Transient Thermal Field Measurements in a High Aspect Ratio Channel Related to Transient Thermochromic Liquid Crystal Experiments

2011 ◽  
Vol 134 (3) ◽  
Author(s):  
Sean C. Jenkins ◽  
Igor V. Shevchuk ◽  
Jens von Wolfersdorf ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Liquid Crystal ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Field Measurements ◽  
Bulk Temperature ◽  
Fluid Temperature ◽  
Thermochromic Liquid Crystal ◽  
Temperature Distributions

Measurements of transient fluid temperature distributions were made in a high aspect ratio (4:1) internally ribbed two-pass channel relating to the measurement of heat transfer using the transient thermochromic liquid crystal (TLC) technique. The temperature field was measured at several positions leading up to and around the 180 deg bend in a two-passage channel to account for variations in the bulk temperature used as a reference for the transient TLC technique. The results showed that the normalized distribution of the temperature field was time invariant, an important result for the validation of heat transfer results using the transient TLC method. The normalized fluid temperature field was shown to be independent of the inlet temperature step and relatively independent of channel Reynolds number. Fluid temperature distributions were shown to be consistent over the length of the inlet channel; however, temperature field measurements made downstream of the bend exhibited a strong asymmetry. Finally, local temperature distributions were used to adjust the reference temperature used in calculating heat transfer coefficient distributions and to show the behavior of heat transfer due to 180 deg bends.

Transient Thermal Field Measurements in a High Aspect Ratio Channel Related to Transient Thermochromic Liquid Crystal Experiments

2007 ◽  
Author(s):  
Sean C. Jenkins ◽  
Igor V. Shevchuk ◽  
Jens von Wolfersdorf ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Liquid Crystal ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Field Measurements ◽  
Bulk Temperature ◽  
Fluid Temperature ◽  
Thermochromic Liquid Crystal ◽  
Temperature Distributions

Measurements of transient fluid temperature distributions were made in a high aspect ratio (4:1) internally ribbed two-pass channel relating to the measurement of heat transfer using the transient thermochromic liquid crystal (TLC) technique. The temperature field was measured at several positions leading up to and around the 180° bend in a two-passage channel to account for variations in the bulk temperature used as a reference for the transient TLC technique. Results showed that the normalized distribution of the temperature field was time-invariant, an important result for the validation of heat transfer results using the transient TLC method. The normalized fluid temperature field was shown to be independent of the inlet temperature step and relatively independent of channel Reynolds number. Fluid temperature distributions were shown to be consistent over the length of the inlet channel, however, temperature field measurements made downstream of the bend exhibited a strong asymmetry. Finally, local temperature distributions were used to adjust the reference temperature used in calculating heat transfer coefficient distributions and to show the behavior of heat transfer due to 180° bends.

Surface Heat Transfer Measurements of a Scaled Rib-Roughened Serpentine Cooling Passage by Use of a Transient Liquid Crystal Technique

1998 ◽  
Author(s):  
Ken-ichi Funazaki ◽  
Kouhei Ishizawa ◽  
Shigemichi Yamawaki
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Surface Heat ◽  
Bulk Temperature ◽  
Test Model ◽  
Thermochromic Liquid Crystal ◽  
Scaled Model ◽  
Surface Heat Transfer ◽  
Cooling Passage ◽  
Straight Duct

This study is aimed at providing heat transfer characteristics of the three-pass turbulated serpentine cooling channel inside a 10:1 scaled model of an actual turbine blade. A transient method using Thermochromic Liquid Crystal (TLC) is employed to measure the surface heat transfer distribution inside the model. Great attention is paid to the streamwise decrease in the mainstream temperature due to the heat absorption into the test model. To overcome this problem, the present study employed the linear interpolating method used by Ekkad and Han (1997) to estimate the local air bulk temperature. The soundness of the measuring method is verified through the heat transfer measurements of straight-duct models with and without turbulence promoting ribs. It follows from the heat transfer measurement of the serpentine model, in conjunction with the flow visualization, that the geometries of the cross-section of the cooling passage influence the flow pattern, resulting in substantial change in heat transfer distribution in the serpentine model in comparison with that of the straight-duct model.

Application of the Transient Heat Transfer Measurement Technique Using TLC in a Network Configuration With Intersecting Circular Passages

2018 ◽  
Author(s):  
Anika Steurer ◽  
Rico Poser ◽  
Jens von Wolfersdorf ◽  
Stefan Retzko
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Mass Flow ◽  
Fluid Temperature ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Flow Network ◽  
Mass Flow Rates ◽  
Time Information

The present study deals with the application of the transient thermochromic liquid crystal (TLC) technique in a flow network of intersecting circular passages as a potential internal turbine component cooling geometry. The investigated network consists of six circular passages with a diameter d = 20mm that intersect coplanar at an angle θ = 40°, the innermost in three, the outermost in one intersection level. Two additional non-intersecting passages serve as references. Such a flow network entails specific characteristics associated with the transient TLC method that have to be accounted for in the evaluation process: the strongly curved surfaces, the mixing and mass flow redistribution at each intersection point, and the resulting gradients between the wall and passage centerline temperatures. All this impedes the choice of a representative fluid reference temperature, which results in deviations using established evaluation methods. An alternative evaluation approach is introduced, which is supported by computational results obtained from steady-state three-dimensional RANS simulations using the SST turbulence model. The presented analysis uncouples local heat transfer coefficients from actually measured local temperatures but uses the time information of the thermocouples instead that represents the fluid temperature step change and evolution along the passages. This experimental time information is transferred to the steady-state numerical bulk temperatures, which are finally used as local references to evaluate the transient TLC experiments. As effective local mass flow rates in the passage sections are considered, the approach eventually allows for a conclusion whether heat transfer is locally enhanced due to higher mass flow rates or the intersection effects.

Study of Nanofluid Natural Convection Phenomena in Rectangular Enclosures

2007 ◽  
Author(s):  
Kau-Fui V. Wong ◽  
Bradley L. Bon ◽  
Santina Vu ◽  
Sing Samedi
Keyword(s):  
Temperature Field ◽  
Aspect Ratio ◽  
Mass Fraction ◽  
Buoyancy Force ◽  
Fluid Temperature ◽  
Non Invasive ◽  
Image Velocimetry ◽  
Anomalous Density ◽  
Mass Fractions ◽  
Invasive Method

Buoyancy induced flows in rectangular enclosures using nanofluids were investigated. The effects of mass fraction concentration of nanoparticles, enclosure aspect ratio and inclination were observed. The nanofluid under investigation was a water-based alumina nanofluid. Since water exhibits an anomalous density extremum near 4°C the additional effect of buoyancy force reversal will also be observed. The opacity of nanofluid does not permit the use of particle image velocimetry, laser induced fluorescence or any other means of flow visualization or visual temperature measurement of the local fluid temperature. Therefore to investigate the temperature field a non-invasive method, namely ultrasound thermometry, will be used to observe the temperature field. The experimental enclosure was validated using water as the initial fluid; measured values of the local fluid temperature were compared with numerical simulations utilizing COMSOL Multiphysics. Nanofluid mass fractions of 10% and 25% were used for comparative purposes of the effects of concentration on the temperature field. Buoyancy force reversal effects were witnessed in both 10% and 25% concentrations. The nanofluid also prolonged the multicellular effects that occur in buoyancy inversion flows. A Rayleigh number inversion was observed for the 25% mass fraction nanofluid. The multicellular regime transitions to boundary layer regime at about Ra=1E+07 when the aspect ratio is 2.625 and at about Ra=2E+08 when the aspect ratio is 1.000, for different concentrations of nanofluid. For these concentrations of nanofluid and aspect ratio equal to 2.625, instability in the core region occurred at about Ra=1.2E+07.

Effects of Variable Viscosity and Thermal Conductivity of CuO-Water Nanofluid on Heat Transfer Enhancement in Natural Convection: Mathematical Model and Simulation

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Eiyad Abu-Nada
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Average Nusselt Number ◽  
Volume Fraction ◽  
Variable Viscosity ◽  
Cylinder Surface ◽  
Transfer Enhancement

Heat transfer enhancement in horizontal annuli using variable thermal conductivity and variable viscosity of CuO-water nanofluid is investigated numerically. The base case of simulation used thermal conductivity and viscosity data that consider temperature property dependence and nanoparticle size. It was observed that for Ra≥104, the average Nusselt number was deteriorated by increasing the volume fraction of nanoparticles. However, for Ra=103, the average Nusselt number enhancement depends on aspect ratio of the annulus as well as volume fraction of nanoparticles. Also, for Ra=103, the average Nusselt number was less sensitive to volume fraction of nanoparticles at high aspect ratio and the average Nusselt number increased by increasing the volume fraction of nanoaprticles for aspect ratios ≤0.4. For Ra≥104, the Nusselt number was deteriorated everywhere around the cylinder surface especially at high aspect ratio. However, this reduction is only restricted to certain regions around the cylinder surface for Ra=103. For Ra≥104, the Maxwell–Garnett and the Chon et al. conductivity models demonstrated similar results. But, there was a deviation in the prediction at Ra=103 and this deviation becomes more significant at high volume fraction of nanoparticles. The Nguyen et al. data and the Brinkman model give completely different predictions for Ra≥104, where the difference in prediction of the Nusselt number reached 50%. However, this difference was less than 10% at Ra=103.

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