Experimental Investigations Into Mixed Convection About a Horizontal Cylinder: Part A — Heat Transfer Using Digital Speckle Pattern Interferometry

2005 ◽  
Author(s):  
Vanessa Egan ◽  
Tara Dalton ◽  
Mark R. D. Davies ◽  
Maurice Whelan
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Speckle Pattern ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Inertia Force ◽  
Convection Flow ◽  
Digital Speckle Pattern Interferometry ◽  
Unsteady Mixed Convection ◽  
Digital Speckle

Mixed convection heat transfer is commonly found in many engineering applications and is particularly relevant to the cooling of electronic components but despite this, the physics of this heat transfer regime is not fully understood. This paper presents an experimental study into buoyancy opposing cross flow, a commonly found mixed convection regime. The experimental configuration comprised a long heated cylinder suspended in a glass walled enclosure. The airflow within the enclosure was controlled using a baffled axial fan to give Reynolds numbers in the range of 32–89. The mean Nusselt numbers were measured about the cylinder for Rayleigh numbers between 1.7E+04–4.0E+04. For the acquisition of full field data the optical techniques, digital speckle pattern interferometry (DSPI) and phase measurement interferometry (PMI), were employed. Buoyancy opposing cross flow created an unsteady flow field about the cylinder at low Reynolds numbers and steady state temperatures. DSPI enabled real-time interferograms to be recorded and results are presented in the form of instantaneous interferograms showing the high frequency fluctuations of the temperature field about the cylinder. Attention is focused on understanding the trend in mean heat transfer values resulting from an increased inertia force and thus providing a significant insight into unsteady mixed convection flow.

Unsteady mixed convection flow at a three-dimensional stagnation point

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Amin Noor ◽  
Roslinda Nazar ◽  
Kohilavani Naganthran ◽  
Ioan Pop
Keyword(s):  
Heat Transfer ◽  
Differential Equations ◽  
Mixed Convection ◽  
Stagnation Point ◽  
Three Dimensional ◽  
Convection Flow ◽  
Mixed Convection Flow ◽  
Content Type ◽  
Flow And Heat Transfer ◽  
Unsteady Mixed Convection

Purpose This paper aims to probe the problem of an unsteady mixed convection stagnation point flow and heat transfer past a stationary surface in an incompressible viscous fluid numerically. Design/methodology/approach The governing nonlinear partial differential equations are transformed into a system of ordinary differential equations by a similarity transformation, which is then solved numerically by a Runge – Kutta – Fehlberg method with shooting technique and a collocation method, namely, the bvp4c function. Findings The effects of the governing parameters on the fluid flow and heat transfer characteristics are illustrated in tables and figures. It is found that dual (upper and lower branch) solutions exist for both the cases of assisting and opposing flow situations. A stability analysis has also been conducted to determine the physical meaning and stability of the dual solutions. Practical implications This theoretical study is significantly relevant to the applications of the heat exchangers placed in a low-velocity environment and electronic devices cooled by fans. Originality/value The case of suction on unsteady mixed convection flow at a three-dimensional stagnation point has not been studied before; hence, all generated numerical results are claimed to be novel.

Influence of Thermal Radiation on the Unsteady Mixed Convection Flow of a Jeffrey Fluid over a Stretching Sheet

2010 ◽  
Vol 65 (8-9) ◽  
pp. 711-719 ◽  
Author(s):  
Tasawar Hayat ◽  
Meraj Mustafa
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Thermal Radiation ◽  
Deborah Number ◽  
Convection Flow ◽  
Jeffrey Fluid ◽  
Mixed Convection Flow ◽  
Suction Parameter ◽  
Unsteady Mixed Convection ◽  
Homotopy Analysis

This study is concerned with the effect of thermal radiation on the unsteady mixed convection flow of a Jeffrey fluid past a porous vertical stretching surface. The arising problems of flow and heat transfer are solved analytically by employing homotopy analysis method (HAM). It is observed that the flow field is influenced appreciably by the unsteadiness parameter ζ , suction parameter S, mixed convection parameter λ , Deborah number β , Prandtl number Pr, and the radiation parameter Nr. Our performed computations depict that the heat transfer rate is increased with increasing values of Pr, Nr, and ζ

Unsteady Mixed Convection Flow of a Reactive Casson Fluid in a Permeable Wall Channel Filled with a Porous Medium

2017 ◽  
Vol 377 ◽  
pp. 166-179 ◽  
Author(s):  
Oluwole Daniel Makinde ◽  
Lazarus Rundora
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Porous Medium ◽  
Mixed Convection ◽  
Shape Parameter ◽  
Casson Fluid ◽  
Convection Flow ◽  
Mixed Convection Flow ◽  
Unsteady Mixed Convection ◽  
Fluid Parameter

In the current paper, we investigate the thermal decomposition in an unsteady mixed convection flow of a reactive Casson fluid in a vertical channel filled with a saturated porous medium. The channel walls are assumed to be permeable with fluid injection through the left wall and suction out of the right wall. There is heat dissipation caused by exothermic chemical reaction within the flow system. The dimensionless form of the momentum and energy equations will be solved numerically using a semi-discretization finite difference method and a fourth order Runge-Kutta-Fehlberg integration scheme. The influence of the Casson fluid parameter, the buoyancy parameter, the porous medium shape parameter, the Eckert number, the suction/injection Reynolds number, Frank-Kamenetskii parameter and the Prandtl number on velocity and temperature profiles, skin friction and Nusselt number as well as the thermal stability criteria are presented graphically and discussed quantitatively. It is revealed that increasing the Casson fluid parameter enhances the flow velocity, the fluid temperature and the skin friction but has a diminishing effect on the wall heat transfer rate. The suction/injection Reynolds number, the porous medium shape parameter and the buoyancy parameter enhance the rate of heat transfer at the channel walls.

An Investigation Into the Heat Transfer and Fluid Flow Around a Circular Cylinder in Buoyancy Assisting Cross Flow

2002 ◽  
Author(s):  
Tara Dalton ◽  
Vanessa Egan ◽  
David Newport ◽  
Mark Davies ◽  
Maurice Whelan
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Circular Cylinder ◽  
Speckle Pattern ◽  
Convection Heat Transfer ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Temperature Fields ◽  
Axial Fan ◽  
Heated Cylinder

There is considerable interest in mixed convection heat transfer in relation to electronic cooling applications but the physics of this flow in certain situations has yet to be understood. In this paper, an investigation of the heat transfer and fluid flow around a two dimensional circular cylinder is made. The experimental configuration comprised a long heated cylinder suspended in a glass walled enclosure. The airflow within the enclosure was controlled using a baffled axial fan to give a range of low Reynolds numbers from 30 to 83. For three Grashof numbers of 2.40E+04, 3.77E+04 and 5.99E+04, the mean Nusselt number around the cylinder was measured for buoyancy assisting cross flow. Optical techniques were employed to extract the full flow and temperature fields about the cylinder. Digital Speckle Pattern Interferometry (DSPI) was employed to measure the temperature field, and Particle Image Velocimetry (PIV) for the velocity field. The presence of the assisting flow was found to stabilise a naturally oscillatory buoyant flow and led to an increase in the heat transfer coefficient over that found in natural flow.

U-RANS Simulation of Mixed-Convection Around a Finite Wall-Mounted Heated Cylinder Cooled by Cross-Flow

2008 ◽  
Author(s):  
Y. Lecocq ◽  
S. Bournaud ◽  
R. Manceau ◽  
B. Duret ◽  
L. Brizzi
Keyword(s):  
Experimental Data ◽  
Mixed Convection ◽  
Cross Flow ◽  
Temperature Fields ◽  
Navier Stokes ◽  
Inertia Force ◽  
Convection Flow ◽  
Test Cases ◽  
Heated Cylinder ◽  
Flow Circulation

VALIDA experiments [1] were carried out within the framework of radioactive waste management to improve the understanding of mixed-convection flow and more particularly the interaction between a global cross-flow circulation and local natural convection effects around a vertical heated cylinder. The VALIDA loop implements a cylinder of 3.1 height to diameter ratio, mounted vertically in an insulated tunnel and cooled by a cross-flow air circulation. The air flow and the temperature fields on the cylinder and in the plume behind it have been numerically studied using Unsteady Reynolds Average Navier Stokes simulation (U-RANS) and compared to experimental data. The purpose of this paper is to present the results of a k-ω SST model on several test cases. The numerical tools used herein are Code_Saturne, EDF finite volume CFD code [2], and Syrthes, EDF finite element code for solid temperatures [9]. For the studied test-cases, Reynolds and Grashof numbers are characteristic of a sub-critical flow regime with laminar boundary layers around the cylinder and a turbulent wake. From the transient downstream air calculations, the plume behind the cylinder and its wall temperatures are analysed and compared to experimental data. The flow pattern strongly depends on the ratio of the buoyancy to the inertia force. Results show satisfactory qualitative and quantitative behaviour.

scholarly journals EXPERIMENTAL STUDY OF HEAT TRANSFER OF A SINGLE-ROW BUNDLE OF FINNED TUBES IN MIXED CONVECTION OF AIR

2017 ◽  
Vol 60 (4) ◽  
pp. 352-366 ◽  
Author(s):  
A. B. Sukhotskii ◽  
G. S. Sidorik
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Reynolds Number ◽  
Free Convection ◽  
Mixed Convection ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Convection Flow ◽  
Single Bundle ◽  
Single Row

The technique and results of experimental study of heat transfer of a single bundle consisting of bimetallic tubes with helically knurled edges, in natural and mixed convection of air are presented. Mixed convection, i.e. a heat transfer, when the contribution of free and forced convection is comparable, was created with the help of the exhaust shaft mounted above the heat exchanger bundle and forced air movement was created by the difference in density of the air in the shaft and the environment. The experimental dependence of the heat transfer of finned single row of bundles in the selected ranges of Grashof and Reynolds numbers has been determined. It is demonstrated that heat transfer in the mixed convection is 2.5−3 times higher than in free one and the growth rate of heat transfer with increasing Reynolds number is more than in the forced convection. Different forms of representation of results of experiments were analyzed and it was determined that the Nusselt number has a single power dependence on the Reynolds number at any height of the exhaust shafts. A linear dependence of the Reynolds number on the square root of the Grashof number was determined as well as the proportionality factors for different shaft heights. It is noted that the characteristics of the motion of air particles in the bundle in free convection is identical to the motion of particles in forced convection at small Reynolds numbers, i.e. a free convection flow smoothly flows into a forced convection one without the typical failures or surges if additional driving forces arise.

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