Pub Date : 2022-01-01DOI: 10.36963/ijtst.2022090401
M. S. Azad
A very simple and economical device used for harnessing freely available energy from sun is solar air heater. But these solar air heaters are inefficient due to the low co-efficient of heat of air. Making artificially rough absorber plate is very common amongst the various techniques applied on solar air heater to enhance the performance. Square elements cut diagonally and glued on the absorber surface to generate the roughness. The impact of roughness parameters such Relative roughness height (RRH) of 0.44 to 0.077, Relative roughness pitch(RRP) of 3 to 9 and square element arm length (ALSE) of 4 mm to 10 mm on the performance of an artificially roughened solar air heater has been numerically explored. The Reynolds number of the absorber plate was adjusted from 4250 to 20000, but the heat flux remained constant at 1000 W/m2. The flow turbulence was handled using the “ANSYS FLUENT software's renormalized group (RNG) k-ε with enhanced wall treatment” turbulence model. In terms of Nusselt number and friction factor, the effects of roughness parameters such as RRP, RRH, and ALSE on the performance of artificially roughened solar air heaters have been explored. To test their increased efficiency, Nusselt number and friction factor of roughened solar air heaters (SAH) has been compared at similar flow conditions with plain one.
{"title":"Thermohydraulic performance and correlation development for solar air heater having rough absorber surface using chamfered-square elements","authors":"M. S. Azad","doi":"10.36963/ijtst.2022090401","DOIUrl":"https://doi.org/10.36963/ijtst.2022090401","url":null,"abstract":"A very simple and economical device used for harnessing freely available energy from sun is solar air heater. But these solar air heaters are inefficient due to the low co-efficient of heat of air. Making artificially rough absorber plate is very common amongst the various techniques applied on solar air heater to enhance the performance. Square elements cut diagonally and glued on the absorber surface to generate the roughness. The impact of roughness parameters such Relative roughness height (RRH) of 0.44 to 0.077, Relative roughness pitch(RRP) of 3 to 9 and square element arm length (ALSE) of 4 mm to 10 mm on the performance of an artificially roughened solar air heater has been numerically explored. The Reynolds number of the absorber plate was adjusted from 4250 to 20000, but the heat flux remained constant at 1000 W/m2. The flow turbulence was handled using the “ANSYS FLUENT software's renormalized group (RNG) k-ε with enhanced wall treatment” turbulence model. In terms of Nusselt number and friction factor, the effects of roughness parameters such as RRP, RRH, and ALSE on the performance of artificially roughened solar air heaters have been explored. To test their increased efficiency, Nusselt number and friction factor of roughened solar air heaters (SAH) has been compared at similar flow conditions with plain one.","PeriodicalId":36637,"journal":{"name":"International Journal of Thermofluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69789186","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}
Pub Date : 2022-01-01DOI: 10.36963/ijtst.2022090305
Ali Benhmidène, Rabeb Jemaii, K. Hidouri, B. Chaouachi
In the present work, we were interested in the study of the oscillatory phenomenon of ammonia-water two-phase flow inside the bubble pump of absorption-diffusion refrigerators. In fact, flow instability can reduce the efficiency of the bubble pump. The simulation of two-phase flow in the bubble pump is conducted by using the drift flow model. Balance equations of the drift flow model and their closure relationships, as well as the numerical method, were developed. The numerical resolution allowed defining the void fraction, the liquid and vapor velocities, the pressure, and the mixing enthalpy against time. The effect of heat flux received by the bubble pump is simulated in the transitional regime. Simulated results of the vapor, liquid, and mass velocities show a flow fluctuation at the beginning of the operation. The duration of the fluctuation increase from 6 s to 12 s by reducing the heat flux from 5 to 2 kW/m².The void fraction profile makes it possible to distinguish that the slug and churn regimes are those which dominate the pump’s operating regime for a heat flux of 2 and 3 kW/m². The pumping action is influenced by the heat flux. A maximum of 10 kW/m² value of heat flux is defined for an obtained minimum of the pumping action.
{"title":"Study of flow fluctuation in the thermal bubble pump tube","authors":"Ali Benhmidène, Rabeb Jemaii, K. Hidouri, B. Chaouachi","doi":"10.36963/ijtst.2022090305","DOIUrl":"https://doi.org/10.36963/ijtst.2022090305","url":null,"abstract":"In the present work, we were interested in the study of the oscillatory phenomenon of ammonia-water two-phase flow inside the bubble pump of absorption-diffusion refrigerators. In fact, flow instability can reduce the efficiency of the bubble pump. The simulation of two-phase flow in the bubble pump is conducted by using the drift flow model. Balance equations of the drift flow model and their closure relationships, as well as the numerical method, were developed. The numerical resolution allowed defining the void fraction, the liquid and vapor velocities, the pressure, and the mixing enthalpy against time. The effect of heat flux received by the bubble pump is simulated in the transitional regime. Simulated results of the vapor, liquid, and mass velocities show a flow fluctuation at the beginning of the operation. The duration of the fluctuation increase from 6 s to 12 s by reducing the heat flux from 5 to 2 kW/m².The void fraction profile makes it possible to distinguish that the slug and churn regimes are those which dominate the pump’s operating regime for a heat flux of 2 and 3 kW/m². The pumping action is influenced by the heat flux. A maximum of 10 kW/m² value of heat flux is defined for an obtained minimum of the pumping action.","PeriodicalId":36637,"journal":{"name":"International Journal of Thermofluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69789654","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}
Pub Date : 2022-01-01DOI: 10.36963/ijtst.2022090503
Reza Elyasi, S. M. Nowee, H. A. Namaghi, Mahdi Tabatabaei Ghomshe
In this investigation, nanofluids including CNT, milled CNT, and decorated Ag/CNT and Cu/CNT have been applied to enhance the thermal performance of a two-phase closed thermosyphon (TPCT). For better dispersing of carbon nanotube (CNT) in water and producing stable nanofluid, CNTs have been functionalized with hydrophilic groups such as carbocyclic acid and hydroxyl. A reducing agent and calcareous process are effective methods for decoration of CNT with NPs. Nanofluids were prepared in different weight concentrations (0.175%, 0.350%, 0.525% and 0.700%). Also, different input powers (40 W, 80 W, 120 W, 160 W, and 200 W) were applied to the evaporator section. According to the experimental results, it can be deduced that the effect of nanotubes functionalization on the thermal performance of thermosyphon decreases by increasing CNT concentration. Moreover, the transmission electron microscopy (TEM) images showed that functional group disjoins CNTs from each other and result in the formation of uniform silver and copper clusters that have been decorated on the surface of CNT. The results demonstrated that in the presence of nanoparticles (NPs), the thermal performance of thermosyphon improved through a reduction in thermal resistance by 34% (at 0.700 wt% for Ag), 36% (at 0.700 wt% for Cu), and 16% (for milled CNT). Furthermore, the decoration of CNTs improved the thermosyphon performance, especially at low input power.
{"title":"Improvement of two-phased closed thermosyphon thermal performance by deploying nanofluids of metal nanoparticles decorated on CNT","authors":"Reza Elyasi, S. M. Nowee, H. A. Namaghi, Mahdi Tabatabaei Ghomshe","doi":"10.36963/ijtst.2022090503","DOIUrl":"https://doi.org/10.36963/ijtst.2022090503","url":null,"abstract":"In this investigation, nanofluids including CNT, milled CNT, and decorated Ag/CNT and Cu/CNT have been applied to enhance the thermal performance of a two-phase closed thermosyphon (TPCT). For better dispersing of carbon nanotube (CNT) in water and producing stable nanofluid, CNTs have been functionalized with hydrophilic groups such as carbocyclic acid and hydroxyl. A reducing agent and calcareous process are effective methods for decoration of CNT with NPs. Nanofluids were prepared in different weight concentrations (0.175%, 0.350%, 0.525% and 0.700%). Also, different input powers (40 W, 80 W, 120 W, 160 W, and 200 W) were applied to the evaporator section. According to the experimental results, it can be deduced that the effect of nanotubes functionalization on the thermal performance of thermosyphon decreases by increasing CNT concentration. Moreover, the transmission electron microscopy (TEM) images showed that functional group disjoins CNTs from each other and result in the formation of uniform silver and copper clusters that have been decorated on the surface of CNT. The results demonstrated that in the presence of nanoparticles (NPs), the thermal performance of thermosyphon improved through a reduction in thermal resistance by 34% (at 0.700 wt% for Ag), 36% (at 0.700 wt% for Cu), and 16% (for milled CNT). Furthermore, the decoration of CNTs improved the thermosyphon performance, especially at low input power.","PeriodicalId":36637,"journal":{"name":"International Journal of Thermofluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69789775","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}
Pub Date : 2021-11-01DOI: 10.36963/ijtst.2022090101
F. R. Saeed, N. B. Mahmood, M. Jasim
Metal foam has found its way in many engineering industries due to its ability to improve the heat transfer rate in thermal applications. Thermal energy storage based on phase change materials (PCMs) have significant importance as a part of renewable energy sources, and thermal management applications, However, low thermal conductivity is the essential drawback associated with the PCMs, especially the organic type of it, such as paraffin. Various experimental and numerical studies performed to test the effect of using metal foam with PCMs, in order to improve PCMs thermal conductivity. Many models suggested for evaluating the effective thermal conductivity of high porosity open cells metal foam, which immersed in base fluids of low thermal conductivity such as air, water, and PCMs. This work achieved numerically by using different models for calculating the effective thermal properties of metal foam with various range of porosities impregnate in paraffin. The study discussed the temperature distribution, which control the heat transfer rate, the behavior of temperatures versus time, and improvements in the melting front phase of the paraffin, under the effect of copper metal foam of various porosities and by applying different models, for estimating the effective thermal conductivity. The results exhibit an augmentation in the effective thermal conductivity with porosity decreasing. The outputs showed paradoxical results using the presented models and the differences between them have been discussed.
{"title":"One-dimensional numerical analysis for the porosity impact of open-cell metal foam on the effective thermal properties of PCMs","authors":"F. R. Saeed, N. B. Mahmood, M. Jasim","doi":"10.36963/ijtst.2022090101","DOIUrl":"https://doi.org/10.36963/ijtst.2022090101","url":null,"abstract":"Metal foam has found its way in many engineering industries due to its ability to improve the heat transfer rate in thermal applications. Thermal energy storage based on phase change materials (PCMs) have significant importance as a part of renewable energy sources, and thermal management applications, However, low thermal conductivity is the essential drawback associated with the PCMs, especially the organic type of it, such as paraffin. Various experimental and numerical studies performed to test the effect of using metal foam with PCMs, in order to improve PCMs thermal conductivity. Many models suggested for evaluating the effective thermal conductivity of high porosity open cells metal foam, which immersed in base fluids of low thermal conductivity such as air, water, and PCMs. This work achieved numerically by using different models for calculating the effective thermal properties of metal foam with various range of porosities impregnate in paraffin. The study discussed the temperature distribution, which control the heat transfer rate, the behavior of temperatures versus time, and improvements in the melting front phase of the paraffin, under the effect of copper metal foam of various porosities and by applying different models, for estimating the effective thermal conductivity. The results exhibit an augmentation in the effective thermal conductivity with porosity decreasing. The outputs showed paradoxical results using the presented models and the differences between them have been discussed.","PeriodicalId":36637,"journal":{"name":"International Journal of Thermofluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44963117","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}
Pub Date : 2021-11-01DOI: 10.36963/ijtst.2022090103
Y. Gangadharaiah, S. Suma, H. Nagarathnamma, T. Chaya
In the present study, the commencement of double-diffusive convection with an internal heat source is studied using a linear instability analysis. The system consists of a fluid layer on top of a porous layer saturated with the same fluid. The boundaries are insulating to temperature perturbations, and the regular perturbation technique is applied to obtain the Rayleigh number. The results of detailed stability characteristics are presented for crucial physical factors, such as thermal Rayleigh number, the inverse Lewis number, depth ratio, the solute Rayleigh number, and heat source strength.
{"title":"Double-diffusive penetrative convection in a fluid overlying a porous layer","authors":"Y. Gangadharaiah, S. Suma, H. Nagarathnamma, T. Chaya","doi":"10.36963/ijtst.2022090103","DOIUrl":"https://doi.org/10.36963/ijtst.2022090103","url":null,"abstract":"In the present study, the commencement of double-diffusive convection with an internal heat source is studied using a linear instability analysis. The system consists of a fluid layer on top of a porous layer saturated with the same fluid. The boundaries are insulating to temperature perturbations, and the regular perturbation technique is applied to obtain the Rayleigh number. The results of detailed stability characteristics are presented for crucial physical factors, such as thermal Rayleigh number, the inverse Lewis number, depth ratio, the solute Rayleigh number, and heat source strength.","PeriodicalId":36637,"journal":{"name":"International Journal of Thermofluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47226510","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}
Pub Date : 2021-11-01DOI: 10.36963/ijtst.2022090102
M. T. Attouchi, S. Larbi, S. Khelladi
In this study, we were interested in free convective heat transfer into cavities with finned surface. The hot horizontal bottom wall with attached fins was under variable (sinusoidal) surface temperature while the cold one, on the upper wall side, was kept at constant temperature. The vertical walls were adiabatic. The developed model is related to laminar natural convection airflow in a finned closed cavity. The considered Rayleigh numbers are in the interval 103 to 106 while the Prandtl number is 0.7. The finite volume method is used in solving the resulting equations. The developed numerical code is validated owing to benchmark solutions of De Vahl Davis and results reported by other authors. The results presented in this work are linked to the velocity distribution around the surfaces of the fins, the isothermal lines, the streamlines and local and average Nusselt numbers for various geometrical parameters. Special consideration is given to the effects of Rayleigh number, the variable surface hot temperature, the fins number and their length on the fluid flow patterns and heat transfer in square cavities.
{"title":"Effect of some parameters on natural convection heat transfer in finned enclosures- a case study","authors":"M. T. Attouchi, S. Larbi, S. Khelladi","doi":"10.36963/ijtst.2022090102","DOIUrl":"https://doi.org/10.36963/ijtst.2022090102","url":null,"abstract":"In this study, we were interested in free convective heat transfer into cavities with finned surface. The hot horizontal bottom wall with attached fins was under variable (sinusoidal) surface temperature while the cold one, on the upper wall side, was kept at constant temperature. The vertical walls were adiabatic. The developed model is related to laminar natural convection airflow in a finned closed cavity. The considered Rayleigh numbers are in the interval 103 to 106 while the Prandtl number is 0.7. The finite volume method is used in solving the resulting equations. The developed numerical code is validated owing to benchmark solutions of De Vahl Davis and results reported by other authors. The results presented in this work are linked to the velocity distribution around the surfaces of the fins, the isothermal lines, the streamlines and local and average Nusselt numbers for various geometrical parameters. Special consideration is given to the effects of Rayleigh number, the variable surface hot temperature, the fins number and their length on the fluid flow patterns and heat transfer in square cavities.","PeriodicalId":36637,"journal":{"name":"International Journal of Thermofluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48046357","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}
Pub Date : 2021-11-01DOI: 10.36963/ijtst.2022090106
U. Srivastva, R. Malhotra, K. R. Kumar, S. Kaushik
This paper describes the experiments to determine the convective heat transfer coefficients on a synthetic heat transfer fluid flowing in a Shell-and-Tube heat exchanger. The analysis of results is carried out by application of the Wilson plot Technique, on the basis of which, the convective heat transfer coefficients were experimentally obtained for the fluid flowing inside the tube. The convective heat transfer coefficient of oil derived through Wilson plot is then compared with the convective heat transfer coefficients obtained using the classical thermal resistance equation. An empirical correlation between the convective heat transfer coefficient of oil with respect to its mean velocity of flow in the tube and the bulk oil temperature has been proposed. A correction factor of 2.3 and exploration of the exponent value of 0.2 pertaining to the velocity of oil was obtained. The values of convective heat transfer coefficients obtained after applying the correction factor are consistent with the values reported in the literature for oil-water heat transfers. The variation of the heat transfer coefficients at different temperatures is attributed to factors like vapor blanketing effect, surface temperature measurement difficulty as well as dependence of convection phenomenon on surface geometry and physical conditions of the fluids. Experimental results obtained for a temperature range of 50-200°C are extrapolated upto 400°C, the actual upper operational fluid temperatures used in concentrated solar parabolic trough power plant. The test method proposed in this paper can be useful for the development of oil as heat transfer fluids, where already established or commercialized oil is compared with the oil under development, in the same test setup and under similar test conditions.
{"title":"Experimental determination of convective heat transfer coefficients of synthetic oil using wilson plot technique","authors":"U. Srivastva, R. Malhotra, K. R. Kumar, S. Kaushik","doi":"10.36963/ijtst.2022090106","DOIUrl":"https://doi.org/10.36963/ijtst.2022090106","url":null,"abstract":"This paper describes the experiments to determine the convective heat transfer coefficients on a synthetic heat transfer fluid flowing in a Shell-and-Tube heat exchanger. The analysis of results is carried out by application of the Wilson plot Technique, on the basis of which, the convective heat transfer coefficients were experimentally obtained for the fluid flowing inside the tube. The convective heat transfer coefficient of oil derived through Wilson plot is then compared with the convective heat transfer coefficients obtained using the classical thermal resistance equation. An empirical correlation between the convective heat transfer coefficient of oil with respect to its mean velocity of flow in the tube and the bulk oil temperature has been proposed. A correction factor of 2.3 and exploration of the exponent value of 0.2 pertaining to the velocity of oil was obtained. The values of convective heat transfer coefficients obtained after applying the correction factor are consistent with the values reported in the literature for oil-water heat transfers. The variation of the heat transfer coefficients at different temperatures is attributed to factors like vapor blanketing effect, surface temperature measurement difficulty as well as dependence of convection phenomenon on surface geometry and physical conditions of the fluids. Experimental results obtained for a temperature range of 50-200°C are extrapolated upto 400°C, the actual upper operational fluid temperatures used in concentrated solar parabolic trough power plant. The test method proposed in this paper can be useful for the development of oil as heat transfer fluids, where already established or commercialized oil is compared with the oil under development, in the same test setup and under similar test conditions.","PeriodicalId":36637,"journal":{"name":"International Journal of Thermofluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44986170","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}
Pub Date : 2021-11-01DOI: 10.36963/ijtst.2022090104
R. Akhter, M. M. Ali
This article explores the influence of natural convection heat transfer in a square enclosure with hexagonal block filled by Al2O3-H2O nanofluid in presence of external magnetic field. The two vertical walls of the enclosure are kept at constant cold temperature, Tc, and the top horizontal wall is insulated whereas the remaining walls of the enclosure are maintained high temperature, Th. The governing equations are formulated using Boussinesq approximations and solved numerically employing built-in-finite element method and then presented graphically in terms of streamlines, isotherms, average Nusselt number and average temperature. It is found that the different values of physical parameters: Rayleigh number (Ra = 103 -106), nanoparticle volume fraction (ϕ = 1% -5%) and Hartman number (Ha = 0-100) affects the streamlines, isotherm contours and heat transfer rate. Comparison of the present results with previously published results on the basis of special cases has been performed and found to be a good agreement.
{"title":"MHD natural convection in nanofluid filled square cavity with isothermally heated hexagonal block","authors":"R. Akhter, M. M. Ali","doi":"10.36963/ijtst.2022090104","DOIUrl":"https://doi.org/10.36963/ijtst.2022090104","url":null,"abstract":"This article explores the influence of natural convection heat transfer in a square enclosure with hexagonal block filled by Al2O3-H2O nanofluid in presence of external magnetic field. The two vertical walls of the enclosure are kept at constant cold temperature, Tc, and the top horizontal wall is insulated whereas the remaining walls of the enclosure are maintained high temperature, Th. The governing equations are formulated using Boussinesq approximations and solved numerically employing built-in-finite element method and then presented graphically in terms of streamlines, isotherms, average Nusselt number and average temperature. It is found that the different values of physical parameters: Rayleigh number (Ra = 103 -106), nanoparticle volume fraction (ϕ = 1% -5%) and Hartman number (Ha = 0-100) affects the streamlines, isotherm contours and heat transfer rate. Comparison of the present results with previously published results on the basis of special cases has been performed and found to be a good agreement.","PeriodicalId":36637,"journal":{"name":"International Journal of Thermofluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47162653","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}
Pub Date : 2021-11-01DOI: 10.36963/ijtst.2022090105
M. Thianwiboon
Flight in the vicinity of the ground is known to be more efficient than flight in a free air stream. However, a nose-down pitching moment created by a typical cambered airfoil generally increases due to ground effect. Thus, a larger tail for the aircraft is required to remain stable, which creates more drag and reduces the efficiency. The pitching moment in the ground effect becomes more complicated because it varies with height above the ground. Thus, the reflexed or S-shaped airfoil was introduced to overcome this effect. The addition of reflex reduces the lift of the airfoil, but it is required for improved stability. This study applied computational fluid dynamics to investigate the aerodynamic characteristics of a reflexed airfoil, N60R, in ground effect over a range of angles of attack from 0° to 20° at a Reynolds number from 0.8106 to 5106 and ground clearance from 5% to 150% of the chord. The numerical results reveal that the boundary layer close to the ground affects the lift, drag, pitching moment coefficients, and center of pressure. As the airfoil operates close to the ground, the lift increased due to a higher pressure build up under the airfoil. Except for a relatively low angle of attack (less than 2°), the lift decreases with a reduction in ground clearance due to loss of upper surface suction. The maximum lift-to-drag ratio, approximately 120, occurred at an angle of attack of 6° and ground clearance of 5%. In summary, this study presents the aerodynamic characteristics of the reflexed airfoil, N60R, over a wide range of angles of attack, Reynolds numbers and ground clearance. Furthermore, regression models for each characteristic were developed and can be used to predict the coefficients of the N60R without the need for consuming time in Computational Fluid Dynamics (CFD) analysis.
{"title":"Numerical aerodynamic analysis of a reflexed airfoil, N60R, in ground effect with regression models","authors":"M. Thianwiboon","doi":"10.36963/ijtst.2022090105","DOIUrl":"https://doi.org/10.36963/ijtst.2022090105","url":null,"abstract":"Flight in the vicinity of the ground is known to be more efficient than flight in a free air stream. However, a nose-down pitching moment created by a typical cambered airfoil generally increases due to ground effect. Thus, a larger tail for the aircraft is required to remain stable, which creates more drag and reduces the efficiency. The pitching moment in the ground effect becomes more complicated because it varies with height above the ground. Thus, the reflexed or S-shaped airfoil was introduced to overcome this effect. The addition of reflex reduces the lift of the airfoil, but it is required for improved stability. This study applied computational fluid dynamics to investigate the aerodynamic characteristics of a reflexed airfoil, N60R, in ground effect over a range of angles of attack from 0° to 20° at a Reynolds number from 0.8106 to 5106 and ground clearance from 5% to 150% of the chord. The numerical results reveal that the boundary layer close to the ground affects the lift, drag, pitching moment coefficients, and center of pressure. As the airfoil operates close to the ground, the lift increased due to a higher pressure build up under the airfoil. Except for a relatively low angle of attack (less than 2°), the lift decreases with a reduction in ground clearance due to loss of upper surface suction. The maximum lift-to-drag ratio, approximately 120, occurred at an angle of attack of 6° and ground clearance of 5%. In summary, this study presents the aerodynamic characteristics of the reflexed airfoil, N60R, over a wide range of angles of attack, Reynolds numbers and ground clearance. Furthermore, regression models for each characteristic were developed and can be used to predict the coefficients of the N60R without the need for consuming time in Computational Fluid Dynamics (CFD) analysis.","PeriodicalId":36637,"journal":{"name":"International Journal of Thermofluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44746881","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}
Pub Date : 2020-10-08DOI: 10.36963/ijtst.2020070404
S. Molli, K. Naikoti
In this paper, unsteady electrically conducting, incompressible, heat and mass transfer Magnetohydrodynamic free convective fluid flow with Cu-nanoparticles over a vertical plate embedded in a porous medium and variable boundary conditions are considered. The governing PDE's have been converted to non-dimensional equations then solved by FET for velocity, temperature and concentration profiles with the influence of buoyancy force due to heat and mass transfer, Prandtl and Schmidt number , time, magnetic and chemical reaction parameter in case of pure fluid and Cu-water nanofluid. The Cu-water nanofluid velocity is low than pure fluid, these are presented through graphical form . Also presented the local Skin-friction coefficient, rate of heat and mass transfer and code of validation through tabular forms.
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