Local Measurements of Disk Heat Transfer in Heated Rotating Cavities for Several Flow Regimes

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
André Günther ◽  
Wieland Uffrecht ◽  
Stefan Odenbach
Keyword(s):  
Heat Flux ◽  
Flow Regimes ◽  
Local Heat ◽  
Heat Fluxes ◽  
Flow Structures ◽  
Back Side ◽  
Wide Range ◽  
Toroidal Vortices ◽  
Axial Heat ◽  
Cooling Air

This paper discusses experimental results from a two-cavity test rig representation of the internal air system of a high-pressure compressor. Thermal steady-state measurements of the time-averaged local heat fluxes on both sides of the middle disk are presented for three different flow regimes: pure axial throughflow of cooling air and axial throughflow of cooling air in two directions with a superposed radial inflow of hot air in one cavity. Mass flow ratios between 1/40 < mrad/max < 2/1 are measured. Tests were carried out for a wide range of non-dimensional parameters: Reφ up to 107, Rez up to 2 × 105, and Cw up to −2.5 × 104. In all cases, the shroud is uniformly heated to approximately 100 °C. The local axial heat fluxes are determined separately for both sides of the middle disk from measurements of the surface temperatures with open spot-welded thermo-couples. The method of heat flux determination and an analysis approach calculating the uncertainties and the sensitivity are described and discussed. The local heat flux results of the different flow paths are compared and interpreted by assumed flow structures. The time-averaged heat flux results can be adequately interpreted by flow structures of two toroidal vortices for axial throughflow and a source-sink flow for the radial inflow. The measurements show that the axial heat flux can change direction, i.e., areas exist where the disk is heated and not cooled by the flow. For axial throughflow, a local minimum of heat flux exists on the impinged side in the range of x = 0.65. On the back side, a heating area exists in all tests in the lower half of the disk (x < 0.6) due to recirculated air of higher temperature. This heating area corresponds to the range of the inner vortex and increases with higher axial and rotational Reynolds numbers.

Local Measurements of Disc Heat Transfer in Heated Rotating Cavities for Several Flow Regimes

2010 ◽  
Author(s):  
Andre´ Gu¨nther ◽  
Wieland Uffrecht ◽  
Stefan Odenbach
Keyword(s):  
Heat Flux ◽  
Reynolds Number ◽  
Flow Regimes ◽  
Local Heat ◽  
Heat Fluxes ◽  
Flow Structures ◽  
Back Side ◽  
Wide Range ◽  
Axial Heat ◽  
Cooling Air

This paper discusses experimental results from a two cavity test rig representative for the internal air system of a high pressure compressor. Thermal steady state measurements of the time-averaged local heat fluxes on both sides of the mid disc are presented for three different flow regimes: pure axial throughflow of cooling air and axial throughflow of cooling air in two directions with a superposed radial inflow of hot air in one cavity. Mass flow ratios between 1/40 &lt; mrad/max &lt; 2/1 are measured. Tests were carried out for a wide range of non-dimensional parameters: Re φ up to 107, Rez up to 2 × 105 and Cw up to −2.5 × 104. In all cases the shroud is uniformly heated to approximately 100°C. The local axial heat fluxes are determined separately for both sides of the mid disc from measurements of the surface temperatures with open spot-welded thermocouples. The method of heat flux determination and an analysis approach calculating the uncertainties and the sensitivity are described and discussed. The local heat flux results of the different flow paths are compared and interpreted by assumed flow structures. The time-averaged heat flux results can adequately be interpreted by flow structures of two toroidal vortices for axial throughflow and a source-sink flow for the radial inflow. The measurements show that the axial heat flux can change the direction, i.e. areas exist where the disc is heated and not cooled by the flow. For axial throughflow a local minimum of heat flux exists on the impinged side in the range of x = 0.65 if the axial Reynolds number is low or the rotational Reynolds number is high. On the back side a heating area exists in all tests in the lower half of the disc (x &lt; 0.6) due to recirculated air of higher temperature. This heating area corresponds to the range of the inner vortex and increases with higher axial and rotational Reynolds numbers.

Inverse Heat Conduction Applied to the Measurement of Heat Fluxes on a Rotating Cylinder: Comparison Between an Analytical and a Numerical Technique

2008 ◽  
Vol 130 (8) ◽  
Author(s):  
Fabien Volle ◽  
Michel Gradeck ◽  
Denis Maillet ◽  
Arsène Kouachi ◽  
Michel Lebouché
Keyword(s):  
Heat Flux ◽  
Numerical Technique ◽  
Rotating Cylinder ◽  
Local Heat ◽  
Heat Fluxes ◽  
Inverse Heat Conduction ◽  
Analytical Technique ◽  
Inner Radius ◽  
Direct Model ◽  
Stable Estimation

A method using either a one-dimensional analytical or a two-dimensional numerical inverse technique is developed for measurement of local heat fluxes at the surface of a hot rotating cylinder submitted to the impingement of a subcooled water jet. The direct model calculates the temperature field inside the cylinder that is submitted to a given nonuniform and time dependent heat flux on its outer surface and to a uniform surface heat source on an inner radius. In order to validate the algorithms, simulated temperature measurements inside the cylinder are processed and used by the two inverse techniques to estimate the wall heat flux. As the problem is improperly posed, regularization methods have been introduced into the analytical and numerical inverse algorithms. The numerical results obtained using the analytical technique compare well with the results obtained using the numerical algorithm, showing a good stable estimation of the available test solutions. Furthermore, real experimental data are used for the estimation, and local boiling curves are plotted and discussed.

Risk-Informed Approach to Debris Bed Coolability Issue

2012 ◽  
Author(s):  
Sergey E. Yakush ◽  
Nazar T. Lubchenko ◽  
Pavel Kudinov
Keyword(s):  
Heat Flux ◽  
Surrogate Model ◽  
Thermal Power ◽  
Local Heat ◽  
Distribution Functions ◽  
Heat Fluxes ◽  
Severe Accident ◽  
Accident Risk ◽  
Dimensional Simulation ◽  
Accident Conditions

Coolability of an ex-vessel debris bed in severe accident conditions is considered from the risk perspective. The concept of “load versus capacity” is employed to quantify the probability of failure (local dryout). Possible choices of “load” and “capacity” in terms of heat fluxes, thermal power or melt mass are discussed. Results of Monte Carlo simulations of distribution functions for the local heat flux and the dryout heat flux at the debris bed top point (defined as the extensions of one-dimensional counterparts) are presented. A surrogate model for the dryout heat flux is developed by the generalization of two-dimensional simulation results. Dryout probabilities are obtained under the conservative assumptions (neglecting the coolability improvement due to side ingress of water into a non-flat debris bed), and from the surrogate model. Outlook is given for the prospective development of the risk-informed approach to debris bed coolability in the context of comprehensive severe accident risk analysis.

Transient Heat Flux Measurements in a Divided-Chamber Diesel Engine

1985 ◽  
Vol 107 (2) ◽  
pp. 439-444 ◽  
Author(s):  
A. C. Alkidas ◽  
R. M. Cole
Keyword(s):  
Heat Flux ◽  
Diesel Engine ◽  
Fluid Motion ◽  
Local Heat ◽  
Relative Increase ◽  
Heat Fluxes ◽  
Main Chamber ◽  
Peak Heat Flux ◽  
Flux Measurements ◽  
Local Heat Flux

Transient surface heat flux measurements were performed at several locations on the cylinder head of a divided-chamber diesel engine. The local heat flux histories were found to be significantly different. These differences are attributed to the spatial nonuniformity of the fluid motion and combustion. Both local time-averaged and local peak heat fluxes decreased with decreasing speed and load. Retarding the combustion timing beyond TDC decreased the peak heat flux in the antechamber but increased the peak heat flux in the main chamber. This is attributed to the relative increase in the portion of fuel that burns in the main chamber with retarded combustion timing.

Attempt of estimating flow characteristics from wall heat fluxes measured using a three-point micro-electro-mechanical systems sensor

2020 ◽  
pp. 146808742091728
Author(s):  
Kazuhito Dejima ◽  
Osamu Nakabeppu
Keyword(s):  
Heat Flux ◽  
Side Information ◽  
Rotational Symmetry ◽  
Mechanical Systems ◽  
Flow Characteristics ◽  
Local Heat ◽  
Heat Fluxes ◽  
Micro Electro Mechanical Systems ◽  
Operation Conditions ◽  
Cross Correlation Analysis

In this study, it was attempted to estimate the flow characteristics in the vicinity of an engine inner wall from the instantaneous local heat fluxes measured using a micro-electro-mechanical systems sensor. As the sensor has three resistance temperature detectors with a size of 315 µm fabricated on a circumference with a diameter of 900 µm in rotational symmetry, it can measure local heat flux on the equivalent scale of the turbulence of in-cylinder flow. The advective velocity and turbulent eddy scale were estimated from heat flux fluctuations using a cross-correlation analysis, and these were compared with results of particle image velocimetry performed under motored operation conditions. As a result, it was found that the micro-electro-mechanical systems sensor has the potential to detect the gas side information such as the wall parallel flow velocity. Although further verification of the physical meanings of the estimated characteristics is necessary, the micro-electro-mechanical systems sensor will become a powerful tool for engine diagnostics.

Geometry Effects on Two-Phase Flow Regimes in a Diabatic Manifolded Microgap Channel

2017 ◽  
Author(s):  
David C. Deisenroth ◽  
Avram Bar-Cohen ◽  
Michael Ohadi
Keyword(s):  
Heat Flux ◽  
Mass Flux ◽  
Electronics Cooling ◽  
Flow Regimes ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Two Phase ◽  
Channel Geometry ◽  
Cooling Channels

Two-phase cooling has become an increasingly attractive option for thermal management of high-heat flux electronics. Cooling channels embedded directly on the back of the heat source (chip) facilitate two-phase boiling/evaporation effectiveness, eliminating many thermal resistances generated by more traditional, remote chip-cooling approaches. Accordingly, manifold-microchannel flow paths in embedded cooling systems can allow very high heat fluxes with low junction temperatures. But, the effect of the feeding manifold design, channel geometry, and the associated shear, stagnation zones, and centripetal accelerations with varying heat flux and mass flux are not well understood. This study builds upon our previous work and elucidates effects of channel geometry, mass flux, and outlet quality on the boiling/evaporation flow regimes in a manifolded microgap channel.

Heat Transfer to Longitudinal Laminar Flow Between Cylinders

1961 ◽  
Vol 83 (4) ◽  
pp. 415-422 ◽  
Author(s):  
E. M. Sparrow ◽  
A. L. Loeffler ◽  
H. A. Hubbard
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Laminar Flow ◽  
Unit Length ◽  
Local Heat ◽  
Bulk Temperature ◽  
Nusselt Numbers ◽  
Spacing Ratio ◽  
Wide Range ◽  
Local Heat Flux

Consideration is given to the fully developed heat-transfer characteristics for longitudinal laminar flow between cylinders arranged in an equilateral triangular array. The analysis is carried out for the condition of uniform heat transfer per unit length. Solutions are obtained for the temperature distribution, and from these, Nusselt numbers are derived for a wide range of spacing-to-diameter ratios. It is found that as the spacing ratio increases, so also does the wall-to-bulk temperature difference for a fixed heat transfer per unit length. Corresponding to a uniform surface temperature around the circumference of a cylinder, the circumferential variation of the local heat flux is computed. For spacing ratios of 1.5 ∼ 2.0 and greater, uniform peripheral wall temperature and uniform peripheral heat flux are simultaneously achieved. A simplified analysis which neglects circumferential variations is also carried out, and the results are compared with those from the more exact formulation.

scholarly journals Experimental Investigation to Evaluate the Effectiveness of Air and Co2 in Impingement Cooling of Electronic Equipment

2013 ◽  
pp. 203-208
Author(s):  
Syed Zakrea ◽  
Siddiq Ali ◽  
Mohammed Ayaz Ahmed ◽  
M. Anwarullah
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Experimental Investigation ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat ◽  
Graphical Form ◽  
Wide Range ◽  
Local Heat Flux

Experimental investigation is conducted to examine the characteristics of forced convective heat transfer from electronic components, subjected to a confined impinging circular jet of Air and CO2. Parameters such as Heat transfer coefficient, Jet velocities, Nozzle-to-chip spacing (aspect ratio) (H/d) have been studied. Nozzle diameter ranged from 2mm to 8mm. Local heat flux measurements are made with different diameters of jet in the range of Reynolds numbers from 5,000 to 44,000 for CO2 and 2,500 to 23,000 for air. H/d is varied from 3 to 45 for both air and CO2. Variations both in the local heat transfer coefficient and Nusselt number are determined as function of Re. Variations of average Nusselt number and local heat flux with time are obtained in a wide range of Re and H/d ratios. The results of the investigation are presented in graphical form and a comparative study of Air and CO2 as coolant is made.

Local Heat Transfer Coefficient During Condensation in a 0.8 mm Diameter Pipe

2006 ◽  
Author(s):  
Alberto Cavallini ◽  
Davide Del Col ◽  
Marko Matkovic ◽  
Luisa Rossetto
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Operating Conditions ◽  
Local Heat Transfer Coefficient ◽  
Wide Range ◽  
The Heat Transfer Coefficient

The first preliminary tests carried on a new experimental rig for measurement of the local heat transfer coefficient inside a circular 0.8 mm diameter minichannel are presented in this paper. The heat transfer coefficient is measured during condensation of R134a and is obtained from the measurement of the heat flux and the direct gauge of the saturation and wall temperatures. The heat flux is derived from the water temperature profile along the channel, in order to get local values for the heat transfer coefficient. The test section has been designed so as to reduce thermal disturbances and experimental uncertainty. A brief insight into the design and the construction of the test rig is reported in the paper. The apparatus has been designed for experimental tests both in condensation and vaporization, in a wide range of operating conditions and for a wide selection of refrigerants.

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