Heiu Jou Shaw

LAMINAR MIXED CONVECTION HEAT TRANSFER IN THREE-DIMENSIONAL HORIZONTAL CHANNEL WITH A HEATED BOTTOM

Mixed convection heat transfer phenomena are studied in a three-dimensional channel with a cavity heated from below. A general purpose computer program is developed to analyze the flow field and temperature distribution in the channel. Numerical computation is performed by using the alternating direction implicit (ADI) method based on the SIMPLER algorithm. The influences of Reynolds number and Grashof number on the Nusselt number of the cavity are discussed. As a convenience to the reader, three-dimensional streaklines and three-dimensional isothermal surfaces are presented.

Laminar forced convection in a channel with arrays of thermal sources

The problem of laminar forced convection in a two-dimensional channel with arrays of thermal sources is studied numerically. The surfaces of the thermal sources are assumed to be isothermal. In order to promote the accuracy of the result, numerical computation is performed with alternating direction implicit (A.D.I.) method and SIMPLER algorithm. The primary purpose of this paper is to study the fundamental heat transfer phenomena in “L.S.I.” packages, which are widely used in microelectric equipments recently. The contribution of this study is not only on academic purpose but also on industrial application. Influence of Reynolds number on Nusselt number of thermal sources is discussed. Calculations are made under the conditions of different arrangements of the thermal sources. Flow patterns, pressure and temperature distributions are demonstrated.ZusammenfassungHier wurde das Problem der laminaren Zwangskonvektion in einem zweidimensionalen Kanal mit einem Wärmequellen-Feld numerisch untersucht. Die Oberflächen der Wärmequellen wurden als isotherm vorausgesetzt. Um die Genauigkeit des Ergebnisses zu verbessern, wurden die numerischen Berechnungen mit dem A.D.I.-Verfahren und dem SIMPLER-Algorithmus durchgeführt. Das grundlegende Ziel dieser Arbeit sind die wesentlichen Wärmeübertragungsphänomene in L.S.I.-Paketen zu untersuchen, welche vorwiegend in Geräten der Mikroelektronik verwendet werden. Diese Untersuchung liefert nicht nur einen Beitrag für akademische Zwecke, sondern ist auch für die industrielle Anwendung gedacht. Der Einfluß der Reynolds-Zahl auf die Nusselt-Zahl der Wärmequellen wurde besprochen. Die Berechnungen wurden für verschiedene Zusammenstellungen der Wärmequellen gemacht. Strömungsbilder, Druck- und Temperaturverteilungen sind dargestellt worden.

TRANSIENT FREE CONVECTION WITH MASS TRANSFER ON A VERTICAL PLATE EMBEDDED IN A HIGH-POROSITY MEDIUM

Abstract The problem of transient free convection is investigated in a high-porosity medium adjacent to a vertical semi-infinite flat plate with a simultaneous step change in wall temperature and wall concentration. The non-Darcian effects of convection, boundary, and inertia are all considered. The coupled nonlinear partial differential equations are solved by using a cubic spline collocation method. The numerical results show that the Darcy model overestimates both the transient heat and the mass transfer rate for a high-porosity medium. When the inertia effect is neglected, there is a minimum in the temporal transient Nusselt and Sherwood numbers before steady state is achieved. The present analysis also investigates the effects of the following parameters on the time required to reach steady state: buoyancy force ratio N, Darcy number Da, inertia coefficient T, and Lewis number Le. The time required to reach steady state decreases as|N| or Da increases and increases as T increases. When Le < 1, the ti...

Two-dimensional orthogonal grid generation techniques

Abstract The techniques for generating two-dimensional orthogonal meshes are discussed in this paper and two different methods are presented for implementing coordinates transformation. The first one is generating meshes allowing grid point freely moving along the boundary, and the other one is contructing meshes with prescribed grid points on the boundary. For the first method, the conformal modulus or scale factors need not be computed just as previous methods did. For the second method, the control functions are iteratively adjusted according to the angle of intersecting grid lines. In this process, the control functions are considered as a part of solutions and is unable to keep controlling the spacing among the grid lines. Instead of control functions, the boundary grid points distribution determines the spacing of grid lines and the existence of orthogonality of meshes. Numerical computations are made to illustrate the determination of different kinds of boundary grid points distribution. The method for parts of boundary grid points fixed are also provided for more wide applications.

Natural convection in partitioned enclosed spaces of solar collector

The two-dimensional, steady, laminar natural convection phenomena in partitioned enclosure of solar collector has been studied numerically. Heat conduction along the partition is considered. An iterative finite-difference scheme is employed to solve the governing equations in the flow field. The effects of Rayleigh number, thermal conductivity ratio, partition angle, tilt angle, and aspect ratio on both the local and average heat transfer coefficients of the solar collector have been discussed. The range of Rayleigh number tested was up to 5 × 104, the thermal conductivity ratio of 4.5 and 30, partition angle from 10 deg to 170 deg, tilt angle from 10 deg to 90 deg, and aspect ratio varied between 0.2 and 10. The results indicate that the convective heat transfer is strongly affected with the aspect ratio of the enclosures.ZusammenfassungDie zweidimensionale, stetige, laminare freie Konvektion in unterteilten Kammern von Solarkollektoren wurde numerisch untersucht. Die Wärmeübertragung entlang dieser Kammern wurde betrachtet. Ein iteratives Finite-Differenzen-Schema wurde angewandt um die Gleichungen, welche das Strömungsfeld beschreiben, zu lösen. Der Einfluß der Rayleigh-Zahl, der thermische Leitfähigkeit, des Kammerwinkels, des Neigungswinkels und der Längenverhältnisse auf die örtlichen und durchschnittlichen Wärmeübertragungskoeffizienten des Solarkollektors wurde diskutiert. Der Bereich der Rayleigh-Zahl erstreckte sich bis zu 5 × 104, das Verhältnis der thermischen Leitfähigkeit betrug 4.5 und 30, der Kammerwinkel lag zwischen 10° und 170°, der Neigungswinkel zwischen 10° und 90° und das Längenverhältnis variierte zwischen 0.2 und 10. Die Ergebnisse beinhalten, daß die konvektive Wärmeübertragung sehr stark durch das Längenverhältnis der Kammern beeinflußt wird.

Natural convection in an enclosure heated from below with a conductive horizontal partition

This paper investigates the phenomenon of natural convection in an enclosure heated from below, fitted with a completely horizontal conductive partition. The horizontal partition is parallel to the two horizontal isothermal enclosure walls, which are maintained at different temperatures, while the vertical walls of the enclosure are adiabatic. The governing equations for stream function, vorticity, and energy are solved with the aid of the cubic spline collocation method. Parametric studies of the effects of the partition on the fluid flow and temperature fields in the enclosure have been performed. Numerical results indicate that the effects of the conductivity ratio of the partition and the aspect ratio of the enclosure on the heat-transfer rate are not significant. However, the location of the partition affects the fluid flow and heat-transfer rate profoundly. Numerical results are also compared with the results obtained from a flow visualization experiment. The streamline distribution obtained from numerical result is shown to be in good agreement with the experimental results.

Cloud-based, service-oriented and knowledge-sharing architecture: its design and application in shipbuilding

In the shipbuilding process, a number of ship specification files are generated. Those files are usually scattered as different file formats in various departments or stored as databases in the heterogeneous systems within a shipyard. Therefore, it is extremely difficult to integrate specification files coming from different stages of shipbuilding, much less to share the integrated information among various departments. Moreover, long-term accumulation of files and continuous expansion of computer systems place a heavy burden on the shipyard, for it must invest more capital in software development and hardware. To address this problem, this study proposed the concept of cloud services. Specifically, the authors constructed a cloud-based, service-oriented and knowledge-sharing architecture which was founded on XML and Web Services technology. Through the newly developed architecture, ship specification files can be structurally integrated and preserved; meanwhile, they can be conveniently transmitted among the heterogeneous systems, with openness between different systems achieved. Thus, all knowledge owned by the shipyard will be efficiently managed, applied and shared. In addition, the shipyard may reduce its investment in IT equipment, including software development and hardware peripherals.

The effects of thermal sources on natural convection in an enclosure

Abstract In this paper, the phenomena of natural convection in an enclosure with isolated thermal sources located on a vertical adiabatic surface is investigated numerically. The arrangement of the problem is pertinent to the positioning of the thermal sources in a container. Flow patterns and temperature profiles in the enclosure and average heat transfer rates on the boundary surfaces are evaluated by a cubic spline collocation method for various thermal sources arrangements and Rayleigh number. It is obvious that the fluid flow and heat transfer in the enclosure is affected strongly by the arrangement of the thermal sources.

Design and estimation of a MCPCB-flat plate heat pipe for LED array module

Recently, high power LED is more and more important due to requirement of illumination. To achieve the greater performance of electric path and heat dissipation ability, the metal core PCB (MCPCB) is used to replace the common FR4 PCB. The MCPCB is composed of copper film, dielectric and metal base. Metal base is made of copper or aluminum and has high thermal conductivity to conduct heat from LED to heat sink. However, the low thermal conductivity of dielectric layer in the middle of MCPCB will cause the temperature raise. In this study, we use 30% diamond powder as the filler of dielectric layer and combined the PCB and flat plate heat pipe (PCB-FPHP) without metal base to enhance the effective thermal conductivity. In order to verify the performance of diamond powder PCB-FPHP, we experimental measured the PCB-FPHP and common MCPCB conducted with 3 different materials include Cu, Al and FPHP by IR camera. The experimental results shows that the thermal resistance of PCB-FPHP is 36%, 78% and 86% lower than MCPCB-FPHP, MCPCB-Cu, and MCPCB-Al respectively. It is obviously that the thermal resistance of metal base and the thermal grease cannot be neglected especially in high power application. The structure of PCB-substrate we propose in this paper can reduce the junction temperature about 0.36°C/W compare with MCPCB-substrate. It is a meaningful number for high power LED application.

The service-oriented, interoperable and knowledge-sharing architecture for ship specifications

In the shipbuilding process, the information flow connected with ship specification files is very complex. These files are usually scattered as different file formats in various departments or stored as a database in the heterogeneous systems within a shipyard. Therefore, it is extremely difficult to integrate the information coming from different stages of shipbuilding, much less to share integrated information among various departments. To address that problem, the authors employ the service-oriented architecture concept to develop the knowledge-sharing architecture for ship specifications (KSASS). Equipped with extensible mark-up language and Web services technology, the KSASS is used to integrate the outline, full and construction specification files, which originate from three phases of shipbuilding. In this way, the database of ship specifications is established which is easily accessible and highly interoperable. The integrated specification files can not only be structurally preserved but also conveniently transmitted among the heterogeneous systems, with the open system achieved. Eventually, the knowledge owned by the shipyard will be efficiently managed, applied and shared.