scholarly journals Dependence of the separative power of an optimised Iguassu gas centrifuge on the velocity of rotor

2017 ◽  
Vol 27 (7) ◽  
pp. 1387-1394 ◽  
Author(s):  
Sergey Vladimirovich Bogovalov ◽  
Vladimir Dmitrievich Borman ◽  
Valentin Dmitrievich Borisevich ◽  
Vladimir Nikolaevich Tronin ◽  
Ivan Vladimirovich Tronin
Keyword(s):  
Computer Simulation ◽  
Angular Momentum ◽  
Binary Mixture ◽  
Power Law ◽  
Gas Flow ◽  
Temperature Drop ◽  
Uranium Isotopes ◽  
Gas Temperature ◽  
Content Type ◽  
Gas Centrifuge

Purpose The purpose of this work is to determine dependence of the separative power of the Iguassu gas centrifuge (GC) on the velocity of the rotor. Design/methodology/approach The dependence is determined by means of computer simulation of the gas flow in the GC and numerical solution of the diffusion equation for the light component of the binary mixture of uranium isotopes. 2D axisymmetric model with the sources/sinks of the mass, angular momentum and energy reproducing the scoops was explored for the computer simulation. Parameters of the model correspond to the parameters of the so-called Iguassu centrifuge. The separative power has been optimised in relation to the pressure of the gas, temperature of the gas, the temperature drop along the rotor, power of the source of angular momentum and energy, feed flow and geometry of the lower baffle. Findings In the result, the optimised separative power depends only on the velocity, length and diameter of the rotor. The dependence on the velocity is described by the power law function with the power law index 2.6 which demonstrate stronger dependence on the velocity than it follows from experimental data. However, the separative power obtained with limitation on the pressure growth with the velocity depends on the velocity on the power ∼ 2 which well agree with the experiments. Originality/value For the first time, the optimised separative power of the GCs have been calculated via numerical simulation of the gas flow and diffusion of the binary mixture of isotope.

Modeling and Simulation of Flow and Uranium Isotopes Separation in Gas Centrifuges Using Implicit Coupled Density-Based Solver in OpenFOAM

2020 ◽  
Author(s):  
Valiyollah Ghazanfari ◽  
Ali Akbar Salehi ◽  
Ali Reza Keshtkar ◽  
Mohammad Mahdi Shadman ◽  
Mohammad Hossein Askari
Keyword(s):  
Gas Flow ◽  
Isotope Separation ◽  
Splitting Method ◽  
Flow Characteristics ◽  
Uranium Isotopes ◽  
Gas Centrifuge ◽  
Total Reflux ◽  
Axial Mass ◽  
Fluent Software ◽  
Isotopes Separation

The performance of a gas centrifuge that is used for isotopes separation is dependent on the gas flow inside it. In this study, for modeling the UF6 gas flow, an Implicit Coupled Density-Based (ICDB) solver, was developed in OpenFOAM. To validate the ICDB solver, the gas flow within the rotor in total reflux state was compared with the analytical solution obtained by Onsager model and the numerical solution obtained by the Fluent software. The results showed that the ICDB solver had acceptable accuracy and validity. Also the computational efficiency of Roe, AUSM (Advection Upstream Splitting Method) and AUSM+ up schemes were compared. The results showed AUSM+ up scheme is efficient. Then, the uranium isotopes separation in a gas centrifuge was simulated. It was revealed that all gas flow characteristics including velocity, pressure, temperature and axial mass flux, as well as uranium isotope separation parameters including separation power and separation coefficients could well be predicted.

Computer Simulation of Drying of Food Products With Superheated Steam in a Rotary Kiln

2010 ◽  
Author(s):  
Koustubh Sinhal ◽  
P. S. Ghoshdastidar ◽  
Bhaskar Dasgupta
Keyword(s):  
Heat Transfer ◽  
Computer Simulation ◽  
Flow Rate ◽  
Rotary Kiln ◽  
Rotational Speed ◽  
Gas Flow ◽  
Superheated Steam ◽  
Gas Temperature ◽  
Gas Flow Rate ◽  
Refractory Wall

The present work reports a computer simulation study of heat transfer in a rotary kiln used for drying and preheating food products such as fruits and vegetables with superheated steam at 1 bar. The heat transfer model includes radiation exchange among the superheated steam, refractory wall and the solid surface, conduction in the refractory wall, and the mass and energy balances of the steam and solids. Finite-difference techniques are used, and the steady state thermal conditions are assumed. The false transient approach is used to solve the wall conduction equation. The solution is initiated at the inlet of the kiln, and proceeds to the exit. The output data consist of distributions of the refractory wall temperature, solid temperature, steam temperature, and the total kiln length. The inlet of the kiln is the outlet of the gas (superheated steam), since the gas flow is countercurrent to the solid. Thus, for a fixed solid and gas temperature at the kiln inlet, the program predicts the inlet temperature of the gas (i.e. at the kiln exit) in order to achieve the specified exit temperature. In the absence of experimental results for food drying in a rotary kiln, the present model has been satisfactorily validated against numerical results of Sass [1] for drying of wet iron ore in a rotary kiln. The results are presented for drying of apple and carrot pieces. A detailed parametric study indicates that the influence of controlling parameters such as percent water content (with respect to dry solids), solids flow rate, gas flow rate, kiln inclination angle and the rotational speed of the kiln on the axial solids and gas temperature profiles and the total predicted kiln length is appreciable. The study reveals that a good design of a rotary kiln requires medium gas flow rate, small angle of inclination and low rotational speed of the kiln.

Computer Simulation of Drying of Food Products With Superheated Steam in a Rotary Kiln

2012 ◽  
Vol 4 (1) ◽  
Author(s):  
Koustubh Sinhal ◽  
P. S. Ghoshdastidar ◽  
Bhaskar Dasgupta
Keyword(s):  
Heat Transfer ◽  
Computer Simulation ◽  
Flow Rate ◽  
Rotary Kiln ◽  
Gas Flow ◽  
Superheated Steam ◽  
Food Products ◽  
Gas Temperature ◽  
Refractory Wall ◽  
Solid Temperature

The present work reports a computer simulation study of heat transfer in a rotary kiln used for drying and preheating food products such as fruits and vegetables with superheated steam at 1 bar. The heat transfer model includes radiation exchange among the superheated steam, refractory wall and the solid surface, conduction in the refractory wall, and the mass and energy balances of the steam and solids. The gas convection is also considered. Finite-difference techniques are used, and the steady state thermal conditions are assumed. The false transient approach is used to solve the wall conduction equation. The solution is initiated at the inlet of the kiln and proceeds to the exit. The output data consist of distributions of the refractory wall temperature, solid temperature, steam temperature, and the total kiln length. The inlet of the kiln is the outlet of the gas (superheated steam), since the gas flow is countercurrent to the solid. Thus, for a fixed solid and gas temperature at the kiln inlet, the program predicts the inlet temperature of the gas (i.e., at the kiln exit) in order to achieve the specified exit temperature of the gas. In the absence of experimental results for food drying in a rotary kiln, the present model has been satisfactorily validated against numerical results of Sass (1967, “Simulation of the Heat-Transfer Phenomena in a Rotary Kiln,” Ind. Eng. Chem. Process Des. Dev., 6(4), pp. 532–535) and limited measured gas temperature as reported by Sass (1967, “Simulation of the Heat-Transfer Phenomena in a Rotary Kiln,” Ind. Eng. Chem. Process Des. Dev., 6(4), pp. 532–535) for drying of wet iron ore in a rotary kiln. The results are presented for drying of apple and carrot pieces. A detailed parametric study indicates that the influence of controlling parameters such as percent water content (with respect to dry solids), solids flow rate, gas flow rate, kiln inclination angle, and the rotational speed of the kiln on the axial solids and gas temperature profiles and the total predicted kiln length is appreciable. The effects of inlet solid temperature and exit gas temperature on the predicted kiln length for carrot drying are also shown in this paper.

scholarly journals Study on Distribution of Wellbore Temperature in Gas Drilling with Gradient Equations

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Zhongxi Zhu ◽  
Chaofei Wang ◽  
Zhigang Guan ◽  
Wanneng Lei
Keyword(s):  
Temperature Distribution ◽  
Gradient Method ◽  
Gas Flow ◽  
Temperature Drop ◽  
Geothermal Gradient ◽  
Cooling Effect ◽  
Formation Temperature ◽  
Gas Temperature ◽  
Local Cooling ◽  
Gas Drilling

Precise calculation of gas temperature profile is the key to gas drilling design. It is traditionally assumed that the gas temperature distribution in the wellbore is equal to the formation temperature, without considering the influence of fluid flow and Joule-Thomson cooling effect. This paper puts forward a gradient equation method for gas temperature distribution in wellbore considering gas flow and Joule-Thomson local cooling of the bit. The method applies pressure, temperature, density, and velocity equations to gas flow in drillstrings and annulus. The solution of the gradient equation is in the form of the fourth-order Runge-Kutta equation. Bottom wellbore temperatures measured at depths of 700 to 2000 m in an actual well are consistent with those predicted by the gradient method. Due to the Joule-Thomson cooling effect at the bit nozzle, the temperature drops by about 30°C. The sensitivity analysis is carried out by gradient method, and the results show that the temperature drop range of different nozzle sizes can reach 60°C due to the Joule-Thomson cooling effect. Stable temperature curves can be established within a few minutes of the gas cycle. Due to the influence of gas flow and Joule-Thomson cooling, the gas temperature in the wellbore deviates significantly from the geothermal temperature in the formation under the flow condition. The temperature of the gas in drillstrings increases as the drill depth increases and then decreases rapidly near the bottom of the hole. As the gas flows upward along the annulus, the gas temperature rises first, surpasses the formation temperature, and then decreases gradually along the geothermal gradient trend.

VIKOR power law-based customer-oriented FMEA with complete unique risk priority numbers

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Randula L. Hettiarachchi ◽  
Pisut Koomsap ◽  
Panarpa Ardneam
Keyword(s):  
Case Studies ◽  
Power Law ◽  
Design Methodology ◽  
Service Sector ◽  
Failure Modes ◽  
Risk Priority Number ◽  
Effect Analysis ◽  
Content Type ◽  
Industrial Sectors ◽  
Inherent Problem

PurposeAn inherent problem on risk priority number (RPN) value duplication of traditional failure modes and effect analysis (FMEA) also exists in two customer-oriented FMEAs. One has no unique value, and another has 1% unique values out of 4,000 possible values. The RPN value duplication has motivated the development of a new customer-oriented FMEA presented in this paper to achieve practically all 4,000 unique values and delivering reliable prioritization.Design/methodology/approachThe drastic improvement is the result of power-law and VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR). By having all three risk factors in a power-law form, all unique values can be obtained, and by applying VIKOR to these power-law terms, the prioritization is more practical and reliable.FindingsThe proposed VIKOR power law-based customer-oriented FMEA can achieve practically all 4,000 unique values and is tested with two case studies. The results are more logical than the results from the other two customer-oriented FMEAs.Research limitations/implicationsThe evaluation has been done on two case studies for the service sector. Therefore, additional case studies in other industrial sectors will be required to confirm the effectiveness of this new customer-oriented RPN calculation.Originality/valueAchieving all 1,000 unique values could only be done by having experts tabulate all possible combinations for the traditional FMEA. Therefore, achieving all 4,000 unique values will be much more challenging. A customer-oriented FMEA has been developed to achieve practically all 4,000 unique risk priority numbers, and that the prioritization is more practical and reliable. Furthermore, it has a connection to the traditional FMEA, which helps explain the traditional one from a broader perspective.

Risk transfer in project finance loans for toll road using credit default swaps

2022 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Wei Yang ◽  
Afshin Firouzi ◽  
Chun-Qing Li
Keyword(s):  
Power Law ◽  
Credit Default Swaps ◽  
Free Cash Flow ◽  
Project Finance ◽  
Cost Of Debt ◽  
Power Law Model ◽  
Data Set ◽  
Content Type ◽  
Toll Road ◽  
Credit Default

Purpose The purpose of this paper is to demonstrate the applicability of the Credit Default Swaps (CDS), as a financial instrument, for transferring of risk in project finance loans. Also, an equation has been derived for pricing of CDS spreads. Design/methodology/approach The debt service cover ratio (DSCR) is modeled as a Brownian Motion (BM) with a power-law model fitted to the mean and half-variance of the existing data set of DSCRs. The survival probability of DSCR is calculated during the operational phase of the project finance deal, using a closed-form analytical method, and the results are verified by Monte Carlo simulation (MCS). Findings It is found that using the power-law model yields higher CDS premiums. This in turn confirms the necessity of conducting rigorous statistical analysis in fitting the best performing model as uninformed reliance on constant time-invariant drift and diffusion model can erroneously result in smaller CDS spreads. A sensitivity analysis also shows that the results are very sensitive to the recovery rate and cost of debt values. Originality/value Insufficiency of free cash flow is a major risk in the toll road project finance and hence there is a need to develop innovative financial instruments for risk management. In this paper, a novel valuation method of CDS is proposed assuming that DSCR follows the BM stochastic process.

scholarly journals Separation of a Binary Mixture with a Large Mass Difference between the Components in a Gas Centrifuge

Atomic Energy ◽  
2013 ◽  
Vol 114 (1) ◽  
pp. 28-32 ◽  
Author(s):  
Yu. V. Abramov ◽  
V. I. Tokmantsev
Keyword(s):  
Binary Mixture ◽  
Mass Difference ◽  
Large Mass ◽  
Gas Centrifuge

Inertia parameter identification of anunknown captured space target

2019 ◽  
Vol 91 (8) ◽  
pp. 1147-1155 ◽  
Author(s):  
Xiaofeng Liu ◽  
Bangzhao Zhou ◽  
Boyang Xiao ◽  
Guoping Cai
Keyword(s):  
Angular Momentum ◽  
Parameter Identification ◽  
Linear Momentum ◽  
Content Type ◽  
Identification Method ◽  
Robot Arms ◽  
Precise Estimation ◽  
Inertia Parameter ◽  
Inertia Parameters ◽  
Space Target

Purpose The purpose of this paper is to present a method to obtain the inertia parameter of a captured unknown space target. Design/methodology/approach An inertia parameter identification method is proposed in the post-capture scenario in this paper. This method is to resolve parameter identification with two steps: coarse estimation and precise estimation. In the coarse estimation step, all the robot arms are fixed and inertia tensor of the combined system is first calculated by the angular momentum conservation equation of the system. Then, inertia parameters of the unknown target are estimated using the least square method. Second, in the precise estimation step, the robot arms are controlled to move and then inertia parameters are once again estimated by optimization method. In the process of optimization, the coarse estimation results are used as an initial value. Findings Numerical simulation results prove that the method presented in this paper is effective for identifying the inertia parameter of a captured unknown target. Practical implications The presented method can also be applied to identify the inertia parameter of space robot. Originality/value In the classic momentum-based identification method, the linear momentum and angular momentum of system, both considered to be conserved, are used to identify the parameter of system. If the elliptical orbit in space is considered, the conservation of linear momentum is wrong. In this paper, an identification based on the conservation of angular momentum and dynamics is presented. Compared with the classic momentum-based method, this method can get a more accurate identification result.

The two sides of CEO pay injustice

2018 ◽  
Vol 16 (1) ◽  
pp. 3-30 ◽  
Author(s):  
Herman Aguinis ◽  
Geoffrey P. Martin ◽  
Luis R. Gomez-Mejia ◽  
Ernest H. O’Boyle ◽  
Harry Joo
Keyword(s):  
Normal Distribution ◽  
Power Law ◽  
Chief Executive Officers ◽  
Risk Sharing ◽  
Chief Executive ◽  
Return On Assets ◽  
Content Type ◽  
Ceo Pay ◽  
Executive Officers ◽  
Two Sides

Purpose The purpose of this study was to examine the extent to which chief executive officers (CEOs) deserve the pay they receive both in terms of over and underpayment. Design/methodology/approach Rather than using the traditional normal distribution view in which CEO performance clusters around the mean with relatively little variance, the authors adopt a novel power law approach. They studied 22 industries and N = 4,158 CEO-firm combinations for analyses based on Tobin’s Q and N = 5,091 for analyses based on return on assets. Regarding compensation, they measured the CEO distribution based on total compensation and three components of CEO total pay: salary, bonus, and value of options exercised. Findings In total, 86 percent of CEO performance and 91 percent of CEO pay distributions fit a power law better than a normal distribution, indicating that a minority of CEOs are producing top value for their firms (i.e. CEO performance) and a minority of CEOs are appropriating top value for themselves (i.e. CEO pay). But, the authors also found little overlap between CEOs who are the top performers and CEOs who are the top earners. Implications The findings shed new light on CEO pay deservingness by using a novel conceptual and methodological lens that highlights systematic over and underpayment. Results suggest a violation of distributive justice and offer little support for agency theory’s efficient contracting hypothesis, which have important implications for agency theory, equity theory, justice theory, and agent risk sharing and agent risk bearing theories. Practical implications Results highlight erroneous practices when trying to benchmark CEO pay based on average levels of performance in an industry because the typical approach to CEO compensation based on averages significantly underpays stars and overpays average performers. Originality/value Results offer new insights on the extent of over and underpayment. The findings uncover an extremely large non-overlap between the top earning and top performing CEOs and to an extent far greater in magnitude than previously suggested.

Computer Simulation of Heat Transfer in Alumina and Cement Rotary Kilns

2021 ◽  
pp. 1-57
Author(s):  
Atinder Pal Singh ◽  
P.S. Ghoshdastidar
Keyword(s):  
Heat Transfer ◽  
Computer Simulation ◽  
Rotary Kiln ◽  
Cement Kiln ◽  
Gas Temperature ◽  
Contact Heat ◽  
Dry Process ◽  
Radiation Exchange ◽  
Covered Wall ◽  
Rotary Kilns

Abstract The paper presents computer simulation of heat transfer in alumina and cement rotary kilns. The model incorporates radiation exchange among solids, wall and gas, convective heat transfer from the gas to the wall and the solids, contact heat transfer between the covered wall and the solids, and heat loss to the surroundings as well as chemical reactions. The mass and energy balances of gas and solids have been performed in each axial segment of the kilns. The energy equation for the wall is solved numerically by the finite-difference method. The dust entrainment in the gas is also accounted for. The solution marches from the solids inlet to the solids outlet. The kiln length predicted by the present model of the alumina kiln is 77.5 m as compared to 80 m of the actual kiln of Manitius et al. (1974, Manitius, A., Kurcyusz, E., and Kawecki, W., “Mathematical Model of an Aluminium Oxide Rotary Kiln,” Ind. Eng. Chem. Process Des. Dev., 13 (2), pp. 132-142). In the second part, heat transfer in a dry process cement rotary kiln is modelled. The melting of the solids and coating formation on the inner wall of the kiln are also taken into account. A detailed parametric study lent a good physical insight into axial solids and gas temperature distributions, and axial variation of chemical composition of the products in both the kilns. The effect of kiln rotational speed on the cement kiln wall temperature distribution is also reported.

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