Pub Date : 2021-01-01DOI: 10.1299/JTST.2021JTST0025
Dhanesh Chandrasekaran, Venkatesan Jayaraman, S. Sasidharan, S. Gomathinayagam
This research article intends to discuss on the role and effects of dispersing solution combustion derived magnesia nanoflakes (~17 nm) within the biodiesel-diesel blends and pure diesel termed as nanofuels, in order to investigate the functional and pollutant emissions of a single-cylinder, electrically loaded, water-cooled diesel engine. The fuels focussed in this study are a blend of palm oil biodiesel and regular diesel dispersed with 50 ppm magnesia nanoflakes, and a pure diesel dispersed with 50 ppm magnesia nanoflakes. These fuels are compared with regular diesel which is considered as the base reference fuel, as well as with the biodiesel-diesel blend. From the experimental measurements, we inferred that the fuel density, viscous nature, and calorific value enhanced with the addition of nanoflakes. As for the engine performance attributes, the brake specific fuel consumption (BSFC) is lessened by 3.08% and 2.88% for particle dispersed biodiesel-diesel blend and particle dispersed diesel, respectively, whereas the brake thermal efficiency (BTE) enhances by 5.04% for particle dispersed biodiesel-diesel blend and 2.74% for particle dispersed diesel. With reference to emission, the unburnt hydrocarbon (UHC), white damp (CO), particulate exhaust or smoke, and the nitrogen oxides (NOx) are reduced by 9.51%, 18.71%, 13.64%, and 5.63%, respectively for particle dispersed biodiesel-diesel blend and 10.35%, 16.54%, 13.64%, 19.47%, and 4.70%, respectively for particle dispersed diesel. To
{"title":"Role of combustion derived magnesia nanoflakes on the combustion, emission and functional characteristics of diesel engine susceptible to palm oil biodiesel-diesel blend","authors":"Dhanesh Chandrasekaran, Venkatesan Jayaraman, S. Sasidharan, S. Gomathinayagam","doi":"10.1299/JTST.2021JTST0025","DOIUrl":"https://doi.org/10.1299/JTST.2021JTST0025","url":null,"abstract":"This research article intends to discuss on the role and effects of dispersing solution combustion derived magnesia nanoflakes (~17 nm) within the biodiesel-diesel blends and pure diesel termed as nanofuels, in order to investigate the functional and pollutant emissions of a single-cylinder, electrically loaded, water-cooled diesel engine. The fuels focussed in this study are a blend of palm oil biodiesel and regular diesel dispersed with 50 ppm magnesia nanoflakes, and a pure diesel dispersed with 50 ppm magnesia nanoflakes. These fuels are compared with regular diesel which is considered as the base reference fuel, as well as with the biodiesel-diesel blend. From the experimental measurements, we inferred that the fuel density, viscous nature, and calorific value enhanced with the addition of nanoflakes. As for the engine performance attributes, the brake specific fuel consumption (BSFC) is lessened by 3.08% and 2.88% for particle dispersed biodiesel-diesel blend and particle dispersed diesel, respectively, whereas the brake thermal efficiency (BTE) enhances by 5.04% for particle dispersed biodiesel-diesel blend and 2.74% for particle dispersed diesel. With reference to emission, the unburnt hydrocarbon (UHC), white damp (CO), particulate exhaust or smoke, and the nitrogen oxides (NOx) are reduced by 9.51%, 18.71%, 13.64%, and 5.63%, respectively for particle dispersed biodiesel-diesel blend and 10.35%, 16.54%, 13.64%, 19.47%, and 4.70%, respectively for particle dispersed diesel. To","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66343207","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/jtst.2021jtst0008
N. Sako, J. Hayashi, Y. Daimon, Hiroumi Tani, H. Kawanabe
numerical
数值
{"title":"Experimental analysis of the spreading of a liquid film on a bipropellant thruster chamber wall","authors":"N. Sako, J. Hayashi, Y. Daimon, Hiroumi Tani, H. Kawanabe","doi":"10.1299/jtst.2021jtst0008","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0008","url":null,"abstract":"numerical","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66342524","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/jtst.2021jtst0014
Riku Yamashita, Satoshi Waku, D. Mori, S. Ueno, K. Tanoue, Y. Moriyoshi
Recently, since international problems such as global warming, air pollution, and energy resource depletion are gradually becoming more serious, combined heat and power and cogeneration systems have been attracting a lot of attention since they can be used as low environmental load power generation systems (Agency for Natural Resources and Energy in Japan, Energy in Japan, 2003). A cogeneration system can recover an engine’s waste heat and provide both heat and electrical energy at the same time, resulting in a high total efficiency of 80%. In Japan, since 65% of the installed cogeneration systems are gas engines and about 49% of the total power generation capacity is fueled by natural gas, increasing the efficiency of natural gas engines, whose efficiency is currently about 40%, enhances the utilization of both heat and electrical energy, thus corresponding to various environmental and customer demands. One of the most effective ways for improving the thermal efficiency of combustion engines and reducing the harmful emissions of undesirable combustion products, such as nitrogen oxides, is the use of lean-burn techniques and exhaust gas recirculation (EGR) (Heywood, 2018). Although such methods have already been in practical use, they still face many technical problems, such as the substantial decrease in the burning velocity and the unstable combustion in the lean or diluted mixture region. To solve these problems, prechamber ignition systems are commonly used in gas engines to improve their inflammability and enhance the combustion characteristics in the lean or diluted mixture region. A prechamber ignition system has a small “prechamber” whose volume is less than 5% of the main chamber’s volume. The combustible mixture is first ignited in the prechamber, resulting in a torch flame that can burn a leaner mixture in the main chamber, where the torch flame is injected from the prechamber into the main chamber. Since the combustion characteristics in gas engines depend on the injected torch Riku YAMASHITA*, Satoshi WAKU*, Daisuke MORI*, Seiya UENO*, Kimitoshi TANOUE* and Yasuo MORIYOSHI** * Oita Univ. Dept. of Mechanical and Energy systems engineering 700 Dannoharu, Oita 870-1192, Japan E-mail: tanoue@oita-u.ac.jp ** Chiba Univ. Graduate School of Engineering 1-33 Yayoicho, Inage Ward, Chiba-shi, Chiba, 263-0022, Japan
近年来，由于全球变暖、空气污染、能源枯竭等国际问题日益严重，热电联产和热电联产系统由于可以作为低环境负荷的发电系统而备受关注(Agency for Natural Resources and energy in Japan, energy in Japan, 2003)。热电联产系统可以回收发动机的余热，同时提供热能和电能，总效率高达80%。在日本，由于已安装的热电联产系统中有65%是燃气发动机，而总发电能力中约有49%是由天然气提供燃料，因此提高天然气发动机的效率(目前效率约为40%)可以提高热能和电能的利用率，从而满足各种环境和客户需求。提高内燃机热效率和减少有害燃烧产物(如氮氧化物)排放的最有效方法之一是使用稀燃技术和废气再循环(EGR) (Heywood, 2018)。虽然这种方法已经在实际应用中，但仍然面临许多技术问题，如燃烧速度大幅降低，稀或稀混合气区域燃烧不稳定等。为了解决这些问题，通常在燃气发动机中采用预燃室点火系统来改善发动机的可燃性，提高稀混合气区或稀混合气区的燃烧特性。预室点火系统有一个小的“预室”，其体积小于主室体积的5%。可燃混合物首先在预室中点燃，产生火炬火焰，该火炬火焰可以在主室中燃烧较稀薄的混合物，火炬火焰从预室注入主室。由于燃气发动机的燃烧特性取决于注入火炬山下陆*，WAKU Satoshi *， MORI Daisuke *，上野星矢*，田上Kimitoshi *和moriyoyasuo **大分大学机械与能源系统工程系700 Dannoharu, Oita 870-1192, Japan E-mail: tanoue@oita-u.ac.jp **千叶大学工程研究生院1-33 Yayoicho，图像区，千叶，2630022,Japan
{"title":"Effect of fuel property on the ignition and combustion characteristics of prechamber ignition","authors":"Riku Yamashita, Satoshi Waku, D. Mori, S. Ueno, K. Tanoue, Y. Moriyoshi","doi":"10.1299/jtst.2021jtst0014","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0014","url":null,"abstract":"Recently, since international problems such as global warming, air pollution, and energy resource depletion are gradually becoming more serious, combined heat and power and cogeneration systems have been attracting a lot of attention since they can be used as low environmental load power generation systems (Agency for Natural Resources and Energy in Japan, Energy in Japan, 2003). A cogeneration system can recover an engine’s waste heat and provide both heat and electrical energy at the same time, resulting in a high total efficiency of 80%. In Japan, since 65% of the installed cogeneration systems are gas engines and about 49% of the total power generation capacity is fueled by natural gas, increasing the efficiency of natural gas engines, whose efficiency is currently about 40%, enhances the utilization of both heat and electrical energy, thus corresponding to various environmental and customer demands. One of the most effective ways for improving the thermal efficiency of combustion engines and reducing the harmful emissions of undesirable combustion products, such as nitrogen oxides, is the use of lean-burn techniques and exhaust gas recirculation (EGR) (Heywood, 2018). Although such methods have already been in practical use, they still face many technical problems, such as the substantial decrease in the burning velocity and the unstable combustion in the lean or diluted mixture region. To solve these problems, prechamber ignition systems are commonly used in gas engines to improve their inflammability and enhance the combustion characteristics in the lean or diluted mixture region. A prechamber ignition system has a small “prechamber” whose volume is less than 5% of the main chamber’s volume. The combustible mixture is first ignited in the prechamber, resulting in a torch flame that can burn a leaner mixture in the main chamber, where the torch flame is injected from the prechamber into the main chamber. Since the combustion characteristics in gas engines depend on the injected torch Riku YAMASHITA*, Satoshi WAKU*, Daisuke MORI*, Seiya UENO*, Kimitoshi TANOUE* and Yasuo MORIYOSHI** * Oita Univ. Dept. of Mechanical and Energy systems engineering 700 Dannoharu, Oita 870-1192, Japan E-mail: tanoue@oita-u.ac.jp ** Chiba Univ. Graduate School of Engineering 1-33 Yayoicho, Inage Ward, Chiba-shi, Chiba, 263-0022, Japan","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66342675","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/JTST.2021JTST0024
Kitti Nilpueng, S. Wongwises
The concept of heat transfer enhancement in a plate fin heat sink (PFHS) using twisted tape is presented. The airflow behavior in the flow channel and heat sink performance are investigated at the Reynolds numbers between 2000 and 5000. The twisted tape and perforated twisted tape with twist ratio between 2.5 and 3.5 are equipped between the fins of the PFHS. For perforated twisted tape, the holes are drilled along the twisted tape length with the ratio of perforation diameter to twisted taped width (d/W) between 0.2 and 0.6. The heat transfer coefficient and pressure drop are enhanced by decreasing the twist ratio and increasing the Reynolds number and the d/W ratio between 0.2 and 0.4. However, they are dropped when the d/W ratio higher than 0.4. The highest thermal performance factors of the plate fin heat sink equipped with twisted tape (PFHSTT) and the plate fin heat sink equipped with perforated twisted tape (PFHSPTT) are 1.28 and 1.33, respectively. The correlations of the Nusselt number and friction factor related to twist ratio and d/W ratio are generated and proposed for designing and selecting in the future. between perforation thermal performance. the impact of the plate the performance of a PFHS. the air bypass the of a good a of the performance of PFHS with different fin forms of sinks. The a frontal a test section and releasing to the ambient air. The wind tunnel was made from a 5-mm thick acrylic plate. The rectangular flow channel had a width of 27 mm, a height of 25 mm, and a length of 1.0 m. A 4.5-inch axial fan, which was controlled with an inverter, was installed at the tunnel entrance. The honeycomb (straightener) was used to eliminate the twisted airflow from the entrance before entering the PFHS. The hot wire anemometer monitored the airflow velocity inside the wind tunnel. To simulate the actual working conditions, the heat sink base was placed on the plate heater surface, which was used as a heat source. Silicone thermal grease was coated on the heater surface to reduce thermal contact resistance. The variable voltage transformer adjusted the supplied heat flux from a 100 W plate heater. The heater was embedded in a Bakelite rectangular rod with a 65-mm width, 65-mm height, and 120-mm length, and the wind tunnel was covered by 10 mm of insulation. To read the temperature of airflow at the PFHS’s entrance and exit, five T-type thermocouples were installed at the center of the flow channel. Two thermocouples were placed before the heat sink at distances of 20 and 40 mm. Similarly, three thermocouples were located after the heat sink at distances of 20, 40, and 60 mm. Four thermocouples were positioned at 1 mm below the base surface to measure the average surface temperature. The distance between thermocouples along the heat sink length was 15 mm. The data logger connected to the computer recorded all temperatures obtained from the thermocouples. A digital manometer logged the pressure difference across the heat sink. To en
{"title":"Thermal performance investigation of a plate fin heat sink equipped with twisted tape and perforated twisted tape","authors":"Kitti Nilpueng, S. Wongwises","doi":"10.1299/JTST.2021JTST0024","DOIUrl":"https://doi.org/10.1299/JTST.2021JTST0024","url":null,"abstract":"The concept of heat transfer enhancement in a plate fin heat sink (PFHS) using twisted tape is presented. The airflow behavior in the flow channel and heat sink performance are investigated at the Reynolds numbers between 2000 and 5000. The twisted tape and perforated twisted tape with twist ratio between 2.5 and 3.5 are equipped between the fins of the PFHS. For perforated twisted tape, the holes are drilled along the twisted tape length with the ratio of perforation diameter to twisted taped width (d/W) between 0.2 and 0.6. The heat transfer coefficient and pressure drop are enhanced by decreasing the twist ratio and increasing the Reynolds number and the d/W ratio between 0.2 and 0.4. However, they are dropped when the d/W ratio higher than 0.4. The highest thermal performance factors of the plate fin heat sink equipped with twisted tape (PFHSTT) and the plate fin heat sink equipped with perforated twisted tape (PFHSPTT) are 1.28 and 1.33, respectively. The correlations of the Nusselt number and friction factor related to twist ratio and d/W ratio are generated and proposed for designing and selecting in the future. between perforation thermal performance. the impact of the plate the performance of a PFHS. the air bypass the of a good a of the performance of PFHS with different fin forms of sinks. The a frontal a test section and releasing to the ambient air. The wind tunnel was made from a 5-mm thick acrylic plate. The rectangular flow channel had a width of 27 mm, a height of 25 mm, and a length of 1.0 m. A 4.5-inch axial fan, which was controlled with an inverter, was installed at the tunnel entrance. The honeycomb (straightener) was used to eliminate the twisted airflow from the entrance before entering the PFHS. The hot wire anemometer monitored the airflow velocity inside the wind tunnel. To simulate the actual working conditions, the heat sink base was placed on the plate heater surface, which was used as a heat source. Silicone thermal grease was coated on the heater surface to reduce thermal contact resistance. The variable voltage transformer adjusted the supplied heat flux from a 100 W plate heater. The heater was embedded in a Bakelite rectangular rod with a 65-mm width, 65-mm height, and 120-mm length, and the wind tunnel was covered by 10 mm of insulation. To read the temperature of airflow at the PFHS’s entrance and exit, five T-type thermocouples were installed at the center of the flow channel. Two thermocouples were placed before the heat sink at distances of 20 and 40 mm. Similarly, three thermocouples were located after the heat sink at distances of 20, 40, and 60 mm. Four thermocouples were positioned at 1 mm below the base surface to measure the average surface temperature. The distance between thermocouples along the heat sink length was 15 mm. The data logger connected to the computer recorded all temperatures obtained from the thermocouples. A digital manometer logged the pressure difference across the heat sink. To en","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66343105","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/JTST.2021JTST0027
Y. Okazaki, Yumeto Takase, Y. Kuwata, K. Suga
To describe permeable roughness e ff ects on turbulence statistics, our previously reported PIV (particle image ve-locimetry) experimental data (Shimizu et al., 2019; Okazaki et al., 2020) of turbulent channel flows over two di ff erent permeable roughness types are assessed. The considered roughness elements were porous transverse square ribs and rectangular sectioned short flat plates which were mounted on porous walls with constant spacings. The spacings were controlled to reproduce the so-called k- and d-type roughness geometries. The values of the pore-per-inch of the materials of the roughness elements and the porous wall were the same in each case. Three di ff erent foamed porous materials were considered while their porosities were approximately 0.8. By the assessment of the logarithmic mean velocity profiles of the two roughness cases, it is confirmed that a linear relationship between the zero-plane displacement and the roughness scale exists. The data of the flat porous walls without roughness elements (Suga et al., 2010; 2017) are also confirmed to have the same trend regardless of the porous media. We found an e ff ective displacement parameter which linearly increases as the pore diameter. Using the pore-scale Reynolds number, we then propose a correlation that describes the value of the variable von K´arm´an constant and a simple formula for estimating the equivalent sand grain roughness height for all cases presently assessed.
为了描述可渗透粗糙度对湍流统计的影响，我们之前报道的PIV(粒子图像定位法)实验数据(Shimizu et al.， 2019;Okazaki et al.， 2020)对两种不同的可渗透粗糙度类型的湍流通道流动进行了评估。所考虑的粗糙度单元是多孔的横向方肋和矩形截面的短平板，它们安装在具有恒定间距的多孔壁上。控制间距以再现所谓的k型和d型粗糙度几何形状。在每种情况下，粗糙度单元和多孔壁材料的每英寸孔隙率值相同。考虑三种不同的泡沫多孔材料，其孔隙率约为0.8。通过对两种粗糙度情况下的平均速度对数曲线的评估，证实了零面位移与粗糙度尺度之间存在线性关系。不含粗糙度元素的平坦多孔壁数据(Suga et al.， 2010;2017)也证实了无论多孔介质如何，都有相同的趋势。我们发现有效位移参数随孔隙直径线性增加。利用孔隙尺度雷诺数，我们提出了一个描述变量von K ' arm '和常数值的相关性，以及一个简单的公式，用于估计目前评估的所有情况下的等效砂粒粗糙度高度。
{"title":"Describing characteristic parameters of turbulence over two-dimensional porous roughness","authors":"Y. Okazaki, Yumeto Takase, Y. Kuwata, K. Suga","doi":"10.1299/JTST.2021JTST0027","DOIUrl":"https://doi.org/10.1299/JTST.2021JTST0027","url":null,"abstract":"To describe permeable roughness e ff ects on turbulence statistics, our previously reported PIV (particle image ve-locimetry) experimental data (Shimizu et al., 2019; Okazaki et al., 2020) of turbulent channel flows over two di ff erent permeable roughness types are assessed. The considered roughness elements were porous transverse square ribs and rectangular sectioned short flat plates which were mounted on porous walls with constant spacings. The spacings were controlled to reproduce the so-called k- and d-type roughness geometries. The values of the pore-per-inch of the materials of the roughness elements and the porous wall were the same in each case. Three di ff erent foamed porous materials were considered while their porosities were approximately 0.8. By the assessment of the logarithmic mean velocity profiles of the two roughness cases, it is confirmed that a linear relationship between the zero-plane displacement and the roughness scale exists. The data of the flat porous walls without roughness elements (Suga et al., 2010; 2017) are also confirmed to have the same trend regardless of the porous media. We found an e ff ective displacement parameter which linearly increases as the pore diameter. Using the pore-scale Reynolds number, we then propose a correlation that describes the value of the variable von K´arm´an constant and a simple formula for estimating the equivalent sand grain roughness height for all cases presently assessed.","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66343364","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/jtst.2021jtst0040
Xuli Liu, Chengjun Jing, Yan Zhao, T. Miyazaki
{"title":"Numerical study on performance of the dew point evaporative cooling system","authors":"Xuli Liu, Chengjun Jing, Yan Zhao, T. Miyazaki","doi":"10.1299/jtst.2021jtst0040","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0040","url":null,"abstract":"","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66344575","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/jtst.2021jtst0003
H. Mamori, K. Fukudome, K. Ogino, N. Fukushima, M. Yamamoto
Direct numerical simulations of turbulent Taylor–Couette flows are performed to investigate the effect of a traveling wave control on torque and heat transfer. In the Taylor–Couette flow, inner and outer cylinders are rotating and immobile, respectively, and the temperature difference between cylinder walls is maintained as constant. The ratio between the inner and outer cylinder is 0.882, and the Reynolds number is set as 84,000. A traveling wave-like blowing and suction is imposed on an inner cylinder wall. A parametric study shows the effect of control parameters on torque and heat transfer. We focused on three characteristic parameter sets: heat transfer enhancement, relaminarization phenomenon, and simultaneous achievement of torque reduction and heat transfer enhancement. We employed identity equations by using three-component decomposition to clarify contributions from advection, turbulence, and diffusion on torque and Stanton number. The results indicated that the traveling wave control affects the turbulence and advection contributions.
{"title":"Heat transfer enhancement and torque reduction by traveling wave-like blowing and suction in turbulent Taylor-Couette flow","authors":"H. Mamori, K. Fukudome, K. Ogino, N. Fukushima, M. Yamamoto","doi":"10.1299/jtst.2021jtst0003","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0003","url":null,"abstract":"Direct numerical simulations of turbulent Taylor–Couette flows are performed to investigate the effect of a traveling wave control on torque and heat transfer. In the Taylor–Couette flow, inner and outer cylinders are rotating and immobile, respectively, and the temperature difference between cylinder walls is maintained as constant. The ratio between the inner and outer cylinder is 0.882, and the Reynolds number is set as 84,000. A traveling wave-like blowing and suction is imposed on an inner cylinder wall. A parametric study shows the effect of control parameters on torque and heat transfer. We focused on three characteristic parameter sets: heat transfer enhancement, relaminarization phenomenon, and simultaneous achievement of torque reduction and heat transfer enhancement. We employed identity equations by using three-component decomposition to clarify contributions from advection, turbulence, and diffusion on torque and Stanton number. The results indicated that the traveling wave control affects the turbulence and advection contributions.","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66342456","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/jtst.2021jtst0012
Takahiro Suzuki, Tatsuaki Nagai, S. Tsushima
Herein, novel simultaneous in situ measurements of electrode slurries used to fabricate polymer electrolyte fuel cell electrodes during the drying process were conducted and analyzed via numerical simulation to understand mass transfer during drying and structure formation mechanism of the electrodes. The structure of the porous electrodes that affects cell performance is formed during drying of the electrode slurries. However, directly observing the state of the opaque electrode slurries is difficult, and thus their drying behavior has not been well understood. This study focuses on the variation in coated film thickness and the variation of electrical resistance of the electrode slurries during drying due to solvent evaporation and solid-phase agglomeration. A novel measurement technique of the electrode slurries’ electrical resistance is developed using a microelectrodeterminal chip. Time-dependent variations of electrical resistance and film thickness during drying are simultaneously measured. The results are analyzed and compared with the numerical simulations results. Electrode material distribution in the slurry varied according to the type of carbon materials. The electrode slurry containing platinum-supported carbon particles as a catalyst formed a sedimentary layer and a surface accumulation layer of the particles. Such drying behavior affected the resultant porous structure in the form of
{"title":"Simultaneous in situ measurements and numerical analysis of mass transfer in polymer electrolyte fuel cell electrode slurries during drying","authors":"Takahiro Suzuki, Tatsuaki Nagai, S. Tsushima","doi":"10.1299/jtst.2021jtst0012","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0012","url":null,"abstract":"Herein, novel simultaneous in situ measurements of electrode slurries used to fabricate polymer electrolyte fuel cell electrodes during the drying process were conducted and analyzed via numerical simulation to understand mass transfer during drying and structure formation mechanism of the electrodes. The structure of the porous electrodes that affects cell performance is formed during drying of the electrode slurries. However, directly observing the state of the opaque electrode slurries is difficult, and thus their drying behavior has not been well understood. This study focuses on the variation in coated film thickness and the variation of electrical resistance of the electrode slurries during drying due to solvent evaporation and solid-phase agglomeration. A novel measurement technique of the electrode slurries’ electrical resistance is developed using a microelectrodeterminal chip. Time-dependent variations of electrical resistance and film thickness during drying are simultaneously measured. The results are analyzed and compared with the numerical simulations results. Electrode material distribution in the slurry varied according to the type of carbon materials. The electrode slurry containing platinum-supported carbon particles as a catalyst formed a sedimentary layer and a surface accumulation layer of the particles. Such drying behavior affected the resultant porous structure in the form of","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66342976","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/jtst.2021jtst0016
C. Cha, H. Lee, C. You, S. Hwang
Moderate Intensity Low Oxygen Diluted (MILD) combustion has been investigated for a long time in order to minimize NOX emission still enhancing thermal efficiencies in the combustion equipment. Many researches about MILD combustion have been recently performed, but studies on MILD combustion of renewable fuel such as ethanol has been very scarce and particularly, specific information on the NOX production in ethanol-air MILD combustion has not been reported yet. In order to satisfy the condition for MILD combustion, internal recirculation is known to be essential in order to entrain the combustion products gas into air and fuel jets of combustion system. In this work, a series of numerical analysis with simplified opposed jet geometry have been done using the OPPDIF in Ansys program. Numerical analysis on how the recirculation ratio (KV) affects NOX emission in the ethanol-air combustion for MILD formation were carried out under the condition of various burnt gas dilution in reactant flow. The results show that the temperature was decreased by the increase of the recirculation ratio and the maximum heat release value became also low by the increase of the recirculation ratio. It was also found that the pyrolysis zone of the heat release was disappeared and the two heat release peaks are merged into one as combustion pattern is changed to MILD combustion mode.
{"title":"MILD combustion of ethanol-air with diluted hot oxidant by recirculation in opposite jet","authors":"C. Cha, H. Lee, C. You, S. Hwang","doi":"10.1299/jtst.2021jtst0016","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0016","url":null,"abstract":"Moderate Intensity Low Oxygen Diluted (MILD) combustion has been investigated for a long time in order to minimize NOX emission still enhancing thermal efficiencies in the combustion equipment. Many researches about MILD combustion have been recently performed, but studies on MILD combustion of renewable fuel such as ethanol has been very scarce and particularly, specific information on the NOX production in ethanol-air MILD combustion has not been reported yet. In order to satisfy the condition for MILD combustion, internal recirculation is known to be essential in order to entrain the combustion products gas into air and fuel jets of combustion system. In this work, a series of numerical analysis with simplified opposed jet geometry have been done using the OPPDIF in Ansys program. Numerical analysis on how the recirculation ratio (KV) affects NOX emission in the ethanol-air combustion for MILD formation were carried out under the condition of various burnt gas dilution in reactant flow. The results show that the temperature was decreased by the increase of the recirculation ratio and the maximum heat release value became also low by the increase of the recirculation ratio. It was also found that the pyrolysis zone of the heat release was disappeared and the two heat release peaks are merged into one as combustion pattern is changed to MILD combustion mode.","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66343017","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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