The Lobe Structure in Ice Accreted on an Aluminium Conductor in The Presence of a Dc Electric Field

1983 ◽  
Vol 4 ◽  
pp. 228-235 ◽  
Author(s):  
Luan C. Phan ◽  
Jean-Louis Laforte ◽  
Du D. Nguyen
Keyword(s):  
Electric Field ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Air Bubbles ◽  
Experimental Conditions ◽  
Charged Droplets ◽  
Water Drops ◽  
The Difference ◽  
Negative Electric Field ◽  
Corona Wind

Supercooled droplets of 38 μm mean volume diameter are accreted on a smooth aluni mum cylinder of 3.15 cm in diameter in order to study the effect of an electrostatic field upon ice formation on a power-line conductor. The results obtained show that ice grown in the presence of an applied negative field of 15 kV cm−1 exhibits a cusped-lobe structure characterized by surfacial outward knobs, convex rings of fine air bubbles and radial lines of large air bubbles; in the same conditions, a positive electric field of 15 kV cm−1 does not produce such lobe features. On the other hand, accretion tests performed in the absence of an electric field with a 33 μm droplet spectrum show that the well-developed cusped-lobe structure appears in ice at low ambient temperature and air velocity. In the present experimental conditions, the formation of cusped lobes observed in the presence of a negative electric field could be explained by a decrease in the temperature of the deposit due to a reduction of impact velocity of the charged droplets and/or an increase in the local heat-transfer coefficient at the surface of the ice accretion. Corona wind from ice points, always in the opposite direction to the impinging droplets, may also reduce their impact velocities. In addition, corona wind and roughness of the surface may contribute to a better evacuation of the latent heat and thus decrease the deposit temperature. The difference between the effects of a negative DC field and those of a DC positive field of the same strength comes from a stronger ionization intensity and/or a stronger deformation of water drops in the negative electric field.

The Lobe Structure in Ice Accreted on an Aluminium Conductor in The Presence of a Dc Electric Field

1983 ◽  
Vol 4 ◽  
pp. 228-235
Author(s):  
Luan C. Phan ◽  
Jean-Louis Laforte ◽  
Du D. Nguyen
Keyword(s):  
Electric Field ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Air Bubbles ◽  
Experimental Conditions ◽  
Charged Droplets ◽  
Water Drops ◽  
The Difference ◽  
Negative Electric Field ◽  
Corona Wind

Supercooled droplets of 38 μm mean volume diameter are accreted on a smooth aluni mum cylinder of 3.15 cm in diameter in order to study the effect of an electrostatic field upon ice formation on a power-line conductor. The results obtained show that ice grown in the presence of an applied negative field of 15 kV cm−1exhibits a cusped-lobe structure characterized by surfacial outward knobs, convex rings of fine air bubbles and radial lines of large air bubbles; in the same conditions, a positive electric field of 15 kV cm−1does not produce such lobe features. On the other hand, accretion tests performed in the absence of an electric field with a 33 μm droplet spectrum show that the well-developed cusped-lobe structure appears in ice at low ambient temperature and air velocity. In the present experimental conditions, the formation of cusped lobes observed in the presence of a negative electric field could be explained by a decrease in the temperature of the deposit due to a reduction of impact velocity of the charged droplets and/or an increase in the local heat-transfer coefficient at the surface of the ice accretion. Corona wind from ice points, always in the opposite direction to the impinging droplets, may also reduce their impact velocities. In addition, corona wind and roughness of the surface may contribute to a better evacuation of the latent heat and thus decrease the deposit temperature. The difference between the effects of a negative DC field and those of a DC positive field of the same strength comes from a stronger ionization intensity and/or a stronger deformation of water drops in the negative electric field.

Heat Transfer in Reciprocating Planar Curved Tube With Piston Cooling Application

2005 ◽  
Vol 128 (1) ◽  
pp. 219-229 ◽  
Author(s):  
Shyy Woei Chang ◽  
Yao Zheng
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Interactive Effects ◽  
Experimental Conditions ◽  
Nusselt Numbers ◽  
Curved Tube ◽  
The Individual ◽  
Cooling Passage ◽  
Piston Cooling

This paper describes an experimental study of heat transfer in a reciprocating planar curved tube that simulates a cooling passage in piston. The coupled inertial, centrifugal, and reciprocating forces in the reciprocating curved tube interact with buoyancy to exhibit a synergistic effect on heat transfer. For the present experimental conditions, the local Nusselt numbers in the reciprocating curved tube are in the range of 0.6–1.15 times of static tube levels. Without buoyancy interaction, the coupled reciprocating and centrifugal force effect causes the heat transfer to be initially reduced from the static level but recovered when the reciprocating force is further increased. Heat transfer improvement and impediment could be superimposed by the location-dependent buoyancy effect. The empirical heat transfer correlation has been developed to permit the evaluation of the individual and interactive effects of inertial, centrifugal, and reciprocating forces with and without buoyancy interaction on local heat transfer in a reciprocating planar curved tube.

Heat Transfer Measurements Using Multiple Thermochromic Liquid Crystals in Symmetric Cooling Channels

2020 ◽  
Author(s):  
Tobias Krille ◽  
Stefan Retzko ◽  
Rico Poser ◽  
Jens von Wolfersdorf
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Single Channels ◽  
Ambient Conditions ◽  
Transfer Coefficients ◽  
Experimental Conditions ◽  
Cooling Channels ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Abstract The transient Thermochromic Liquid Crystal (TLC) method is applied to determine the distribution of the local heat transfer coefficients using a configuration with parallel cooling channels at an engine relevant Reynolds number. The rectangular channels with a moderate aspect ratio and a high length-to-diameter ratio are equipped with one-sided oblique ribs with high blockage, which is a promising configuration for turbine near wall cooling applications. In this arrangement, the three inner channels should experience same flow and thermal conditions. Numerical simulations are performed to substantiate this assumption. The symmetric single channels are sprayed with narrowband TLC with various indication temperatures. Multiple experiments were conducted. All start at ambient conditions before the fluid is heated up to several temperatures between 46°C and 73°C. The results show that the determined local heat transfer coefficients and therefore the Nusselt numbers vary significantly for the different experimental conditions especially at locations of high heat transfer coefficient behind the ribs. A simplified procedure with respect to measurement uncertainties is applied to enable an easy and fast valuation on the data quality. This might be used within the data reduction analysis for such experiments directly. The approach is illustrated using the obtained experimental data.

Experimental Investigation of Corona Wind Heat Transfer Enhancement With a Heated Horizontal Flat Plate

1995 ◽  
Vol 117 (2) ◽  
pp. 309-315 ◽  
Author(s):  
B. L. Owsenek ◽  
J. Seyed-Yagoobi ◽  
R. H. Page
Keyword(s):  
Heat Transfer ◽  
Infrared Camera ◽  
Local Heat Transfer ◽  
Threshold Value ◽  
Local Heat ◽  
Heated Plate ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Efficiency ◽  
Corona Wind

Corona wind enhancement of free convection was investigated with the needle-plate geometry in air. High voltage was applied to a needle suspended above a heated plate, and heat transfer coefficients were computed by measuring the plate surface temperature distribution with an infrared camera. Local heat transfer coefficients greater than 65 W/m2 K were measured, an enhancement of more than 25:1 over natural convection. The enhancement extended over a significant area, often reaching beyond the 30 cm measurement radius. At high power levels, Joule heating significantly reduced the effective impingement point heat transfer coefficient. The corona wind was found to be more efficient with positive potential than with negative. The heat transfer efficiency was optimized with respect to electrode height and applied voltage. The needle-plate heat transfer effectiveness improved rapidly with increasing height, and became relatively insensitive to height above a threshold value of about 5 cm.

A Comparison of the Transient and Heated-Coating Methods for the Measurement of Local Heat Transfer Coefficients on a Pin Fin

1989 ◽  
Vol 111 (4) ◽  
pp. 877-881 ◽  
Author(s):  
J. W. Baughn ◽  
P. T. Ireland ◽  
T. V. Jones ◽  
N. Saniei
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Uniform Heat Flux ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
The Difference

Measurements of the local heat transfer coefficients on a pin fin (i.e., a short cylinder in crossflow) in a duct have been made using two methods, both of which employ liquid crystals to map an isotherm on the surface. The transient method uses the liquid crystal to determine the transient response of the surface temperature to a change in the fluid temperature. The local heat transfer coefficient is determined from the surface response time and the thermal properties of the substrate. The heated-coating method uses an electrically heated coating (vacuum-deposited gold in this case) to provide a uniform heat flux, while the liquid crystal is used to locate an isotherm on the surface. The two methods compare well, especially the value obtained near the center stagnation point of the pin fin where the difference in the thermal boundary condition of the two methods has little effect. They are close but differ somewhat in other regions.

scholarly journals Local Heat Transfer Analysis in a Single Microchannel with Boiling DI-Water and Correlations with Impedance Local Sensors

Energies ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 6473
Author(s):  
Mohammadmahdi Talebi ◽  
Sahba Sadir ◽  
Manfred Kraut ◽  
Roland Dittmeyer ◽  
Peter Woias
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cross Section ◽  
Flow Boiling ◽  
Rectangular Cross Section ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Experimental Conditions ◽  
Impedance Measurements

Determination of local heat transfer coefficient at the interface of channel wall and fluid was the main goal of this experimental study in microchannel flow boiling domain. Flow boiling heat transfer to DI-water in a single microchannel with a rectangular cross section was experimentally investigated. The rectangular cross section dimensions of the experimented microchannel were 1050 μm × 500 μm and 1500 μm × 500 μm. Experiments under conditions of boiling were performed in a test setup, which allows the optical and local impedance measurements of the fluids by mass fluxes of 22.1 kg·m−2·s−1 to 118.8 kg·m−2·s−1 and heat fluxes in the range of 14.7 kW·m−2 to 116.54 kW·m−2. The effect of the mass flux, heat flux, and flow pattern on flow boiling local heat transfer coefficient and pressure drop were investigated. Experimental data compared to existing correlations indicated no single correlation of good predictive value. This was concluded to be the case due to the instability of flow conditions on one hand and the variation of the flow regimes over the experimental conditions on the other hand. The results from the local impedance measurements in correlation to the optical measurements shows the flow regime variation at the experimental conditions. From these measurements, useful parameters for use in models on boiling like the 3-zone model were shown. It was shown that the sensing method can shed a precise light on unknown features locally in slug flow such as residence time of each phases, bubble frequency, and duty cycle.

An Experimental Investigation of Heat Transfer Around A Tube in A Bank

1976 ◽  
Vol 98 (3) ◽  
pp. 503-508 ◽  
Author(s):  
S. Aiba ◽  
Y. Yamazaki
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Static Pressure ◽  
Strong Dependence ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Free Shear Layer ◽  
Pitch Ratio ◽  
The Difference

An experimental investigation of heat transfer and flow around the second cylinder of three cylinders in cross flow of air was conducted. The cylinders were situated in tandem at equal distances between centers. Their in-line pitch ratio was in the range 1.3 ≦ c/d ≦ 5.0 (c = center-to-center distance; d = diameter); the Reynolds number was 40000. Heat transfer results indicate a strong dependence on the difference between the maximum static pressure on the surface and the static pressure at the front stagnation point of the second cylinder. The maximum local heat transfer around the second cylinder occurs at the position where the free vortex layer (free shear layer) shed from the first cylinder attaches. However, the turbulence intensity near the wall at this same position is lower than that at other angular positions.

scholarly journals Heat Transfer Measurements Using Multiple Thermochromic Liquid Crystals in Symmetric Cooling Channels

2021 ◽  
pp. 1-22
Author(s):  
Tobias Krille ◽  
Stefan Retzko ◽  
Rico Poser ◽  
Jens Von Wolfersdorf
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Single Channels ◽  
Ambient Conditions ◽  
Transfer Coefficients ◽  
Experimental Conditions ◽  
Cooling Channels ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Abstract The transient Thermochromic Liquid Crystal (TLC) method is applied to determine the distribution of the local heat transfer coefficients using a configuration with parallel cooling channels at an engine relevant Reynolds number. The rectangular channels with a moderate aspect ratio and a high length-to-diameter ratio are equipped with one-sided oblique ribs with high blockage, which is a promising configuration for turbine near wall cooling applications. In this arrangement, the three inner channels should experience same flow and thermal conditions. Numerical simulations are performed to substantiate this assumption. The symmetric single channels are sprayed with narrowband TLC with various indication temperatures. Multiple experiments were conducted. All start at ambient conditions before the fluid is heated up to several temperatures between 46°C and 73°C. The results show that the determined local heat transfer coefficients and therefore the Nusselt numbers vary significantly for the different experimental conditions especially at locations of high heat transfer coefficient behind the ribs. A simplified procedure with respect to measurement uncertainties is applied to enable an easy and fast valuation on the data quality. This might be used within the data reduction analysis for such experiments directly. The approach is illustrated using the obtained experimental data.

Entrainment Effects on Impingement Heat Transfer: Part II—Local Heat Transfer Measurements

1985 ◽  
Vol 107 (4) ◽  
pp. 910-915 ◽  
Author(s):  
B. R. Hollworth ◽  
L. R. Gero
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Air Jet ◽  
Impingement Heat Transfer ◽  
Local Recovery ◽  
The Difference

Convective heat transfer was measured for a heated axisymmetric air jet impinging on a flat surface. It was found that the local heat transfer coefficient does not depend explicitly upon the temperature mismatch between the jet fluid and the ambient fluid if the convection coefficient is defined in terms of the difference between the local recovery temperature and target surface temperature. In fact, profiles of local heat transfer coefficients defined in this manner were found to be identical to those measured for isothermal impinging jets.

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