scholarly journals The Thermal—Flow Processes and Flow Pattern in a Pulsating Heat Pipe—Numerical Modelling and Experimental Validation

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5952
Author(s):  
Przemysław Błasiak ◽  
Marcin Opalski ◽  
Parthkumar Parmar ◽  
Cezary Czajkowski ◽  
Sławomir Pietrowicz
Keyword(s):  
Heat Pipe ◽  
High Speed ◽  
Numerical Models ◽  
Input Parameter ◽  
Experimental Studies ◽  
Internal Flow ◽  
Numerical Analyses ◽  
Flow Structures ◽  
Pulsating Heat Pipe ◽  
Fixed Temperature

The aim of the article is to numerically model a two-dimensional multiphase flow based on the volume of fluid method (VOF) in a pulsating heat pipe (PHP). The current state of knowledge regarding the modeling of these devices was studied and summarised. The proposed model is developed within open source software, OpenFOAM, based on the predefined solver called interPhaseChangeFoam. The analyses were carried out in terms of the influence of four different mass transfer models between the phases, proposed by Tanasawa, Lee, Kafeel and Turan, and Xu et al. on the shape and dynamics of the internal flow structures. The numerical models were validated against data obtained from a specially designed experimental setup, consisting of three bends of pulsating heat pipes. The numerical calculations were carried out with ethanol being treated as a working medium and the initial and boundary conditions taken directly from the measurement procedures. The variable input parameter for the model was the heat flux implemented in the evaporation section and a fixed temperature applied to the condensation section. The flow structures obtained from the numerical analyses were compared and discussed with the flow structures gained from experimental studies by employing a high speed camera. In addition, to verify the quantitative results obtained from the numerical analyses with the experimental data, a technique called particle image velocimetry (PIV) was used for the velocity vector field. For the analysed velocity ranges, the relative error obtained was reached at the level of 10%.

scholarly journals Numerical and Experimental Study of Phase Transformations in Welding Processes / Badania Numeryczne I Doświadczalne Przemian Fazowych W Procesach Spawania

2015 ◽  
Vol 60 (4) ◽  
pp. 2559-2568 ◽  
Author(s):  
W. Piekarska
Keyword(s):  
Solid State ◽  
Heat Source ◽  
Phase Transformations ◽  
High Speed ◽  
Numerical Models ◽  
Experimental Studies ◽  
Butt Joint ◽  
Heat Of Fusion ◽  
Large Temperature ◽  
Welding Processes

The paper concerns the mathematical and numerical modeling of phase transformations in solid state occurring during welding. The analysis of the influence of heating rate, cooling rate and maximum temperatures of thermal cycles on the kinetics of phase transformations is presented. On the basis of literature data and experimental studies the evaluation of classic mathematical and numerical models of phase transformation is presented with respect to the advanced methods of welding by using a high speed and a high power heat source. The prediction of the structure composition in laser welded butt-joint made of S460 steel is performed, where phase transformations are calculated on the basis of modified numerical models. Temperature distributions are determined as well as the shape and size of fusion zone and heat affected zone (HAZ). Temperature field is obtained by the solution of transient heat transfer equation with convective term and external volumetric heat source taken into account. Latent heat of fusion, evaporation and heats generated during phase transformations in solid state are considered in the numerical algorithm due to the large temperature range present in analyzed process. Results of the numerical prediction of structure composition in HAZ are presented in this work. Obtained results of computer simulations are compared to experimental research performered on the laser welded joint.

Experimental Investigation of Fluid Motion in Pulsating Heat Pipe

2015 ◽  
Author(s):  
Hyung Yun Noh ◽  
Sung Jin Kim
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Latent Heat ◽  
High Speed ◽  
Fluid Motion ◽  
Pulsating Heat Pipe ◽  
Operating Characteristics ◽  
Two Phase ◽  
Saturation State ◽  
Circulation Mode

In this research, operating characteristics and heat transfer phenomena in 2-turn pulsating heat pipe operating in a circulation mode were experimentally investigated. Temperature, pressure and high-speed flow visualization data were obtained with the variation of diameters (1.2 mm, 1.7 mm and 2.2 mm) and input powers. The overall pressure variation from start-up to steady state was measured using the pressure transmitters in the evaporator section. Heat transfer phenomena were investigated using homogeneous-equilibrium model. Thermodynamic state of two-phase mixture at the exit of evaporator is identified as a saturation state using obtained temperature and pressure data. The ratio of sensible heat to latent heat changed with the variation of diameters and input powers. It was found that each evaporator has a different ratio and latent heat was dominant in most experimental cases.

Investigation of Material Deformation by the High-Speed Water Slugs

2002 ◽  
Author(s):  
O. Petrenko ◽  
E. S. Geskin ◽  
G. A. Atanov ◽  
B. Goldenberg ◽  
A. Semko
Keyword(s):  
Shock Waves ◽  
Nozzle Exit ◽  
High Speed ◽  
Numerical Models ◽  
Water Pressure ◽  
Experimental Studies ◽  
Surface Cleaning ◽  
Water Velocity ◽  
Material Deformation ◽  
The Impact

Water constitutes an attractive manufacturing tool It is readily available and clean. The waterjets are conventionally used for surface cleaning, material removal, and surface modification. The intrinsic shortcomings of such an application are the need in the use of expensive and heavy pumping facilities and, what are more important, peculiarities of the waterjet-substrate interaction which limit material deformation by the incoming jet. These shortcomings are eliminated if the workpiece is impacted by the array of the water slugs, generated by the direct injection of high-intensity energy pulses into the water vessel (barrel) and ejection the portion of the water via the nozzle attached into the barrel. Such a device (barrel-nozzle combination) will constitute an effective and versatile manufacturing tool. Understanding of the phenomena that occur in the course of the energy injection into the water is necessary for the design of the desired device. The phenomena in question are determined by the ratio between the speed of the water in the barrel in the course of the energy injection and the speed of the shock waves in the water. If this ratio is much less than unity, the exit velocity is determined by the ratio between the cross section areas of the nozzle exit and the barrel. If the ratio in question approaches the unity, the water velocity at the nozzle exit is determined by the impact pressure. The device utilizing this principle is termed the water extruder. If however, the ratio is much more than unity the exit water velocity is determined by the superposition of shock waves developed in the fluid. This device termed the water cannon is able to accelerate the water slug to the speed far exceeding 1,000 m/sec. The numerical and experimental studies of water extruder were carried out. The numerical models were constructed and the variation of the water velocity and the water pressure in the barrel were investigated. Experimental setup for the study of the water extruder was constructed by the modification of Remington power tool. The experiments involved the piercing of metal strips. The effect of operational conditions on the maximal depth of the piecing was determined. Another series of experiments involved the study of the slug impact on plastic (lead) and brittle (concrete) materials. The effect of the stand off distance on the removal of both kinds of material was investigated. As the result the suggestions about the way of construction of the water extruders and their practical applications were made.

Development of Two-Dimensional Bubble Movement and Development Benchmark Dataset for Numerical Validation

2012 ◽  
Author(s):  
Gholamreza Keshavarzi ◽  
Tracie J. Barber ◽  
Guan Yeoh
Keyword(s):  
High Speed ◽  
Numerical Models ◽  
Experimental Studies ◽  
Fluid Flows ◽  
Full Time ◽  
Two Phase ◽  
Point Of Interest ◽  
Time Shape ◽  
Computational Resources ◽  
Bubble Movement

The motion and transport of bubbles in fluid flows have many engineering applications. The rise of a bubble has been a point of interest for both numerical and experimental studies. Various tracking methodologies have been developed, including markers, level sets and volume tracking. In order to validate numerical models of bubble flow, detailed experimental data describing the transient bubble shape is needed. This is best found from a 2D comparison rather than 3D experiment because computational resources for determining an accurate shape can be maximized. No real full time shape and subsequent deformation of this 2D bubble has yet been demonstrated. In this paper 2D bubble experiments have been conducted, in which a single bubble has been injected inside a close-walled tank and the rising of the bubble has been captured through a high speed camera. This data is now being used as a benchmark for numerical interface capturing and two phase flow methodology validations.

scholarly journals Electromagnetic reducers in electromechanical systems

2021 ◽  
pp. 42-46
Author(s):  
Igor Tkachuk ◽  
Mykhailo Kovalenko
Keyword(s):  
Wind Turbines ◽  
High Speed ◽  
Numerical Models ◽  
Mechanical Energy ◽  
Experimental Studies ◽  
Total Weight ◽  
Electromechanical Systems ◽  
Low Speed ◽  
Electric Generator ◽  
Additional Noise

      Currently, due to the rising cost of electricity, low-power wind turbines (1-5 kW) are often used to supply consumers with electricity. In this case, wind turbines are used with both horizontal and vertical axes of rotation, the speed of which at an average wind speed V = 5 ÷ 10 m / s and is quite low, and is approximately n = 100 - 300 rpm. A low-speed electric generator for a wind generator with such a speed of rotation with a direct connection of the wind rotor shaft and the electric generator has a large number of poles and reaches a fairly large size. Therefore, magnifying gears (multiplexers) are often used and can increase the speed of the electric generator several times and, thus, reduce the mass of its active part, because the electromagnetic moment is proportional to the volume of the electric machine. However, manual transmissions are a source of additional noise, require frequent maintenance and reduce the durability of the wind turbine. This article will use permanent magnet reducers for wind turbines, which, unlike mechanical reducers, do not create additional noise, do not require lubrication, their durability is higher, operating costs are also significantly reduced, while the magnetic reducer can be integrated with an electric generator. at a wind rotor power P = 4 kW and speed n = 100-300 rpm, high-speed electric generator and magnetic reducer have approximately 2 times less total weight of magnets and 1.7 times less total weight of active materials (magnetic reducer + electric generator) than a low-speed multipole external generator. The aim of the study is to develop and implement an electromagnetic reducer in electromechanical systems. The basis of such systems are high-coercive magnets. To achieve this goal, the following tasks are set: - literary-patent search on the research topic; - selection of a prototype of a magnetic reducer and calculation of its main parameters; - development of graphical and numerical models to evaluate the effectiveness of the developed prototype; - optimization of the design of the magnetic reducer; - development of a system for converting mechanical energy with low potential into electricity; - prototyping and experimental studies of the system of conversion of mechanical energy with low potential into electrical energy

The Oscillation Behaviour of Liquid Metal in Arc Welding

2007 ◽  
Vol 539-543 ◽  
pp. 3877-3882 ◽  
Author(s):  
M.J.M. Hermans ◽  
B.Y.B. Yudodibroto ◽  
Yoshinori Hirata ◽  
G. den Ouden ◽  
I.M. Richardson
Keyword(s):  
Liquid Metal ◽  
Weld Pool ◽  
Arc Welding ◽  
High Speed ◽  
Numerical Models ◽  
Experimental Studies ◽  
Intermediate Step ◽  
Filler Wire ◽  
Research Activities ◽  
Penetration Control

This paper gives an historic overview and new developments of research activities in the field of the oscillatory behaviour of liquid metal in arc welding. Early work focused on the oscillation behaviour of the weld pool in Gas Tungsten Arc Welding (GTAW). Agitated weld pools exhibit specific modes of oscillation, the frequency of which can be measured from the arc voltage data and is conditioned by the geometry of the weld pool and the properties of the liquid metal. Of technological interest is the alteration of the oscillation behaviour for partially and fully penetrated situations, which can be used for penetration control during welding. A logical extension of the research activities was related to the influence of filler wire addition on the oscillation behaviour. An intermediate step towards the description of Gas Metal Arc Welding (GMAW), is the situation of GTAW with cold filler wire supply. It was found that both the liquid weld pool and the pendant liquid droplet at the tip of the filler wire experience an oscillation, which obscures the influence of the individual contributions of both liquid masses on the voltage data. It was shown that online penetration control is still possible, provided that the metal is transferred in an uninterrupted way, i.e. the filler wire flows smoothly into the weld pool. For GMAW, in which detached droplets collide with the weld pool surface, the difficulties are even more prominent. Recent work is related to this issue. Monitoring of the phenomena occurring at the weld pool and the pendant droplet become problematic by means of the voltage data. Observations by means of high-speed video imaging will be discussed. Apart from the experimental studies, efforts are undertaken in numerical simulations of the processes. A good correlation is obtained between experimental data and the results of the numerical models.

Investigation of Temperature Distribution in High-Speed End Mill Assisted by Heat Pipe Cooling

2011 ◽  
Vol 418-420 ◽  
pp. 1154-1157
Author(s):  
Qing Hua Song ◽  
Hua Wei Ju ◽  
Wei Xiao Tang
Keyword(s):  
Experimental Study ◽  
Temperature Field ◽  
Heat Pipe ◽  
High Speed ◽  
Experimental Studies ◽  
Solid Cylinder ◽  
End Mill ◽  
Milling Operations ◽  
Cylinder Model ◽  
Pipe Mill

A combined numerical and experimental study is performed to analyze the feasibility of using heat pipe cooling in milling applications. In this model, it is assumed that the end mill is subjected to a static heat source which verifies the analysis and feasibility of using heat pipe cooling in milling operations. The performance of heat pipe mill model is approximated using a solid cylinder model of pure conduction. Both the numerical and experimental studies show that the use of a heat pipe in a mill can reduce the temperature field significantly.

scholarly journals Nasal architecture: form and flow

2008 ◽  
Vol 366 (1879) ◽  
pp. 3225-3246 ◽  
Author(s):  
D.J Doorly ◽  
D.J Taylor ◽  
A.M Gambaruto ◽  
R.C Schroter ◽  
N Tolley
Keyword(s):  
Experimental Studies ◽  
Internal Flow ◽  
Control Flow ◽  
Flow Structures ◽  
Single Subject ◽  
Nasal Airflow ◽  
New Findings ◽  
Intimate Relation ◽  
Dynamical Features ◽  
And Control

Current approaches to model nasal airflow are reviewed in this study, and new findings presented. These new results make use of improvements to computational and experimental techniques and resources, which now allow key dynamical features to be investigated, and offer rational procedures to relate variations in anatomical form. Specifically, both replica and simplified airways of a single subject were investigated and compared with the replica airways of two other individuals with overtly differing geometries. Procedures to characterize and compare complex nasal airway geometry are first outlined. It is then shown that coupled computational and experimental studies, capable of obtaining highly resolved data, reveal internal flow structures in both intrinsically steady and unsteady situations. The results presented demonstrate that the intimate relation between nasal form and flow can be explored in greater detail than hitherto possible. By outlining means to compare complex airway geometries and demonstrating the effects of rational geometric simplification on the flow structure, this work offers a fresh approach to studies of how natural conduits guide and control flow. The concepts and tools address issues that are thus generic to flow studies in other physiological systems.

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