Pei-Pei Ding

Droplet formation of a thermal sideshooter inkjet printhead

The present study aims to provide numerical predictions on the droplet formation process for a thermal sideshooter inkjet printhead, which directly aAects the printing quality of the printhead. The calculation procedure starts from the heat up of the printhead by an input electrical pulse, then obtains the pressure impulse response curve due to the formation and collapse of a bubble in the ink, the ink flow motion in the ink nozzle, and finally the evolution process of the ejected ink droplet outside the ink nozzle. The governing continuity and momentum equations for the flow motion in the ejected ink droplet are solved on the Eulerian frame by an implicit finite-diAerence scheme. The ink droplet leading is then updated to the new location from the newly obtained velocity. A comparison is made between the present numerical predictions with experimental results. A good agreement has been found. In addition, the present study shows the eAects of the operating voltage of electrical pulse, the ink properties, and the gravity on the breakoA time of ejected droplet from the ink nozzle exit and the separation time of the long tail from main droplet. ” 1998 Elsevier Science Inc. All rights reserved.

Film cooling performance on curved walls with compound angle hole configuration.

Abstract: In order to explore the effect of compound angle holes on film cooling over a convex wall and a concave wall, the present study adopts the transient liquid crystal thermography for conducting the film cooling measurement on simple hole and expanded‐hole configurations. Two compound angles of 0 and 45 deg are tested at an elevated mainstream turbulence condition (Tu) of 3.8 %. The test pieces have the different radius of curvature (2r/D) of 92.5 on convex and 86.5 on concave, and the same pitch to diameter ratio (P/D) of 3 on both convex and concave walls. All measurements were conducted under the mainstream Reynolds number (Red) of 1700 on convex and 2300 on concave with the density ratio between coolant and mainstream (ρc/ρm) of 0.98. In current study, the effect of blowing ratio (M) on film cooling performance is investigated by varying the range of blowing ratio from 0.5 and 2.0. The present measured results show that the forward‐expanded hole injection provides better surface protection than the simple hole injection. As far as the injection angle is concerned, compound angle injection provides higher film effectiveness than simple angle injection. However, the forward‐expanded hole injection (β= 0°) has the best performance on both convex and concave surfaces.

The selection criterion of injection temperature pair for transient liquid crystal thermography on film cooling measurements

Abstract For the general application of liquid crystal thermography on film cooling measurement, two separate tests with different injection flow temperature rises are conducted under the same free-stream temperature and flow conditions. Therefore, a pair of equations for the two separate test conditions is solved to obtain heat transfer coefficient and film cooling effectiveness. An error could possibly occur in evaluating the film cooling effectiveness if an improper pair of injection temperatures was chosen. To reduce the data reduction error, a better mean to select an adequate pair of heated injection temperatures is recommended in current study.

Disk-shaped miniature heat pipe (DMHP) with radiating micro grooves for a TO can laser diode package

A mounting base integrated with disk-shaped miniature heat pipe (DMHP) is designed for laser diode TO can package in the present study. The heat spreading performance of the disk-shaped miniature heat pipe is also presented. The present mounting base is made of aluminum (6061 T6) other than the conventional TO can package with oxygen free copper. The mounting base shows different thermal resistance with different working fluid charge volume. By optimizing the working fluid charge volume, the thermal resistance of the present mounting base will become lower than the conventional base with an oxygen free copper disk for TO can package. Moreover, this novel design can be manufactured on a massive scale and the fabrication cost can thus be effectively reduced.

Experimental evaluation of thermal performance of Gifford–McMahon regenerator using an improved single-blow model with radial conduction

Abstract An improved single-blow model with nonuniform radial temperature distribution was developed and employed to measure the thermal performance of a Gifford–McMahon regenerator. In the present study, a test facility was established to conduct the single-blow measurement for evaluating the thermal performance of the regenerator with large NTU values (NTU ⩾ 150) . A comparison on the NTU value of the test regenerator between this improved model and two prior models is shown. Empirical correlations were presented to show the relationships of the friction factor and the Nusselt number vs. the Reynolds number for the test regenerator.

An improved data reduction method for transient liquid crystal thermography on film cooling measurements

Abstract This study proposes an improved data reduction method for the applications of transient liquid crystal thermography on film cooling effectiveness measurements. On the evaluations of film cooling effectiveness and heat transfer coefficient, an “equivalent step temperature” (EST) is proposed to replace the Duhamel’s superposition principle which is conventionally used to account for the actual temperature rises in both free-stream and injection flows rather than the ideal step temperature changes. For obtaining both values at over thousands of measured locations, the current data reduction method can effectively reduce the calculation time as compared with the conventional Duhamel’s superposition method, but adds only negligible errors.

Effect of surface characteristics on capillary flow in triangular microgrooves

Abstract The present work aims to study the effect of surface characteristics on the maximum wetted axial length ( x max ) of a triangular microgrooves plate. A series of triangular microgrooves with upper width ( W ) of 0.4 mm and the vertex angle ( α ) of 60° was machined on oxygen-free copper plate. The measured microgrooves plates include one with non-etched surface texture with lined incisions left by machining tool, and another with chemically etched surface texture with micro cavities. Methanol and ethanol were used as working fluid. The tilt angles of test device ( β ) and the applied heat flux ( q b ″) were varied for measurement. The present result shows that the surface texture with micro cavities will have 10–35% longer wetted axial length as compared with surface texture with lined incisions. The surface texture performed by chemical etching is effective in increasing the capillary performance of low surface tension fluid. A baseline check shows good agreement among the present experimental result and previous study.

FILM COOLING OVER A CONCAVE SURFACE THROUGH TWO STAGGERED ROWS OF COMPOUND ANGLE HOLES

Abstract Experimental results of film cooling effectiveness over a concave surface with two staggered rows are presented by employing transient liquid crystal thermography. Four different discrete hole configurations are used for the injection of jet flow, including a straight circular hole configuration with a spanwise injection angle (β) of 0° and three forward‐expanded hole configurations with β = 0°, 45° and 90° respectively. In all test models there are two staggered rows of discrete holes with streamwise injection angle (γ ) of 35°. Blowing ratios (M) are 0.5, 1.0, and 2.0. The effects of blowing ratio, hole expanded angle, and injection angle orientation on film cooling performance are investigated. The jet flow with M = 0.5 is fairly uniform along the wall surface. The lift‐off phenomenon can be found in the jet flow with β = 0° for both cases of simple and compound angles at M = 1.0 and also exists among all test cases at M = 2.0 except for β = 90°. The lift‐off effect results in a decrease in both η and h /h0. At β = 0°, the jet flow with a forward‐expanded hole gives higher η and lower h /h0 than a simple angle hole. At a fixed blowing ratio, the jet flow with compound angle holes has lower q /q0 and thus provides better wall protection than that with simple angle holes. In the present study, the compound angle with β = 0° at M = 2.0 provides the best film‐cooling protection over the concave surface among all the test configurations.

Air Bubble Generation Through a Submerged Micro-Hole

The aim of the present study are visualization and prediction of passively generated air bubbles through a submerged micro-hole. A simple orifice model, which has been used in most previous studies for bubble formation through an orifice, is modified by considering the friction loss of air flow in a micro-hole with moderate length-to-diameter ratio (4.38 to 13.64). The required driving pressure difference for the generation and detachment of an air bubble can be obtained. In the measurement, liquid was constantly drained out of a test chamber to induce a gradual decrease in chamber air pressure. Air bubblewas generated once a threshold pressure difference was reached. The generations of air bubble were observed at liquid drained rates of 0.006, 0.01, 0.02, 0.035, 0.05, and 0.100 ml s−1 through test plates with hole diameters of 1200, 580, 220, 130, 92, and 60 μm, respectively. The predicted volume of a detached bubble and the threshold driving pressure difference for bubble generation and detachment agree well with the measured results. The pressure difference variation in the test chamber can be well predicted by this proposed approach.

Film Cooling Over a Concave Surface Through a Row of Expanded Holes

This paper presents heat transfer coefficient and film cooling effectiveness measurements over a constant curvature concave surface. The coolant flow is ejected into the mainstream through a row of either simple holes or forward-expanded holes maintained at a streamwise injection angle (γ) of 35°. A transient liquid crystal thermography was employed to measure both the local heat transfer coefficient and film cooling effectiveness over the film-cooled concave test piece. With a pitch-to-diameter ratio (P/d) of 3, each forward-expanded injection hole has an expanded angle of 8° at the exit plane. In current study, the effect of blowing ratio (M) on film cooling performance was also investigated by varying the blowing ratio range from 0.5 to 1.5. Measurements were performed at mainstream Reynolds number (Red) of 2000 with turbulence intensity (Tu) of 2%, and coolant-to-mainstream density ratio (ρc/ρm) of 1.05. The curvature strength (2r/d) of test piece is 86.5. Comparisons were made with baseline cases of concave surface test piece with simple hole configuration done in prior studies. For forward-expanded hole configuration, measured results showed that both the laterally averaged heat transfer coefficient and film cooling effectiveness increase with increasing blowing ratio downstream of X/d = 10. A better film protection effect can be observed at M = 0.5 since coolant flows ejected at this blowing ratio might stay closer to the concave surface than other blowing ratios in present tested range for both hole configurations. As far as the hole shape is concerned, the forward-expanded hole injection provides better surface protection than the simple hole injection.Copyright