APCChE 2019

Hall E, 2nd pm, Day 4, Thursday Abstracts

Session 3. Heat transfer and thermal engineering

E421 [Keynote] On the performance enhancement of spray cooling with the inverse Marangoni effect: chasing the heat
Sung TSANG, Chia-Hsuan LIN, Chen-li SUN
National Taiwan University, Taipei 10617 Taiwan

By inducing the inverse Marangoni convection, we successfully utilize a self-rewetting fluid to enhance the evaporative cooling of a spray system. The self-rewetting fluid is able to produce a surface-tension-driven fluid flow, which continuously replenishes the heated region to prevent dryout. As a result, cooling rate can be drastically increased. We find that the formation of a liquid film after the spray discharge is vital to this cooling enhancement, which requires a superhydrophilic surface and a proper spray height. Once the inverse Marangoni convection commences, the total heat transfer can be augmented three to seven times for a single pulse of spray. On the other hand, using the self-rewetting fluid in an intermittent spray system can be beneficial because comparable heat transfer rate can be delivered by spraying the self-rewetting fluid at much lower frequency. Although a longer spray pulse increases the heat transfer rate per cycle, the spray frequency also decreases for a given duty cycle which is unfavorable when a given time span is considered. Despite the moderate cooling rate per cycle for a shorter spray pulse, the time-averaged heat transfer rate is improved by the increase in spray frequency. For a fixed pulse duration, lower duty cycle leads to more sparse spray, higher surface temperature, and stronger inverse Marangoni convection. However, the resultant cooling rate is poorer and dry-out may occur if the duty cycle becomes too small. For large cooling-area application, we add more spray heads and find that deploying more nozzles helps to reduce the fluctuation in surface temperature but has little effect on the cooling rate. Increasing the spray frequency not only improve the cooling rate but also reduce temperature fluctuation. This enhancement becomes more apparent as the number of nozzles increases.

E423 Effect of Marangoni convection in a droplet containing surfactant on thin film shape
Kyushu University

In recent years, printed electronics, in which wiring of electronic devices are formed by an inkjet method, has been focused. However, when a droplet is deposited on substrate by the inkjet method, there is a problem that it is difficult to control the width and the shape of the thin film. In our laboratory, it has been reported that the addition of surfactant to the coating solution causes Marangoni convection towards the center of the droplet at the surface due to the difference of surface tension, and the film becomes finer. However, the relationship between the flow in droplet and the shape of the film after drying droplet has not been clarified. Therefore, the purpose of this study is to clarify the effect of Marangoni convection on thin film shape by visualizing the flow inside droplet. Samples of the anisole-polystyrene solution with a surfactant are prepared. Each of them includes surfactant in various concentration and a small amount of fluorescent polymer as tracer. Surfactant in each solution is one of the four. Then a small amount of powder fluorescent polymer was added to each solution as tracer. Two experiments for prepared solutions were conducted, which are the dropping them on substrate and measurement of surface tension. Each solution was deposited on a hydrophilic substrate as a droplet with diameter of 80 micrometers using an inkjet method. Finally, the internal flow of droplet during evaporation and the shape of the thin film after drying were observed. Surface tension was measured for solutions including surfactant in various concentrations. As a result, it was revealed that the thin film after drying of a droplet became fine and ring shape tends to be suppressed by Marangoni convection. Additionally, the measurement of surface tension showed that the visualized flow is Marangoni convection.

E424 Formation mechanism of amorphous silicon nanoparticles synthesized by induction thermal plasma
Xiaoyu ZHANG, Kentaro YAMANO, Ririko HAYASHIDA, Hirotaka SONE, Manabu TANAKA, Takayuki WATANABE
Kyushu University, Fukuoka, Japan

This study focus on the synthesis of amorphous silicon nanoparticles by induction thermal plasma and understanding the formation mechanism. Crystalline Si powder with 5 μm of average diameter was injected into the induction thermal plasma at 20 kW-4MHz under atmospheric pressure. The powder feed rate ranges from 64 mg/min to 400 mg/min. Counter-flow quenching gas up to 70 L/min was axially injected from downstream of the torch to enhance the quenching effect for silicon nanoparticles. In the high temperature plasma region, the raw materials immediately evaporate. In the tail region of the plasma flame, supersaturated Si vapor starts to nucleate and then condenses onto its nucleus forming Si nanoparticles. The effect of the operating parameters such as quenching gas flow rate and powder feed rate have been investigated. The collected particles were characterized by using X-ray diffraction (XRD) and transmission electron microscopy. The amorphization degree was defined as the mass fraction of amorphous silicon in the silicon nanoparticles including both crystal and amorphous, and was calculated by internal standard method with XRD results. The obtained results show that higher quenching gas flow rate and lower feed rate lead to smaller diameter with higher amorphization degree. Figure 1 shows the diffraction patterns of nanoparticles with diameter which is equal to 140 nm and 8 nm, respectively. Smaller nanoparticles in Fig. 1 (b) are amorphous because of the appearance of the diffuse rings, while most small nanoparticles agglomerated together. For huge nanoparticle in Fig. 1 (a), some clear and regular diffraction spots are observed in the patterns, and means that the sample is crystal. This research indicates that induction thermal plasma can be used to synthesize pure amorphous material at a single step.

E425 Screening and Performance Evaluation of Hydrogen Bond Donors (HBDs) and Acceptors (HBAs) as CH4 hydrate inhibitors
Woojin GO1, Dongyoung LEE1, Ki-Sub KIM2, Yongwon SEO1
1 School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea
2 School of Chemical and Materials Engineering, Korea National University of Transportation, Chungbuk 27469, Republic of Korea

Oil and gas pipeline blockage due to gas hydrate formation in the deep ocean should be well managed because it would lead to environmental disasters and economic losses. To avoid this issue, researchers have been searching for effective hydrate inhibitors. Kinetic hydrate inhibitors (KHIs) are well-known substances to suppress gas hydrate formation with a small dosage (typically less than 1 wt%) whereas thermodynamic hydrate inhibitors (THIs) require a dosage up to 60 wt%. In this study, we examined inhibition performances of specific HBDs and HBAs using a high-pressure autoclave reactor and a high-pressure micro-differential scanning calorimeter (HP μ-DSC). We used a ramping method with a gradual decrease of temperature (0.2K/min) to measure onset points of hydrate formation which was detected by an abrupt pressure drop. The onset temperatures obtained by this method enabled us to estimate the performance of each inhibitor molecule as a KHI. Furthermore, we used COSMO-RS (COnductor like Screening MOdel for Real Solvents) program to see how the molecular structure and electron distributions of these HBDs and HBAs can affect CH4 hydrate inhibition. We obtained an electron density histogram named σ-profile and a characteristic function named σ-potential to visualize relationships between experimental results and screening results of each molecule. These results will demonstrate how HBD and HBA molecules affect CH4 hydrate inhibition with molecular interaction between inhibitor molecules and host water molecules and contribute to guiding us in the search of effective and environmentally benign inhibitors.

E426 Stable operation of rotary stoker furnace for industrial waste
Koichi SHINOHARA1,2, Daisuke KONO1, Masayoshi MINAKAMI1, Tatsuya KAWAJIRI1, Shuji HIRONAKA2, Jun FUKAI2
2 Kyushu University

Incineration is one of the most general methods to treat industrial waste. Much amount of bottom ash is landfilled without being reused. Reduction of components such as harmful metals contained in bottom ash under appropriate incineration conditions makes it possible to reduce the amount of landfill waste and to increase the amount of reuse bottom ash. Management of conditions to control of bottom ash content has to be done for various kinds of industrial waste whose contents changes every day.
As the first step to improve incineration conditions, the effect of the primary air supplied to the bottom of a rotary stoker furnace is mainly investigated in this study.
Combustion characteristics of industry waste with typical component are numerically investigated using a combustion simulation program. It is confirmed that auxiliary fuel is necessary to burn the waste when preheated primary air is not supplied. On the other hand, preheated primary air enhances dry rate of input materials and enables to burn the waste without auxiliary fuel.
On practical process (commercial facility), components and calorific values of input material are commonly controlled by mixing some kinds of wastes. The preheated primary air effects on reduction of bottom ash amount, decrease of auxiliary fuel consumption and stabilization of furnace operation. The fluctuation ranges of the measured values such as temperatures in the facility are narrowed by preheated primary air, being independent of components of the input materials. This is mainly because the air enhances dry rate in the furnace. Consequently, preheated primary air is found to result in stable operation.