Detailed velocity and heat transfer measurements of an advanced insert for impingement cooling

Impinging jet cooling technique has been widely used extensively in various industrial processes, namely, cooling and drying of films and papers, processing of metals and glasses, cooling of gas turbine blades and most recently cooling of various components of electronic devices. Due to high heat removal rate the jet impingement cooling of the hot surfaces is being used in nuclear industries. During the loss of coolant accidents (LOCA) in nuclear power plant, an emergency core cooling system (ECCS) cool the cluster of clad tubes using consisting of fuel rods. Controlled cooling, as an important procedure of thermal-mechanical control processing technology, is helpful to improve the microstructure and mechanical properties of steel. In industries for heat transfer efficiency and homogeneous cooling performance which usually requires a jet impingement with improved heat transfer capacity and controllability. It provides better cooling in comparison to air. Rapid quenching by water jet, sometimes, may lead to formation of cracks and poor ductility to the quenched surface. Spray and mist jet impingement offers an alternative method to uncontrolled rapid cooling, particularly in steel and electronics industries. Mist jet impingement cooling of downward facing hot surface has not been extensively studied in the literature. The present experimental study analyzes the heat transfer characteristics a 0.15mm thick hot horizontal stainless steel (SS-304) foil using Internal mixing full cone (spray angle 20 deg) mist nozzle from the bottom side. Experiments have been performed for the varied range of water pressure (0.7–4.0 bar) and air pressure (0.4–5.8 bar). The effect of water and air inlet pressures, on the surface heat flux has been examined in this study. The maximum surface heat flux is achieved at stagnation point and is not affected by the change in nozzle to plate distance, Air and Water flow rates.

Download Full-text

Investigations of Flow and Heat Transfer Characteristics in a Channel Impingement Cooling Configuration with a Single Row of Water Jets

Energies ◽

10.3390/en14144327 ◽

2021 ◽

Vol 14 (14) ◽

pp. 4327

Author(s):

Min-Seob Shin ◽

Santhosh Senguttuvan ◽

Sung-Min Kim

Keyword(s):

Heat Transfer ◽

Local Heat Transfer ◽

Target Surface ◽

Channel Height ◽

Heat Transfer Characteristics ◽

Transfer Coefficients ◽

Impingement Cooling ◽

Average Heat ◽

Transfer Characteristics ◽

Flow And Heat Transfer

The present study experimentally and numerically investigates the effect of channel height on the flow and heat transfer characteristics of a channel impingement cooling configuration for various jet Reynolds numbers in the range of 2000–8600. A single array consisting of eleven jets with 0.8 mm diameter injects water into the channel with 2 mm width at four different channel heights (3, 4, 5, and 6 mm). The average heat transfer coefficients at the target surface are measured by maintaining a temperature difference between the jet exit and the target surface in the range of 15–17 °C for each channel height. The experimental results show the average heat transfer coefficient at the target surface increases with the jet Reynolds number and decreases with the channel height. An average Nusselt number correlation is developed based on 85 experimentally measured data points with a mean absolute error of less than 4.31%. The numerical simulation accurately predicts the overall heat transfer rate within 10% error. The numerical results are analyzed to investigate the flow structure and its effect on the local heat transfer characteristics. The present study advances the primary understanding of the flow and heat transfer characteristics of the channel impingement cooling configuration with liquid jets.

Download Full-text

Impingement Cooling Flow and Heat Transfer Under Acoustic Excitations

Journal of Heat Transfer ◽

10.1115/1.2824187 ◽

1997 ◽

Vol 119 (4) ◽

pp. 810-817 ◽

Cited By ~ 30

Author(s):

C. Gau ◽

W. Y. Sheu ◽

C. H. Shen

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Shear Layer ◽

Turbulence Intensity ◽

Pressure Level ◽

Unstable Wave ◽

Impingement Cooling ◽

Cooling Flow ◽

Acoustic Excitations ◽

Excitation Pressure

Experiments are performed to study (a) slot air jet impingement cooling flow and (b) the heat transfer under acoustic excitations. Both flow visualization and spectral energy evolution measurements along the shear layer are made. The acoustic excitation at either inherent or noninherent frequencies can make the upstream shift for both the most unstable waves and the resulting vortex formation and its subsequent pairing processes. At inherent frequencies the most unstable wave can be amplified, which increases the turbulence intensity in both the shear layer and the core and enhances the heat transfer. Both the turbulence intensity and the heat transfer increase with increasing excitation pressure levels Spl until partial breakdown of the vortex occurs. At noninherent frequencies, however, the most unstable wave can be suppressed, which reduces the turbulence intensity and decreases the heat transfer. Both the turbulence intensity and the heat transfer decreases with increasing Spl, but increases with increasing Spl when the excitation frequency becomes dominant. For excitation at high Reynolds number with either inherent or noninherent frequency, a greater excitation pressure level is needed to cause the enhancement or the reduction in heat transfer. During the experiments, the inherent frequencies selected for excitation are Fo/2 and Fo/4, the noninherent frequencies are 0.71 Fo, 0.75 Fo, and 0.8 Fo, the acoustic pressure level varies from 70 dB to 100 dB, and the Reynolds number varies from 5500 to 22,000.

Download Full-text

Investigations on the Heat Transfer and Flow Characteristics in a Trapezoid Duct for Turbine Blade Leading Edge

Volume 5A: Heat Transfer ◽

10.1115/gt2018-75156 ◽

2018 ◽

Author(s):

Hai-yong Liu ◽

Cun-liang Liu ◽

Lin Ye

Keyword(s):

Heat Transfer ◽

Heat Transfer Enhancement ◽

Cross Flow ◽

Side Wall ◽

Swirl Flow ◽

Transfer Enhancement ◽

Impingement Cooling ◽

Exit Side ◽

Target Wall ◽

The Cross

To evaluate the application of the impingement cooling in a trapezoidal duct, particularly the influence on internal cooling of the cross flow and swirl flow. Experimental and numerical studies have been performed. The experiment focuses on the heat transfer characteristics in the duct, when the numerical simulation focuses on the flow characteristics. Four Reynolds numbers (10000, 20000, 30000 and 40000), six cross flow mass flow ratios (0, 0.1, 0.2, 0.3, 0.4 and 0.5) and two impingement angle (35° and 45°) are considered in both the experiment and the numerical simulation. The temperature on the target wall and the exit side wall is measured by the thermocouples, when the realizable k-ε turbulence model and enhanced wall treatment are performed using a commercial code Fluent. The results show that only part of the jets contribute in the heat transfer enhancement on the target wall, the other jets improve a large anticlockwise vortex occupied the upper part of the duct and drive strong swirl flow. The heat transfer on the exit side wall is enhanced by the swirl flow. The cross flow is induced in the duct by the outflow of the end exit hole. It deflects the jets and abates the impingement cooling on the target wall in the downstream region but has no evidently effect on the heat transfer on the exit side wall. Higher impingement angle helps to augment the impingement cooling on the target wall and improves the resistance ability of the jets against the effect of the cross flow. The heat transfer enhancement ability on the target wall and exit side wall in the present duct is compared to that of a smooth duct. The Nusselt number of the former is about 3 times higher than that of the latter. It indicates that the impingement and swirl play equally important roles in the heat transfer enhancement in the present duct. Empirical dimensionless correlations based on the present experiment data are presented in the paper.

Download Full-text

Impingement/Effusion Cooling With Low Coolant Mass Flow

Volume 5C: Heat Transfer ◽

10.1115/gt2017-63484 ◽

2017 ◽

Cited By ~ 3

Author(s):

H. I. Oguntade ◽

G. E. Andrews ◽

A. D. Burns ◽

D. B. Ingham ◽

M. Pourkashanian

Keyword(s):

Heat Transfer ◽

Mass Flow ◽

Wall Heat Transfer ◽

Internal Wall ◽

Cooling Effectiveness ◽

Impingement Cooling ◽

Impingement Heat Transfer ◽

Design Changes ◽

Wall Impingement ◽

The Individual

A low coolant mass flow impingement/effusion design for a low NOx combustor wall cooling application was predicted, using conjugate heat transfer (CHT) computational fluid dynamics (CFD). The effusion geometry had 4306/m2 effusion holes in a square array with a hole diameter of D and pitch of X and X/D of 1.9. It had previously been shown experimentally and using CHT/CFD to have the highest adiabatic and overall cooling effectiveness for this number of effusion holes. The effect of adding an X/D of 4.7 impingement jet wall with a 6.6 mm impingement gap, Z, and Z/D of 2.0, on the overall cooling effectiveness was predicted for several coolant mass flow rates, G kg/sm2bar. At low G the internal wall heat transfer dominated the overall cooling effectiveness. The addition of impingement cooling to effusion cooling gave only a small increase in the overall cooling effectiveness at all G at 127mm downstream of the start of effusion cooling. An overall cooling effectiveness >0.7 was predicted for a low G of 0.30 kg/sm2bar. This represents about 15% of the combustion air for a typical industrial gas turbine combustor and design changes to reduce this further were suggested based on the predictions of this geometry. The main benefit of the impingement cooling was at the start of the effusion cooling, where the overall cooling effectiveness was dominated by the internal wall impingement and effusion cooling. The separate effusion and impingement cooling were also predicted for comparison with their combination. This showed that the combination of impingement and effusion was not the sum of the individual effusion and impingement heat transfer. The predictions showed that the aerodynamic interactions decreased the effusion and impingement internal wall heat transfer.

Download Full-text

Surface Curvature Effect on Slot-Air-Jet Impingement Cooling Flow and Heat Transfer Process

Journal of Heat Transfer ◽

10.1115/1.2911214 ◽

1991 ◽

Vol 113 (4) ◽

pp. 858-864 ◽

Cited By ~ 152

Author(s):

C. Gau ◽

C. M. Chung

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Transfer Process ◽

Convex Surface ◽

Heat Transfer Process ◽

Surface Curvature ◽

Curvature Effect ◽

Impingement Cooling ◽

Cooling Flow ◽

Air Jet

Experiments are performed to study surface curvature effects on the impingement cooling flow and the heat transfer processes over a concave and a convex surface. A single air jet issuing from different size slots continuously impinges normally on the concave side or the convexside of a heated semicylindrical surface. An electrical resistance wire is used to generate smoke, which allows us to visualize the impinging flow structure. The local heat transfer Nusselt number along the surfaces is measured. For impingement on a convex surface, three-dimensional counterrotating vortices on the stagnation point are initiated, which result in the enhancement of the heat transfer process. For impingement on a concave surface, the heat transfer Nusselt number increases with increasing surface curvature, which suggests the initiation of Taylor–Go¨rtler vortices along the surface. In the experiment, the Reynolds number ranges from 6000 to 350,000, the slot-to-plate spacing from 2 to 16, and the diameter-to-slot-width ratio D/b from 8 to 45.7. Correlations of both the stagnation point and the average Nusselt number over the curved surface, which account for the surface curvature effect, are presented.

Download Full-text

Experimental Investigation of Submerged Impinging Jet Using Cu-Water Nanofluid

2010 14th International Heat Transfer Conference, Volume 5 ◽

10.1115/ihtc14-22040 ◽

2010 ◽

Author(s):

Qiang Li ◽

Yimin Xuan ◽

Feng Yu ◽

Junjie Tan

Keyword(s):

Heat Transfer ◽

Experimental Investigation ◽

Volume Fraction ◽

Cooling System ◽

Heated Surface ◽

Particle Volume Fraction ◽

Jet Impingement ◽

Particle Volume ◽

Impingement Cooling ◽

System Pressure

An experimental investigation was performed to study the heat transfer and flow features of Cu-water nanofluids (Cu particles with 26 nm diameter) in a submerged jet impingement cooling system. Three particular nozzle-to-heated surface distances (2, 4 and 6 mm) and four particle volume fractions (1.5%, 2.0%, 2.5% and 3.0%) are involved in the experiment. The experimental results reveal that the suspended nanoparticles increase the heat transfer performance of the base liquid in the jet impingement cooling system. Within the range of experimental parameters considered, it has been found that highest surface heat transfer coefficients can be achieved using a nozzle-to-surface distance of 4 mm and the nanofluid with 3.0% particle volume fraction. In addition, the experiments show that the system pressure drop of the dilute nanofluids is almost equal to that of water under the same entrance velocity.

Download Full-text

Conjugate Heat Transfer Characteristics of Double Wall Cooling on a Film Plate With Gradient Thickness

Volume 7B: Heat Transfer ◽

10.1115/gt2020-14275 ◽

2020 ◽

Author(s):

Juan He ◽

Qinghua Deng ◽

Weilun Zhou ◽

Wei He ◽

Tieyu Gao ◽

...

Keyword(s):

Heat Transfer ◽

Conjugate Heat Transfer ◽

Flow Direction ◽

Plate Thickness ◽

Heat Transfer Characteristics ◽

Cooling Effectiveness ◽

Cooling Performance ◽

Impingement Cooling ◽

Blowing Ratio ◽

Double Wall

Abstract Double wall cooling, consisting of internal impingement cooling and external film cooling, is an advanced cooling method of gas turbines. In this paper, the flow and conjugate heat transfer characteristics of double wall cooling which has a film plate with gradient thickness are analyzed numerically. The detailed overall cooling effectiveness distributions are obtained by solving steady three dimensional Reynolds-averaged Navier-Stokes equations. In the double wall cooling scheme, seven vertical film holes and six impingement holes are staggered with same diameter (D), and the hole pitch of them are both set to 6D in flow direction and lateral direction. The gradient thickness along the flow direction is realized by setting the angle (α) between the lower surface of the film plate and the horizontal plane at −1.5 deg and 1.5 deg respectively. By comparing the results of four broadly used turbulence models with experimental data, SST k-ω is selected as the optimal turbulence model for double wall cooling analysis in this paper. In addition, the number of grids are finally determined to be 5.2 million by grid sensitivity calculation. The influence of the thickness gradient on the overall cooling effectiveness is revealed by comparing with the constant thickness film plate (Baseline 1 and 2), and all the cases are performed under four various coolant mass flow rates, which correspond to blowing ratios ranging from 0.25 to 1.5. The calculated results show that the thickening of the film plate downstream is beneficial to improve overall cooling effectiveness at low blowing ratio, which is benefit from two aspects. One is the thicken film plate weakens the flow separation in film hole and velocity of film hole outlet, another is the thicken film plate makes the impingement channels convergence, and impingement cooling is strengthened to some extent. However, with the increase of blowing ratio, the increasing trend gradually weakens due to the jet-off and limited impinge ability. For thickening film plate, the variations of the double wall cooling configurations are considered at initial film plate thickness tf of 2D and 3D, it is found that the ability to improve the overall cooling effectiveness by thickening the film plate downstream decrease as the initial film plate thickness increases, which is due to the increase of heat transfer resistance, and another finding is the cooling effectiveness of downstream thickening film plate with initial thickness of 2D is higher than that of 3D, which will provide a theoretical foundation both for improving cooling performance and reducing turbine blade weight at the same time. The influence of initial impingement gap H is also observed, and the study come to the fact that the best cooling performance occurred in H = 2D.

Download Full-text