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Journal of Engineering Thermophysics
Journal Prestige (SJR): 0.435 Citation Impact (citeScore): 1 Number of Followers: 4 Hybrid journal (It can contain Open Access articles) ISSN (Print) 1990-5432 - ISSN (Online) 1810-2328 Published by Springer-Verlag [2626 journals] |
- Numerical Simulation of Wave Formation and Heat Transfer in Falling Liquid
Films at Unsteady Heat Release- Abstract: The presented mathematical model enables calculation of the wave surface profile, as well as the fields of velocity and temperature, in falling wavy liquid films. Numerical simulation of wave formation and heat transfer intensity was performed for falling films of liquid nitrogen. Different activation functions for input perturbations were checked for films with different parameters. The dependencies of the time till boiling onset and total local evaporation time on the heat flux density were calculated for different inlet Reynolds numbers. Generalization of the simulation results resulted in a regime map, which describes different mechanisms of film flow decay. The presented results of numerical simulation are in satisfactory agreement with the experimental data.
PubDate: 2020-02-01
- Abstract: The presented mathematical model enables calculation of the wave surface profile, as well as the fields of velocity and temperature, in falling wavy liquid films. Numerical simulation of wave formation and heat transfer intensity was performed for falling films of liquid nitrogen. Different activation functions for input perturbations were checked for films with different parameters. The dependencies of the time till boiling onset and total local evaporation time on the heat flux density were calculated for different inlet Reynolds numbers. Generalization of the simulation results resulted in a regime map, which describes different mechanisms of film flow decay. The presented results of numerical simulation are in satisfactory agreement with the experimental data.
- Mechanism of Disappearance of Vortex Breakdown in a Confined Flow
- Abstract: This experimental and numerical work explains why a vortex breakdown bubble first emerges and then disappears as the fluid rotation speeds up. To this end, we explore a flow in a sealed cylindrical container with one end disk rotating and all other walls stationary. The rotation drives the meridional circulation: the fluid filling the container moves away from the rotating disk along the sidewall, converges to the axis near the stationary disk, and goes back to the rotating disk near the axis. As the rotation speed Re increases, a cell of counter circulation—a vortex breakdown bubble (VBB)—emerges, expands, contracts, and disappears. On the (h, Re) map, the boundary of the VBB region consists of two branches, which meet and terminate at a fold point as h decreases (\(\mathrm{h} =H/R\), where \(H\) is the height and \(R\) is the radius of the cylinder). This study is the first to focus on the VB disappearance and explains the geometry of VBB region: why the VBB first emerges and then disappears as Re increases at a fixed h. In a few words, the mechanism is as follows. The convergence of the swirling flow to the axis reduces the pressure above the center of the stationary disk. Suction because of the reduced pressure creates a VBB and attracts it closer to the disk. This VBB shift deteriorates the flow convergence to the axis and concentrates the meridional circulation near the sidewall. The pressure grows above the still disk, the suction weakens, which kills the VBB, and the fluid stagnates near the axis. This mechanism is even more pronounced in a two-fluid flow.
PubDate: 2020-02-01
- Abstract: This experimental and numerical work explains why a vortex breakdown bubble first emerges and then disappears as the fluid rotation speeds up. To this end, we explore a flow in a sealed cylindrical container with one end disk rotating and all other walls stationary. The rotation drives the meridional circulation: the fluid filling the container moves away from the rotating disk along the sidewall, converges to the axis near the stationary disk, and goes back to the rotating disk near the axis. As the rotation speed Re increases, a cell of counter circulation—a vortex breakdown bubble (VBB)—emerges, expands, contracts, and disappears. On the (h, Re) map, the boundary of the VBB region consists of two branches, which meet and terminate at a fold point as h decreases (\(\mathrm{h} =H/R\), where \(H\) is the height and \(R\) is the radius of the cylinder). This study is the first to focus on the VB disappearance and explains the geometry of VBB region: why the VBB first emerges and then disappears as Re increases at a fixed h. In a few words, the mechanism is as follows. The convergence of the swirling flow to the axis reduces the pressure above the center of the stationary disk. Suction because of the reduced pressure creates a VBB and attracts it closer to the disk. This VBB shift deteriorates the flow convergence to the axis and concentrates the meridional circulation near the sidewall. The pressure grows above the still disk, the suction weakens, which kills the VBB, and the fluid stagnates near the axis. This mechanism is even more pronounced in a two-fluid flow.
- Crisis of Nucleate Boiling in a Finite-Height Horizontal Layer of Liquid
- Abstract: This paper presents the results of measurement and calculation within an upgraded Zuber model of critical heat flux (CHF) during nucleate boiling in thin horizontal layers of liquid. The layer height was increased in regimes of developed nucleate boiling. The two-phase layer was foam with vapor columns ascending at the corners of a rectangular square lattice. In the calculations, the foam was considered as an isotropic homogeneous system. The model assumes that the diameter of the vapor columns and the critical Helmholtz instability wavelength are independent of the foam density and are determined by the length of the most dangerous Rayleigh--Taylor instability wavelength. The proposed model fits the CHF experimental data for boiling liquid and can explain the CHF decrease in solutions with addition of surfactants that increase foaming.
PubDate: 2020-02-01
- Abstract: This paper presents the results of measurement and calculation within an upgraded Zuber model of critical heat flux (CHF) during nucleate boiling in thin horizontal layers of liquid. The layer height was increased in regimes of developed nucleate boiling. The two-phase layer was foam with vapor columns ascending at the corners of a rectangular square lattice. In the calculations, the foam was considered as an isotropic homogeneous system. The model assumes that the diameter of the vapor columns and the critical Helmholtz instability wavelength are independent of the foam density and are determined by the length of the most dangerous Rayleigh--Taylor instability wavelength. The proposed model fits the CHF experimental data for boiling liquid and can explain the CHF decrease in solutions with addition of surfactants that increase foaming.
- Title High-Power Heat Release in Supercritical Water: Insight into the
Heat Transfer Deterioration Problem- Abstract: The investigation is focused on the phenomenon of heat transfer deterioration (HTD), inhibiting the use of supercritical fluids in the processes in which high-power local heat release is possible. The ordinary discussion is based solely on the data of quasi-stationary measurements. In order to clarify the intrinsic nature of HTD as an essentially non-stationary phenomenon, it is worthwhile to take into account the peculiarities of heat transfer confined in time and space. In the present paper, we briefly discuss the characteristic features of such heat transfer in supercritical water. The characteristic heating time was \(10^{-3}\div 10^{-2}\) s and the heat flux density through the wall increased up to 15 MW/m\(^{2}\). The results provide the heat transfer pattern under conditions of predominance of the heat conduction mode. Exactly this mode most closely corresponds to the regime of high-power local heat release in a viscous sublayer. We also propose that the effect of threshold decrease in the heat transfer intensity (typical of pulse processes in supercritical transitions) may be a fundamental factor for occurrence of the HTD mode.
PubDate: 2020-02-01
- Abstract: The investigation is focused on the phenomenon of heat transfer deterioration (HTD), inhibiting the use of supercritical fluids in the processes in which high-power local heat release is possible. The ordinary discussion is based solely on the data of quasi-stationary measurements. In order to clarify the intrinsic nature of HTD as an essentially non-stationary phenomenon, it is worthwhile to take into account the peculiarities of heat transfer confined in time and space. In the present paper, we briefly discuss the characteristic features of such heat transfer in supercritical water. The characteristic heating time was \(10^{-3}\div 10^{-2}\) s and the heat flux density through the wall increased up to 15 MW/m\(^{2}\). The results provide the heat transfer pattern under conditions of predominance of the heat conduction mode. Exactly this mode most closely corresponds to the regime of high-power local heat release in a viscous sublayer. We also propose that the effect of threshold decrease in the heat transfer intensity (typical of pulse processes in supercritical transitions) may be a fundamental factor for occurrence of the HTD mode.
- Statistical Signature of Vortex Filaments in Classical Turbulence: Dog or
Tail'- Abstract: The title of this paper echoes the title of a paragraph in the famous book by Frisch on classical turbulence. In the relevant chapter, the author discusses the role of the statistical dynamics of vortex filaments in the fascinating problem of turbulence and the possibility of a breakthrough in constructing an advanced theory. This aspect arose due to the large amount of evidence, both experimental and numerical, that the vorticity field in turbulent flows has a pronounced filamentary structure. In fact, there is unquestionably a strong relationship between the dynamics of chaotic vortex filaments and turbulent phenomena. However, the question arises as to whether the basic properties of turbulence (cascade, scaling laws, etc.) are a consequence of the dynamics of the vortex filaments (the `dog' concept) or the latter have only a marginal significance (the `tail' concept). Based on well-established results regarding the dynamics of quantized vortex filaments in superfluids, we illustrate how these dynamics can lead to the main elements of the theory of turbulence. We cover key topics such as the exchange of energy between different scales, the possible origin of Kolmogorov-type spectra, and the free decay behavior.
PubDate: 2020-02-01
- Abstract: The title of this paper echoes the title of a paragraph in the famous book by Frisch on classical turbulence. In the relevant chapter, the author discusses the role of the statistical dynamics of vortex filaments in the fascinating problem of turbulence and the possibility of a breakthrough in constructing an advanced theory. This aspect arose due to the large amount of evidence, both experimental and numerical, that the vorticity field in turbulent flows has a pronounced filamentary structure. In fact, there is unquestionably a strong relationship between the dynamics of chaotic vortex filaments and turbulent phenomena. However, the question arises as to whether the basic properties of turbulence (cascade, scaling laws, etc.) are a consequence of the dynamics of the vortex filaments (the `dog' concept) or the latter have only a marginal significance (the `tail' concept). Based on well-established results regarding the dynamics of quantized vortex filaments in superfluids, we illustrate how these dynamics can lead to the main elements of the theory of turbulence. We cover key topics such as the exchange of energy between different scales, the possible origin of Kolmogorov-type spectra, and the free decay behavior.
- Thermal Diffusivity Measurement of Cerium in the Temperature Range of
300-1800 K- Abstract: The thermal conductivity of cerium in the solid and liquid states, including the phase transition, in the temperature range of 293–1800 K was measured for the first time by the laser-pulse method with an accuracy of 2–5%. Comparison of the results with the available literature data was made. Data for the 293–400 K temperature range were obtained for the first time. Reference tables on the thermal conductivity and thermal diffusivity of cerium were developed for scientific and practical use.
PubDate: 2020-02-01
- Abstract: The thermal conductivity of cerium in the solid and liquid states, including the phase transition, in the temperature range of 293–1800 K was measured for the first time by the laser-pulse method with an accuracy of 2–5%. Comparison of the results with the available literature data was made. Data for the 293–400 K temperature range were obtained for the first time. Reference tables on the thermal conductivity and thermal diffusivity of cerium were developed for scientific and practical use.
- Convective Type Models of Industrial Processes in Column Apparatuses 1.
Chemical Reactions- Abstract: A new approach for modeling chemical processes in industrial column apparatuses is presented. An exact approach for solving the equations in the convective type models is used. The use of experimental data for the average concentration at the column end for a specific process and column makes it possible to find out model parameters related with radial non-uniformity of velocity. These parameters enable application of the average-concentration model for modeling of chemical processes with different reaction rates.
PubDate: 2020-02-01
- Abstract: A new approach for modeling chemical processes in industrial column apparatuses is presented. An exact approach for solving the equations in the convective type models is used. The use of experimental data for the average concentration at the column end for a specific process and column makes it possible to find out model parameters related with radial non-uniformity of velocity. These parameters enable application of the average-concentration model for modeling of chemical processes with different reaction rates.
- Analytical Modeling of Heat and Mass Transfer of Radiative MHD Casson
Fluid over an Exponentially Permeable Stretching Sheet with Chemical
Reaction- Abstract: Aspire of this study is to study the effect of heat source, suction/injection, and chemical reaction on dissipative and radiative MHD flow of a Casson fluid over an exponentially permeable stretching sheet. Series solutions are obtained for converted non-dimensional ordinary differential equations using an analytical technique known as the homotopy analysis method (HAM). A decisive approach of convergence of series solutions is also furnished. The acquired results are in excellent correlation with the previous results. The nature of different parameters like the magnetic parameter, exponential parameter, suction/injection parameter, the Casson parameter, radiation parameter, the Prandtl number, the Eckert number, heat source parameter, Schmidt number, and chemical reaction parameter are discussed using tables and graphs.
PubDate: 2020-02-01
- Abstract: Aspire of this study is to study the effect of heat source, suction/injection, and chemical reaction on dissipative and radiative MHD flow of a Casson fluid over an exponentially permeable stretching sheet. Series solutions are obtained for converted non-dimensional ordinary differential equations using an analytical technique known as the homotopy analysis method (HAM). A decisive approach of convergence of series solutions is also furnished. The acquired results are in excellent correlation with the previous results. The nature of different parameters like the magnetic parameter, exponential parameter, suction/injection parameter, the Casson parameter, radiation parameter, the Prandtl number, the Eckert number, heat source parameter, Schmidt number, and chemical reaction parameter are discussed using tables and graphs.
- Fluid Flow and Heat Transfer Studies on a Discretely and Differently
Heated Electronic Board- Abstract: The article presents the results of a comprehensive fundamental numerical study of the problem of conjugate mixed convection with surface radiation from a vertical electronic board with multiple different discrete heat sources. The governing equations for the fluid flow and heat transfer, which are considered in their full strength, are transformed from a primitive variable form to a stream-function-vorticity formulation and are subsequently normalized. The equations thus obtained are converted into an algebraic form using the finite volume method. The governing equations for the temperature distribution along the board were deduced from the appropriate energy balance between various energy interactions the board is engaged in. These equations are solved by the Gauss–Siedel iterative technique. The cooling medium is air, which is assumed to be radiation transparent. The computer code was specially written. The effects of the fluid flow velocity, material properties, and surface properties on the thermal behavior of the board are studied. The dependence of the pumping power on the surface emissivity of the board in different mixed convection regimes and for different materials was probed into. The singular role exhibited by buoyancy in the present problem is elucidated.
PubDate: 2020-02-01
- Abstract: The article presents the results of a comprehensive fundamental numerical study of the problem of conjugate mixed convection with surface radiation from a vertical electronic board with multiple different discrete heat sources. The governing equations for the fluid flow and heat transfer, which are considered in their full strength, are transformed from a primitive variable form to a stream-function-vorticity formulation and are subsequently normalized. The equations thus obtained are converted into an algebraic form using the finite volume method. The governing equations for the temperature distribution along the board were deduced from the appropriate energy balance between various energy interactions the board is engaged in. These equations are solved by the Gauss–Siedel iterative technique. The cooling medium is air, which is assumed to be radiation transparent. The computer code was specially written. The effects of the fluid flow velocity, material properties, and surface properties on the thermal behavior of the board are studied. The dependence of the pumping power on the surface emissivity of the board in different mixed convection regimes and for different materials was probed into. The singular role exhibited by buoyancy in the present problem is elucidated.
- Combustion of Sludge-Lignin in Water-Oxygen Mixture
- Abstract: The paper presents the results of investigation of the products of oxidation of sludge-lignin (waste from the Baikal pulp and paper mill) in H\(_{2}\)O/O\(_{2}\) mixture in the autoclave and semi-flow modes at uniform heating of the reactor up to 750 K. The time dependencies of the reactor wall temperature and the power of ohmic heaters imply that the oxidation starts at 440 K and the maximum oxidation rate is realized at 583-643 K. Mass spectrometry measurements of the composition of the volatile products yielded the temperature dependency of the degree of removal of carbon occurring in CO and CO\(_{2}\) from sludge-lignin. Using physical and chemical methods of analysis it was shown that Al\(_{2}\)O\(_{3}\) (AlOOH in the autoclave mode), Fe\(_{2}\)O\(_{3}\), SiO\(_{2}\), AlPO\(_{4}\), and CaSO\(_{4}\) were major components of the residue after the sludge-lignin conversion. Formation of HCl and H\(_{2}\)SO\(_{4}\) in the course of oxidation of chlorine- and sulfur-containing organic compounds was found to cause corrosion of stainless steel.
PubDate: 2020-02-01
- Abstract: The paper presents the results of investigation of the products of oxidation of sludge-lignin (waste from the Baikal pulp and paper mill) in H\(_{2}\)O/O\(_{2}\) mixture in the autoclave and semi-flow modes at uniform heating of the reactor up to 750 K. The time dependencies of the reactor wall temperature and the power of ohmic heaters imply that the oxidation starts at 440 K and the maximum oxidation rate is realized at 583-643 K. Mass spectrometry measurements of the composition of the volatile products yielded the temperature dependency of the degree of removal of carbon occurring in CO and CO\(_{2}\) from sludge-lignin. Using physical and chemical methods of analysis it was shown that Al\(_{2}\)O\(_{3}\) (AlOOH in the autoclave mode), Fe\(_{2}\)O\(_{3}\), SiO\(_{2}\), AlPO\(_{4}\), and CaSO\(_{4}\) were major components of the residue after the sludge-lignin conversion. Formation of HCl and H\(_{2}\)SO\(_{4}\) in the course of oxidation of chlorine- and sulfur-containing organic compounds was found to cause corrosion of stainless steel.
- Computational Modeling of Turbulent Flows
- Abstract: The article presents an improved numerical method developed for calculating turbulent flows basing on the algorithm SIMPLE, Rhie–Chow interpolation on non-staggered grids, and monotonic second and third order accurate TDV schemes. The use of high-order difference schemes for calculation of viscous flows enables achievement of significantly better resolution of the algorithm on coarse grids, which decisively affects the efficiency of two-dimensional and especially three-dimensional calculations.
PubDate: 2020-02-01
- Abstract: The article presents an improved numerical method developed for calculating turbulent flows basing on the algorithm SIMPLE, Rhie–Chow interpolation on non-staggered grids, and monotonic second and third order accurate TDV schemes. The use of high-order difference schemes for calculation of viscous flows enables achievement of significantly better resolution of the algorithm on coarse grids, which decisively affects the efficiency of two-dimensional and especially three-dimensional calculations.
- Geometrical Evaluation of a Channel with Alternated Mounted Blocks under
Mixed Convection Laminar Flows Using Constructal Design- Abstract: This work presents a numerical study of incompressible, laminar, two-dimensional, mixed convection flows in horizontal channels with two rectangular alternated blocks mounted in the surfaces. The influence of the geometry and positioning of the blocks on the heat transfer rate is evaluated using Constructal Design. The problem is subjected to two geometric constraints associated with the areas of the channel and the two blocks and three degrees of freedom: \(H_{1}/L_{1}\) (the ratio of the height to the width of the upstream block), \(H_{2}/L_{2}\) (the ratio of the height to the width of the downstream block), and \(L_{3}\) (the horizontal distance between the centers of the blocks). The purpose is to maximize the heat transfer rate per length unit \(q'\) considering three different Reynolds (\(Re_{H}= 10\), 100, and 200) and Grashof numbers (\(Gr_{H} = 650\), 6,500, and 65,000). The conservation equations of mass, momentum, and energy are solved using the Finite Volume Method, and the buoyance forces are modeled with the Boussinesq approximation. In general, the best performance is reached for the largest intrusion of the blocks. However, changes in \(Gr_{H}\) and \(Re_{H}\) affected the optimal distance (\(L_{3})_{o}\), and for \(Gr_{H}=65,000\) non-symmetrical blocks led to the best performance, showing the importance of design investigation for different flow conditions.
PubDate: 2020-02-01
- Abstract: This work presents a numerical study of incompressible, laminar, two-dimensional, mixed convection flows in horizontal channels with two rectangular alternated blocks mounted in the surfaces. The influence of the geometry and positioning of the blocks on the heat transfer rate is evaluated using Constructal Design. The problem is subjected to two geometric constraints associated with the areas of the channel and the two blocks and three degrees of freedom: \(H_{1}/L_{1}\) (the ratio of the height to the width of the upstream block), \(H_{2}/L_{2}\) (the ratio of the height to the width of the downstream block), and \(L_{3}\) (the horizontal distance between the centers of the blocks). The purpose is to maximize the heat transfer rate per length unit \(q'\) considering three different Reynolds (\(Re_{H}= 10\), 100, and 200) and Grashof numbers (\(Gr_{H} = 650\), 6,500, and 65,000). The conservation equations of mass, momentum, and energy are solved using the Finite Volume Method, and the buoyance forces are modeled with the Boussinesq approximation. In general, the best performance is reached for the largest intrusion of the blocks. However, changes in \(Gr_{H}\) and \(Re_{H}\) affected the optimal distance (\(L_{3})_{o}\), and for \(Gr_{H}=65,000\) non-symmetrical blocks led to the best performance, showing the importance of design investigation for different flow conditions.
- Thermal Processes in Electronic Equipment at Uncertainty
- Abstract: At present, electronic systems are thermally designed on the basis of the assumption that all the parameters and factors that determine the thermal processes are fully known and unambiguously determined, id est, that they are determinate. However, the practice of creation and operation of real electronic systems shows that the real values of determining parameters and factors, as well as the thermal processes and temperature distributions, are uncertain and can take any values within some intervals of their variation with an equal probability. The disregard for the interval stochastic character of the thermal processes leads to design errors and development of uncompetitive electronic systems. This article elaborates a method that permits modeling non-stationary interval stochastic thermal processes in an electronic system at interval uncertainty of input factors and parameters. The method is based on obtaining equations for non-stationary statistical measures (mathematical expectations, variances, mean square deviations, and covariances) of thermal processes at specified statistical measures of input data. The article gives an example of applying the elaborated method to thermal processes in a real electronic system that consists of electronic modules with printed circuit boards, as well as integrated microcircuits, resistors, and other electronic components installed on them.
PubDate: 2020-02-01
- Abstract: At present, electronic systems are thermally designed on the basis of the assumption that all the parameters and factors that determine the thermal processes are fully known and unambiguously determined, id est, that they are determinate. However, the practice of creation and operation of real electronic systems shows that the real values of determining parameters and factors, as well as the thermal processes and temperature distributions, are uncertain and can take any values within some intervals of their variation with an equal probability. The disregard for the interval stochastic character of the thermal processes leads to design errors and development of uncompetitive electronic systems. This article elaborates a method that permits modeling non-stationary interval stochastic thermal processes in an electronic system at interval uncertainty of input factors and parameters. The method is based on obtaining equations for non-stationary statistical measures (mathematical expectations, variances, mean square deviations, and covariances) of thermal processes at specified statistical measures of input data. The article gives an example of applying the elaborated method to thermal processes in a real electronic system that consists of electronic modules with printed circuit boards, as well as integrated microcircuits, resistors, and other electronic components installed on them.
- Title Analytical Study of Conjugated Heat Transfer of a Microchannel Fluid
Flow between Two Parallel Plates- Abstract: The conjugated temperature distributions of a microchannel fluid flow between two semi-infinite parallel plates are obtained analytically. The variables separation and transformation techniques are implemented to introduce the degenerate hypergeometric differential equation, the solution of which is given in terms of Kummer’s functions. The eigenvalues of the corresponding transcendental characteristic equation are obtained using a mathematical solver software package. Non-dimensional analysis of the governing equations introduced the parameter of “solid-fluid heat conduction ratio” \(k_k\). Values of this parameter are considered to present two limiting case solutions, namely, the adiabatic boundary solution, when \(k_k\approx 0\) and the isothermal boundary solution, when \(k_k> 100\). The Nusselt number \(Nu\) of the two limiting solutions is obtained and compared accurately with the corresponding values from the literature. The effect of the Knudsen number \(Kn\), the Biot number \(Bi\), and the conductivity ratio \(k_k\) on the temperature, temperature jump, and the Nusselt number is investigated. It is found that the temperature jump near the flow entrance becomes more significant with increase in \(Kn\), \(Bi\), or \(k_k\). On the other hand, the Nusselt number is found to increase with growing \(Kn\) and decrease with increasing \(Bi\) or \(k_k\).
PubDate: 2020-02-01
- Abstract: The conjugated temperature distributions of a microchannel fluid flow between two semi-infinite parallel plates are obtained analytically. The variables separation and transformation techniques are implemented to introduce the degenerate hypergeometric differential equation, the solution of which is given in terms of Kummer’s functions. The eigenvalues of the corresponding transcendental characteristic equation are obtained using a mathematical solver software package. Non-dimensional analysis of the governing equations introduced the parameter of “solid-fluid heat conduction ratio” \(k_k\). Values of this parameter are considered to present two limiting case solutions, namely, the adiabatic boundary solution, when \(k_k\approx 0\) and the isothermal boundary solution, when \(k_k> 100\). The Nusselt number \(Nu\) of the two limiting solutions is obtained and compared accurately with the corresponding values from the literature. The effect of the Knudsen number \(Kn\), the Biot number \(Bi\), and the conductivity ratio \(k_k\) on the temperature, temperature jump, and the Nusselt number is investigated. It is found that the temperature jump near the flow entrance becomes more significant with increase in \(Kn\), \(Bi\), or \(k_k\). On the other hand, the Nusselt number is found to increase with growing \(Kn\) and decrease with increasing \(Bi\) or \(k_k\).
- Effect of Nozzle Geometry on Particle Size Distribution in Atomized Spray
of Metastable Superheated Liquid- Abstract: Abstract It is experimentally shown that diverging nozzles with a cone angle of 12o -14° and a length of 10-15 mm provide the finest atomization of metastable superheated liquid with a submicron droplet fraction at a level of 65-70%.
PubDate: 2019-10-01
- Abstract: Abstract It is experimentally shown that diverging nozzles with a cone angle of 12o -14° and a length of 10-15 mm provide the finest atomization of metastable superheated liquid with a submicron droplet fraction at a level of 65-70%.
- Effects of Generative/Destructive Chemical Reaction on Mass Transport in
Williamson Liquid with Variable Thermophysical Properties- Abstract: Abstract This investigation discusses the effects of first order chemical (generative/destructive) reaction on the transport in a species of variable mass conductance in a Williamson liquid of variable diffusion coefficient. The problem is modeled using conservation laws with temperature dependent variable diffusion coefficients models. Several numerical experiments are carried out to analyze the effects of chemical reaction on the concentration of reacting species. During numerical experiments, it is observed that a constructive chemical reaction increases the concentration of the species, whereas the concentration decreases when the rate of destructive chemical reaction grows. The rate of diffusion of species rises with growth of the mass conductance due to rise in the temperature. The rate of diffusion of solute from a wall into the fluid is a growing function of the mass diffusion coefficient. It is observed that the diffusion of solute in the fluid accelerates when the diffusion coefficient increases due to the rise in temperature. This observation is true for both the cases of constant and variable viscosity. Both generative and destructive chemical reactions have a significant impact on the rate of diffusion of solute from the wall into the fluid. The concentration of solute decreases when the rate of destructive chemical reaction grows. However, opposite behavior of concentration field is noted for the case of generative chemical reaction.
PubDate: 2019-10-01
- Abstract: Abstract This investigation discusses the effects of first order chemical (generative/destructive) reaction on the transport in a species of variable mass conductance in a Williamson liquid of variable diffusion coefficient. The problem is modeled using conservation laws with temperature dependent variable diffusion coefficients models. Several numerical experiments are carried out to analyze the effects of chemical reaction on the concentration of reacting species. During numerical experiments, it is observed that a constructive chemical reaction increases the concentration of the species, whereas the concentration decreases when the rate of destructive chemical reaction grows. The rate of diffusion of species rises with growth of the mass conductance due to rise in the temperature. The rate of diffusion of solute from a wall into the fluid is a growing function of the mass diffusion coefficient. It is observed that the diffusion of solute in the fluid accelerates when the diffusion coefficient increases due to the rise in temperature. This observation is true for both the cases of constant and variable viscosity. Both generative and destructive chemical reactions have a significant impact on the rate of diffusion of solute from the wall into the fluid. The concentration of solute decreases when the rate of destructive chemical reaction grows. However, opposite behavior of concentration field is noted for the case of generative chemical reaction.
- Experimental Study of Drying Ratio and Humidity of Silica Sand Materials
- Abstract: Problem statement This study investigates the relationship between heating and humidity of silica sand materials in vibrating drying machines. Hence, a prototype of drying plant for one-meter length is designed, including choosing the parameters of the drying machine and computing the factors that affect drying process in addition to studying materials’ characteristics and hot air flow effect. Approach Studying these new factors will provide better understanding of drying process and increase the abilities for improvement. This study defines the efficient parameters of material and hot air movement, humidity, necessary drying temperature to specify quality of material drying. Results Four samples of silica sand with different amounts of water at three different temperatures are tested experimentally. The relationships of both drying ratio and humidity with temperature were determined. Conclusion The results of this study can be implemented in many fields of the industry where dryers and silica sand are used. The application of the temperature relations can improve the revenue by increasing the quality of drying material. For further study, it is recommended to apply various temperatures on different types of materials while defining the effect of evacuation pipe on drying material is advised.
PubDate: 2019-10-01
- Abstract: Problem statement This study investigates the relationship between heating and humidity of silica sand materials in vibrating drying machines. Hence, a prototype of drying plant for one-meter length is designed, including choosing the parameters of the drying machine and computing the factors that affect drying process in addition to studying materials’ characteristics and hot air flow effect. Approach Studying these new factors will provide better understanding of drying process and increase the abilities for improvement. This study defines the efficient parameters of material and hot air movement, humidity, necessary drying temperature to specify quality of material drying. Results Four samples of silica sand with different amounts of water at three different temperatures are tested experimentally. The relationships of both drying ratio and humidity with temperature were determined. Conclusion The results of this study can be implemented in many fields of the industry where dryers and silica sand are used. The application of the temperature relations can improve the revenue by increasing the quality of drying material. For further study, it is recommended to apply various temperatures on different types of materials while defining the effect of evacuation pipe on drying material is advised.
- Experimental Investigation of Thermal Effect on the Characteristic
Behavior of Thermoelectric Generators: Applicable as a Power Source for
Low Earth Orbit Satellites- Abstract: Abstract Generation of the power on low earth orbit satellites remains based particularly on photogeneration (solar cells), whereas other sources of energy, such as heat, remain unexploited. Indeed, exchange of heat is considered generally on board spacecraft as hostile, destructive and undesirable, thereby different means are used to reduce its effect on board spacecraft. Heat being an important source of energy, remains badly exploited on spacecraft and its applications remain limited. We present in this paper one of the methods used to convert heat energy into electrical energy by using a thermoelectric device; the goal becomes therefore to choose a device capable to provide best performance through a comparative analysis between different commercial thermoelectric generator devices to be able subsequently to make a choice of the component to be used for future design. This analysis will allow us thereafter to design a thermoelectric generator as a power source for a small satellite in eclipse by exploiting the internal/external thermal properties of the spacecraft in orbit.
PubDate: 2019-10-01
- Abstract: Abstract Generation of the power on low earth orbit satellites remains based particularly on photogeneration (solar cells), whereas other sources of energy, such as heat, remain unexploited. Indeed, exchange of heat is considered generally on board spacecraft as hostile, destructive and undesirable, thereby different means are used to reduce its effect on board spacecraft. Heat being an important source of energy, remains badly exploited on spacecraft and its applications remain limited. We present in this paper one of the methods used to convert heat energy into electrical energy by using a thermoelectric device; the goal becomes therefore to choose a device capable to provide best performance through a comparative analysis between different commercial thermoelectric generator devices to be able subsequently to make a choice of the component to be used for future design. This analysis will allow us thereafter to design a thermoelectric generator as a power source for a small satellite in eclipse by exploiting the internal/external thermal properties of the spacecraft in orbit.
- Desorption of Aqueous Solution of Lithium Bromide on Enhanced Surfaces in
a Single-Stage Lithium-Bromide Absorption Chiller- Abstract: Abstract This article presents values of heat transfer coefficients at pool boiling of aqueous solution of lithium bromide on smooth and fin tubes. The experimental studies were performed under conditions typical of absorption chiller with single-stage desorption. More exactly, the condensation pressure was about 7.8–8.5 kPa, and the concentration of lithium bromide solution was 60–61 wt%. The outer diameter of the smooth and fin tubes was 16.0 mm; the inner diameter was 12.0 mm. The surface roughness factor of the fin tubes ranged from 2.7 to 6.0. The studies have shown that for fin tubes the heat transfer coefficient reduced to a surface unit is up to 30 percent higher as compared with a smooth tube.
PubDate: 2019-10-01
- Abstract: Abstract This article presents values of heat transfer coefficients at pool boiling of aqueous solution of lithium bromide on smooth and fin tubes. The experimental studies were performed under conditions typical of absorption chiller with single-stage desorption. More exactly, the condensation pressure was about 7.8–8.5 kPa, and the concentration of lithium bromide solution was 60–61 wt%. The outer diameter of the smooth and fin tubes was 16.0 mm; the inner diameter was 12.0 mm. The surface roughness factor of the fin tubes ranged from 2.7 to 6.0. The studies have shown that for fin tubes the heat transfer coefficient reduced to a surface unit is up to 30 percent higher as compared with a smooth tube.
- Hydrodynamic Instability of Vaporization Front in Superheated Liquid
- Abstract: Abstract The well-known description of hydrodynamic instability of planar interfacial boundary at liquid combustion is applied to analysis of stability of a stationary analytical solution for the shape of the phase interface during propagation of self-sustaining evaporation front along a flat heater in superheated liquid. The applicability of the criterion of hydrodynamic instability of planar interphacial surface to the problem with a curved interface is considered. The dependences of the boundary of the perturbed evaporation surface and the range of wavelengths of unstable linear perturbations on the main physical parameters are obtained. It is shown that under certain conditions, no interfacial instability appears in the front part of the vapor cavity. The possibility of change in the mode of propagation of the evaporation front due to instability to azimuthal disturbances is analyzed.
PubDate: 2019-10-01
- Abstract: Abstract The well-known description of hydrodynamic instability of planar interfacial boundary at liquid combustion is applied to analysis of stability of a stationary analytical solution for the shape of the phase interface during propagation of self-sustaining evaporation front along a flat heater in superheated liquid. The applicability of the criterion of hydrodynamic instability of planar interphacial surface to the problem with a curved interface is considered. The dependences of the boundary of the perturbed evaporation surface and the range of wavelengths of unstable linear perturbations on the main physical parameters are obtained. It is shown that under certain conditions, no interfacial instability appears in the front part of the vapor cavity. The possibility of change in the mode of propagation of the evaporation front due to instability to azimuthal disturbances is analyzed.