scholarly journals Local Heat Transfer Distributions in Confined Multiple Air Jet Impingement

2000 ◽  
Vol 123 (3) ◽  
pp. 165-172 ◽  
Author(s):  
Suresh V. Garimella ◽  
Vincent P. Schroeder
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Air Jets ◽  
Air Jet ◽  
Multiple Jets ◽  
Single Jet ◽  
Radial Outflow ◽  
Target Spacing

Heat transfer from a discrete heat source to multiple, normally impinging, confined air jets was experimentally investigated. The jets issued from short, square-edged orifices with still-developing velocity profiles on to a foil heat source which produced a constant heat flux. The orifice plate and the surface containing the heat source were mounted opposite each other in a parallel-plates arrangement to effect radial outflow of the spent fluid. The local surface temperature was measured in fine increments over the entire heat source. Experiments were conducted for different jet Reynolds numbers (5000<Re<20,000), orifice-to-target spacing 0.5<H/d<4, and multiple-orifice arrangements. The results are compared to those previously obtained for single air jets. A reduction in orifice-to-target spacing was found to increase the heat transfer coefficient in multiple jets, with this effect being stronger at the higher Reynolds numbers. With a nine-jet arrangement, the heat transfer to the central jet was higher than for a corresponding single jet. For a four-jet arrangement, however, each jet was found to have stagnation-region heat transfer coefficients that were comparable to the single-jet values. The effectiveness of single and multiple jets in removing heat from a given heat source is compared at a fixed total flow rate. Predictive correlations are proposed for single and multiple jet impingement heat transfer.

The Effect of Entrainment Temperature on Jet Impingement Heat Transfer

1984 ◽  
Vol 106 (1) ◽  
pp. 27-33 ◽  
Author(s):  
S. A. Striegl ◽  
T. E. Diller
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Recirculation Region ◽  
Measured Temperature ◽  
Air Jets ◽  
Impingement Heat Transfer ◽  
Single Jet ◽  
Multiple Plane

An experimental study was done to determine the effect of entrainment temperature on the local heat transfer rates to single and multiple, plane, turbulent impinging air jets. To determine the effect of entrainment of the surrounding fluid, the single jet issued into an environment at a temperature which was varied between the initial temperature of the jet and the temperature of the heated impingement plate. An analytical model was used to correlate the measured heat transfer rate to a single jet. The effect of the entrainment temperature in a single jet was then used to analyze the effect of entrainment from the recirculation region between the jets of a jet array. Using the measured temperature in the recirculation region to include the effect of entrainment, the single jet correlations were successfully applied to multiple jets.

Heat Transfer to a Ducted, Semiconfined Impinging Synthetic Air Jet

2010 ◽  
Author(s):  
Daniel Rylatt ◽  
Tadhg S. O’Donovan
Keyword(s):  
Heat Transfer ◽  
Turbulent Mixing ◽  
Reynolds Numbers ◽  
Cooling Performance ◽  
Air Jets ◽  
Air Jet ◽  
Wide Range ◽  
Experimental Parameters ◽  
Impingement Surface

Heat transfer to confined impinging synthetic air jets is investigated experimentally. The influence of ducting on the cooling performance of synthetic air jets is of particular interest. Heat transfer to the jets is reported for a wide range of experimental parameters including nozzle to impingement surface spacings (0.5 to 5 jet diameters), Reynolds numbers (2000, 3000 and 4000) and non-dimensional Stroke lengths, L0/D (10 15 and 20 respectively). A range of ducting outlet sizes were also investigated (1, 1.2, 1.4 jet diameters). It has been found that ducting can have the effect of reducing the turbulent mixing of the flow but overall enhances the rate of heat transfer to the jet at low H/D &lt; 2. The largest ducting outlet of 1.4 jet diameters has also been shown to outperform the others across the whole range of variables tested.

Numerical Study on Stagnation Point Heat Transfer by Jet Impingement in a Confined Narrow Gap

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Y. Q. Zu ◽  
Y. Y. Yan ◽  
J. Maltson
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Computational Cost ◽  
Jet Impingement ◽  
Diameter Ratio ◽  
Eddy Simulation ◽  
Plate Length ◽  
Flow And Heat Transfer ◽  
Air Jet ◽  
Target Spacing

In this paper, the heat transfer characteristics of a circular air jet vertically impinging on a flat plate near to the nozzle (H/d=1–6, where H is the nozzle-to-target spacing and d is the diameter of the jet) are numerically analyzed. The relative performance of seven turbulent models for predicting this type of flow and heat transfer is investigated by comparing the numerical results with available benchmark experimental data. It is found that the shear-stress transport (SST) k−ω model and the large Eddy simulation (LES) time-variant model can give better predictions for the performance of fluid flow and heat transfer; especially, the SST k−ω model should be the best compromise between computational cost and accuracy. In addition, using the SST k−ω model, the effects of jet Reynolds number (Re), jet plate length-to-jet diameter ratio (L/d), target spacing-to-jet diameter ratio (H/d), and jet plate width-to-jet diameter ratio (W/d) on the local Nusselt number (Nu) of the target plate are examined; a correlation for the stagnation Nu is presented.

Heat Transfer Investigation with Multiple Jet Impingement

2020 ◽  
Vol 12 (3) ◽  
Author(s):  
Niranjan Murthy ◽  
B.K. Naveenkumar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Research Work ◽  
Jet Impingement ◽  
Test Surface ◽  
Simple Relationship ◽  
Flux Flow ◽  
Air Jets ◽  
Air Jet

An experimental study was carried out to study the effect of multiple jet impingement on a virtual electronic component using water and air as working fluids. It consists of an electrically heated test plate of size 20mm×20mm. Heat flux is varied between 25 to 250W/cm2 was dissipated using 0.25 and 0.5mm diameter jets placed in a 7×7 array with a pitch of 3mm. The difference in temperature between test surface and fluid inlet is within 30 degC for water jets and within 75 degC for air jet experiments. Experiments were conducted by changing the heat flux, flow rate and distance between the test surface and jet exit and [iv] horizontal and vertical positioning of the jets. It was found that heat flux, jet diameter and Reynolds number are important factors in determining the heat transfer. The effects of distance between test surface and jet exit [Z] and positioning of the jets were insignificant. Though the multiple jet impingement heat transfer problem is complex, the heat transfer results could be correlated using a simple relationship in the form of Nu = AqmRen. The constant (m) which indicates the effect of heat flux has the value of 0.8 and 0.9 depending upon the jet diameter and the coolant. The constant (n) which indicates the influence of Reynolds number has the value of 0.25 for both water and air jets. The value of constant (A) is different for water and air jets. The correlation developed in this research work can be effectively used to design multiple water and air jet cooling system for electronic components.

Confined and Submerged Liquid Jet Impingement Heat Transfer

1995 ◽  
Vol 117 (4) ◽  
pp. 871-877 ◽  
Author(s):  
S. V. Garimella ◽  
R. A. Rice
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Source ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Liquid Jet ◽  
Local Surface Temperature ◽  
Radial Outflow

The local heat transfer from a small heat source to a normally impinging, axisymmetric, and submerged liquid jet, in confined and unconfined configurations, was experimentally investigated. A single jet of FC-77 issuing from a round nozzle impinged onto a square foil heater, which dissipated a constant heat flux. The nozzle and the heat source were both mounted in large round plates to ensure axisymmetric radial outflow of the spent fluid. The local surface temperature of the heat source was measured at different radial locations (r/d) from the center of the jet in fine increments. Results for the local heat transfer coefficient distribution at the heat source are presented as functions of nozzle diameter (0.79 ≤ d ≤ 6.35 mm), Reynolds number (4000 to 23,000), and nozzle-to-heat source spacing (1 ≤ Z/d ≤ 14). Secondary peaks in the local heat transfer observed at r/d ≈ 2 were more pronounced at the smaller (confined) spacings and larger nozzle diameters for a given Reynolds number, and shifted radially outward from the stagnation point as the spacing increased. The secondary-peak magnitude increased with Reynolds number, and was higher than the stagnation value in some instances. Correlations are proposed for the stagnation and average Nusselt numbers as functions of these parameters.

Measurement Errors and Uncertainty Quantification of a 2D-PIV Experimental Setup for Jet Flow Characterization

2020 ◽  
Author(s):  
Flavia Barbosa ◽  
Carlos Costa ◽  
Senhorinha Teixeira ◽  
Jose Carlos Teixeira
Keyword(s):  
Heat Transfer ◽  
Uncertainty Quantification ◽  
Measurement Errors ◽  
Jet Impingement ◽  
Velocity Fields ◽  
Mean Velocity ◽  
Air Jets ◽  
Air Jet ◽  
High Heat Transfer ◽  
Wide Range

Abstract The study of the flow interaction and the heat transfer between air jets and a surface is of paramount importance in industrial processes that apply air jet impingement. To ensure a good performance of the process, high heat transfer rates and uniformization of the flow over the target plate are required. To perform this analysis, a PIV technique was implemented for the measurement of the flow velocity fields. However, as any real experiment, the values recorded by the PIV method are subjected to several errors that compromise the reliability and accuracy of the measurements. These errors can have different sources, from the installation and alignment to the particles seeding and calibration procedure. To maximize the accuracy of the experimental results, this paper focus on the identification of measurement errors and uncertainty quantification of an experimental set up specially built for the analysis of the interaction between air jets and a target surface. This work presents an analysis of the system, and the source of errors are identified, quantified and, when possible, corrected. The particle seeding is characterized and its efficiency for the flow tracking is analyzed. The setup was tested to fully characterize the flow field in terms of mean velocity profile and turbulence intensity over a wide range of Reynolds numbers and temperature. Several velocity fields are then measured until convergence of the flow quantities is reached. The combination of these measurements with high spatial resolution and low measurement errors allow to obtain accurate and precise measurements.

Evaporation of Water With Single and Multiple Impinging Air Jets

1991 ◽  
Vol 113 (3) ◽  
pp. 696-704 ◽  
Author(s):  
T. A. Trabold ◽  
N. T. Obot
Keyword(s):  
Diameter Ratio ◽  
Water Evaporation ◽  
Predictive Equations ◽  
Air Jets ◽  
Air Jet ◽  
Geometric Conditions ◽  
Multiple Jets ◽  
Circular Jets ◽  
Single Jet ◽  
Exit Temperature

An experimental investigation of impingement water evaporation under a single jet and arrays of circular jets was made. The parametric study included the effects of jet Reynolds number and standoff spacing for both single and multiple jets, as well as surface-to-nozzle diameter ratio and fractional nozzle open area for single and multiple jets, respectively. The nozzle exit temperature of the air jet, about the same as that of the laboratory, was 3–6° C higher than that of the evaporating water. Predictive equations are provided for mass transfer coefficient in terms of the flow and geometric conditions.

Effect of Pin Fins on Jet Impingement Heat Transfer on A Rotating Disk

2021 ◽  
Author(s):  
Pratik S. Bhansali ◽  
Kishore Ranganath Ramakrishnan ◽  
Srinath Ekkad
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Jet Impingement ◽  
Rotating Disk ◽  
Disk Surface ◽  
Reynolds Numbers ◽  
Turbine Disk ◽  
Large Space ◽  
Air Jet ◽  
Pin Fins

Abstract Heat transfer on rotating surfaces is a predominant phenomenon in rotating machinery as in the case of the gas turbine disk. The gas turbine disk needs to be cooled as well as protected from the ingress of hot turbine gases in the stator-rotor cavity. In the current study, an experimental investigation of the heat transfer of an impinging air jet on a surface rotating at low rotational Reynolds number has been carried out. Addition of pin-fins on the disk surface is an effective way to enhance the heat transfer between the disk and the jet of cooling air. The effect of addition of an inline array of square pin fins on the rotating disk heat transfer has been investigated in this study. Steady state measurements have been carried out using thermocouples embedded at different locations in an aluminum disk with an array of square pin-fins rotating in a large space. Experiments have been conducted at rotational Reynolds numbers (ReR) of 5,487–12,803 based on the disk diameter (D) and jet Reynolds numbers (Re) of 5,000–18,000 based on the jet diameter (d). Two different ratios of jet to nozzle spacing and jet diameter (z/d) of 2 and 4 and three different impingement locations – at eccentricities (ε) – 0, 0.33 and 0.67 have been considered. The diameter of the impinging jet has been kept constant in order to maintain an equal jet footprint across all the cases. The area averaged Nusselt number over the surface with pin fins has been compared with a smooth rotating disk of equal diameter. Results indicate that for the smooth surface, ε and ReR have negligible effect on Nu. However, addition of pin fins enhance Nu by a factor between 1.5 and 3.9 in the present study. Qualitative visualization of flow field has been performed using the commercial simulation package Ansys Fluent to further understand the heat transfer trends.

Enhancement of Air Cooling Limits for Telecom Heat Sink Applications Using Impinging Air Jets

2003 ◽  
Author(s):  
Eric Sansoucy ◽  
Patrick H. Oosthuizen ◽  
Gamal Refai-Ahmed
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Heat Sink ◽  
Numerical Study ◽  
Target Surface ◽  
Air Cooling ◽  
Air Jet ◽  
Model Average ◽  
Nozzle Plate ◽  
Target Spacing

A numerical study was carried out to investigate the heat transfer rate from a parallel flat plate heat sink under a turbulent impinging air jet. The target surface was confined by a horizontal nozzle plate. The jet was discharged from a sharpedged nozzle in the nozzle plate. The numerical model included the standard k-ε turbulence model. Average Nusselt numbers are reported for Pr = 0.7, 5000 ≤ Re ≤ 30000, L/d = 2.5 and 0.833 at H/d = 3 where L, H and d define the length of the square heat source, nozzle-to-target spacing and nozzle diameter, respectively. Enhancements of heat transfer rates, relative to the bare heat source, were found to vary from 1.9 to 3.5 and 4.1 to 12.0 in the presence of a base and a heat sink, respectively. The coefficient of enhancement was strongly dependent on the Re. The spacing H/d was also altered for L/d = 2.5 at Re = 30000. The enhancement in heat transfer due to the heat sink was shown to increase slightly with nozzle-to-target spacing. The Nusselt number was correlated in terms of Re, fluid properties and geometric parameters of the configuration.

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