An Approximate Analysis of the Influence of Aerodynamic Heating and Initial Twist on the Torsional Stiffness of Thin Wings

1960 ◽  
Vol 27 (2) ◽  
pp. 332-334
Author(s):  
Lit S. Han
Keyword(s):  
Critical Temperature ◽  
Temperature Difference ◽  
Torsional Stiffness ◽  
Aerodynamic Heating ◽  
Approximate Analysis ◽  
Fiber Stress ◽  
Aspect Ratios ◽  
Thin Wing ◽  
Approximate Formulas

In the present paper, approximate formulas are derived, based on the “fiber-stress” concept, for the combined influence of aerodynamic heating and initial twist on the torsional stiffness of a thin wing. Criteria are established for calculating the critical temperature difference between that of the edges and that of the mid-chord position, for preventing possible aeroelastic reversals or buckling. Formulas are valid for wings with large aspect ratios.

Numerical Simulation of Thermocapillary Convection in an Annular Pool of Silicone Oil Heated From Inner Wall

2007 ◽  
Author(s):  
Wanyuan Shi ◽  
Nobuyuki Oshima ◽  
Nobuyuki Imaishi
Keyword(s):  
Numerical Simulation ◽  
Critical Temperature ◽  
Temperature Gradient ◽  
Numerical Simulations ◽  
Temperature Difference ◽  
Significant Influence ◽  
Thermocapillary Convection ◽  
Silicone Oil ◽  
Annular Pool ◽  
Surface Temperature Gradient

Thermocapillary convection in a shallow annular pool (depth d = 1 mm) of silicone oil (0.65 cSt, Pr = 6.7), heated from the inner wall, is investigated by numerical simulations. Under a fixed value of temperature difference between the outer and inner walls, surface temperature gradient in the inner heated pool is about 10% higher than that in the outer heated pool. Accordingly, the critical temperature difference for the incipience of HTW (ΔTc = 4.58K) is smaller than that (ΔTc = 5.0K) in the outer heated pool. Numerical simulations indicate that two groups of HTW, propagating in opposite azimuthal directions to each other, coexist and produce interference patterns in the inner heated pool. Rotation of the pool around its axis gives no significant influence on the behavior of HTW in the inner heated pool. The characteristics of HTW are discussed in contrast with those in the outer heated pool.

scholarly journals Thermal delay of drop coalescence

2017 ◽  
Vol 833 ◽  
Author(s):  
Michela Geri ◽  
Bavand Keshavarz ◽  
Gareth H. McKinley ◽  
John W. M. Bush
Keyword(s):  
Critical Temperature ◽  
Residence Time ◽  
Temperature Difference ◽  
Initial Temperature ◽  
Theoretical Study ◽  
Fluid Viscosity ◽  
Drop Coalescence ◽  
Thermocapillary Flows ◽  
Silicone Oils ◽  
Thermal Delay

We present the results of a combined experimental and theoretical study of drop coalescence in the presence of an initial temperature difference $\unicode[STIX]{x0394}T_{0}$ between a drop and a bath of the same liquid. We characterize experimentally the dependence of the residence time before coalescence on $\unicode[STIX]{x0394}T_{0}$ for silicone oils with different viscosities. Delayed coalescence arises above a critical temperature difference $\unicode[STIX]{x0394}T_{c}$ that depends on the fluid viscosity: for $\unicode[STIX]{x0394}T_{0}>\unicode[STIX]{x0394}T_{c}$, the delay time increases as $\unicode[STIX]{x0394}T_{0}^{2/3}$ for all liquids examined. This observed dependence is rationalized theoretically through consideration of the thermocapillary flows generated within the drop, the bath and the intervening air layer.

The Effect of the Temperature Difference on the Performance of Photovoltaic-Thermoelectric Hybrid Systems

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
M. El Mliles ◽  
Y. El Kouari ◽  
A. Hajjaji
Keyword(s):  
Critical Temperature ◽  
Hybrid System ◽  
Temperature Difference ◽  
Efficiency Enhancement ◽  
Cell Efficiency ◽  
High Power Factor ◽  
Pv Cell ◽  
Te Material ◽  
Increasing Temperature ◽  
Selection Of

The performance of the photovoltaic-thermoelectric (PV-TE) hybrid system was examined using three types of PV cells and a thermoelectric generator (TEG) based on bismuth telluride. The investigated PV cells are amorphous silicon (a-Si), monocrystalline silicon (mono-Si), and cadmium telluride (CdTe). The results showed that the TEG contribution can overcome the degradation of the PV cell efficiency with increasing temperature at the minimal working condition. This condition corresponds to the critical temperature difference across the TEG that guarantees the same efficiency of the hybrid system as that of the PV cell alone at 298 K. The obtained results showed that the critical temperature difference is 13.3 K, 44.1 K, and 105 K for the a-Si, CdTe, and mono-Si PV cell, respectively. In addition, the general expression of the temperature difference across the TEG needed for an efficiency enhancement by a ratio of r compared with a PV cell alone at 298 K was given. For an efficiency enhancement by 5 % (r = 1.05), the temperature difference required is 30.2 K, 61.3 K, and 116.1 K for the a-Si, CdTe, and mono-Si PV cells, respectively. These values cannot be achieved practically only in the case of the a-Si PV cell. Moreover, a TE material with a high power factor can reduce this temperature difference and improve the performance of the hybrid system. This work provides a tool that may be useful during the selection of the PV cell and the TE material for the hybrid system.

scholarly journals Elastic foundation effect on nonlinear thermo-vibration of embedded double-layered orthotropic graphene sheets using differential quadrature method

2012 ◽  
Vol 227 (4) ◽  
pp. 862-879 ◽  
Author(s):  
Ali Ghorbanpour Arani ◽  
Reza Kolahchi ◽  
Ali Akbar Mosallaie Barzoki ◽  
Mohammad Reza Mozdianfard ◽  
S Mosatafa Noudeh Farahani
Keyword(s):  
Aspect Ratio ◽  
Graphene Sheet ◽  
Temperature Difference ◽  
Frequency Ratio ◽  
Differential Quadrature Method ◽  
Differential Quadrature ◽  
Graphene Sheets ◽  
Nonlinear Frequency ◽  
Quadrature Method ◽  
Aspect Ratios

In this article, transverse nonlinear vibration of orthotropic double-layered graphene sheets embedded in an elastic medium (spring and shear constants of the Winkler and Pasternak models) under thermal gradient is studied using nonlocal elasticity orthotropic plate theory. The equations of motion are derived based on application of Hamilton’s principles. These are coupled, two-dimensional and time-dependent equations, which cannot be solved analytically due to their nonlinear terms. Hence, differential quadrature method is employed to solve the governing differential equations for the two boundary conditions of simply and clamped support in all four sides. The plots for the ratio of nonlinear to linear frequencies versus maximum transverse amplitude for armchair and zigzag graphene sheet structures are presented to investigate the effects of nonlocal parameters, Winkler and Pasternak effects, temperature, and various aspect ratios. The study also indicates that the nonlinear effect represented by nonlinear frequency ratio is considerable at lower Winkler and Pasternak constants, length aspect ratio and thickness aspect ratio while it might be neglected for higher values of these parameters. Regarding the influence of temperature difference on support type, with increased temperature difference, nonlinear frequency ratio increases when the graphene sheet is simply supported, but for clamped one, no specific change in nonlinear frequency ratio is observed.

An Experimental Synthesis of Quartz, Albite, and Analcite

1950 ◽  
Vol 87 (1) ◽  
pp. 41-44 ◽  
Author(s):  
Gilbert Wilson
Keyword(s):  
Critical Temperature ◽  
Low Temperature ◽  
Temperature Difference ◽  
Quartz Sand ◽  
Sodium Aluminate

AbstractQuartz sand, sodium aluminate and water were heated together in a bomb to above the critical temperature. The apparatus was designed to give a temperature difference of about 100°C. between the two ends of the bomb. Quartz, albite, and analcite were formed in the low temperature end of the bomb.

Effect of Geometry and Operating Parameters on Simulated SOFC Stack Temperature Uniformity

2011 ◽  
Author(s):  
Brian J. Koeppel ◽  
Kevin Lai ◽  
Moe A. Khaleel
Keyword(s):  
Temperature Field ◽  
Temperature Difference ◽  
Thermal Stresses ◽  
Temperature Response ◽  
Maximum Temperature ◽  
Uniform Temperature ◽  
Counter Flow ◽  
Thermal Exchange ◽  
Aspect Ratios ◽  
Uniform Temperature Field

A uniform temperature field is desirable in the solid oxide fuel cell stack to avoid local hot regions that contribute to material degradation, thermal stresses, or very high current densities. Various geometric and operational design changes were simulated by numerical modeling of co-flow and counter-flow multi-cell stacks, and the effects on stack maximum temperature, stack temperature difference, and maximum cell temperature difference were characterized. The results showed that 11–17% methane fuel composition for on-cell steam reforming and a reduced reforming rate of 25–50% of the nominal rate was beneficial for a more uniform temperature field. Fuel exhaust recycling up to 30% was shown to provide lower temperature differences for reforming fuel in the co-flow stack, but counter-flow stacks with hydrogen fuel showed higher temperature differences. Cells with large aspect ratios showed a more uniform temperature response due to either the strong influence of the inlet gas temperatures or the greater thermal exchange with the furnace boundary condition. Improved lateral heat spreading with thicker interconnects was demonstrated, but greater improvements towards a uniform thermal field for the same amount of interconnect mass could be achieved using thicker heat spreader plates appropriately distributed along the stack height.

The effect of stiffness and geometric parameters on the nonlinear aeroelastic performance of high aspect ratio wings

2016 ◽  
Vol 231 (10) ◽  
pp. 1824-1850 ◽  
Author(s):  
F Afonso ◽  
G Leal ◽  
J Vale ◽  
É Oliveira ◽  
F Lau ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Nonlinear Behavior ◽  
Geometric Parameters ◽  
Torsional Stiffness ◽  
Design Parameters ◽  
Sweep Angle ◽  
Flutter Speed ◽  
Wing Model ◽  
Aspect Ratios

The increase in wing aspect ratio is gaining interest among aircraft designers in conventional and joined-wing configurations due to the higher lift-to-drag ratios and longer ranges. However, current transport aircraft have relatively small aspect ratios due their increased structural stiffness. The more flexible the wing is more prone to higher deflections under the same operating condition, which may result in a geometrical nonlinear behavior. This nonlinear effect can lead to the occurrence of aeroelastic instabilities such as flutter sooner than in an equivalent stiffer wing. In this work, the effect of important stiffness (inertia ratio and torsional stiffness) and geometric (sweep and dihedral angles) design parameters on aeroelastic performance of a rectangular high aspect ratio wing model is assessed. The torsional stiffness was observed to present a higher influence on the flutter speed than the inertia ratio. Here, the decrease of the inertia ratio and the increase of the torsional stiffness results in higher flutter and divergence speeds. With respect to the geometric parameters, it was observed that neither the sweep angle nor the dihedral angle variations caused a substantial influence on the flutter speed, which is mainly supported by the resulting smaller variations in torsion and bending stiffness due to the geometric changes.

Convective temperature oscillations in molten gallium

1974 ◽  
Vol 64 (3) ◽  
pp. 565-576 ◽  
Author(s):  
D. T. J. Hurle ◽  
E. Jakeman ◽  
C. P. Johnson
Keyword(s):  
Magnetic Field ◽  
Experimental Study ◽  
Critical Temperature ◽  
Transverse Magnetic Field ◽  
Temperature Difference ◽  
Companion Paper ◽  
Transverse Magnetic ◽  
Temperature Oscillations ◽  
Over The Top

An experimental study of the occurrence of temperature oscillations in molten gallium contained in a rectangular boat and heated from the side is reported. The dependence of the critical temperature difference across the boat for which oscillations set in upon the boat dimensions and upon the strength of a transverse magnetic field is described. The dependence of the frequency of oscillation on these parameters is also reported together with measurements of the variation of the phase of the oscillations over the top surface of the melt. The results are discussed in relation to the theory in the companion paper by Gill (1974).

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