Graduation date: 1975

A unique channel surface enhancement technique via diffusion-bonding a layer of conductive fine wire mesh onto the heating wall was developed and used to experimentally study flow boiling enhancement in parallel microchannels. Each channel was 1000 μm wide and 510 μm high. A dielectric working fluid, HFE 7000, was used during the study. Two fine meshes as well as two mesh materials were investigated and compared. According to the flow boiling curves for each channel, the amount of wall superheat was greatly reduced for all the mesh channels at four stream-wise locations; and the critical heat fluxes (CHF) for mesh channels were significantly higher than that for a bare channel in the low vapor quality region. According to the plots of local flow boiling heat transfer coefficient h versus vapor quality, a consistent increasing trend for h with vapor quality was observed for all the tested channels until the vapor quality reached approximately 0.4. However, the three mesh channels showed much higher values of h than the bare channel, with the 100 mesh copper performing the best. Visualization using a high-speed camera was performed thereafter to provide some insights to this enhancement mechanism. A significant increase in nucleation sites and bubble generation was observed, and departure rates inside the mesh channels were attributed to the flow boiling enhancement. A sudden increase of h for mesh channels can also be attributed to the characteristics of nucleate boiling and indicates that nucleate boiling was the dominant heat transfer mode. Another interesting point observed was that the 100 mesh bronze outperformed the 200 mesh bronze for most of the studies. This suggests that nucleations happened inside the mesh openings, instead of on the mesh openings. In addition, an optimal mesh size should exist for HFE 7000 flow boiling. / Graduation date: 2006

Graduation date: 2001

Production of surimi represents a potential utilization of a number of low-valued fish species, one of which, Pacific whiting, represents the largest biomass off the West Coast of the United States. However, a protease enzyme softens the fish flesh in Pacific whiting and limits the expansion of surimi production. Many studies have demonstrated the importance of time and temperature in minimizing the texture softening. An optimal design of the surimi seafood process is possible only when an accurate prediction of the time-varying temperature distribution throughout the surimi product can be obtained. This provides a measure of the heating rate and the extent of thermal processing. Such a prediction necessitates a study of the surface heat transfer coefficient which is one of the most important parameters for the heat transfer analysis. Associated with automated-machinery processing of surimi seafoods, a full understanding of the heat transfer coefficient (h) is especially important because high-quality surimi products using Pacific whiting only can be obtained through rapid and controlled heating. This study was intended to determine transient surface heat transfer coefficients in a steam heating environment, simulating the widely-used steam heating of thin-sheet surimi paste in the seafood industry. In determining the heat transfer coefficient, many different methods have been used including the inverse calculation method, the lumped mass method and the heat flux method. This study employed all three to measure and model the heat transfer coefficient (h) under similar steam conditions. A comparative evaluation was made to define the best method and model for the h determination. The inverse calculation method produced an h model which, when applied to a heat transfer analysis, provided the best agreement between predicted and experimental temperature profiles at three locations in surimi paste during a 1000-sec cooking period. The lumped mass method overestimated the heat transfer coefficients to food; the heat flux method gave inconsistent measurements. It is a classic inverse problem to estimate surface heat transfer coefficients from temperature measurements inside a product, a procedure which involves solution of the inverse heat conduction problem and parameter optimization. A whole domain function specification procedure was developed for the inverse calculation method. This procedure simulates heat transfer coefficients as specified functions by estimating all the unknown parameters in the functions over the total time interval. A nonlinear regression computer program was written for the inverse calculation of surface heat transfer coefficients, incorporating the implict Crank-Nicolson scheme for the finite-difference formulation of the one-dimensional heat conduction problem and the downhill simplex method for parameter optimization. This inverse calculation method provided relatively accurate models of the surface heat transfer coefficient. / Graduation date: 1997

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

The Circumferential Slot Virtual Impactor (CSVI) and The XMX/2A are two virtual impactors designed for sampling aerosol particles from a dilute environment by separating the aerosol into a fine and a coarse particle fraction. Dust particles in the ambient air may deposit within the virtual impactors and affect their performances. In this study the effect of dust loading within the CSVI on the efficiency of transmission was determined for particles from 0.49 to 9.9 mm in aerodynamic diameter (AD), and the performance of the three stage XMX/2A aerosol concentrator was characterized with 1 mm-9.9 ?m AD polystyrene latex microspheres (PSL). In the first experimental configuration, the two-stage CSVI had a first stage inflow of 100 L/min and a second stage minor flow of 1 L/min, each stage operating at an inflow/minor flow ratio of 10. An In-line Virtual Impactor (IVI) was used as a pre-separator for sampling inlets to exclude large particles. When the 100 L/min IVI with the two-stage CSVI was tested with Arizona Fine Road Dust (ARD A-2) particles, the transmission efficiency dropped to 50% when the dust entering the two-stage CSVI accumulated to about 100 mg. When it was tested with ASHRAE dust, a decrease of 43% in the efficiency was detected after more than 200mg ASHRAE dust entered the two-stage CSVI. After cleaning the CSVI unit, the transmission efficiency returned to 99%, which indicated that the dust dissemination resulted in the plugging of the CSVI unit. The transmission efficiency of CSVI dropped more quickly below 50% when tested with the ARD A-2 dust, which had smaller particle sizes. In the second configuration, XMX/2A, a three-stage aerosol concentrator designed to draw 800 L/min of air was used at a measured sampling flow rate of 742 L/min. XMX/2A equipped with an inlet was tested with 1 mm-9.9 mm AD PSL in a testing chamber. The peak transmission efficiency of XMX/2A was 39.5% for 8 mm AD PSL. By using the room air as cooling air and introducing dilution air to the flow cell, the transmission efficiency of each particle size increased. A combination of monodisperse PSL and oleic acid particles represent the performance of CSVI. In the IVI-CSVI dust test, the CSVI unit SN003 had the best performance when tested with ASHRAE dust. XMX/2A had relatively low transmission efficiency when tested with PSL particles in the chamber.

Planetary gear trains have the advantages of compactness, light weight, high speed reduction and differential drive, and can provide several speed ratios by means of selecting different clutches and brakes. They are widely used in the automatic transmissions for automobiles. The purpose of this work is to develop a systematic methodology for the design of automatic transmissions for automobiles. First, the specification is established by using concept of fundamental geared entities. Second, a methodology of structure synthesis is developed for establishing gear trains graphs table with up to three fundamental geared entities. Third, a method for systematically enumerating all possible clutching sequences is established and a method for position of clutches and brakes is developed to establish automatic transmissions graphs table. Forth, a procedure for the selecting of a most efficient clutching sequence associated with a automatic transmission is developed. Finally, the systematic theory integrates preceding methodologies and a computer software package is to developed. The computer software package provides user a powerful tool to design automatic transmissions for automobiles.

Transmission mechanism is usually modeled as a rigid component in most control tasks of manufacturing processes. Nevertheless, experimental studies have shown that the inherent compliant characteristic of transmission mechanisms seriously degrades the whole system¡¦s performance. This paper presents an adaptive control strategy to overcome positioning difficulty of a transmission system with a variable compliance. A flexible joint, consisting of sixteen linear springs, is designed for actual positioning experiments. In order to enhance variation of the compliance, an eccentric load is located behind the flexible joint. Therefore, the axial compliance is not fixed and will change according to the load¡¦s angular position. The proposed controller is developed on an adaptive control structure to provide capability of fast adaptation to compliance variation. Besides, the robustness of the control system is also specifically emphasized to improve positioning performance with respect to model uncertainty and unknown disturbances. The control law is obtained by applying the Lyapunov¡¦s theorem. Effectiveness of the presented control method is demonstrated on trajectory control of an experimental transmission mechanism with the flexible joint under variable compliance conditions.

The Balun Core is used in this paper to design a balance to unbalance 1:1 wideband transmission line transformer, because magnetism this package of Balun core witch cover good, leak magnetism inductance to be relatively little, can give consideration to characteristic, low frequency of section, and because the volume is small can make transmission line short, also can give consideration to necessary high frequency too. And wide bandwidth transmission line transformers (TLTs), in many kinds of RF circuit, offer wide frequency band impedance transform, usually in equipment and characteristic impedance of system match. If load or the secondary circuit and impedance mismatch of the signal source or the equipment end, unable to reach the best power of transmission, most power loss because of impedance mismatch, and inserting loss increasing too. With higher frequency and wide bandwidth of utilization component at present, so wideband impedance match is importance.