Pub Date : 2021-01-01DOI: 10.1299/jtst.2021jtst0033
Rikiya Shiono, I. Kano
the capacity of MC for heat flux values from 2.17 to 33.53 W/cm 2 at a system pressure of 100 kPa, an inlet degree of Abstract In this study, the cooling capabilities of flow boiling heat transfer aided by electrohydrodynamic (EHD) force and diamond-electrodeposited boiling surface is investigated in a micro-slit channel (MSC). The MSC uses a two-phase flow cooling system, in which an electric field is applied to a dielectric liquid using a slit electrode. To reduce the wall temperature below 60 °C and promote cooling in electronic devices, a dielectric liquid with a saturation temperature of 15 °C HCFO-1224yd (AGC, AMOLEA, CF 3 CF = CHCI) was selected as a working fluid. Moreover, the entire system was pressurized using nitrogen gas to suppress liquid flow instabilities due to the generation of cavitation at the saturated system pressure. To enhance boiling heat transfer, the surface was electrically deposited with fine diamond particles (mixture of particles with diameters 20 and 1.5 m), and an electric field of −5 kV/mm was applied between the surface and slit electrode. The experiments were conducted under various system pressures (75–230 kPa), mass flow rates (1.67–5.00 g/s), and degrees of subcooling (5–15 K) to evaluate the heat transfer performance. The electric field was effective in increasing both the critical heat flux (CHF) and heat transfer coefficient (HTC). The high electric field enhanced the boiling heat transfer until the inflow liquid entirely evaporated. Increasing the mass flow rate was also effective in increasing the CHF and HTC at lower wall temperatures, resulting in a maximum of 101 W/cm 2 at 64 °C and 37 kW/m 2 ·K at 52 °C, respectively. Increasing the system pressure improved the HTC but elevated the wall temperature. Subcooling was effective in increasing HTC. Increase in either pressure or subcooling did not change the CHF because the entire inflow liquid evaporated in the MSC chamber due to the electric field
{"title":"Experimental study on heat transfer enhancement in subcooled flow boiling under pressurized conditions","authors":"Rikiya Shiono, I. Kano","doi":"10.1299/jtst.2021jtst0033","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0033","url":null,"abstract":"the capacity of MC for heat flux values from 2.17 to 33.53 W/cm 2 at a system pressure of 100 kPa, an inlet degree of Abstract In this study, the cooling capabilities of flow boiling heat transfer aided by electrohydrodynamic (EHD) force and diamond-electrodeposited boiling surface is investigated in a micro-slit channel (MSC). The MSC uses a two-phase flow cooling system, in which an electric field is applied to a dielectric liquid using a slit electrode. To reduce the wall temperature below 60 °C and promote cooling in electronic devices, a dielectric liquid with a saturation temperature of 15 °C HCFO-1224yd (AGC, AMOLEA, CF 3 CF = CHCI) was selected as a working fluid. Moreover, the entire system was pressurized using nitrogen gas to suppress liquid flow instabilities due to the generation of cavitation at the saturated system pressure. To enhance boiling heat transfer, the surface was electrically deposited with fine diamond particles (mixture of particles with diameters 20 and 1.5 m), and an electric field of −5 kV/mm was applied between the surface and slit electrode. The experiments were conducted under various system pressures (75–230 kPa), mass flow rates (1.67–5.00 g/s), and degrees of subcooling (5–15 K) to evaluate the heat transfer performance. The electric field was effective in increasing both the critical heat flux (CHF) and heat transfer coefficient (HTC). The high electric field enhanced the boiling heat transfer until the inflow liquid entirely evaporated. Increasing the mass flow rate was also effective in increasing the CHF and HTC at lower wall temperatures, resulting in a maximum of 101 W/cm 2 at 64 °C and 37 kW/m 2 ·K at 52 °C, respectively. Increasing the system pressure improved the HTC but elevated the wall temperature. Subcooling was effective in increasing HTC. Increase in either pressure or subcooling did not change the CHF because the entire inflow liquid evaporated in the MSC chamber due to the electric field","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":"66343665","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.2021jtst0032
T. Moriyama, Wataru Kimura, Hiroki Asai, K. Yamamoto
In this study, OH chemiluminescence of methane-hydrogen premixed flames formed on a Bunsen burner was investigated. As for the chemiluminescence intensity, we obtained the values at the edge of the flame and at the central axis of the flame, compared with the value calculated by the inverse Abel transform. It was found that the value at the central axis of the flame was less dependent on the measurement position than that at the edge of the flame, because the effect of integrated chemiluminescence intensity on the optical path was small. In addition, four filters with different center wavelengths were tested. Although the chemiluminescence intensity was changed by the filter, the dependence of the chemiluminescence intensity on the equivalence ratio was almost the same. For more discussion, the OH concentration and the heat release rate predicted by the numerical simulation of a one-dimensional methane-hydrogen flame were compared with the OH chemiluminescence and the burning velocity in experiments. It was revealed that, even when hydrogen was added by keeping the total equivalence ratio constant, the OH chemiluminescence intensity was proportional to the production rate of excited OH* produced by the reaction of CH and O 2 concentrations. Similarly, the OH chemiluminescence intensity was apparently related with the heat release rate.
{"title":"OH chemiluminescence of methane-hydrogen premixed flames","authors":"T. Moriyama, Wataru Kimura, Hiroki Asai, K. Yamamoto","doi":"10.1299/jtst.2021jtst0032","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0032","url":null,"abstract":"In this study, OH chemiluminescence of methane-hydrogen premixed flames formed on a Bunsen burner was investigated. As for the chemiluminescence intensity, we obtained the values at the edge of the flame and at the central axis of the flame, compared with the value calculated by the inverse Abel transform. It was found that the value at the central axis of the flame was less dependent on the measurement position than that at the edge of the flame, because the effect of integrated chemiluminescence intensity on the optical path was small. In addition, four filters with different center wavelengths were tested. Although the chemiluminescence intensity was changed by the filter, the dependence of the chemiluminescence intensity on the equivalence ratio was almost the same. For more discussion, the OH concentration and the heat release rate predicted by the numerical simulation of a one-dimensional methane-hydrogen flame were compared with the OH chemiluminescence and the burning velocity in experiments. It was revealed that, even when hydrogen was added by keeping the total equivalence ratio constant, the OH chemiluminescence intensity was proportional to the production rate of excited OH* produced by the reaction of CH and O 2 concentrations. Similarly, the OH chemiluminescence intensity was apparently related with the heat release rate.","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":"66343853","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.2021JTST0020
Nae-Hyun Kim
{"title":"Airside heat transfer and pressure drop of an aluminum heat exchanger having a new louver fin with leading edge extension","authors":"Nae-Hyun Kim","doi":"10.1299/JTST.2021JTST0020","DOIUrl":"https://doi.org/10.1299/JTST.2021JTST0020","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":"66343257","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.2021jtst0006
D. Utsumi, Seia Fujii, Y. Hagiwara
The freezing of water droplets deposited or impinged on cold surfaces causes many problems in traffic lights, power transmission wires and heat exchangers. Thus, the suppression of the freezing of these droplets is very important. In this study, we carried out two-dimensional numerical simulation on the freezing of the water droplets on a horizontal cold surface using a Phase-field method. A new equation was developed to predict an increase in the total volume of the droplets due to the freezing. The changes in the physical properties of supercooled water with temperature were taken into account for an impinged droplet. The computational results for deposited droplets showed that a projection was formed on the cap of a frozen droplet and that the volume of ice was 8.8% higher than the volume of a deposited water droplet in its unfrozen state. However, the change in the mass due to the freezing was less than 0.001%. Also, a concave shape of the freezing front was predicted after an ice layer was formed. This was consistent with the results for freezing droplets observed by other researchers. Moreover, similar results were obtained in the case of impinged droplets. With these, a projection was formed. The volume of ice was 8.1% higher than the volume of the impinging droplet in the air, while the change in the mass was less than 0.0023%. The predicted freezing fronts were similar to that observed in previous studies.
{"title":"Numerical simulation on the freezing of deposited or impinged water droplets on a cold surface","authors":"D. Utsumi, Seia Fujii, Y. Hagiwara","doi":"10.1299/jtst.2021jtst0006","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0006","url":null,"abstract":"The freezing of water droplets deposited or impinged on cold surfaces causes many problems in traffic lights, power transmission wires and heat exchangers. Thus, the suppression of the freezing of these droplets is very important. In this study, we carried out two-dimensional numerical simulation on the freezing of the water droplets on a horizontal cold surface using a Phase-field method. A new equation was developed to predict an increase in the total volume of the droplets due to the freezing. The changes in the physical properties of supercooled water with temperature were taken into account for an impinged droplet. The computational results for deposited droplets showed that a projection was formed on the cap of a frozen droplet and that the volume of ice was 8.8% higher than the volume of a deposited water droplet in its unfrozen state. However, the change in the mass due to the freezing was less than 0.001%. Also, a concave shape of the freezing front was predicted after an ice layer was formed. This was consistent with the results for freezing droplets observed by other researchers. Moreover, similar results were obtained in the case of impinged droplets. With these, a projection was formed. The volume of ice was 8.1% higher than the volume of the impinging droplet in the air, while the change in the mass was less than 0.0023%. The predicted freezing fronts were similar to that observed in previous studies.","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":"66342403","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.2021jtst0002
A. Mitsuishi, Masahiro Takahashi, Takaaki Shimura, K. Iwamoto, A. Murata
The present study models the flow configuration in a tube downstream of multi-branching in a catalytic converter. Convective heat transfer in a thin circular straight pipe is analyzed by direct numerical simulation (DNS). Forced transverse vibration is applied to the pipe itself to enhance the heat transfer. The main computational domain is sufficiently long to capture the spatial development of the vibration effect with the inflow-outflow boundary condition. The representative Reynolds number is set to be less than that in a driver domain which generates the turbulent inflow of the main domain. Profiles of the Nusselt number exhibit that the positive effect of the vibration on the heat transfer becomes apparent at certain downstream locations. The distance to its location is short with the high vibration frequency keeping the amplitude constant. In the region where the heat transfer is enhanced, the main flow with high temperature is shifted to one side and the other side of the pipe wall in the vibration direction alternatingly with the appearance of the organized streamwise vortices. The flow structure in the present spatially developing configuration is governed mainly by the vibration frequency although the terminal heat transfer performance is approximately a function of the velocity amplitude of the vibration.
{"title":"Effect of spatial development on convective heat transfer enhancement in a pipe with transverse vibration","authors":"A. Mitsuishi, Masahiro Takahashi, Takaaki Shimura, K. Iwamoto, A. Murata","doi":"10.1299/jtst.2021jtst0002","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0002","url":null,"abstract":"The present study models the flow configuration in a tube downstream of multi-branching in a catalytic converter. Convective heat transfer in a thin circular straight pipe is analyzed by direct numerical simulation (DNS). Forced transverse vibration is applied to the pipe itself to enhance the heat transfer. The main computational domain is sufficiently long to capture the spatial development of the vibration effect with the inflow-outflow boundary condition. The representative Reynolds number is set to be less than that in a driver domain which generates the turbulent inflow of the main domain. Profiles of the Nusselt number exhibit that the positive effect of the vibration on the heat transfer becomes apparent at certain downstream locations. The distance to its location is short with the high vibration frequency keeping the amplitude constant. In the region where the heat transfer is enhanced, the main flow with high temperature is shifted to one side and the other side of the pipe wall in the vibration direction alternatingly with the appearance of the organized streamwise vortices. The flow structure in the present spatially developing configuration is governed mainly by the vibration frequency although the terminal heat transfer performance is approximately a function of the velocity amplitude of the vibration.","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":"66342431","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.2021jtst0038
Satoshi Nakatsuru, A. Kaewpradap, Ryosuke Nogi, T. Katsumi, Daisuke Sato, S. Kadowaki
researchers. The important parameters of premixed flames, i.e. the burning velocity, Markstein length and flame thickness, were experimentally obtained 2014), and the emission and heat transfer were estimated 2012). Moreover, the mixture of hydrogen and hydrocarbon is also gathering attention, and several research papers have published Abstract In this paper, the characteristics of hydrogen-propane-butane-air lean premixed flames on a flat flame burner were experimentally studied. To elucidate the shape and fluctuation of premixed flames, the cell width, RMS of fluctuation, peak frequency and reconstructed attractor were obtained from the direct photographic images and time series of light emission intensity. The cellular flames were observed at sufficiently low equivalence ratios; the flat flames were found under the other conditions. When the concentration of hydrogen was higher, the flat flames were formed at lower equivalence ratios. As the equivalence ratio became lower, the cell width and RMS increased in the range of cellular flames, which was due to high instability level. At low (high) equivalence ratios, moreover, the size of attractor was large (small) and the trajectory was unstable (quasi periodic). The experimental results revealed the instability characteristics of hydrogen-propane-butane-air lean premixed flames, and the obtained findings were applicable to the safe control of lean premixed flames.
{"title":"The shape and fluctuation of hydrogen-propane-butane-air lean premixed flames formed on a flat flame burner","authors":"Satoshi Nakatsuru, A. Kaewpradap, Ryosuke Nogi, T. Katsumi, Daisuke Sato, S. Kadowaki","doi":"10.1299/jtst.2021jtst0038","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0038","url":null,"abstract":"researchers. The important parameters of premixed flames, i.e. the burning velocity, Markstein length and flame thickness, were experimentally obtained 2014), and the emission and heat transfer were estimated 2012). Moreover, the mixture of hydrogen and hydrocarbon is also gathering attention, and several research papers have published Abstract In this paper, the characteristics of hydrogen-propane-butane-air lean premixed flames on a flat flame burner were experimentally studied. To elucidate the shape and fluctuation of premixed flames, the cell width, RMS of fluctuation, peak frequency and reconstructed attractor were obtained from the direct photographic images and time series of light emission intensity. The cellular flames were observed at sufficiently low equivalence ratios; the flat flames were found under the other conditions. When the concentration of hydrogen was higher, the flat flames were formed at lower equivalence ratios. As the equivalence ratio became lower, the cell width and RMS increased in the range of cellular flames, which was due to high instability level. At low (high) equivalence ratios, moreover, the size of attractor was large (small) and the trajectory was unstable (quasi periodic). The experimental results revealed the instability characteristics of hydrogen-propane-butane-air lean premixed flames, and the obtained findings were applicable to the safe control of lean premixed flames.","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":"66344184","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.2021jtst0017
N. Unno, K. Yuki, J. Taniguchi, S. Satake
{"title":"Effect of the gap height between the vibration plate and heating surface on boiling heat transfer in a boiling bubble resonator","authors":"N. Unno, K. Yuki, J. Taniguchi, S. Satake","doi":"10.1299/jtst.2021jtst0017","DOIUrl":"https://doi.org/10.1299/jtst.2021jtst0017","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":"66343031","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.2021JTST0028
S. Wiriyasart, P. Naphon
In this study, a constant fill ratio vapor chamber using water and ferrofluid as the coolants on the thermal performance and thermal optimization to provide the cooling range are presented. The liquid flow rate of the condenser side ranges from 0.029−0.099 kg/s, the input power of 100−300 W, heat source size of 30 mm × 30 mm, and the water and ferrofluid with φ=0 %, φ=0.005 % and φ=0.05 % as coolants are investigated. The results indicate that the minimum thermal resistance of a traditional vapor chamber of 0.126 C/W at m = 0.075 kg/s and vapor chamber with a mini channel of 0.077 C/W at m = 0.049 kg/s at φ=0.005 % are obtained. The vapor chamber with and without mini channel at a certain fill ratio of 26 % and 33 %, the heat source size of 30 mm × 30 mm, and the mass flow rate of ≥ 0.042 kg/s are withstanding the heat load range from 100–200 W. However, to achieve the high heat load range from 100–300 W, the vapor chamber with mini channel using the Fe3O4 ferrofluid φ=0.005 % is covering the entire cooling range and is recommended in electronic cooling applications.
{"title":"Transient thermal performance of constant fill ratio vapor chamber with different coolants","authors":"S. Wiriyasart, P. Naphon","doi":"10.1299/JTST.2021JTST0028","DOIUrl":"https://doi.org/10.1299/JTST.2021JTST0028","url":null,"abstract":"In this study, a constant fill ratio vapor chamber using water and ferrofluid as the coolants on the thermal performance and thermal optimization to provide the cooling range are presented. The liquid flow rate of the condenser side ranges from 0.029−0.099 kg/s, the input power of 100−300 W, heat source size of 30 mm × 30 mm, and the water and ferrofluid with φ=0 %, φ=0.005 % and φ=0.05 % as coolants are investigated. The results indicate that the minimum thermal resistance of a traditional vapor chamber of 0.126 C/W at m = 0.075 kg/s and vapor chamber with a mini channel of 0.077 C/W at m = 0.049 kg/s at φ=0.005 % are obtained. The vapor chamber with and without mini channel at a certain fill ratio of 26 % and 33 %, the heat source size of 30 mm × 30 mm, and the mass flow rate of ≥ 0.042 kg/s are withstanding the heat load range from 100–200 W. However, to achieve the high heat load range from 100–300 W, the vapor chamber with mini channel using the Fe3O4 ferrofluid φ=0.005 % is covering the entire cooling range and is recommended in electronic cooling applications.","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":"66343451","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.2021JTST0018
Y. Seki, Ryuji Kobayashi, Wookyung Kim, T. Johzaki, T. Endo
the run-up distance to DDT, obstacles were installed in a tube or channel promote the flame acceleration in the initial phase. A spiral-coil the Shchelkin spiral or orifice plates frequently used as obstacles 1988) 2001) 2002) 2012). Furthermore, the roles of these obstacles in the two DDT phases have been clarified to some degree. When orifice plates are continuously arranged in a channel, the flow induced by the flame repeatedly experiences contraction and expansion. These periodic contractions and expansions cause flame folding, resulting in flame acceleration (Ciccarelli et al., 2005). By contrast, strong shock waves are formed by an accelerating flame, and reflected by the obstacles (Gamezo et al., 2008). Then, the reflected shock waves generate hot regions that produce detonation via the Zel’dovich gradient Abstract We experimentally investigated the promotion of deflagration-to-detonation transition (DDT) in hydrogen–air mixtures contained in a tube in which straight-shaped rods were installed as obstacles. In the experiments, the number of obstacle rods, their spacing, their blockage ratio, and the equivalence ratio of the hydrogen–air mixture were varied as the governing parameters. The obstacle rods had a spacing of 10 or 20 mm and a blockage ratio of 0.32, 0.41, or 0.51. As a result of an optimization of the obstacle-rod conditions, when fourteen rods, whose blockage ratio was 0.32, were installed in a tube with a spacing of 20 mm and with a hydrogen–air mixture with equivalence ratios from 0.8 to 1.2, the run-up distance to the DDT was shortened to approximately 20 times the tube diameter.
在滴滴涕的助跑距离上，在管道或通道中设置障碍物，在初始阶段促进火焰加速。一种螺旋状的圆盘，常被用作障碍物的谢尔金螺旋或孔板(1988)2001)2002)2012)。此外，在一定程度上阐明了这些障碍在滴滴涕两个阶段中的作用。当孔板连续布置在通道内时，火焰引起的流动反复经历收缩和膨胀。这些周期性的收缩和膨胀导致火焰折叠，从而导致火焰加速(Ciccarelli et al.， 2005)。相比之下，强激波由加速火焰形成，并被障碍物反射(Gamezo et al.， 2008)。摘要本文通过实验研究了在装有直形棒作为障碍物的管内氢气-空气混合物中爆燃-爆轰过渡(DDT)的促进作用。实验中，障碍棒的数量、间距、堵塞比和氢气-空气混合物的等效比随控制参数的变化而变化。障碍棒的间距为10或20毫米，阻塞比分别为0.32、0.41或0.51。通过对障碍棒条件的优化，将14根堵塞比为0.32的障碍棒安装在间距为20mm、当量比为0.8 ~ 1.2的氢气-空气混合气中，可将到滴滴涕的助跑距离缩短至约为管径的20倍。
{"title":"Promotion of deflagration-to-detonation transition by repeated obstacle rods","authors":"Y. Seki, Ryuji Kobayashi, Wookyung Kim, T. Johzaki, T. Endo","doi":"10.1299/JTST.2021JTST0018","DOIUrl":"https://doi.org/10.1299/JTST.2021JTST0018","url":null,"abstract":"the run-up distance to DDT, obstacles were installed in a tube or channel promote the flame acceleration in the initial phase. A spiral-coil the Shchelkin spiral or orifice plates frequently used as obstacles 1988) 2001) 2002) 2012). Furthermore, the roles of these obstacles in the two DDT phases have been clarified to some degree. When orifice plates are continuously arranged in a channel, the flow induced by the flame repeatedly experiences contraction and expansion. These periodic contractions and expansions cause flame folding, resulting in flame acceleration (Ciccarelli et al., 2005). By contrast, strong shock waves are formed by an accelerating flame, and reflected by the obstacles (Gamezo et al., 2008). Then, the reflected shock waves generate hot regions that produce detonation via the Zel’dovich gradient Abstract We experimentally investigated the promotion of deflagration-to-detonation transition (DDT) in hydrogen–air mixtures contained in a tube in which straight-shaped rods were installed as obstacles. In the experiments, the number of obstacle rods, their spacing, their blockage ratio, and the equivalence ratio of the hydrogen–air mixture were varied as the governing parameters. The obstacle rods had a spacing of 10 or 20 mm and a blockage ratio of 0.32, 0.41, or 0.51. As a result of an optimization of the obstacle-rod conditions, when fourteen rods, whose blockage ratio was 0.32, were installed in a tube with a spacing of 20 mm and with a hydrogen–air mixture with equivalence ratios from 0.8 to 1.2, the run-up distance to the DDT was shortened to approximately 20 times the tube diameter.","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":"66342566","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.2021JTST0022
M. Komiyama, Takafumi Kumazaki, S. Nishida
The flow fields under unburned conditions were measured and the precession movement of the vortex core was clarified (Shtork et al., 2007). Numerical simulation was applied to analyze vortex breakdown, which occurred in an actual gas turbine combustor (Turrell et al., 2004). Abstract Lean premixed combustion can be expected to reduce the high-temperature area and NOx emission. However, it has a risk of flashback due to flame propagation. It can be thought to modulate the gas swirl intensity to prevent flashback and to stabilize combustion. In this research, we developed time-variable-angle swirl vanes which had 56 mm of the inner diameter, 70 mm of the outer diameter and consisted of 36 vanes, each vane was directly connected to a stepping motor, and the swirl intensity could be changed periodically by keeping the constant air ratio and flow rate. We confirmed the periodical movement of the swirl vane angle using a high-speed camera. The flame position could be made reciprocating move upstream and downstream by the periodic change of the swirl vane angle. The upstream direction flow at the tip of the flame appeared when the flame moved in the upstream direction with increasing vane angle and the downstream direction flow appeared when that moved in the downstream direction with decreasing the vane angle. When the flame propagation was changed from upstream direction to downstream, the upstream direction flow near the flame tip was weakened. In advance of changing the flame propagation from upstream direction to downstream, the axial velocity near the flame tip changed from decreasing to increasing.
测量了未燃烧条件下的流场，明确了涡芯的进动(Shtork et al.， 2007)。采用数值模拟方法对实际燃气轮机燃烧室发生的涡击穿进行了分析(Turrell et al.， 2004)。精益预混燃烧有望减少高温面积和NOx排放。但是，由于火焰传播，它有闪回的危险。它可以被认为是调节气体涡流强度，以防止闪回和稳定燃烧。本文研制了内径为56 mm，外径为70 mm的时变角度旋流叶片，由36个叶片组成，每个叶片直接与步进电机相连，在保持一定的空气比和流量的情况下，可以周期性地改变旋流强度。我们用高速摄像机确认了旋流叶片角度的周期性运动。通过旋流叶片角度的周期性变化，可以实现火焰位置的上下往复运动。随着叶片角度的增大，火焰向上游运动时，火焰尖端出现上游方向流动;随着叶片角度的减小，火焰向下游运动时，火焰尖端出现下游方向流动。当火焰从上游向下游传播时，火焰尖端附近的上游流动减弱。在火焰从上游向下游传播之前，火焰尖端附近的轴向速度由减小变为增大。
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