Following the Kyoto Protocol and the more recent Kigali agreement, Hydrofluoroolefins (HFOs) are considered as the low global warming drop-in or substitute refrigerants for hydrofluorocarbons (HFCs) which have high global warming potential. The HFO R1234yf gained significant importance as a replacement for R134a in automobile air conditioning. In this context, the performance of a two-slab automotive evaporator with R1234yf numerical simulation is reported in this paper. The simulation is conducted by considering the heat transfer from air to the outside wetted surface consisting of louvered fins and tube wall, from there to the inside tube wall, and from there to the bulk of the boiling refrigerant inside the tube. The combined effect of heat and mass transfer from air to the wetted surface is described by the enthalpy potential method. For the two-phase and superheating regions suitable heat transfer correlations are employed. The results show that the refrigerant side heat transfer coefficient increases with increase in vapour quality up to around 80% and then decreases with further increase in the vapour quality. The major contribution to the cooling capacity is the latent heat abstraction during the flow boiling process occurring inside the tube. The temperatures of the condensate water film surface and the inner and outer tube wall surfaces are nearer to the bulk temperature of the refrigerant because of the high heat transfer coefficient on the refrigerant side. Results are also presented for the refrigerant side pressure drop and the evaporator exit air temperature and humidity ratio.
{"title":"Performance of Flat-Tube Louvered-Fin Automotive Evaporator With R1234yf","authors":"H. M. Gurudatt, G. Narasimham, B. Sadashive Gowda","doi":"10.1115/imece2022-94116","DOIUrl":"https://doi.org/10.1115/imece2022-94116","url":null,"abstract":"\u0000 Following the Kyoto Protocol and the more recent Kigali agreement, Hydrofluoroolefins (HFOs) are considered as the low global warming drop-in or substitute refrigerants for hydrofluorocarbons (HFCs) which have high global warming potential. The HFO R1234yf gained significant importance as a replacement for R134a in automobile air conditioning. In this context, the performance of a two-slab automotive evaporator with R1234yf numerical simulation is reported in this paper. The simulation is conducted by considering the heat transfer from air to the outside wetted surface consisting of louvered fins and tube wall, from there to the inside tube wall, and from there to the bulk of the boiling refrigerant inside the tube. The combined effect of heat and mass transfer from air to the wetted surface is described by the enthalpy potential method. For the two-phase and superheating regions suitable heat transfer correlations are employed. The results show that the refrigerant side heat transfer coefficient increases with increase in vapour quality up to around 80% and then decreases with further increase in the vapour quality. The major contribution to the cooling capacity is the latent heat abstraction during the flow boiling process occurring inside the tube. The temperatures of the condensate water film surface and the inner and outer tube wall surfaces are nearer to the bulk temperature of the refrigerant because of the high heat transfer coefficient on the refrigerant side. Results are also presented for the refrigerant side pressure drop and the evaporator exit air temperature and humidity ratio.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"1 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":"125406449","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}
Sandwich structures have been widely used as thermal and load-bearing materials in astronautic and aeronautic applications. owing to their advantages of high specific strength and stiffness. Among them, the X-type lattice cored sandwich panel has a superior thermal performance, with a larger pressure drop. In order to solve the disadvantage of higher pressure drop of the X-type lattice, this paper propose a new structure of helix lattice sandwich panel by modifying the structure of the X-type lattice at a similar porosity level. Forced convection of air in the helix lattice sandwich panel was numerically studied based on the validated model in available literature. The flow and heat transfer characteristics between the helix lattice and X-type lattice were compared. Results reveal that the fluid flow pattern of the helix lattice and the X-type lattice have similarities and differences. The similarity is that both of them cause a spiral type of flow and two same type of secondary flow, the difference is that compared with X-type lattice, the smaller blockage of flow area by the ligaments of the helix lattice leads to a large smooth mainstream. Besides, the overall Nusselt number of the helix lattice is slightly lower than that of X-type one with an average value of 6.69% at a certain Reynolds number, the same material thermal conductivity and similar porosity level. Although the flow pattern in the helix lattice is similar to that in X-type lattice, the smooth mainstream in the helix lattice inevitably limited the flow mixing which lead to a lower area-averaged Nusslet number on both the substrates and the ligaments relative to X-type one. However, in terms of pressure drop, the helix lattice is significantly lower than the X-type lattice due to smaller flow area blockage and smooth ligament structure, which is reduced by nearly half. The helix lattice core sandwich panel can maintain a high level heat transfer performance with little loss of pressure drop. For a given pumping power, the helix lattice outperforms X-type lattice by up to 6.65%. Furthermore, as the pumping power increases, the heat transfer performance of the helix lattice will be better than X-type lattice. Therefore, it can be considered that the helix lattice core sandwich panel solves the disadvantage of relatively high pressure drop in the X-type lattice, greatly reduced the pressure drop and the required pumping power with less heat transfer performance loss. The helix lattice core sandwich panel has a superior comprehensive heat transfer performance than X-type one.
{"title":"Numerical Study on Convective Heat Transfer Performance in Helix Lattice Sandwich Panel","authors":"Shulei Li, Shibo Zhang, G. Xie, Hongbin Yan","doi":"10.1115/imece2022-95310","DOIUrl":"https://doi.org/10.1115/imece2022-95310","url":null,"abstract":"\u0000 Sandwich structures have been widely used as thermal and load-bearing materials in astronautic and aeronautic applications. owing to their advantages of high specific strength and stiffness. Among them, the X-type lattice cored sandwich panel has a superior thermal performance, with a larger pressure drop. In order to solve the disadvantage of higher pressure drop of the X-type lattice, this paper propose a new structure of helix lattice sandwich panel by modifying the structure of the X-type lattice at a similar porosity level. Forced convection of air in the helix lattice sandwich panel was numerically studied based on the validated model in available literature. The flow and heat transfer characteristics between the helix lattice and X-type lattice were compared. Results reveal that the fluid flow pattern of the helix lattice and the X-type lattice have similarities and differences. The similarity is that both of them cause a spiral type of flow and two same type of secondary flow, the difference is that compared with X-type lattice, the smaller blockage of flow area by the ligaments of the helix lattice leads to a large smooth mainstream. Besides, the overall Nusselt number of the helix lattice is slightly lower than that of X-type one with an average value of 6.69% at a certain Reynolds number, the same material thermal conductivity and similar porosity level. Although the flow pattern in the helix lattice is similar to that in X-type lattice, the smooth mainstream in the helix lattice inevitably limited the flow mixing which lead to a lower area-averaged Nusslet number on both the substrates and the ligaments relative to X-type one. However, in terms of pressure drop, the helix lattice is significantly lower than the X-type lattice due to smaller flow area blockage and smooth ligament structure, which is reduced by nearly half. The helix lattice core sandwich panel can maintain a high level heat transfer performance with little loss of pressure drop. For a given pumping power, the helix lattice outperforms X-type lattice by up to 6.65%. Furthermore, as the pumping power increases, the heat transfer performance of the helix lattice will be better than X-type lattice. Therefore, it can be considered that the helix lattice core sandwich panel solves the disadvantage of relatively high pressure drop in the X-type lattice, greatly reduced the pressure drop and the required pumping power with less heat transfer performance loss. The helix lattice core sandwich panel has a superior comprehensive heat transfer performance than X-type one.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"77 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":"115988501","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}
Tarun Malhotra, Dorian Davis, D. Adams, Fisseha L. Gebre, Jiajun Xu
Geothermal heat pumps present a very intricate installation process and requires a vast amount of space which can cause a financial hurdle for most users. The geothermal system makes use of the constant ground temperature at the minimum of 5 ft depth with a thermal conductive working fluid and specified length of pipping. The system undergoes the necessary heat transfer that will be used as part of the heating or cooling process. In this study, an additively manufactured heat exchanger was designed and developed to address this issue. The design has an innovative coiled inner pipping to reduce the space needed for its installation, as well as combining the heat exchanger component with a drill bit design to simplify and reduce the cost of installation. We used CREO 8.0 to make a detailed drawing and CAD model of the system, which will then be simulated on ANSYS fluent software. During the simulation we studied the performance of heat transfer. In addition, this study also analyzes the coefficient of heat transfer and fluid pressure drop as a function of Reynolds number. For production of the system an additive manufacturing technique was used to manufacture the prototype.
{"title":"Design of an Improved Vertical Spiral Closed Loop Geothermal Heat Exchanger","authors":"Tarun Malhotra, Dorian Davis, D. Adams, Fisseha L. Gebre, Jiajun Xu","doi":"10.1115/imece2022-94381","DOIUrl":"https://doi.org/10.1115/imece2022-94381","url":null,"abstract":"\u0000 Geothermal heat pumps present a very intricate installation process and requires a vast amount of space which can cause a financial hurdle for most users. The geothermal system makes use of the constant ground temperature at the minimum of 5 ft depth with a thermal conductive working fluid and specified length of pipping. The system undergoes the necessary heat transfer that will be used as part of the heating or cooling process. In this study, an additively manufactured heat exchanger was designed and developed to address this issue. The design has an innovative coiled inner pipping to reduce the space needed for its installation, as well as combining the heat exchanger component with a drill bit design to simplify and reduce the cost of installation. We used CREO 8.0 to make a detailed drawing and CAD model of the system, which will then be simulated on ANSYS fluent software. During the simulation we studied the performance of heat transfer. In addition, this study also analyzes the coefficient of heat transfer and fluid pressure drop as a function of Reynolds number. For production of the system an additive manufacturing technique was used to manufacture the prototype.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"1 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":"114055425","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 is to create a computational fluid dynamics (CFD) simulation of the cake filtration process for Agrilectric Research. Cake filtration is the process by which solid particulate is filtered out of a mixture of fluid and solid phases. As the mixture flows through the system, the particulate accumulates on a filter cloth to form a filter cake, which acts as an added filtering medium to the system. The results obtained from this project can be used to aid Agrilectric in the development of their experimental testing methods by providing the ability to measure and predict filtration properties and to experiment with different filter cake designs to improve filtration methods and performance, without reliance on empirical data. The work was completed using the Workbench platform with the Fluent solver from the Ansys Student software bundle. A 20 cm long, 10 cm diameter filter cell was modeled and meshed through Workbench and was imported into Fluent to conduct the simulation. The flow of a mixture of water and a particulate phase of rice hull ash (RHA) was simulated using the Eulerian multiphase model. This would show the movement of the RHA through the system and the accumulation of the particulate on a filter cloth over time. The filter cloth was modeled using a porous cell zone to mimic filtering properties. The simulated solution shows RHA flowing into the system and initially passing through the filter cloth. After some time, a packed layer of particulate forms across the width of the filter cloth that allows a filter cake to accumulate in the system. The results from the multiphase simulation prove that with more research and simulation development, the model can be improved to represent a realistic cake filtration system which can be used to supplement or to replace existing laboratory testing.
{"title":"Simulation for Optimization of a Filter Cake System","authors":"A. Johnson, Allison LeBleu, Ning Zhang","doi":"10.1115/imece2022-95717","DOIUrl":"https://doi.org/10.1115/imece2022-95717","url":null,"abstract":"\u0000 The purpose of this project is to create a computational fluid dynamics (CFD) simulation of the cake filtration process for Agrilectric Research. Cake filtration is the process by which solid particulate is filtered out of a mixture of fluid and solid phases. As the mixture flows through the system, the particulate accumulates on a filter cloth to form a filter cake, which acts as an added filtering medium to the system. The results obtained from this project can be used to aid Agrilectric in the development of their experimental testing methods by providing the ability to measure and predict filtration properties and to experiment with different filter cake designs to improve filtration methods and performance, without reliance on empirical data.\u0000 The work was completed using the Workbench platform with the Fluent solver from the Ansys Student software bundle. A 20 cm long, 10 cm diameter filter cell was modeled and meshed through Workbench and was imported into Fluent to conduct the simulation. The flow of a mixture of water and a particulate phase of rice hull ash (RHA) was simulated using the Eulerian multiphase model. This would show the movement of the RHA through the system and the accumulation of the particulate on a filter cloth over time. The filter cloth was modeled using a porous cell zone to mimic filtering properties.\u0000 The simulated solution shows RHA flowing into the system and initially passing through the filter cloth. After some time, a packed layer of particulate forms across the width of the filter cloth that allows a filter cake to accumulate in the system.\u0000 The results from the multiphase simulation prove that with more research and simulation development, the model can be improved to represent a realistic cake filtration system which can be used to supplement or to replace existing laboratory testing.","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":"128309093","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}
An experimental study was conducted to compare heat transfer performance between three micro fin array configurations for transient and steady periodic operation. The study evaluates the time a microchannel takes to reach steady-state conditions for a given flow rate and heat input. It is crucial to investigate the response of the thermal device to overcome a sudden overheating. The experiment aims to analyze the effects of flow boiling in microchannels for extended periods. The study focuses on three novel microchannel cooling devices with different micro fin array configurations. The first design consists of an array of parallel straight fins. The second design resembles the first with the addition of diagonal cuts separating the channel into segments. The third and final design adds another set of diagonal cuts in the opposite direction, creating a diamond lattice of micro fins. It is believed that adding flow-disrupting geometries such as those found in designs 2 and 3 will be beneficial for both single and two-phase flow by improving flow mixing and reducing flow instability, respectively. The experimental results of each fin configuration were compared against a smooth plate (dummy channel) used as a reference. Each device was tested at flow rate of 0.1 to 0.5 ml/min at different heat inputs up to 500W. Temperature and pressure sensors located at the inlet and outlet of the channel measured and gathered fluid data every second for 1800 seconds. The surface temperature near the center of the channel was also collected every second. Once the system achieved steady-state conditions, the surface temperatures at the inlet and outlet of the plate were gathered to ensure correct readings. For this experiment, distilled water is the selected working fluid. Previous experimental studies have shown that adding turbulence caused by cut segments, like those in designs 2 and 3, may significantly improve the heat transfer effectiveness for flow boiling. The experimental results revealed a heat transfer enhancement during flow boiling for designs 2 and 3. Furthermore, for single-phase flow at low heat inputs, the straight parallel micro fins array exerted the highest pressure drop. The pressure drops for designs 2 and 3 were similar during flow boiling. The present study included the straight fin array design to a variable flow rate and increment heat input every 300 seconds. It was found that while the surface temperature data can easily be used as a reference to determine the onset of flow boiling, it cannot be used to detect flow instability effectively. Conversely, the pressure drop across the device provides valuable data for determining the onset of flow instability but is not very effective when used to assess flow boiling. As a result, a composite plot overlaying the surface temperature and pressure drop of the device over time is a great way to determine the onset of each phenomenon simultaneously.
{"title":"Extended Analysis of Micro Fin Array Configurations for Single- and Two-Phase Flow","authors":"Colton Frear, Gerardo Carbajal, Edwar Romero-Ramirez","doi":"10.1115/imece2022-95984","DOIUrl":"https://doi.org/10.1115/imece2022-95984","url":null,"abstract":"\u0000 An experimental study was conducted to compare heat transfer performance between three micro fin array configurations for transient and steady periodic operation. The study evaluates the time a microchannel takes to reach steady-state conditions for a given flow rate and heat input. It is crucial to investigate the response of the thermal device to overcome a sudden overheating. The experiment aims to analyze the effects of flow boiling in microchannels for extended periods. The study focuses on three novel microchannel cooling devices with different micro fin array configurations. The first design consists of an array of parallel straight fins. The second design resembles the first with the addition of diagonal cuts separating the channel into segments. The third and final design adds another set of diagonal cuts in the opposite direction, creating a diamond lattice of micro fins. It is believed that adding flow-disrupting geometries such as those found in designs 2 and 3 will be beneficial for both single and two-phase flow by improving flow mixing and reducing flow instability, respectively. The experimental results of each fin configuration were compared against a smooth plate (dummy channel) used as a reference. Each device was tested at flow rate of 0.1 to 0.5 ml/min at different heat inputs up to 500W. Temperature and pressure sensors located at the inlet and outlet of the channel measured and gathered fluid data every second for 1800 seconds. The surface temperature near the center of the channel was also collected every second. Once the system achieved steady-state conditions, the surface temperatures at the inlet and outlet of the plate were gathered to ensure correct readings. For this experiment, distilled water is the selected working fluid. Previous experimental studies have shown that adding turbulence caused by cut segments, like those in designs 2 and 3, may significantly improve the heat transfer effectiveness for flow boiling. The experimental results revealed a heat transfer enhancement during flow boiling for designs 2 and 3. Furthermore, for single-phase flow at low heat inputs, the straight parallel micro fins array exerted the highest pressure drop. The pressure drops for designs 2 and 3 were similar during flow boiling. The present study included the straight fin array design to a variable flow rate and increment heat input every 300 seconds. It was found that while the surface temperature data can easily be used as a reference to determine the onset of flow boiling, it cannot be used to detect flow instability effectively. Conversely, the pressure drop across the device provides valuable data for determining the onset of flow instability but is not very effective when used to assess flow boiling. As a result, a composite plot overlaying the surface temperature and pressure drop of the device over time is a great way to determine the onset of each phenomenon simultaneously.","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":"129425893","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}
Narayana Teja Ayyadevara, Ravi Kumar Kavali, B. Subramanian
A state-of-the-art integrated heating and cooling facility is established to conduct accelerated tests on large, vertically-oriented alloy rotors, spinning at high speeds. Accelerated testing for such components is accomplished by imposing a cyclically varying thermal stress field in addition to the existing mechanical stress field to estimate the impact on their creep and fatigue life. The cyclic thermal stresses are generated by repeatedly subjecting a rotor to mechanical loading, through alternate transient heating and cooling processes. These transient heating and cooling cycles are carefully designed to maintain specific temperature gradients in the rotor. Such accelerated testing helps provide an accurate estimate of the expected life of a rotor under actual field operating conditions. Thermal effects seen during cooling of large rotor shafts rotating at high speeds, by forced convection is an important subject area, both in academia and industry. In the present application, this feature gains importance in the development of new rotor-alloy materials for utilization in turbines of modern thermal power plants operating at advanced ultra-supercritical conditions. During the cooling phase of the thermal cycle, cylindrical alloy rotors spinning at high speeds (up to 3000 rpm) are enclosed in a cylindrical cavity and are cooled from high temperatures (∼800 °C) with inert gas, by means of forced convection. There is a need to perform many such cooling cycles to establish alloy material characteristics. The direction of cooling gas flow is neither longitudinal nor transverse to the rotor orientation, making this a unique cooling phenomenon. A comprehensive study is undertaken to predict rotor surface cooling, based on a combination of influencing parameters like gas mass flow, annular dimension, and rotor speeds. It is essential to arrive at the best combination of these parameters for obtaining the desired Rotational Heat Transfer Coefficient (RHTC) data. Mean RHTC for each case gives an insight into rotor cooling rates for this unique cooling disposition. Several simulations have been conducted using Computational Fluid Dynamics (CFD) to obtain temperature profiles along the rotor surface and cross-sections during the cooling period. This is supplemented by experimentation with sufficient instrumentation on these rotors. Establishing accurate correlations from the outputs obtained numerically would lead to considerable savings in terms of fixed costs, experimentation time, energy consumed and human resources deployed. This exercise will support tests on multiple such rotor alloy materials in a shorter time frame, thus speeding up the development of next-generation thermal power plants with the highest order of plant efficiency and reduced emissions.
{"title":"Study of Rotational Heat Transfer Coefficients in Enclosed Flow Over High-Speed Rotors","authors":"Narayana Teja Ayyadevara, Ravi Kumar Kavali, B. Subramanian","doi":"10.1115/imece2022-96470","DOIUrl":"https://doi.org/10.1115/imece2022-96470","url":null,"abstract":"\u0000 A state-of-the-art integrated heating and cooling facility is established to conduct accelerated tests on large, vertically-oriented alloy rotors, spinning at high speeds. Accelerated testing for such components is accomplished by imposing a cyclically varying thermal stress field in addition to the existing mechanical stress field to estimate the impact on their creep and fatigue life. The cyclic thermal stresses are generated by repeatedly subjecting a rotor to mechanical loading, through alternate transient heating and cooling processes. These transient heating and cooling cycles are carefully designed to maintain specific temperature gradients in the rotor. Such accelerated testing helps provide an accurate estimate of the expected life of a rotor under actual field operating conditions.\u0000 Thermal effects seen during cooling of large rotor shafts rotating at high speeds, by forced convection is an important subject area, both in academia and industry. In the present application, this feature gains importance in the development of new rotor-alloy materials for utilization in turbines of modern thermal power plants operating at advanced ultra-supercritical conditions. During the cooling phase of the thermal cycle, cylindrical alloy rotors spinning at high speeds (up to 3000 rpm) are enclosed in a cylindrical cavity and are cooled from high temperatures (∼800 °C) with inert gas, by means of forced convection. There is a need to perform many such cooling cycles to establish alloy material characteristics. The direction of cooling gas flow is neither longitudinal nor transverse to the rotor orientation, making this a unique cooling phenomenon. A comprehensive study is undertaken to predict rotor surface cooling, based on a combination of influencing parameters like gas mass flow, annular dimension, and rotor speeds. It is essential to arrive at the best combination of these parameters for obtaining the desired Rotational Heat Transfer Coefficient (RHTC) data. Mean RHTC for each case gives an insight into rotor cooling rates for this unique cooling disposition. Several simulations have been conducted using Computational Fluid Dynamics (CFD) to obtain temperature profiles along the rotor surface and cross-sections during the cooling period. This is supplemented by experimentation with sufficient instrumentation on these rotors. Establishing accurate correlations from the outputs obtained numerically would lead to considerable savings in terms of fixed costs, experimentation time, energy consumed and human resources deployed. This exercise will support tests on multiple such rotor alloy materials in a shorter time frame, thus speeding up the development of next-generation thermal power plants with the highest order of plant efficiency and reduced emissions.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"21 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":"129179328","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}
B. Buonomo, M. R. Golia, O. Manca, S. Nardini, R. E. Plomitallo
Energy storage systems have become increasingly important to reduce environmental impact and to solve the mismatch between temporal and methodical energy demanded and the energy produced. The purpose of this paper is to describe the results obtained from the numerical simulation of the Latent Heat Thermal Energy Storage System (LHTESS) with a geometry of a vertical shell and tube, made of aluminum metal foam filled with a paraffin wax phase change material (PCM). In the numerical simulations the inner surface of the hollow cylinder is assumed to be at a constant temperature above the PCM melting temperature, the external surface to lose heat toward the outside external ambient, and the top and bottom surfaces are considered adiabatic. The phase change process is modeled with the enthalpy-porosity theory, while the Darcy-Forchheimer model and the Local Thermal Non-Equilibrium (LTNE) assumption are adopted to analyze the aluminum foam-filled by the paraffin. The results of numerical simulations, concerning LHTESS charging phase, are reported as a function of time and are compared in terms of melting time, average temperature, and energy storage rate. The presence of the metal foam is known to significantly improve heat transfer in the LHTESS, and the obtained results show that it is necessary to consider systems with an external heat loss to simulate real operating conditions and understand how this different heat transfer coefficient affects system storage.
{"title":"Latent Heat Thermal Energy Storage in Shell and Tube With PCM and Metal Foam in LTNE With External Heat Losses","authors":"B. Buonomo, M. R. Golia, O. Manca, S. Nardini, R. E. Plomitallo","doi":"10.1115/imece2022-95703","DOIUrl":"https://doi.org/10.1115/imece2022-95703","url":null,"abstract":"\u0000 Energy storage systems have become increasingly important to reduce environmental impact and to solve the mismatch between temporal and methodical energy demanded and the energy produced.\u0000 The purpose of this paper is to describe the results obtained from the numerical simulation of the Latent Heat Thermal Energy Storage System (LHTESS) with a geometry of a vertical shell and tube, made of aluminum metal foam filled with a paraffin wax phase change material (PCM). In the numerical simulations the inner surface of the hollow cylinder is assumed to be at a constant temperature above the PCM melting temperature, the external surface to lose heat toward the outside external ambient, and the top and bottom surfaces are considered adiabatic. The phase change process is modeled with the enthalpy-porosity theory, while the Darcy-Forchheimer model and the Local Thermal Non-Equilibrium (LTNE) assumption are adopted to analyze the aluminum foam-filled by the paraffin. The results of numerical simulations, concerning LHTESS charging phase, are reported as a function of time and are compared in terms of melting time, average temperature, and energy storage rate. The presence of the metal foam is known to significantly improve heat transfer in the LHTESS, and the obtained results show that it is necessary to consider systems with an external heat loss to simulate real operating conditions and understand how this different heat transfer coefficient affects system storage.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"7 4 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":"114334349","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 absorption coefficient of molecular gases exhibits strong oscillations with wavelength. Thus, solution of the Radiative Transfer Equation (RTE) in a medium comprised of combustion gases require repeated solution of the gray RTE, rendering such calculations computationally very expensive. Popular methods to solve the RTE include the Finite Angle Method (FAM) and the Spherical Harmonics Method (PN). FAM, the finite-angle variant of the discrete ordinates method, produces accurate solutions when used with sufficient angular resolution. However, it has high computational cost. The lowest order Spherical Harmonics Method (P1) requires solution of a single elliptic partial differential equation and is very efficient in comparison to FAM. It yields accurate solutions for fairly isotropic intensity fields. In this study, a Hybrid solver for the nongray RTE is proposed that capitalizes upon the efficiency of the P1 method and the accuracy of the FAM. Depending on the spectral (or band) optical thickness, an appropriate solution method is chosen. The objective is to determine optimal parameters for selecting the solution method that can provide the best compromise between accuracy and computational cost. Using the statistical narrow band (SNB) model for carbon dioxide and water vapor, the nongray radiative transfer equation is solved in inhomogeneous media enclosed in multidimensional enclosures. Two different approaches — cut-off and filter optical thickness — are investigated for selecting the solution method. Several problems, both two-dimensional and three-dimensional, and with and without coupling to other modes of heat transfer are considered. The filter approach was found to be the best choice for prediction of the radiative source, while the cut-off approach was found to be the best for prediction of wall radiative heat fluxes.
{"title":"Hybrid Solver for the Radiative Transport Equation in Nongray Combustion Gases","authors":"N. Jajal, S. Mazumder","doi":"10.1115/imece2022-94556","DOIUrl":"https://doi.org/10.1115/imece2022-94556","url":null,"abstract":"\u0000 The absorption coefficient of molecular gases exhibits strong oscillations with wavelength. Thus, solution of the Radiative Transfer Equation (RTE) in a medium comprised of combustion gases require repeated solution of the gray RTE, rendering such calculations computationally very expensive. Popular methods to solve the RTE include the Finite Angle Method (FAM) and the Spherical Harmonics Method (PN). FAM, the finite-angle variant of the discrete ordinates method, produces accurate solutions when used with sufficient angular resolution. However, it has high computational cost. The lowest order Spherical Harmonics Method (P1) requires solution of a single elliptic partial differential equation and is very efficient in comparison to FAM. It yields accurate solutions for fairly isotropic intensity fields. In this study, a Hybrid solver for the nongray RTE is proposed that capitalizes upon the efficiency of the P1 method and the accuracy of the FAM. Depending on the spectral (or band) optical thickness, an appropriate solution method is chosen. The objective is to determine optimal parameters for selecting the solution method that can provide the best compromise between accuracy and computational cost. Using the statistical narrow band (SNB) model for carbon dioxide and water vapor, the nongray radiative transfer equation is solved in inhomogeneous media enclosed in multidimensional enclosures. Two different approaches — cut-off and filter optical thickness — are investigated for selecting the solution method. Several problems, both two-dimensional and three-dimensional, and with and without coupling to other modes of heat transfer are considered. The filter approach was found to be the best choice for prediction of the radiative source, while the cut-off approach was found to be the best for prediction of wall radiative heat fluxes.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"233 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":"114531605","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}
Rachmat Hermawan, Didi Rooscote, Agung Sidang Kustiawan, H. Nugraha
Failure in the boiler tube is one of the major causes of the force outages in a coal-fired power plant. This paper presents a failure investigation on the high-strength alloy ASME SA213 T91 superheater tube of a 600 MW class coal-fired power plant due to coal switching. The research investigated the fuel quality and the materials using the material characterization method and mechanical testing. The potential slagging and fusibility were found based on coal properties. A wide-open rupture with thick and blunt edges is exposed in the tube failure. Several steps for failure investigation were performed. Microstructures of the failed tube show numerous creep voids estimated < 2.5 microns and decomposed into spheroids as evidenced by a decrease in the hardness number 165 HV nearest location of failure. Exposure to high temperatures in the long-term causes the formation of an oxide scale layer on the fireside tube. The thickness of the oxide scale on the inner side tube > 600 microns also accelerates tube failure and shortened creep life is shown by a time rupture value from 16.29 to 0.26 hours with higher operating hoop stress near to failure location. Changes in fuel characteristics are indicated by the value of fusibility of 1190°C and slagging index of 0.473 which can worsen the condition of overheating from the increase in metal temperature. Higher flue gas temperatures due to the coal switching characteristic and higher metal temperatures of tubes above 570°C were identified as the cause of overheating. The finding confirmed that the superheater tube failed by long-term overheating.
{"title":"Failure Investigation of Secondary Superheater (SSH) Tube Boiler in the Coal Switching Case","authors":"Rachmat Hermawan, Didi Rooscote, Agung Sidang Kustiawan, H. Nugraha","doi":"10.1115/imece2022-96706","DOIUrl":"https://doi.org/10.1115/imece2022-96706","url":null,"abstract":"\u0000 Failure in the boiler tube is one of the major causes of the force outages in a coal-fired power plant. This paper presents a failure investigation on the high-strength alloy ASME SA213 T91 superheater tube of a 600 MW class coal-fired power plant due to coal switching. The research investigated the fuel quality and the materials using the material characterization method and mechanical testing. The potential slagging and fusibility were found based on coal properties. A wide-open rupture with thick and blunt edges is exposed in the tube failure. Several steps for failure investigation were performed. Microstructures of the failed tube show numerous creep voids estimated < 2.5 microns and decomposed into spheroids as evidenced by a decrease in the hardness number 165 HV nearest location of failure. Exposure to high temperatures in the long-term causes the formation of an oxide scale layer on the fireside tube. The thickness of the oxide scale on the inner side tube > 600 microns also accelerates tube failure and shortened creep life is shown by a time rupture value from 16.29 to 0.26 hours with higher operating hoop stress near to failure location. Changes in fuel characteristics are indicated by the value of fusibility of 1190°C and slagging index of 0.473 which can worsen the condition of overheating from the increase in metal temperature. Higher flue gas temperatures due to the coal switching characteristic and higher metal temperatures of tubes above 570°C were identified as the cause of overheating. The finding confirmed that the superheater tube failed by long-term overheating.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"57 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":"121695722","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}
Divyprakash Pal, Maharshi B Shukla, I. Perez-Raya, S. Kandlikar
Heat transfer due to the convective boiling mechanism in the microchannel plays an important role in heat transfer during boiling. Therefore, it is relevant to find ways to manipulate the vapor bubbles such that convection heat transfer is enhanced. This numerical study investigates the effects of different geometrical parameters on bubble movement through a micro tapered gap. The objective is to identify an optimal configuration such that the bubble moves at the fastest possible speed when it travels through the micro gap. To conduct this research a model is created using ANSYS-Fluent which uses the Volume of Fluid (VOF) interface tracking method. The multiphase VOF model tracks the air-water interface. A bubble is generated inside the microchannel in which fluid is flowing. The overall domain of the model consists of the surface at the bottom, having an orifice through which the air bubble is generated. Three different cases of an angled tapered surface are created 5°, 10°, and 15°. The airflow rate is kept constant throughout each simulation. Simulation results show the impact of the tapered angle on the bubble’s flow movement and flow direction. Liquid and air velocity contours can be used to analyze the flow. The impact of the taper angles on the movement and flow direction of the air bubble is discussed. It is observed that the performed simulations help to better understand the experimental observation of bubble motion; the simulations give clear evidence of the fluid dynamic behavior along the tapered microchannel.
{"title":"Numerical Simulation for Analyzing Interfacial Velocity and Interfacial Forces of a Bubble Motion in Taper Micro Gap","authors":"Divyprakash Pal, Maharshi B Shukla, I. Perez-Raya, S. Kandlikar","doi":"10.1115/imece2022-97021","DOIUrl":"https://doi.org/10.1115/imece2022-97021","url":null,"abstract":"\u0000 Heat transfer due to the convective boiling mechanism in the microchannel plays an important role in heat transfer during boiling. Therefore, it is relevant to find ways to manipulate the vapor bubbles such that convection heat transfer is enhanced. This numerical study investigates the effects of different geometrical parameters on bubble movement through a micro tapered gap. The objective is to identify an optimal configuration such that the bubble moves at the fastest possible speed when it travels through the micro gap. To conduct this research a model is created using ANSYS-Fluent which uses the Volume of Fluid (VOF) interface tracking method. The multiphase VOF model tracks the air-water interface. A bubble is generated inside the microchannel in which fluid is flowing. The overall domain of the model consists of the surface at the bottom, having an orifice through which the air bubble is generated. Three different cases of an angled tapered surface are created 5°, 10°, and 15°. The airflow rate is kept constant throughout each simulation. Simulation results show the impact of the tapered angle on the bubble’s flow movement and flow direction. Liquid and air velocity contours can be used to analyze the flow. The impact of the taper angles on the movement and flow direction of the air bubble is discussed. It is observed that the performed simulations help to better understand the experimental observation of bubble motion; the simulations give clear evidence of the fluid dynamic behavior along the tapered microchannel.","PeriodicalId":292222,"journal":{"name":"Volume 8: Fluids Engineering; Heat Transfer and Thermal Engineering","volume":"34 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":"114307983","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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