Enhanced Impingement Heat Transfer: The Influence of Impingement X/D for Interrupted Rib Obstacles (Rectangular Pin Fins)

2004 ◽  
Author(s):  
G. E. Andrews ◽  
R. A. A. Abdul Hussain ◽  
M. C. Mkpadi
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Pressure Loss ◽  
Smooth Wall ◽  
Flow Rates ◽  
Impingement Heat Transfer ◽  
Main Effect ◽  
Pin Fins ◽  
Hole Arrays ◽  
Square Hole

Impingement flat wall cooling, with 15.2 mm pitch square hole arrays, was investigated in the presence of an array of interrupted rib obstacles. These ribs took the form of rectangular pin-fins with a 50% blockage to the crossflow. One side exit of the air was used and there was no initial crossflow. Three hole diameters were investigated, which allowed the impingement wall pressure loss to be varied at constant coolant mass flow rate. Combustor wall cooling was the main application of the work, where a low wall cooling pressure loss is required if the air is subsequently to be fed to a low NOx combustor. The results showed that the increase in surface average impingement heat transfer, relative to that for a smooth wall, was small and greatest for an X/D of 3.06 at 15%. The main effect of the interrupted ribs was to change the influence of crossflow, which produced a deterioration in the heat transfer with distance compared with a smooth impingement wall. With the interrupted ribs the heat transfer increased with distance. If the heat transfer was compared at the trailing edge of the test section, where the upstream crossflow was at a maximum, then at high coolant flow rates the increase in heat transfer was 21%, 47% and 25% for X/D of 4.66, 3.06 and 1.86 respectively.

Enhanced Impingement Heat Transfer: The Influence of Impingement X/D for Interrupted Rib Obstacles (Rectangular Pin Fins)

2004 ◽  
Vol 128 (2) ◽  
pp. 321-331 ◽  
Author(s):  
G. E. Andrews ◽  
R. A. A. Abdul Hussain ◽  
M. C. Mkpadi
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Cross Flow ◽  
Smooth Wall ◽  
Flow Rates ◽  
Impingement Heat Transfer ◽  
Main Effect ◽  
Pin Fins ◽  
Hole Arrays ◽  
Square Hole

Impingement flat wall cooling, with 15.2 mm pitch square hole arrays, was investigated in the presence of an array of interrupted rib obstacles. These ribs took the form of rectangular pin-fins with a 50% blockage to the cross flow. One side exit of the air was used, and there was no initial cross flow. Three hole diameters were investigated, which allowed the impingement wall pressure loss to be varied at constant coolant mass flow rate. Combustor wall cooling was the main application of the work, where a low wall cooling pressure loss is required if the air is subsequently to be fed to a low NOx combustor. The results showed that the increase in surface average impingement heat transfer, relative to that for a smooth wall, was small and greatest for an X∕D of 3.06 at 15%. The main effect of the interrupted ribs was to change the influence of cross flow, which produced a deterioration in the heat transfer with distance compared to a smooth impingement wall. With the interrupted ribs the heat transfer increased with distance. If the heat transfer was compared at the trailing edge of the test section, where the upstream cross flow was at a maximum, then at high coolant flow rates the increase in heat transfer was 21%, 47%, and 25% for X∕D of 4.66, 3.06, and 1.86, respectively.

scholarly journals Predictions of Impingement Heat Transfer With Dimples, Pin-Fins and Zig-Zag Rib Obstacles: Conjugate Heat Transfer Computational Fluid Dynamics Predictions

2019 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Cross Flow ◽  
Target Surface ◽  
Smooth Wall ◽  
Transfer Enhancement ◽  
Air Mass ◽  
Impingement Jet ◽  
Impingement Heat Transfer ◽  
Pin Fins

Abstract Regenerative cooling of low NOx gas turbine combustors was investigated using impingement heat transfer with all the combustion air used for wall cooling prior to passing to the flame stabiliser. 10 rows of impingement holes were modelled. Three obstacles were compared with smooth wall impingement heat transfer. The CHT/CFD methodology used was that validated against experimental results in previous publications of the authors. The impingement heat transfer enhancement geometries investigated were circular pin-fins, dimples and zig-zag ribs, which were aligned transverse to the direction of the cross-flow on the impingement target surface. The obstacles were equally spaced on the centre-line between each row of impingement jets transverse to the cross-flow. One heat transfer enhancement obstacle was used per impingement jet air hole. The CFD calculations were carried out for an air mass flux G of 1.08, 1.48 and 1.94 kg/sm2bara, which are the high flow rates used for regenerative combustor wall cooling. Comparison of the current CFD predictions and previous CFD work, that have experimental data, were made for the flow pressure loss and the surface and locally X2 average HTC, h. It was concluded that none of the obstacles in the impingement gap a significant increase in the surface averaged heat transfer coefficient (HTC). The impact of the obstacles was to increase the flow maldistribution due to the increased pressure loss. This resulted is less heat transfer from the reduced air mass flow in the first 4 holes and increased heat transfer in the last 4 holes, relative to the smooth wall results. The main effect of the obstacles was to increase the heat transfer to the impingement jet surface. The dimpled surface was predicted to have a very poor performance, with significantly reduced impingement heat transfer. This was due to the impingement jets being deflected away from the target surface by the shape of the dimples and this reduced the surface heat transfer.

Impingement Jet Cooling With Ribs and Pin Fin Obstacles in Co-Flow Configurations: Conjugate Heat Transfer Computational Fluid Dynamic Predictions

2016 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Conjugate Heat Transfer ◽  
Coolant Flow ◽  
Experimental Results ◽  
Hole Density ◽  
Flow Rates ◽  
Pin Fin ◽  
Impingement Jet ◽  
Pin Fins

Conjugate heat transfer (CHT) computational fluid dynamics (CFD) predictions were carried out for impingement heat transfer with obstacle (fins) walls on the target surface midway between the impingement jets and aligned in the direction of the crossflow (direction of outflow of the impingement cooling air) to minimise the pressure loss increase due to the fins. A single sided flow exit was used in a geometry that was applicable to reverse flow cooling of low NOx combustors, but was also relevant to turbine blade and nozzle cooling. A 10 × 10 row of impingement jet holes (hole density n of 4306 m−2) was used, which had ten rows of holes in the cross-flow direction. One heat transfer enhancement obstacle per impingement jet was investigated and compared with previously published experimental results, for Nimonic 75 metal walls, for flow pressure loss and surface averaged heat transfer coefficients. Two different shaped obstacles were investigated with an impingement gap, Z, of 10mm: a continuous rectangular rib 4.5mm high (H) and 3.0 mm thick and a rectangular pin-fin rib with ten 8mm high (H) pins that were 8.6mm wide and 3.0 mm thick. The obstacles were equally spaced on the centreline between each row of impingement jets aligned with the crossflow. The impingement jet pitch to diameter X/D and gap to diameter Z/D ratios were kept constant at 4.66 and 3.06 for X, Z and D of 15.24, 10.00 and 3.27 mm, respectively. The two obstacles investigated had obstacle height to diameter ratio H/D of 1.38 and 2.45. The computations were carried out for three different air coolant mass fluxes G of 1.08, 1.48 and 1.94 kg/sm2bar. The pressure loss ΔP/P and surface average heat transfer coefficient (HTC) h predictions for all three G showed good agreement with the experimental results. The predicted results were also compared with the impingement jet single exit flow, for a smooth target wall of the same impingement hole configuration. A significant increase in the overall surface averaged heat transfer was predicted and measured for the co-flow configuration with rectangular pin-fins. This was a 20% improvement at low coolant flow rates for the rectangular pin fin obstacles and 15% for the ribs. At high coolant flow rates the improvement was smaller at 5% for the rectangular pin fins and 1% for the rectangular ribs.

scholarly journals Temperature log simulations in high-enthalpy boreholes

2019 ◽  
Vol 7 (1) ◽  
Author(s):  
Jia Wang ◽  
Fabian Nitschke ◽  
Maziar Gholami Korzani ◽  
Thomas Kohl
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Temperature Gradient ◽  
Flow Rate ◽  
Fluid Loss ◽  
Flow Conditions ◽  
Flow Rates ◽  
High Enthalpy ◽  
Fluid Losses ◽  
Lateral Heat

Abstract Temperature logs have important applications in the geothermal industry such as the estimation of the static formation temperature (SFT) and the characterization of fluid loss from a borehole. However, the temperature distribution of the wellbore relies on various factors such as wellbore flow conditions, fluid losses, well layout, heat transfer mechanics within the fluid as well as between the wellbore and the surrounding rock formation, etc. In this context, the numerical approach presented in this paper is applied to investigate the influencing parameters/uncertainties in the interpretation of borehole logging data. To this end, synthetic temperature logs representing different well operation conditions were numerically generated using our newly developed wellbore simulator. Our models account for several complex operation scenarios resulting from the requirements of high-enthalpy wells where different flow conditions, such as mud injection with- and without fluid loss and shut-in, occur in the drill string and the annulus. The simulation results reveal that free convective heat transfer plays an important role in the earlier evolution of the shut-in-time temperature; high accuracy SFT estimation is only possible when long-term shut-in measurements are used. Two other simulation scenarios for a well under injection conditions show that applying simple temperature correction methods on the non-shut-in temperature data could lead to large errors for SFT estimation even at very low injection flow rates. Furthermore, the magnitude of the temperature gradient increase depends on the flow rate, the percentage of fluid loss and the lateral heat transfer between the fluid and the rock formation. As indicated by this study, under low fluid losses (< 30%) or relatively higher flow rates (> 20 L/s), the impact of flow rate and the lateral heat transfer on the temperature gradient increase can be ignored. These results provide insights on the key factors influencing the well temperature distribution, which are important for the choice of the drilling data to estimate SFT and the design of the inverse modeling scheme in future studies to determine an accurate SFT profile for the high-enthalpy geothermal environment.

Heat Transfer and Pressure Loss Characteristics of Pin-Fins With Different Shapes in a Wide Channel

2017 ◽  
Author(s):  
Jin Xu ◽  
Jiaxu Yao ◽  
Pengfei Su ◽  
Jiang Lei ◽  
Junmei Wu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Bottom Surface ◽  
Number Range ◽  
Pin Fin ◽  
Nominal Diameter ◽  
Pin Fins

Convective heat transfer enhancement and pressure loss characteristics in a wide rectangular channel (AR = 4) with staggered pin fin arrays are investigated experimentally. Six sets of pin fins with the same nominal diameter (Dn = 8mm) are tested, including: Circular, Elliptic, Oblong, Dropform, NACA and Lancet. The relative spanwise pitch (S/Dn = 2) and streamwise pitch (X/Dn = 4.5) are kept the same for all six sets. Same nominal diameter and arrangement guarantee the same blockage area in the channel for each set. Reynolds number based on channel hydraulic diameter is from 10000 to 70000 with an increment of 10000. Using thermochromic liquid crystal (R40C20W), heat transfer coefficients on bottom surface of the channel are achieved. The obtained friction factor, Nusselt number and overall thermal performance are compared with the previously published data from other groups. The averaged Nusselt number of Circular pin fins is the largest in these six pin fins under different Re. Though Elliptic has a moderate level of Nusselt number, its pressure loss is next to the lowest. Elliptic pin fins have pretty good overall thermal performance in the tested Reynolds number range. When Re>40000, Lancet has a same level of performance as Circular, but its pressure loss is much lower than Circular. These two types are both promising alternative configuration to Circular pin fin used in gas turbine blade.

scholarly journals Enhancement of Impingement Heat Transfer With the Crossflow Normal to Ribs and Pins Between Each Row of Holes

2018 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pressure Loss ◽  
Cross Flow ◽  
Experimental Results ◽  
Hole Density ◽  
Impingement Heat Transfer ◽  
The Cross ◽  
Flow Maldistribution

Impingement heat transfer investigations with obstacle (fins) on the target surface were carried out with the obstacles aligned normal to the cross-flow. Conjugate heat transfer (CHT) computational fluid dynamics (CFD) analysis were used for the geometries previously been investigated experimentally. A 10 × 10 row of impingement jet holes or hole density, n, of 4306 m−2 with ten rows of holes in the cross-flow direction was used. The impingement hole pitch X to diameter D, X/D, and gap Z to diameter, Z/D, ratios were kept constant at 4.66 and 3.06 for X, D and Z of 15.24, 3.27 and 10.00 mm, respectively. Nimonic 75 test walls were used with a thickness of 6.35 mm. Two different shaped obstacles of the same flow blockage were investigated: a continuous rectangular ribbed wall of 4.5 mm height, H, and 3.0 mm thick and 8 mm high rectangular pin-fins that were 8.6 mm wide and 3.0 mm thick. The obstacles were equally spaced on the centre-line between each row of impingement jets and aligned normal to the cross-flow. The two obstacles had height to diameter ratios, H/D, of 1.38 and 2.45, respectively. Comparison of the predictions and experimental results were made for the flow pressure loss, ΔP/P, and the surface average heat transfer coefficient (HTC), h. The computations were carried out for air coolant mass flux, G, of 1.08, 1.48 and 1.94 kg/sm2bar. The pressure loss and surface average HTC for all the predicted G showed reasonable agreement with the experimental results, but the predictions for surface averaged h were below the measured values by 5–10%. The predictions showed that the main effect of the ribs and pins was to increase the pressure loss, which led to an increased flow maldistribution between the ten rows of holes. This led to lower heat transfer over the first 5 holes and higher heat transfer over the last 3 holes and the net result was little benefit of either obstacle relative to a smooth wall. The results were significantly worse than the same obstacles aligned for co-flow, where the flow maldistribution changes were lower and there was a net benefit of the obstacles on the surface averaged heat transfer coefficient.

Heat Transfer Enhancement for Gas Turbine Blade Leading Edge Cooling Using Curved Double-Wall/Vortex Cooling With Various Disturbing Objects

2019 ◽  
Author(s):  
Xiaojun Fan ◽  
Liang Li ◽  
Jiefeng Wang ◽  
Fan Wu
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Loss ◽  
Total Pressure ◽  
Leading Edge ◽  
Total Pressure Loss ◽  
Wall Impingement ◽  
Pin Fins ◽  
Cooling Passage ◽  
Double Wall

Abstract A new double-wall cooling configuration combined with the vortex cooling is established to study the cooling behavior for the gas turbine blade leading edge. This configuration consists of multiple nozzles, a curved inner cooling passage, a row of bridge holes and a curved outer cooling passage with 4 kinds of disturbing objects (namely smooth wall, pin-fins, dimples and protrusions). Numerical simulations are performed based on the 3D viscous steady Reynolds Averaged Navier-Stokes (RANS) equations and the k-ω turbulence model. The cooling behavior of the Double-wall/vortex cooling configuration is compared with the Double-wall/impingement cooling configuration at the same conditions. Generally, the Double-wall/vortex cooling configuration has a better cooling performance. It is found the Nusselt number of the inner surface for the Double-wall/vortex cooling configuration is 46.7% higher. However, the Double-wall/impingement cooling configuration has a smaller friction coefficient and a total pressure loss. Different disturbing objects have significant influences on the heat transfer performance of the outer surface. The Nusselt number of disturbing objects (pin-fins, dimples and protrusions) is much higher than the smooth wall, and the value is 1.27–2.22 times larger. Configuration with protrusions has the highest globally-averaged Nusselt number. For the heat transfer performance of the inner surface and the total pressure loss coefficient, disturbing objects have no obvious influence. As bridge holes row increases, the overall cooling performance is improved. The globally-averaged Nusselt number of the outer target is enhanced while the total pressure loss is reduced.

scholarly journals Numerical Investigation of Mixing Characteristic for CH4/Air in Rotating Detonation Combustor

2020 ◽  
Vol 10 (4) ◽  
pp. 1298
Author(s):  
Shan Jin ◽  
Qingyang Meng ◽  
Zhiming Li ◽  
Ningbo Zhao ◽  
Hongtao Zheng ◽  
...  
Keyword(s):  
Mass Flow ◽  
Flow Rate ◽  
Pressure Loss ◽  
Equivalence Ratio ◽  
Numerical Study ◽  
Ignition Energy ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Critical Ignition ◽  
Rotating Detonation

The mixing process of fuel and oxidizer is a very critical factor affecting the real operating performance of non-premixed rotating detonation combustor. In this paper, a two-dimensional numerical study is carried out to investigate the flow and mixing characteristics of CH4/air in combustor with different injection structures. On this basis, the effect of CH4/air mixing on the critical ignition energy for forming detonation is theoretically analyzed in detail. The numerical results indicate that injection strategies of CH4 and air can obviously affect the flow filed characteristic, pressure loss, mixing uniformity and local equivalence ratio in combustor, which further affect the critical ignition energy for forming detonation. In the study for three different mass flow rates (the mass flow rates of air are 12.01 kg/s,8.58 kg/s and 1.72 kg/s, respectively), when air is radially injected into combustor (fuel/air are injected perpendicular to each other), although the mixing quality of CH4 and air is improved, the total pressure loss is also increased. In addition, the comparative analysis also shows that the increase of mass flow rate of CH4/air can decrease the difference of the critical ignition energy for forming detonation at a constant total equivalence ratio. The ignition energy decreases with the decrease of the total flow rate and then increases gradually.

Heat Transfer Study of a Novel Low-Crossflow Design for Jet Impingement

2004 ◽  
Author(s):  
Ryan Hebert ◽  
Srinath V. Ekkad ◽  
Vivek Khanna ◽  
Mario Abreu ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Impingement Heat Transfer ◽  
Hole Arrays ◽  
Transient Liquid Crystal Technique ◽  
Rate Requirement ◽  
Transfer Study

Impingement heat transfer is significantly affected by initial cross-flow or by the presence of cross-flow from upstream spent jets. In this study, a zero cross-flow design is presented. The zero-crossflow design creates spacing between hole arrays to allow for spent flow to be directed away from impinging jets. Three configurations with different impingement holes placements are studied and compared with pure impingement with spent crossflow cases for the same jet Reynolds number. Three jet Reynolds numbers are studied for Rej = 10000, 20000, and 30000. Detailed heat transfer distributions are obtained using the transient liquid crystal technique. The zero-cross flow design clearly shows minimal degradation of impingement heat transfer due to crossflow compared to conventional design with lower mass flow rate requirement and lesser number of overall impingement holes due to the reduced cross-flow effect on the impingement region.

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