Full Coverage Impingement Heat Transfer: Influence of the Number of Holes

1987 ◽  
Vol 109 (4) ◽  
pp. 557-563 ◽  
Author(s):  
G. E. Andrews ◽  
J. Durance ◽  
C. I. Hussain ◽  
S. N. Ojobor
Keyword(s):  
Heat Transfer ◽  
Diameter Ratio ◽  
Hole Diameter ◽  
Unit Surface Area ◽  
Impingement Cooling ◽  
Impingement Heat Transfer ◽  
Large N ◽  
Small Influence ◽  
Unit Surface ◽  
Square Array

The choice of hole diameter in impingement cooling requires the number of holes to be specified and design information is provided for this purpose. The correlations for impingement cooling usually take geometry effects into account by using the pitch-to-diameter ratio (X/D) and this is independent of the number of holes and specified purely by the desired pressure loss at a given flow rate. Impingement heat transfer from a square array of holes was studied for a range of coolant flows G from 0.1 to 1.8 kg/sm2 at a fixed X/D of approximately 10. The number of holes per unit surface area N was varied by a factor of 70 at a constant gap-to-hole diameter ratio Z/D of 4.5 and constant gaps of 3 mm and 10 mm. It was shown that there was a range of N over which there was only a small influence on heat transfer at constant G. However, heat transfer fell at large N due to crossflow effects and at low N due to inadequate surface coverage of the impingement flow.

Impingement/Effusion Cooling With Low Coolant Mass Flow

2017 ◽  
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.

An Analysis of Heat Transfer to Axial Dispersed Flow between Rod Bundles under Reactor Emergency Cooling Conditions

1980 ◽  
Vol 102 (3) ◽  
pp. 508-512 ◽  
Author(s):  
S. Wong ◽  
L. E. Hochreiter
Keyword(s):  
Heat Transfer ◽  
Diameter Ratio ◽  
Circular Pipe ◽  
Rod Bundles ◽  
Dispersed Flow ◽  
Rod Bundle ◽  
Cooling Conditions ◽  
Flow Heat ◽  
Square Array ◽  
The Heat Transfer Coefficient

Analysis is carried out for dispersed flow heat transfer under reactor emergency cooling conditions. The present formulation explicitly reveals an extra dependence of the heat transfer coefficient and Nusselt number on the mean vapor temperature for droplet dispersed flow which is not found in single phase flow heat transfer. The heat transfer results obtained from three different geometries—an infinite square array of cylindrical rods, an annulus and a circular pipe—are compared; all have the same hydraulic diameter. It is found that, within the framework of the present analysis, results for the annulus and the rod bundles agree well when the pitch-to-diameter ratio is 1.5 or greater. The circular pipe is in general a poor approximation for rod bundle geometries except at a pitch-to-diameter ratio of about 1.3 which is typical of present day light water reactor fuel assemblies.

scholarly journals Impingement/Effusion Cooling: Overall Wall Heat Transfer

1988 ◽  
Author(s):  
G. E. Andrews ◽  
A. A. Asere ◽  
C. I. Hussain ◽  
M. C. Mkpadi ◽  
A. Nazari
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Transfer Coefficients ◽  
Film Cooling Effectiveness ◽  
Impingement Cooling ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer ◽  
Combined Heat Transfer

Experimental results are presented for the overall heat transfer coefficient within an impingement/effusion wall, using a transient cooling technique. This was previously used for determining the effusion hole heat transfer alone. Two impingement/effusion geometries were used with an 8 mm gap and the same impingement wall with an X/D of 11. The separate impingement and effusion short hole heat transfer coefficients were also determined. The impingement/effusion overall heat transfer was 45% and 30% higher than the impingement heat transfer alone for the two test geometries. The greater increase was for the higher pressure loss effusion wall. It was shown that the combined heat transfer was predominantly the addition of the impingement and effusion heat transfer coefficients but the interaction effects were significant and resulted in an approximately 15% deterioration in the combined heat transfer coefficient. Overall film cooling effectiveness was obtained that showed a significant improvement with the addition of the impingement cooling, but still had a major effusion film cooling contribution.

Parametric Study on Micro-Roughness Shapes for Enhanced Jet Impingement Heat Transfer

2020 ◽  
Author(s):  
Ramaswamy Devakottai ◽  
Srivatsan Madhavan ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Leading Edge ◽  
Jet Impingement ◽  
Diameter Ratio ◽  
External Diameter ◽  
Concentric Cylinder ◽  
Pin Fin ◽  
Plate Spacing ◽  
Impingement Heat Transfer

Abstract Development of efficient cooling technologies are imperative to support the constant push for higher turbine inlet temperatures to achieve increased overall turbine efficiency. High-pressure stage turbine blades are subjected to hostile environment involving high temperature turbulent flow exiting from the combustor section. The blade leading edge is subjected to flow stagnation and hence requires special attention in terms of both, internal and external cooling. This study is focused on improving the internal side heat transfer coefficient by installing novel micro-roughness elements on the target wall. The study is based on Singh, Prashant, et al. “Effect of micro-roughness shapes on jet impingement heat transfer and fin-effectiveness.” International Journal of Heat and Mass Transfer 132 (2019): 80–95, where different micro-roughness shapes were investigated experimentally and numerically. The authors proposed that the novel concentric-cylinder shaped roughened geometry exhibited highest fin-effectiveness. Present study reports the effect of three micro-roughness shapes, viz. cylindrical, cubic and concentric cylinder. Conjugate heat transfer study was performed, and the heat transfer performance was reported in the form of local Nusselt number and globally averaged fin-effectiveness. An array jet configuration of 5 × 5 jets with a jet-to-jet spacing of X/Djet = Y/Djet = 3 and jet-to-target plate spacing of Z/Djet = 1 was maintained for jet-diameter based Reynolds number (ReDjet) ranging from 3,000 to 12,000. Investigation on the effect of pin-fin shapes shows that the concentric-shaped micro pin-fin element had the highest fin-effectiveness of 2.45 at ReDjet = 12,000. Further, pin-fin optimization studies were performed for the concentric cylinder pin-fin shape, where the effect of pin-fin height and the effect of internal to external diameter ratio was studied. The pin-fin effectiveness increased with increase in height and diameter ratio, and a maximum fin effectiveness was observed for maximum pin-fin height.

Experimental/Numerical Study of Multiple Rows of Confined Jet Impingement Normal to a Surface at Close Distances

2012 ◽  
Author(s):  
M. E. Taslim ◽  
N. Rosso
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Numerical Study ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Hole Diameter ◽  
Impingement Cooling ◽  
Discharge Coefficients ◽  
Hexahedral Elements ◽  
D Values

Impingement cooling is used in a variety of applications ranging from industrial bakeries, paper processing, heat exchangers and specially gas turbine engines of all sizes to name a few. Convective impingement cooling has been studied numerous times in a variety of configurations. However little work has been conducted regarding impingement between two surfaces separated by less than one impingement jet hole diameter. This configuration is of special interest for gas turbine cooling applications such as in shrouds, combustor liners and airfoils cooling cavities where small holes are used to cool and purge cavities between two adjacent pieces of hardware. In this study, flow and temperature fields as well as heat transfer coefficients for confined jet impingement are being investigated for multiple rows of round jets impinging normal to a target surface less than one hole diameter from the jet origin. The experiments were conducted for five rows of jets with five jets on each row and steady-state liquid crystal thermography for heat transfer measurements were utilized. Numerical results were obtained from a three-dimensional unstructured computational fluid dynamics model with over 4 million hexahedral elements. For turbulence modeling, the realizable k–ε was employed in combination with enhanced wall treatment approach for the near wall regions. Other available RANS turbulence models such as k–ω, v2f and large eddy simulation were tried for selected geometries and results are compared with those of k–ε model. Nusselt numbers on the target areas and discharge coefficients for flow across the jet holes are reported for jet Reynolds numbers ranging from 10000 to 50000, pitch-to-diameter, P/d, values of 2,3 and 4, each for jet distance-to-diameter Z/d, values of 0.3, 0.4, 0.5, 0.6, 0.8, 1, 2 and 3. Comparisons are made between the test and numerically-obtained results in order to evaluate the employed turbulence models and validate the numerically obtained results. Results showed severe reduction in discharge coefficients as the jet holes were brought closer to each other and closer to the target wall. Heat transfer performance for the hole lateral spacing of P/d = 4 was found to be superior to that for P/d = 2 or P/d = 3.

Impact of Surface Micro-Structures on Liquid Micro-Jet Array Impingement Cooling: Comparison Between Single-Phase and Phase Change Heat Transfer

2011 ◽  
Author(s):  
Avijit Bhunia ◽  
Ya-Chi Chen ◽  
Chung-Lung Chen
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Single Phase ◽  
Nucleation Site ◽  
Impingement Cooling ◽  
Structured Surface ◽  
Impingement Heat Transfer ◽  
Plain Surface ◽  
Micro Structures ◽  
Jet Array

This article investigates liquid micro-jet array impingement cooling of a micro-structured surface. An array of 16 free-surface DI water jets, each 125 μm in diameter, and jet Reynolds number ranging between 816 and 2124, is used. A parametric study is carried out with micro-studs of varying size and spacing, implemented on a 1 cm2 base area surface. Based on the decades of research on heat transfer enhancement by surface modification, one would intuitively think that impingement cooling of a micro-structured surface will always be better than that of a plain surface. The current results are in contrary. The micro-structures actually degrade single-phase impingement heat transfer, compared to a plain surface. On the other hand, in the phase change regime they significantly enhance heat transfer, leading to a clear choice of optimal structure. The results are explained in the light of thin film dynamics, heat transfer surface area enhancement and nucleation site density.

scholarly journals Impingement Heat Transfer From Rib Roughened Surface Within Arrays of Circular Jet: The Effect of the Relative Position of the Jet Hole to the Ribs

1997 ◽  
Author(s):  
Chang Haiping ◽  
Zhang Dalin ◽  
Huang Taiping
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Gas Turbine ◽  
Relative Position ◽  
Two Dimensional ◽  
Test Results ◽  
Impingement Cooling ◽  
Impingement Heat Transfer ◽  
Roughened Surface ◽  
Rib Roughened

Impingement heat transfer from rib roughened surface within two-dimensional arrays of circular jet has been investigated experimentally. After the jet impinges on the rib roughened surface parallel to the jet plate, it is constrained to exit in a single direction along the channel formed by the jet plate and the rib roughened surface. An initial crossflow is present which approaches the arrays through an upstream extension of the channel. The configurations considered are intended to simulate the impingement cooling midchord region of the gas turbine aerofoils in case where an initial crossflow is also present. The study covered four different relative positions of the jet hole to the ribs: jet hole before the rib (−p/4), jet hole on the rib, jet hole behind the rib (+p/4) and jet hole between the ribs (midst,+p/2). The tests were performed for Reynolds number Re = 8000 and 15000, and the nondimensional jet-to-surface spacing z/d = 1.4, 2.0 and 3.0. The test results show that the impingement heat transfer from the rib roughened surface can be considerably improved by adequately arranging the relative position of the jet hole to the ribs.

Conjugate Heat Transfer CFD Predictions of the Surface Averaged Impingement Heat Transfer Coefficients for Impingement Cooling With Backside Cross-Flow

2013 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Reyad A. A. Abdul Hussain ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Conjugate Heat Transfer ◽  
Cross Flow ◽  
Heat Transfer Analysis ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer ◽  
Square Array ◽  
Velocity Turbulence

A 10 row impingement heat transfer configuration with a single sided exit at the end of the impingement gap was modelled using conjugate heat transfer CFD. The predictions were compared with experimental results for an electrically heated, 6.35mm thick, metal wall of nimonic-75, which was impingement cooled. The geometry investigated was a square array of inline impingement 10 × 10 holes with X/D of 4.66 and Z/D of 3.06, where D = 3.27mm. The use of metal walls enabled the local surface averaged heat transfer coefficient h, to be estimated from an imbedded thermocouple that logged the rate of cooling when the heating was removed. Conjugate heat transfer analysis provided local h values, which were surface averaged for comparison with the measured h. The CFD results also provided velocity, turbulence and Nusselt number distributions on the target and impingement jet surfaces. The aerodynamics data enabled the pressure loss of the system to be predicted, which compared well with experimental measurements. The predicted surface distributions of Nusselt number were similar to the surface turbulence kinetic energy distributions, which demonstrated the importance of turbulence in convective heat transfer. Surface averaged heat transfer coefficients were predicted and are in good agreement with the measurements for five coolant mass flow rates. The predicted and measured results for surface averaged h were similar to measurements of other investigators for similar impingement geometries.

Conjugate Heat Transfer CFD Predictions of Impingement Heat Transfer: The Influence of Hole Pitch to Diameter Ratio X/D at Constant Impingement Gap Z

2014 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Reyad A. A. Abdul Husain ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Conjugate Heat Transfer ◽  
Diameter Ratio ◽  
Average Heat Transfer Coefficient ◽  
Impingement Jet ◽  
Impingement Heat Transfer ◽  
Target Wall ◽  
Good Agreement

Conjugate heat transfer (CHT) computational fluid dynamic (CFD) predictions, were carried out for a 10 × 10 square array of impingement holes, for a range of pitch to diameter ratio X/D from 1.9 to 11.0 at a constant impingement gap Z of 10mm and pitch X of 15.24mm. The variation of X/D changes the impingement wall pressure loss for the same coolant mass flow rate and also changes the interaction with the impingement gap cross-flow. The experimental technique to determine the surface averaged heat transfer, used the lumped capacity method with Nimonic-75 metal walls with imbedded thermocouples and a step change in the hot wall cooling to determine the heat transfer coefficient h from the transient cooling of the metal wall. The test wall was electrically heated to about 80°C and then transiently cooled by the impingement flow and the lumped capacitance method was used to measure the locally surface average heat transfer coefficient. The predictions and measurements were carried out at an impingement jet mass flux of 1.93kg/sm2bar, which is a typical coolant flow rate for regenerative impingement cooling of low NOx gas turbine combustor walls. The computations were conducted for a fixed hot side temperature of 353K that was imposed at the hot face of the target wall. The wall temperatures as a function of distance along the gap were computed together with the impingement gap aerodynamics. Surface average heat transfer coefficient h and pressure loss predictions were in good agreement with the experimental measurements. However, there was less good agreement for the axial variation of the local surface averaged h for lower values of X/D. The surface averaged heat transfer to the impingement jet wall was also computed and shown to be roughly 70% of target wall impingement heat transfer.

scholarly journals Experimental Investigation on Impingement Heat Transfer From Rib Roughened Surface Within Arrays of Circular Jet: Effect of Geometric Parameters

1998 ◽  
Author(s):  
Chang Haiping ◽  
Zhang Jingyu ◽  
Huang Taiping
Keyword(s):  
Heat Transfer ◽  
Flux Ratio ◽  
Hole Diameter ◽  
Geometric Parameters ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Impingement Heat Transfer ◽  
Roughened Surface ◽  
Turbine Airfoils ◽  
Rib Roughened

Impingement heat transfer from rib roughened surface within two-dimensional arrays of circular jet with initial crossflow has been investigated experimentally. The configurations considered are intended to simulate the impingement cooled midchord region of the gas turbine airfoils in case where an initial crossflow is present. Many factors affect the heat transfer. The relative positions of the jet hole to the ribs and the geometric parameters have the significant effect on the heat transfer characteristics and have been experimentally studied. The investigation on the effect of the relative position of the jet hole to the ribs has been presented in an other paper. The effects of the geometric parameters such as jet hole spacing, jet-to-surface spacing, rib pitch-to-height ratio and rib height-to-hole diameter ratio on the heat transfer characteristics are considered in this paper. The experimentation is conducted under the conditions of Reynolds number 7,000–15,000 and the crossflow-to-jet mass flux ratio based on each channel/jet hole area 0∼0.5. With three jet hole spacing to jet hole diameter ratios, five jet-to-surface spacings, three rib pitch-to-height ratios and three rib height-to-hole diameter ratios, a great number of experimental data has been obtained. Based on this, the effects of the geometric parameters on the heat transfer characteristics have been obtained qualitatively and quantitatively. It can be used for evaluating the efficiency of the impingement heat transfer.

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