Influence of lateral temperature gradients on the failure modes at power cycling

2021 ◽  
pp. 1-1
Author(s):  
Xing Liu ◽  
Erping Deng ◽  
Hao Wang ◽  
Clemens Herrmann ◽  
Thomas Basler ◽  
...  
Keyword(s):  
Failure Modes ◽  
Temperature Gradients ◽  
Power Cycling ◽  
Lateral Temperature

Effects of spatially varying roof cooling on thermal convection at high Rayleigh number in a fluid with a strongly temperature-dependent viscosity

2009 ◽  
Vol 629 ◽  
pp. 109-137 ◽  
Author(s):  
A. M. JELLINEK ◽  
A. LENARDIC
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Rayleigh Number ◽  
Surface Area ◽  
Large Scale ◽  
Local Heat ◽  
Temperature Gradients ◽  
Local Heat Flux ◽  
Transfer Properties ◽  
Lateral Temperature

We investigate the effects of an insulating lid of variable spatial extent on convection in the stagnant-lid regime under thermally steady-state conditions. Using a combination of laboratory experiments, numerical simulations and scaling analyses we characterize the qualitative structure and quantitative heat transfer properties of flows in terms of the fractional extent L of an insulating lid applied at the cold boundary, the thermal resistance of the lid, the magnitude of the temperature dependence of the fluid viscosity Λ and the effective Rayleigh number Rae for the composite system. A partial insulating lid has two main effects: (i) To increase the mean interior temperature and reduce the average viscosity of the system, which enhances fluid motions, and (ii) to impart a lateral asymmetry to the thermal structure of the cold boundary that leads, in turn, to lateral temperature gradients that drive an overturning flow. Consequently, whereas flow in the uninsulated stagnant-lid regime is in the form of ‘small-scale’ rising and sinking thermals, there is an additional ‘large-scale’ circulation in the presence of partial insulation. The structure, wavelength and heat transfer properties of this large-scale stirring depends on L, Λ and Rae. For given Rae – Λ conditions we find optimal values of L at which there occur well-defined maxima in the rate of overturn, the local heat flux carried into the uninsulated part of the cold boundary and in the global average heat flux Nu carried across the system. Whereas both the rate of overturning and local heat flux are associated with the largest lateral temperature gradients, the optimal basal heat flux depends also on a tradeoff with the fractional surface area of the lid. Remarkably, maximal values of the global heat flux can significantly exceed that of the uninsulated stagnant-lid case. The occurrence of such maxima is insensitive to the mechanical boundary conditions applied and is not strongly influenced by lid shape. However, the magnitude and location of optimal heat fluxes depends in a complicated way on the lid surface area and shape, as well as the structure of the hot and cold boundary layers and the wavelength of the large-scale flow.

Melioration of Pyroelectric Cells for Power Conversion

2012 ◽  
Vol 479-481 ◽  
pp. 2199-2205
Author(s):  
Chun Ching Hsiao ◽  
Chin Yu Chang ◽  
An Shen Siao ◽  
Jing Chih Ciou
Keyword(s):  
Temperature Variation ◽  
Power Conversion ◽  
Temperature Gradients ◽  
Electrode Design ◽  
Cutting Depth ◽  
Temperature Variations ◽  
Variation Rate ◽  
Rapid Temperature ◽  
Temperature Variation Rate ◽  
Lateral Temperature

Trenching PZT material in a thicker PZT pyroelectric cell to improve the temperature variation rate was proposed in this study to enhance the efficiency of thermal energy-harvesting conversion by pyroelectricity. A thicker pyroelectric cell is beneficial in generating electricity pyroelectrically, but it opposes rapid temperature variations. Therefore, the PZT sheet was fabricated to produce deeper trenches to cause lateral temperature gradients induced by the trenched electrode, enhancing the temperature variation rate under homogeneous heat irradiation. When the trenched electrode type with an electrode width of 200 μm and a cutting depth of 150 μm was used to fabricate the PZT pyroelectric cell with a 200 μm thick PZT sheet, the temperature variation rate was improved by about 55%. Therefore, the trenched electrode design did indeed enhance the temperature variation rate and the efficiency of pyroelectric energy converters.

scholarly journals Statistical evaluation of vertical and lateral temperature gradients in concrete box-girders

2021 ◽  
Vol 1895 (1) ◽  
pp. 012068
Author(s):  
Sallal R Abid ◽  
Hussein Al-Bugharbee ◽  
Jasim M. Mhalhal ◽  
Thaar S. Al-Gasham ◽  
Nildem Tayşi ◽  
...  
Keyword(s):  
Statistical Evaluation ◽  
Temperature Gradients ◽  
Box Girders ◽  
Lateral Temperature

scholarly journals Effects of microtopography on texture, temperature and heat flow in Arctic and sub-Arctic snow

1994 ◽  
Vol 19 ◽  
pp. 63-68 ◽  
Author(s):  
Matthew Sturm ◽  
Jonathan Holmgren
Keyword(s):  
Heat Flux ◽  
Heat Flow ◽  
Snow Depth ◽  
In Situ Measurements ◽  
Temperature Gradients ◽  
Substantial Fraction ◽  
Model Based ◽  
Vertical Heat ◽  
Lateral Temperature

Arctic and sub-Arctic snow is deposited on ground that can have significant microrelief due to tundra hummocks and tussocks. The microrelief, a substantial fraction of the total snow depth, causes basal layers of snow (usually depth hoar) to be discontinuous. In-situ measurements made at four locations in Alaska indicate lateral temperature gradients up to 60°C m−1exist at the snow/ground interface due to the microtopography. For all sites, the winter average range of temperature along a 1.5 m transect at the interface varied from 4°C to greater than 7°C. Heat-flux transducers placed at the tops and bases of tussocks indicated that vertical heat flow was consistently 1.4 to 2.1 times higher at the top than the base. Results of a conductive model based on tussock height are consistent with these measurements.

Ageing and Failure Modes of IGBT Modules in High-Temperature Power Cycling

2011 ◽  
Vol 58 (10) ◽  
pp. 4931-4941 ◽  
Author(s):  
Vanessa Smet ◽  
Francois Forest ◽  
Jean-Jacques Huselstein ◽  
Frédéric Richardeau ◽  
Zoubir Khatir ◽  
...  
Keyword(s):  
High Temperature ◽  
Failure Modes ◽  
Igbt Modules ◽  
Power Cycling

Reverse-Pass Cooling Systems for Improved Performance

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Benjamin Kirollos ◽  
Thomas Povey
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Film Cooling ◽  
Guide Vane ◽  
Temperature Gradients ◽  
Pass System ◽  
Forward Pass ◽  
Counter Current ◽  
Lateral Temperature ◽  
Current Arrangement

Total heat transfer between a hot and a cold stream of gas across a nonporous conductive wall is greatest when the two streams flow in opposite directions. This counter-current arrangement outperforms the co-current arrangement because the mean driving temperature difference is larger. This simple concept, whilst familiar in the heat exchanger community, has received no discussion in papers concerned with cooling of hot-section gas turbine components (e.g., turbine vanes/blades, combustor liners, afterburners). This is evidenced by the fact that there are numerous operational systems which would be significantly improved by the application of “reverse-pass” cooling. That is, internal coolant flowing substantially in the opposite direction to the mainstream flow. A reverse-pass system differs from a counter-current system in that the cold fluid is also used for film cooling. Such systems can be realized when normal engine design constraints are taken into account. In this paper, the thermal performance of reverse-pass arrangements is assessed using bespoke 2D numerical conjugate heat transfer models, and compared to baseline forward-pass and adiabatic arrangements. It is shown that for a modularized reverse-pass arrangement implemented in a flat plate, significantly less coolant is required to maintain metal temperatures below a specified limit than for the corresponding forward-pass system. The geometry is applicable to combustor liners and afterburners. Characteristically, reverse-pass systems have the benefit of reducing lateral temperature gradients in the wall. The concept is demonstrated by modeling the pressure and suction surfaces of a typical nozzle guide vane with both internal and film cooling. For the same cooling mass flow rate, the reverse-pass system is shown to reduce the peak temperature on the suction side (SS) and reduce lateral temperature gradients on both SS and pressure side (PS). The purpose of this paper is to demonstrate that by introducing concepts familiar in the heat exchanger community, engine hot-section cooling efficiency can be improved whilst respecting conventional manufacturing constraints.

Experiments on convective layer formation and merging in a differentially heated slot

1979 ◽  
Vol 91 (3) ◽  
pp. 451-464 ◽  
Author(s):  
R. A. Wirtz ◽  
C. S. Reddy
Keyword(s):  
Heat Transfer ◽  
Side Wall ◽  
Temperature Gradients ◽  
Layer Formation ◽  
Density Jump ◽  
Convective Layer ◽  
Subsequent Layer ◽  
Lateral Temperature ◽  
New System ◽  
Lateral Heat

This work describes experiments in which a stably stratified salt solution is subjected to steady lateral temperature gradients. The criteria for the onset of layered convection are observed to agree with previously published stability analysis. Convective layers formed in this way are found to be statically unstable; they always merge two into one to form a new system. This process continues until the density jump at the solute interface between layers is larger than the density deficit produced by the side wall heating/cooling. The eventual stable system develops into well-mixed convective layers separated by sharp solute interfaces. The conditions for any subsequent layer intermixing and its effect on the lateral heat transfer across the slot, are also described.

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