SIMULTANEOUS MEASUREMENTS OF TIME-RESOLVED SURFACE HEAT FLUX AND FREESTREAM TURBULENCE AT A STAGNATION POINT

1990 ◽  
Author(s):  
S.G. Simmons ◽  
Jon M. Hager ◽  
Thomas E. Diller
Keyword(s):  
Heat Flux ◽  
Stagnation Point ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Freestream Turbulence ◽  
Time Resolved ◽  
Simultaneous Measurements

Boiling Heat Transfer Characteristics of Rotary Hollow Cylinders with In-Line and Staggered Multiple Arrays of Water Jets

2021 ◽  
Author(s):  
Mohammad Jahedi ◽  
Bahram Moshfegh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Stagnation Point ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Maximum Heat ◽  
Water Jets ◽  
Maximum Heat Flux ◽  
Inner Surface ◽  
Hollow Cylinders

Abstract Transient heat transfer studies of quenching rotary hollow cylinders with in-line and staggered multiple arrays of jets have been carried out experimentally. The study involves three hollow cylinders (Do/d = 12 to 24) with rotation speed 10 to 50 rpm, quenched by subcooled water jets (ΔTsub=50-80 K) with jet flow rate 2.7 to 10.9 L/min. The increase in area-averaged and maximum heat flux over quenching surface (Af) has been observed in the studied multiple arrays with constant Qtotal compared to previous studies. Investigation of radial temperature distribution at stagnation point of jet reveals that the footprint of configuration of 4-row array is highlighted in radial distances near the outer surface and vanishes further down toward the inner surface. The influence of the main quenching parameters on local average surface heat flux at stagnation point is addressed in all the boiling regimes where the result indicates jet flow rate provides strongest effect in all the boiling regimes. Effectiveness of magnitude of maximum heat flux in the boiling curve for the studied parameters is reported. The result of spatial and temporal heat flux by radial conduction in the solid presents projection depth of cyclic variation of surface heat flux in the radial axis as it disappears near inner surface of hollow cylinder. In addition, correlations are proposed for area-averaged Nusselt number as well as average and maximum local heat flux at stagnation point of jet for the in-line and staggered multiple arrays.

Effect of Subcooling and Nozzle Diameter on Heat Transfer Characteristics of Downward Facing Hot Surfaces Using Mist Jet

2018 ◽  
Author(s):  
Avadhesh Kumar Sharma ◽  
Monika Meena ◽  
Anirudh Soni ◽  
Santosh K. Sahu
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Stagnation Point ◽  
Surface Heat Flux ◽  
Jet Impingement ◽  
Surface Heat ◽  
Nozzle Diameter ◽  
Initial Surface ◽  
Ir Camera ◽  
Impingement Cooling

The jet impingement cooling is always preferred over the other cooling methods due to its high heat removal capability. However, rapid quenching may lead to the formation of cracks and poor ductility to the quenched surface. Mist jet impingement cooling offers an alternative method to uncontrolled rapid cooling, particularly in steel and electronic industries. In mist cooling, the droplets are atomized by compressed air. Experiments are performed under transient conditions using two full-cone spray nozzles (Lechler Pneumatic atomizing nozzle 136.115.xx.A2 and 136.134.xx.A2) to study the effect of subcooling and nozzle diameter on surface heat flux. The hot surface used for the experiment is a stainless steel foil (AISI-304) of thickness 0.15mm. The initial surface temperature of the plate is maintained at 500±10°C with the help of an AC transformer. Infrared thermal image camera (A655sc, FLIR System) is used for data estimation. The IR camera and the nozzle are positioned on either side of the plate. The variation in surface temperature has been acquired at 8 different spatial points. It has been observed that that as we move away from the stagnation point then irrespective of air and water flow rates surface heat flux decreases. The maximum surface heat flux obtained at the stagnation point. With the increase in diameter surface heat flux increases irrespective of pressure values. The correlation between qm/qstag experimental and predicted values has been shown.

scholarly journals Stagnation-Point Flow toward a Vertical, Nonlinearly Stretching Sheet with Prescribed Surface Heat Flux

2013 ◽  
Vol 2013 ◽  
pp. 1-6
Author(s):  
Sin Wei Wong ◽  
M. A. Omar Awang ◽  
Anuar Ishak
Keyword(s):  
Heat Flux ◽  
Differential Equations ◽  
Stagnation Point ◽  
Surface Heat Flux ◽  
Velocity Ratio ◽  
Surface Heat ◽  
Stagnation Point Flow ◽  
Buoyant Flows ◽  
Keller Box Method ◽  
Nonlinearly Stretching Sheet

An analysis is carried out to study the steady two-dimensional stagnation-point flow of an incompressible viscous fluid towards a stretching vertical sheet. It is assumed that the sheet is stretched nonlinearly, with prescribed surface heat flux. This problem is governed by three parameters: buoyancy, velocity exponent, and velocity ratio. Both assisting and opposing buoyant flows are considered. The governing partial differential equations are transformed into a system of ordinary differential equations and solved numerically by finite difference Keller-box method. The flow and heat transfer characteristics for different values of the governing parameters are analyzed and discussed. Dual solutions are found in the opposing buoyant flows, while the solution is unique for the assisting buoyant flows.

Hybrid nanofluid flow on a shrinking cylinder with prescribed surface heat flux

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Iskandar Waini ◽  
Anuar Ishak ◽  
Ioan Pop
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Stagnation Point ◽  
Surface Heat Flux ◽  
Temporal Stability ◽  
Surface Heat ◽  
Physical Parameters ◽  
Hybrid Nanofluid ◽  
Content Type ◽  
Long Run

Purpose This study aims to investigate the flow impinging on a stagnation point of a shrinking cylinder subjected to prescribed surface heat flux in Al2O3-Cu/water hybrid nanofluid. Design/methodology/approach Using similarity variables, the similarity equations are obtained and then solved using bvp4c in MATLAB. The effects of several physical parameters on the skin friction and heat transfer rate, as well as the velocity and temperature profiles are analysed and discussed. Findings The outcomes show that dual solutions are possible for the shrinking case, in the range λc<λ<−1, where λc is the bifurcation point of the solutions. Meanwhile, the solution is unique for λ≥−1. Besides, the boundary layer is detached on the surface at λc, where the value of λc is affected by the hybrid nanoparticle φhnf and the curvature parameter γ. Moreover, the friction and the heat transfer on the surface increase with the rising values φhnf and γ. Finally, the temporal stability analysis shows that the first solution is stable in the long run, whereas the second solution is not. Originality/value The present work considers the problem of stagnation point flow impinging on a shrinking cylinder containing Al2O3-Cu/water hybrid nanofluid, with prescribed surface heat flux. This paper shows that two solutions are obtained for the shrinking case. Further analysis shows that only one of the solutions is stable as time evolves.

Time-resolved surface heat flux measurements in the wing/body junction vortex

10.2514/3.595 ◽  
1994 ◽  
Vol 8 (4) ◽  
pp. 656-663 ◽  
Author(s):  
D. J. Lewis ◽  
R. L. Simpson ◽  
T. E. Diller
Keyword(s):  
Heat Flux ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Time Resolved ◽  
Flux Measurements

High Frequency Surface Heat Flux Imaging of Bypass Transition

2004 ◽  
Vol 127 (2) ◽  
pp. 241-250 ◽  
Author(s):  
Richard J. Anthony ◽  
Terry V. Jones ◽  
John E. LaGraff
Keyword(s):  
Heat Flux ◽  
High Frequency ◽  
Surface Heat Flux ◽  
Imaging Technique ◽  
Surface Heat ◽  
Complex Nature ◽  
Bypass Transition ◽  
Freestream Turbulence ◽  
University Of Oxford ◽  
The University

A high-frequency surface heat flux imaging technique was used to investigate bypass transition induced by freestream turbulence. Fundamental experiments were carried out at the University of Oxford using high-density thin film arrays on a flat plate wind tunnel model. Bypass transition was induced by grid-generated turbulence with varying intensities of 2.3%, 4.2%, and 17% with a fixed integral length scale of approximately 12mm. Unique high resolution temporal heat flux images are shown which detail significant differences between unsteady surface heat flux events induced by freestream turbulence and the classical Emmons-type spots which many turbomachinery transition models are based on. The temporal imaging technique presented allows study of unsteady surface heat transfer in detail, and helps elucidate the complex nature of transition in the high-disturbance environment of turbomachinery.

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