the Eulers beam theory and the energy method. The accuracy of the present closed form solution is verified through comparing with the experimentally measured data conducted in the published works. The error of the present closed form solution is within 1% compared to the experimentally measured data. The present closed form solution is more accurate than the past works and is very simple and highly accurate for implementation in the design and mechanical characterization of the micro devices.

Bifurcation analysis of a microcantilever in AFM system

The atomic force microscope system (AFM) has become a popular and useful instrument to measure the intermolecular forces with atomic resolution that can be applied in electronics, biological analysis, materials, semiconductors, etc. This paper studies the bifurcation phenomenon and complex nonlinear dynamic behavior of the probe tip between the sample and microcantilever of an atomic force microscope using the differential transformation method. The dynamic behavior of the probe tip is characterized with reference to bifurcation diagrams, phase portraits, power spectra, Poincare maps, and maximum Lyapunov exponent plots produced using the time-series data obtained from differential transformation method. The results indicate that the probe tip behavior is significantly dependent on the magnitude of the vibrational amplitude. Specifically, the probe tip motion changes from T-periodic to 3T-periodic, then from 6T-periodic to multi-periodic, and finally to chaotic motion with windows of periodic motion as the vibrational amplitude is increased from 0 to 5.0. Furthermore, it is demonstrated that the differential transformation method is in good agreement for the considered system.

Estimating the Wall Heat Flux of Unsteady Conjugated Forced Convection Between Two Corotating Disks Using an Inverse Solution Scheme

An inverse solution scheme based on the conjugate gradient method with the minimization of the object function is presented for estimating the unknown wall heat flux of conjugated forced convection flows between two corotating disks from temperature measurements acquired within the flow field. The validity of the proposed approach is demonstrated via the estimation of three time- and space-dependent heat flux profiles. A good agreement is observed between the estimated results and the exact solution in every case. In general, the accuracy of the estimated results is found to improve as the temperature sensors are moved closer to the unknown boundary surface and the error in the measured temperature data is reduced. DOI: 10.1115/1.2976788

Development of an Novel Adaptive Suspension System Based on Ball-Screw Mechanism

For the passive and semi-active suspensions are characterized as with constant parameters which cannot cope with time-variant road conditions, the suspension results are difficult to be satisfied. Although, the active ones are better than previous two on suspension performance, until now which are still far from real application for the drawbacks of complicated structure, large volume, costly, and difficult maintenance. Here, Ball Screw (BS) is with the characteristics of smaller volume, precise positioning, and well handling high-speed forward and backward transmissions. Instead of hydraulic or pneumatic mechanisms used for vehicle suspension, BS is adopted to be the main body of the proposed New Adaptive Suspension System (NASS). Besides, in order to overcome the unavoidable time-delay resulted from mechanical or computational operations, the Kalman filter, integrated with suspension controller, is used to estimate the road conditions. The effectiveness and feasibility of this proposal are confirmed through simulation studies.

A Solution Processed ZnO Thin Film

The effect of Zinc-Oxide (ZnO) thin film annealed in different ambiences is presented. To achieve low cost and environmentally friendly process, ZnO aqueous solution is synthesized by dissolving zinc acetate dihydrate in deionized water directly. Zinc oxide aqueous solution of high solubility and stability is presented. High quality and dense Zinc oxide thin film is formed by spin coating. Annealing temperatures are in the range of 300 °C~500 °C, and annealing ambiences of both air and N2 are discussed.