scholarly journals Experimental Investigation of Micro Cooling Units on Impingement Jet Array Flow Pressure Loss and Heat Transfer Characteristics

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4757
Author(s):  
Zhong Ren ◽  
Xiaoyu Yang ◽  
Xunfeng Lu ◽  
Xueying Li ◽  
Jing Ren
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Nusselt Number ◽  
Pressure Loss ◽  
Discharge Coefficient ◽  
Flow System ◽  
Target Surface ◽  
Viscous Sublayer ◽  
Heat Transfer Characteristics ◽  
Impingement Jet

With the development in additive manufacturing, the use of surface treatments for gas turbine design applications has greatly expanded. An experimental investigation of the pressure loss and heat transfer characteristics within impingement jet arrays with arrays of target surface micro cooling units is presented. The discharge coefficient and Nusselt number are measured and determined for an evaluation of the pressure loss of the flow system and heat transfer level, respectively. Considered are effects of impingement jet Reynolds number ranging from 1000 to 15,000 and micro cooling units (square pin fin) height (h) with associated values of 0.01, 0.02, 0.05, 0.2, and 0.4 D, where D is the impingement hole diameter. Presented are variations of Nusselt number, and Nusselt number ratio, discharge coefficient, discharge coefficient ratio, discharge coefficient correlation. Depending upon the micro cooling unit height, discharge coefficient ratios slightly decrease with height, and the ratio values generally remain unit value (1.0). When Rej = 1000 and 2500 for several cooling units height values, discharge coefficient ratios show the pressure loss decreases about 2–18% and 3–6%, respectively, when compared to the data of a baseline smooth target surface plate. The observed phenomenon is due to the effects of flow blockage of micro cooing units, local flow separation, and near-wall viscous sublayer reattachment. Results also show that heat transfer levels increase 20–300% for some of the tested toughened target surface plates when compared to smooth target surface plates. The heat transfer level enhancement is because of an increase in thermal transport and near-wall mixing, as well as the increased wetted area. In addition, micro cooling units elements break the viscous sublayer and cause greater turbulence intensity when compared to the smooth target surface. Overall, results demonstrate that the target surface micro cooling units do not result in a visible increment in pressure loss and reduce pressure loss of the flow system for some of the tested patterns. Moreover, results show the significant ability of micro cooling units to enhance the surface heat transfer capability of impingement cooling relative to smooth target surfaces.

Study of Heat Transfer Characteristics of a Single Jet Impinging on a Conical Surface

2020 ◽  
Author(s):  
Bo Su ◽  
Wei-jiang Xu ◽  
Zhi-ping Li ◽  
Tian-liang Zhou ◽  
Fei Lu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Stagnation Point ◽  
Target Surface ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Maximum Value ◽  
Conical Target ◽  
Single Jet

Abstract In this paper, the heat transfer performance of single jet impinging conical surface is investigated based on transient liquid crystal experiments. Because of different target surface structures, impingement heat transfer will have different heat transfer characteristics. In order to better understand the heat transfer mechanism of the impinging conical target surface, this paper studies the three jet Reynolds number (Re) ranged from 25000 to 70000, three the dimensionless nozzle-to-surface distance (H/D) from 0.75 to 6 on heat transfer characteristics. The liquid crystal thermal imaging technology is used in the experiment to obtain the heat transfer efficiency of jet heat transfer on the conical target surface. The research in this paper shows that the larger the jet Reynolds number, the larger the Nusselt number at the stagnation point. It is worth noting that the maximum Nusselt number is not necessarily obtained at the stagnation point. When Re = 70000 and H/D = 0.75, the maximum value of the Nusselt number is 1.24 times the stagnation point. The larger the Reynolds number, the smaller the impingement distance, and the more obvious the secondary maxima. At the same impingement distance, when the Reynolds number is larger, the position of the secondary maxima appears earlier. When Re = 25000, H/D = 3.5, 6 and Re = 45000, H/D = 6, the local Nusselt number monotonously decreases from the maximum value at the stagnation point along the flow, and it appears secondary maxima in other experimental conditions. Within the scope of this study, the overall heat transfer performance is better when the dimensionless distance between the jet hole and the target surface is 3.5.

Experimental Investigation on Heat Transfer and Friction Factor in Open Matrix Sub-Channels

2021 ◽  
Author(s):  
Anjana Narottambhai Prajapati ◽  
Andallib Tariq
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Nusselt Number ◽  
Friction Factor ◽  
Elevated Temperatures ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Aspect Ratios ◽  
Factor Ratio ◽  
The Matrix

Abstract Matrix cooling has opened new possibilities for enhancing the convective heat transfer coefficients without compromising upon the structural rigidity and the life of the gas turbine blade at elevated temperatures. However, the dense structure of the matrix significantly increases the flow resistance, and imposes the limitation to its usage. Recently, a matrix with a gap on the sidewalls called open matrix has been proposed by few researchers to reduce the associated pressure penalties. This detailed experimental investigation aims to study the open matrix channel flow, and presents the effects of varying sidewall gaps on heat transfer characteristics and friction factor in the open matrixes having rib angle 45o for three different sub-channel aspect ratios 1.2, 0.8, and 0.4. Liquid crystal thermography has been utilized to discern the detailed heat transfer characteristics. Results have been evaluated in terms of augmentation Nusselt number, friction factor ratio, and overall thermal performance factor over the Reynolds numbers 5800 -14000. The closed matrixes provided the highest augmentation in Nusselt number, and the gaps on the sidewall have shown an overall reduction in augmentation Nusselt number in most cases. However, the suitable sidewall gap showed the effective reduction in pressure penalties for the smaller sub-channel aspect ratios. The highest augmentation Nusselt number amongst the open matrixes has been found as 3.83 with a reduced friction factor ratio for the matrix with a 4 mm gap in sub-channel aspect ratio = 0.8 (i.e. 4 sub-channels) at Re = 8100.

Effect of Target Wall Curvature on Heat Transfer and Pressure Loss From Jet Array Impingement

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
John Harrington ◽  
Jahed Hossain ◽  
Wenping Wang ◽  
Jayanta Kapat ◽  
Michael Maurer ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Loss ◽  
Flow Distribution ◽  
Target Surface ◽  
Temperature Sensitive ◽  
Target Plate ◽  
Target Wall ◽  
The Impact ◽  
Jet Array

Experiments to investigate the effect of target wall curvature on heat transfer and pressure loss from jet array impingement are performed. A jet plate configuration is studied with constant hole diameters and spacings. The geometry of the jet plate has streamwise jet spacings of 5.79 jet diameters, spanwise jet spacings of 4.49 jet diameters, and a jet-to-target plate distance of 3 jet diameters. For the curved case, the radius of the target plate is r/D = 31.57. A flat target wall setup with identical geometric spacing is also tested for direct comparison. Jet spacings were chosen such that validation and comparison can be made with open literature. For all configurations, spent air is drawn out in a single direction, which is tangential to the target plate curvature. Average jet Reynolds numbers ranging from 55,000 to 125,000 are tested. A steady-state measurement technique utilizing temperature-sensitive paint (TSP) is used on the target surface to obtain Nusselt number distributions. Pressure taps placed on the sidewall of the channel are used to evaluate the flow distribution in the impingement channel. Alongside the experimental work, CFD was performed utilizing the v2 − f turbulence model to better understand the relationship between the flow field and the heat transfer on the target surface. The main target of the current study is to quantify the impact of target wall radius and the decay of heat transfer after the impingement section, and to check the open literature correlations. It was found that the target wall curvature did not cause any significant changes in either the flow distribution or the heat transfer level. Comparisons with established correlations show similar level but different trends in heat transfer, potentially caused by differences in L/D. CFD results were able to show agreement in streamwise pitch-averaged Nusselt number levels with experimental results for the curved target plate at higher Re numbers.

Enhancement of Impingement Cooling in a High Cross Flow Channel Using Shaped Impingement Cooling Holes

2009 ◽  
Vol 132 (2) ◽  
Author(s):  
Andrew C. Chambers ◽  
David R. H. Gillespie ◽  
Peter T. Ireland ◽  
Robert Kingston
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cross Flow ◽  
Target Surface ◽  
Impingement Cooling ◽  
Turbine Cooling ◽  
Impingement Jet ◽  
Coefficient Distribution ◽  
Cooling Passage ◽  
Experimental Rig

Impingement systems are common place in many turbine cooling applications. Generally these systems consist of a target plate that is cooled by the impingement of multiple orthogonal jets. While it is possible to achieve high target surface heat transfer with this configuration, the associated pressure drop is generally high and the cooling efficiency low. Furthermore, especially in large impingement arrays, the buildup of cross flow from upstream jets can be significant and results in deflection of downstream impingement jets reducing the resultant heat transfer coefficient distribution. This paper presents a computational and experimental investigation into the use of shaped elliptical or elongated circular impingement holes designed to improve the penetration of the impinging jet across the coolant passage. This is of particular interest where there is significant cross flow. Literature review and computational investigations are used to determine the optimum aspect ratio of the impingement jet. The improved heat transfer performance of the modified design is then tested in an experimental rig with varying degrees of cross flow at engine representative conditions. In all cases, a 16% increase in the Nusselt number on the impingement target surface in the downstream half of the cooling passage was achieved. Under the first four impingement holes, a Nusselt number enhancement of 28–77% was achieved, provided no additional cross flow was present in the passage. When appropriately aligned, a significant reduction in the stress concentration factor caused by the addition of a hole can be achieved using this design.

An Experimental Investigation on Heat Transfer Characteristics of Hot Surface by Using CuO–Water Nanofluids in Circular Jet Impingement Cooling

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Mayank Modak ◽  
Sandesh S. Chougule ◽  
Santosh K. Sahu
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Jet Impingement ◽  
Test Surface ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Hot Surface ◽  
Plate Distance

In the present study, an experimental investigation has been carried out to analyze the heat transfer characteristics of CuO–water nanofluids jet on a hot surface. A rectangular stainless steel foil (AISI-304, 0.15 mm thick) used as the test surface is electrically heated to obtain the required initial temperature (500 °C). The distribution of surface heat flux on the target surface is evaluated from the recorded thermal images during transient cooling. The effect of nanoparticle concentration and Reynolds number of the nanofluids on the heat transfer characteristics is studied. Tests are performed for varied range of Reynolds number (5000 ≤ Re ≤ 12,000), two different CuO–water nanofluids concentration (Ф = 0.15%, 0.6%) and two different nozzle to plate distance (l/d = 6, 12). The enhancement in Nusselt number for CuO–water nanofluids was found to be 14% and 90%, for nanofluids concentration of Ф = 0.15% and Ф = 0.60%, respectively, compared to pure water. The test surface characteristics after nanofluids jet impingement are studied using scanning electron microscope (SEM). Based on the investigation, a correlation among various parameters, namely, Reynolds number (Re), Prandtl number (Pr), nozzle to plate distance (l/d), and Nusselt number (Nu), is presented.

Effect of Rotation on Heat Transfer of a Concave Surface With Array Impingement Jet

2013 ◽  
Author(s):  
Eui Yeop Jung ◽  
Chan Ung Park ◽  
Dong Hyun Lee ◽  
Jun Su Park ◽  
Sehjin Park ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Stagnation Point ◽  
Turbine Blades ◽  
Leading Edge ◽  
Target Surface ◽  
Concave Surface ◽  
Heat Transfer Characteristics ◽  
Impingement Jet ◽  
Transfer Characteristics ◽  
Inner Surface

Turbine blades are directly exposed to hot oncoming combustion gases, so their leading edges require effective cooling techniques. Here, we investigated the heat transfer characteristics in a concave duct with an array of impingement jets, including the effect of rotation. The concave duct was used to simulate the inner surface of the leading edge of a blade. The inner surface was cooled by the impingement array jet method. The jet Reynolds number (Re) based on the jet nozzle diameter was fixed at 3,000, and the ratio of the height to target surface (H/d) was set to 2.0. The injection holes (d = 5 mm) were positioned in a staggered pattern, and the rotation number was about 0.032. We focused on the effects of rotating position orientations. We investigated front, leading, and trailing orientations. Naphthalene sublimation method was used to determine the local heat/mass transfer distributions, and the flow pattern was obtained by numerical simulation. Crossflow in the jet arrays was generated by the spent air from the impingement jet. The crossflow changes the flow characteristics at the stagnation point along the streamwise direction on a concave surface. Rotation of the duct increased the flow mixing compared with the stationary case. The jet flow was deflected because of the Coriolis force in the leading and trailing orientations. However, in the front orientation, the heat transfer characteristics showed deflection in the clockwise direction in the developing flow away from the stagnation point. Overall, the averaged heat transfer values were enhanced in the rotating cases. The trailing orientation case showed the highest averaged heat transfer among all tested cases.

Effect of Target Wall Curvature on Heat Transfer and Pressure Loss From Jet Array Impingement

2015 ◽  
Author(s):  
John Harrington ◽  
Arash Nayebzadeh ◽  
Jonathan Winn ◽  
Wenping Wang ◽  
Jayanta Kapat ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Loss ◽  
Flow Distribution ◽  
Target Surface ◽  
Temperature Sensitive ◽  
Target Plate ◽  
Target Wall ◽  
The Impact ◽  
Jet Array

Experiments to investigate the effect of target wall curvature on heat transfer and pressure loss from jet array impingement are performed. A jet plate configuration is studied with constant hole diameters and spacings. The geometry of the jet plate has streamwise jet spacings of 5.79 jet diameters, spanwise jet spacings of 4.49 jet diameters, and a jet-to-target plate distance of 3 jet diameters. For the curved case, the radius of the target plate is r/D=31.57. A flat target wall setup with identical geometric spacing is also tested for direct comparison. Jet spacings were chosen such that validation and comparison can be made with open literature. For all configurations, spent air is drawn out in a single direction which is tangential to the target plate curvature. Average jet Reynolds numbers ranging from 50,000 to 150,000 are tested. A steady-state measurement technique utilizing Temperature Sensitive Paint is used on the target surface to obtain Nusselt number distributions. Pressure taps placed on the sidewall of the channel are used to evaluate the flow distribution in the impingement channel. Alongside the experimental work, CFD was performed utilizing the v2-f turbulence model to better understand the relationship between the flow field and the heat transfer on the target surface. The main target of the current study is to quantify the impact of target wall radius, the decay of heat transfer after the impingement section and to check the open literature correlations. It was found that the target wall curvature caused higher heat transfer levels, with array-average Nusselt numbers increasing by an average of 28% when compared to the similar plane case. In the post-impingement section, increases in heat transfer levels were also seen with the curved case by up to 60%. Finally, CFD results were able to show agreement in stagnation point Nusselt number levels with experimental results for the curved target plate.

Numerical Study on Flow and Heat Transfer Characteristics of Jet Impingement

2011 ◽  
Author(s):  
Xinjun Wang ◽  
Rui Liu ◽  
Xiaowei Bai ◽  
Jinling Yao
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Target Surface ◽  
Heat Transfer Characteristics ◽  
Impingement Cooling ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

A mathematical model used for studying jet impingement cooling characteristics is established, and the rationality of the calculation model and method is confirmed by the experimental data. The CFX software is used to numerically simulate the jet impingement cooling characteristics on a gas turbine blade. The effects of various parameters, such as the arrays of impinging nozzles, the jet Reynolds number, the jet-to-jet distance, the ratio of nozzle-to-surface spacing to jet diameter H/d, and the radius of curvature of the target surface, on the flow and heat transfer characteristics of a impingement cooling process are studied. The results indicate that the impingement jets can make complex vortex in the cooling channel, the flow boundary layer is extremely thin and highly turbulent. Underneath each impingement nozzle, there will appear a low temperature area and a peak of Nusselt number on the impingement target surface, the distribution of temperature and Nusselt number on the target surface are associated with arrangement of impingement nozzles. The average Nusselt number of the in-line arrangement nozzles is higher than that of the staggered arrangement ones. With the increasing of jet Reynolds number, the velocity impinging on the target surface and Nusselt number increase. However, heat transfer of impingement cooling on target surface is not sensitive to the jet nozzles distance; the velocity impinging on the target surface and Nusselt number decrease with the increasing of the H/d value. For the curved target surface cases, the average Nusselt number of the target surface and the effect of heat transfer decreased with the increasing of curvature radius R.

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.

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