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1

Experimental investigation and performance prediction of SAH using different arc rib roughness geometries - A comparative study

Singh Jitendra, Lanjewar Atul

Archives of Thermodynamics

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2024

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Vol. 45, no 1

33--44

EN

This study aims to investigate and compare the thermal performance of a solar air heater using a passive technique to enhance heat transfer between the absorber plate and the flowing fluid. The technique involves generating turbulence near the heat transferring surface through the use of artificial rib roughness. The study focuses on two different novel roughness geometries: full symmetrical arc rib roughness and half symmetrical arc rib roughness. By introducing additional gaps and varying the number of gaps in the roughness geometries, the study examines their effects on the solar air heaters thermal performance. The artificially roughened surface creates different turbulent zones, which are essential to the development of different types of turbulence in the vicinity of the heat transferring surface. The study finds that an optimal escalation in Nusselt number and friction factor by 2.36 and 3.45 times, respectively, occurs at certain gap numbers as 6 and ng as 5 for full symmetrical arc rib roughness. The maximum thermal-hydraulic performance parameter of 1.66 is attained at a Reynolds number of 6 000. The study also conducts correlation, mathematical modeling, and performance prediction under different operating circumstances.

2

Enhancement of heat transfer in helical coil heat exchangers using nano-fluids

Parveez Malik, Hanief Mohammad

Chemical and Process Engineering

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2022

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Vol. 43, nr 2

279--283

EN

Investigation for heat transfer behaviour of Al2O3 and CuO nano-fluid in helical coil heat exchangers was carried out in this study. The thermo-physical properties of the fluids have temperature dependent nature. The main emphasis was to depict the influence of nano-particle concentration by volume on the characteristics of temperature, rate of heat transfer and heat transfer coefficients (convective). In order to enhance efficiency, density and thermal conductivity are considered to be the most important variables. In comparison to water and for equal flow rate, the rate of heat transfer of nano-fluid increases conspicuously. Efficiency of the helical coil heat exchanger increased by 38.80%.

3

Effect of aspect ratio of enclosure on free convection from horizontal cylinders in Bingham plastic fluids

Baranwal Ashok Kumar, Gupta Anoop Kumar, Tiwari Anurag Kumar, Melnik Roderick

Chemical and Process Engineering

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2022

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Vol. 43, nr 2

271--277

EN

Heat transfer in steady free convection from differentially heated cylinders enclosed in a rectangular duct filled with Bingham plastic fluids has been solved numerically for the ranges of the dimensionless groups as, Rayleigh number, 102 Ra 106; Prandtl number, 10 Pr 100 and, Bingham number, 0 Bn 50 for aspect ratios AR = 05, 0.6, 0.7, 0.8, 0.9 and 2. The streamlines, isotherm contours, yield surfaces, local and average Nusselt numbers were analysed and discussed. It is found that as the aspect ratio of the enclosure increases from 0.5 to 0.9, the average Nusselt number on the surface of the hot cylinder increases as a larger amount of fluid takes part in convection. Moreover, at sufficiently large Bingham numbers, yield stress forces dominate over buoyancy causing the flow to cease and thus the Nusselt number approaches its conduction limit. Finally, the Nusselt number approaches its conduction limit once the maximum Bingham number is reached.

4

Effect of aiding buoyancy on heat transfer from an isothermal square cylinder in power-law fluids

Mishra Pragya, Mishra Lubhani, Tiwari Anurag Kumar

Chemical and Process Engineering

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2022

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Vol. 43, nr 2

265–-270

EN

The aim of the present study was to explore the influence of aiding buoyancy on mixed convection heat transfer in power-law fluids from an isothermally heated unconfined square cylinder. Extensive numerical results on drag coefficient and surface averaged values of the Nusselt number are reported over a wide range of parameters i.e. Richardson number, 01 Ri 5, power-law index, 04 𝑛 18, Reynolds number, 01 Re 40, and Prandtl number, 1 Pr 100. Further, streamline profiles and isotherm contours are presented herein to provide an insight view of the detailed flow kinematics

5

Behaviour of a non-newtonian fluid in a helical tube under the influence of thermal buoyancy

Ramla Mohamed, Laidoudi Houssem, Bouzit Mohamed

Acta Mechanica et Automatica

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2022

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Vol. 16, no. 2

111--118

EN

This work is an evaluative study of heat transfer in the helical-type heat exchanger. The fluid used is non-Newtonian in nature and is defined by Oswald’s model. The work was performed numerically by solving each of the Navier–Stokes equations and the energy equation using the package ANSYS-CFX. Following are the aspects that have been dealt with in this paper: the effects of thermal buoyan-cy, fluid nature and the tube shape on the heat transfer, and the fluid comportment. The interpretation of the obtained results was done by analyzing the isotherms and the streamlines. The mean values of the Nusselt number were also obtained in terms of the studied parame-ters. The results of this research enabled us to arrive at the following conclusion: the intensity of thermal buoyancy and the nature of the fluid affect the heat transfer distribution but keep the overall rate of heat transfer the same.

6

Flow features of thermophoretic MHD viscous fluid flow past a converging channel with heat source and chemical reaction

Kalita B. K., Choudhury R.

International Journal of Applied Mechanics and Engineering

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2021

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Vol. 26, no. 3

72--83

EN

A boundary layer flow of an electrically conducting viscous fluid past a converging channel in the presence of thermophoresis, heat source, chemical reaction, viscous dissipation and simultaneous heat and mass transfer characteristics is studied in the paper. An external magnetic field of uniform strength is applied transversely to the channel. The similarity solution has been used to transform the partial differential equations that represent the problem into a boundary value problem of coupled ordinary differential equations, which in turn are solved numerically using MATLAB’s built in solver bvp4c. Numerical computations are carried out to solve the problem and graphical illustrations are made to get the physical insight of the same. The convergent channel flow problem of an incompressible electrically conducting viscous fluid in the presence of a magnetic field has a wide range of applicability in different areas of engineering, specially in industrial metal casting and control of molten metal flow.

7

Numerical modeling of heat transfer in Al2O3/H2O nanofluid flowing through a Bessel-like converging pipe

Iweka Chukwuka S., Fadodun Olatomide G.

Archives of Thermodynamics

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2021

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Vol. 42, no 2

121--153

EN

This paper studies hydrodynamic and heat transfer performance of Al2O3/H2O nanofluid flowing through a Bessel-like converging pipe in laminar flow regime using the computational fluid dynamic approach. A parametric study was carried out on the effect of Reynolds number (300– 1200), convergence index (0-3) and nanoparticle concentration (0–3%) on the both hydrodynamic and thermal fields. The results showed the pressure drop profile along the axial length of the converging pipes is parabolic compared to the downward straight profile obtained in a straight pipe. Furthermore, an increase in convergence index, Reynolds number and nanoparticle concentration were found to enhance convective heat transfer performance. Also, a new empirical model was developed to estimates the average Nusselt number as a function of aforementioned variables. Finally, the result of the thermohydraulic performance evaluation criterion showed that the usage of Bessel-like converging pipes is advantageous at a low Reynolds number.

8

The complex Ginzburg Landau model for an oscillatory convection in a rotating fluid layer

Manjula S. H., Kiran P., Reddy P. Raj, Bhadauria B. S.

International Journal of Applied Mechanics and Engineering

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2020

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Vol. 25, no. 1

75--91

EN

A weakly nonlinear thermal instability is investigated under rotation speed modulation. Using the perturbation analysis, a nonlinear physical model is simplified to determine the convective amplitude for oscillatory mode. A non-autonomous complex Ginzburg-Landau equation for the finite amplitude of convection is derived based on a small perturbed parameter. The effect of rotation is found either to stabilize or destabilize the system. The Nusselt number is obtained numerically to present the results of heat transfer. It is found that modulation has a significant effect on heat transport for lower values of ωf while no effect for higher values. It is also found that modulation can be used alternately to control the heat transfer in the system. Further, oscillatory mode enhances heat transfer rather than stationary mode.

9

Numerical investigation and sensitivity analysis of turbulent heat transfer and pressure drop of Al2O3/H2O nanofluid in straight pipe using response surface methodology

Fadodun Olatomide G., Amosun Adebimpe A., Salau Ayodeji O., Olaloye David O., Ogundeji Johnson A., Ibitoye Francis I., Balogun Fatai A.

Archives of Thermodynamics

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2020

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Vol. 41, no 1

3--30

EN

In this paper, investigation of the effect of Reynolds number, nanoparticle volume ratio, nanoparticle diameter and entrance temperature on the convective heat transfer and pressure drop of Al2O3/H2O nanofluid in turbulent flow through a straight pipe was carried out. The study employed a computational fluid dynamic approach using single-phase model and response surface methodology for the design of experiment. The Reynolds average Navier-Stokes equations and energy equation were solved using k-ε turbulent model. The central composite design method was used for the response-surface-methodology. Based on the number of variables and levels, the condition of 30 runs was defined and 30 simulations were performed. New models to evaluate the mean Nusselt number and pressure drop were obtained. Also, the result showed that all the four input variables are statistically significant to the pressure drop while three out of them are significant to the Nusslet number. Furthermore, sensitivity analysis carried out showed that the Reynolds number and volume fraction have a positive sensitivity to both the mean Nusselt number, and pressure drop, while the entrance temperature has negative sensitivities to both.

10

Heat transfer and friction factor correlation for inclined spherical ball roughened solar air heater

Murmu Ramesh, Kumar Parmanand, Singh Hari N.

Archives of Thermodynamics

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2020

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Vol. 41, no 2

3--34

EN

Flow mechanism under roughened solar air heater is quite complex. This paper is an effort towards determining the governing equations for heat transfer and friction factor for inclined spherical balls roughened ducts. With the availability of these equations, it is easier to predict the thermal and thermohydraulic performance of such roughened solar air heaters. The governing equations are derived based on the experimental data generated under actual outdoor condition at the test rig designed and fabricated at the terrace of the Mechanical Engineering Department, the National Institute of Technology Jamshedpur in India, in terms of roughness and flow parameters. Maximum augmentation in Nusselt number and friction factor for varying relative roughness pitch, relative roughness height, spherical ball height to diameter ratio, and angle of attack was respectively found to be of the order of 2.1 to 3.54 times, 1.87 to 3.21 times, 2.89 to 3.27 times and 1.74 to 3.56 times for Nusselt number and 0.84 to 1.79 times, 1.46 to 1.91 times, 1.67 to 2.34 times and 1.21 to 2.67 times for friction factor in comparison to non-roughened duct. The optimum roughness parameters under present investigation have been found.

11

Augmentation in heat transfer and friction of three sides over one side dimple roughened solar duct

Kumar Vikash

Archives of Thermodynamics

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2020

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Vol. 41, no 3

57--89

EN

Providing roughness is an effective method to heat fluids to high temperature. Present paper make use of concave dimple roughness on one and three sides of roughened ducts aimed at determining rise in heat transfer and friction of three sides over one side roughened duct. Three sides roughened duct produces high heat transfer compared to one side roughened. Results are shown as a rise in Nusselt number and friction factor of three sides over one side roughened duct. Experimental investigation was conducted under actual outdoor condition at National Institute of Technology Jamshedpur, India to test various sets of roughened collectors. Roughness parameter varied as relative roughness pitch 8–15, relative roughness height 0.018–0.045, dimple depth to diameter ratio 1–2, Reynolds number 2500– 13500 at fixed aspect ratio (width/hight) 8. Highest enhancement in Nusselt number for varying relative roughness pitch, height, and diameter ratio was respectively found as 2.6 to 3.55 times, 1.91 to 3.42 times and 3.09 to 3.94 times compared to one side dimple roughened duct. Highest rise in friction for three sides over one side roughened duct for these varying parameters was respectively found as 1.62 to 2.79 times, 1.52 to 2.34 times and 2.21 to 2.56 times. To visualize the effect of roughness parameter on heat transfer and friction factor, variation in Nusselt number and friction factor for varying roughness parameters with Reynolds number is shown.

12

Vertical heat transport at infinite Prandtl number for micropolar fluid

Caggio M., Kalita P., Łukaszewicz G., Mizerski K. A.

Archives of Mechanics

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2020

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Vol. 72, nr 6

525--553

EN

We investigate the upper bound on the vertical heat transport in the fully 3D Rayleigh–Bénard convection problem at the infinite Prandtl number for a micropolar fluid. We obtain a bound, given by the cube root of the Rayleigh number, with a logarithmic correction. The derived bound is compared with the optimal known one for the Newtonian fluid. It follows that the (optimal) upper bound for the micropolar fluid is less than the corresponding bound for the Newtonian fluid at the same Rayleigh number. Moreover, strong microrotational diffusion effects can entirely suppress the heat transfer. In the Newtonian limit our purely analytical findings fully agree with estimates and scaling laws obtained from previous theories significantly relying on phenomenology.

13

Application of Nanoparticles in the Process of Phase Change Paraffin in a Chamber

Alizadeh As’ad

Advances in Science and Technology. Research Journal

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2019

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Vol. 13, no 3

113--119

EN

In this study, melting of a phase changing material enriched with nanoparticles in a circular ring-rectangular enclosure was investigated and the results were analyzed. At the beginning of the melting process in the absence of a natural displacement, the mechanism of conduction heat transfer around the hot cylinder is the dominant mechanism. Over time, natural displacement gradually appears and deforms the melting boundary above the cylinder. Over time, when the thickness of the liquid phase grows, the thermal resistance increases, this can be verified by reviewing the Nusselt chart. So this phenomenon reduces the rate of melting and temperature changes. The results show that increasing the nanoparticle volume fraction due to increased conductivity and decreasing latent heat causes an increase in the melting rate and the amount of energy absorbed. From the study of various volume fractions, it can be concluded that the use of a higher volume fraction of 3% is more appropriate both in terms of energy and in terms of the melting rate. However, it should be taken into account that if the melting rate exceeds this value, it may cause agglomeration and deposition of nanoparticles and reducing system efficiency.

14

Wpływ geometrii dysz stosowanych w strumieniowych układach chłodzenia na wymianę ciepła

Marzec K.

Modelowanie Inżynierskie

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2018

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T. 37, nr 68

75--84

PL

W ramach badań objętych niniejszą pracą analizowano wpływ zastosowania różnej geometrii dysz (cylindryczne, zbieżne oraz rozbieżne) na rozkład wartości liczby Nusselta podczas chłodzenia płaskiej płyty z wykorzystaniem strumieniowego układu chłodzenia składającego się z dziesięciu równomiernie rozmieszczonych dysz skierowanych prostopadle do powierzchni chłodzonej. Pierwszym krokiem prowadzonych badań było określenie najkorzystniejszej wartości parametru Y/D. Bezwymiarowa wartość Y/D określa odległość pomiędzy dyszą a powierzchnią chłodzącą Y w odniesieniu do średnicy dyszy D. Określenie tego bezwymiarowego współczynnika stanowiło podstawę do wykonania dalszych obliczeń cieplno-przepływowych układów chłodzenia o różnej geometrii dysz chłodzących. Równania opisujące przepływy oraz wymianę ciepła rozwiązano numerycznie metodą elementów skończonych za pomocą solvera Ansys CFX wykorzystując metodę RANS.

EN

This study analyzed the influence of application of various nozzle shape (cylindrical, convergent and divergent) on the Nusselt number distribution under impinged cooling of a flat surface. Cooling system composed of an inline array of ten uniformly arranged jets directed perpendicularly to the target surface. At the beginning of the calculations the most effective dimensionless factor Y/D was determined. This parameter described distance between nozzle and cooled surface Y in relation to the jet diameter D. Defining most effective Y/D parameter was a basis for further examinations of the impinging jets with various geometry of the cooling nozzles. The analyses of the flow and heat transfer characteristics were carried out using finite element method, software Ansys CFX and RANS approach.

15

Transient natural convection in partitioned enclosures

Zemani F., Sabeur-Bendehina A.

Mechanics and Mechanical Engineering

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2018

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Vol. 22, nr 4

1015--1030

EN

In this paper, the natural convection flow in a cavity heated differentially with a partition placed in the middle of the hot wall is numerically simulated. The aspect ratio of the geometry, Prandtl number are fixed at 0.24, 6.64, respectively, for different partitions lengths; however the Rayleigh number values were ranging from 106 to 3:77 x 109 in order to observe the transition regime. The fluid flow and the heat transfer described in terms of continuity, linear momentum and energy equations were predicted by using the finite volume method. To approach the physical reality experience, calculations were performed in a cavity with the same size and same priority of the fluid with an average temperature Tm imposed on the cooled wall, also another simulation with an average temperature Tm imposed on the horizontal wall. Time evolution, isotherms and mean Nusselt number are presented for all investigated values. Representative results illustrating the effects of the partition length for the heat transfer and the thermal boundary layer are also reported and discussed. The results indicate that the flow and heat transfer properties are altered by the presence of the partition, especially in the initial stage. In a certain sense, the partition blocks the flow and forces it to come off the hot wall. Since the partition parameters are critical for the transient natural convection ow in the cavity, different partition lengths on the warm wall have been studied.

16

Numerical study of natural convection in a vertical cylindrical partially annular

Medebber M. A., Retiel N.

Mechanics and Mechanical Engineering

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2018

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Vol. 22, nr 1

77--92

EN

A study of free convection in a vertical cylinder partially annulus is conducted numerically. Uniform temperature is imposed cross a vertical wall, while the top and bottom walls are adiabatic. The governing equations are solved numerically by using a finite volume method. The coupling between the continuity and momentum equations is effected using the SIMPLER algorithm. Solutions have been obtained for Prandtl numbers equal to 7.0, Rayleigh numbers of 103 to 106 and height ratios of 0 to 1. The influence of physical and geometrical parameters on the streamlines, isotherms, average Nusselt has been numerically investigated.

17

Thermal and hydraulic phenomena in boundary layer of minijets impingement on curved surfaces

Kura T., Fornalik-Wajs E., Wajs J.

Archives of Thermodynamics

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2018

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Vol. 39, no 1

147--166

EN

Presented work considers flow and thermal phenomena occurring during the single minijet impingement on curved surfaces, heated with a constant heat flux, as well as the array of minijets. Numerical analyses, based on the mass, momentum and energy conservation laws, were conducted, regarding single phase and two-phase simulations. Focus was placed on the proper model construction, in which turbulence and boundary layer modeling was crucial. Calculations were done for various inlet parameters. Initial single minijet results served as the basis for the main calculations, which were conducted for two jet arrays, with flat and curved heated surfaces. Such complex geometries came from the cooling systems of electrical devices, and the geometry of cylindrical heat exchanger. The results, regarding Nusselt number, heated surface temperature, turbulence kinetic energy, production of entropy and vorticity, were presented and discussed. For assumed geometrical parameters similar results were obtained.

18

Numerical investigation of local heat transfer distribution on surfaces with a non-uniform temperature under an array of impinging jets with various nozzle shapes

Marzec K., Kucaba-Piętal A.

Journal of Theoretical and Applied Mechanics

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2017

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Vol. 55 nr 4

1313--1324

EN

Numerical calculations of heat transfer characteristics of an impingement cooling system with a non-uniform temperature on a cooled surface using ANSYS CFX have been performed. The influence of a surface heat flux qw(x) and a nozzle shape on the Nusselt number distribution on the cooled surface has been studied. The setup consisted of a cylindrical plenum with an inline array of ten impingement jets. Cylindrical, convergent divergent shapes of nozzles and linear temperature distribution on the cooled surface have been considered for various heat fluxes qw (x). Results indicate that geometry of the cylindrical nozzles resulted in the highest Nusselt numbers along the cooled surface. The line of the averaged Nusselt number has a trend to increase in the direction of the flow for the cooling system with increasing values of the surface heat flux q(x). This tendency can be observed for all presented shapes of jets. On the other hand, for decreasing functions of the heat flux qw (x), the Nusselt number distribution is more uniform. It can be observed for all types of nozzles. Very similar values of the Nusselt number occur especially for the non-uniform heat flux 5000-2500W/m². For constant values of the heat flux q(x) = 5000W/m², the line of the average Nusselt number has a trend to increase slightly in the direction of the flow. Numerical analysis of different mesh density results in good convergence of the GCI index, what excludes mesh size dependency. The presented study is an extension of the paper (Marzec and Kucaba-Piętal, 2016) and aims at answering the question how the Nusselt number distribution on the cooled surface is affected by various geometries of nozzles for a non-uniform surface heat flux qw (x).

19

Jednomianowy model liczby Nusselta w pomiarze zmiennej temperatury metodą "w ciemno" przy niestacjonarnych przepływach

Nabielec J., Jamróz P.

Zeszyty Naukowe Wydziału Elektrotechniki i Automatyki Politechniki Gdańskiej

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2016

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Nr 49

79--84

PL

Pomiar zmiennej w czasie temperatury medium poruszającego się ze zmienną prędkością obarczony jest istotnym błędem dynamicznym. Jego źródłem są zależne od tej prędkości właściwości dynamiczne toru pomiarowego określone przez współczynnik dynamiki. Metoda "w ciemno" umożliwia zidentyfikowanie jego chwilowych wartości i skorygowanie błędu dynamicznego na drodze numerycznej. Zadanie to jest dobrze postawione przy wykorzystaniu jednomianowej reprezentacji liczby Nusselta, od której zależy chwilowa wartość tego współczynnika. W artykule zaprezentowano podstawy teoretyczne metody pomiarowej, wyniki badań symulacyjnych oraz eksperymentalnej jej weryfikacji.

EN

Measurement result of time-varying temperature of the medium moving at a variable velocity is encumbered with a significant dynamic error. The main reason of that error are the dynamic properties of the measurement channel described by the dynamic coefficient. The “blind” correction method gives a possibility of identifying the instantaneous values of this factor and numerically correcting the dynamic error. This task is well defined when the monomial Nusselt number is used in a dynamic coefficient model. The article presents the theoretical basis of the measurement method, the simulation results and experimental verification.

20

Soret and Dufour effects on MHD free convective flow past a vertical porous plate in the presence of heat generation

Reddy G. V. R.

International Journal of Applied Mechanics and Engineering

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2016

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Vol. 21, no. 3

649--665

EN

An MHD fluid flow is examined over a vertical plate in the presence of Dufour and Soret effects. The resulting momentum, energy and concentration equations are then made similar by introducing the usual similarity transformations. These similar equations are then solved numerically using the Runge-Kutta fourth order method with shooting technique. The effects of various parameters on the dimensionless velocity, temperature and concentration profiles as well as the local values of the skin-friction coefficient, the Nusselt number and Sherwood number are displayed graphically and in a tabular form. A comparison with previously published work is obtained and an excellent agreement is found.