Tzu-Chen Hung

Waste heat recovery of organic Rankine cycle using dry fluids

A Rankine cycle using organic fluids as working fluids, called organic Rankine cycle (ORC), is potentially feasible in recovering low enthalpy containing heat sources. Efficient operation of the ORC depends heavily on two factors: working conditions of the cycle and the thermodynamic properties of the working fluids. The working fluids under investigation are Benzene (C6H6), Toluene (C7H8), p-Xylene (C8H10), R113 and R123. Among the working fluids under investigation, p-Xylene shows the highest efficiency while Benzene shows the lowest. The study also shows that the irreversibility depends on the type of heat source. Generally speaking, p-Xylene has the lowest irreversibility in recovering a high temperature waste heat, while R113 and R123 have a better performance in recovering a low temperature waste heat.

Conjugate heat transfer analysis for the passive enhancement of electronic cooling through geometric modification in a mixed convection domain

A two-dimensional model has been developed for numerical prediction of viscous laminar flow, mixed convection, and conjugate heat transfer between parallel plates with uniform block heat sources and with openings on the integrated circuit board. A control volume pressure-based finite difference numerical scheme, PISO, is used to solve this problem. The differential pressure below and above the openings of the board induces upward streams, which break the stagnant region between the blocks and, consequently, enhance the heat dissipation. Geometrically, parametric study has indicated that an opening at the appropriate location makes a flatter temperature distribution and a lower peak temperature. Because of the existence of both natural convection and opening-induced passive flow streams, the resulting flow field depends on the inlet conditions and the magnitude of the heat source. The enhancement of heat transfer is reflected by a global increase of Nusselt number on the blocks, and is especially apparent ...

Investigations of the Thermal Spreading Effects of Rectangular Conduction Plates and Vapor Chamber

This study examines the spreading ability of rectangular plates numerically, analytically, and experimentally. The effect of aspect ratio, defined as an equivalent radius of a heater divided by that of a spreader plate, is investigated. The numerical results show a very good agreement with the analytical solutions. From the calculated results, the spreading resistance of the conduction plates with a small aspect ratio is higher than the one-dimensional conduction resistance. Calculated results also show that the spreading ability of a metal plate would be affected slightly by the external convective heat-transfer coefficient when the ratio of the longitudinal heat convection to the lateral heat spreading is less than 0.1. In addition to the numerical analysis, experimental comparisons between copper∕aluminum plates and a vapor chamber having the same thickness have been conducted. The experimental results show that the thermal resistance of the metal plates is independent of input power whereas that of the vapor chamber shows a noticeable drop with increased power. For the influence of concentrated heat source, the surface temperature distributions for the metal plates become concentrated with a reduced aspect ratio. However, the variations of the aspect ratio and the input power would yield minor effects to the surface temperature distribution of the vapor chamber. As compared with the conduction plates, the vapor chamber would offer a lower temperature rise and a more uniform temperature distribution. Thus, the vapor chamber provides a better choice as a heat spreader for concentrated heat sources.

A CONCEPTUAL DESIGN OF THERMAL MODELING FOR EFFICIENTLY COOLING AN ARRAY OF HEATED

This study aims at providing a means of evaluating heat transfer performance of electronic package systems so that technically sound design decisions can be made. Pressure implicit with splitting of operators (PISO), a control volume (CV) pressure-based scheme, was utilized to solve the governing equations for conjugate heat transfer phenomena, which covered the flow regimes from purely natural convection to mixed convection with a Reynolds number (Re) of up to 1000. It is found that the high Re flow is not a necessary condition to yield a better heat transfer effect. The application of a passive concept associated with an appropriate geometric arrangement would yield better cooling. When the number of chips and the associate heat release rate are increased, the case of purely natural convection with interchip openings has shown a better cooling capability. A crucial conclusion lies in how to efficiently employ the passive concept of fluid mechanics to induce a thinner boundary layer.

NUMERICAL SIMULATIONS FOR THE PHENOMENA OF VORTEX-INDUCED VIBRATION AND HEAT TRANSFER OF A CIRCULAR CYLINDER

Fluid–structure interaction and heat transfer of a circular cylinder located in a spatially and temporally uniform, two-dimensional, laminar flow field was investigated. A pressure-based high-order upwind scheme using the PISO algorithm was applied to the simulation of vortex-induced vibration and heat transfer. The cylinder was allowed to move under the influence of a resultant force due to both pressure and shear drags. Combining cylinder movement with the Navier--Stokes equations, the behavior of natural coupling and heat transfer was hence simulated. The present study successfully simulated the motion of a cylinder and the associated vortex pattern as well as the “lock-in” phenomenon. In the flow field under natural coupling, the trajectory of the cylinder movement follows the shape of an “8”. Meanwhile, the motion pattern is sensitive to the variation of lift and drag coefficients. Heat transferred from a vibrating cylinder under natural coupling is enhanced as compared to the case of a fixed cylinder, especially when Reynolds number exceeds 400. If the vibration pattern can be precisely controlled, interference to the thermal boundary layer is expected to contribute to the enhancement of cylinder heat transfer.

Cogeneration approach for near shore internal combustion power plants applied to seawater desalination

The present study utilizes the waste heat streams, jacket water and exhaust gas from a Diesel engine as the heat source for desalination of seawater. The seawater is preheated to a saturated state, and then, throttling and heat exchange processes are alternately employed for generation of fresh water. The exit brine is eventually crystallized to salt via the wind. In the evaluation, the temperature differences among the stages of the evaporator significantly influence the generation rate of fresh water. Accompanying the use of plastic heat exchangers, the brine related dirt problem could be avoided. The appropriate arrangement of the waste heat utilization could not only omit installation of the warm water discharge system but also prevent damage to the underwater ecology. The study successfully shows the feasibility of application of waste heat from combustion engines in the desalination of seawater.

An Innovative Improvement of Engineering Learning System Using Computational Fluid Dynamics Concept

An innovative concept of an electronic learning system has been established in an attempt to achieve a technology that provides engineering students with an instructive and affordable framework for learning engineering‐related courses. This system utilizes an existing Computational Fluid Dynamics (CFD) package, Active Server Pages (ASP) programming, Hyper Text Markup Language (HTML) web page, and a database in the development of a user‐friendly interface for the e‐learning system. The structure of this learning system includes three components: a pre‐processor which creates and defines the problems, a control program which links CFD package; searches for the identical problem with previously executed results or creates a new CFD execution and then saves the results in the database, and a post‐processor which yields a graphic presentation of the computational results. This system would provide engineering students with a solid comprehension of the physical phenomena by changing the input parameters of a specific problem.

Effects of Thermal Radiation for Electronic Cooling on Modified PCB Geometry under Natural Convection

In this study, the discrete ordinates method (DOM) model is employed to estimate the effect of thermal radiation from multiple heat sources in a natural-convection flow field. It is found that the flow field around the chips can be altered by natural convection as induced by radiative heat transfer. The influence of thermal radiation is higher than 65% when the chipboard is in a vertical orientation. Furthermore, even if the chip surface temperature is only 317 K, the influence of radiative heat transfer is still up to 18%. Therefore, radiative heat transfer cannot be ignored for electronic component computational fluid dynamics simulation under natural convection.

An innovative improvement of engineering learning system using computational fluid dynamics concept

Abstract An innovative concept of an electronic learning system has been established in an attempt to achieve a technology that provides engineering students with an instructive and affordable framework for learning engineering-related courses. This system utilizes an existing Computational Fluid Dynamics (CFD) package, Active Server Pages programming, Hyper Text Markup Language web page, and a database in the development of a user-friendly interface for the e-learning system. The structure of this learning system includes three components: a pre-processor which creates and defines the problems, a control program which links CFD package; searches for the identical problem with previously executed results or creates a new CFD execution and then saves the results in the database, and a post-processor which yields a graphic presentation of the computational results. This system would provide engineering students with a solid comprehension of the physical phenomena by changing the input parameters of a specific problem.

Triple Cycle: A Conceptual Arrangement of Multiple Cycle Toward Optimal Energy Conversion

The purpose of this study is to find a maximum work output from various combinations of thermodynamic cycles from a viewpoint of the cycle systems. Three systems were discussed in this study: a fundamental combined cycle and two other cycles evolved from the fundamental dual combined cycle: series-type and parallel-type triple cycles. In each system, parametric studies were carried out in order to find optimal configurations of the cycle combinations based on the influences of tested parameters on the systems. The study shows that the series-type triple cycle exhibits no significant difference as compared with the combined cycle. On the other hand, the efficiency of the parallel-type triple cycle can be raised, especially in the application of recovering low-enthalpy-content waste heat. Therefore, by properly combining with a steam Rankine cycle, the organic Rankine cycle is expected to efficiently utilize residual yet available energy to an optimal extent. The present study has pointed out a conceptual design in multiple-cycle energy conversion systems.