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1
Content available On a couple-stress Rivlin-Ericksen ferromagnetic fluid heated from below with varying gravity, rotation, magnetic field and suspended particles flowing through a porous medium
Rahul, Sharma Naveen
International Journal of Applied Mechanics and Engineering
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2022
|
Vol. 27, no. 2
177--198
EN
The thermal instability of a couple-stress Rivlin-Ericksen ferromagnetic fluid with varying gravity field, suspended particles, rotation and magnetic field flowing through a porous medium is investigated. The dispersion relation has been developed and solved analytically using the normal mode approach and linear stability theory. The effect of suspended particles, rotation, couple stress, permeability and magnetic field on the fluid layer has been investigated. For stationary conventions, it is found that suspended particles always have a destabilizing effect for λ>0 and a stabilizing effect for λ<0 and couple-stress, magnetic field and permeability of the medium have a stabilizing effect on the thermal instability under certain conditions. In the absence of the rotation couple-stress has a stabilizing effect if λ >0 and a destabilizing effect if λ<0. Rotation has a stabilizing effect if λ >0 and a destabilizing effect if λ<0. In the absence of rotation permeability has a stabilizing effect if λ<0 and a destabilizing effect if λ>0. Magnetisation always has a stabilizing effect ( λ>0 or λ<0).
2
Content available remote Thermal instability of a Rivlin-Ericksen nanofluid saturated by a Darcy-Brinkman porous medium: a more realistic model
Rana G. C., Chand R., Sharma V.
Engineering Transactions
|
2016
|
Vol. 64, iss. 3
271--286
EN
In this paper, we study thermal instability in a horizontal layer of Rivlin-Ericksen elasticoviscous nanofluid in porous medium. Brinkman model is used as a porous medium and RivlinEricksen fluid model is used to describe the rheological behavior of nanofluid. In the earlier model (Chand and Rana [18]), we constrained both temperature and nanoparticle volume fractions at the boundaries of Rivlin-Ericksen nanofluid layer. In this paper, we assume that the value of temperature can be constrained on the boundaries, while the nanoparticle flux is zero on the boundaries. The considered boundary condition neutralizes the possibility of oscillatory convection due to the absence of two opposing forces, and only stationary convection occurs, in which Rivlin-Ericksen elastico-viscous nanofluid behaves like an ordinary nanofluid. The effects of Lewis number, medium porosity, modified diffusivity ratio, Darcy-Brinkman number and concentration Rayleigh number in stationary convection are discussed analytically and numerically. The results of this study are in good agreement with the results published earlier.
3
Content available remote Charakterystyki cieplen łożyska foliowego pracującego w podwyższonej temperaturze w warunkach rozbiegu, wybiegu i pracy ze stałą prędkością obrotową
Bagiński P., Banaszek S., Żywica G., Kiciński J.
Mechanik
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2015
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R. 88, nr 7CD
21--28
PL
W artykule zaprezentowano pomiary drgań węzłów łożyskowych wirnika posadowionego na aerodynamicznych łożyskach foliowych oraz pomiary rozkładu temperatur łożyska podczas pracy układu wirnikowego w podwyższonej temperaturze. Przeprowadzone badania pozwalają na określenie charakterystyk pracy układu wirnikowego w różnych warunkach, ilości i rozkładu generowanego ciepła, a także własności dynamicznych łożyska. Badania mogą również posłużyć do oceny bezpieczeństwa użytkowania oraz trwałości zaproponowanego układu wirnikowego.
EN
The paper presents the bearings vibration measurements of the rotor supported by aerodynamic foil bearings and the temperature distribution in the bearing during operation at elevated temperatures. The conducted experimental investigation allows to determine the operating conditions of such a rotor system, the amount and distribution of heat as well as the dynamic properties of the bearing. The results of the studies may help to carry out an evaluation of the durability and safety-in-use of the proposed rotor system.
4
Content available remote The test rig and investigation of the high-speed rotor supported by foil bearings at increased temperature
Bagiński P., Żywica G., Breńkacz Ł.
Zeszyty Naukowe. Cieplne Maszyny Przepływowe - Turbomachinery / Politechnika Łódzka
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2014
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nr 146
31--44
EN
This article presents the test plan and the design-build process to build the test rig for high-speed foil bearings whose main aim is to detect the thermal instability in FB. The authors present numerical analysis of the dynamic properties of rotors supported by air foil bearings. The calculations were performed on two versions of the rotor and two values of the clamping force concerning pressing the top foil onto the shaft. In addition, the article discusses the method for selecting the maximum dynamic load that can be safely applied for the rotors. For the calculation and presentation of the results the MESWIR and the GRAF-MESWIR software were used.
5
Content available remote Opracowanie stanowiska badawczego oraz koncepcja badań wysokoobrotowych łożysk foliowych
Bagiński P., Żywica G.
Mechanik
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2014
|
R. 87, nr 7CD
19—26
PL
Artykuł prezentuje koncepcje planu badań oraz proces budowy stanowiska badawczego wysokoobrotowych łożysk foliowych, opracowane w celu wykrycia zjawiska niestabilności termicznej w łożyskach foliowych (ŁF). Na początku pracy autorzy wyjaśnili, co rozumie się pod terminem niestabilności termicznej, następnie opisano koncepcję planu badań, jaki będzie realizowany na zbudowanym stanowisku. W etapie końcowej części artykułu opisano stanowisko do badań łożysk foliowych.
EN
This article presents the concepts of the study plan and the process of building the test rig for high-speed foil bearings whose main aim was to detect the thermal instability in FB. At the beginning of the work the authors explained what is meant by “thermal instability”, later described the concept of the study plan which will be implemented on the test rig. In the last step the article describes in detail the test rig for foil bearings.
6
Content available Hydromagnetic thermal instability of compressible Walters' (Model B') rotating fluid permeated with suspended particles in porous medium
Rana G. C., Jamwal H. S.
Studia Geotechnica et Mechanica
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2013
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Vol. 35, nr 4
75--88
EN
In this paper, the thermal instability of compressible Walters’ (Model B′) rotating fluid permeated with suspended particles (fine dust) in porous medium in hydromagnetics is considered. By applying normal mode analysis method, the dispersion relation has been derived and solved analytically. It is observed that the rotation, magnetic field, suspended particles and viscoelasticity introduce oscillatory modes. For stationary convection, Walters’ (Model B′) elastico-viscous fluid behaves like an ordinary Newtonian fluid and it is observed that rotation has stabilizing effect, suspended particles are found to have destabilizing effect on the system, whereas the medium permeability has stabilizing or destabilizing effect on the system under certain conditions. The magnetic field has destabilizing effect in the absence of rotation, whereas in the presence of rotation, magnetic field has stabilizing or destabilizing effect under certain conditions.
7
Content available Hall effect on thermal instability of viscoelastic dusty fluid in porous medium
Singh M., Gupta R. K.
International Journal of Applied Mechanics and Engineering
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2013
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Vol. 18, no. 3
871--886
EN
The effect of Hall currents and suspended dusty particles on the hydromagnetic stability of a compressible, electrically conducting Rivlin-Ericksen elastico viscous fluid in a porous medium is considered. Following the linearized stability theory and normal mode analysis the dispersion relation is obtained. For the case of stationary convection, Hall currents and suspended particles are found to have destabilizing effects whereas compressibility and magnetic field have stabilizing effects on the system. The medium permeability, however, has stabilizing and destabilizing effects on thermal instability in contrast to its destabilizing effect in the absence of the magnetic field. The critical Rayleigh numbers and the wave numbers of the associated disturbances for the onset of instability as stationary convection are obtained and the behavior of various parameters on critical thermal Rayleigh numbers are depicted graphically. The magnetic field, Hall currents and viscoelasticity parameter are found to introduce oscillatory modes in the systems, which did not exist in the absence of these parameters.
8
Content available Effect of magnetic field on thermal instability of Oldroydian viscoelastic rotating fluid in porous medium
Thakur R. C., Rana G. C.
International Journal of Applied Mechanics and Engineering
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2013
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Vol. 18, no. 2
555--569
EN
In this paper, we investigate the effect of a vertical magnetic field on thermal instability of an Oldroydian visco-elastic rotating fluid in a porous medium. By applying the normal mode analysis method, the dispersion relation governing the effects of rotation, magnetic field and medium permeability is derived and solved analytically and numerically. For the case of stationary convection, the Oldroydian viscoelastic fluid behaves like an ordinary Newtonian fluid and it is observed that rotation has a stabilizing effect while the magnetic field and medium permeability have a stabilizing/destabilizing effect under certain conditions on thermal instability of the Oldroydian viscoelastic fluid in a porous medium. The oscillatory modes are introduced due to the presence of rotation, the magnetic field and gravity field. It is also observed that the ‘principle of exchange of stability’ is invalid in the presence of rotation and the magnetic field.
9
Content available remote Thermal instability of Walters' (model B') elastico-viscous compressible fluid in the presence of Hall current
Kumar S., Gupta D., Jaswal R., Rana G. C.
Studia Geotechnica et Mechanica
|
2011
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Vol. 33, nr 3
61-72
EN
The thermal instability of a compressible elastico-viscous fluid is examined for viscoelastic polymeric solutions in the presence of uniform vertical magnetic field to include the Hall-current. These solutions are known as Walters' (model B') fluids and their rheology is approximated by the Walters' (model B') constitutive relations, proposed by WALTERS [12]. It is found that the stability criterion is independent of the effects of viscosity and viscoelasticity and is dependent on the magnitude of the magnetic field and Hall current. The magnetic field is found to stabilize a certain wave number range of the unstable configuration. The Hall current has destabilizing and stabilizing effects on the system.
10
Content available remote Effect of Hall currents on thermal instability of compressible dusty viscoelastic fluid in porous medium
Kumar P.
Studia Geotechnica et Mechanica
|
2011
|
Vol. 33, nr 4
25-38
EN
The thermal instability of compressible Walters B' viscoelastic fluid in porous medium is considered to include the effects of Hall currents and suspended particles. Following the linearized stability theory and normal mode analysis, the dispersion relation is obtained. For the case of stationary convection, Hall currents and suspended particles are found to have destabilizing effects whereas compressibility and magnetic field have stabilizing effects on the system. The medium permeability, however, has stabilizing and destabilizing effects on thermal instability in contrast to its destabilizing effect in the absence of magnetic field. The magnetic field, Hall currents and viscoelasticity parameter are found to introduce oscillatory modes in the system.
11
Content available remote Thermal instability of Rivlin-Ericksen elastico-viscous fluid permeated with suspended particles in hydrodynamics in a porous medium
Singh M., Gupta R. K.
International Journal of Applied Mechanics and Engineering
|
2011
|
Vol. 16, no 4
1169-1179
EN
The thermal instability of a layer of a Rivlin-Ericksen elastico-viscous fluid permeated with suspended particles in a porous medium acted on by a uniform magnetic field is considered. For stationary convection, the Rivlin-Ericksen elastico-viscous field behaves like a Newtonian fluid. The magnetic field is found to have a stabilizing effect, whereas suspended particles and medium permeability have a destabilizing effect for the case of stationary convection. The magnetic field introduces oscillatory modes in the systems, which were non-existent in its absence.
12
Content available remote Thermal instability of Rivlin-Ericksen elasto-viscous rotating fluid permeating with suspended particles under variable gravity field in porous medium
Rana G. C., Kumar S.
Studia Geotechnica et Mechanica
|
2010
|
Vol. 32, nr 4
39-54
EN
The problem of thermal instability of the Rivlin-Ericksen elasto-viscous fluid in a porous medium is considered in the presence of uniform rotation, suspended particles and variable gravity field. The rotation, gravity field, suspended particles and viscoelasticity introduce oscillatory modes. It is found that the principle of the exchange of stabilities is valid, provided that some condition is fulfilled. In a stationary convection, suspended particles are found to have destabilizing effect on the system, while rotation has stabilizing effect on the system under certain conditions. The effect of rotation, suspended particles, and medium permeability have also been shown graphically.
13
Content available remote Thermal instability of compressible electrically conducting couple-stress fluid in the presence of a uniform magnetic field
Singh M., Kumar P.
International Journal of Applied Mechanics and Engineering
|
2009
|
Vol. 14, no 3
879-889
EN
The problem of thermal instability of compressible, electrically conducting couple-stress fluid in the presence of a uniform magnetic field is considered. Following the linearized stability theory and normal mode analysis, the dispersion relation is obtained. For stationary convection, the compressibility, couple-stress and magnetic field postpone the onset of convection. Graphs have been plotted by giving numerical values to the parameters to depict the stability characteristics. The principle of exchange of stabilities is found to be satisfied. The magnetic field introduces oscillatory modes in the system that were non-existent in its absence. The case of overstability is also studied wherein a sufficient condition for the non-existence of overstability is obtained.
14
Content available remote Analiza czasu trwania I fazy pożaru w pomieszczeniu
Pofit-Szczepańska M., Konecki M.
Biuletyn Wojskowej Akademii Technicznej
|
2003
|
Vol. 52, nr 3
93-108
PL
Zanalizowano zjawisko rozgorzenia jako stanu niestabilności termicznej fazy gazowej powstałej nad powierzchnią spalania, w pomieszczeniu objętym pożarem. Rozgorzenie decyduje o przejściu pierwszej fazy pożaru w drugą, w pełni rozwiniętą fazę pożaru. W analizie wykorzystano korelację doswiadczalną McCaffreya, Quintierea i Harkleroada do wyprowadzenia ogólnej zależności, pozwalającej na obliczenie czasu do rozgorzenia. Obliczenia czasów do rozgorzenia wykonano dla pożarów o różnej dynamice, przy założeniu, że początek pożaru powstaje, a następnie rozwija się w środku pomieszczenia, bezpośrednio przy ścianie i w jego narożniku. W ocenie szybkości rozwoju pożaru uwzględniono wkład cieplny palnych wykładzin ściennych istniejących w pomieszczeniu. Uzyskane wyniki czasów do rozgorzenia przy wykorzystaniu korelacji MQH porównano z obliczeniami tej samej wielkości dla tych samych warunków z uzyskanymi przy wykorzystaniu zaawansowanej wersji modelu CFAST oraz z danymi doświadczalnymi.
EN
Using the known MQH fire test data correlation an expression for time to flashover in a relatively small rooms in the building was derived. For different fire dynamics and the source positions (for fires in the middle of a room, fires flush with walls, for fires in corners and for combustion of lining materials ignited in a corner) some calculations of time to flashover were carried out. Finally, the theoretical and large scale experimental results have been compared and discussed.
15
Content available remote On Bénard convection in a porous medium in the presence of throughflow and rotation in hydromagnetics
Sunil, Bharti P. K., Sharma R. C.
Archives of Mechanics
|
2003
|
Vol. 55, nr 3
257-274
EN
The effect of throughflow on a layer of a rotating fluid heated from below in porous medium in the presence of vertical magnetic field is considered. For the case of stationary convection, the rotation has always a stabilizing effect. The medium permeability has always a destabilizing effect whereas the magnetic field and the throughflow have always a stabilizing effects in the absence of rotation. But in the presence of rotation, the medium permeability is found to have a destabilizing effect whereas the magnetic field and the throughflow have a stabilizing effects under certain conditions. Graphs have been plotted by giving numerical values to the parameters, to depict the stability characteristics. The magnetic field and rotation introduce oscillatory modes in the system, which were nonexistent in their absence. The sufficient conditions for non-existence of the overstability are also obtained.
16
Content available remote On thermal convection in micropolar fluids in presence of suspended particles
Mohan H., Kumar P., Anjula
Studia Geotechnica et Mechanica
|
2002
|
Vol. 24, nr 3-4
53--63
PL
Opisano niestabilność termiczną płynów mikropolamych w obecności cząstek zawieszonych. Sprzężenie między ruchem wirowym a strumieniami ciepła może być przyczyną nadstabilnych stanów w układzie. Zawieszone cząstki wprowadzają także drgania w układzie, a wartość liczby Rayleigha zmniejsza się ze zwiększeniem liczby cząstek zawieszonych.
EN
The thermal instability of micropolar fluids in the presence of suspended particles has been considered. The coupling between spin and heat fluxes may bring overstable modes in the system. The suspended particles also introduce oscillatory modes in the system and the Rayleigh number is found to decrease with the increase in suspended particles.
17
Content available remote Thermal instability of friction pairs
Petrokovets M. I., Bogdanovich P. N., Tkachuk D. V.
Problemy Eksploatacji
|
1998
|
nr 3
189-198
PL
Rozważa się niestabilność termiczną par ciernych. Szczególną uwagę poświęcono niestabilności termicznej, która może być odpowiedzialna za zużycie zmęczeniowe. Przedstawiono badania doświadczalne niestabilności termosprężystej. Omówiono inne postacie niestabilności termicznej, między innymi niestabilność spowodowaną zależnością współczynnika tarcia od temperatury, reakcje tribochemiczne oraz zmiany sposobu tarcia.
EN
Thermal instability of friction pairs is considered. Particular attention is given to the thermoelastic instability which can be responsible for fatigue wear. Experimental study of thermoelastic instability is reported. Other modes of thermal instability are discussed, among them instabilities caused by temperature dependence of coefficient of friction, tribochemical reactions, or change in friction mode.
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