Pub Date : 2022-01-01DOI: 10.36963/ijtst.2022090201
M. Rahman, M. M. Ali, M. R. Kazi, M. Hakim
A numerical study is carried out to explore the influence of external magnetic field on mixed convective heat transfer in a partitioned rectangular cavity with on side moving wall. The vertical walls are isothermally heated while the horizontal walls are thermally insulated. The left vertical wall is moving in + y direction and remaining walls are maintained no-slip condition. A magnetic field of uniform strength is imposed transverse to the temperature gradient. The governing equations are solved utilizing the finite element method for several physical parameters including Richardson number, Hartmann number and Prandtl number. The numerical results are presented graphically using streamlines, isotherms, local and average Nusselt numbers. It is observed that the flow filed is affected significantly for moving wall and the variation in Hartmann and Richardson numbers. The velocity field is found more effective in natural convection regime than forced convection. The results demonstrated that maximum amount of heat transfer is obtained in natural convection domination and higher values of Prandtl number. The enhancement of heat transfer rate is found 14.25% more at higher Prandtl number (Pr =2.56) than lower (Pr =0.71) and it reduction is found 3.03% more at Ha = 50 compared to Ha = 0.
{"title":"MHD mixed convection in a partitioned rectangular enclosure","authors":"M. Rahman, M. M. Ali, M. R. Kazi, M. Hakim","doi":"10.36963/ijtst.2022090201","DOIUrl":"https://doi.org/10.36963/ijtst.2022090201","url":null,"abstract":"A numerical study is carried out to explore the influence of external magnetic field on mixed convective heat transfer in a partitioned rectangular cavity with on side moving wall. The vertical walls are isothermally heated while the horizontal walls are thermally insulated. The left vertical wall is moving in + y direction and remaining walls are maintained no-slip condition. A magnetic field of uniform strength is imposed transverse to the temperature gradient. The governing equations are solved utilizing the finite element method for several physical parameters including Richardson number, Hartmann number and Prandtl number. The numerical results are presented graphically using streamlines, isotherms, local and average Nusselt numbers. It is observed that the flow filed is affected significantly for moving wall and the variation in Hartmann and Richardson numbers. The velocity field is found more effective in natural convection regime than forced convection. The results demonstrated that maximum amount of heat transfer is obtained in natural convection domination and higher values of Prandtl number. The enhancement of heat transfer rate is found 14.25% more at higher Prandtl number (Pr =2.56) than lower (Pr =0.71) and it reduction is found 3.03% more at Ha = 50 compared to Ha = 0.","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":"47198193","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.2022090403
Suwimon Saneewong Na Ayuttaya
An influence of the electrostatic precipitator process was numerically investigated for heat transfer enhancement on saturated porous samples in a k-ε turbulent model. The condition of the water entering a test section was the inlet temperature was 30 oC (303 K), and inlet velocity was tested in the range of 1 – 2.5 m/s. The electrical voltage and time varied between 0 – 30 kV and 0 – 1 s, respectively. The initial temperature of saturated porous samples was 10 oC (283 K), and both first and second samples were set in semicircle shapes. The numerical results within the water channel showed that the electric field and electric potential zone appeared and were concentrated when using the electrostatic precipitator process. The high electric voltage could increase disturbance and turbulence within the water channel. The maximum flow field zone appeared above the saturated porous sample area, and the maximum velocity field increased with the inlet velocity and electrical voltage. The maximum pressure was increased to the high voltages, but the pressure was marginally increased with high inlet velocity. The vorticity contour for an electrostatic precipitator process was more concentrated than without the electrostatic precipitator process. Therefore, the temperature contour line in case of high inlet velocity, electrical voltage, and time can be more disturbing than the other cases. In addition, heat from the water was transferred within the sample, so the temperature within the porous sample gradually increased. The fluid velocity within the front porous sample was more within the saturated porous samples than within the porous back sample. Therefore, the flow could move through and within the samples and induce temperature within both saturated porous samples. Finally, the heat transfer within samples was enhanced by fluid flow in the water channel, so the local heat transfer coefficient within samples was induced by the fluid velocity in the water channel.
{"title":"Heat transfer enhancement on saturated porous samples using electrostatic precipitator process in k-ε turbulent model","authors":"Suwimon Saneewong Na Ayuttaya","doi":"10.36963/ijtst.2022090403","DOIUrl":"https://doi.org/10.36963/ijtst.2022090403","url":null,"abstract":"An influence of the electrostatic precipitator process was numerically investigated for heat transfer enhancement on saturated porous samples in a k-ε turbulent model. The condition of the water entering a test section was the inlet temperature was 30 oC (303 K), and inlet velocity was tested in the range of 1 – 2.5 m/s. The electrical voltage and time varied between 0 – 30 kV and 0 – 1 s, respectively. The initial temperature of saturated porous samples was 10 oC (283 K), and both first and second samples were set in semicircle shapes. The numerical results within the water channel showed that the electric field and electric potential zone appeared and were concentrated when using the electrostatic precipitator process. The high electric voltage could increase disturbance and turbulence within the water channel. The maximum flow field zone appeared above the saturated porous sample area, and the maximum velocity field increased with the inlet velocity and electrical voltage. The maximum pressure was increased to the high voltages, but the pressure was marginally increased with high inlet velocity. The vorticity contour for an electrostatic precipitator process was more concentrated than without the electrostatic precipitator process. Therefore, the temperature contour line in case of high inlet velocity, electrical voltage, and time can be more disturbing than the other cases. In addition, heat from the water was transferred within the sample, so the temperature within the porous sample gradually increased. The fluid velocity within the front porous sample was more within the saturated porous samples than within the porous back sample. Therefore, the flow could move through and within the samples and induce temperature within both saturated porous samples. Finally, the heat transfer within samples was enhanced by fluid flow in the water channel, so the local heat transfer coefficient within samples was induced by the fluid velocity in the water channel.","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":"69789670","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.2022090504
Y. Gangadharaiah
The onset of thermocapillary convective motion in a self-rewetting fluid layer overlying a porous medium with thermally dependent surface tension is studied analytically. Surface tension is assumed to be a quadratic function of temperature. The top surface of a fluid layer is deformably free and the bottom is rigid. We considered boundaries to be insulating to temperature perturbations. The governing equation that satisfies the composite system is analyzed by the normal mode approach and solved by the regular perturbation technique for linear stability. A mathematical expression is derived for the critical Marangoni number by solving coupled equations. The influence of crispation number, thermal diffusivity ratio, and other physical parameters involved therein are analyzed for the convective stability of the bilayer system. It has been found that the start of convection is delayed when the crispation number goes down and the thermal diffusivity ratio goes up. Also, the impact of the ratio of the thickness of the fluid to the thickness of the porous matrix and the other physical parameters on controlling the convective motion of the configuration is examined in detail.
{"title":"Onset of surface driven convection in selfrewetting fluid layer overlying a porous medium","authors":"Y. Gangadharaiah","doi":"10.36963/ijtst.2022090504","DOIUrl":"https://doi.org/10.36963/ijtst.2022090504","url":null,"abstract":"The onset of thermocapillary convective motion in a self-rewetting fluid layer overlying a porous medium with thermally dependent surface tension is studied analytically. Surface tension is assumed to be a quadratic function of temperature. The top surface of a fluid layer is deformably free and the bottom is rigid. We considered boundaries to be insulating to temperature perturbations. The governing equation that satisfies the composite system is analyzed by the normal mode approach and solved by the regular perturbation technique for linear stability. A mathematical expression is derived for the critical Marangoni number by solving coupled equations. The influence of crispation number, thermal diffusivity ratio, and other physical parameters involved therein are analyzed for the convective stability of the bilayer system. It has been found that the start of convection is delayed when the crispation number goes down and the thermal diffusivity ratio goes up. Also, the impact of the ratio of the thickness of the fluid to the thickness of the porous matrix and the other physical parameters on controlling the convective motion of the configuration is examined in detail.","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":"69789787","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.2022090502
Z. Babaie, Foad Moslem, M. Masdari, M. Tahani
In recent years, energy harvesting from vortex-induced vibration (VIV) of a cylinder as a renewable source of energy has been increased. The main goal is to enhance the harnessed hydrokinetic energy of the VIV converters. In this work, the effect of adding a rotational degree of freedom by giving eccentricity to the circular cylinder is investigated on vibration and rotational response as well as hydrokinetic energy conversion. Simulations are done at the Reynolds number ranging from 2×10^3 to 13×10^3. Twodimensional unsteady Reynolds-averaged Navier–Stokes equations (URANS), supplemented with SST turbulence models, are solved on moving mesh, and arbitrary Lagrangian-Eulerian formulation is employed to accommodate the deforming boundaries. For the freely rotating and vibrating cylinder, results demonstrate that increasing the inlet velocity increases the vibration amplitude, and the cylinder experiences complete rotation in some of the flow times. Moreover, adding a rotational degree of freedom causes hydrodynamic instability, in which the location of separation points changes and makes a wide wake pattern with unstable vortexes behind the cylinder. As a result, the harnessed power and energy conversion efficiency of the system is increased. The freely vibrating-rotating system generates a maximum power of 0.024 (W), and the energy conversion efficiency increases and fluctuates around 11.2%.
{"title":"Numerical investigation on VIV energy harvesting enhancement with adding eccentricity to a circular cylinder","authors":"Z. Babaie, Foad Moslem, M. Masdari, M. Tahani","doi":"10.36963/ijtst.2022090502","DOIUrl":"https://doi.org/10.36963/ijtst.2022090502","url":null,"abstract":"In recent years, energy harvesting from vortex-induced vibration (VIV) of a cylinder as a renewable source of energy has been increased. The main goal is to enhance the harnessed hydrokinetic energy of the VIV converters. In this work, the effect of adding a rotational degree of freedom by giving eccentricity to the circular cylinder is investigated on vibration and rotational response as well as hydrokinetic energy conversion. Simulations are done at the Reynolds number ranging from 2×10^3 to 13×10^3. Twodimensional unsteady Reynolds-averaged Navier–Stokes equations (URANS), supplemented with SST turbulence models, are solved on moving mesh, and arbitrary Lagrangian-Eulerian formulation is employed to accommodate the deforming boundaries. For the freely rotating and vibrating cylinder, results demonstrate that increasing the inlet velocity increases the vibration amplitude, and the cylinder experiences complete rotation in some of the flow times. Moreover, adding a rotational degree of freedom causes hydrodynamic instability, in which the location of separation points changes and makes a wide wake pattern with unstable vortexes behind the cylinder. As a result, the harnessed power and energy conversion efficiency of the system is increased. The freely vibrating-rotating system generates a maximum power of 0.024 (W), and the energy conversion efficiency increases and fluctuates around 11.2%.","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":"69789487","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.2022090405
Ali Benhmidène, Lena J-T Strömberg
The main factor for the proper functioning of the thermal generator-bubble pump of the diffusion-absorption cycles is the amount of heat required to maintain the necessary vaporization for pumping fluids. An excess of heat or the opposite reduces its efficiency. The present study aims to simulate the critical heat flux (CHF) and the onset nucleate boiling heat flux (ONBHF) versus mass flow in the generator-bubble pump of absorption-diffusion machines. The bubble pump studied is a vertical heated tube of diameter range is between 4 and 12mm, in which flowing an ammonia-water mixing. To achieve our goal a new approach based on the curves of the variation of the pressure drop as a function of the mass flow rate has been adopted. The pressure drops have been simulated using the two-fluid model. The critical heat fluxes simulated as a function of mass flow rate are compared with those obtained from four correlations. A good agreement has been obtained with the correlation of Shah and Zhang et al. Simulation results allow defining the optimum range of mass flow that should be used in the same application. We found that the mass flow rate should be higher than 40kg/m².s for the diameters of the studied tubes.
{"title":"A new approach to simulate the critical and the onset nucleate boiling heat fluxes for a thermal generator-bubble pump","authors":"Ali Benhmidène, Lena J-T Strömberg","doi":"10.36963/ijtst.2022090405","DOIUrl":"https://doi.org/10.36963/ijtst.2022090405","url":null,"abstract":"The main factor for the proper functioning of the thermal generator-bubble pump of the diffusion-absorption cycles is the amount of heat required to maintain the necessary vaporization for pumping fluids. An excess of heat or the opposite reduces its efficiency. The present study aims to simulate the critical heat flux (CHF) and the onset nucleate boiling heat flux (ONBHF) versus mass flow in the generator-bubble pump of absorption-diffusion machines. The bubble pump studied is a vertical heated tube of diameter range is between 4 and 12mm, in which flowing an ammonia-water mixing. To achieve our goal a new approach based on the curves of the variation of the pressure drop as a function of the mass flow rate has been adopted. The pressure drops have been simulated using the two-fluid model. The critical heat fluxes simulated as a function of mass flow rate are compared with those obtained from four correlations. A good agreement has been obtained with the correlation of Shah and Zhang et al. Simulation results allow defining the optimum range of mass flow that should be used in the same application. We found that the mass flow rate should be higher than 40kg/m².s for the diameters of the studied tubes.","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":"69789412","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.2022090402
Gabriel Kaldjob Pom, J. Hona, Valjacques Nyemb Nsoga, Médard Marcus Nganbe II
In this study, a fluid is expelled by the suction process from the intermediate space between to porous plates in transverse movement in order to model the functioning of a compartment of a rocket motor. This transverse motion of the plates can reduce or increase the flow domain in order to enhance the performance of the motor. From a theoretical point of view which is the present contribution, the problem is described by the velocity and the pressure gradient known as the flow field components which are determined under different values of the Reynolds number and the expansion or contraction ratio representing the control parameters of the problem. It is found that, the decrease of the magnitude of the axial pressure gradient by expanding the space occupied by the fluid causes flow reversal in the case of low suction Reynolds numbers. The reduction of the flow domain increases the magnitude of the axial pressure gradient and destroys the backward flow for all the suction Reynolds numbers. This reduction or contraction of the flow field causes a linear profile of the radial velocity and a linear behavior of the axial pressure gradient.
{"title":"On the behavior of the flow field components from the momentum equation for a functioning model of rocket motors","authors":"Gabriel Kaldjob Pom, J. Hona, Valjacques Nyemb Nsoga, Médard Marcus Nganbe II","doi":"10.36963/ijtst.2022090402","DOIUrl":"https://doi.org/10.36963/ijtst.2022090402","url":null,"abstract":"In this study, a fluid is expelled by the suction process from the intermediate space between to porous plates in transverse movement in order to model the functioning of a compartment of a rocket motor. This transverse motion of the plates can reduce or increase the flow domain in order to enhance the performance of the motor. From a theoretical point of view which is the present contribution, the problem is described by the velocity and the pressure gradient known as the flow field components which are determined under different values of the Reynolds number and the expansion or contraction ratio representing the control parameters of the problem. It is found that, the decrease of the magnitude of the axial pressure gradient by expanding the space occupied by the fluid causes flow reversal in the case of low suction Reynolds numbers. The reduction of the flow domain increases the magnitude of the axial pressure gradient and destroys the backward flow for all the suction Reynolds numbers. This reduction or contraction of the flow field causes a linear profile of the radial velocity and a linear behavior of the axial pressure gradient.","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":"69789582","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.2022090501
S. Steven, Linda Windari, Novebriantika Novebriantika, Pasymi Pasymi, E. Restiawaty, Y. Bindar
Rice husk combustion in the suspension furnace is not an easy matter. Until now, there are still many obstacles faced in its process as characterized by low combustion conversion. The main cause is the poor air-particle contact as well as the probability of particle elutriation out of the furnace chamber before combustion completely occurs. Thus, in-depth and detailed understanding of air and rice husk cold flow structures in the furnace chamber, as proposed in this study, becomes necessary. The simulation study was conducted using Reynold stress model (RSM) for fluid flow quantification whereas discrete phase model was utilized for particle flow quantification. The simulation results reveal that cylindrical chamber gives a more significant particle residence time rather than rectangular chamber for every similar excess air amount. Besides, providing burner with a tangential air inlet of 90o results in high turbulence, intense swirl phenomenon, and long particle residence time. Moreover, the furnace chamber equipped with a smaller burner diameter and longer burner length together will augment the air-particle contact in the furnace chamber. Despite providing the best condition for the furnace, the design must not forget to consider the economical aspect.
{"title":"Investigation of air and rice husk cold flow structures in the suspension furnace chamber through a simulation study","authors":"S. Steven, Linda Windari, Novebriantika Novebriantika, Pasymi Pasymi, E. Restiawaty, Y. Bindar","doi":"10.36963/ijtst.2022090501","DOIUrl":"https://doi.org/10.36963/ijtst.2022090501","url":null,"abstract":"Rice husk combustion in the suspension furnace is not an easy matter. Until now, there are still many obstacles faced in its process as characterized by low combustion conversion. The main cause is the poor air-particle contact as well as the probability of particle elutriation out of the furnace chamber before combustion completely occurs. Thus, in-depth and detailed understanding of air and rice husk cold flow structures in the furnace chamber, as proposed in this study, becomes necessary. The simulation study was conducted using Reynold stress model (RSM) for fluid flow quantification whereas discrete phase model was utilized for particle flow quantification. The simulation results reveal that cylindrical chamber gives a more significant particle residence time rather than rectangular chamber for every similar excess air amount. Besides, providing burner with a tangential air inlet of 90o results in high turbulence, intense swirl phenomenon, and long particle residence time. Moreover, the furnace chamber equipped with a smaller burner diameter and longer burner length together will augment the air-particle contact in the furnace chamber. Despite providing the best condition for the furnace, the design must not forget to consider the economical aspect.","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":"69789475","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.2022090204
A. M. M. Bezerra, G. Tapia, M. A. V. Cavalcanti, G. Marinho
Heat transfer is a vitally important mechanism in thermal control of living beings. It is no different for rats and mice, which are widely used for academic, pharmaceutical and medicinal research. The objective of the present study was to estimate the convective heat transfer in rats and mice confined in a vivarium at the UFRN’s Institute of Tropical Medicine. Twenty rats and twelve mice were used for the experiment, where the following measurements were made: surface skin temperature, body length, and weight. The study was able to determine mathematically an approximation of the natural and forced convection heat transfer rates produced by rats and mice, comparing them under the condition of 22°C in a controlled vivarium environment.
{"title":"Convection heat transfer analysis in rats and mice","authors":"A. M. M. Bezerra, G. Tapia, M. A. V. Cavalcanti, G. Marinho","doi":"10.36963/ijtst.2022090204","DOIUrl":"https://doi.org/10.36963/ijtst.2022090204","url":null,"abstract":"Heat transfer is a vitally important mechanism in thermal control of living beings. It is no different for rats and mice, which are widely used for academic, pharmaceutical and medicinal research. The objective of the present study was to estimate the convective heat transfer in rats and mice confined in a vivarium at the UFRN’s Institute of Tropical Medicine. Twenty rats and twelve mice were used for the experiment, where the following measurements were made: surface skin temperature, body length, and weight. The study was able to determine mathematically an approximation of the natural and forced convection heat transfer rates produced by rats and mice, comparing them under the condition of 22°C in a controlled vivarium environment.","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":"43510621","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.2022090404
Esam I Jassim
The aim of the present study is to develop a new technique for assessing the sustainability of concentric heat exchanger through quantifying the deterioration caused by energy destruction and entropy generation. The study also addresses the interconnection between heat capacity rate, flow rate, exchange flow configuration, and the sources of energy destruction. The degradation of the exchanger performance is portrayed by the newly-developed coefficients. The outcome of the study shows that heat capacity rates of cold and hot fluids have remarkable impact on the effectiveness of the heat exchanger, particularly when the ratio of such capacity rate is close to unity. Quantitively speaking, by doubling the cold fluid flow rate, the effectiveness declines by ~13% since the minimum capacity ratio is also doubled. However, as the flowrate of the cold fluid further increases, the effectiveness ameliorates by ~ 6.5 % for parallel flow and 37.5% for counter flow, succeeding the reduction in the minimum capacity ratio by ~25% and 34 %, respectively. Experimental observation confirmed that deterioration due to irreversibility production generates eminent penalties in the exchanger performance, decreasing the exergy efficiency up to 52%.
{"title":"Evaluating the deterioration of a concentric heat exchanger using energy and exergy degradation factors","authors":"Esam I Jassim","doi":"10.36963/ijtst.2022090404","DOIUrl":"https://doi.org/10.36963/ijtst.2022090404","url":null,"abstract":"The aim of the present study is to develop a new technique for assessing the sustainability of concentric heat exchanger through quantifying the deterioration caused by energy destruction and entropy generation. The study also addresses the interconnection between heat capacity rate, flow rate, exchange flow configuration, and the sources of energy destruction. The degradation of the exchanger performance is portrayed by the newly-developed coefficients. The outcome of the study shows that heat capacity rates of cold and hot fluids have remarkable impact on the effectiveness of the heat exchanger, particularly when the ratio of such capacity rate is close to unity. Quantitively speaking, by doubling the cold fluid flow rate, the effectiveness declines by ~13% since the minimum capacity ratio is also doubled. However, as the flowrate of the cold fluid further increases, the effectiveness ameliorates by ~ 6.5 % for parallel flow and 37.5% for counter flow, succeeding the reduction in the minimum capacity ratio by ~25% and 34 %, respectively. Experimental observation confirmed that deterioration due to irreversibility production generates eminent penalties in the exchanger performance, decreasing the exergy efficiency up to 52%.","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":"69789278","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.2022090202
H. Benhacine, B. Mahfoud, M. Salmi
Numerical simulations were performed to investigate the bifurcation in swirling flow between two coaxial vertical cylinders produced by the thermal gradient. The suppressed effects of an axial magnetic field on both vortex breakdown and fluid layers are analyzed. The governing Navier-Stokes, temperature, and potential equations are solved by using the finite-volume method. A conducting fluid is placed in the gap between two coaxial cylinders characterized by a small Prandtl number (Pr = 0.032). Three annular gaps were R = 0.7, 0.8, and 0.9 compared in terms of flow stability, and heat transfer rates. The combination of aspect ratio =1.5 and Reynolds number, Re=1500 is the detailed case in this study. In the hydrodynamic case, vortex breakdown takes place near the inner cylinder due to the increased pumping action of the Ekman boundary layer. In addition, the competition between buoyancy and viscous forces develops a fluid layered structure. It is shown that the onset of the oscillatory instability set in by increasing Reynolds number to the critical value. The results show that with an intensified magnetic field, the vortex breakdown disappears, the number of fluid layers will be reduced and the onset of the oscillatory instability will be retarded. Stability diagrams corresponding to the limits of transition from the multiple fluid layers to the one fluid layer are obtained.
{"title":"Stability of conducting fluid flow between coaxial cylinders under thermal gradient and axial magnetic field","authors":"H. Benhacine, B. Mahfoud, M. Salmi","doi":"10.36963/ijtst.2022090202","DOIUrl":"https://doi.org/10.36963/ijtst.2022090202","url":null,"abstract":"Numerical simulations were performed to investigate the bifurcation in swirling flow between two coaxial vertical cylinders produced by the thermal gradient. The suppressed effects of an axial magnetic field on both vortex breakdown and fluid layers are analyzed. The governing Navier-Stokes, temperature, and potential equations are solved by using the finite-volume method. A conducting fluid is placed in the gap between two coaxial cylinders characterized by a small Prandtl number (Pr = 0.032). Three annular gaps were R = 0.7, 0.8, and 0.9 compared in terms of flow stability, and heat transfer rates. The combination of aspect ratio =1.5 and Reynolds number, Re=1500 is the detailed case in this study. In the hydrodynamic case, vortex breakdown takes place near the inner cylinder due to the increased pumping action of the Ekman boundary layer. In addition, the competition between buoyancy and viscous forces develops a fluid layered structure. It is shown that the onset of the oscillatory instability set in by increasing Reynolds number to the critical value. The results show that with an intensified magnetic field, the vortex breakdown disappears, the number of fluid layers will be reduced and the onset of the oscillatory instability will be retarded. Stability diagrams corresponding to the limits of transition from the multiple fluid layers to the one fluid layer are obtained.","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":"46003778","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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