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1 – 10 of 577Mehdi Bidabadi, Sadegh Sadeghi, Pedram Panahifar, Davood Toghraie and Alireza Rahbari
This study aims to present a basic mathematical model for investigating the structure of counter-flow non-premixed laminar flames propagating through uniformly-distributed organic…
Abstract
Purpose
This study aims to present a basic mathematical model for investigating the structure of counter-flow non-premixed laminar flames propagating through uniformly-distributed organic fuel particles considering preheat, drying, vaporization, reaction and oxidizer zones.
Design/methodology/approach
Lycopodium particles and air are taken as biofuel and oxidizer, respectively. Dimensionalized and non-dimensionalized forms of mass and energy conservation equations are derived for each zone taking into account proper boundary and jump conditions. Subsequently, to solve the governing equations, an asymptotic method is used. For validation purpose, results achieved from the present analysis are compared with reliable data reported in the literature under certain conditions.
Findings
With regard to the comparisons, although different complex non-homogeneous differential equations are solved in this paper, acceptable agreements are observed. Finally, the impacts of significant parameters including fuel and oxidizer Lewis numbers, equivalence ratio, mass particle concentration, fuel and oxidizer mass fractions and lycopodium initial temperature on the flame temperature, flame front position and flow strain rate are elaborately explained.
Originality/value
An asymptotic method for mathematical modeling of counter-flow non-premixed multi-zone laminar flames propagating through lycopodium particles.
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Abstract
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Maher M. Abou Al‐Sood and Madjid Birouk
The purpose of this paper is to develop a three‐dimensional (3D) numerical model capable of predicting the vaporization rate of a liquid fuel droplet exposed to a convective…
Abstract
Purpose
The purpose of this paper is to develop a three‐dimensional (3D) numerical model capable of predicting the vaporization rate of a liquid fuel droplet exposed to a convective turbulent airflow at ambient room temperature and atmospheric pressure conditions.
Design/methodology/approach
The 3D Reynolds‐Averaged Navier‐Stokes equations, together with the mass, species, and energy conservation equations were solved in Cartesian coordinates. Closure for the turbulence stress terms for turbulent flow was accomplished by testing two different turbulence closure models; the low‐Reynolds number (LRN) k‐ε and shear‐stress transport (SST). Numerical solution of the resulted set of equations was achieved by using blocked‐off technique with finite volume method.
Findings
The present predictions showed good agreement with published turbulent experimental data when using the SST turbulence closure model. However, the LRN k‐ε model produced poor predictions. In addition, the simple numerical approach employed in the present code demonstrated its worth.
Research limitations/implications
The present study is limited to ambient room temperature and atmospheric pressure conditions. However, in most practical spray flow applications droplets evaporate under ambient high‐pressure and a hot turbulent environment. Therefore, an extension of this study to evaluate the effects of pressure and temperature will make it more practical.
Originality/value
It is believed that the numerical code developed is of great importance to scientists and engineers working in the field of spray combustion. This paper also demonstrated for the first time that the simple blocked‐off technique can be successfully used for treating a droplet in the flow calculation domain.
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B. Sorli, F. Pascal‐Delannoy, A. Foucaran, A. Giani and A. Boyer
This article describes a new humidity sensor using the technique of differential thermal analysis (DTA). The energy of water vaporisation is estimated via the measurement of the…
Abstract
This article describes a new humidity sensor using the technique of differential thermal analysis (DTA). The energy of water vaporisation is estimated via the measurement of the Seebeck voltage of miniature thermocouples used in differential mode on a Peltier module causing condensation from the ambient air. This sensor uses the sensitivity of alloys V2VI3 containing [Bi, Te, Sb, Se], 400‐440μV.K–1. Experimental measurements have been performed in a climatic chamber at constant temperature. The time variation of the differential Seebeck voltage with relative humidities HR varying from 10 to 90 per cent makes it possible to identify with precision the point of water evaporation. For each value of the relative humidity, it is directly a function of the condensate mass. The integration of these curves over time makes it possible to calculate the energy of vaporisation and the condensate mass.
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Kaiwen Pang, Yaojun Li, Wei Yang and Zhuqing Liu
This study aims to develop and validate a new cavitation model that considers thermodynamic effects for high-temperature water flows.
Abstract
Purpose
This study aims to develop and validate a new cavitation model that considers thermodynamic effects for high-temperature water flows.
Design/methodology/approach
The Rayleigh–Plesset equation and “B-factor” method proposed by Franc are used to construct a new cavitation model called “thermodynamic Zwarte–Gerbere–Belamri” (TZGB) by introducing the thermodynamic effects into the original ZGB model. Furthermore, the viscous term of the Rayleigh–Plesset equation is considered in the TZGB model, and the model coefficients are formulated as a function of temperature. Cavitating flows around the NACA0015 hydrofoil under different water temperatures (25°C, 50°C and 70°C) at the angle of attack of 5° are calculated.
Findings
Results of the investigated temperatures show good agreement with the available experimental data. Given that the thermodynamic and viscosity effects are included in the TZGB model and the model coefficients are treated as a function of temperature, the TZGB model shows better performance in predicting the pressure coefficient distribution and length of cavity than the original ZGB cavitation model and other models do. The TZGB model aims to determine the thermodynamic and viscosity effects and perform better than the other models in predicting the mass transfer rate, particularly in high-temperature water.
Originality/value
The TZGB model shows potential in predicting the cavitating flows at high temperature and the computational cost of this model is similar to that of the original ZGB model.
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Yaasin Abraham Mayi, Alexis Queva, Morgan Dal, Gildas Guillemot, Charlotte Metton, Clara Moriconi, Patrice Peyre and Michel Bellet
During thermal laser processes, heat transfer and fluid flow in the melt pool are primary driven by complex physical phenomena that take place at liquid/vapor interface. Hence…
Abstract
Purpose
During thermal laser processes, heat transfer and fluid flow in the melt pool are primary driven by complex physical phenomena that take place at liquid/vapor interface. Hence, the choice and setting of front description methods must be done carefully. Therefore, the purpose of this paper is to investigate to what extent front description methods may bias physical representativeness of numerical models of laser powder bed fusion (LPBF) process at melt pool scale.
Design/methodology/approach
Two multiphysical LPBF models are confronted: a Level-Set (LS) front capturing model based on a C++ code and a front tracking model, developed with COMSOL Multiphysics® and based on Arbitrary Lagrangian–Eulerian (ALE) method. To do so, two minimal test cases of increasing complexity are defined. They are simplified to the largest degree, but they integrate multiphysics phenomena that are still relevant to LPBF process.
Findings
LS and ALE methods provide very similar descriptions of thermo-hydrodynamic phenomena that occur during LPBF, providing LS interface thickness is correctly calibrated and laser heat source is implemented with a modified continuum surface force formulation. With these calibrations, thermal predictions are identical. However, the velocity field in the LS model is systematically underestimated compared to the ALE approach, but the consequences on the predicted melt pool dimensions are minor.
Originality/value
This study fulfils the need for comprehensive methodology bases for modeling and calibrating multiphysical models of LPBF at melt pool scale. This paper also provides with reference data that may be used by any researcher willing to verify their own numerical method.
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Wenbin Gao, Weifeng Huang, Tao Wang, Ying Liu, Zhihao Wang and Yuming Wang
By modeling and analyzing the two-phase mechanical seal of the fan-shaped groove end face, which is prone to phase change, an effective method to study the flow field of the…
Abstract
Purpose
By modeling and analyzing the two-phase mechanical seal of the fan-shaped groove end face, which is prone to phase change, an effective method to study the flow field of the mechanical seal when both cavitation and boiling exist simultaneously is found.
Design/methodology/approach
Based on the finite volume method, a fluid model was developed to investigate a two-phase mechanical seal. The validity of the proposed model was verified by comparing with some classical models.
Findings
By modeling and analyzing the two-phase mechanical seal of the fan-shaped groove end face, which is prone to phase change, the analysis of the gap flow field of the mechanical seal was realized when cavitation and boiling existed simultaneously.
Originality/value
Based on the model proposed for different conditions, the pressure and phase states in the shallow groove sealing gap were compared. The phase change rate between the mechanical seal faces was also investigated.
Peer review
The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2019-0537/
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M. Glasmacher and H.‐J. Pucher
Laser Beam Micro Welding represents an alternative joining technique to the well known soldering processes. Hereby the leads are welded directly to the conducting tracks of the…
Abstract
Laser Beam Micro Welding represents an alternative joining technique to the well known soldering processes. Hereby the leads are welded directly to the conducting tracks of the circuit board. The advantages such as high temperature strength, reduced manufacturing time and simplified material separation at the end of the life‐cycle can be used successfully, if the drawbacks such as sensitive process behaviour are well controlled. To obtain this objective, the basic principles of laser beam heating and characteristic process stages of different micro welding scenarios are discussed. Applying simplified solutions of the equation of heat conduction, good parameter sets can be found for different welding applications. These examples show the potential of laser beam welding in the field of microelectronics.
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Zhang Guoyuan and Yan Xiu-Tian
A hybrid bearing of advanced cryogenic rocket engine turbopump is designed. For cryogenic fluid propellants (such as liquid oxygen) as the lubrication of bearing, bearings…
Abstract
Purpose
A hybrid bearing of advanced cryogenic rocket engine turbopump is designed. For cryogenic fluid propellants (such as liquid oxygen) as the lubrication of bearing, bearings operating close to liquid-vapor region (near the critical point or slightly sub-cooled) are likely to develop a two phase flow region. The paper aims to discuss these issues.
Design/methodology/approach
In this paper, an all liquid, liquid-vapor mixture, and all vapor, i.e. a continuous vaporization bulk flow model of density and viscosity for mixture fluid, is presented, and the general Reynolds equation and energy equation with two phase flow as lubricants is solved. The static and dynamic performance of a 50-mm-radius hybrid bearing are obtained under 20,000 rpm speed and 10 MPa supply pressure.
Findings
The results show that the variations of performance of bearing operating under cryogenic liquid oxygen are not bounded by the all liquid and all vapor cases in the liquid-vapor mixture range. There behaviours are attributed to the large change in the compressibility character of the flow.
Research limitations/implications
For validating the correctness of analytical model, an experimental study on the liquid-vapor nitrogen mixture lubricated hybrid journal bearings is being carried out where low-viscosity nitrogen was selected as the lubricant for the sake of safety. Soon after, the authors will discuss the results and publish them in the new papers.
Originality/value
An all liquid, liquid-vapor mixture, and all vapor, i.e. a continuous vaporization bulk flow model of density and viscosity for mixture fluid, is presented. The static and dynamic performance of hybrid bearings with two phase flow as lubricants are obtained.
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1963—the year of reports. When looking back there is a tendency to associate a particular year with a specific occurrence or happening. Some years are easy to label in this way;…
Abstract
1963—the year of reports. When looking back there is a tendency to associate a particular year with a specific occurrence or happening. Some years are easy to label in this way; for example, 1939 was the year of the war, 1945 the year of the peace and so on. What about 1963? We have already labelled it in our mind as ‘the year of the reports’. Admittedly they have been sandwiched into the latter half of the year but we are beginning to feel that life without either discussion of a presented report or expectation of a new report is not normal.