Numerical Study on the Effect of Vortex Generators on the Aerodynamic Drag of a High-Speed Train

A relatively high aerodynamic drag is an important factor that hinders the further acceleration of high-speed trains.Using the shear stress transport(SST)k-ωturbulence model,the effect of various vortex generator types on the aerodynamic characteristics of an ICE2(Inter-city Electricity)train has been investigated.The results indi-cate that the vortex generators with wider triangle,trapezoid,and micro-ramp arranged on the surface of the tail car can significantly change the distribution of surface pressure and affect the vorticity intensity in the wake.This alteration effectively reduces the resistance of the tail car.Meanwhile,the micro-ramp vortex generator with its convergent structure at the rear exhibits enhancedflow-guiding capabilities,resulting in a 15.4%reduction in the drag of the tail car.

Analysis of pseudo-random number generators in QMC-SSE method

In the quantum Monte Carlo(QMC)method,the pseudo-random number generator(PRNG)plays a crucial role in determining the computation time.However,the hidden structure of the PRNG may lead to serious issues such as the breakdown of the Markov process.Here,we systematically analyze the performance of different PRNGs on the widely used QMC method known as the stochastic series expansion(SSE)algorithm.To quantitatively compare them,we introduce a quantity called QMC efficiency that can effectively reflect the efficiency of the algorithms.After testing several representative observables of the Heisenberg model in one and two dimensions,we recommend the linear congruential generator as the best choice of PRNG.Our work not only helps improve the performance of the SSE method but also sheds light on the other Markov-chain-based numerical algorithms.

Application of Vortex Generators to Remove Heat Trapped in Closed Channels

The utilization of vortex generators to increase heat transfer from cylinders installed inside a duct is investigated.In particular,a channel containing eight cylinders with volumetric heat sources is considered for different values of the Reynolds number.The effective possibility to use vortex generators with different sizes to increase heat transfer and,consequently,reduce the surface temperature of the cylinders is examined.Also,the amount of pressure drop inside the channel due to the presence of vortex generators is considered and compared with the cases without vortex generators.The results show that although the addition of generators increases the pressure drop,it strongly contributes to increase the heat transfer coefficient inside the duct(up to 80–90%).

Waste Heat Recovery from a Drier Receiver of an A/C Unit Using Thermoelectric Generators

Thermoelectric generators(TEGs)are considered promising devices for waste heat recovery from various systems.The Seebeck effect can be utilized to generate power using the residual heat emitted by the filter dryer receiver(FDR)of an air conditioning(A/C)system,which would otherwise go to waste.The study aims to build a set of thermoelectric generators(TEG)to collect the waste heat of the FDR and generate low-power electricity.A novel electrical circuit with two transformers is designed and fabricated to produce a more stable voltage for operation and charging.The thermoelectric generator(TEGs)was installed on the FDR of the A/C unit.The test showed that climate conditions have a significant impact on the output power generated from the system.The results showed that the peak voltage recorded in the current study is 5.2 V per day(wet,cold,and wind weather)with an output power of 0.2 W.These values are acceptable for powering the load and charging a single battery with 3.5 V as the voltage increases battery 0.1 V/20 min charge.A case study of operating the emergency signs in a building was considered.The current heat recovery system is deemed to be easily installed and can be connected to a network of TEGs to produce more power.

Thermoelectric generators and their applications:Progress,challenges,and future prospects

Our community currently deals with issues such as rising electricity costs,pollution,and global warming.Scientists work to improve energy harvesting-based power generators in order to reduce their impacts.The Seebeck effect has been used to illustrate the capacity of thermoelectric generators(TEGs)to directly convert thermal energy to electrical energy.They are also ecologically beneficial since they do not include chemical products,function quietly because they lack mechanical structures and/or moving components,and may be built using different fabrication technologies such as three-dimentional(3D)printing,silicon technology,and screen printing,etc.TEGs are also position-independent and have a long operational lifetime.TEGs can be integrated into bulk and flexible devices.This review gives further investigation of TEGs,beginning with a full discussion of their operating principle,kinds,materials utilized,figure of merit,and improvement approaches,which include various thermoelectric material arrangements and utilised technologies.This paper also discusses the use of TEGs in a variety of disciplines such as automobile and biomedical.

EXPONENTIALLY BOUNDED C-SEMIGROUP AND INTEGRATED SEMIGROUP WITH NONDENSELY DEFINED GENERATORS I: APPROXIMATION:

In this paper, by Laplace transform version of the Trotter-Kato approximation theorem and the integrated C-semigroup introduced by Myadera, the authors obtained some Trotter-Kato approximation theorems on exponentially bounded C-semigroups, where the range of C (and so the domain of the generator) may not be dense. The authors deduced the corresponding results on exponentially bounded integrated semigroups with nondensely generators. The results of this paper extended and perfected the results given by Lizama, Park and Zheng.

Investigation of production of medical ^(82)Sr and ^(68)Ge for ^(82)Sr/^(82)Rb and ^(68)Ge/^(68)Ga generators via proton accelerator

How to operate^(82)Sr/^(82)Rb and ^(68)Ge/^(68)Ga generators used in the positron emission tomography scan process is explained, and the importance of ^(82)Sr and ^(68)Ge radionuclides for these generators is revealed. To produce medical ^(82)Sr and ^(68)Ge by means of a proton accelerator in an irradiation time of 24 h, a proton beam current of250 l A, and an energy range E_(proton)= 100 →5 MeV, the cross sections and the neutron emission spectrum curves of(p,xn) reaction processes on Rb-85, Ga-69 and Ga-71 targets were calculated, and the activities and yields of the product were simulated for the reaction processes. Additionally, the integral yields of the reaction processes were determined via the calculated cross-sectional curves and the mass stopping power obtained from the X-PMSP program. Furthermore, based on the obtained results, the appropriate reaction processes for the production of ^(82)Sr and ^(68)Ge isotopes on Rb-85, Ga-69, and Ga-71 targets are discussed.

CFD-Based Simulation and Analysis of Hydrothermal Aspects in Solar Channel Heat Exchangers with Various Designed Vortex Generators

The hydrothermal behavior of air inside a solar channel heat exchanger equipped with various shaped ribs is analyzed numerically.The bottom wall of the exchanger is kept adiabatic,while a constant value of the temperature is set at the upper wall.The duct is equipped with a flat rectangular fin on the upper wall and an upstream V-shaped baffle on the lower wall.Furthermore,five hot wall-attached rib shapes are considered:trapezoidal,square,triangular pointing upstream(type Ⅰ),triangular pointing downstream(type Ⅱ),and equilateral-triangular(type Ⅲ)cross sections.Effects of the flow rates are also inspected for various Reynolds numbers in the turbulent regime(1.2×10^(4)-3.2×10^(4)).The highest performance(η)value is given for the Ⅱ-triangular rib case in all Re values,while the square-shaped ribs show a significant decrease in the η along the achieved Re range.The η value at Remax is 2.567 for the Ⅱ-triangular roughness case.Compared with the other simulated cases,this performance is decreased by about 3.768%in the case of Ⅰ-triangular ribs,15.249% in the case of Ⅲ-triangular ribs,20.802% in the case of trapezoidal ribs,while 27.541% in the case of square ribs,at the same Remax.Also,a comparison ismade with air-heat exchangers that have non-rough walls and contain cross-shaped VGs presented previously,in order to highlight the effectiveness of the rough surface presence in the baffled and finned channels.The obtained results indicated that the triangular-shaped rib(type Ⅱ)has the most significant hydrothermal behavior than the other cases.This indicates the necessity of roughness heat transfer surfaces for finned and baffled channels to improve significantly the performance of the air-heat exchangers they contain.

Simulating the Turbulent Hydrothermal Behavior of Oil/MWCNT Nanofluid in a Solar Channel Heat Exchanger Equipped with Vortex Generators

Re-engineering the channel heat exchangers(CHEs)is the goal of many recent studies,due to their great importance in the scope of energy transport in various industrial and environmental fields.Changing the internal geometry of the CHEs by using extended surfaces,i.e.,VGs(vortex generators),is the most common technique to enhance the efficiency of heat exchangers.This work aims to develop a newdesign of solar collectors to improve the overall energy efficiency.The study presents a new channel design by introducing VGs.The FVM(finite volume method)was adopted as a numerical technique to solve the problem,with the use of Oil/MWCNT(oil/multi-walled carbon nano-tubes)nanofluid to raise the thermal conductivity of the flow field.The study is achieved for a Re number ranging from12×10^(3) to 27×10^(3),while the concentration(φ)of solid particles in the fluid(Oil)is set to 4%.The computational results showed that the hydrothermal characteristics depend strongly on the flow patterns with the presence of VGs within the CHE.Increasing the Oil/MWCNT rates with the presence of VGs generates negative turbulent velocities with high amounts,which promotes the good agitation of nanofluid particles,resulting in enhanced great transfer rates.

Two-Capacitor Electrostatic Microgenerators

All modes of operation of a two-capacitor generator based on overflow of the charge accumulated in capacitors through the load resistance between two capacitors with antiphase modulated capacitances by means of in-plane or out-of-plane shift of the electrode plates under action of a mechanical force are analyzed paying the especial attention to fabrication of the generators with small sizes. Numerical solutions for all the modes are obtained, and they are found to be universal. Analytical estimates of the maximum power of the generator as a function of the capacitances modulation factor are derived. Experimental investigations of a two-capacitor rotational electric generator show that its characteristics are consistent with the analysis performed and that this analysis can be used to describe all specific features of operation of particular generators. Applications of the devices in micro-design for feeding the remote sensors are discussed.

On Multiplicative Generators of n-Dimensional Overlap Functions

In this paper, inspired by the multiplicative generators of overlap functions, we mainly propose the concepts of multiplicative generator pairs of n-dimensional overlap functions, in order to extend the dimensionality of overlap functions from 2 to n. We present the condition under which the pair (g, h) can multiplicatively generate an n-dimensional overlap function Og,h. we focus on the homogeneity and idempotency property on multiplicatively generated n-dimensional overlap functions.

A Novel Model Calculated Distribution Systems Planning Intergrated Distribution Generators for Competitive Electricity Markets

Recently, the distributed generator (DG) has been successfully studied and applied in distribution system at many countries around the world. Many planning models of the DG integrated distribution system have been proposed. These models can choose the optimization locations, capacities and technologies of DG with the objective function minimizing power loss, investment costs or total life cycle costs of the investment project. However, capacity of DG that uses renewable energy resources is natural variability according to primary energy. This study proposed a planning model of optimized distribution system that integrates DG in the competitive electricity market. Model can determine equipment sizing and timeframe requiring for upgrading equipment of distribution system as well as select DG technologies with power variable constraints of DG. The objective function is minimizing total life cycle cost of the investment project. The proposed model is calculated and tested for a 48-bus radial distribution system in the GAMS programming language.

A review on chemical oxygen supply technology within confined spaces: Challenges, strategies, and opportunities toward chemical oxygen generators(COGs)

Chemical oxygen generators(COGs)have been used worldwide in confined spaces as an emergency oxygen supply technology,mainly because they are independent and have a long shelf life.However,a number of challenges related to COGs remain unsolved,and a literature review of the current state of the technology is needed.First,the present article summarizes the basic information and applications of COGs,including their oxygen production mechanism,components,forming technology,and ignition system.Four current challenges encountered in applying COGs are discussed,along with the strategies adopted thus far to solve these problems,as found in the published literature.The literature survey reveals that,although much effort has been devoted to controlling the oxygen production rate and the heat output of COGs,the mechanism of producing toxic gases remains unclear and a reliable and safe ignition system has not been fully developed.Finally,future opportunities in the development of COGs are briefly listed.

Calculation of time-varying equivalent inductance and resistance of helical flux compression generators using the 2D filamentary method and dynamic matrix concept in the frequency domain

In this paper we present an approach to calculate the time-varying equivalent inductance and resistance of helical flux compression generators accurately. This approach is based on the 2D filamentary method and uses the dynamic matrix concept. By using this method, it is possible to consider both the effects of the armature presence and frequency on the inductance and resistance of the HFCGs. The latter effect has not been discussed in previous open literature. The validation of the presented method has been verified by measurement results.

Identification of Preferable Distributed Generators Locations for Congestion Relief in Multi-Bus Power Network

Installation of Distributed Generator (DG) is a well accepted method to improve power system operation from the point of reducing congestion and improving voltage profiles. For best results, Distributed Generators should be placed at strategic locations to exploit maximum benefits out of them. The (N-1) contingency criterion has been taken into account in this work. Most congested lines of the grids are ranked by congestion Index and considered to study the impact of DG penetration on congestion. The present paper proposes contribution factors of Distributed Generators for the placement of DG to keep the line flow within the capacity of each transmission line of the network. The results obtained from IEEE 30-bus test system indicate that the proposed methods are capable of identifying desirable DG location and its maximum allowable size. The influence of DG on bus voltage profile has also been demonstrated in this paper.

The Particularities of Coal-fired MHD Generators

This paper describes the particularities of coal-fired MHD generators in two aspects: the pysical phenomena near the electrode and the mathematical modeling.

Plasma Simulation of Dielectric-lined Multiwave Cerenkov Generators Producing High Power Millimeter Waves

This paper presents the concept of a Dielectric-lined Multiwave Cerenkov Generator producing high power millimeter waves, which has been investigated with a two and onehalf dimensional electromagnetic relativistic Particle-in-Cell (PIC) plasma simulation code. Themodified device can operate in a lower diode-voltage regime with much higher radiation efficiencyand slight downshift of operation frequency. There exist the optima for the permittivity of thedielectric liner and for the magnitude of the guiding magnetic field. The required intensity of theguiding field is reduced by the introduction of the liner. The enhanced propagation of the electronbeam is studied in the presence of the liner.

The Power of Group Generators and Relations: An Examination of the Concept and Its Applications

This paper investigates the approach of presenting groups by generators and relations from an original angle. It starts by interpreting this familiar concept with the novel notion of “formal words” created by juxtaposing letters in a set. Taking that as basis, several fundamental results related to free groups, such as Dyck’s Theorem, are proven. Then, the paper highlights three creative applications of the concept in classifying finite groups of a fixed order, representing all dihedral groups geometrically, and analyzing knots topologically. All three applications are of considerable significance in their respective topic areas and serve to illustrate the advantages and certain limitations of the approach flexibly and comprehensively.

Study of Eppler 423 Airfoil with Gurney Flap and Vortex Generators

In the past extensive research has been carried out, to study the effect of Gurney flap (GF) on symmetric and cambered airfoil for its usage in low Reynolds number regime. Use of GF at the trailing edge of the airfoil enhances the lift due to increase in the effective camber of the airfoil, which in turn improves the aerodynamic efficiency i.e. Cl/Cd. In the present study, Eppler 423 airfoil is used to first understand the aerodynamics of such a highly cambered airfoil and later GF of various sizes were added on it to understand the change in flow dynamics achieved by adding the GF and their impact on aerodynamic parameters such as Cl, Cd and Cl/Cd. Eppler 423 being a highly cambered airfoil produces high lift coefficient and smoother stall and by adding the GF of various sizes the performance of Eppler 423 improves tremendously and reason for this enhanced performance and effect of size of GF are presented in this paper. Vortex Generators (VG) generate counter rotating vortices that allow the flow to remain attached even at high angles of attack. Also, effect of adding VG at the leading edge of Eppler 423 aerofoil is presented in this paper. At last, results obtained from combination of VG at leading edge and GF at trailing edge on Eppler 423 aerofoil are discussed at length.

The Additive Generators of <i>n</i>-Dimensional Overlap Functions

In this paper, we introduce the concepts of additive generators and additive generator pair of n-dimensional overlap functions, in order to extend the dimensionality of overlap functions from 2 to n. We mainly discuss the conditions under which an n-dimensional overlap function can be expressed in terms of its generator pair.