Pub Date : 2021-01-01DOI: 10.1299/jtst.2021jtst0011
S. Sawada, Daisuke Okada, N. Nakatsuka, Kazuki Tainaka, T. Hori, J. Hayashi, F. Akamatsu
In the pulverized coal combustion, coal particles cross over a steep temperature gradient formed by a diffusion flame. This temperature gradient affects the particle temperature. This study has experimentally investigated effects of field temperature and residence time in high-temperature regions on the flame structure of single coal particles, since the substances of the devolatilization process varied due to the particle heating rate. The inlet velocity and the oxygen concentration of a laminar couterflow vary to control the residence time and the temperature gradient, respectively. A magnified two-color pyrometry was carried out to understand flame structure and the time series of flame and particle temperature. The results showed that the increase of oxygen concentration raises the volatile matter combustion temperature and flame diameter, and prolongs duration of the volatile matter combustion. The char combustion temperature decreases as the flow velocity increases. The maximum effective flame diameter increases linearly with increasing volatile matter combustion temperature regardless of particle size. This suggested an increase in flame interference distance. The maximum flame diameter increases monotonically with increasing volatile matter combustion temperature. the diluent the ignition of single-particle coal prolongs the duration of volatile matter an with a Hencken burner in an oxy-fuel and of coal particles. The simulation showed that it is essential to consider the CO 2 gasification reaction when simulating char combustion in an oxy-fuel combustion environment. Köser et al. performed highly repeated OH-LIF measurements on single coal particles. They used a laminar flow reactor that provided a hot oxygen-rich exhaust gas environment. Time-resolved imaging of the OH distribution at 10 kHz allowed to identify post-reaction and post-combustion zones and visualize the time evolution of coal particles during combustion. These studies show that a an increase in combustion temperature. interact with each other. Both of them change due to changes in field conditions. Therefore, the aim of this study is to clarify the effects of residence time and field temperature on the flame structure and temperature of the coal particle simultaneously. The temperature of the field and the residence time were changed by the O 2 concentration diluted with the inert gas nitrogen and the flow velocity. This study measured the time-series soot temperature, particle temperature, and particle diameter during pulverized coal combustion.
{"title":"Effects of ambient temperature on the combustion processes of single pulverized coal particle","authors":"S. Sawada, Daisuke Okada, N. Nakatsuka, Kazuki Tainaka, T. Hori, J. Hayashi, F. Akamatsu","doi":"10.1299/jtst.2021jtst0011","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0011","url":null,"abstract":"In the pulverized coal combustion, coal particles cross over a steep temperature gradient formed by a diffusion flame. This temperature gradient affects the particle temperature. This study has experimentally investigated effects of field temperature and residence time in high-temperature regions on the flame structure of single coal particles, since the substances of the devolatilization process varied due to the particle heating rate. The inlet velocity and the oxygen concentration of a laminar couterflow vary to control the residence time and the temperature gradient, respectively. A magnified two-color pyrometry was carried out to understand flame structure and the time series of flame and particle temperature. The results showed that the increase of oxygen concentration raises the volatile matter combustion temperature and flame diameter, and prolongs duration of the volatile matter combustion. The char combustion temperature decreases as the flow velocity increases. The maximum effective flame diameter increases linearly with increasing volatile matter combustion temperature regardless of particle size. This suggested an increase in flame interference distance. The maximum flame diameter increases monotonically with increasing volatile matter combustion temperature. the diluent the ignition of single-particle coal prolongs the duration of volatile matter an with a Hencken burner in an oxy-fuel and of coal particles. The simulation showed that it is essential to consider the CO 2 gasification reaction when simulating char combustion in an oxy-fuel combustion environment. Köser et al. performed highly repeated OH-LIF measurements on single coal particles. They used a laminar flow reactor that provided a hot oxygen-rich exhaust gas environment. Time-resolved imaging of the OH distribution at 10 kHz allowed to identify post-reaction and post-combustion zones and visualize the time evolution of coal particles during combustion. These studies show that a an increase in combustion temperature. interact with each other. Both of them change due to changes in field conditions. Therefore, the aim of this study is to clarify the effects of residence time and field temperature on the flame structure and temperature of the coal particle simultaneously. The temperature of the field and the residence time were changed by the O 2 concentration diluted with the inert gas nitrogen and the flow velocity. This study measured the time-series soot temperature, particle temperature, and particle diameter during pulverized coal combustion.","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":"66342899","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.2021jtst0005
M. Tange, K. Kuribayashi, A. Abdelghany
Boiling heat transfer has a combination of sensible heat transfer of liquid and latent heat transfer due to vaporization. To examine the sensible heat transfer in boiling, thermometry of liquid in liquid-vapor multiphase flow must play a significant role. Although there are several optical methods proposed for the thermometry of boiling phenomena, it is challenging to directly measure the temperature field of boiling at relatively high heat flux due to many boiling bubbles' interruption of the illumination and observation. This study proposes a novel thermometry method using a confined space, a sandwiched space between two transparency plates, and two-color laser induced fluorescence thermometry to measure the liquid temperature distribution around multiple boiling bubbles. The confined space restricted the fluid motion to make it possible to illuminate and observe the almost whole area of interest. The intensity ratio of the two kinds of fluorescent dye exhibits the local and temporal temperature without any invasion of physical probes. We successfully observed the scavenging of superheated liquid from the heat transfer surface to demonstrate this method's utility. The temporal temperature changes at several positions extracted from experimental data with this method were consistent with the boiling bubble behavior. We also discussed remained issues on the method.
{"title":"Temperature measurement around multiple boiling bubbles in a confined space using two-color laser-induced fluorescence","authors":"M. Tange, K. Kuribayashi, A. Abdelghany","doi":"10.1299/jtst.2021jtst0005","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0005","url":null,"abstract":"Boiling heat transfer has a combination of sensible heat transfer of liquid and latent heat transfer due to vaporization. To examine the sensible heat transfer in boiling, thermometry of liquid in liquid-vapor multiphase flow must play a significant role. Although there are several optical methods proposed for the thermometry of boiling phenomena, it is challenging to directly measure the temperature field of boiling at relatively high heat flux due to many boiling bubbles' interruption of the illumination and observation. This study proposes a novel thermometry method using a confined space, a sandwiched space between two transparency plates, and two-color laser induced fluorescence thermometry to measure the liquid temperature distribution around multiple boiling bubbles. The confined space restricted the fluid motion to make it possible to illuminate and observe the almost whole area of interest. The intensity ratio of the two kinds of fluorescent dye exhibits the local and temporal temperature without any invasion of physical probes. We successfully observed the scavenging of superheated liquid from the heat transfer surface to demonstrate this method's utility. The temporal temperature changes at several positions extracted from experimental data with this method were consistent with the boiling bubble behavior. We also discussed remained issues on the method.","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":"66342215","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.2021jtst0004
Kendai Kawakami, Shosuke Sakamoto, Hirofumi Tanigawa, T. Tsuruta
{"title":"A study on transition process to MEB by limiting boiling space","authors":"Kendai Kawakami, Shosuke Sakamoto, Hirofumi Tanigawa, T. Tsuruta","doi":"10.1299/jtst.2021jtst0004","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0004","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":"66342498","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.2021jtst0039
H. Matsushima, A. Almerbati
Prediction and optimization of water-cooling performance of a pin fin heat sink with variable pin diameters along a flow direction is attempted. We have developed a simple analyze procedure for pin fin heat sink that enables to evaluate the row-by-row performance when diameters of fins are morphed along a flow direction. Validity of the procedure is confirmed for uniform and non-uniform pin diameter cases. The Taguchi method is applied to an optimization method. Optimal design among the considered cases, in which the thermal resistance is minimum, corresponds to the configuration where the pin diameter equals 3 mm constructed from copper. This holds for constant inlet velocity and constant pumping power cases. Optimum structure of heat sink considering simultaneous parameters (minimum thermal resistance, pressure drop and mass) occurs when the heat sink is built from aluminum with a pin diameter of 2 mm. These three parameters influence the design of the heat sink. For instance, when the thermal resistance and the pressure drop are significant, optimum structure is a “wing like shape” with larger pin diameter near the central rows and copper as material. However, when the thermal resistance and the heat sink mass are of interest, the optimum structure associated with the larger pin diameter constructed from aluminum. Also, when we consider the pressure drop and heat sink mass, the optimum design is the one where the pin diameter is 1 mm built from aluminum.
{"title":"Optimal structure of a water cooled pin fin heat sink by Taguchi method depending on various requirements","authors":"H. Matsushima, A. Almerbati","doi":"10.1299/jtst.2021jtst0039","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0039","url":null,"abstract":"Prediction and optimization of water-cooling performance of a pin fin heat sink with variable pin diameters along a flow direction is attempted. We have developed a simple analyze procedure for pin fin heat sink that enables to evaluate the row-by-row performance when diameters of fins are morphed along a flow direction. Validity of the procedure is confirmed for uniform and non-uniform pin diameter cases. The Taguchi method is applied to an optimization method. Optimal design among the considered cases, in which the thermal resistance is minimum, corresponds to the configuration where the pin diameter equals 3 mm constructed from copper. This holds for constant inlet velocity and constant pumping power cases. Optimum structure of heat sink considering simultaneous parameters (minimum thermal resistance, pressure drop and mass) occurs when the heat sink is built from aluminum with a pin diameter of 2 mm. These three parameters influence the design of the heat sink. For instance, when the thermal resistance and the pressure drop are significant, optimum structure is a “wing like shape” with larger pin diameter near the central rows and copper as material. However, when the thermal resistance and the heat sink mass are of interest, the optimum structure associated with the larger pin diameter constructed from aluminum. Also, when we consider the pressure drop and heat sink mass, the optimum design is the one where the pin diameter is 1 mm built from aluminum.","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":"66344283","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.2021jtst0013
A. Sciazko, Takaaki Shimura, Y. Komatsu, N. Shikazono
In the present study, solid oxide cells (SOCs) were operated in the electricity generation (solid oxide fuel cell, SOFC) mode and the hydrogen production (solid oxide electrolysis cell, SOEC) mode. The fuel electrodes fabricated with nickel-gadolinia doped ceria (Ni-GDC) and nickel-yttria stabilized zirconia (Ni-YSZ) composites were investigated. The correlations between changes in the microstructure and degradation of electrochemical performance are discussed. The degradation mechanisms correlated with Ni phase were found to be similar for Ni-GDC and Ni-YSZ electrodes. On the other hand, the stability of the ceramic phase differs significantly between the two electrode materials.
{"title":"Ni-GDC and Ni-YSZ electrodes operated in solid oxide electrolysis and fuel cell modes","authors":"A. Sciazko, Takaaki Shimura, Y. Komatsu, N. Shikazono","doi":"10.1299/jtst.2021jtst0013","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0013","url":null,"abstract":"In the present study, solid oxide cells (SOCs) were operated in the electricity generation (solid oxide fuel cell, SOFC) mode and the hydrogen production (solid oxide electrolysis cell, SOEC) mode. The fuel electrodes fabricated with nickel-gadolinia doped ceria (Ni-GDC) and nickel-yttria stabilized zirconia (Ni-YSZ) composites were investigated. The correlations between changes in the microstructure and degradation of electrochemical performance are discussed. The degradation mechanisms correlated with Ni phase were found to be similar for Ni-GDC and Ni-YSZ electrodes. On the other hand, the stability of the ceramic phase differs significantly between the two electrode materials.","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":"66342537","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.2021jtst0010
Y. Atagi, M. Shimura, M. Tanahashi
To yield an effective control to impede the progress of combustion oscillation and to lead to the development of completely stable combustors, it is necessary to reveal the mechanism of the destabilization. For revealing the destabilization characteristics of combustion oscillation, methane-air turbulent lean premixed flames in a swirl-stabilized combustor were investigated by high-speed simultaneous measurements of stereoscopic particle image velocimetry (SPIV) arranged side by side, OH planar laser induced fluorescence (OH PLIF), OH chemiluminescence and pressure fluctuation. The transition process from stable state to unstable state of combustion oscillation is defined based on the root-mean-square (rms) values of pressure fluctuation p’rms. Experimental condition was set as the swirl number of 1.14, equivalence ratio of 0.69 and total flow rate of 350 L/min where the transition process is observed. In the transition process, magnitudes of fluctuating properties gradually gain. Pressure fluctuation phase-based analyses clarified that, as the transition process advances, intermittent large-scale vortical motion in the outside of sheer layer expands and approach the inlet, which has a close affinity with the growth of oscillation with making burnt regions involve unburnt regions. The transition process holds well for the Rayleigh criteria in that heat release fluctuates approximately the same phase of pressure fluctuation. On the other hand, in-flow velocity fluctuates in the antiphase of pressure fluctuation.
{"title":"Simultaneous OH PLIF/Chemiluminescence and stereoscopic PIV measurements of combustion oscillation onset in turbulent swirling lean premixed flames","authors":"Y. Atagi, M. Shimura, M. Tanahashi","doi":"10.1299/jtst.2021jtst0010","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0010","url":null,"abstract":"To yield an effective control to impede the progress of combustion oscillation and to lead to the development of completely stable combustors, it is necessary to reveal the mechanism of the destabilization. For revealing the destabilization characteristics of combustion oscillation, methane-air turbulent lean premixed flames in a swirl-stabilized combustor were investigated by high-speed simultaneous measurements of stereoscopic particle image velocimetry (SPIV) arranged side by side, OH planar laser induced fluorescence (OH PLIF), OH chemiluminescence and pressure fluctuation. The transition process from stable state to unstable state of combustion oscillation is defined based on the root-mean-square (rms) values of pressure fluctuation p’rms. Experimental condition was set as the swirl number of 1.14, equivalence ratio of 0.69 and total flow rate of 350 L/min where the transition process is observed. In the transition process, magnitudes of fluctuating properties gradually gain. Pressure fluctuation phase-based analyses clarified that, as the transition process advances, intermittent large-scale vortical motion in the outside of sheer layer expands and approach the inlet, which has a close affinity with the growth of oscillation with making burnt regions involve unburnt regions. The transition process holds well for the Rayleigh criteria in that heat release fluctuates approximately the same phase of pressure fluctuation. On the other hand, in-flow velocity fluctuates in the antiphase of pressure fluctuation.","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":"66342751","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.2021jtst0009
Yuto Takehara, A. Sekimoto, Y. Okano, T. Ujihara, S. Dost
Silicon carbide (SiC) is a power semiconductor used to supply and control the electric power source. Top-Seeded Solution Growth (TSSG) method is a promising technique for producing high-quality SiC single crystals. In order to achieve a highand uniform-growth rate in this growth technique, however, the complex fluid flow developing in the growth melt/solution, mainly induced by the electromagnetic field of the induction-heating coils, free surface tension gradient, and buoyancy, must be well-controlled. Our previous studies have shown that the applications of a static magnetic field and seed rotation are effective in controlling the components of this melt flow and the associated control parameters were optimized effectively using the Bayesian optimization. In this study, we analyze the optimal state determined by the Bayesian optimization in more detail and it is found that the separation of the Marangoni flow near the seed edge leads to a non-uniform growth rate. In addition, the most sensitive region of the melt flow is determined by using an explainable machine learning technique based on a convolutional neural network and the sensitivity map obtained by SmoothGrad. This machine learning technique automatically predicts the preferred melt flow pattern that would lead to high-quality crystal growth. The interpretations by the explainable machine learning technique used in the present study are consistent with those of previous studies carried out on the optimization of the TSSG method.
{"title":"Explainable machine learning for the analysis of transport phenomena in top-seeded solution growth of SiC single crystal","authors":"Yuto Takehara, A. Sekimoto, Y. Okano, T. Ujihara, S. Dost","doi":"10.1299/jtst.2021jtst0009","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0009","url":null,"abstract":"Silicon carbide (SiC) is a power semiconductor used to supply and control the electric power source. Top-Seeded Solution Growth (TSSG) method is a promising technique for producing high-quality SiC single crystals. In order to achieve a highand uniform-growth rate in this growth technique, however, the complex fluid flow developing in the growth melt/solution, mainly induced by the electromagnetic field of the induction-heating coils, free surface tension gradient, and buoyancy, must be well-controlled. Our previous studies have shown that the applications of a static magnetic field and seed rotation are effective in controlling the components of this melt flow and the associated control parameters were optimized effectively using the Bayesian optimization. In this study, we analyze the optimal state determined by the Bayesian optimization in more detail and it is found that the separation of the Marangoni flow near the seed edge leads to a non-uniform growth rate. In addition, the most sensitive region of the melt flow is determined by using an explainable machine learning technique based on a convolutional neural network and the sensitivity map obtained by SmoothGrad. This machine learning technique automatically predicts the preferred melt flow pattern that would lead to high-quality crystal growth. The interpretations by the explainable machine learning technique used in the present study are consistent with those of previous studies carried out on the optimization of the TSSG method.","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":"66342237","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.2021JTST0023
M. Saito, Keisuke Komada, D. Sakaguchi, H. Ueki
ratio of inertia to surface tension. The droplet breakup constructed analysis Abstract Targeting the evaluation of the universal droplet breakup process, measurements were made on diesel fuel sprays injected from two solenoid type injectors with different specifications. The velocity and size of the spray droplets were measured using a laser 2-focus velocimeter (L2F). The velocity of small droplets that follow the flow was taken as the air velocity. The Weber number was evaluated using the velocity of the droplets relative to air as the representative velocity. Since the spray expands in a conical shape with the nozzle hole at its apex, the measurement points were placed on a straight line from the apex, which is the estimated flight direction of droplets. The change in droplet size in the flight direction was considered to be due to secondary breakup, and the rate of decrease in droplet size during this process was evaluated. It was confirmed that the velocity and size of the droplets inside the spray injected from the two injectors varied over time, and the spatial distribution of the Weber number and the rate of droplet size decrease in the middle of the injection period was non-uniform and different. It was found that there is a positive correlation between the Weber number and the rate of droplet size decrease for both sprays, and that the relationship is nearly identical despite the fact that the characteristics are different between the two sprays. The secondary breakup process was shown to be independent of the injection conditions such as the diameter and number of nozzle holes.
{"title":"Droplet size decrease rate of secondary breakup in diesel fuel sprays","authors":"M. Saito, Keisuke Komada, D. Sakaguchi, H. Ueki","doi":"10.1299/JTST.2021JTST0023","DOIUrl":"https://doi.org/10.1299/JTST.2021JTST0023","url":null,"abstract":"ratio of inertia to surface tension. The droplet breakup constructed analysis Abstract Targeting the evaluation of the universal droplet breakup process, measurements were made on diesel fuel sprays injected from two solenoid type injectors with different specifications. The velocity and size of the spray droplets were measured using a laser 2-focus velocimeter (L2F). The velocity of small droplets that follow the flow was taken as the air velocity. The Weber number was evaluated using the velocity of the droplets relative to air as the representative velocity. Since the spray expands in a conical shape with the nozzle hole at its apex, the measurement points were placed on a straight line from the apex, which is the estimated flight direction of droplets. The change in droplet size in the flight direction was considered to be due to secondary breakup, and the rate of decrease in droplet size during this process was evaluated. It was confirmed that the velocity and size of the droplets inside the spray injected from the two injectors varied over time, and the spatial distribution of the Weber number and the rate of droplet size decrease in the middle of the injection period was non-uniform and different. It was found that there is a positive correlation between the Weber number and the rate of droplet size decrease for both sprays, and that the relationship is nearly identical despite the fact that the characteristics are different between the two sprays. The secondary breakup process was shown to be independent of the injection conditions such as the diameter and number of nozzle holes.","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":"66343492","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.2021jtst0031
Nae-Hyun Kim
For a cooling or heating coil of a building air conditioning system, large diameter tubes (over 12.7 mm) with wave fins are frequently used. Furthermore, there have been attempts to apply oval tubes to the heating or cooling coils. In this study, nine samples - three herringbone wave fin/round tube, three smooth wave fin/round tube and three smooth wave fin/oval tube samples – were tested under dry condition. All of the samples had the same original tube diameter (12.7 mm). For the smooth wave fin samples, fins were identical, and for the round tube samples, fin corrugation angles were almost the same. Tests were conducted varying the frontal air velocity from 1.0 to 4.0 m/s. Results showed that the round tube samples yielded higher conductance per volume ( ) than the oval tube sample. Similarly, the smooth wave fin samples yielded a higher conductance per volume than the herringbone wave fin samples. At one row configuration, however, a significant difference among samples existed between the heat transfer conductance per volume and the heat transfer coefficient, and the reason was explained by the difference in fin efficiency between the round and the oval geometry. The pressure drops of the round tube samples were larger than those of the oval tube samples. Similarly, the smooth wave fin samples yielded larger pressure drops than the herringbone wave fin samples. A performance evaluation revealed that the smooth wave fin samples yielded larger heat transfer conductances per volume than the herringbone wave fin samples at the same pumping power per volume.
{"title":"Effects of fin corrugation and tube geometry on the airside performance of fin-and-tube heat exchangers - Part I; dry surface","authors":"Nae-Hyun Kim","doi":"10.1299/jtst.2021jtst0031","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0031","url":null,"abstract":"For a cooling or heating coil of a building air conditioning system, large diameter tubes (over 12.7 mm) with wave fins are frequently used. Furthermore, there have been attempts to apply oval tubes to the heating or cooling coils. In this study, nine samples - three herringbone wave fin/round tube, three smooth wave fin/round tube and three smooth wave fin/oval tube samples – were tested under dry condition. All of the samples had the same original tube diameter (12.7 mm). For the smooth wave fin samples, fins were identical, and for the round tube samples, fin corrugation angles were almost the same. Tests were conducted varying the frontal air velocity from 1.0 to 4.0 m/s. Results showed that the round tube samples yielded higher conductance per volume ( ) than the oval tube sample. Similarly, the smooth wave fin samples yielded a higher conductance per volume than the herringbone wave fin samples. At one row configuration, however, a significant difference among samples existed between the heat transfer conductance per volume and the heat transfer coefficient, and the reason was explained by the difference in fin efficiency between the round and the oval geometry. The pressure drops of the round tube samples were larger than those of the oval tube samples. Similarly, the smooth wave fin samples yielded larger pressure drops than the herringbone wave fin samples. A performance evaluation revealed that the smooth wave fin samples yielded larger heat transfer conductances per volume than the herringbone wave fin samples at the same pumping power per volume.","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":"66343611","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.2021jtst0036
Daiki Matsugi, Yosuke Hasebe, T. Yamazaki, T. Matsuoka, Yuji Nakamura
Experimental investigations of burning characteristics of a tested specimen consisting of a polyethylene foam soaked in 100 wt% hydrogen peroxide are made. All experiments are carried out in a large volume chamber, which newly introduced in our previous work at an initial pressure range from p = 0.1 to p = 0.35 MPa in absolute with various fuel porosity range from ε = 0.6 to ε = 0.9, which corresponds to global equivalence ratios from φ = 0.51 to φ = 3.8. Temperature measurements using an R-type thermocouple embedded into the specimen are then conducted to investigate thermal structure (e.g., profiles of temperature and temperature gradients and burning surface temperature) of the burning specimen for deep understandings of the burning process. Following forced ignition at top surface of the specimen, steady successive-burning process is successfully observed for all conditions studied in this work. Burning rates (a rate at which the top surface moves downward) are measured by carefully tracking the top surface of the specimen by adopting an image processing software. Findings show that overall burning rates at the rate from 1 to 3.2 mm/s are obtained and influenced by pressure and the fuel porosity. Additionally, results of the direct temperature measurements reveal that the temperature gradient in the gas-phase layer near the top surface (burning surface) of the specimen increases as pressure increases, resulting in an increase in the overall burning rate. The top surface temperature and its pressure dependency, and a global activation energy at the top surface temperature of the specimen are experimentally measured accordingly.
{"title":"Experimental investigation of burning characteristics of porous combustible soaked in liquid oxidizer","authors":"Daiki Matsugi, Yosuke Hasebe, T. Yamazaki, T. Matsuoka, Yuji Nakamura","doi":"10.1299/jtst.2021jtst0036","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0036","url":null,"abstract":"Experimental investigations of burning characteristics of a tested specimen consisting of a polyethylene foam soaked in 100 wt% hydrogen peroxide are made. All experiments are carried out in a large volume chamber, which newly introduced in our previous work at an initial pressure range from p = 0.1 to p = 0.35 MPa in absolute with various fuel porosity range from ε = 0.6 to ε = 0.9, which corresponds to global equivalence ratios from φ = 0.51 to φ = 3.8. Temperature measurements using an R-type thermocouple embedded into the specimen are then conducted to investigate thermal structure (e.g., profiles of temperature and temperature gradients and burning surface temperature) of the burning specimen for deep understandings of the burning process. Following forced ignition at top surface of the specimen, steady successive-burning process is successfully observed for all conditions studied in this work. Burning rates (a rate at which the top surface moves downward) are measured by carefully tracking the top surface of the specimen by adopting an image processing software. Findings show that overall burning rates at the rate from 1 to 3.2 mm/s are obtained and influenced by pressure and the fuel porosity. Additionally, results of the direct temperature measurements reveal that the temperature gradient in the gas-phase layer near the top surface (burning surface) of the specimen increases as pressure increases, resulting in an increase in the overall burning rate. The top surface temperature and its pressure dependency, and a global activation energy at the top surface temperature of the specimen are experimentally measured accordingly.","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":"66344332","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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