Wen-Jei Yang

Literature Survey on Biomedical Applications of Thermography

Thermography is a noninvasive technique through which temperatures are monitored and recorded, thereby allowing visualization of heat flow. There are three types of thermography: liquid crystal thermography (LCT), infrared thermography (IRT) and microwave thermography (MWT). This paper presents a survey of the literature pertinent to the biomedical applications of these types of thermography. The noninvasive and high resolution characteristics of the thermographic systems make them valuable diagnostic as well as therapeutic aids. Typical research areas include detection of blood flow, diagnosis of joint inflammation and cancer, thermal modeling of various body parts, and use in reproductive problems. The survey discloses that thermography has found applications in various fields in medicine, veterinary medicine, pharmacy, and dentistry.

Flow characteristics in flow networks

A flow network is a system of mutually intersecting holes in a plate or an assembly of plates. The flow at each intersection is characterized by a collision of two flow streams, resulting in complex flow patterns through the downstream holes. In the case of multiple intersections, the flow is periodically disrupted at each succeeding intersection, thus preventing the formation of a fully-developed flow through the holes.An experimental study is presented in this paper to determine flow characteristics in flow networks with various geometry. The intersecting pressure loss coefficient which represents the performance of flow networks is defined and its magnitude empirically determined as functions of geometric and flow conditions. A method is developed to measure the ramming loss in an intersection tube. Flow visualization by means of hydrogen bubble method is applied to observe flow patterns and mixing behavior in the flow network. A physical model is developed to predict the intersection pressure loss in flow networks.

Mechanisms of nucleate pool boiling on composite surfaces

Abstract A previous experimental study [1] has disclosed that nucleate pool boiling heat transfer coefficients on a graphite-copper composite surface are three to six times higher than those on a pure copper surface. Three programs are executed in order to explore the cause for such a high thermal performance: An experiment is conducted on nucleate pool boiling of R113 on a composite surface, a computer program is developed to determine the temperature distribution inside a composite cylinder heated from the lower end with incipient boiling on the upper end, and the microstructure of the composite surface is examined by means of a scanning electronic microscope (SEM). The computer results indicate that (i) Each fiber acts like a fin transporting higher heat flux, resulting in the composite body having a higher average temperature at any cross sections than that of a pure base material, and (ii) There exists a criterion for the tip of graphite fibers to function as a hot spot, i.e. a potential site for macro-bubble nucleation. The SEM discovers micro trenches and intermingled winding trails on the matrix surface between graphite fiber tips which may serve as the nucleation sites for microbubbles. The experiments in support of both hypotheses about the nucleation site.

Two-tier model for nucleate pool boiling on microconfifured composite surfaces

Abstract A new model is developed to describe the heat transfer mechanism in nucleate pool boiling on a microconfigured composite surface. Both the microlayer and macrolayer thickness are determined from the model. This model can be extended to explain the nucleate boiling on plain surfaces. The enhancement mechanisms of heat transfer for the nucleate boiling on the microconfigured surface are analyzed.

APPLICATIONS OF MICROWAVE RADIATION IN MEDICINE

This paper presents major medical applications of microwave radiation in therapy and diagnostics of disorders of thermoregulation, especially hyperthermia and thermography. Microwave thermography is a thermal imaging system produced by self-emission, using emissivity differences to extend our vision beyond the shortwave red. Human tissues are partially transparent to microwaves, thus it is possible to detect the microwave of subcutaneous tissues in thermography, and to allow microwave energy penetration through subcutaneous tissues for deep-tissue heating in hyperthermia. The physics of microwave thermography together with the microwave properties and emission of body tissues are introduced. It is followed by reviews of the literature pertinent to microwave hyperthermia in therapy and treatment. Recent development in this field is briefly discussed.

Natural convection in evaporating sessile drops with crystal growth

Laser shadowgraphy is employed to study interracial instability and natural convection inside a minute drop evaporating on a plate with internal crystal growth. Both pure and binary liquids are considered. Two methods of crystal growth are developed, one by the bulksupercooling method and the other by the pointsupercooling method. Interracial instability is determined by the characteristics of periphery shape of the shadowgraph, while the shadowgraphic image describes the nature of flow behavior inside the drop. While internal crystallization plays no role in interfacial instability, it exerts a profound found influence on natural convection.

Mechanics of transport phenomena in multi-component sessile drops with solidification

Abstract An experimental study is performed to determine the mechanics of transport phenomena in multicomponent sessile drops with internal solidification. These drops are cooled at the center of the drop base or over the enter base of the drop. Both the interfacial and internal flow structures are examined by means of laser shadowgraphy, while the microstructures are investigated using a microscope-video system. Three different degrees of cooling rate are imposed on the drops: low, medium and high cooling. It is disclosed that the center cooling at a low rate produces a radial flow induced by component separation but without solidification and Marangoni type (surface-tension induced) flow. In contrast, a high cooling rate results in Marangoni convection accompanied by solidification but no component separation. The effect of Prandtl number on the Marangoni flow velocity is determined. The interfacial disturbance is suppressed by center cooling but not by bulk cooling which induces the formation of Bernard cells. The impact of flow patterns on the mechanical property of melt solidification is discussed.

Experimental Investigation of Thermal Performance of Vapor Chamber Heat Sinks

This work experimentally studies the thermal performance of plate-fin vapor chamber heat sinks using infrared thermography. The effects of the fin width, the fin height and the Reynolds number on the thermal performance are considered. The results show that generated heat is transferred more uniformly to the base plate by a vapor chamber heat sink than by a similar aluminum heat sink. Therefore, the maximum temperature is effectively reduced. The overall thermal resistance of the vapor chamber heat sink declines as the Reynolds number increases, but the strength of the effect falls. The effect of the fin dimensions on the thermal performance is stronger at a lower Reynolds number.Copyright