Pub Date : 2020-01-01DOI: 10.1299/jtst.2020jtst0016
Y. Kametani, Fukuda Yutaka, T. Osawa, Y. Hasegawa
In order to drastically accelerate the development processes of advanced heat exchangers, a new design framework integrating shape optimization, rapid prototyping and experimental validation is proposed. For the optimal design of heat transfer surfaces, a new adjoint-based shape optimization algorithm taking into account unsteady turbulent transport is developed. The present shape optimization algorithm is applied to two di ff erent conventional pin-fin arrays with circular cross sections so as to maximize the analogy factor, i.e., the ratio of heat transfer and pumping power for driving the fluid. The resultant optimal fin shapes are elongated in the streamwise direction and also characterized by bump-like structures formed on the upstream side of the pins. Investigation of numerical results reveals that the pressure drop of the optimal shape is significantly reduced by the suppression of vortex shedding behind the fin, whereas the heat transfer performance is maintained by the extended surface. The optimal shapes are fabricated by a resin-based additive manufacturing technique. A single-blow method allows to evaluate the heat transfer coe ffi cient of low-thermal conductivity materials by measuring the inlet and outlet air temperature only, while the pressure loss is estimated from the pressure measurements at the upstream and downstream of the text matrix by Pit ˆ ot-tubes. As a result, significant improvement of thermal hydraulic performance is experimentally confirmed for the optimal pin-fin arrays as predicted by numerical analyses. The governing equations are non-dimensionalized by a friction velocity based on mean pressure gradient, u (cid:3) (cid:28) , a friction temperature based on uniform heating source, (cid:18) (cid:3) (cid:28) and channel-half width (cid:14) (cid:3) , respectively. The friction-based Reynolds number is set to be Re (cid:28) = u (cid:3) (cid:28) (cid:14) (cid:3) =(cid:23) (cid:3) = 200 (Case 1), 300 (Case 2) which corresponds to an initial bulk Reynolds number of Re b = 500. The Prandtl number is set to Pr = 0 : 71. The fourth and fifth terms in the right-hand-side of Eq. (6) represent the driving force equivalent to a mean pressure gradient and an artificial body force for embedding a solid region in the Cartesian coordinate system by a volume penalization method (Goldstein et al., 1993; Schneider, 2005). Note that ϕ is non-zero only in the solid phase (see, Eq. (4)), so that the damping force acts only in the solid phase in order to eliminate the fluid velocity. Similarly, an isothermal condition on the solid surface is imposed via the last term on the right-hand-side of the energy equation. A periodic boundary condition is applied to the streamwise ( x (cid:0) ) and spanwise ( z (cid:0) ) directions, while the no-slip u = 0 and iso-thermal wall (cid:18) = 0 is applied on the two parallel walls. The grid spacings nondimensionalized by (cid:14) (cid:3) in the x (cid:0) , y (cid:0) , and z (cid:0) directions are ( ∆ x ; ∆ y ; ∆ z
{"title":"A new framework for design and validation of complex heat transfer surfaces based on adjoint optimization and rapid prototyping technologies","authors":"Y. Kametani, Fukuda Yutaka, T. Osawa, Y. Hasegawa","doi":"10.1299/jtst.2020jtst0016","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0016","url":null,"abstract":"In order to drastically accelerate the development processes of advanced heat exchangers, a new design framework integrating shape optimization, rapid prototyping and experimental validation is proposed. For the optimal design of heat transfer surfaces, a new adjoint-based shape optimization algorithm taking into account unsteady turbulent transport is developed. The present shape optimization algorithm is applied to two di ff erent conventional pin-fin arrays with circular cross sections so as to maximize the analogy factor, i.e., the ratio of heat transfer and pumping power for driving the fluid. The resultant optimal fin shapes are elongated in the streamwise direction and also characterized by bump-like structures formed on the upstream side of the pins. Investigation of numerical results reveals that the pressure drop of the optimal shape is significantly reduced by the suppression of vortex shedding behind the fin, whereas the heat transfer performance is maintained by the extended surface. The optimal shapes are fabricated by a resin-based additive manufacturing technique. A single-blow method allows to evaluate the heat transfer coe ffi cient of low-thermal conductivity materials by measuring the inlet and outlet air temperature only, while the pressure loss is estimated from the pressure measurements at the upstream and downstream of the text matrix by Pit ˆ ot-tubes. As a result, significant improvement of thermal hydraulic performance is experimentally confirmed for the optimal pin-fin arrays as predicted by numerical analyses. The governing equations are non-dimensionalized by a friction velocity based on mean pressure gradient, u (cid:3) (cid:28) , a friction temperature based on uniform heating source, (cid:18) (cid:3) (cid:28) and channel-half width (cid:14) (cid:3) , respectively. The friction-based Reynolds number is set to be Re (cid:28) = u (cid:3) (cid:28) (cid:14) (cid:3) =(cid:23) (cid:3) = 200 (Case 1), 300 (Case 2) which corresponds to an initial bulk Reynolds number of Re b = 500. The Prandtl number is set to Pr = 0 : 71. The fourth and fifth terms in the right-hand-side of Eq. (6) represent the driving force equivalent to a mean pressure gradient and an artificial body force for embedding a solid region in the Cartesian coordinate system by a volume penalization method (Goldstein et al., 1993; Schneider, 2005). Note that ϕ is non-zero only in the solid phase (see, Eq. (4)), so that the damping force acts only in the solid phase in order to eliminate the fluid velocity. Similarly, an isothermal condition on the solid surface is imposed via the last term on the right-hand-side of the energy equation. A periodic boundary condition is applied to the streamwise ( x (cid:0) ) and spanwise ( z (cid:0) ) directions, while the no-slip u = 0 and iso-thermal wall (cid:18) = 0 is applied on the two parallel walls. The grid spacings nondimensionalized by (cid:14) (cid:3) in the x (cid:0) , y (cid:0) , and z (cid:0) directions are ( ∆ x ; ∆ y ; ∆ z","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66340783","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 : 2020-01-01DOI: 10.1299/jtst.2020jtst0023
S. Amirthalingam, B. Thangavel
Nanofluids which act as coolants in various thermal applications have been promising in accomplishing the primary objective of heat transfer. However, the impact of such fluids on flow lines in the form of enhanced friction factor through unacceptable viscosity rise is an issue to be addressed. On the other hand, these fluids are expected to deteriorate the environment when used or disposed. Hence this research focuses on preparing a bionanofluid and investigating on its primary properties, the thermal conductivity and viscosity. The bionanofluid is prepared by dispersing neem (azadirachta indica) assisted zinc oxide nanoparticles in a binary mixture of ethylene glycol-water (50:50 by volume), at volume concentrations of φ=0.05, 0.2 and 0.5%. To compare the properties of these bionanofluids, additional nanofluids were prepared by dispersing combustion derived pure zinc oxide at same volume concentration. By XRD analysis, the average crystallite size of neem assisted ZnO and pure ZnO was found to be 36 nm and 32 nm. Based on the SEM images, the particles were found to be much closely packed in bioparticles than combustion derived ones. The zeta potential of the nanofluids was found to be 30 mV at pH 6.5, at which the stability is deemed excellent. The thermal conductivity and viscosity of the nanofluids were measured under varying volume concentration and temperature ranging between 20oC and 50oC. Though the thermal conductivity of the conventional ZnO nanofluid is 3.8% higher than the ZnO bionanofluid, the viscosity is 2% lower for the latter than the former, which is highly expected from any nanofluid for an efficient thermal transport.
{"title":"On the thermal conductivity and viscosity of bionanofluid with neem (Azadirachta indica) assisted zinc oxide nanoparticles","authors":"S. Amirthalingam, B. Thangavel","doi":"10.1299/jtst.2020jtst0023","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0023","url":null,"abstract":"Nanofluids which act as coolants in various thermal applications have been promising in accomplishing the primary objective of heat transfer. However, the impact of such fluids on flow lines in the form of enhanced friction factor through unacceptable viscosity rise is an issue to be addressed. On the other hand, these fluids are expected to deteriorate the environment when used or disposed. Hence this research focuses on preparing a bionanofluid and investigating on its primary properties, the thermal conductivity and viscosity. The bionanofluid is prepared by dispersing neem (azadirachta indica) assisted zinc oxide nanoparticles in a binary mixture of ethylene glycol-water (50:50 by volume), at volume concentrations of φ=0.05, 0.2 and 0.5%. To compare the properties of these bionanofluids, additional nanofluids were prepared by dispersing combustion derived pure zinc oxide at same volume concentration. By XRD analysis, the average crystallite size of neem assisted ZnO and pure ZnO was found to be 36 nm and 32 nm. Based on the SEM images, the particles were found to be much closely packed in bioparticles than combustion derived ones. The zeta potential of the nanofluids was found to be 30 mV at pH 6.5, at which the stability is deemed excellent. The thermal conductivity and viscosity of the nanofluids were measured under varying volume concentration and temperature ranging between 20oC and 50oC. Though the thermal conductivity of the conventional ZnO nanofluid is 3.8% higher than the ZnO bionanofluid, the viscosity is 2% lower for the latter than the former, which is highly expected from any nanofluid for an efficient thermal transport.","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66341371","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 : 2020-01-01DOI: 10.1299/jtst.2020jtst0034
Yuya Yamada, M. Nishikawara, H. Yanada
A loop heat pipe (LHP) is a heat transport device driven by capillary pressure in porous media and the vapor–liquid phase change of a working fluid. LHPs are widely used in the electronic cooling systems of spacecraft (Okamoto et al., 2016), insulated gate bipolar transistors (Dupont et al., 2013), laptops (Lin et al., 2013), and other thermal engineering applications. As shown in Fig. 1, an LHP consists of an evaporator, a condenser, a vapor line, a liquid line, and a compensation chamber (CC). Unlike conventional heat pipes, the wick is enclosed in the evaporator, enabling long transport lengths and large radiation areas. The operating characteristics and working mechanisms of LHPs are reviewed in Maydanik (2005), Ku (1999), and Launay et al. (2007). The wick shape as well as porous materials and capillary structures critically affects the evaporator performance, but the design of the wick shape is complicated, which is focused in this paper. Some papers have attempted enhancement of the evaporator heat-transfer coefficient by parametric studies with respect to the shape (e.g., contact surface area between casing and wick, groove number, groove width, groove pitch, groove cross-sectional shape, groove location (in a wick or casing) and wick thickness) with a cylindrical or flat evaporator (North et al., 1997; Riehl et al., 2008; Kiseev et al., 2010; Yakomaskin et al., 2013; Yakomaskin, 2016; Kuroi and Nagano, 2012; Hodot et al., 2013; Wu et al., 2014; Uchida, 2014; Zhang et al., 2012). Especially, the heat-transfer coefficient was significantly improved by forming microgrooves on the wick surface (North et al., 1997; Riehl et al., 2008; Kiseev et al., 2010; Yakomaskin et al., 2013; Yakomaskin, *Department of Mechanical Engineering, Toyohashi Univ. of Tech. 1-1, Hibarigaoka, Tempaku-cho, Toyohashi, Aichi 441-8580, Japan **currently at Panasonic Co. 1006, Oaza Kadoma, Kadoma-shi, Osaka 571-8501, Japan ***Department of Mechanical Engineering, Worcester Polytechnic Inst. 100 Institute Road, Worcester, MA, 01609, USA E-mail: nishikawara@me.tut.ac.jp
环形热管是由多孔介质中的毛细压力和工作流体的气液相变驱动的传热装置。lhp广泛应用于航天器的电子冷却系统(Okamoto et al.， 2016)、绝缘栅双极晶体管(Dupont et al.， 2013)、笔记本电脑(Lin et al.， 2013)和其他热工应用。如图1所示，LHP由蒸发器、冷凝器、蒸汽管线、液体管线和补偿室(CC)组成。与传统的热管不同，该热管芯被封闭在蒸发器中，可以实现长传输长度和大辐射区域。Maydanik(2005)、Ku(1999)和Launay et al.(2007)综述了lhp的工作特点和工作机制。灯芯形状以及多孔材料和毛细管结构对蒸发器的性能有重要影响，但灯芯形状的设计较为复杂，本文对此进行了重点研究。一些论文试图通过参数化研究来提高蒸发器的传热系数，这些参数包括圆柱形或平面蒸发器的形状(例如，机匣与灯芯之间的接触面面积、凹槽数量、凹槽宽度、凹槽间距、凹槽横截面形状、凹槽位置(在灯芯或机匣中)和灯芯厚度)(North et al.， 1997;Riehl et al.， 2008;Kiseev et al.， 2010;Yakomaskin et al.， 2013;Yakomaskin, 2016;Kuroi and Nagano, 2012;Hodot et al.， 2013;Wu et al.， 2014;田,2014;Zhang等人，2012)。特别是，通过在灯芯表面形成微槽，传热系数显著提高(North et al.， 1997;Riehl et al.， 2008;Kiseev et al.， 2010;Yakomaskin et al.， 2013;Yakomaskin， *日本爱知市丰桥市天paku町Hibarigaoka 1-1号机械工程系**目前就职于松下公司1006，日本大阪多马市小坂多马市571-8501 ***伍斯特工业大学机械工程系，美国马萨诸塞州伍斯特研究所路100号，01609,E-mail: nishikawara@me.tut.ac.jp
{"title":"Numerical exploration of optimal microgroove shape in loop-heat-pipe evaporator","authors":"Yuya Yamada, M. Nishikawara, H. Yanada","doi":"10.1299/jtst.2020jtst0034","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0034","url":null,"abstract":"A loop heat pipe (LHP) is a heat transport device driven by capillary pressure in porous media and the vapor–liquid phase change of a working fluid. LHPs are widely used in the electronic cooling systems of spacecraft (Okamoto et al., 2016), insulated gate bipolar transistors (Dupont et al., 2013), laptops (Lin et al., 2013), and other thermal engineering applications. As shown in Fig. 1, an LHP consists of an evaporator, a condenser, a vapor line, a liquid line, and a compensation chamber (CC). Unlike conventional heat pipes, the wick is enclosed in the evaporator, enabling long transport lengths and large radiation areas. The operating characteristics and working mechanisms of LHPs are reviewed in Maydanik (2005), Ku (1999), and Launay et al. (2007). The wick shape as well as porous materials and capillary structures critically affects the evaporator performance, but the design of the wick shape is complicated, which is focused in this paper. Some papers have attempted enhancement of the evaporator heat-transfer coefficient by parametric studies with respect to the shape (e.g., contact surface area between casing and wick, groove number, groove width, groove pitch, groove cross-sectional shape, groove location (in a wick or casing) and wick thickness) with a cylindrical or flat evaporator (North et al., 1997; Riehl et al., 2008; Kiseev et al., 2010; Yakomaskin et al., 2013; Yakomaskin, 2016; Kuroi and Nagano, 2012; Hodot et al., 2013; Wu et al., 2014; Uchida, 2014; Zhang et al., 2012). Especially, the heat-transfer coefficient was significantly improved by forming microgrooves on the wick surface (North et al., 1997; Riehl et al., 2008; Kiseev et al., 2010; Yakomaskin et al., 2013; Yakomaskin, *Department of Mechanical Engineering, Toyohashi Univ. of Tech. 1-1, Hibarigaoka, Tempaku-cho, Toyohashi, Aichi 441-8580, Japan **currently at Panasonic Co. 1006, Oaza Kadoma, Kadoma-shi, Osaka 571-8501, Japan ***Department of Mechanical Engineering, Worcester Polytechnic Inst. 100 Institute Road, Worcester, MA, 01609, USA E-mail: nishikawara@me.tut.ac.jp","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66341724","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 : 2020-01-01DOI: 10.1299/jtst.2020jtste01
N. Giannetti, Kiyoshi Saito, Hiroaki Yoshimura
{"title":"Errata: Formulation of steady-state void fraction through the principle of minimum entropy production [Journal of Thermal Science and Technology (2020jtst0025)]","authors":"N. Giannetti, Kiyoshi Saito, Hiroaki Yoshimura","doi":"10.1299/jtst.2020jtste01","DOIUrl":"https://doi.org/10.1299/jtst.2020jtste01","url":null,"abstract":"","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66341867","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 : 2020-01-01DOI: 10.1299/jtst.2020jtst0005
Nae-Hyun Kim
As slit area, m 2 At heat transfer area at the mid-plane of the tube wall, m 2 bf slope of the saturated air enthalpy curve at fin temperature, J/kgK br slope of the saturated air enthalpy curve between tube wall and water temperature, J/kgK bt slope of the saturated air enthalpy curve at tube wall temperature, J/kgK C heat capacity, W/K cp specific heat, J/kgK D tube diameter including fin collar thickness, m f friction factor h heat transfer coefficient, W/mK hs height of the slit, m i enthalpy, J/kg j Colburn j factor k thermal conductivity, W/mK Abstract In this study, two kinds of corrugated louver fin-and-tube heat exchangers – one having one corrugation per row and the other having two corrugations per row – were tested under wet condition, and the results were compared with those of the standard louver fin and the plain fin samples. The highest j and f factor were obtained for the double corrugated louver fin sample, followed by the single corrugated inclined louver fin sample, the standard louver fin sample and then the plain fin sample. This result is in contradiction with those obtained under dry condition, where the standard louver fin sample yielded the highest j and f factor. The high j and f factor of the corrugated louver fin sample may be due to the improved condensate drainage over the standard louver fin sample. Corrugated channels along with louvers of high louver angle of the corrugated louver fin samples appear to have resulted better condensate drainage. All the enhanced fin samples yielded larger heat transfer capacity than plain fin samples at the same pumping power. Furthermore, the largest heat transfer capacity per pumping power was obtained for the double corrugated louver fin sample, followed by the single corrugated louver fin sample and then the standard louver fin sample.
{"title":"An experimental investigation on the airside performance of fin-and-tube heat exchangers having corrugated louver fins - Part II; wet surface","authors":"Nae-Hyun Kim","doi":"10.1299/jtst.2020jtst0005","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0005","url":null,"abstract":"As slit area, m 2 At heat transfer area at the mid-plane of the tube wall, m 2 bf slope of the saturated air enthalpy curve at fin temperature, J/kgK br slope of the saturated air enthalpy curve between tube wall and water temperature, J/kgK bt slope of the saturated air enthalpy curve at tube wall temperature, J/kgK C heat capacity, W/K cp specific heat, J/kgK D tube diameter including fin collar thickness, m f friction factor h heat transfer coefficient, W/mK hs height of the slit, m i enthalpy, J/kg j Colburn j factor k thermal conductivity, W/mK Abstract In this study, two kinds of corrugated louver fin-and-tube heat exchangers – one having one corrugation per row and the other having two corrugations per row – were tested under wet condition, and the results were compared with those of the standard louver fin and the plain fin samples. The highest j and f factor were obtained for the double corrugated louver fin sample, followed by the single corrugated inclined louver fin sample, the standard louver fin sample and then the plain fin sample. This result is in contradiction with those obtained under dry condition, where the standard louver fin sample yielded the highest j and f factor. The high j and f factor of the corrugated louver fin sample may be due to the improved condensate drainage over the standard louver fin sample. Corrugated channels along with louvers of high louver angle of the corrugated louver fin samples appear to have resulted better condensate drainage. All the enhanced fin samples yielded larger heat transfer capacity than plain fin samples at the same pumping power. Furthermore, the largest heat transfer capacity per pumping power was obtained for the double corrugated louver fin sample, followed by the single corrugated louver fin sample and then the standard louver fin sample.","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66340238","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 : 2020-01-01DOI: 10.1299/jtst.2020jtst0035
Y. Okumura
Most gasification processes including updraft/downdraft gasifiers and entrained flow gasifiers involve partial combustion, wherein the combustion heat (approximately 800–1100 °C) is used. In the reduction zone of gasifiers, biomass pyrolysis and biochar gasification proceed in the presence of the H2O vapor and heat, and CO2 in the combustion area. (Thurner et al., 1981; Di-Blasi et al., 2001; Matsumoto et al., 2009; Guo et al., 2014; Ram et al., 2019.) Because the pyrolysis rate is much higher than the gasification rate of biochar, the overall conversion rate is controlled by the gasification rate of char. That is, the overall gasification rate is limited by the slow gasification rate of char. (Zhang et al., 2008; Okumura et al., 2009; Seo et al., 2010.) Many studies have been performed on the gasification of biochar. The gasification rate of biochar varies greatly with the experimental device and the type of biomass, even when the same gasification temperature is used. In addition, pore development in the biochar during gasification with H2O and CO2 agents, especially the relation between gasification reaction rate and interface area, has been rarely studied. The present study compared in detail the gasification rate of biochar in H2O gasifying agent with that in CO2 gasifying agent at 1073–1273 K using the same experimental apparatus and the same char samples, under the same pyrolysis conditions. The results showed that the gasification rate constant of the biochar was approximately 3–10 times higher under H2O compared to the CO2 gasifying agent. The specific surface area of woody biochar during H2O gasification was compared with that observed during CO2 gasification. When the overall gasification rates were almost same, the increase in the specific surface area of the pores under the H2O atmosphere was similar to that processed under the CO2 atmosphere i.e., no significant differences in pore development or physical shape were observed between the CO2 and H2O gasifying agents. * Faculty of Engineering and Design, Kagawa University Hayashi-cho, Takamatsu,761-0396, Japan E-mail: okumura.yukihiko@kagawa-u.ac.jp
大多数气化过程，包括上升气流/下降气流气化炉和夹带流气化炉涉及部分燃烧，其中燃烧热(约800-1100°C)被使用。在气化炉还原区，生物质热解和生物炭气化是在H2O蒸汽和热量存在的情况下进行的，而在燃烧区则有CO2存在。(Thurner et al.， 1981;Di-Blasi et al.， 2001;Matsumoto等人，2009;郭等，2014;Ram等人，2019。)由于热解速率远高于生物炭的气化速率，因此整体转化率受炭的气化速率控制。也就是说，整体气化速率受到焦炭气化速率缓慢的限制。(张等，2008;Okumura等人，2009;Seo et al.， 2010)。人们对生物炭的气化进行了许多研究。即使在相同的气化温度下，生物炭的气化速率随实验装置和生物质类型的不同而变化很大。另外，对于生物炭在H2O和CO2作用下气化过程中的孔隙发育，特别是气化反应速率与界面面积之间的关系研究较少。本研究在1073 ~ 1273 K条件下，使用相同的实验设备、相同的炭样，详细比较了生物炭在H2O气化剂和CO2气化剂中的气化率。结果表明，生物炭在H2O条件下的气化速率常数约为CO2气化剂的3-10倍。将木质生物炭在H2O气化过程中的比表面积与CO2气化过程中的比表面积进行了比较。当总气化速率几乎相同时，H2O气氛下气孔比表面积的增加与CO2气氛下相似，即CO2和H2O两种气化剂在气孔发育和物理形态上没有显著差异。*香川大学工程与设计学院，高松，761-0396，日本E-mail: okumura.yukihiko@kagawa-u.ac.jp
{"title":"Detailed gasification process of woody biomass-derived char with H2O and CO2 gasifying agents","authors":"Y. Okumura","doi":"10.1299/jtst.2020jtst0035","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0035","url":null,"abstract":"Most gasification processes including updraft/downdraft gasifiers and entrained flow gasifiers involve partial combustion, wherein the combustion heat (approximately 800–1100 °C) is used. In the reduction zone of gasifiers, biomass pyrolysis and biochar gasification proceed in the presence of the H2O vapor and heat, and CO2 in the combustion area. (Thurner et al., 1981; Di-Blasi et al., 2001; Matsumoto et al., 2009; Guo et al., 2014; Ram et al., 2019.) Because the pyrolysis rate is much higher than the gasification rate of biochar, the overall conversion rate is controlled by the gasification rate of char. That is, the overall gasification rate is limited by the slow gasification rate of char. (Zhang et al., 2008; Okumura et al., 2009; Seo et al., 2010.) Many studies have been performed on the gasification of biochar. The gasification rate of biochar varies greatly with the experimental device and the type of biomass, even when the same gasification temperature is used. In addition, pore development in the biochar during gasification with H2O and CO2 agents, especially the relation between gasification reaction rate and interface area, has been rarely studied. The present study compared in detail the gasification rate of biochar in H2O gasifying agent with that in CO2 gasifying agent at 1073–1273 K using the same experimental apparatus and the same char samples, under the same pyrolysis conditions. The results showed that the gasification rate constant of the biochar was approximately 3–10 times higher under H2O compared to the CO2 gasifying agent. The specific surface area of woody biochar during H2O gasification was compared with that observed during CO2 gasification. When the overall gasification rates were almost same, the increase in the specific surface area of the pores under the H2O atmosphere was similar to that processed under the CO2 atmosphere i.e., no significant differences in pore development or physical shape were observed between the CO2 and H2O gasifying agents. * Faculty of Engineering and Design, Kagawa University Hayashi-cho, Takamatsu,761-0396, Japan E-mail: okumura.yukihiko@kagawa-u.ac.jp","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66341735","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 : 2020-01-01DOI: 10.1299/jtst.2020jtst0030
T. Endo, Ryuji Kobayashi, S. Kuwajima, Y. Seki, Wookyung Kim, T. Johzaki
The characteristics of the propagation of a detonation from a cylindrical tube of constant cross section into a diverging cone were experimentally investigated using the smoked-foil technique for three explosive gas mixtures: C2H2+2.5O2, 2H2+O2+4.5Ar, and C2H4+3O2+0.44N2. The initial pressure and the cone enlargement angle were varied as governing parameters. The results were summarized in terms of the ratio between the inner diameter of the cylindrical tube through which a detonation initially propagated and the detonation cell width d and of the cone enlargement half angle . Four patterns of detonation propagation were observed in the diverging cone: continuous propagation, re-initiation on the cone wall, re-initiation apart from the cone wall, and failure. The obtained results were qualitatively consistent with past experimental results reported by other researchers. However, quantitatively, the obtained results were dependent on the explosive gas mixtures, particularly on the so-called critical tube diameter. Actually, when the critical values of d against detonation failure were normalized by that corresponding to 90 , ° a single curve unifying all data to some degree was obtained. In addition, some characteristics of the detonation behavior in the diverging cone were explained by simple models.
{"title":"Detonation propagation from a cylindrical tube into a diverging cone","authors":"T. Endo, Ryuji Kobayashi, S. Kuwajima, Y. Seki, Wookyung Kim, T. Johzaki","doi":"10.1299/jtst.2020jtst0030","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0030","url":null,"abstract":"The characteristics of the propagation of a detonation from a cylindrical tube of constant cross section into a diverging cone were experimentally investigated using the smoked-foil technique for three explosive gas mixtures: C2H2+2.5O2, 2H2+O2+4.5Ar, and C2H4+3O2+0.44N2. The initial pressure and the cone enlargement angle were varied as governing parameters. The results were summarized in terms of the ratio between the inner diameter of the cylindrical tube through which a detonation initially propagated and the detonation cell width d and of the cone enlargement half angle . Four patterns of detonation propagation were observed in the diverging cone: continuous propagation, re-initiation on the cone wall, re-initiation apart from the cone wall, and failure. The obtained results were qualitatively consistent with past experimental results reported by other researchers. However, quantitatively, the obtained results were dependent on the explosive gas mixtures, particularly on the so-called critical tube diameter. Actually, when the critical values of d against detonation failure were normalized by that corresponding to 90 , ° a single curve unifying all data to some degree was obtained. In addition, some characteristics of the detonation behavior in the diverging cone were explained by simple models.","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66341889","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 : 2020-01-01DOI: 10.1299/jtst.2020jtst0010
Akito Fujii, K. Fujiwara, Y. Ueki, M. Shibahara
Heat transfer with phase change is applied in various industrial fields such as power generation industry, air conditioning systems and cooling of electronic devices. In the above mentioned industrial devices, condensation is one of the important processes, and the enhancement of heat transfer coefficients in condensation processes benefits us from a thermal efficiency point of view. In the case of condensation on a solid surface, it is known that condensation heat transfer coefficients change through the modification of physical and chemical properties of condensation surface, and the enhancements of condensation heat transfer coefficient by designed nano and micro structure pattern on a heat transfer surface have been reported (Chen et al., 2011; Miljikovic et al., 2013; Hou et al., 2015). However, there is limited general knowledge on how the structures influence energy transfer during the condensation. In order to understand the effects of the structures at the nanometer scale (nanostructures) attached to a heat transfer surface in the condensation processes, a molecular dynamics point of view is necessary because the molecular-scale condensation occurs on a surface at the nanometer scale at the initial stage of the condensation heat transfer phenomena. Before now, a number of studies have been carried out to estimate the heat transfer of molecular scale (Kimura and Maruyama, 2002; Vera and Yildiz, 2015) and the effects of the nanostructures on the heat transfer surface during condensation (Uno et al., 2016, 2018; Gao et al., 2019). However, there were few researches which investigated the effect of the local segment of the nanostructure on the heat transfer surface during condensation. Therefore, we investigated the condensation behavior and heat transfer mechanism in each segment of the surface with the nanostructure, which would be the basis of the detailed design of the heat transfer surface with the optimal nanostructured pattern which realizes high condensation heat transfer coefficient. In this study, we especially focused on the condensation behaviors and the local heat transfer in condensation processes on a solid surface with a cuboid structure. The classical molecular dynamics Akito FUJII*, Kunio FUJIWARA*, Yoshitaka UEKI* and Masahiko SHIBAHARA* *Graduate School of Engineering, Osaka University 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan E-mail: fujii.akito.mte@gmail.com Received: 17 March 2020; Revised: 11 May 2020; Accepted: 1 June 2020
相变传热在发电工业、空调系统、电子设备冷却等各个工业领域都有广泛的应用。在上述工业装置中，冷凝是重要的过程之一，从热效率的角度来看，冷凝过程中传热系数的提高有利于我们。对于固体表面的冷凝，已知冷凝传热系数是通过改变冷凝表面的物理和化学性质而改变的，并且有报道通过设计传热表面的纳米和微观结构图案来增强冷凝传热系数(Chen et al.， 2011;Miljikovic et al.， 2013;侯等人，2015)。然而，关于结构如何影响凝结过程中的能量转移的一般知识有限。为了理解纳米尺度结构(纳米结构)在冷凝传热过程中的作用，分子动力学的观点是必要的，因为在冷凝传热现象的初始阶段，分子尺度的冷凝发生在纳米尺度表面上。在此之前，已经进行了许多研究来估计分子尺度的传热(Kimura和Maruyama, 2002;Vera and Yildiz, 2015)以及纳米结构对冷凝过程传热表面的影响(Uno et al.， 2016, 2018;Gao等人，2019)。然而，对于冷凝过程中纳米结构局部部分对传热面影响的研究却很少。因此，我们研究了纳米结构在表面各部分的冷凝行为和换热机理，为实现高冷凝换热系数的最佳纳米结构换热表面的详细设计奠定了基础。在本研究中，我们重点研究了长方体结构固体表面上的冷凝行为和冷凝过程中的局部传热。经典分子动力学，藤井昭东*，藤原国雄*，上木义孝*，柴原正彦* *，大阪大学工程研究生院2-1，日本，大阪，565-0871 E-mail: fujii.akito.mte@gmail.com收到:2020年3月17日;修订日期:2020年5月11日;录用日期:2020年6月1日
{"title":"Molecular dynamics simulation on effects of nanostructure on interfacial thermal resistance during condensation","authors":"Akito Fujii, K. Fujiwara, Y. Ueki, M. Shibahara","doi":"10.1299/jtst.2020jtst0010","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0010","url":null,"abstract":"Heat transfer with phase change is applied in various industrial fields such as power generation industry, air conditioning systems and cooling of electronic devices. In the above mentioned industrial devices, condensation is one of the important processes, and the enhancement of heat transfer coefficients in condensation processes benefits us from a thermal efficiency point of view. In the case of condensation on a solid surface, it is known that condensation heat transfer coefficients change through the modification of physical and chemical properties of condensation surface, and the enhancements of condensation heat transfer coefficient by designed nano and micro structure pattern on a heat transfer surface have been reported (Chen et al., 2011; Miljikovic et al., 2013; Hou et al., 2015). However, there is limited general knowledge on how the structures influence energy transfer during the condensation. In order to understand the effects of the structures at the nanometer scale (nanostructures) attached to a heat transfer surface in the condensation processes, a molecular dynamics point of view is necessary because the molecular-scale condensation occurs on a surface at the nanometer scale at the initial stage of the condensation heat transfer phenomena. Before now, a number of studies have been carried out to estimate the heat transfer of molecular scale (Kimura and Maruyama, 2002; Vera and Yildiz, 2015) and the effects of the nanostructures on the heat transfer surface during condensation (Uno et al., 2016, 2018; Gao et al., 2019). However, there were few researches which investigated the effect of the local segment of the nanostructure on the heat transfer surface during condensation. Therefore, we investigated the condensation behavior and heat transfer mechanism in each segment of the surface with the nanostructure, which would be the basis of the detailed design of the heat transfer surface with the optimal nanostructured pattern which realizes high condensation heat transfer coefficient. In this study, we especially focused on the condensation behaviors and the local heat transfer in condensation processes on a solid surface with a cuboid structure. The classical molecular dynamics Akito FUJII*, Kunio FUJIWARA*, Yoshitaka UEKI* and Masahiko SHIBAHARA* *Graduate School of Engineering, Osaka University 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan E-mail: fujii.akito.mte@gmail.com Received: 17 March 2020; Revised: 11 May 2020; Accepted: 1 June 2020","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/jtst.2020jtst0010","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66340088","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 : 2020-01-01DOI: 10.1299/jtst.2020jtst0001
Huanyu Di, Yahui Zhang, T. Shen
Combustion control is a significant topic for achieving high efficiency and low emissions of internal combustion engines. Recently, in-cylinder pressure sensor-based closed-loop control strategies have become the preferred solution. However, their practical applications in automotive industries are limited due to the intensive acquisition of pressure series for a whole cycle and subsequent calculation of combustion indicators. This paper proposes a method for in-cylinder pressure information extraction and combustion phase estimation of spark ignition (SI) engines based on pressure measurements at several points coordinated by the crank angle. First, nonlinear dynamics analysis is introduced to analyze the system of in-cylinder pressure evolution, which is proved to be a deterministic nonlinear dynamic system with chaotic characteristics. Then, a 3-dimensional system state variable is determined to replace the pressure series during combustion. Second, with the determined system state variable, the in-cylinder pressure series during combustion and the combustion phase are learned and estimated by a machine learning method, namely, extreme learning machine (ELM). As a result, only pressure measurements at 3 points and ELM estimation models are required, instead of intensive data acquisition and calculation. The experimental validations carried out on a gasoline engine test bench have proved that the reconstruction and estimation results are accurate and that the method can perform well in real-time combustion control.
{"title":"Chaos theory-based time series analysis of in-cylinder pressure and its application in combustion control of SI engines","authors":"Huanyu Di, Yahui Zhang, T. Shen","doi":"10.1299/jtst.2020jtst0001","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0001","url":null,"abstract":"Combustion control is a significant topic for achieving high efficiency and low emissions of internal combustion engines. Recently, in-cylinder pressure sensor-based closed-loop control strategies have become the preferred solution. However, their practical applications in automotive industries are limited due to the intensive acquisition of pressure series for a whole cycle and subsequent calculation of combustion indicators. This paper proposes a method for in-cylinder pressure information extraction and combustion phase estimation of spark ignition (SI) engines based on pressure measurements at several points coordinated by the crank angle. First, nonlinear dynamics analysis is introduced to analyze the system of in-cylinder pressure evolution, which is proved to be a deterministic nonlinear dynamic system with chaotic characteristics. Then, a 3-dimensional system state variable is determined to replace the pressure series during combustion. Second, with the determined system state variable, the in-cylinder pressure series during combustion and the combustion phase are learned and estimated by a machine learning method, namely, extreme learning machine (ELM). As a result, only pressure measurements at 3 points and ELM estimation models are required, instead of intensive data acquisition and calculation. The experimental validations carried out on a gasoline engine test bench have proved that the reconstruction and estimation results are accurate and that the method can perform well in real-time combustion control.","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/jtst.2020jtst0001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66340372","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 : 2020-01-01DOI: 10.1299/jtst.2020jtst0019
Kengo Wada, Hiroaki Fujiwara, M. Kaneda, K. Suga
Natural convection of a paramagnetic fluid through a partially-heated vertical channel is numerically studied in the presence of a magnetic field from two block magnets placed behind the heated wall. Magnets are aligned with opposite orientations. This magnet orientation induces strong magnetic force normal to the magnet at the magnet junction due to short distance between poles. When the temperature-dependent magnetic susceptibility changes due to wall heating near the magnet, the magnetothermal force is induced remarkably near the magnet junction. This additional force overlaps to the natural convection along the heated wall and results in the changes of heat and fluid flow along the heated wall. It is found that, flow becomes slow and the local heat transfer is suppressed below the elevation of the magnet junction, and the flow acceleration and heat transfer enhancement are observed above the junction elevation, of which effects depend on the relative magnet elevation to the heated wall. It is also found that the transition to vibrating flow occurs at the specific magnet elevation. The timeaveraged Nusselt number suggests this vibrating convection has the potential to enhance the heat transfer remarkably because this magnetically-induced flow vibration continues along the heated wall up to the outlet.
{"title":"Magnetothermal force effect on natural convection through a partially-heated vertical channel","authors":"Kengo Wada, Hiroaki Fujiwara, M. Kaneda, K. Suga","doi":"10.1299/jtst.2020jtst0019","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0019","url":null,"abstract":"Natural convection of a paramagnetic fluid through a partially-heated vertical channel is numerically studied in the presence of a magnetic field from two block magnets placed behind the heated wall. Magnets are aligned with opposite orientations. This magnet orientation induces strong magnetic force normal to the magnet at the magnet junction due to short distance between poles. When the temperature-dependent magnetic susceptibility changes due to wall heating near the magnet, the magnetothermal force is induced remarkably near the magnet junction. This additional force overlaps to the natural convection along the heated wall and results in the changes of heat and fluid flow along the heated wall. It is found that, flow becomes slow and the local heat transfer is suppressed below the elevation of the magnet junction, and the flow acceleration and heat transfer enhancement are observed above the junction elevation, of which effects depend on the relative magnet elevation to the heated wall. It is also found that the transition to vibrating flow occurs at the specific magnet elevation. The timeaveraged Nusselt number suggests this vibrating convection has the potential to enhance the heat transfer remarkably because this magnetically-induced flow vibration continues along the heated wall up to the outlet.","PeriodicalId":17405,"journal":{"name":"Journal of Thermal Science and Technology","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66340576","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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