Analytical Model for Rewetting Temperature during Jet Impingement Surface Quenching (original) (raw)
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International Journal of Heat and Mass Transfer, 2012
The transient cooling of hot stainless steel surface of 0.25 mm thickness is done with round water jet impingement. Initially, the surface was heated up to the temperature of 800°C before the water was injected through straight tube type nozzle of 2.5 mm diameter and 250 mm length. During impingement cooling, the surface temperature was measured up to 12 mm radial distance away from the stagnation point. The jet exit to surface spacing, z/d, and jet Reynolds number, Re, varied in the range of 4-16 and 5000-24,000 respectively. The surface rewetting and transient heat flux of the test-surface was studied for these operating parameters.
Effect of Jet Diameter on Surface Quenching at Different Spatial Locations
An experimental investigation has been carried out to study the cooling of a hot horizontal Stainless Steel surface of 3mm thickness, which has 800±10°C initial temperature. A round water jet of 22 ± 1 o C temperature was injected over the hot surface through straight tube type nozzles of 2.5-4.8mm diameter and 250mm length. The experiments were performed for the jet exit to target surface spacing of 4 times of jet diameter and jet Reynolds number of 5000 -24000. The effect of change in jet Reynolds number on the surface quenching has been investigated form the stagnation point to 16mm spatial location.
Review of Correlations on Jet Impingement Cooling
2015
Jet impingement study is of significant importance because of its numerous applications in various industries. Its fluid flow properties and heat transfer characteristics are giving interesting results by which its popularity increases .If also number of researchers worked till date there is scope for further work. Besides theoretical and experimental analysis number of equations developed .The Nusselt number generated because of use of jet is a function of jet diameter, Reynolds Number, Target to height spacing, jet inclination, and fluid properties in general. The paper reviews correlations related to varieties of jets and will be useful for further study in this area.
Wetting Speed during Quenching of Hot Surface by Impinging Jet
2017
Hot S tainless Steel (S S-304) horizontal surface of different initial temperatures are cooled by water jet of 33 ºC temperature and 3 mm diameter. The surface cooling performance is investigated with flow rate of 1.2 and 5.10 lpm. The test surface is of 150 mm long, 150 mm wide and 2 mm thickness. S urface is initially heated up to certain temperature in furnace and cooled by downward impinging jet. The process of surface cooling is recorded by a camera and the wetting speed over the hot surface is determined. The wetting speed on the hot surface is observed in the range of 2-35 mm/s for 10 mm-40 mm spatial locations. It has been observed that the wetting speed increases with rise in flow rate and reduces for higher downstream spatial locations and surface initial temperature. Index Terms-Jet Impingement, Wetting speed, S tagnation point, S urface quenching.
Rewetting of a hot horizontal surface through mist jet impingement cooling
International Journal of Heat and Mass Transfer, 2013
An experimental investigation has been carried out to study the rewetting behaviour of a hot horizontal stainless steel surface during the mist jet impingement cooling. The experiments have been performed to study the rewetting behaviour for three different initial surface temperatures viz. 255, 355, 565°C. An axis-symmetric nozzle has been used to develop the mist jet of constant flow rate. The variation in surface temperature has been acquired up to 20 mm downstream spatial locations away from the stagnation point. It has been observed that unlike liquid jet impingement cooling the rise in surface initial temperature increases the rewetting temperature and the wetting delay increase with rise in the initial surface temperature but the rewetting velocity reduces. Further, the maximum surface heat flux is the highest at 20 mm spatial location for 565°C initial surface temperature. Whereas, at the stagnation point, the maximum surface heat flux is not affected by the change in surface initial temperature.
Numerical and Experimental Investigations on Jet Impingement Cooling
World Academy of Science, Engineering and Technology, International Journal of Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering, 2013
Effective cooling of electronic equipment has emerged as a challenging and constraining problem of the new century. In the present work the feasibility and effectiveness of jet impingement cooling on electronics were investigated numerically and experimentally. Studies have been conducted to see the effect of the geometrical parameters such as jet diameter (D), jet to target spacing (Z) and ratio of jet spacing to jet diameter (Z/D) on the heat transfer characteristics. The values of Reynolds numbers considered are in the range 7000 to 42000. The results obtained from the numerical studies are validated by conducting experiments. From the studies it is found that the optimum value of Z/D ratio is 5. For a given Reynolds number, the Nusselt number increases by about 28% if the diameter of the nozzle is increased from 1mm to 2mm. Correlations are proposed for Nusselt number in terms of Reynolds number and these are valid for air as the cooling medium. Keywords—CFD, heat transfer coeff...
Study of Jet Impingement Heat Transfer
Jet impingement systems provide an effective and simple means for the enhancement of convective processes due to the high heat and mass transfer rates that can be achieved. The range of industrial applications that impinging jets are being used in today is wide. A number of researchers have studied the forced convection heat transfer from jet arrays. This review paper gives various experimental and numerical approaches on jet impingement heat transfer process. In the course of the review, the flow and heat transfer characteristics of multiple impinging jets are introduced. Influencing factors on heat transfer are discussed, which include the effects of cross flow, jet Reynolds number, jet pattern, separation distance between a jet and target plate, and of the open area. In the review of numerical works, the suitability of the turbulent models in predicting local heat transfer rates for multi-jet systems is discussed.
Numerical Simulation Of Minimum Distance Jet Impingement Heat Transfer
2012
Impinging jets are used in various industrial areas as a cooling and drying technique. The current research is concerned with the means of improving the heat transfer for configurations with a minimum distance of the nozzle to the impingement surface. The impingement heat transfer is described using numerical methods over a wide range of parameters for an array of planar jets. These parameters include varying jet flow speed, width of nozzle, distance of nozzle, angle of the jet flow, velocity and geometry of the impingement surface. Normal pressure and shear stress are computed as additional parameters. Using dimensionless characteristic numbers the parameters and the results are correlated to gain generalized equations. The results demonstrate the effect of the investigated parameters on the flow.
International Journal of Heat and Mass Transfer, 2007
Impinging jets are a means of achieving high heat transfer coefficients both locally and on an area averaged basis. The temporal nature of both the fluid flow and heat transfer has been investigated for Reynolds numbers from 10,000 to 30,000 and non-dimensional surface to jet exit distance, H/D, from 0.5 to 8. At the impingement surface simultaneous acquisition of both local heat flux and local velocity signal has facilitated a comprehensive analysis of the effect that fluid flow has on the heat transfer. Results are presented in the form of surface heat transfer and fluid velocity signal spectra, and coherence and phase difference between the corresponding velocity and heat flux signals. It has been shown that the evolution of vortices with distance from the jet exit has an influence on the magnitude of the heat transfer coefficient in the wall jet.