Rong-Horng Chen

The Influence of Horizontal Longitudinal Vibrations and the Condensation Section Temperature on the Heat Transfer Performance of a Heat Pipe

This study is primarily focused on the influence of horizontal longitudinal vibrations and the condensation section temperature on the heat transfer performance of a grooved cylindrical copper heat pipe, with a length of 600 mm and an outer diameter of 8 mm. Longitudinal vibrations with frequencies of 3, 4, 5, 6, and 9 Hz and amplitudes of 2.8, 5, 10, 15, 20, and 25 mm, which would give accelerations in the range of 0.1–1.01 g, were experimentally tested. The condensation section temperature was set at 20, 30, or 40°C. A heating jacket and a cooling sleeve were installed at the evaporation and condensation sections of the test cell to mimic a constant heat flux and a constant temperature boundary, respectively. When the heat pipe started to vibrate horizontally in the longitudinal direction, this vibration caused an increase in the heat transfer of the heat pipe that was directly proportional to the input vibration energy below 500 mm2 Hz2. When the value of the vibration energy exceeded this value, the heat transfer enhancement per unit vibration energy decreased rapidly. Along with the decrease in the condensation section temperature, the average temperature of the heating section decreases. The influence of the condensation section temperature on the maximum heat transfer is much greater than that of the vibrations.

Reduction of Nitric Oxide Emission From a SI Engine by Water Injection at the Intake Runner

The effects of pulsed water injection at the intake port of a modern port fuel injection gasoline engine were investigated. A port water injection system was developed and the water injector was installed on the intake runner of the single cylinder motorcycle engine at a location upstream of the fuel injector. The results show that with a water-gasoline injection ratio of 1, more than 80% of NOx emission can be removed. The trade-off was a 25% reduction in torque output at 4000 rpm and 20% throttle opening; however, the decrease on torque can be controlled to be within 5% by reducing water-gasoline mass ratios to less than 0.6. We also performed NOx emission modeling using one-dimensional gas dynamics code with extended Zeldovich mechanism, and consistent results were found between numerical prediction and experimental measurements. The port water injection approach appears to be an effective means for reducing NOx emission from a gasoline engine at low speed and high load conditions without largely sacrificing the performances on torque output and unburned hydrocarbon emissions.Copyright

Impact of a compound drop on a dry surface

The impact of a water-in-oil compound drop on a dry quartz surface was studied. The impact outcomes depended on a core-to-overall mass ratio and a Weber number. For a Weber number less than 570 and a core-to-overall mass ratio ranging from 0.07 to 0.7, five collision patterns were observed: complete deposition, shell deposition with core partial rebound, shell splash with core-shell deposition, shell splash with core partial rebound, and shell splash with core-shell partial rebound. Past research has indicated that the splash phenomenon depends strongly on liquid properties such as surface tension and viscosity in addition to the properties of the solid surface and the surrounding gas. The liquid properties in a compound drop were made non-uniform by the presence of additional interfaces in the interior of the liquid drop.

Micro-explosion of a water-in-hexadecane compound drop

The micro-explosion of a water-in-oil compound drop, without emulsification, was investigated experimentally. The compound drop, composed of a water core encased by an n-hexadecane shell, was suspended and heated to micro-explosion. The heating process and the micro-explosion behavior were recorded by a high-speed video system, and the temperature history of the compound drop was measured under three ambient temperatures, namely 320°C, 400°C and 500°C. The behaviors of the micro-explosion were grouped into three modes, namely direct explosion, partial explosion, and swelling, according to the outcomes of micro-explosion recorded by the high-speed video camera. At an ambient temperature of 400°C or 500°C, the micro-explosion onset time was observed to increase with the micro-explosion temperature; but this trend was not as obvious for the ambient temperature of 320°C. The intensity, judged from the production of secondary drops, of the micro-explosion rose as the micro-explosion time lengthened because the accumulation of thermal energy within the oversaturated water core drop grew to a higher extent.

Burning Behavior of Gas-in-Oil Compound Drops

In this study, a gas-in-oil compound-drop stream was produced by the breaking up of an oil jet with gas core, and its burning characteristics were observed. The compound jet broke up into stable compound drops if the spacing between bubbles was greater than the circumference of the compound jet. The outer diameter of the compound drops was about 1.8 times of the inner diameter of the outer tube and the ratios of inner to outer diameters of the compound drop depended only on the gas-to-liquid velocity ratios. After entering a high-temperature environment, the gas-in-oil compound drop exploded shortly due to the rupture of the oil shell. The gas core was released immediately and formed a microfuel jet. The burning of a gas-in-oil compound drop could be separated into two stages: explosion of the compound drop and burning of the remaining single-phase drop. The explosion intensity is relatively weaker compared with the microexplosion of an emulsion drop or a liquid-in-liquid compound drop.

Collision outcome of a water drop on the surface of a deep diesel fuel pool

This study investigated the collision of water drops with diesel fuel. The target liquid was selected not only because this interaction is commonly observed in many fires but also because diesel fuel exhibits similar viscosity to heavy oils on fire. Investigated collision phenomena include water drop disintegration, cavity development, droplet ejection from the underside of the cavity, droplet ejection from the liquid (diesel fuel) crown rim, and formation of water-in-diesel compound drops. Results suggest that the number of water droplets from the disintegrated water drop increases non-linearly with increased Weber number. At a Weber number of 700, the number of water droplets reached a maximum while their size was minimized.

The influence of longitudinal vibrations on the heat transfer performance of inclined heat pipes

This study focused on investigating the influence of longitudinal vibrations, the condensation section temperature, and the inclination angles on the heat transfer performance of grooved cylindrical copper heat pipes with lengths of 600 and 150 mm and an outer diameter of 8 mm. The inclination angles of the tested heat pipes were 0°, ±45°, and ±90°. Longitudinal vibrations with frequencies of 3, 4, 5, 6, and 9 Hz and amplitudes of 2.8, 5, 10, 15, 20, and 25 mm, which resulted in accelerations between 0.1 and 1.01 g, were experimentally tested. The condensation section temperatures were set at 20°C, 30°C, and 40°C. A heating jacket and a cooling sleeve were installed at the evaporation and condensation sections of the test cell to simulate a constant heat flux and a constant temperature boundary, respectively. The results showed that with the heat pipe placed with the condensation section on top and the evaporation section on bottom, a fairly low and constant thermal resistance (approximately 0.25 K/W for the 600-mm heat pipe and 0.75–1.2 K/W for the 150-mm heat pipe) was obtained, both with and without heat pipe vibration and regardless of the condensation section temperature.