Suyi Huang

Wärmeübergang bei freier Konvektion um elliptische Rohre

An interferometric study of heat transfer with free convection around elliptical axisymmetric bodies is presented. Measurements of local and average heat transfer coefficients were performed with horizontally orientated elliptical cylinders of various slenderness. The orientation of the major axis of the ellipse was changed between zero and vertical inclination. For comparison some measurements were also done with cylindrical tubes.Based on the experimental data, empirical correlations were elaborated, describing the local and the global heat transfer around a cylindrical tube. For elliptical tubes an equation is given for the average heat transfer coefficient, in which a geometrical coefficient takes in account the slenderness of the ellipse.ZusammenfassungEs wird über interferometrische Messungen des Wärmeübergangs bei freier Konvektion um achsensymmetrische elliptische Körper berichtet. In den Messungen wurde sowohl der örtliche als auch der mittlere Wärmeübergangskoeffizient für verschiedene Schlankheitsgrade des elliptischen Querschnittes bei horizontaler Rohrachse erfaßt. Variiert wurde auch die Orientierung der Hauptachse der Ellipse zwischen horizontaler und vertikaler Ausrichtung. Zum Vergleich wurden auch Messungen an zylindrischen Rohren durchgeführt.Aufbauend auf den experimentellen Ergebnissen wurden empirische Gleichungen entwickelt, die den örtlichen und den mittleren Wärmeübergangskoeffizienten an horizontalen, runden Zylindern bei freier Konvektion vorhersagen lassen. Für elliptische Zylinder wird eine einfache Gleichung mitgeteilt, die den mittleren Wärmeübergangskoeffizienten abhängig von einem Formkoeffizienten angibt.

Fluid Dynamics in Microchannels

1.1 Need for microchannels research In contrast to external flow, the internal flow is one for which the fluid is confined by a surface. Hence the boundary layer develops and eventually fills the channel. The internal flow configuration represents a convenient geometry for heating and cooling fluids used in chemical processing, environmental control, and energy conversion technologies [1]. In the last few decades, owing to the rapid developments in micro-electronics and biotechnologies, the applied research in micro-coolers, micro-biochips, micro-reactors, and micro-fuel cells have been expanding at a tremendous pace. Among these micro-fluidic systems, microchannels have been identified to be one of the essential elements to transport fluid within a miniature area. In addition to connecting different chemical chambers, microchannels are also used for reactant delivery, physical particle separation, fluidic control, chemical mixing, and computer chips cooling. Generally speaking, the designs and the process controls of Micro-Electro-MechanicalSystems (MEMS) and micro-fluidic systems involved the impact of geometrical configurations on the temperature, pressure, and velocity distributions of the fluid on the micrometer (10-6 m) scale (Table 1.1). Therefore, in order to fabricate such micro devices effectively, it is extremely important to understand the fundamental mechanisms involved in fluid flow and heat transfer characteristics in microchannels since their behavior affects the transport phenomena for the bulk of MEMS and micro-fluidic applications. Overall, the published studies based on an extensive literature reviews include a variety of fluid types, microchannel cross-section configurations, flow rates, analytical techniques, and channel materials. The issues and related areas associated with the microchannels are summarized in the following table (Table 1.2).

Heat transfer enhancement by filling metal porous medium in central area of tubes

Abstract Given that the fluid within the tubes of some industrial heat exchangers is under a state of fully developed laminar flow with a constant Nu number, increasing the surface area for heat transfer will significantly increase the flow resistance. In this paper, we filled metal porous medium with high thermal conductivity, high porosity and high filling radius in the central area of fully developed laminar flow within the tube, and established corresponding numerical models for fluid flow and heat transfer. Numerical simulation results indicate that after filling the tube with metal porous medium, the temperature profiles within the porous medium area are very uniform, and the temperature difference between the tube wall and the fluid decreases significantly which correspondingly results in a notable increase of Nu number; meanwhile, the characteristic of flow field redistribution occurs within the enhanced tube, but the total flow resistance composed of the Darcy resistance and inertial resis...

Single-Phase Heat Transfer and Fluid Flow Phenomena of Microchannel Heat Exchangers

Thanhtrung Dang1, Jyh-tong Teng2, Jiann-cherng Chu2, Tingting Xu3, Suyi Huang3, Shiping Jin3 and Jieqing Zheng4 1Department of Heat and Refrigeration Technology, Hochiminh City University of Technical Education,Hochiminh City, 2Department of Mechanical Engineering, Chung Yuan Christian University, Chung-Li, 3School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, 4College of Mechanical Engineering, Jimei University, Xiamen, Fujian, 1Vietnam 2Taiwan 3,4P. R. China

Semipermeable Membrane Mass Transfer in Pressure-Retarded Osmosis Process

Pressure-retarded osmosis (PRO) is a feasible process in developing salinity power, which emerges in estuaries in large. Semipermeable membrane mass transfer plays an important role in PRO power generation. However, existing mass transfer models were hard to be validated due to the lack of suitable membranes and membrane modules. This paper presented a comprehensive PRO mass transfer model of semipermeable membrane, which included impacts of both internal and external concentration polarizations, as well as brine dilution and pressure loss. The model was solved by numerical method; and commercial asymmetric flat sheet membrane CA-3000 was taken as the instance. Concentration and hydraulic pressure, as well as brine flux were studied in the paper. Massive concentration gradient was observed in porous layer and effective concentration difference was much lower than expected; moreover, each brine concentration was found to have an optimal pressure for power density. An additional PRO process simulation was done with FLUENT software under the same condition. Two simulation curves approached closely. The paper could be referred for membrane optimization in PRO process.

Image reconstruction of three dimensional temperature field from projections in optical tomography

It is well known that determination of temperature fields by holographic interferometry is a successful method in the measurement of thermophysics. In this paper, some practical algorithms for image reconstruction from projections are presented to produce the temperature field. Algorithms being developed include that the Radon transform integral equation is directly solved by a grid method, and that the Radon inversion formula is numerically evaluated by two-dimensional Fourier transform technique. Some examples are given to verify the validity of the above methods in practice. A heat air flow above conbustor with a rectangular hole is investigated by holographic interferometric system, and temperature distributions of two sections in the air flow field have been reconstructed by this methods.ZusammenfassungDie holographische Interferometrie ist in der Wärmetechnik als sehr geeignete Meßmethode zur Ermittlung von Temperaturfeldern bekannt. In dieser Arbeit werden einige praktische Algorithmen zur Bildrekonstruktion und damit Temperaturfeldermittlung aus Projektionsabbildungen angegeben. Diese enthalten ein Verfahren, das die aus der Radon-Transformation resultierende Integralgleichung mit Hilfe einer Gittermethode unmittelbar zu lösen gestattet, wobei die Radon-Umkehrtransformation numerisch über die zweidimensionale Fourier-Transformation bewältigt wird. Einige Beispiele belegen die praktische Anwendbarkeit der oben genannten Methoden. Mit Hilfe des holographischen Interferometersystems wird die Strömung erwärmter Luft über einer Brennkammer mit rechteckiger Öffnung untersucht und die Temperaturverteilung in zwei Schritten des Strömungsfeldes vermittels der beschriebenen Methode rekonstruiert.