Marco Bizzarri, Paolo Conti, L. Glicksman, E. Schito, D. Testi
The purpose of our study is to evaluate the surface temperature distribution on a radiant floor, particularly focusing on space cooling operations, to assess the presence of non-uniformities. In fact, knowing the temperature difference between the average superficial temperature and the coldest spot can be a useful indication for condensation prevention. Primarily, we performed an experimental campaign in test rooms using temperature sensors and liquid crystal thermography. This allowed us to evaluate the floor temperature distribution both on a local scale, influenced by the discontinuous presence of buried water pipes, and on a macro scale, influenced by internal use, objects, and boundary conditions of the surrounding space. Then, the experimental temperature field on the radiant floor surface has been compared with analytical and numerical models in steady-state and transient phases, respectively. The results indicate limited superficial temperature variations that become more significant at larger tube spacings and under transient conditions. In particular, the numerical transient analysis showed that shortly after a step change in the pipe's temperature boundary condition, a larger variation is locally observable on the floor, which then decays to the new steady-state conditions, presenting more uniformity. However, local effects are generally overshadowed by macro effects, especially for practical scenarios where many objects, furnishings, and different boundary conditions are present. Finally, as a conservative guideline for the cooling system control, we recommend maintaining the average superficial floor temperature at least 1°C above the dew point, to account for the described non-uniformities.
{"title":"Evaluation by Liquid Crystal Thermography of Transient Surface Temperature Distribution in Radiant Floor Cooling Applications and Assessment of Analytical and Numerical Models","authors":"Marco Bizzarri, Paolo Conti, L. Glicksman, E. Schito, D. Testi","doi":"10.1115/1.4064707","DOIUrl":"https://doi.org/10.1115/1.4064707","url":null,"abstract":"\u0000 The purpose of our study is to evaluate the surface temperature distribution on a radiant floor, particularly focusing on space cooling operations, to assess the presence of non-uniformities. In fact, knowing the temperature difference between the average superficial temperature and the coldest spot can be a useful indication for condensation prevention. Primarily, we performed an experimental campaign in test rooms using temperature sensors and liquid crystal thermography. This allowed us to evaluate the floor temperature distribution both on a local scale, influenced by the discontinuous presence of buried water pipes, and on a macro scale, influenced by internal use, objects, and boundary conditions of the surrounding space. Then, the experimental temperature field on the radiant floor surface has been compared with analytical and numerical models in steady-state and transient phases, respectively. The results indicate limited superficial temperature variations that become more significant at larger tube spacings and under transient conditions. In particular, the numerical transient analysis showed that shortly after a step change in the pipe's temperature boundary condition, a larger variation is locally observable on the floor, which then decays to the new steady-state conditions, presenting more uniformity. However, local effects are generally overshadowed by macro effects, especially for practical scenarios where many objects, furnishings, and different boundary conditions are present. Finally, as a conservative guideline for the cooling system control, we recommend maintaining the average superficial floor temperature at least 1°C above the dew point, to account for the described non-uniformities.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139790044","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}
Natural convection in fluid-saturated, horizontal porous-media is quintessential to many applications like geothermal reservoirs and solar thermal storage systems. Researchers have dedicated substantial effort over the years in pursuit of altering natural convection within a horizontal porous-media (Darcy-Bénard) system. Although significant research efforts have been directed towards understanding the effects of bounding walls in horizontal (Rayleigh-Bénard) convection systems, similar investigations for Darcy-Bénard convection systems are still lacking. Therefore, the present study examines the effect of thermal properties of horizontal bounding plates on porous-media Nusselt number at high Rayleigh-Darcy numbers (105-107). Numerical simulations are performed by employing Darcy-Forchheimer model within a three-dimensional cylindrical computational domain to emulate Darcy-Bénard systems for two aspect ratios (1 and 2)and six different plate materials having non-dimensional plate thicknesses of 0.02, 0.08, and 0.16. Polypropylene and compressed CO2 gas are chosen as solid and fluid phases for the porous media, respectively, that encompass a range of Darcy numbers (10-6-10-3). Findings reveal that when the ratio of thermal resistances of porous layer and plates falls below 4.61, the corrected Nusselt number deviates by more than 10% from the corresponding ideal Nusselt number with infinitely conducting bounding plates. The study also proposes a correction factor to estimate this deviation, which shows a good agreement with numerical results.
{"title":"Effect of Finite Thermal Conductivity Bounding Walls On Darcy-bénard Convection","authors":"Parvez Alam, Umesh Madanan","doi":"10.1115/1.4064687","DOIUrl":"https://doi.org/10.1115/1.4064687","url":null,"abstract":"\u0000 Natural convection in fluid-saturated, horizontal porous-media is quintessential to many applications like geothermal reservoirs and solar thermal storage systems. Researchers have dedicated substantial effort over the years in pursuit of altering natural convection within a horizontal porous-media (Darcy-Bénard) system. Although significant research efforts have been directed towards understanding the effects of bounding walls in horizontal (Rayleigh-Bénard) convection systems, similar investigations for Darcy-Bénard convection systems are still lacking. Therefore, the present study examines the effect of thermal properties of horizontal bounding plates on porous-media Nusselt number at high Rayleigh-Darcy numbers (105-107). Numerical simulations are performed by employing Darcy-Forchheimer model within a three-dimensional cylindrical computational domain to emulate Darcy-Bénard systems for two aspect ratios (1 and 2)and six different plate materials having non-dimensional plate thicknesses of 0.02, 0.08, and 0.16. Polypropylene and compressed CO2 gas are chosen as solid and fluid phases for the porous media, respectively, that encompass a range of Darcy numbers (10-6-10-3). Findings reveal that when the ratio of thermal resistances of porous layer and plates falls below 4.61, the corrected Nusselt number deviates by more than 10% from the corresponding ideal Nusselt number with infinitely conducting bounding plates. The study also proposes a correction factor to estimate this deviation, which shows a good agreement with numerical results.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139852073","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 paper presents an experimental study on the droplet size and velocity, as well as temperature distribution, of a two-fluid atomizer (dj=1.6mm; spray nozzle exit diameter) through optical non-intrusive interferometric particle image (IPI) and particle image velocimetry (PIV) measurements with five different air liquid ratios (Rs) at three spray heights with three target-plate initial temperatures. Cold flow visualization was made for the spray height of 50 mm at 25oC. The Saunter-mean diameter (d32) was measured at the target temperature of 25°C without heating and found to be in the range of 34.22µm to 42.62µm in terms of a correlation with We(dj) Re(dj). The measured impact velocity at the spray height of 50 mm was of 10m/s to 30m/s with three different initial target temperatures. It was found that the impact velocity displayed a strong function of the initial temperature. Furthermore, both the cooling curve and transient boiling curve were obtained with the identified cooling/boiling parameters of the cooling rate, critical heat flux (CHF), Leidenfrost temperature (LFT), as well as the onset of nucleate boiling (ONB). The best cooling performance was found at R=0.242 for a spray height of 50 mm with the corresponding cooling rate of -19.1°/s, CHF of 486 W/cm2, and heat transfer coefficient (HTC) of 2.85 W/cm2K.
{"title":"Spray Cooling Heat Transfer of a Two-Fluid Spray Atomizer","authors":"S. Hsieh, Ching-Feng Huang, Jhen Lin, Yu-Ru Chen","doi":"10.1115/1.4064686","DOIUrl":"https://doi.org/10.1115/1.4064686","url":null,"abstract":"\u0000 The paper presents an experimental study on the droplet size and velocity, as well as temperature distribution, of a two-fluid atomizer (dj=1.6mm; spray nozzle exit diameter) through optical non-intrusive interferometric particle image (IPI) and particle image velocimetry (PIV) measurements with five different air liquid ratios (Rs) at three spray heights with three target-plate initial temperatures. Cold flow visualization was made for the spray height of 50 mm at 25oC. The Saunter-mean diameter (d32) was measured at the target temperature of 25°C without heating and found to be in the range of 34.22µm to 42.62µm in terms of a correlation with We(dj) Re(dj). The measured impact velocity at the spray height of 50 mm was of 10m/s to 30m/s with three different initial target temperatures. It was found that the impact velocity displayed a strong function of the initial temperature. Furthermore, both the cooling curve and transient boiling curve were obtained with the identified cooling/boiling parameters of the cooling rate, critical heat flux (CHF), Leidenfrost temperature (LFT), as well as the onset of nucleate boiling (ONB). The best cooling performance was found at R=0.242 for a spray height of 50 mm with the corresponding cooling rate of -19.1°/s, CHF of 486 W/cm2, and heat transfer coefficient (HTC) of 2.85 W/cm2K.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139853808","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}
Natural convection in fluid-saturated, horizontal porous-media is quintessential to many applications like geothermal reservoirs and solar thermal storage systems. Researchers have dedicated substantial effort over the years in pursuit of altering natural convection within a horizontal porous-media (Darcy-Bénard) system. Although significant research efforts have been directed towards understanding the effects of bounding walls in horizontal (Rayleigh-Bénard) convection systems, similar investigations for Darcy-Bénard convection systems are still lacking. Therefore, the present study examines the effect of thermal properties of horizontal bounding plates on porous-media Nusselt number at high Rayleigh-Darcy numbers (105-107). Numerical simulations are performed by employing Darcy-Forchheimer model within a three-dimensional cylindrical computational domain to emulate Darcy-Bénard systems for two aspect ratios (1 and 2)and six different plate materials having non-dimensional plate thicknesses of 0.02, 0.08, and 0.16. Polypropylene and compressed CO2 gas are chosen as solid and fluid phases for the porous media, respectively, that encompass a range of Darcy numbers (10-6-10-3). Findings reveal that when the ratio of thermal resistances of porous layer and plates falls below 4.61, the corrected Nusselt number deviates by more than 10% from the corresponding ideal Nusselt number with infinitely conducting bounding plates. The study also proposes a correction factor to estimate this deviation, which shows a good agreement with numerical results.
{"title":"Effect of Finite Thermal Conductivity Bounding Walls On Darcy-bénard Convection","authors":"Parvez Alam, Umesh Madanan","doi":"10.1115/1.4064687","DOIUrl":"https://doi.org/10.1115/1.4064687","url":null,"abstract":"\u0000 Natural convection in fluid-saturated, horizontal porous-media is quintessential to many applications like geothermal reservoirs and solar thermal storage systems. Researchers have dedicated substantial effort over the years in pursuit of altering natural convection within a horizontal porous-media (Darcy-Bénard) system. Although significant research efforts have been directed towards understanding the effects of bounding walls in horizontal (Rayleigh-Bénard) convection systems, similar investigations for Darcy-Bénard convection systems are still lacking. Therefore, the present study examines the effect of thermal properties of horizontal bounding plates on porous-media Nusselt number at high Rayleigh-Darcy numbers (105-107). Numerical simulations are performed by employing Darcy-Forchheimer model within a three-dimensional cylindrical computational domain to emulate Darcy-Bénard systems for two aspect ratios (1 and 2)and six different plate materials having non-dimensional plate thicknesses of 0.02, 0.08, and 0.16. Polypropylene and compressed CO2 gas are chosen as solid and fluid phases for the porous media, respectively, that encompass a range of Darcy numbers (10-6-10-3). Findings reveal that when the ratio of thermal resistances of porous layer and plates falls below 4.61, the corrected Nusselt number deviates by more than 10% from the corresponding ideal Nusselt number with infinitely conducting bounding plates. The study also proposes a correction factor to estimate this deviation, which shows a good agreement with numerical results.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139792262","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}
Despite the significant and ongoing interest in Green's functions from scientists, engineers and mathematicians, the area remains underdeveloped with respect to understanding problems from laminar fluid flow and magnetohydrodynamics in porous media. The purpose of this paper is to partially address this gap by constructing a new and explicit representation of the Green's function for a boundary value problem that is derived from laminar flow in channels with porous walls in the presence of a transverse magnetic field. We discuss some interesting consequences of our constructed Green's function, including: the establishment of an equivalent integral equation; and the generation of new information regarding solutions to our boundary value problem. We discover that, for any given transverse magnetic field, our laminar flow problem has a unique solution in a particular location provided the Reynolds number is sufficiently small, and that the solution may be approximated by Picard iterations.
{"title":"Green's Function for Laminar Flow in Channels with Porous Walls in the Presence of a Transverse Magnetic Field","authors":"C. Tisdell","doi":"10.1115/1.4064689","DOIUrl":"https://doi.org/10.1115/1.4064689","url":null,"abstract":"\u0000 Despite the significant and ongoing interest in Green's functions from scientists, engineers and mathematicians, the area remains underdeveloped with respect to understanding problems from laminar fluid flow and magnetohydrodynamics in porous media. The purpose of this paper is to partially address this gap by constructing a new and explicit representation of the Green's function for a boundary value problem that is derived from laminar flow in channels with porous walls in the presence of a transverse magnetic field. We discuss some interesting consequences of our constructed Green's function, including: the establishment of an equivalent integral equation; and the generation of new information regarding solutions to our boundary value problem. We discover that, for any given transverse magnetic field, our laminar flow problem has a unique solution in a particular location provided the Reynolds number is sufficiently small, and that the solution may be approximated by Picard iterations.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139791439","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 paper presents an experimental study on the droplet size and velocity, as well as temperature distribution, of a two-fluid atomizer (dj=1.6mm; spray nozzle exit diameter) through optical non-intrusive interferometric particle image (IPI) and particle image velocimetry (PIV) measurements with five different air liquid ratios (Rs) at three spray heights with three target-plate initial temperatures. Cold flow visualization was made for the spray height of 50 mm at 25oC. The Saunter-mean diameter (d32) was measured at the target temperature of 25°C without heating and found to be in the range of 34.22µm to 42.62µm in terms of a correlation with We(dj) Re(dj). The measured impact velocity at the spray height of 50 mm was of 10m/s to 30m/s with three different initial target temperatures. It was found that the impact velocity displayed a strong function of the initial temperature. Furthermore, both the cooling curve and transient boiling curve were obtained with the identified cooling/boiling parameters of the cooling rate, critical heat flux (CHF), Leidenfrost temperature (LFT), as well as the onset of nucleate boiling (ONB). The best cooling performance was found at R=0.242 for a spray height of 50 mm with the corresponding cooling rate of -19.1°/s, CHF of 486 W/cm2, and heat transfer coefficient (HTC) of 2.85 W/cm2K.
{"title":"Spray Cooling Heat Transfer of a Two-Fluid Spray Atomizer","authors":"S. Hsieh, Ching-Feng Huang, Jhen Lin, Yu-Ru Chen","doi":"10.1115/1.4064686","DOIUrl":"https://doi.org/10.1115/1.4064686","url":null,"abstract":"\u0000 The paper presents an experimental study on the droplet size and velocity, as well as temperature distribution, of a two-fluid atomizer (dj=1.6mm; spray nozzle exit diameter) through optical non-intrusive interferometric particle image (IPI) and particle image velocimetry (PIV) measurements with five different air liquid ratios (Rs) at three spray heights with three target-plate initial temperatures. Cold flow visualization was made for the spray height of 50 mm at 25oC. The Saunter-mean diameter (d32) was measured at the target temperature of 25°C without heating and found to be in the range of 34.22µm to 42.62µm in terms of a correlation with We(dj) Re(dj). The measured impact velocity at the spray height of 50 mm was of 10m/s to 30m/s with three different initial target temperatures. It was found that the impact velocity displayed a strong function of the initial temperature. Furthermore, both the cooling curve and transient boiling curve were obtained with the identified cooling/boiling parameters of the cooling rate, critical heat flux (CHF), Leidenfrost temperature (LFT), as well as the onset of nucleate boiling (ONB). The best cooling performance was found at R=0.242 for a spray height of 50 mm with the corresponding cooling rate of -19.1°/s, CHF of 486 W/cm2, and heat transfer coefficient (HTC) of 2.85 W/cm2K.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139793926","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}
Despite the significant and ongoing interest in Green's functions from scientists, engineers and mathematicians, the area remains underdeveloped with respect to understanding problems from laminar fluid flow and magnetohydrodynamics in porous media. The purpose of this paper is to partially address this gap by constructing a new and explicit representation of the Green's function for a boundary value problem that is derived from laminar flow in channels with porous walls in the presence of a transverse magnetic field. We discuss some interesting consequences of our constructed Green's function, including: the establishment of an equivalent integral equation; and the generation of new information regarding solutions to our boundary value problem. We discover that, for any given transverse magnetic field, our laminar flow problem has a unique solution in a particular location provided the Reynolds number is sufficiently small, and that the solution may be approximated by Picard iterations.
{"title":"Green's Function for Laminar Flow in Channels with Porous Walls in the Presence of a Transverse Magnetic Field","authors":"C. Tisdell","doi":"10.1115/1.4064689","DOIUrl":"https://doi.org/10.1115/1.4064689","url":null,"abstract":"\u0000 Despite the significant and ongoing interest in Green's functions from scientists, engineers and mathematicians, the area remains underdeveloped with respect to understanding problems from laminar fluid flow and magnetohydrodynamics in porous media. The purpose of this paper is to partially address this gap by constructing a new and explicit representation of the Green's function for a boundary value problem that is derived from laminar flow in channels with porous walls in the presence of a transverse magnetic field. We discuss some interesting consequences of our constructed Green's function, including: the establishment of an equivalent integral equation; and the generation of new information regarding solutions to our boundary value problem. We discover that, for any given transverse magnetic field, our laminar flow problem has a unique solution in a particular location provided the Reynolds number is sufficiently small, and that the solution may be approximated by Picard iterations.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139851312","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}
Hakduck Kim, Seungtaek Lee, Heechang Lim, Juhun Song
In this study, coal samples with different moisture contents were prepared using a drying and humidification system. Coal samples were placed in a crucible and ignited using a heating wire, to which power was applied during coal combustion. The combustion radiance of coal samples with three moisture contents (0, 20, and 50%) was measured using a narrow-angle radiometer at three temperatures (10, 25, and 50 °C). A numerical simulation model was developed to predict the unsteady radiation characteristics of a coal layer burning on one-dimensional planar plates. The unsteady energy balance equation and radiative transfer equation were solved using the semi-implicit Runge-Kutta method and discrete ordinates method. In addition, the effect of dew condensation on the radiance was investigated. The greatest reduction in radiance was observed during the burning of the high-moisture coal. Furthermore, the effect of ash (converted from coal) on radiance was examined. The results demonstrated that certain changes in the optical properties during the burning of coal to ash can alter the absorption as well as anisotropic scattering, and thereby the radiance, as combustion proceeds.
{"title":"Dependence of Radiance of Burning Coal Bed On Ash Formation and Dew Condensation","authors":"Hakduck Kim, Seungtaek Lee, Heechang Lim, Juhun Song","doi":"10.1115/1.4064667","DOIUrl":"https://doi.org/10.1115/1.4064667","url":null,"abstract":"\u0000 In this study, coal samples with different moisture contents were prepared using a drying and humidification system. Coal samples were placed in a crucible and ignited using a heating wire, to which power was applied during coal combustion. The combustion radiance of coal samples with three moisture contents (0, 20, and 50%) was measured using a narrow-angle radiometer at three temperatures (10, 25, and 50 °C). A numerical simulation model was developed to predict the unsteady radiation characteristics of a coal layer burning on one-dimensional planar plates. The unsteady energy balance equation and radiative transfer equation were solved using the semi-implicit Runge-Kutta method and discrete ordinates method. In addition, the effect of dew condensation on the radiance was investigated. The greatest reduction in radiance was observed during the burning of the high-moisture coal. Furthermore, the effect of ash (converted from coal) on radiance was examined. The results demonstrated that certain changes in the optical properties during the burning of coal to ash can alter the absorption as well as anisotropic scattering, and thereby the radiance, as combustion proceeds.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139854592","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}
Hakduck Kim, Seungtaek Lee, Heechang Lim, Juhun Song
In this study, coal samples with different moisture contents were prepared using a drying and humidification system. Coal samples were placed in a crucible and ignited using a heating wire, to which power was applied during coal combustion. The combustion radiance of coal samples with three moisture contents (0, 20, and 50%) was measured using a narrow-angle radiometer at three temperatures (10, 25, and 50 °C). A numerical simulation model was developed to predict the unsteady radiation characteristics of a coal layer burning on one-dimensional planar plates. The unsteady energy balance equation and radiative transfer equation were solved using the semi-implicit Runge-Kutta method and discrete ordinates method. In addition, the effect of dew condensation on the radiance was investigated. The greatest reduction in radiance was observed during the burning of the high-moisture coal. Furthermore, the effect of ash (converted from coal) on radiance was examined. The results demonstrated that certain changes in the optical properties during the burning of coal to ash can alter the absorption as well as anisotropic scattering, and thereby the radiance, as combustion proceeds.
{"title":"Dependence of Radiance of Burning Coal Bed On Ash Formation and Dew Condensation","authors":"Hakduck Kim, Seungtaek Lee, Heechang Lim, Juhun Song","doi":"10.1115/1.4064667","DOIUrl":"https://doi.org/10.1115/1.4064667","url":null,"abstract":"\u0000 In this study, coal samples with different moisture contents were prepared using a drying and humidification system. Coal samples were placed in a crucible and ignited using a heating wire, to which power was applied during coal combustion. The combustion radiance of coal samples with three moisture contents (0, 20, and 50%) was measured using a narrow-angle radiometer at three temperatures (10, 25, and 50 °C). A numerical simulation model was developed to predict the unsteady radiation characteristics of a coal layer burning on one-dimensional planar plates. The unsteady energy balance equation and radiative transfer equation were solved using the semi-implicit Runge-Kutta method and discrete ordinates method. In addition, the effect of dew condensation on the radiance was investigated. The greatest reduction in radiance was observed during the burning of the high-moisture coal. Furthermore, the effect of ash (converted from coal) on radiance was examined. The results demonstrated that certain changes in the optical properties during the burning of coal to ash can alter the absorption as well as anisotropic scattering, and thereby the radiance, as combustion proceeds.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139794763","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}
In this study, Y-shaped micro-mixers with mixing chamber design optimized as rotation and chaotic advection in the fluid domain increases with the chamber. Motivated by the advantages of Y-shaped mixers, a parametric study was performed for inlet angles (α, β), inlet channel eccentricities (x-ecc, z-ecc) and length scale ratios (L1/L2, D1/D2 and Vsp). z-eccentricity is introduced in addition to x-eccentricity to create a design that further enhances the swirl and chaotic advection inside mixing chamber for the first time. The results reveal that the maximum mixing efficiency can be achieved for Reynolds number of 81 and α, β, x-ecc, z-ecc, D1/D2, and L1/L2 values of 210°, 60°, 20 µm, 20 µm, 1.8 and 4, respectively. In addition, the proposed Y-shaped micro-mixer leads to a lower the pressure drop (at least 50% reduction for all Reynolds numbers) in comparison to competing design. The maximum reduction in pressure drop is 72% less than the CSC (Re= 81) with mixing efficiency of 88% and pressure drop of 9244.4 Pa. Overall, an outstanding mixing efficiency was offered over a wide range of Reynolds numbers with distinctly low pressure drop and a compact micro-mixer design, which could be beneficial for a wide variety of applications where volume and pumping power are limited.
{"title":"Optimization of Y-Shaped Micro-Mixers with a Mixing Chamber for Increased Mixing Efficiency and Decreased Pressure Drop","authors":"Umut Ege Samancioglu, Ali Kosar, E. Çetkin","doi":"10.1115/1.4064443","DOIUrl":"https://doi.org/10.1115/1.4064443","url":null,"abstract":"\u0000 In this study, Y-shaped micro-mixers with mixing chamber design optimized as rotation and chaotic advection in the fluid domain increases with the chamber. Motivated by the advantages of Y-shaped mixers, a parametric study was performed for inlet angles (α, β), inlet channel eccentricities (x-ecc, z-ecc) and length scale ratios (L1/L2, D1/D2 and Vsp). z-eccentricity is introduced in addition to x-eccentricity to create a design that further enhances the swirl and chaotic advection inside mixing chamber for the first time. The results reveal that the maximum mixing efficiency can be achieved for Reynolds number of 81 and α, β, x-ecc, z-ecc, D1/D2, and L1/L2 values of 210°, 60°, 20 µm, 20 µm, 1.8 and 4, respectively. In addition, the proposed Y-shaped micro-mixer leads to a lower the pressure drop (at least 50% reduction for all Reynolds numbers) in comparison to competing design. The maximum reduction in pressure drop is 72% less than the CSC (Re= 81) with mixing efficiency of 88% and pressure drop of 9244.4 Pa. Overall, an outstanding mixing efficiency was offered over a wide range of Reynolds numbers with distinctly low pressure drop and a compact micro-mixer design, which could be beneficial for a wide variety of applications where volume and pumping power are limited.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139380770","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}
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