Identification of Dominant Heat Transfer Modes Associated With the Impingement of an Elliptical Jet Array

1999 ◽  
Vol 122 (2) ◽  
pp. 240-247 ◽  
Author(s):  
S. C. Arjocu ◽  
J. A. Liburdy
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Thermochromic Liquid Crystal ◽  
Aspect Ratios ◽  
Low Reynolds ◽  
The Heat Transfer Coefficient

The characteristics of the impinging heat transfer of a three-by-three square array of submerged, elliptic impinging jets was studied. Low Reynolds number conditions, 300 to 1500, are considered for two different elliptic jet aspect ratios, with the impingement distance ranging from 1 to 6 jet hydraulic diameters. A transient thermochromic liquid crystal method was used to map the local heat transfer coefficient distribution. The results are reported for the unit cell under the center jet and detail the mean heat transfer as well as the characteristics of the spatial variation of the heat transfer coefficient. The average heat transfer is found to depend inversely on the elliptic jet aspect ratio at these low Reynolds numbers. Distributions of the heat transfer coefficient, h, are also used to obtain proper orthogonal decompositions of h which are used to identify major spatially distributed features. [S0022-1481(00)02102-2]

Heat Transfer Enhancement by Turbulent Impinging Jets

2000 ◽  
Author(s):  
M. Kumagai ◽  
R. S. Amano ◽  
M. K. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Stokes Equations ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Abstract A numerical and experimental investigation on cooling of a solid surface was performed by studying the behavior of an impinging jet onto a fixed flat target. The local heat transfer coefficient distributions on a plate with a constant heat flux were computationally investigated with a normally impinging axisymmetric jet for nozzle diameter of 4.6mm at H/d = 4 and 10, with the Reynolds numbers of 10,000 and 40,000. The two-dimensional cylindrical Navier-Stokes equations were solved using a two-equation k-ε turbulence model. The finite-volume differencing scheme was used to solve the thermal and flow fields. The predicted heat transfer coefficients were compared with experimental measurements. A universal function based on the wave equation was developed and applied to the heat transfer model to improve calculated local heat transfer coefficients for short nozzle-to-plate distance (H/d = 4). The differences between H/d = 4 and 10 due to the correlation among heat transfer coefficient, kinetic energy and pressure were investigated for the impingement region. Predictions by the present model show good agreement with the experimental data.

scholarly journals A Statistical Evaluation of the Influence of Different Material and Process Parameters on the Heat Transfer Coefficient in Gravity Die Casting

Metals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1367
Author(s):  
Nino Wolff ◽  
Golo Zimmermann ◽  
Uwe Vroomen ◽  
Andreas Bührig-Polaczek
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Die Casting ◽  
Local Heat Transfer ◽  
Mold Temperature ◽  
Local Heat ◽  
Mold Material ◽  
Transfer Coefficients ◽  
The Heat Transfer Coefficient

Local heat transfer in gravity die casting is of great importance for precision in terms of distortion, mechanical properties, and the quality of the castings due to its effect on solidification. Depending on contact conditions such as liquid melt to solid mold, a gap between mold and component, or contact pressure between casting and mold as a result of shrinkage, there are very large differences in heat transfer. The influences of mold material, mold coating and its influence of aging, mold temperature control, and layout on the heat transfer coefficient (HTC) were investigated experimentally for different contact cases. The experiments were carried out on a rotationally symmetrical experimental setup with modular exchangeable die inserts and cores using an AlSi7Mg0.3 alloy. From the results of the individual test series, the quantitative shares of the above-mentioned influencing variables in the respective effective heat transfer coefficients were determined by means of analysis of variance. From this, the parameters having the most significant influence on the local heat balance were derived.

Experimental and Numerical Investigation of Impingement Cooling in a Combustor Liner Heat Shield

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Sebastian Spring ◽  
Diane Lauffer ◽  
Bernhard Weigand ◽  
Matthias Hase
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Numerical Investigation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Shield ◽  
Impingement Cooling ◽  
Combustor Liner ◽  
The Heat Transfer Coefficient

A combined experimental and numerical investigation of the heat transfer characteristics inside an impingement cooled combustor liner heat shield has been conducted. Due to the complexity and irregularity of heat shield configurations, standard correlations for regular impingement fields are insufficient and detailed investigations of local heat transfer enhancement are required. The experiments were carried out in a perspex model of the heat shield using a transient liquid crystal method. Scaling of the model allowed to achieve jet Reynolds numbers of up to Rej=34,000 without compressibility effects. The local air temperature was measured at several positions within the model to account for an exact evaluation of the heat transfer coefficient. Analysis focused on the local heat transfer distribution along the heat shield target plate, side rims, and central bolt recess. The results were compared with values predicted by a standard correlation for a regular impingement array. The comparison exhibited large differences. While local values were up to three times larger than the reference value, the average heat transfer coefficient was approximately 25% lower. This emphasized that standard correlations are not suitable for the design of complex impingement cooling pattern. For thermal optimization the detailed knowledge of the local variation of the heat transfer coefficient is essential. From the present configuration, some concepts for possible optimization were derived. Complementary numerical simulations were carried out using the commercial computational fluid dynamics (CFD) code ANSYS CFX. The motivation was to evaluate whether CFD can be used as an engineering design tool in the optimization of the heat shield configuration. For this, a validation of the numerical results was required, which for the present configuration was achieved by determining the degree of accuracy to which the measured heat transfer rates could be computed. The predictions showed good agreement with the experimental results, both for the local Nusselt number distributions as well as for averaged values. Some overprediction occurred in the stagnation regions, however, the impact on overall heat transfer coefficients was low and average deviations between numerics and experiments were in the order of only 5–20%. The numerical investigation showed that contemporary CFD codes can be used as suitable means in the thermal design process.

Local Heat Transfer Coefficient Distribution With Air Impingement Into a Cavity

1972 ◽  
Author(s):  
F. Burggraf
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Local Heat Transfer Coefficient ◽  
Cavity Surface ◽  
Transfer Coefficients ◽  
Coefficient Distribution

Impingement heat transfer coefficients are presented for a row of holes impinging into an oval cavity with the spent air leaving through holes on one or both sides of the cavity. The distribution around the cavity surface is obtained and is correlated with a survey of the recent literature. In addition, local heat flux gages were used with an impingement jet air supply which could be changed in location along the axis of the test section. This permitted the determination of local heat transfer coefficient distribution over the surface both around the cavity and also in the region between the impinging jets. This two-dimensional distribution is shown to be influenced by the bleed geometry and the shape of the impinging jet holes.

scholarly journals Thermal-mechanical characteristics of stationary and pulsating gas flows in a gas-dynamic system (in relation to the exhaust system of an engine)

2021 ◽  
pp. 171-171
Author(s):  
Leonid Plotnikov
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Dynamic System ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Stationary Flow ◽  
Local Heat ◽  
Gas Flows ◽  
Gas Dynamic ◽  
The Heat Transfer Coefficient

It is a relevant objective in thermal physics and in building reciprocating internal combustion engines (RICE) to obtain new information about the thermal-mechanical characteristics of both stationary and pulsating gas flows in a complex gas-dynamic system. The article discusses the physical features of the gas dynamics and heat transfer of flows along the length of a gas-dynamic system typical for RICE exhaust systems. Both an experimental set-up and experimental techniques are described. An indirect method for determining the local heat transfer coefficient of gas flows in pipelines with a constant temperature hot-wire anemometer is proposed. The regularities of changes in the instantaneous values of the flow rate and the local heat transfer coefficient in time for stationary and pulsating gas flows in different elements of the gas-dynamic system are obtained. The regularities of the change in the turbulence number of stationary and pulsating gas flows along the length of RICE gas-dynamic systems are established (it is shown that the turbulence number for a pulsating gas flow is 1.3-2.1 times higher than for a stationary flow). The regularities of changes in the heat transfer coefficient along the length of the engine?s gas-dynamic system for stationary and pulsating gas flows were identified (it was established that the heat transfer coefficient for a stationary flow is 1.05-1.4 times higher than for a pulsating flow). Empirical equations are obtained to determine the turbulence number and heat transfer coefficient along the length of the gas-dynamic system.

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.

Uneven Wall Heat Flux Effect on Local Heat Transfer in Rotating Two-Pass Channels With Two Opposite Ribbed Walls

1996 ◽  
Vol 118 (4) ◽  
pp. 864-876 ◽  
Author(s):  
Shou-Shing Hsieh ◽  
Wei-Jen Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Secondary Flows ◽  
Fluid Temperature ◽  
Bulk Fluid ◽  
Aspect Ratios ◽  
Uneven Heating

The influence of rotation and uneven heating condition on the local heat transfer coefficient in rotating, two-pass rib-roughened (rib height e/DH ≈ 0.17 − 0.20; rib pitch p/e = 5) rectangular channels with cross-sectional aspect ratios of 1 and 1.5 were studied for Reynolds numbers from 5000 to 25,000 and rotation numbers from 0 to 0.6152. Regionally averaged Nusselt number variations along the duct have been determined over the trailing and leading surfaces for two pass channels. In general, Coriolis-induced secondary flows are shown to enhance local heat transfer over the trailing (leading) surface in the first (second) pass compared to a duct without rotation. Centrifugal buoyancy is shown to influence the heat transfer response with heat transfer being imposed on both leading and trailing surfaces as the wall-to-bulk fluid temperature difference is increased with other controlling parameters fixed. Results also indicate a slight decrease in heat transfer coefficient for an increase in passage aspect ratio. Results are compared with previous studies. It is found that the results agree quite well with those reported by other works for two-pass flow channels.

scholarly journals Detailed Measurements of Local Heat Transfer Coefficient and Adiabatic Wall Temperature Beneath an Array of Impinging Jets

1993 ◽  
Author(s):  
Kenneth W. Van Treuren ◽  
Zuolan Wang ◽  
Peter T. Ireland ◽  
Terry V. Jones
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Wall Temperature ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Local Heat Transfer Coefficient ◽  
Target Plate ◽  
Adiabatic Wall

A transient method of measuring the local heat transfer under an array of impinging jets has been developed. The use of a temperature sensitive coating consisting of three encapsulated thermochromic liquid crystal materials has allowed the calculation of both the local adiabatic wall temperature and the local heat transfer coefficient over the complete surface of the target plate. The influence of the temperature of the plate through which the impingement gas flows on the target plate heat transfer has been quantified. Results are presented for a single inline array configuration over a range of jet Reynolds numbers.

The Local Heat-Transfer Coefficient Around a Heated Horizontal Cylinder in an Intense Sound Field

1962 ◽  
Vol 84 (3) ◽  
pp. 245-250 ◽  
Author(s):  
R. M. Fand ◽  
J. Roos ◽  
P. Cheng ◽  
J. Kaye
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Sound Field ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Horizontal Cylinder ◽  
Local Heat Transfer Coefficient ◽  
The Heat Transfer Coefficient

In order to achieve a better understanding of the physical mechanism of interaction between free convection and sound, an experimental investigation of the local heat-transfer coefficient around the circumference of a heated horizontal cylinder, both in the presence and absence of a strong stationary sound field, has been carried out. The results show that superposition of intense sound upon the free-convection temperature-velocity field about a heated horizontal cylinder increases the heat-transfer coefficient both on the under and upper portions of the cylinder’s surface. In the presence of a sound field for which SPL = 146 db (re 0.0002 microbar) and f = 1500 cps, the maximum measured increases in the local heat-transfer coefficient on the under and upper portions of a 3/4-in-diam cylinder—relative to the free convection case at the same temperature potential—were found to be approximately 250 and 1200 per cent, respectively. A comparison of these results with earlier flow-visualization studies indicates that the relatively large percentage increase in the heat-transfer coefficient on the upper portion of the cylinder is caused by the oscillating vortex flow which is characteristic of thermoacoustic streaming. The reasons for the increase in the heat-transfer coefficient on the lower portion of the cylinder appear to be: (a) An increase in laminar boundary-layer velocities (steady components) in this region; and (b) modification of the boundary-layer temperature profile due to acoustically induced oscillations (unsteady components) within the laminar boundary layer. The experimental data presented can be used to check the validity of future analytical investigations of thermoacoustic phenomena.

Effects of Cooling Films on the Heat Transfer Coefficient on a Flat Plate With Zero Mainstream Pressure Gradient

1985 ◽  
Vol 107 (1) ◽  
pp. 105-110 ◽  
Author(s):  
N. Hay ◽  
D. Lampard ◽  
C. L. Saluja
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Polymer Surface ◽  
Flux Ratio ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
The Heat Transfer Coefficient

The influence of injection of cooling films through a row of holes on the heat transfer coefficient on a flat plate is investigated for a range of mass flux ratio using a heat-mass transfer analogy. Injection angles of 35 deg and 90 deg are covered. The experimental technique employed uses a swollen polymer surface and laser holographic interferometry. The results presented show the change in local heat transfer coefficient over the no-injection values at the centerline and off-centerline locations for various streamwise stations. The effect of injection on laterally averaged heat transfer coefficients is also assessed.

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