Won Tae Kim

Design of a Two-Phase Loop Thermosyphon for Telecommunications System ( I) - Experiments and Visualization -

A two-phase loop thermosyphon system is developed for the B-ISDN telecommunications system and its performance is evaluated, both experimentally and by visualization techniques. The design of the thermosyphon system proposed is aimed to cool multichip modules (MCM) upto heat flux of 8 W/cm2. The results indicate that in the loop thermosyphon system, cooling heat flux is capable of 12 W/cm2 with two condensers under the forced convection cooling of the condenser section with acetone or FC-87 as the working fluid. The instability of the working fluid flow within the loop is observed using the visualization techniques and temperature fluctuation is stabilized with orifice insertion.

Design of a Two-Phase Loop Thermosyphon for Telecommunications System ( II ) - Analysis and Simulation -

A computer simulation is performed for a two-phase loop thermosyphon for the B-ISDN telecommunications. The aim of this code development is to provide capabilities to predict the affects of many variables on the performance of the proposed TLT system using different empirical correlations obtained from the literature for the evaporation and condensation, and the shape factors available. In the present study, the simulation code is based on the sectorial thermal resistance network built on the flow regimes of the two-phase flows involved. The nodal resistances are solved by the typical Gauss-Seidal iteration method. The code can predict whether the proposed design is possible based on the flooding limit calculation of the system and its results are compared with the experimental results.

NDT Analysis of Metal Materials with Internal Defects Using Active Infrared Thermography Method

This study is aimed to analyze the thermal imaging patterns presented by infrared(IR) thermography at which the metal with internal defects are thermally heated. Through the knowledge of non-destructive testing which infrared thermography can be applied to detect the defects inside the materials, there are two materials experimented; one is stainless steel and the other is cast-iron. Thermally, each material of specimens is heated at the base of the material and kept with constant temperature, The artificial defects in the specimen are formulated. Under the shape and location of the defects, temperature profiles are also measured and validated using the computer simulation. It is concluded that the characteristics of thermal patterns obtained from IR thermography are consistent with those of measurement and computations.

Design of a two-phase loop thermosyphon for telecommunications system (II)

A two-phase loop thermosyphon system is developed for the B-ISDN telecommunications system and its performance is evaluated both experimentally and by visualization techniques. The design of the thermosyphon system proposed is aimed to cool muliichip modules (VICM) upto heat flux of 8 W/cm2. The results indicate that in the loop thermosyphon system, cooling heat flux is capable of 12 W/cm2 with two condensers under the forced convection cooling of the condenser section with acetone or FC-87 as the working fluid. The instability of the working fluid flow within the loop is observed using the visualization techniques and temperature fluctuation is stabilized with orifice insertion.

Detection of Subsurface Defects in Metal Materials Using Infrared Thermography; Image Processing and Finite Element Modeling

Infrared thermography is an emerging approach to non-contact, non-intrusive, and non-destructive inspection of various solid materials such as metals, composites, and semiconductors for industrial and research interests. In this study, data processing was applied to infrared thermography measurements to detect defects in metals that were widely used in industrial fields. When analyzing experimental data from infrared thermographic testing, raw images were often not appropriate. Thus, various data analysis methods were used at the pre-processing and processing levels in data processing programs for quantitative analysis of defect detection and characterization; these increased the infrared non-destructive testing capabilities since subtle defects signature became apparent. A 3D finite element simulation was performed to verify and analyze the data obtained from both the experiment and the image processing techniques.

Infrared Thermography and Modeling to the Concrete Deck with Internal Defects as a Non-Destructive Testing

This work is aimed to investigate the temperature characteristics at the surface of the concrete decks, to detect the existence of internal defects buried in the solid in such a way that enables the quantitative determination of temperature distributions from the concrete. For this purpose, it is supposed that the signature for temperature characteristics is performed experimentally by means of Infrared (IR) thermography. A quantitative analysis of computational model developed by FVM implement that temperature distributions on the surface of the concrete with the internal defects have a significant feature by the dimension of defect, thermal conductivities of a variety of materials filled in the defect. According to the distance reaching the defects from the surface, the thermal imaging affected by temperature differences are compared, The simulations are also evaluated with the thermal pattern acquired by a qualitative IR thermography in a local district of the concrete deck Nomenclature i, j subscript, tensor, g gravitation, m 2 /sec T temperature, °C u velocity, m/sec x coordinate, m symbol β therrmal expansion factor, 1/°C ρ density, m/kg ∆ difference, Introduction Thermal imaging technology using the infrared thermography is one of prospective non-contact and non-destructive technologies. Measuring temperatures of each point on the structure expanded to the broad object area, it provides an image of temperature distribution on an object. Over the year, the importance of infrared imaging technology in NDT for mechanical and electrical facilities has been increasing popularity mainly because it makes remote inspection possible by sensing the thermal radiation emitted from the warm object. With development of infrared imaging systems, this test features safety based on non-contact, high-speed measuring, and easy record preservation. IR thermal imaging as the method of NDT is used for inspecting whether outer finish materials of buildings are exfoliated. Since asphalt covers the deck, it is not possible to see with naked eyes until exfoliation goes further. Also, it is not easy to detect and predict in a variety of deteriorations to be + Corresponding author . Tel.: +82-41-330-1283; Fax:+82-41-330-1269 E-mail address: kwt@kongju.ac.kr Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 938-943 doi:10.4028/www.scientific.net/KEM.270-273.938

Measurement of Performance and Heat Transport in Thermoacoustic Refrigerator

In this study, a thermoacoustic refrigerator, using a resonant standing acoustic wave, has been built. Refrigerants are helium, nitrogen, air. The description of thermoacoustic refrigerator was presented. The temperature ratio (cold part temperature over hot part temperature) and the COP (Coefficient Of Performance) normalized by Carnots COP are plotted versus the thermal load applied to the cold end for various speaker power. Introduction CFC refrigerants used in various refrigerators are primary sources deleting ozone. Since bans have been imposed on their use, production of CFC refrigerants are expected to stop in 2016. For this reason, alternative refrigerants and new refrigeration technologies are being developed. Thermoacoustic refrigeration has been recently researched as a new refrigeration technology. It is one of low-temperature refrigeration technologies, which do not require large power compared with vapor compression refrigerator. In thermoacoustic refrigeration, speaker substitutes for conventional refrigerators compressor, and environment-friendly gases like helium and argon are used instead of CFC. Thermoacoustic refrigerator has a relatively simple structure, ensuring easy maintenance and high mechanical reliability. Glass artisans in the 18th century found that a sound was generated from the opening of glass tube when cold glass tube was joined with hot glass tube. Sondhauss[1] conducted a test on the relation between tube size and sound level. In 1896, Rayleigh[2] used qualitative method to provide correct explanations on thermoacoustic phenomenon. Taconics vibration, a similar phenomenon, induces extremely high amplitude when one end of a tube filled with gas is kept at normal temperature and other end is contacted with liquid helium. Taconis[3] also used qualitative method to explain the phenomenon. Example of first acoustic heat pump is pulse tube refrigerator. Gifford and Longsworth[4] succeeded in generating temperature ratio Tc/Th = 1/2 by applying low-frequency and high-amplitude vibration on the end of closed tube. Merlki and Thomann[5] generated the standing wave on the tube wall where constant temperature was kept, and Resonator Stack Parcel of gas dq dq Hotter Colder 4dk Plate