Impingement Cooling in Narrow Rectangular Channel With Novel Surface Features

2016 ◽  
Author(s):  
Sarwesh Narayan Parbat ◽  
Sin Chien Siw ◽  
Minking K. Chyu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Rectangular Channel ◽  
Jet Impingement ◽  
Test Case ◽  
Target Plate ◽  
Surface Features ◽  
Baseline Case ◽  
The Heat Transfer Coefficient

This paper describes a detailed experimental investigation of narrow jet impingement channel with surface features. Three novel surface features: aerofoil shaped dimple cavities on the target plate, chevron elements extending between the jet issuing plate and the target plate and 45 degree wedges mounted on the jet-issuing plate, are proposed. The narrow rectangular channel is 254 mm × 57.2 mm × 19.1 mm (10” × 2.25” × 0.75”) in dimensions and consists of five jets with a constant diameter, D of 9.525 mm (0.375”). The inter-jet spacing and jet-to-target plate distance is 4D and 2D, respectively. Three test cases with different novel surface features are proposed, and the effect of these surface features on the distribution of heat transfer coefficient on the target plate is characterized using the transient liquid crystal technique. In the first test case, dimpulated surface features are introduced on the target plate. The second case consists of chevron elements which extend between the jet issuing plate and the target plate, while the third case has 45 degree wedges mounted on the jet-issuing plate. The smooth jet impingement channel is used as a baseline case for comparison of the heat transfer coefficient distribution on the target plate. The Reynolds number is defined based on the jet diameter, D and bulk velocity of the jet. The experiments were performed at Reynolds number ranging between 61,000 to 98,000. In order to gain a better insight of the flow field within the channel for each of these features, a steady state numerical simulation was performed for each case using the commercially available software, ANSYS CFX. The boundary conditions for these simulations were set as close to the experimental conditions as possible. For turbulence closure, the Shear Stress Transport (SST) model was used which has been shown to be reasonably accurate with moderate computational costs. The numerical results are in favorable trend compared to the values obtained through experimentation. However, in certain regions, the SST turbulence model has overpredicted the heat transfer coefficient values. The results show that the first test case with dimpulated surface features exhibits the highest heat transfer enhancement among all the tested configurations. This enhancement is approximately 25 percent higher than that of the baseline case. The presence of the chevron elements has minimized the deflection of the jets due to crossflow, but, inhibited the spreading of the impinging jets on the target plate. This, in turn, has reduced the local heat transfer performance quite substantially. In case of the 45 degree wedges, the heat transfer enhancement was augmented at the downstream, which was ultimately caused by the diversion of the crossflow towards the target plate.

Experimental Investigation of Air–Water Mist Jet Impingement Cooling Over a Heated Cylinder

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Chunkyraj Khangembam ◽  
Dushyant Singh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Stagnation Point ◽  
Jet Impingement ◽  
Water Mist ◽  
Heated Cylinder ◽  
Air Jet ◽  
The Heat Transfer Coefficient

Experimental investigation on heat transfer mechanism of air–water mist jet impingement cooling on a heated cylinder is presented. The target cylinder was electrically heated and was maintained under the boiling temperature of water. Parametric studies were carried out for four different values of mist loading fractions, Reynolds numbers, and nozzle-to-surface spacings. Reynolds number, Rehyd, defined based on the hydraulic diameter, was varied from 8820 to 17,106; mist loading fraction, f ranges from 0.25% to 1.0%; and nozzle-to-surface spacing, H/d was varied from 30 to 60. The increment in the heat transfer coefficient with respect to air-jet impingement is presented along with variation in the heat transfer coefficient along the axial and circumferential direction. It is observed that the increase in mist loading greatly increases the heat transfer rate. Increment in the heat transfer coefficient at the stagnation point is found to be 185%, 234%, 272%, and 312% for mist loading fraction 0.25%, 0.50%, 0.75%, and 1.0%, respectively. Experimental study shows identical increment in stagnation point heat transfer coefficient with increasing Reynolds number, with lowest Reynolds number yielding highest increment. Stagnation point heat transfer coefficient increased 263%, 259%, 241%, and 241% as compared to air-jet impingement for Reynolds number 8820, 11,493, 14,166, and 17,106, respectively. The increment in the heat transfer coefficient is observed with a decrease in nozzle-to-surface spacing. Stagnation point heat transfer coefficient increased 282%, 248%, 239%, and 232% as compared to air-jet impingement for nozzle-to-surface spacing of 30, 40, 50, and 60, respectively, is obtained from the experimental analysis. Based on the experimental results, a correlation for stagnation point heat transfer coefficient increment is also proposed.

Heat Transfer Experiments in a Confined Jet Impingement Configuration Using Transient Techniques

2010 ◽  
Author(s):  
Florian Hoefler ◽  
Nils Dietrich ◽  
Jens von Wolfersdorf
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Direction ◽  
Jet Impingement ◽  
Thermochromic Liquid Crystal ◽  
Transient Techniques ◽  
Nusselt Numbers ◽  
The Heat Transfer Coefficient ◽  
Good Agreement

A confined jet impingement configuration has been investigated in which the matter of interest is the convective heat transfer from the airflow to the passage walls. The geometry is similar to gas turbine applications. The setup is distinct from usual cooling passages by the fact that no crossflow and no bulk flow direction are present. The flow exhausts through two staggered rows of holes opposing the impingement wall. Hence, a complex 3-D vortex system arises, which entails a complex heat transfer situation. The transient Thermochromic Liquid Crystal (TLC) method was used to measure the heat transfer on the passage walls. Due to the nature of the experiment, the fluid as well as the wall temperature vary with location and time. As a prerequisite of the transient TLC technique, the heat transfer coefficient is assumed to be constant over the transient experiment. Therefore, additional measures were taken to qualify this assumption. The linear relation between heat flux and temperature difference could be verified for all measurement sites. This validates the assumption of a constant heat transfer coefficient which was made for the transient TLC experiments. Nusselt number evaluations from all techniques show a good agreement, considering the respective uncertainty ranges. For all sites the Nusselt numbers range within ±9% of the values gained from the TLC measurement.

Predicting Heat Transfer From Unsteady Synthetic Jets

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Mehmet Arik ◽  
Tunc Icoz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Small Scale ◽  
Wide Range ◽  
The Heat Transfer Coefficient

Synthetic jets are piezo-driven, small-scale, pulsating devices capable of producing highly turbulent jets formed by periodic entrainment and expulsion of the fluid in which they are embedded. The compactness of these devices accompanied by high air velocities provides an exciting opportunity to significantly reduce the size of thermal management systems in electronic packages. A number of researchers have shown the implementations of synthetic jets on heat transfer applications; however, there exists no correlation to analytically predict the heat transfer coefficient for such applications. A closed form correlation was developed to predict the heat transfer coefficient as a function of jet geometry, position, and operating conditions for impinging flow based on experimental data. The proposed correlation was shown to predict the synthetic jet impingement heat transfer within 25% accuracy for a wide range of operating conditions and geometrical variables.

Convective heat transfer and fluid flow characteristics in fin and oval-tube heat exchanger

2021 ◽  
Vol 15 (2) ◽  
pp. 7936-7947
Author(s):  
Yamina Abdoune ◽  
Sahel Djamel ◽  
Benzeguir Redouane ◽  
Alem Karima
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Tube Heat Exchanger ◽  
Baseline Case ◽  
Oval Tube ◽  
The Heat Transfer Coefficient

The forced convective heat transfer behavior of a turbulent air flow, steady and Newtonian over a fin and oval-tube heat exchanger has been examined numerically. Where, the effect of the tube tilt angle (α) on the heat transfer coefficient and the friction factor was tested. The inclination angle of the oval-tubes going from 0° (Baseline case) to 90° with a step of 10°. The fluid flows and heat transfer characteristics are presented for Reynolds numbers ranging from 3.000 to 12.000. All investigations are carried out with the help of the CFD ANSYS Fluent. Heat transfer coefficient results in the term of the Nusselt number are validated with the available experimental data and a maximum deviation of 9 % is observed. Reasonable agreement is found. The obtained results show that the tube's inclination angle of 20° is the best design which significantly removes the hot spots behind the tubes, thus giving an increase in the heat transfer coefficient of 13 % compared to the baseline case. In addition, useful correlations are developed to predict Nusselt number and friction factor in the fin and oval-tube heat exchanger.

Effect of Acceleration on the Heat Transfer Coefficient on a Film-Cooled Surface

1991 ◽  
Vol 113 (3) ◽  
pp. 464-471 ◽  
Author(s):  
H. D. Ammari ◽  
N. Hay ◽  
D. Lampard
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Mass Transfer ◽  
Experimental Investigation ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Density Ratio ◽  
Baseline Case ◽  
Density Ratios ◽  
The Heat Transfer Coefficient

Results are presented of an experimental investigation into the influence of mainstream acceleration on the heat transfer coefficient downstream of injection through a row of 35 deg holes in a flat plate. A mass transfer analogue technique was used, with two uniform acceleration parameters, K ( = v(du∞/dx)/u2∞, of 1.9 × 10−6 and 5.0×10−6 in addition to the zero acceleration baseline case. Two injectants, air and carbon dioxide, were employed to give coolant-to-mainstream density ratios of 1.0 and 1.52, respectively. The blowing rate varied from 0.5 to 2.0. The heat transfer coefficient beneath the film decreased progressively as the acceleration increased, with maximum reductions from the zero acceleration datum case of about 27 percent. In the presence of acceleration, the heat transfer coefficient at a given blowing rate was dependent on the density ratio, an increase in the density ratio leading to a decrease in the heat transfer coefficient. An empirical correlation of the data over most of the range of densities and blowing rates of the experiments has been developed.

Experimental and Numerical Investigation of Thermal Performance of Synthetic Jet Impingement

2020 ◽  
Author(s):  
Pushpanjay K. Singh ◽  
Rohit Kothari ◽  
Santosh K. Sahu ◽  
Prabhat K. Upadhyay ◽  
Shashwat Singh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Test Specimen ◽  
Electronics Cooling ◽  
Jet Impingement ◽  
Synthetic Jet ◽  
Geometrical Parameters ◽  
The Heat Transfer Coefficient ◽  
Plate Distance

Abstract Synthetic jet potentially useful in electronics cooling is investigated both numerically and experimentally. In the present study, a confined three dimensional synthetic jet with sinusoidal moving wall is considered. Computations are carried out using the FLUENT software with the coupled user defined function describing the diaphragm movement. In this study the effect of various geometrical parameters influencing the flow field and heat transfer are investigated. The effects of change in orifice geometry (circular, square and rectangular), orifice aspect ratio, and jet-to-plate distance are studied for a given hydraulic diameter. The heat transfer results obtained from the synthetic jet is compared with the continuous jet. An electromagnetic actuator is used as an oscillating diaphragm for the generation of synthetic jet. A stainless steel foil with 0.05 mm thickness is used as the test specimen. The surface temperature of the test specimen is measured by using a thermal imaging technique during synthetic jet impingement and a constant temperature anemometer has been employed for velocity measurement. Tests are carried out for Reynolds number of 5448, varied range of jet-to-plate distance (1–18). The maximum value of the heat transfer coefficient is found to be 16 times more than the heat transfer coefficient for natural convection.

Evaporation of lignin-lean black liquor

TAPPI Journal ◽  
2015 ◽  
Vol 14 (7) ◽  
pp. 441-450
Author(s):  
HENRIK WALLMO, ◽  
ULF ANDERSSON ◽  
MATHIAS GOURDON ◽  
MARTIN WIMBY
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Black Liquor ◽  
Salt Content ◽  
Solubility Limit ◽  
Lignin Removal ◽  
Kraft Black Liquor ◽  
Black Liquors ◽  
The Heat Transfer Coefficient

Many of the pulp mill biorefinery concepts recently presented include removal of lignin from black liquor. In this work, the aim was to study how the change in liquor chemistry affected the evaporation of kraft black liquor when lignin was removed using the LignoBoost process. Lignin was removed from a softwood kraft black liquor and four different black liquors were studied: one reference black liquor (with no lignin extracted); two ligninlean black liquors with a lignin removal rate of 5.5% and 21%, respectively; and one liquor with maximum lignin removal of 60%. Evaporation tests were carried out at the research evaporator in Chalmers University of Technology. Studied parameters were liquor viscosity, boiling point rise, heat transfer coefficient, scaling propensity, changes in liquor chemical composition, and tube incrustation. It was found that the solubility limit for incrustation changed towards lower dry solids for the lignin-lean black liquors due to an increased salt content. The scaling obtained on the tubes was easily cleaned with thin liquor at 105°C. It was also shown that the liquor viscosity decreased exponentially with increased lignin outtake and hence, the heat transfer coefficient increased with increased lignin outtake. Long term tests, operated about 6 percentage dry solids units above the solubility limit for incrustation for all liquors, showed that the heat transfer coefficient increased from 650 W/m2K for the reference liquor to 1500 W/m2K for the liquor with highest lignin separation degree, 60%.

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