Huang-Hsiu Tsai

Liquid flow in a micro-channel

An experimental study with MPIV (micro particle image velocimetry) flow visualization of incompressible liquid flow in a microchannel is presented. Deionized water served as a working medium. The channel was microfabricated in a PMMA substrate using an excimer laser, and was 115 µm deep, 200 µm wide and 24 000 µm long with a hydraulic diameter of about 146 µm. The pressure drop between the inlet and the outlet of the duct as well as mass flow rates were measured and friction factors were calculated for different Reynolds numbers. Data were discussed and compared with those of previous investigations of similar studies. Moreover, time evolutions of the microflow at the middle of the microchannel at Re = 50, 100, 470 and 900 were photographed. Hydrodynamic entry length correlations were found for both laminar and turbulent flow in the present microchannel.

Nucleate pool boiling characteristics from coated tube bundles in saturated R-134a

Abstract Nucleate pool boiling heat transfer from plasma coated copper tube bundles with porous copper (Cu) immersed in saturated R-134a was experimentally studied. The bundle is composed of 15 tubes (of which the number of heated/instrumented tubes was varied) arranged in four different configurations with a pitch-to-diameter ratio of 1.5. The influences of various parameters, for instance, bundle arrangements and heat flux were clarified. Tests were conducted with both increasing and decreasing the heat flux. The data presented indicated that at low heat fluxes, the vertical-in-line tube bundles have the highest bundle factor. A configuration factor was proposed which can be used to characterize the geometric arrangements of the bundles.

Turbulent heat transfer and flow characteristics in a horizontal circular tube with strip-type inserts. Part II. Heat transfer

This paper is the second of two papers that presents the results of an extensive study of turbulent heat transfer and pressure drop in a horizontal tubes with strip-type inserts. Experimental data were taken for air for a class of strip inserts (longitudinal strip and crossed-strip). The insert was characterized by the parameters of 1 6 AR 6 5 and R � ( ¼ 0.5 and 1). Friction factor data (from Part I) and temperature measurements were used to understand the underlying physical phenomena responsible for the heat transfer enhancement for 6500 6 Re 6 19 500. Nusselt numbers were between four and two times the bare tube values at low Re and high Re, respectively. Performance evaluation index R1 (constant pumping power) and R2 (constant heat duty) were made and an optimum condition would be thus found.

Turbulent heat transfer and flow characteristics in a horizontal circular tube with strip-type inserts. Part I. Fluid mechanics

Abstract This paper is the first of two papers that present the result of a study of turbulent flow and pressure drop in a horizontal tube with strip type inserts. Experimental data taken for air for a class of strip type inserts (longitudinal, LS and cross, CS inserts) used as a tube side heat transfer augmentative device for a single-phase cooling mode operation are presented. To broaden the understanding of the underlying physical phenomena responsible for the heat transfer enhancement, flow mechanisms through velocity measurements are combined with pressure drop measurements to develop friction factor correlations for 6500⩽Re⩽19 500 where Re is the Reynolds number. Friction factor increases were typically between 1.1 and 1.5 from low Re(≅6500) to high Re(≅19 500) with respect to bare tubes.

LDV assisted bubble dynamic parameter measurements from two enhanced tubes boiling in saturated R-134a

LDV measurements and heat transfer experiments for nucleate pool boiling from two horizontal enhanced tubes with porous copper on copper surfaces immersed in saturated R-134a were conducted. The influence of tube position (alignment) and tube pitch on bubble dynamics and boiling characteristics were studied. Photographs indicate that the average number of bubbles increases with heat fluxes, which is the same as those in previous studies of single tube. However, the bubble departure diameters of the upper tube show an opposite trend with an increase as compared to previous single-tube studies. LDV measurements show that the present tube arrangement has significant influence on local velocity in both magnitude and trend. The heat transfer mechanism and modeling for the upper tube were studied and developed.

Dsmc Simulation for constant-wall-temperature Heat Transfer in a Short Parallel Plate Microchannel

The heat transfer characteristics of low speed gas flows through a short parallel plate microchannel (L/D(subscript h)=6) are examined using the direct simulation Monte Carlo (DSMC) method. Computations were carried out for nitrogen, argon, and helium gas. Micro pressure driven flows are simulated with the inlet value of the Knudsen numbers ranging from 0.09 to 0.2. The effects of varying wall temperature, pressure, inlet flow and gas transport properties on the wall heat transfer and velocity distribution were examined. Heat transfer from the channel was also calculated and compared with those of previous studies. Molecular diffusion dominates over both slip and transition flow regimes. Finally, the averaged Nusselt number ((average)Nu) was correlated in simple form of the averaged Peclet number ((average)Pe and Knudsen number ((average)Kn ) in the transition flow regime.

Gaseous Slip Flow in a Micro-Channel

An experimental and theoretical study of low Reynolds number compressible gas flow in a micro channel is presented. Nitrogen gas was used. The channel was microfabricated on silicon wafers and were 50 μm deep, 200 μm wide and 24000 μm long. The Knudsen number ranged from 0.001 to 0.02. Pressure drop were measured at different mass flow rates in terms of Re and found in good agreement with those predicted by analytical solutions in which a 2-D continuous flow model with first slip boundary conditions are employed and solved by perturbation methods.Copyright