The stability of buoyancy‐driven rolls aligned with a shear flow when the temperature gradient is nonlinear

1985 ◽  
Vol 28 (1) ◽  
pp. 31-36 ◽  
Author(s):  
A. D. W. Jones
Keyword(s):  
Temperature Gradient ◽  
Shear Flow ◽  
The Stability

scholarly journals Thermodynamic and Energy Efficiency Analysis of a Domestic Refrigerator Using Al2O3 Nano-Refrigerant

2021 ◽  
Vol 13 (10) ◽  
pp. 5659
Author(s):  
Farhood Sarrafzadeh Javadi ◽  
Rahman Saidur
Keyword(s):  
Temperature Gradient ◽  
Technological Changes ◽  
Nanoparticle Concentration ◽  
Evaporator Temperature ◽  
Domestic Refrigerator ◽  
The Past ◽  
Nano Lubricant ◽  
The Stability ◽  
Energy Efficiency Analysis ◽  
Al2o3 Nanofluid

Refrigeration systems have experienced massive technological changes in the past 50 years. Nanotechnology can lead to a promising technological leap in the refrigeration industry. Nano-refrigerant still remains unknown because of the complexity of the phase change process of the mixture including refrigerant, lubricant, and nanoparticle. In this study, the stability of Al2O3 nanofluid and the performance of a nano-refrigerant-based domestic refrigerator have been experimentally investigated, with the focus on the thermodynamic and energy approaches. It was found that by increasing the nanoparticle concentration, the stability of nano-lubricant was decreased and evaporator temperature gradient was increased. The average of the temperature gradient increment in the evaporator was 20.2% in case of using 0.1%-Al2O3. The results showed that the energy consumption of the refrigerator reduced around 2.69% when 0.1%-Al2O3 nanoparticle was added to the system.

The stability of filamentary vorticity in two-dimensional geophysical vortex-dynamics models

1991 ◽  
Vol 231 ◽  
pp. 575-598 ◽  
Author(s):  
D. W. Waugh ◽  
D. G. Dritschel
Keyword(s):  
Green Function ◽  
Shear Flow ◽  
Stream Function ◽  
Potential Vorticity ◽  
Two Dimensional ◽  
Interaction Range ◽  
Inversion Operator ◽  
The Green Function ◽  
The Stability ◽  
Background Shear

The linear stability of filaments or strips of ‘potential’ vorticity in a background shear flow is investigated for a class of two-dimensional, inviscid, non-divergent models having a linear inversion relation between stream function and potential vorticity. In general, the potential vorticity is not simply the Laplacian of the stream function – the case which has received the greatest attention historically. More general inversion relationships between stream function and potential vorticity are geophysically motivated and give an impression of how certain classic results, such as the stability of strips of vorticity, hold under more general circumstances.In all models, a strip of potential vorticity is unstable in the absence of a background shear flow. Imposing a shear flow that reverses the total shear across the strip, however, brings about stability, independent of the Green-function inversion operator that links the stream function to the potential vorticity. But, if the Green-function inversion operator has a sufficiently short interaction range, the strip can also be stabilized by shear having the same sense as the shear of the strip. Such stabilization by ‘co-operative’ shear does not occur when the inversion operator is the inverse Laplacian. Nonlinear calculations presented show that there is only slight disruption to the strip for substantially less adverse shear than necessary for linear stability, while for co-operative shear, there is major disruption to the strip. It is significant that the potential vorticity of the imposed flow necessary to create shear of a given value increases dramatically as the interaction range of the inversion operator decreases, making shear stabilization increasingly less likely. This implies an increased propensity for filaments to ‘roll-up’ into small vortices as the interaction range decreases, a finding consistent with many numerical calculations performed using the quasi-geostrophic model.

Regulated hypothermia in the hypothyroid rat induced by administration of propylthiouracil

1997 ◽  
Vol 272 (5) ◽  
pp. R1390-R1395 ◽  
Author(s):  
Y. Yang ◽  
C. J. Gordon
Keyword(s):  
Drinking Water ◽  
Heat Stress ◽  
Temperature Gradient ◽  
Serum Levels ◽  
Male Rats ◽  
Light Phase ◽  
Grooming Behavior ◽  
Ambient Temperatures ◽  
Wide Range ◽  
The Stability

Propylthiouracil (PTU), an antithyroidal drug that reduces serum L-thyroxine (T4) and 3,5,3'-triiodothyronine (T3), is presumed to lower core temperature (T0) by impairing metabolic thermogenesis. However, it is not understood why PTU-treated animals cannot use behavioral and other thermoeffectors to maintain normal Tc. Male rats were administered PTU in drinking water (0.05 mg/ml) while the following parameters were measured: 1) Tc and motor activity (MA) recorded by radiotelemetry for 24 h at ambient temperatures (Ta) of 10-30 degrees C; 2) selected Ta, MA, and Tc in a temperature gradient; and 3) Tc, MA, and grooming behavior during exposure to heat stress (TH = 34.5 degrees C) for 2 h. PTU reduced serum levels of T4, and T3 by 95 and 60%, respectively. Tc decreased after 3 days of PTU treatment; a 0.5 degree C decrease in Tc persisted throughout the PTU treatment. PTU rats exposed to Ta of 10-30 degrees C maintained a consistent hypothermic Tc during the light phase; however, a deficit in the stability of Tc at night was noted during exposure to 10 degrees C. In the temperature gradient, PTU rats selected warmer Ta, but their Tc was maintained at the same hypothermic levels as observed at fixed Ta values of 15-30 degrees C. Heat stress caused Tc of control rats to increase to 39 degrees C, whereas Tc of the PTU rats was maintained below 38 degrees C. The regulation of Tc at hypothermic levels over a wide range of Ta values and when rats were housed in a temperature gradient indicates that chronic PTU induces a state of regulated hypothermia.

Low-frequency modulation of thermal instability

1970 ◽  
Vol 43 (2) ◽  
pp. 385-398 ◽  
Author(s):  
S. Rosenblat ◽  
D. M. Herbert
Keyword(s):  
Temperature Gradient ◽  
Asymptotic Solution ◽  
Frequency Modulation ◽  
Thermal Instability ◽  
Low Frequency ◽  
Experimental Results ◽  
Stability Criteria ◽  
The Stability ◽  
Boussinesq Fluid

A Boussinesq fluid is heated from below. The applied temperature gradient is the sum of a steady component and a low-frequency sinusoidal component. An asymptotic solution is obtained which describes the behaviour of infinitesimal disturbances to this configuration. The solution is discussed from the viewpoint of the stability or otherwise of the basic state, and possible stability criteria are analyzed. Some comparison is made with known experimental results.

Role of the shear flow profile on the stability of magnetic islands

2002 ◽  
Vol 9 (1) ◽  
pp. 371-374 ◽  
Author(s):  
A. I. Smolyakov ◽  
E. Lazzaro ◽  
R. Coelho ◽  
T. Ozeki
Keyword(s):  
Shear Flow ◽  
Flow Profile ◽  
Magnetic Islands ◽  
The Stability
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