Droplet impacts on solid surfaces produce a wide variety of phenomena such as spreading, splashing, jetting, receding, and rebounding. In microholed surfaces, downward jets through the hole can be caused by the high impact inertia during the spreading phase of the droplet over the substrate as well as the cavity collapse during recoil phase of the droplet. We investigate the dynamics of the jet formed through the single hole during the impacting phase of the droplet on a micro-holed hydrophilic substrate. The sub-millimeter circular holes are created on the 0.2 mm-thickness hydrophilic plastic films using a 0.5 mm punch. Great care has been taken to ensure that the millimeter-sized droplets of water dispensed by a syringe pump through a micropipette tip can impact directly over the microholes. A high-speed video photography camera is employed to capture the full event of impacting and jetting. A MATLAB code has been developed to process the captured videos for data analysis. We study the effect of impact velocity on the jet formation including jet velocity, ejected droplet volume, and breakup process. We find that the Weber number significantly affects outcomes of the drop impact and jetting mechanism. We also examine the dynamic contact angle of the contact line during the spreading and the receding phase.
{"title":"Jet Formation After Droplet Impact on Microholed Hydrophilic Surfaces","authors":"M. N. E. Alam, H. Tan","doi":"10.1115/imece2022-95146","DOIUrl":"https://doi.org/10.1115/imece2022-95146","url":null,"abstract":"\u0000 Droplet impacts on solid surfaces produce a wide variety of phenomena such as spreading, splashing, jetting, receding, and rebounding. In microholed surfaces, downward jets through the hole can be caused by the high impact inertia during the spreading phase of the droplet over the substrate as well as the cavity collapse during recoil phase of the droplet. We investigate the dynamics of the jet formed through the single hole during the impacting phase of the droplet on a micro-holed hydrophilic substrate. The sub-millimeter circular holes are created on the 0.2 mm-thickness hydrophilic plastic films using a 0.5 mm punch. Great care has been taken to ensure that the millimeter-sized droplets of water dispensed by a syringe pump through a micropipette tip can impact directly over the microholes. A high-speed video photography camera is employed to capture the full event of impacting and jetting. A MATLAB code has been developed to process the captured videos for data analysis. We study the effect of impact velocity on the jet formation including jet velocity, ejected droplet volume, and breakup process. We find that the Weber number significantly affects outcomes of the drop impact and jetting mechanism. We also examine the dynamic contact angle of the contact line during the spreading and the receding phase.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128865704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Computational Fluid Dynamics (CFD) analysis are widely used in modern risk assessment procedure in order to understand detonations during a given situation or an accident. Combustion regimes including deflagration, detonation transition and detonation are extremely important. Hydrodynamic instabilities during detonation make it even harder to simulated. Numerous lingering numerical challenges still exists in the areas of simulating gas detonation flows. Among these challenges is the inability of many high order numerical schemes to simulated gas denotation and wave propagation without getting into regions of negative density or negative pressure. Many existing high order schemes, which may have proven record of accomplishment in terms of their accuracies and efficiencies in handling complex flow fields, will often times facilitate the development of negative density or negative pressure in their efforts to simulate the physics associated with the time evolution of gas detonation flow fields. This effort describes the application of a positivity-preserving density and pressure scheme, named the Integro-Differential scheme (IDS), to the detonation gas dynamic problem. Among the problems of interest to this study are the 1-D shock tube problem, 2-D explosion problem and implosion detonations problems. The purpose of solve 1-D problem is to prove IDS has acceptable numerical stability and less dissipation as a computational fluid dynamics (CFD) scheme. Of particular interest to this paper is the implosion detonations problem. The implosion problem was analyzed on a square domain of dimension: 0 <= x <= 0.3; 0 <= y <= 0.3, with reflecting walls, and with zero initial velocities. The results indicated that the IDS was able to successfully capture the flow physics within the implosion problem. And the wall pressure and temperature data from the 2-D unsteady result and use extract line way to analysis.
计算流体动力学(CFD)分析被广泛应用于现代风险评估程序中，以了解在给定情况或事故中的爆炸。燃烧状态包括爆燃、爆轰过渡和爆轰是极其重要的。爆炸过程中流体动力的不稳定性使得模拟更加困难。在气体爆轰流模拟领域仍然存在着许多悬而未决的数值难题。在这些挑战中，许多高阶数值方案无法在不进入负密度或负压区域的情况下模拟气体的延伸和波的传播。许多现有的高阶方案，可能在处理复杂流场的准确性和效率方面已经证明了成就的记录，在努力模拟与气体爆轰流场时间演化相关的物理过程时，往往会促进负密度或负压的发展。这一努力描述了一种名为积分-微分格式(IDS)的保正密度和压力格式在爆轰气体动力学问题中的应用。本研究感兴趣的问题包括一维激波管问题、二维爆炸问题和内爆问题。求解一维问题的目的是为了证明IDS作为一种计算流体力学(CFD)格式具有可接受的数值稳定性和较小的耗散。本文特别感兴趣的是内爆爆问题。在维数为0 <= x <= 0.3的方域上分析了内爆问题;0 <= y <= 0.3，有反射壁，初速度为零。结果表明，IDS能够成功捕获内爆问题中的流动物理特性。并将壁面压力和温度数据从二维非定常结果中提取出来，并采用提取线的方法进行分析。
{"title":"Revealing the Richtmyer-Meshkov Instability Within Gas Dynamic Detonations","authors":"Yang Gao, Dehua Feng, F. Ferguson","doi":"10.1115/imece2022-95224","DOIUrl":"https://doi.org/10.1115/imece2022-95224","url":null,"abstract":"\u0000 Computational Fluid Dynamics (CFD) analysis are widely used in modern risk assessment procedure in order to understand detonations during a given situation or an accident. Combustion regimes including deflagration, detonation transition and detonation are extremely important. Hydrodynamic instabilities during detonation make it even harder to simulated. Numerous lingering numerical challenges still exists in the areas of simulating gas detonation flows. Among these challenges is the inability of many high order numerical schemes to simulated gas denotation and wave propagation without getting into regions of negative density or negative pressure. Many existing high order schemes, which may have proven record of accomplishment in terms of their accuracies and efficiencies in handling complex flow fields, will often times facilitate the development of negative density or negative pressure in their efforts to simulate the physics associated with the time evolution of gas detonation flow fields. This effort describes the application of a positivity-preserving density and pressure scheme, named the Integro-Differential scheme (IDS), to the detonation gas dynamic problem. Among the problems of interest to this study are the 1-D shock tube problem, 2-D explosion problem and implosion detonations problems. The purpose of solve 1-D problem is to prove IDS has acceptable numerical stability and less dissipation as a computational fluid dynamics (CFD) scheme. Of particular interest to this paper is the implosion detonations problem. The implosion problem was analyzed on a square domain of dimension: 0 <= x <= 0.3; 0 <= y <= 0.3, with reflecting walls, and with zero initial velocities. The results indicated that the IDS was able to successfully capture the flow physics within the implosion problem. And the wall pressure and temperature data from the 2-D unsteady result and use extract line way to analysis.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132307521","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Numerical investigation of electrohydrodynamic (EHD) conduction pumping driven fluid flow and heat transfer in a flexible minichannel has been performed. The two-way coupled set of governing equations for fluid flow, heat transfer, electric potential, and charge transport are programmed into the existing finite-volume framework of OpenFOAM. A two-species charge transport model which considers the field-enhanced dissociation due to Onsager-Wien effect has been adopted. The ability of EHD conduction pumping mechanism to induce flow in straight and curved configurations of a minichannel are demonstrated. The flow and heat transfer characteristics are quantified in terms of mean velocity, maximum velocity, maximum wall temperaturen and mean Nusselt number. Even at low applied voltages (≤ 1kV), EHD conduction pumping is able to induce flow and heat transfer in the minichannel, in both the configurations. At 1kV applied voltage, the fall in heat transfer in 90° bent configuration is only 4%, as compared to that in the straight minichannel. Results of this study reveal that EHD conduction based pumping is a viable option in flexible minichannel heat sinks.
{"title":"Electrohydrodynamic Conduction Pumping Driven Flow and Heat Transfer in a Flexible Minichannel","authors":"Deepak Selvakumar Ramachandran, Hyoungsoon Lee","doi":"10.1115/imece2022-89251","DOIUrl":"https://doi.org/10.1115/imece2022-89251","url":null,"abstract":"\u0000 Numerical investigation of electrohydrodynamic (EHD) conduction pumping driven fluid flow and heat transfer in a flexible minichannel has been performed. The two-way coupled set of governing equations for fluid flow, heat transfer, electric potential, and charge transport are programmed into the existing finite-volume framework of OpenFOAM. A two-species charge transport model which considers the field-enhanced dissociation due to Onsager-Wien effect has been adopted. The ability of EHD conduction pumping mechanism to induce flow in straight and curved configurations of a minichannel are demonstrated. The flow and heat transfer characteristics are quantified in terms of mean velocity, maximum velocity, maximum wall temperaturen and mean Nusselt number. Even at low applied voltages (≤ 1kV), EHD conduction pumping is able to induce flow and heat transfer in the minichannel, in both the configurations. At 1kV applied voltage, the fall in heat transfer in 90° bent configuration is only 4%, as compared to that in the straight minichannel. Results of this study reveal that EHD conduction based pumping is a viable option in flexible minichannel heat sinks.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131446387","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. M. Rahman, R. Warrier, A. Untăroiu, Christopher R. Martin
A three-dimensional (3D) computational model is presented in this paper that illustrates the detailed electrical characteristics, and the current-voltage (i-v) relationship throughout the preheating process of premixed methane-oxygen oxyfuel cutting flame subject to electric bias voltages. As such, the equations describing combustion, electrochemical transport for charged species, and potential are solved through a commercially available finite-volume Computational Fluid Dynamics (CFD) code. The reactions of the methane-oxygen (CH4 – O2) flame were combined with a reduced mechanism, and additional ionization reactions that generate three chemi-ions, H3O+, HCO+, and e−, to describe the chemistry of ions in flames. The electrical characteristics such as ion migrations and ion distributions are investigated for a range of electric potential, V ∈ [−5V, +5V]. Since the physical flame is comprised of twelve Bunsen-like conical flame, inclusion of the third dimension imparts the resolution of fluid mechanics and the interaction among the individual cones. It was concluded that charged ‘sheaths’ are formed at both torch and workpiece surfaces, subsequently forming three distinct regimes in the i-v relationship. The i-v characteristics obtained out of the current study have been compared to the previous experimental and two-dimensional (2D) computational model for premixed flame. In this way, the overall model generates a better understanding of the physical behavior of the oxyfuel cutting flames, along with a more validated i-v characteristics. Such understanding might provide critical information towards achieving an autonomous oxyfuel cutting process.
{"title":"Electrical Characteristics of the Oxyfuel Preheat Flame: 3D Computational Model Subject to Electric Bias Voltages","authors":"S. M. Rahman, R. Warrier, A. Untăroiu, Christopher R. Martin","doi":"10.1115/imece2022-95787","DOIUrl":"https://doi.org/10.1115/imece2022-95787","url":null,"abstract":"\u0000 A three-dimensional (3D) computational model is presented in this paper that illustrates the detailed electrical characteristics, and the current-voltage (i-v) relationship throughout the preheating process of premixed methane-oxygen oxyfuel cutting flame subject to electric bias voltages. As such, the equations describing combustion, electrochemical transport for charged species, and potential are solved through a commercially available finite-volume Computational Fluid Dynamics (CFD) code. The reactions of the methane-oxygen (CH4 – O2) flame were combined with a reduced mechanism, and additional ionization reactions that generate three chemi-ions, H3O+, HCO+, and e−, to describe the chemistry of ions in flames. The electrical characteristics such as ion migrations and ion distributions are investigated for a range of electric potential, V ∈ [−5V, +5V]. Since the physical flame is comprised of twelve Bunsen-like conical flame, inclusion of the third dimension imparts the resolution of fluid mechanics and the interaction among the individual cones. It was concluded that charged ‘sheaths’ are formed at both torch and workpiece surfaces, subsequently forming three distinct regimes in the i-v relationship. The i-v characteristics obtained out of the current study have been compared to the previous experimental and two-dimensional (2D) computational model for premixed flame. In this way, the overall model generates a better understanding of the physical behavior of the oxyfuel cutting flames, along with a more validated i-v characteristics. Such understanding might provide critical information towards achieving an autonomous oxyfuel cutting process.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128450460","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The purpose of this project was to design and optimize a portable miniature cooling system. The device functions as a cooling shirt, which is particularly useful in high-temperature environments where maintaining a healthy body temperature is a concern. The design cooling capacity of the system is 0.586 kW, where it provides a circulating cooling fluid temperature of 21.1 °C, with an ambient temperature of 35 °C using refrigerant R-134A for the prototype. The circulating cooling fluid consists of a loop that is pumped through a brazed plate heat exchanger on the evaporator side of the system. The prototype used water for initial testing. Examples of high-temperature environments include a tradesperson working in an attic during the summer (i.e., HVAC technician and electrician). The device is not limited to only high-temperature environments. It could be used in many other applications, such as health care or physical therapy settings. Certain spinal injuries can cause the human body to lose the ability to regulate its core temperature. This could result in a scenario of the body overheating during physical therapy sessions. This device could help regulate core body temperatures when overheating is a major risk. An additional application includes the possible treatment of sports-related concussions and other sports-related injuries. Targeting specific areas for cooling could potentially increase recovery time when compared to standard ice treatments. Another example application may include certain military aircraft. Pilots can experience periods of thermal discomfort during flight. A greenhouse effect happens in aircraft that contain large window areas such as the V-22 helicopter. The device could potentially be used to offset the higher heat loads experienced during flights. In conclusion, in this paper, a benchmark study, which included the design, fabrication, and testing of a working prototype by using the off-the-shelf components, was presented. The COP of the prototype was tested at different settings. The percent error between the theoretical and actual COP was calculated to be about 19%. The sources of error were discussed. The future studies will include simulations in commercially available software such as AxCYCLE to reduce the percent error between the design and actual working conditions as well as further downsizing of the device by using customized cycle components.
{"title":"Design of a Miniature HVAC System to Function As a Multipurpose Cooling Shirt","authors":"J. Gale, S. Cesmeci","doi":"10.1115/imece2022-94091","DOIUrl":"https://doi.org/10.1115/imece2022-94091","url":null,"abstract":"\u0000 The purpose of this project was to design and optimize a portable miniature cooling system. The device functions as a cooling shirt, which is particularly useful in high-temperature environments where maintaining a healthy body temperature is a concern. The design cooling capacity of the system is 0.586 kW, where it provides a circulating cooling fluid temperature of 21.1 °C, with an ambient temperature of 35 °C using refrigerant R-134A for the prototype. The circulating cooling fluid consists of a loop that is pumped through a brazed plate heat exchanger on the evaporator side of the system. The prototype used water for initial testing. Examples of high-temperature environments include a tradesperson working in an attic during the summer (i.e., HVAC technician and electrician). The device is not limited to only high-temperature environments. It could be used in many other applications, such as health care or physical therapy settings. Certain spinal injuries can cause the human body to lose the ability to regulate its core temperature. This could result in a scenario of the body overheating during physical therapy sessions. This device could help regulate core body temperatures when overheating is a major risk. An additional application includes the possible treatment of sports-related concussions and other sports-related injuries. Targeting specific areas for cooling could potentially increase recovery time when compared to standard ice treatments. Another example application may include certain military aircraft. Pilots can experience periods of thermal discomfort during flight. A greenhouse effect happens in aircraft that contain large window areas such as the V-22 helicopter. The device could potentially be used to offset the higher heat loads experienced during flights. In conclusion, in this paper, a benchmark study, which included the design, fabrication, and testing of a working prototype by using the off-the-shelf components, was presented. The COP of the prototype was tested at different settings. The percent error between the theoretical and actual COP was calculated to be about 19%. The sources of error were discussed. The future studies will include simulations in commercially available software such as AxCYCLE to reduce the percent error between the design and actual working conditions as well as further downsizing of the device by using customized cycle components.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127182578","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A magnetic field can interact with a conductive fluid to form a magnetohydrodynamic effect, which can change the flow and heat transfer characteristics of the fluid. This introduces broad application prospects for magnetic field control of conductive gases in tubes, which is useful for thrust control of aero-engine nozzles, energy control of magnetohydrodynamic power generation channels, and anti-ablation of high-temperature tube walls. In this study, distributions of parameters, including the induced current, the electromagnetic force, and the Joule heat, in circular tubes under a solenoid magnetic field and an electromagnet magnetic field, are obtained and variations in the flow and heat transfer characteristics of conductive gases are analyzed through numerical simulations. The research results show that an applied solenoid magnetic field suppresses the turbulence and heat transfer of a conductive gas to a small extent, and that the suppression effect is isotropic. However, an applied electromagnet magnetic field significantly suppresses the turbulence and heat transfer of the conductive gas, and the suppression effect is anisotropic. Within a certain range of Hartmann number (Ha), the average Nusselt number at the tube wall decreases with increases in the Ha of the electromagnet magnetic field.
{"title":"Effects of a Solenoid Magnetic Field and an Electromagnet Magnetic Field on the Turbulent Flow and Heat Transfer of Conductive Gases in Circular Tubes","authors":"Qijin Zhao, Baoquan Mao, Xianghua Bai","doi":"10.1115/imece2022-94866","DOIUrl":"https://doi.org/10.1115/imece2022-94866","url":null,"abstract":"\u0000 A magnetic field can interact with a conductive fluid to form a magnetohydrodynamic effect, which can change the flow and heat transfer characteristics of the fluid. This introduces broad application prospects for magnetic field control of conductive gases in tubes, which is useful for thrust control of aero-engine nozzles, energy control of magnetohydrodynamic power generation channels, and anti-ablation of high-temperature tube walls. In this study, distributions of parameters, including the induced current, the electromagnetic force, and the Joule heat, in circular tubes under a solenoid magnetic field and an electromagnet magnetic field, are obtained and variations in the flow and heat transfer characteristics of conductive gases are analyzed through numerical simulations. The research results show that an applied solenoid magnetic field suppresses the turbulence and heat transfer of a conductive gas to a small extent, and that the suppression effect is isotropic. However, an applied electromagnet magnetic field significantly suppresses the turbulence and heat transfer of the conductive gas, and the suppression effect is anisotropic. Within a certain range of Hartmann number (Ha), the average Nusselt number at the tube wall decreases with increases in the Ha of the electromagnet magnetic field.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127249584","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kyle Larsen, Hessam Gharavi, R. Gerlick, Heechang Bae
Numerous practical applications exist where dispersed solid particles are transported within a turbulent accelerating or deceleration gaseous flow. The large density variation between phases creates the potential for significant differences in velocity known as slip. Flow over a backward facing step provides a well characterized, turbulent, decelerating flow useful for measuring the relative velocities of the solid and gaseous phases in order to determine velocity slip and particle drag. Numerous investigations have been conducted to determine the gas phase velocity in a backward facing step for both laminar and turbulent flows and therefore the gas phase flow is well known and documented. Furthermore, some studies have also been conducted to determine the velocity of various sizes of spherical particles in a backward facing step and compared with their corresponding gas phase velocities. Few, if any, velocity measurements have been made for non-spherical particles in a backward facing step. In this work, a Phase Doppler Particle Analyzer (PDPA) was used to measure gas and particle phase velocities in a backward facing step. The step produced a 2:1 increase in cross sectional area with a Reynolds number of 22,000 (based on step height) upstream of the step. Spherical particles of 1–10 μm with an average diameter of 4 μm were used to measure the gas phase velocity. At least three sizes in the range of 38–212 μm for four different particle shapes were studied. The shapes included spheres, flakes, gravel, and cylinders. Since the PDPA is not able to measure the size of the non-spherical particles, the particles were first separated into size bins and a technique was developed using the Photo Multiplier Tubes (PMT) gain to isolate the particles size of interest for each size measured. The same technique was also used to measure terminal velocities of particles in quiescent air. This paper will discuss the results of the measurement of the particles and show that for the gas phase velocity and spherical solid phase particles that the measurements were in good agreement with previous measurements in the literature. However, for the non-spherical particles it will be shown that the drag coefficients were an order of magnitude higher in turbulent flows when compared to the literature values which are based on particles moving through a still fluid. This information is valuable for modeling turbulent two-phase flows since most assumptions of the drag are based on correlations from empirical data with particles moving through still fluid.
{"title":"Investigation of Velocity and Drag With Spherical and Non-Spherical Particles","authors":"Kyle Larsen, Hessam Gharavi, R. Gerlick, Heechang Bae","doi":"10.1115/imece2022-95749","DOIUrl":"https://doi.org/10.1115/imece2022-95749","url":null,"abstract":"\u0000 Numerous practical applications exist where dispersed solid particles are transported within a turbulent accelerating or deceleration gaseous flow. The large density variation between phases creates the potential for significant differences in velocity known as slip. Flow over a backward facing step provides a well characterized, turbulent, decelerating flow useful for measuring the relative velocities of the solid and gaseous phases in order to determine velocity slip and particle drag. Numerous investigations have been conducted to determine the gas phase velocity in a backward facing step for both laminar and turbulent flows and therefore the gas phase flow is well known and documented. Furthermore, some studies have also been conducted to determine the velocity of various sizes of spherical particles in a backward facing step and compared with their corresponding gas phase velocities. Few, if any, velocity measurements have been made for non-spherical particles in a backward facing step. In this work, a Phase Doppler Particle Analyzer (PDPA) was used to measure gas and particle phase velocities in a backward facing step. The step produced a 2:1 increase in cross sectional area with a Reynolds number of 22,000 (based on step height) upstream of the step. Spherical particles of 1–10 μm with an average diameter of 4 μm were used to measure the gas phase velocity. At least three sizes in the range of 38–212 μm for four different particle shapes were studied. The shapes included spheres, flakes, gravel, and cylinders. Since the PDPA is not able to measure the size of the non-spherical particles, the particles were first separated into size bins and a technique was developed using the Photo Multiplier Tubes (PMT) gain to isolate the particles size of interest for each size measured. The same technique was also used to measure terminal velocities of particles in quiescent air. This paper will discuss the results of the measurement of the particles and show that for the gas phase velocity and spherical solid phase particles that the measurements were in good agreement with previous measurements in the literature. However, for the non-spherical particles it will be shown that the drag coefficients were an order of magnitude higher in turbulent flows when compared to the literature values which are based on particles moving through a still fluid. This information is valuable for modeling turbulent two-phase flows since most assumptions of the drag are based on correlations from empirical data with particles moving through still fluid.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128125924","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
New Zealand and many countries gained heightened awareness of indoor air quality (IAQ) issues, and increased investment, according to the World Health Organization (WHO) guidelines, to improve their IAQ and reduce air pollution in commercial and residential buildings. Additionally, some countries have introduced new standards for indoor environments, such as the New Zealand “healthy homes” standard. At the same time, COVID-19 pandemic forced many people to spend much more time in indoor spaces, due to stay-at-home, or lockdown orders by governments. This increased attention on other aspects of indoor environmental quality, such as occupants’ satisfaction with thermal comfort parameters, presents an additional parameter for research and in the development of standards. From a medical perspectives, infectious respiratory diseases, such as influenza or COVID-19, are transmitted by airborne droplets. In this work, we assess a Polyester Filter and UV light (PFUV) dehumidifier device performance in an office with two occupants (one uninfected and the other one infected with a disease with airborne transmission using computational fluid dynamics (CFD) approach. Two positions for locating the PFUV dehumidifier in an office with a scenario in which one person is exhaling infected air and the other occupant must inhale and exhale from the shared air. The CFD model illustrated the best position of the device to distribute the air velocity contours. Further, based on the CFD model which was validated via the IAQ and comfort kit (Testo 400) thermal comfort analysis showed that the room is slightly cold.
{"title":"Vapour Cough Visualization for COVID-19 – Computational Modelling Approach","authors":"M. Al-Rawi, A. Al-Jumaily","doi":"10.1115/imece2022-94143","DOIUrl":"https://doi.org/10.1115/imece2022-94143","url":null,"abstract":"\u0000 New Zealand and many countries gained heightened awareness of indoor air quality (IAQ) issues, and increased investment, according to the World Health Organization (WHO) guidelines, to improve their IAQ and reduce air pollution in commercial and residential buildings. Additionally, some countries have introduced new standards for indoor environments, such as the New Zealand “healthy homes” standard. At the same time, COVID-19 pandemic forced many people to spend much more time in indoor spaces, due to stay-at-home, or lockdown orders by governments. This increased attention on other aspects of indoor environmental quality, such as occupants’ satisfaction with thermal comfort parameters, presents an additional parameter for research and in the development of standards. From a medical perspectives, infectious respiratory diseases, such as influenza or COVID-19, are transmitted by airborne droplets. In this work, we assess a Polyester Filter and UV light (PFUV) dehumidifier device performance in an office with two occupants (one uninfected and the other one infected with a disease with airborne transmission using computational fluid dynamics (CFD) approach. Two positions for locating the PFUV dehumidifier in an office with a scenario in which one person is exhaling infected air and the other occupant must inhale and exhale from the shared air. The CFD model illustrated the best position of the device to distribute the air velocity contours. Further, based on the CFD model which was validated via the IAQ and comfort kit (Testo 400) thermal comfort analysis showed that the room is slightly cold.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"56 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115632042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Ortega, Alejandro Amador, A. Choudhuri, Md Mahamudur Rahman
This work experimentally characterizes the critical heat flux (CHF) and minimum film boiling heat flux (MFBHF) in additively manufactured cooling channels for regeneratively-cooled rocket engines during high pressure saturated internal forced convective boiling of liquid nitrogen (LN2). Three different channels with hydraulic diameters of 1.8 mm, 2.3 mm and 2.5 mm were fabricated by the National Aeronautics and Space Administration (NASA) Marshall Space Flight Center (MSFC). The channels were fabricated using Powder Bed Fusion (PBF) advanced 3D printing of the rocket engine material, GR-Cop42, a copper-chrome-niobium alloy. The fabricated channels were tested using a custom-built cryogenic High Heat Flux Test Facility capable of operating up to 4 MPa of pressure and 10 MW/m2 of heat flux. The channels were asymmetrically heated from the bottom to simulate the performance of the cooling channels of a rocket engine. The high-pressure flow boiling tests were performed at 1.38 MPa with respective saturation temperature of 109 K using LN2 as the working fluid in horizontal orientation of the channels. The volumetric flowrate of LN2 is held approximately constant at 47 cm3/s for all channels. The experiments were performed beyond the CHF to ensure film boiling inside the channels, and then gradually decreased the given power until MFBHF was reached. A CHF of 543 kW/m2 and a MFBHF heat flux of 486 kW/m2 were achieved for the 1.8 mm hydraulic diameter channel. Furthermore, the experimentally measured CHF values were compared with the correlations available in literature. More than 84% increase in CHF has been experimentally measured for the additively manufactured rough cooling channels as compared to the CHF prediction based on literature correlation for smooth channels.
{"title":"Experimental Characterization of Critical Heat Flux and Minimum Film Boiling Heat Flux for Additively Manufactured Cooling Channels for Liquid Nitrogen Saturated Flow Boiling","authors":"D. Ortega, Alejandro Amador, A. Choudhuri, Md Mahamudur Rahman","doi":"10.1115/imece2022-95562","DOIUrl":"https://doi.org/10.1115/imece2022-95562","url":null,"abstract":"\u0000 This work experimentally characterizes the critical heat flux (CHF) and minimum film boiling heat flux (MFBHF) in additively manufactured cooling channels for regeneratively-cooled rocket engines during high pressure saturated internal forced convective boiling of liquid nitrogen (LN2). Three different channels with hydraulic diameters of 1.8 mm, 2.3 mm and 2.5 mm were fabricated by the National Aeronautics and Space Administration (NASA) Marshall Space Flight Center (MSFC). The channels were fabricated using Powder Bed Fusion (PBF) advanced 3D printing of the rocket engine material, GR-Cop42, a copper-chrome-niobium alloy. The fabricated channels were tested using a custom-built cryogenic High Heat Flux Test Facility capable of operating up to 4 MPa of pressure and 10 MW/m2 of heat flux. The channels were asymmetrically heated from the bottom to simulate the performance of the cooling channels of a rocket engine. The high-pressure flow boiling tests were performed at 1.38 MPa with respective saturation temperature of 109 K using LN2 as the working fluid in horizontal orientation of the channels. The volumetric flowrate of LN2 is held approximately constant at 47 cm3/s for all channels. The experiments were performed beyond the CHF to ensure film boiling inside the channels, and then gradually decreased the given power until MFBHF was reached. A CHF of 543 kW/m2 and a MFBHF heat flux of 486 kW/m2 were achieved for the 1.8 mm hydraulic diameter channel. Furthermore, the experimentally measured CHF values were compared with the correlations available in literature. More than 84% increase in CHF has been experimentally measured for the additively manufactured rough cooling channels as compared to the CHF prediction based on literature correlation for smooth channels.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"187 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116400833","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The transition from laminar to turbulent flow is of great interest since it is one of the most difficult and unsolved problems in fluids engineering. The transition processes are significantly important because the transition has a huge impact on almost all systems that come in contact with a fluid flow by altering the mixing, transport, and drag properties of fluids even in simple pipe and channel flows. Generally, in most transportation systems, the transition to turbulence causes a significant increase in drag force, energy consumption, and, therefore, operating cost. Thus, understanding the underlying mechanisms of the laminar-to-turbulent transition can be a major benefit in many ways, especially economically. There have been substantial previous studies that focused on testing the stability of laminar flow and finding the critical amplitudes of disturbances necessary to trigger the transition in various wall-bounded systems, including circular pipes and square ducts. However, there is still no fundamental theory of transition to predict the onset of turbulence. In this study, we perform direct numerical simulations (DNS) of the transition flows from laminar to turbulence in a channel flow. Specifically, the effects of different magnitudes of perturbations on the onset of turbulence are investigated. The perturbation magnitudes vary from 0.001 (0.1%) to 0.05 (5%) of a typical turbulent velocity field, and the Reynolds number is from 5,000 to 40,000. Most importantly, the transition behavior in this study was found to be in good agreement with other reported studies performed for fluid flow in pipes and ducts. With the DNS results, a finite amplitude stability curve was obtained. The critical magnitude of perturbation required to cause transition was observed to be inversely proportional to the Reynolds number for the magnitude from 0.01 to 0.05. We also investigated the temporal behavior of the transition process, and it was found that the transition time or the time required to begin the transition process is inversely correlated with the Reynolds number only for the magnitude from 0.02 to 0.05, while different temporal behavior occurs for smaller perturbation magnitudes. In addition to the transition time, the transition dynamics were investigated by observing the time series of wall shear stress. At the onset of transition, the shear stress experiences an overshoot, then decreases toward sustained turbulence. As expected, the average values of the wall shear stress in turbulent flow increase with the Reynolds number. The change in the wall shear stress from laminar to overshoot was, of course, found to increase with the Reynolds number. More interestingly was the observed change in wall shear stress from the overshoot to turbulence. The change in magnitude appears to be almost insensitive to the Reynolds number and the perturbation magnitude. Because the change in wall shear stress is directly proportional to the pumping power, these ob
{"title":"Dynamics of Laminar-to-Turbulent Transition in a Wall-Bounded Channel Flow Up to Re=40,000","authors":"Mohsin Al Barwani, Jae Sung Park","doi":"10.1115/imece2022-94489","DOIUrl":"https://doi.org/10.1115/imece2022-94489","url":null,"abstract":"\u0000 The transition from laminar to turbulent flow is of great interest since it is one of the most difficult and unsolved problems in fluids engineering. The transition processes are significantly important because the transition has a huge impact on almost all systems that come in contact with a fluid flow by altering the mixing, transport, and drag properties of fluids even in simple pipe and channel flows. Generally, in most transportation systems, the transition to turbulence causes a significant increase in drag force, energy consumption, and, therefore, operating cost. Thus, understanding the underlying mechanisms of the laminar-to-turbulent transition can be a major benefit in many ways, especially economically. There have been substantial previous studies that focused on testing the stability of laminar flow and finding the critical amplitudes of disturbances necessary to trigger the transition in various wall-bounded systems, including circular pipes and square ducts. However, there is still no fundamental theory of transition to predict the onset of turbulence. In this study, we perform direct numerical simulations (DNS) of the transition flows from laminar to turbulence in a channel flow. Specifically, the effects of different magnitudes of perturbations on the onset of turbulence are investigated. The perturbation magnitudes vary from 0.001 (0.1%) to 0.05 (5%) of a typical turbulent velocity field, and the Reynolds number is from 5,000 to 40,000. Most importantly, the transition behavior in this study was found to be in good agreement with other reported studies performed for fluid flow in pipes and ducts. With the DNS results, a finite amplitude stability curve was obtained. The critical magnitude of perturbation required to cause transition was observed to be inversely proportional to the Reynolds number for the magnitude from 0.01 to 0.05. We also investigated the temporal behavior of the transition process, and it was found that the transition time or the time required to begin the transition process is inversely correlated with the Reynolds number only for the magnitude from 0.02 to 0.05, while different temporal behavior occurs for smaller perturbation magnitudes. In addition to the transition time, the transition dynamics were investigated by observing the time series of wall shear stress. At the onset of transition, the shear stress experiences an overshoot, then decreases toward sustained turbulence. As expected, the average values of the wall shear stress in turbulent flow increase with the Reynolds number. The change in the wall shear stress from laminar to overshoot was, of course, found to increase with the Reynolds number. More interestingly was the observed change in wall shear stress from the overshoot to turbulence. The change in magnitude appears to be almost insensitive to the Reynolds number and the perturbation magnitude. Because the change in wall shear stress is directly proportional to the pumping power, these ob","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"92 3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116694661","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","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：