Pub Date : 2020-01-01DOI: 10.1299/jtst.2020jtst0017
Tatsuro Yamazaki, Y. Oda, R. Matsumoto, M. Katsuki
Pulsating turbulent channel flows under constant temperature difference (CTD) condition and uniform heat flux heating (UHF) condition are studied by direct numerical simulation (DNS). The main objective of the present study is to clarify how the dissimilarity between momentum transfer and heat transfer appeared in the pulsating flows, in which the dissimilarity may originate from the CTD condition dissimilar to the no-slip condition of the velocity field rather than from the thermo-fluid physics under pulsation. Simulations have been performed for three pulsation frequencies under the friction Reynolds number at steady-state, Re s = 300. Comparing the phase-averaged quantities under CTD and UHF conditions, it is found that the frequency dependence of the temperature oscillations in the near-wall region is almost the same regardless of the thermal boundary condition although the time-averaged temperature profiles are different. As a result, the ratio of Stanton number to friction factor, which works as a barometer of the analogy, changes during the pulsation period at both CTD and UHF conditions. Besides, the oscillation amplitude becomes larger as the pulsation frequency increases. Therefore, it was confirmed that the dissimilarity appears regardless of the thermal boundary condition. In addition, turbulent Prandtl number shows similar cyclic behavior to the ratio of Stanton number to friction factor. Time variations of each component constituting turbulent Prandtl number reveal that increasing dissimilarity at the high frequency is mainly attributed to the amplified oscillation of velocity gradient near the wall, where Reynolds shear stress and turbulent heat flux are kept at around the time-averaged values because the near-wall vortex structures cannot follow the rapid change of flow At + = 0.0044, vortex structures and distribution of Nu show a large change during flow pulsation; high region in red color changes with the coarse the do
{"title":"Effect of thermal wall condition on the dissimilarity of momentum and heat transfer in pulsating channel flow","authors":"Tatsuro Yamazaki, Y. Oda, R. Matsumoto, M. Katsuki","doi":"10.1299/jtst.2020jtst0017","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0017","url":null,"abstract":"Pulsating turbulent channel flows under constant temperature difference (CTD) condition and uniform heat flux heating (UHF) condition are studied by direct numerical simulation (DNS). The main objective of the present study is to clarify how the dissimilarity between momentum transfer and heat transfer appeared in the pulsating flows, in which the dissimilarity may originate from the CTD condition dissimilar to the no-slip condition of the velocity field rather than from the thermo-fluid physics under pulsation. Simulations have been performed for three pulsation frequencies under the friction Reynolds number at steady-state, Re s = 300. Comparing the phase-averaged quantities under CTD and UHF conditions, it is found that the frequency dependence of the temperature oscillations in the near-wall region is almost the same regardless of the thermal boundary condition although the time-averaged temperature profiles are different. As a result, the ratio of Stanton number to friction factor, which works as a barometer of the analogy, changes during the pulsation period at both CTD and UHF conditions. Besides, the oscillation amplitude becomes larger as the pulsation frequency increases. Therefore, it was confirmed that the dissimilarity appears regardless of the thermal boundary condition. In addition, turbulent Prandtl number shows similar cyclic behavior to the ratio of Stanton number to friction factor. Time variations of each component constituting turbulent Prandtl number reveal that increasing dissimilarity at the high frequency is mainly attributed to the amplified oscillation of velocity gradient near the wall, where Reynolds shear stress and turbulent heat flux are kept at around the time-averaged values because the near-wall vortex structures cannot follow the rapid change of flow At + = 0.0044, vortex structures and distribution of Nu show a large change during flow pulsation; high region in red color changes with the coarse the do","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":"66340838","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.2020jtst0021
Ayato Takii, M. Yamakawa, S. Asao, K. Tajiri
Six degrees of freedom turning flight simulation is presented for a tilt-rotor aircraft represented by V-22 Osprey, considering interaction of fluid and rigid body in a coupled manner. A tilt-rotor aircraft has a hovering function like a helicopter by turning axes of rotor toward the sky during takeoff or landing. On the other hand, it behaves as a reciprocating aircraft by turning axes of rotor forward in flight. The tilt-rotor aircraft is known to be susceptible to instable state compared to conventional aircraft. For realizing Digital Flight of turning flight of the aircraft, combination with the Moving Computational Domain (MCD) method and the multi-axis sliding mesh approach is applied. In the MCD method, the whole of the computational domain itself moves with the bodies included inside the domain, which makes an airplane possible to fly freely in the physical space without any restriction of region size. Moreover, this method is also applied to rotation of rotors. The multi-axis sliding mesh approach is computational technique to enable us to deal with multiple rotating axes of different direction, and it is used to rotate two rotors and change flight attitude of the aircraft. As a result of the coupled computation between flow field and rigid body using above approach, the airplane gained lift and propulsion by rotating the rotor and flew in turning by operating flight control surfaces such as flaperons, elevator and rudders. Moreover, the manipulating variables of flight control surfaces needed for turning flight, flight attitude of the aircraft and generated lift were found. Differences of fluid flow between straight flight and turning flight were also captured.
{"title":"Turning flight simulation of tilt-rotor plane with fluid-rigid body interaction","authors":"Ayato Takii, M. Yamakawa, S. Asao, K. Tajiri","doi":"10.1299/jtst.2020jtst0021","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0021","url":null,"abstract":"Six degrees of freedom turning flight simulation is presented for a tilt-rotor aircraft represented by V-22 Osprey, considering interaction of fluid and rigid body in a coupled manner. A tilt-rotor aircraft has a hovering function like a helicopter by turning axes of rotor toward the sky during takeoff or landing. On the other hand, it behaves as a reciprocating aircraft by turning axes of rotor forward in flight. The tilt-rotor aircraft is known to be susceptible to instable state compared to conventional aircraft. For realizing Digital Flight of turning flight of the aircraft, combination with the Moving Computational Domain (MCD) method and the multi-axis sliding mesh approach is applied. In the MCD method, the whole of the computational domain itself moves with the bodies included inside the domain, which makes an airplane possible to fly freely in the physical space without any restriction of region size. Moreover, this method is also applied to rotation of rotors. The multi-axis sliding mesh approach is computational technique to enable us to deal with multiple rotating axes of different direction, and it is used to rotate two rotors and change flight attitude of the aircraft. As a result of the coupled computation between flow field and rigid body using above approach, the airplane gained lift and propulsion by rotating the rotor and flew in turning by operating flight control surfaces such as flaperons, elevator and rudders. Moreover, the manipulating variables of flight control surfaces needed for turning flight, flight attitude of the aircraft and generated lift were found. Differences of fluid flow between straight flight and turning flight were also captured.","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":"66341105","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.2020jtst0029
Takehiko Seo, H. Kaneko, M. Mikami
In order to understand turbulent combustion and its combustion characteristics, laminar flame speed is often used. Laminar flame speed plays an important role in turbulent combustion models used in engine combustion simulation. However, there are few reports on laminar flame speed of liquid fuel under high pressure condition simulating the inside of an engine cylinder. In this study, the measuring system using simple compact equipment was developed to obtain laminar flame speed of liquid fuel with the double kernel method under high pressure conditions. In this equipment, as easily ignited at high pressure, laser induced breakdown ignition technique was used. The experiments were conducted on propane-air premixed gas so that it could be easily compared with the reports of other researchers. The experiment was conducted on propane/air premixture so that it could be easily compared with the other reports. A detailed investigation of the time history of the flame separation revealed that the conventional method of calculating the laminar flame speed used in the double kernel method was not suitable for this measuring system. Therefore, a new calculation method for the laminar flame speed was studied, and the pressure dependence of the laminar flame speed of the propane/air premixture was investigated. As a result, it was found that it was in good agreement with other reports. The laminar flame speed measurement system developed in this study is considered to be useful. upper part of the chamber and a cartridge heater (CT16-125, Nippon Heater) is attached to the lower part of the chamber to control the initial temperature. A fixed amount of propane and air is supplied to the chamber by using a partial pressure method to form a premixed gas with the equivalence of 1.
{"title":"Study of laminar flame speed measurement under high pressure condition using double kernel method by laser-induced breakdown ignition","authors":"Takehiko Seo, H. Kaneko, M. Mikami","doi":"10.1299/jtst.2020jtst0029","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0029","url":null,"abstract":"In order to understand turbulent combustion and its combustion characteristics, laminar flame speed is often used. Laminar flame speed plays an important role in turbulent combustion models used in engine combustion simulation. However, there are few reports on laminar flame speed of liquid fuel under high pressure condition simulating the inside of an engine cylinder. In this study, the measuring system using simple compact equipment was developed to obtain laminar flame speed of liquid fuel with the double kernel method under high pressure conditions. In this equipment, as easily ignited at high pressure, laser induced breakdown ignition technique was used. The experiments were conducted on propane-air premixed gas so that it could be easily compared with the reports of other researchers. The experiment was conducted on propane/air premixture so that it could be easily compared with the other reports. A detailed investigation of the time history of the flame separation revealed that the conventional method of calculating the laminar flame speed used in the double kernel method was not suitable for this measuring system. Therefore, a new calculation method for the laminar flame speed was studied, and the pressure dependence of the laminar flame speed of the propane/air premixture was investigated. As a result, it was found that it was in good agreement with other reports. The laminar flame speed measurement system developed in this study is considered to be useful. upper part of the chamber and a cartridge heater (CT16-125, Nippon Heater) is attached to the lower part of the chamber to control the initial temperature. A fixed amount of propane and air is supplied to the chamber by using a partial pressure method to form a premixed gas with the equivalence of 1.","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":"66341778","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.2020jtst0009
Dongliang Zhang, Xiaoqing Huang, Ning Cai, Liang Wang, Zhao Zhang
The objectives of this study were to: (i) build simulation model for mult-unit air conditioning (AC) system with digital scroll compressor (DSC) and validate its precision by experiments; (ii) build system energy consumption calculation model by simulation. Lumped parameter model of compressor and electronic expansion valve, and district lumped parameter model of condenser and evaporator were employed in simulation program of multi-unit AC system with DSC. The results indicated that errors between simulated value and experimental data of system hourly energy consumption were within 10%. The simulation model showed good precision. Simulation results indicated that system hourly energy consumption differences caused by indoor unit operating number were less than 15%, which can be neglected. Thus, hourly energy consumption (HW), hourly energy efficiency ratio (HEER) and hourly heating performance factor (HHPF) calculation model of multi-unit AC system with DSC were built based on simulation results. Simulation results indicated that the variation of HW with part load ratio (PLR) and outdoor air temperature presented concave surface distribution and the variations of HEER and HHPF with PLR and and outdoor air temperature presented convex surface distribution. The model provides a tool for energy saving optimization and seasonal energy consumption evaluation of multi-unit AC system with DSC.
{"title":"Study on energy consumption model of multi-unit air conditioning system with digital scroll compressor","authors":"Dongliang Zhang, Xiaoqing Huang, Ning Cai, Liang Wang, Zhao Zhang","doi":"10.1299/jtst.2020jtst0009","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0009","url":null,"abstract":"The objectives of this study were to: (i) build simulation model for mult-unit air conditioning (AC) system with digital scroll compressor (DSC) and validate its precision by experiments; (ii) build system energy consumption calculation model by simulation. Lumped parameter model of compressor and electronic expansion valve, and district lumped parameter model of condenser and evaporator were employed in simulation program of multi-unit AC system with DSC. The results indicated that errors between simulated value and experimental data of system hourly energy consumption were within 10%. The simulation model showed good precision. Simulation results indicated that system hourly energy consumption differences caused by indoor unit operating number were less than 15%, which can be neglected. Thus, hourly energy consumption (HW), hourly energy efficiency ratio (HEER) and hourly heating performance factor (HHPF) calculation model of multi-unit AC system with DSC were built based on simulation results. Simulation results indicated that the variation of HW with part load ratio (PLR) and outdoor air temperature presented concave surface distribution and the variations of HEER and HHPF with PLR and and outdoor air temperature presented convex surface distribution. The model provides a tool for energy saving optimization and seasonal energy consumption evaluation of multi-unit AC system with DSC.","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.2020jtst0009","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66340517","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.2020jtst0014
K. Abe
{"title":"Performance of a hybrid LES/RANS model combined with a wall function for predicting quite high Reynolds-number turbulent channel flows up to Reτ=6×107","authors":"K. Abe","doi":"10.1299/jtst.2020jtst0014","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0014","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":"66340598","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.2020jtst0024
H. Saputro, L. Fitriana, F. Munir, M. Mikami
Indonesia has implemented a policy of using diesel fuel containing 20 percent biofuel (commonly known as B20 biodiesel), as stated in Energy and Mineral Resources Ministerial Decree No. 23/2013. This study investigated the flame-spread characteristics of biodiesel (B20) in a microgravity environment through drop tower facilities. This is due to the difficulty in creating droplet sizes similar to the real liquid sprays in the combustion chamber of diesel engines. The experiment used biodiesel (B20) droplets with a diameter 1 mm. The results show that the biodiesel (B20) droplets have characteristics of a flame–spread limit distance SBC/dC0limit = 7. This paper discusses the characteristics of biodiesel (B20) droplets in detail.
{"title":"Flame-spread behavior of biodiesel (B20) in a microgravity environment","authors":"H. Saputro, L. Fitriana, F. Munir, M. Mikami","doi":"10.1299/jtst.2020jtst0024","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0024","url":null,"abstract":"Indonesia has implemented a policy of using diesel fuel containing 20 percent biofuel (commonly known as B20 biodiesel), as stated in Energy and Mineral Resources Ministerial Decree No. 23/2013. This study investigated the flame-spread characteristics of biodiesel (B20) in a microgravity environment through drop tower facilities. This is due to the difficulty in creating droplet sizes similar to the real liquid sprays in the combustion chamber of diesel engines. The experiment used biodiesel (B20) droplets with a diameter 1 mm. The results show that the biodiesel (B20) droplets have characteristics of a flame–spread limit distance SBC/dC0limit = 7. This paper discusses the characteristics of biodiesel (B20) droplets in detail.","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":"66341454","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.2020jtst0027
Tetsutoshi Kan, T. Sawachi, Yuki Nagumo
JIS B 8628, “Air-to-air heat and energy exchanger and ventilators” provides standards for evaluating the performance of the energy recovery ventilators. JIS B 8628 was established in 2000, and revised in 2003. In 2017, JIS B 8628 was revised furthermore to ensure consistency with ISO 16494, which was established in 2014. For that purpose, the two room setup and the ducted setup, which are prescribed in ISO 16494 with specified pressure conditions at inlet and outlet of energy recovery ventilators for the airflow test, the tracer gas test and the thermal performance test, were added in JIS B 8628 (2017). In Japan, either the two room setup or the ducted setup is being used by manufacturers to determine the performance values, which are referred to when the compliance of total building energy performance to the Building Energy Efficiency Act is claimed. However, no studies have yet focused on the difference of the test results between the two room setup and the ducted setup. In this study, authors applied those setups and the test setup prescribed in JIS B 8628 (2003) to four energy recovery ventilators and compared their results. As for the airflow-static pressure characteristics, the curves obtained by the three test setups generally correspond to each other, except for the curves for the air exhaust line obtained by JIS B 8628 (2003). The unit exhaust air transfer ratio values obtained by the ducted setup and JIS B 8628 (2003) tend to be greater than those by the two room setup. As for the thermal performance represented by the total effectiveness, differences among the three test setups can be observed when there is a difference of the unit exhaust air transfer ratio and/or the ratio of the supply airflow rate to the return airflow rate.
JIS B 8628“空气对空气热交换器和通风器”提供了评估能量回收通风器性能的标准。JIS B 8628于2000年制定，2003年修订。2017年，JIS B 8628进一步修订，以确保与2014年建立的ISO 16494保持一致。为此，在JIS B 8628(2017)中增加了ISO 16494中规定的两个房间设置和管道设置，在能量回收通风机的进出口处规定了用于气流试验、示踪气体试验和热性能试验的压力条件。在日本，制造商要么采用双房间设置，要么采用管道设置，以确定性能值，这是在声称符合《建筑能源效率法》的建筑总能源性能时所参考的。然而，目前还没有研究集中在两个房间设置和管道设置之间的测试结果的差异。在本研究中，作者将上述装置与JIS B 8628(2003)规定的测试装置应用于4台能量回收风机，并对其结果进行了比较。对于气流-静压特性，除了日本标准JIS B 8628(2003)的排风管线曲线外，三种试验装置得到的曲线基本一致。由导管装置和JIS B 8628(2003)获得的单位排风传动比值往往大于由两个房间装置获得的值。以总效能为代表的热工性能，当机组排风量换气量和/或送风风量与回风风量之比存在差异时，可以观察到三种试验装置之间的差异。
{"title":"An experimental study on how the difference between the test setups specified in JIS B 8628 and JIS B 8639 affects the performance values of energy recovery ventilators","authors":"Tetsutoshi Kan, T. Sawachi, Yuki Nagumo","doi":"10.1299/jtst.2020jtst0027","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0027","url":null,"abstract":"JIS B 8628, “Air-to-air heat and energy exchanger and ventilators” provides standards for evaluating the performance of the energy recovery ventilators. JIS B 8628 was established in 2000, and revised in 2003. In 2017, JIS B 8628 was revised furthermore to ensure consistency with ISO 16494, which was established in 2014. For that purpose, the two room setup and the ducted setup, which are prescribed in ISO 16494 with specified pressure conditions at inlet and outlet of energy recovery ventilators for the airflow test, the tracer gas test and the thermal performance test, were added in JIS B 8628 (2017). In Japan, either the two room setup or the ducted setup is being used by manufacturers to determine the performance values, which are referred to when the compliance of total building energy performance to the Building Energy Efficiency Act is claimed. However, no studies have yet focused on the difference of the test results between the two room setup and the ducted setup. In this study, authors applied those setups and the test setup prescribed in JIS B 8628 (2003) to four energy recovery ventilators and compared their results. As for the airflow-static pressure characteristics, the curves obtained by the three test setups generally correspond to each other, except for the curves for the air exhaust line obtained by JIS B 8628 (2003). The unit exhaust air transfer ratio values obtained by the ducted setup and JIS B 8628 (2003) tend to be greater than those by the two room setup. As for the thermal performance represented by the total effectiveness, differences among the three test setups can be observed when there is a difference of the unit exhaust air transfer ratio and/or the ratio of the supply airflow rate to the return airflow rate.","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":"66341632","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.2020jtst0032
Masatoshi Ishii, T. Hatakeyama, M. Ishizuka
The SPICE model of phase change material (PCM) for thermal network transient calculation was investigated. The nonlinear behavior of PCM due to latent heat was modeled by using the voltage dependent current source and the capacitor. A latent heat is stored in the capacitor as electric charges. Corresponding to the PCM phase state, such as solid, liquid and mixed phases, the dependent current source is controlled with PCM temperature and the latent heat quantity of PCM. Since the melting point of PCM has a distribution, the model in which multiple PCM models having different melting points and capacitor capacities were connected in parallel was employed. To validate the numerical simulation model, the aluminum case with PCM sealed inside was prepared. The sample was heated with a rubber heater from the bottom with different heat quantities. The temperature changes of the upper and lower surfaces were measured with thermocouples. The results showed the error between simulated and measured values were below ±4 °C and the calculation time took below real-time. This simulation model can be applied to cooling system optimization and temperature control system. of the maximum latent heat quantity of PCM divided into 15 blocks. The lower melting point (thin line) and the higher melting point (dotted line) show the time changes of the endothermic and exothermic reactions up to the maximum latent heat amount of 35 J, which is half of the maximum latent heat amount of center melting point. It shows the relationship between the change of latent heat quantity for each melting point of PCM and the stepwise change of PCM temperature. It was confirmed that the PCM temperature was maintained while the latent heat was generated at each melting point of each layer. The analysis result with an applied heat flow of 8W shows the latent heat quantity of higher melting point of top PCM layer doesn’t reach the upper limit. It indicates that the third PCM layer was not completely melted. In this experiment, the aluminum case was heated from the bottom. Therefore, it was shown that in the temperature behavior of PCM when the temperature rose, when the amount of heat applied was small, PCM melts in order from the low melting point regardless of the layer. On the other hand, when the amount of heat applied increases, the internal temperature distribution of the PCM increases, which indicates that the lower melting part of PCM in the lower layer melts before the lower melting part of PCM in the upper layer. In the cooling process, it can be confirmed that the upper layer has exothermic reaction earlier than the intermediate layer, and there was also a heat dissipation from the upper surface. The developed model can estimate not only the temperature but also the transient of the latent heat inside the PCM. Thus, this model can be a very useful tool for cooling system optimization.
{"title":"Thermal network calculation model for phase change material with SPICE circuit simulator","authors":"Masatoshi Ishii, T. Hatakeyama, M. Ishizuka","doi":"10.1299/jtst.2020jtst0032","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0032","url":null,"abstract":"The SPICE model of phase change material (PCM) for thermal network transient calculation was investigated. The nonlinear behavior of PCM due to latent heat was modeled by using the voltage dependent current source and the capacitor. A latent heat is stored in the capacitor as electric charges. Corresponding to the PCM phase state, such as solid, liquid and mixed phases, the dependent current source is controlled with PCM temperature and the latent heat quantity of PCM. Since the melting point of PCM has a distribution, the model in which multiple PCM models having different melting points and capacitor capacities were connected in parallel was employed. To validate the numerical simulation model, the aluminum case with PCM sealed inside was prepared. The sample was heated with a rubber heater from the bottom with different heat quantities. The temperature changes of the upper and lower surfaces were measured with thermocouples. The results showed the error between simulated and measured values were below ±4 °C and the calculation time took below real-time. This simulation model can be applied to cooling system optimization and temperature control system. of the maximum latent heat quantity of PCM divided into 15 blocks. The lower melting point (thin line) and the higher melting point (dotted line) show the time changes of the endothermic and exothermic reactions up to the maximum latent heat amount of 35 J, which is half of the maximum latent heat amount of center melting point. It shows the relationship between the change of latent heat quantity for each melting point of PCM and the stepwise change of PCM temperature. It was confirmed that the PCM temperature was maintained while the latent heat was generated at each melting point of each layer. The analysis result with an applied heat flow of 8W shows the latent heat quantity of higher melting point of top PCM layer doesn’t reach the upper limit. It indicates that the third PCM layer was not completely melted. In this experiment, the aluminum case was heated from the bottom. Therefore, it was shown that in the temperature behavior of PCM when the temperature rose, when the amount of heat applied was small, PCM melts in order from the low melting point regardless of the layer. On the other hand, when the amount of heat applied increases, the internal temperature distribution of the PCM increases, which indicates that the lower melting part of PCM in the lower layer melts before the lower melting part of PCM in the upper layer. In the cooling process, it can be confirmed that the upper layer has exothermic reaction earlier than the intermediate layer, and there was also a heat dissipation from the upper surface. The developed model can estimate not only the temperature but also the transient of the latent heat inside the PCM. Thus, this model can be a very useful tool for cooling system optimization.","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":"66342034","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.2020jtst0003
Anek Bunkwang, T. Matsuoka, Y. Nakamura
The dynamic behavior, especially in the transition to oscillation mode (in-phase and anti-phase), of two interacting non-premixed methane-air jet flames was investigated experimentally. A well-controllable experimental system for the present purpose was constructed and key parameters; such as fuel flowrate ( Q ), burner diameter ( d ), and burner separation distance ( L ), were varied systematically. A well-known periodic motion of the flame was observed and the frequency monitored by thermocouples mounted adjacent to the burner exit. Time-variation of flame shape was recorded by a high speed camera associated with the optical imaging visualization. It was found that the flickering frequency was insensitive to the fuel flowrate, Q , implying that inertia played secondary role in the transition. Instead, the burner critical separation distance for the transition ( 𝐿 𝑐𝑟𝑡 ) varied when various burner diameters were used, confirming that the difference in distance played an important role in the transition. It was found that the critical condition could be summarized by an updated correlation as 𝑑 × 𝐿 𝑐𝑟𝑡3 ~𝑐𝑜𝑛𝑠𝑡. This is slightly different from the one recently proposed by Yang et al. (2019), which was given under a narrower range of the fire scale. Accordingly, the critical condition can also be described by the critical value of the updated global parameter, such as 𝛼 3 𝐺𝑟 4/3 , where 𝛼 and 𝐺𝑟 denote the length ratio ( 𝐿 𝑐𝑟𝑡 / d ) and Grashof number based on the burner diameter, respectively. “flame flickering (or flame puffing)” and the frequency is an important characteristic, as well as the quantity. Previous studies (Hamins et al., 1992; Cetegen and Ahmed, 1993; Cetegen and Dong, 2000), have confirmed the prominent scaling relation, f ~ d -1/2 , in a wide range of fire scales ( d ) irrespective of the kinds of fuel. Cetegen and Ahmed (1993) developed a mathematical model to predict the dynamic frequency based on the convective time scale of flame flickers. Since the main convective flow is induced by the buoyancy, the burner scale acts as representative scale to control the magnitude of buoyancy-induced flow velocity. From a fluid dynamics point of view, the buoyancy-induced flow forms the shedding toroidal vortex along the flame. In this way, the relation between the fire scale and dynamic frequency of the flame is correlated as described. Most recently, Xia et al. (2018) introduced vortex-dynamical principles and attempted to observe the relation between flame and vortex dynamics. According to their work, the total vorticity (circulation) of the toroidal vortex shows independency on the geometric shape of burner port; rather it is dictated by the vertical length of vortex sheet. This is consistent with the experimental observation that the pinching-off length of the flame is nearly identical. When two buoyant flames are positioned close to each other, the interaction of inner-side shear layer, where the
实验研究了两种非预混甲烷-空气相互作用火焰的动力学行为，特别是过渡到振荡模式(同相和反相)时的动力学行为。构建了可控的实验系统，确定了关键参数;如燃料流量(Q)、燃烧器直径(d)、燃烧器分离距离(L)等参数均有系统变化。一个众所周知的周期性运动的火焰被观察到，并通过安装在燃烧器出口附近的热电偶监测频率。利用高速摄像机记录火焰形状随时间的变化，并辅以光学成像可视化。研究发现，闪变频率对燃油流量Q不敏感，表明惯性在过渡过程中起次要作用。相反，当使用不同的燃烧器直径时，过渡的燃烧器临界分离距离(𝐿𝑐𝑟𝑡)是不同的，这证实了距离的差异在过渡中发挥了重要作用。发现临界条件可以用更新后的相关关系来概括为𝑑×𝐿𝑐𝑟𝑡3 ~𝑐𝑜𝑛𝑠𝑡。这与Yang等人(2019)最近提出的结果略有不同，后者是在更窄的火灾规模范围内给出的。相应的，临界条件也可以用更新后的全局参数的临界值来描述，如:rgr 3𝐺𝑟4/3，其中，rgr和𝐺𝑟分别表示基于燃烧器直径的长度比(𝐿𝑐𝑟𝑡/ d)和Grashof数。“火焰闪烁(或火焰膨化)”的一个重要特征是频率，以及数量。前人的研究(Hamins et al.， 1992;Cetegen和Ahmed, 1993;Cetegen和Dong, 2000)证实了显著的尺度关系，f ~ d -1/2，在广泛的火灾尺度(d)中，与燃料种类无关。Cetegen和Ahmed(1993)根据火焰闪烁的对流时间尺度，建立了预测火焰闪烁动态频率的数学模型。由于主要的对流是由浮力诱导的，所以燃烧器尺度作为控制浮力诱导流速大小的代表性尺度。从流体力学的角度来看，浮力诱导的流动沿火焰形成脱落的环形涡。这样，火焰规模与火焰动态频率之间的关系就像所描述的那样关联起来。最近，Xia等人(2018)介绍了涡动力学原理，并试图观察火焰与涡动力学之间的关系。根据他们的工作，环形涡的总涡量(环流)与燃烧器口的几何形状无关;相反，它是由旋涡片的垂直长度决定的。这与实验观察到的火焰掐断长度几乎相同是一致的。当两个浮力火焰彼此靠近时，内部剪切层的相互作用，其中
{"title":"Mode transition of interacting buoyant non-premixed flames","authors":"Anek Bunkwang, T. Matsuoka, Y. Nakamura","doi":"10.1299/jtst.2020jtst0003","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0003","url":null,"abstract":"The dynamic behavior, especially in the transition to oscillation mode (in-phase and anti-phase), of two interacting non-premixed methane-air jet flames was investigated experimentally. A well-controllable experimental system for the present purpose was constructed and key parameters; such as fuel flowrate ( Q ), burner diameter ( d ), and burner separation distance ( L ), were varied systematically. A well-known periodic motion of the flame was observed and the frequency monitored by thermocouples mounted adjacent to the burner exit. Time-variation of flame shape was recorded by a high speed camera associated with the optical imaging visualization. It was found that the flickering frequency was insensitive to the fuel flowrate, Q , implying that inertia played secondary role in the transition. Instead, the burner critical separation distance for the transition ( 𝐿 𝑐𝑟𝑡 ) varied when various burner diameters were used, confirming that the difference in distance played an important role in the transition. It was found that the critical condition could be summarized by an updated correlation as 𝑑 × 𝐿 𝑐𝑟𝑡3 ~𝑐𝑜𝑛𝑠𝑡. This is slightly different from the one recently proposed by Yang et al. (2019), which was given under a narrower range of the fire scale. Accordingly, the critical condition can also be described by the critical value of the updated global parameter, such as 𝛼 3 𝐺𝑟 4/3 , where 𝛼 and 𝐺𝑟 denote the length ratio ( 𝐿 𝑐𝑟𝑡 / d ) and Grashof number based on the burner diameter, respectively. “flame flickering (or flame puffing)” and the frequency is an important characteristic, as well as the quantity. Previous studies (Hamins et al., 1992; Cetegen and Ahmed, 1993; Cetegen and Dong, 2000), have confirmed the prominent scaling relation, f ~ d -1/2 , in a wide range of fire scales ( d ) irrespective of the kinds of fuel. Cetegen and Ahmed (1993) developed a mathematical model to predict the dynamic frequency based on the convective time scale of flame flickers. Since the main convective flow is induced by the buoyancy, the burner scale acts as representative scale to control the magnitude of buoyancy-induced flow velocity. From a fluid dynamics point of view, the buoyancy-induced flow forms the shedding toroidal vortex along the flame. In this way, the relation between the fire scale and dynamic frequency of the flame is correlated as described. Most recently, Xia et al. (2018) introduced vortex-dynamical principles and attempted to observe the relation between flame and vortex dynamics. According to their work, the total vorticity (circulation) of the toroidal vortex shows independency on the geometric shape of burner port; rather it is dictated by the vertical length of vortex sheet. This is consistent with the experimental observation that the pinching-off length of the flame is nearly identical. When two buoyant flames are positioned close to each other, the interaction of inner-side shear layer, where the","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.2020jtst0003","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66340507","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.2020jtst0022
Di Liu, Bing-xi Sun, Jiawen Song, Taiping Wang, Xingyu Ma
To investigate the influences of thermal and pressure loads on the structural deformation of the Liquid Oxygen/Methane rocket engine combustion chamber, a complete thermo-structural analysis scheme including fluid-thermal analysis and structural finite element analysis is developed and then verified to be reasonable. By conducting fluid-thermal analysis, the detailed distribution of the thermal and pressure loads is obtained. These results are utilized as body loads and surface loads in structural finite element analysis. Then, the stress-strain responses of the combustion chamber and the accumulation process of the deformation induced by thermal and pressure loads were studied in detail. The main conclusions are as follows: Under the action of thermal loads alone, the most pronounced residual mechanical strain is at the upstream of the nozzle divergent segment. Reducing the temperature difference between the hot run and the pre-cooling phase can be a feasible improvement measure for this issue. Under the action of the pressure loads alone, the bottom of the cooling channel bends toward the centerline of the combustion chamber. Properly increasing the thickness of the channel bottom near the coolant inlet is deemed to be an effective measure to reduce this bending trend. Under the combined action of thermal and pressure loads, the structural deformation characteristics are determined by the combination of thermal loads and pressure loads, rather than mainly by thermal loads. The accumulation rate of mechanical strain at the channel bottom corner is much rapider than the other positions. Turning the sharp bottom corner of the cooling channel into rounded corner is an alternative method of suppressing strain accumulation.
{"title":"Effects of thermal and pressure loads on structural deformation of liquid oxygen/methane engine combustion chamber","authors":"Di Liu, Bing-xi Sun, Jiawen Song, Taiping Wang, Xingyu Ma","doi":"10.1299/jtst.2020jtst0022","DOIUrl":"https://doi.org/10.1299/jtst.2020jtst0022","url":null,"abstract":"To investigate the influences of thermal and pressure loads on the structural deformation of the Liquid Oxygen/Methane rocket engine combustion chamber, a complete thermo-structural analysis scheme including fluid-thermal analysis and structural finite element analysis is developed and then verified to be reasonable. By conducting fluid-thermal analysis, the detailed distribution of the thermal and pressure loads is obtained. These results are utilized as body loads and surface loads in structural finite element analysis. Then, the stress-strain responses of the combustion chamber and the accumulation process of the deformation induced by thermal and pressure loads were studied in detail. The main conclusions are as follows: Under the action of thermal loads alone, the most pronounced residual mechanical strain is at the upstream of the nozzle divergent segment. Reducing the temperature difference between the hot run and the pre-cooling phase can be a feasible improvement measure for this issue. Under the action of the pressure loads alone, the bottom of the cooling channel bends toward the centerline of the combustion chamber. Properly increasing the thickness of the channel bottom near the coolant inlet is deemed to be an effective measure to reduce this bending trend. Under the combined action of thermal and pressure loads, the structural deformation characteristics are determined by the combination of thermal loads and pressure loads, rather than mainly by thermal loads. The accumulation rate of mechanical strain at the channel bottom corner is much rapider than the other positions. Turning the sharp bottom corner of the cooling channel into rounded corner is an alternative method of suppressing strain accumulation.","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":"66341317","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：