Influences of Small Jet-to-Wall Spacings on Heat Transfer Characteristics and Flow-Field Entrainment Effects of Microscale Jets

2021 ◽  
Vol 143 (3) ◽  
Author(s):  
Prabhakar Subrahmanyam ◽  
B. K. Gnanavel
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Inlet System ◽  
Potential Core ◽  
Transfer Characteristics ◽  
The Impact

Abstract Detailed heat transfer distributions of multiple microscaled tapered jets orthogonally impinging on the surface of a high-power density silicon wall is presented. The tapered jets issued from two different impingement setup are studied—(a) single circular nozzle and (b) dual circular nozzles. Jets are issued from the inlet(s) at four different Reynolds numbers {Re = 8000, 12,000, 16,000, 20,000}. The spacing between the tapered nozzle jets and the bare die silicon wall (z/d) is adjusted to be 4, 8, 12, and 16 jet nozzle diameters away from impinging influence. The impact of varying the nozzle to the silicon wall (z/d) standoff spacing up to 16 nozzle jet diameters and its effects on flow fields on the surface of the silicon, specifically the entrainment pattern on the silicon surface, is presented. Heat transfer characteristics of impinging jets on the hot silicon wall is investigated by means of large eddy simulations (LES) at a Reynolds of 20,000 on each of the four z/d spacing and compared against its equivalent Reynolds-averaged Navier–Stokes (RANS) cases. Highest heat transfer coefficients are obtained for the dual inlet system. A demarcation boundary region connecting all the microvortices between impinging jets is prominently visible at smaller z/d spacing—the region where the target silicon wall is within the sphere of influence of the potential core of the jet. This research focuses on the underlying physics of multiple tapered nozzles jet impingement issued from single and dual nozzles and its impact on turbulence, heat transfer distributions, entrainment, and other pertinent flow-field characteristics.

Heat Transfer Characteristics of an Angled Array Impinging Jet on a Concave Duct

2012 ◽  
Author(s):  
Eui Yeop Jung ◽  
Chan Ung Park ◽  
Dong Hyun Lee ◽  
Kyung Min Kim ◽  
Ta-kwan Woo ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Stagnation Points ◽  
Transfer Characteristics ◽  
Jet Cooling

This study investigated the heat transfer characteristics of an array jet cooling system on a concave surface. Two types of injection holes were used: one for impinging jets normal to the impingement surface, and the other for angled impinging jets. For the normal jets, the jet Reynolds number (Re) based on the hole diameter varied from 3,000 to 10,000, and the height-to-diameter ratio (H/d) was fixed at 1.0. There were 15 injection holes positioned in a staggered 3×5 array. For the angled jets, Re was set to 5,000 and H/d was also fixed at 1.0. Naphthalene sublimation method was used to determine the heat transfer coefficients on the targeted plates. For normal impinging jet cooling, separate peaks were observed at the stagnation regions due to the curvature effect. Since a crossflow was generated by air spent from the jet arrays, the crossflow effect increased as it moved downstream. Due to the interaction between the crossflow and impinging jets, the peak values at the stagnation points increased downstream. The heat transfer coefficient on the targeted plate increased with Re. The average Sh of the angled jets was higher than that of the normal jets, as the obliquely impinging jet increased the mass flow rate and mass interaction between the jet impingement points.

Numerical Simulation Study of Impinging Jet Impact Fin Surface on Heat Transfer Characteristics

2013 ◽  
Vol 663 ◽  
pp. 586-591 ◽  
Author(s):  
Li Ming Zhou ◽  
Lei Zhu ◽  
Jing Quan Zhao ◽  
Meng Zheng
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Thermal Resistance ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Transfer Characteristics ◽  
Jet Impact ◽  
Jet Array

Three-dimensional numerical simulation was implemented to analyze the heat transfer characteristics for jet impingement impact fin surface. 60 calculation cases were simulated to investigate the effects of different fin surfaces on heat transfer characteristics, and 12 jet array impingement cases were calculated for comparison. The results shown that the fin shape, the height and the fin arrangement were the critical factors to affect the jet impingement and the best combination were existed in a certain range. The thermal resistance of cylinder fin arranged in order was34.7 percent higher than that of cylinder fin arranged staggered. The thermal resistance of square fin arranged in order was38.9 percent higher than that of square fin arranged staggered .The heat transfer coefficients of impinging jet impact fin surface were better than that of jet array impingement. The fitting correlations on heat transfer of impinging jet impact fin surface were given.

Computational Investigation of Flow and Heat Transfer Characteristics of Impingement Cooling Channel

2013 ◽  
Author(s):  
B. V. N. Ramakumar ◽  
D. S. Joshi ◽  
Murari Sridhar ◽  
Jong S. Liu ◽  
Daniel C. Crites
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Heat Transfer Analysis ◽  
Computational Investigation ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Impingement Cooling ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
High Heat Transfer

Impingement cooling offers very high heat transfer coefficients. Flow field, involved in impingement cooling is dominated by stagnation zone, transition zone and developing zone. Understanding of complex flow phenomenon and its effects on heat transfer characteristics is useful for efficient designing of impingement channels. Computational fluid dynamics (CFD) has emerged as a powerful tool for the analysis of flow and heat transfer systems. Honeywell has been investigating the use of CFD to determine the characteristics of various complex turbine blade cooling heat transfer augmentation methods such as impingement. The objective of this study is to develop CFD methodology which is suitable for computational investigation of flow and heat transfer analysis of impingement cooling through validation. Single row of circular jets impinging on concave (curved) surface has been considered for this study. The validation was accomplished with the test results of Bunker and Metzger [10] and with the correlations of Chupp et al. [7]. The parameters which are varied in this study include jet Reynolds number (Re2B = 6750–10200), target plate distance to jet diameter ratio (Z/d = 3 and 4), and target surface sharpness (i.e. radius ratio, r* = 0.2, 0.4 and 1) the simulations are performed under steady state conditions. Predicted results are compared for local endwall heat transfer results along the curve length of the mid span target wall. Flow field results obtained at different locations are presented to understand the heat transfer behavior.

Experimental and Numerical Investigation of Heat Transfer Characteristics of Inline and Staggered Arrays of Impinging Jets

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Yunfei Xing ◽  
Sebastian Spring ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Local Heat Transfer ◽  
Impinging Jets ◽  
Design Tool ◽  
Thermal Design ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Transfer Characteristics ◽  
Plate Spacing

A combined experimental and numerical investigation of the heat transfer characteristics within an array of impinging jets has been conducted. The experiments were carried out in a perspex model using a transient liquid crystal method. Local jet temperatures were measured at several positions on the impingement plate to account for an exact evaluation of the heat transfer coefficient. The effects of the variation in different impingement patterns, jet-to-plate spacing, crossflow schemes, and jet Reynolds number on the distribution of the local Nusselt number and the related pressure loss were investigated experimentally. In addition to the measurements, a numerical investigation was conducted. The motivation was to evaluate whether computational fluid dynamics (CFD) can be used as an engineering design tool in the optimization of multijet impingement configurations. This required, as a first step, a validation of the numerical results. For the present configuration, this was achieved assessing the degree of accuracy to which the measured heat transfer rates could be computed. The overall agreement was very good and even local heat transfer coefficients were predicted at high accuracy. The numerical investigation showed that state-of-the-art CFD codes can be used as suitable means in the thermal design process of such configurations.

scholarly journals Effect of Rotation Number on Heat Transfer Characteristics of a Row of Impinging Jets in Confined Channel

2020 ◽  
Vol 77 (1) ◽  
pp. 161-171
Author(s):  
Thantup Nontula ◽  
Natthaporn Kaewchoothong ◽  
Wacharin Kaew-apichai ◽  
Chayut Nuntadusit
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rotation Number ◽  
Turbine Blades ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Internal Cooling ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Impingement Surface

Jet impingement has been applied for internal cooling in gas turbine blades. In this study, heat transfer characteristics of impinging jets from a row of circular orifices were investigated inside a flow channel with rotations. The Reynolds number (Re) based on the jet mean velocity was fixed at 6,700. Whereas, the rotation number (Ro) of a channel was varied from 0 to 0.0099. The jet-to-impingement distance ratio (L/Dj) and jet pitch ratio (P/Dj) were respective 2 and 4, Dj is a jet diameter of 5 mm. The thermochromic liquid crystals (TLCs) technique was used to measure the heat transfer coefficient distributions on an impingement surface. The results show that heat transfer enhancement on a jet impingement surface depended on the effects of crossflow and Coriolis force. The local Nusselt number at X/Dj?20 on the leading side (LS) was higher than on the trailing side (TS) while heat transfer on the LS at 20?X/Dj?40 gained the lowest, compared to on the TS. The average Nusselt number ratios ( ) on the TS at Ro = 0.0049 gave higher than on the LS of around 2.17%. On the other hand, the on the TS at Ro = 0.0099 was less than the LS of about 0.08%.

Correlations of the Convective Heat Transfer in Annular Channels With Rotating Inner Cylinder

1998 ◽  
Author(s):  
Ralf Jakoby ◽  
Soksik Kim ◽  
Sigmar Wittig
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Vortex Formation ◽  
Taylor Vortex ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Annular Channels ◽  
The Impact

In the internal air system of gas turbine engines or generators, a large variety of different types of annular channels with rotating cylinders are found. Even though the geometry is very simple, the flow field in such channels can be completely three-dimensional and also unsteady. From the literature it is well-known, that the basic two-dimensional flow field breaks up into a pattern of counter-rotating vortices, as soon as the critical speed of the inner cylinder is exceeded. The presence of a superimposed axial flow leads to a helical shape of the vortex pairs, which are moving through the channel. For the designer of cooling air systems there are several open questions. Does the formation of a Taylor-vortex flow field significantly affect the convective heat transfer behaviour of the channel flow? Is there a stability problem even for high axial Reynolds-numbers and where is the location of the stability boundary? After all, the general influence of rotation on the heat transfer characteristics has to be known. By the results of flow field and heat transfer measurements, the impact of rotation and the additional influence of Taylor-vortex formation on the heat transfer characteristics in annular channels with axial throughflow will be discussed. The flow field was investigated by time-dependant LDA-measurements, which revealed detailed information about the flow conditions. By a spectral analysis of the measured data, the different flow regimes could be identified. Based on these results, the heat transfer from the hot gas to the rotating inner shaft was determined with a steady-state method. Thus, the influence of the different physical phenomena such as rotation with and without Taylor-vortex formation or the flow development could be separated and quantified. Finally, correlations of the measured results were derived for technical applications.

scholarly journals Heat Transfer Characteristics of Swirling Impinging Jets

2009 ◽  
Author(s):  
Karl J. Brown ◽  
Darina B. Murray ◽  
Tim Persoons ◽  
Tadhg S. O’Donovan
Keyword(s):  
Heat Transfer ◽  
Swirling Flow ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
High Heat ◽  
Impinging Jets ◽  
Heat Transfer Characteristics ◽  
Impingement Cooling ◽  
Transfer Characteristics ◽  
High Reynolds

Impinging jets are used in a wide number of industrial cooling applications due to their high heat and mass transfer abilities. The current research is concerned with the effect of swirl on the heat transfer characteristics of jet impingement cooling. Two inserts were designed order to generate swirling flow. These two designs, “Swirl Insert A” and “Swirl Insert B”, were tested at various Reynolds numbers, between 8000 and 16000 inclusive, and at H/D = 0.5 and 1. The jet was directed downwards onto a 25μm thick stainless steel foil which was ohmically heated. Images were recorded using a thermal imaging camera focused on the underside of the foil. These images were then analysed using Matlab and the Nusselt number profile was obtained. It was found that, while both swirl inserts establish an improvement in the heat transfer by comparison to that of a jet with no swirl, the “Swirl Insert B” design performed better that the “Swirl Insert A” design for high Reynolds number at H/D = 0.5 and consistently for H/D = 1. It was also discovered that, while both the “No Insert” and “Swirl Insert B” results did not change dramatically with an alteration in H/D, “Swirl Insert A” decreased by ∼10%.

Correlations of the Convection Heat Transfer in Annular Channels With Rotating Inner Cylinder

1999 ◽  
Vol 121 (4) ◽  
pp. 670-677 ◽  
Author(s):  
R. Jakoby ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Stability Boundary ◽  
Vortex Formation ◽  
Taylor Vortex ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Annular Channels ◽  
Steady State Method ◽  
The Impact

In the internal air system of gas turbine engines or generators, a large variety of different types of annular channels with rotating cylinders are found. Even though the geometry is very simple, the flow field in such channels can be completely three-dimensional and also unsteady. From the literature it is well-known that the basic two-dimensional flow field breaks up into a pattern of counter-rotating vortices as soon as the critical speed of the inner cylinder is exceeded. The presence of a superimposed axial flow leads to a helical shape of the vortex pairs that are moving through the channel. For the designer of cooling air systems there are several open questions. Does the formation of a Taylor-vortex flow field significantly affect the convective heat transfer behavior of the channel flow? Is there a stability problem even for high axial Reynolds-numbers and where is the location of the stability boundary? After all, the general influence of rotation on the heat transfer characteristics has to be known. By the results of flow field and heat transfer measurements, the impact of rotation and the additional influence of Taylor-vortex formation on the heat transfer characteristics in annular channels with axial throughflow will be discussed. The flow field was investigated by time-dependant LDA-measurements, which revealed detailed information about the flow conditions. By a spectral analysis of the measured data, the different flow regimes could be identified. Based on these results, the heat transfer from the hot gas to the rotating inner shaft was determined with a steady-state method. Thus, the influence of the different physical phenomena such as rotation with and without Taylor-vortex formation or the flow development could be separated and quantified. Finally, correlations of the measured results were derived for technical applications.

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