Conjugate conduction and convection underneath a downward facing non-isothermal extended surface: A numerical study

2014 ◽  
Vol 88 ◽  
pp. 15-26 ◽  
Author(s):  
Biplab Das ◽  
Asis Giri
Keyword(s):  
Numerical Study ◽  
Extended Surface ◽  
Conjugate Conduction

Parametric Analysis of a Bayonet Tube With a Special Type of Extended Surface

2010 ◽  
Author(s):  
L. Almanza-Huerta ◽  
A. Hernandez-Guerrero ◽  
M. Krarti ◽  
J. M. Luna
Keyword(s):  
Heat Transfer ◽  
Parametric Analysis ◽  
Numerical Study ◽  
Systematic Investigation ◽  
Heat Transfer Characteristics ◽  
Maximum Heat ◽  
Turbulent Transition ◽  
Maximum Heat Transfer ◽  
Internal Fluid ◽  
Extended Surface

The present paper provides a numerical study of a parametric analysis of a bayonet tube with a special type of extended surface during the laminar-turbulent transition. The working internal fluid is air. Attention is focused on the heat transfer characteristics of the tube. The results constitute a systematic investigation of the effect of the extended surface located along the annulus of the bayonet on the overall heat transfer rate. The effects of the variation of some parameters related to the extended surface aiming to attain the maximum heat transfer with the minimum pressure drop are discussed. Comparisons between designs with and without extended surface are also made.

FREE CONVECTION FROM A WINDOW GLAZING WITH A VENETIAN BLIND: NUMERICAL MODEL DEVELOPMENT

1999 ◽  
Vol 23 (1B) ◽  
pp. 159-172 ◽  
Author(s):  
J. Phillips ◽  
D. Naylor ◽  
S.J. Harrison ◽  
P.H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Radiation Heat Transfer ◽  
Model Development ◽  
Plate Spacing ◽  
Venetian Blinds ◽  
The Difference ◽  
Visualization Experiments ◽  
Conjugate Conduction

The present numerical study examines the influence of horizontal louvres (Venetian blinds) on the convective heat transfer from a vertical isothermal surface. A steady, laminar, two dimensional, conjugate conduction/convection solution to this problem has been obtained using the finite element method. Detailed comparisons are made with temperature field and local Nusselt number data obtained using a Mach-Zehnder Interferometer. Also, numerically predicted stream function contours are compared to streamlines obtained from flow visualization experiments. All results are obtained for Pr = 0.7, as the intended application of this study is for air. Results show that as the blind tip-to-plate spacing decreases, the difference between numerical solutions and experimental results increase. This suggests that radiation heat transfer may be a significant factor at smaller blind spacings.

Heat Transfer From an Isothermal Vertical Surface With Adjacent Heated Horizontal Louvers: Validation

2002 ◽  
Vol 124 (6) ◽  
pp. 1078-1087 ◽  
Author(s):  
M. Collins ◽  
S. J. Harrison ◽  
D. Naylor ◽  
P. H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Transfer Rate ◽  
Numerical Study ◽  
Surface Flux ◽  
Element Model ◽  
Vertical Surface ◽  
Two Dimensional ◽  
Local Surface ◽  
Conjugate Conduction ◽  
Steady Laminar

The present study examines the influence of heated, horizontal, and rotateable louvers on the convective heat transfer from a heated or cooled vertical isothermal surface. The system represents an irradiated Venetian blind adjacent to the indoor surface of a window. Detailed temperature field and local surface flux data were obtained using a Mach-Zehnder Interferometer for two window temperatures (warm and cool compared to ambient) and irradiation levels, two louver to plate spacings, and three louver angles. The results have been compared to a steady, laminar, two-dimensional, conjugate conduction/convection/radiation finite element model of this problem. The effect of the heated louvers on the heat transfer rate from the plate surface has been demonstrated and the results of the numerical study have been validated.

Numerical Modeling of Radiative and Convective Heat Transfer From an Irradiated Complex Window Assembly

2000 ◽  
Author(s):  
M. Collins ◽  
S. J. Harrison ◽  
P. H. Oosthuizen ◽  
D. Naylor
Keyword(s):  
Heat Transfer ◽  
Radiative Heat ◽  
Numerical Study ◽  
Two Dimensional ◽  
Plate Surface ◽  
The Finite Element Method ◽  
Radiation Model ◽  
Conjugate Conduction ◽  
Plate Distance ◽  
Steady Laminar

Abstract The present numerical study examines the influence of heated, horizontal, and rotateable louvers on the convective and radiative heat transfer from a hot or cold vertical isothermal surface. The system models absorption of solar energy in a Venetian blind adjacent to the indoor surface of a window. Building on previous analyses, a steady, laminar, two-dimensional, conjugate conduction / convection / radiation model of this problem has been developed, and solutions have been obtained using the finite element method. Validation of the model against existing solutions has been undertaken. Results were obtained for two window temperatures (warm and cool compared to ambient), two louver to plate spacings, and three louver angles. The results clearly demonstrate the effect of the model variables on heat transfer from the plate surface. With few exceptions, steady periodicity along the plate was clearly demonstrated. More importantly, increased independence of the results from the louver angle as louver to plate distance increased was demonstrated.

Numerical Study on Enhanced Paraffin/Air Heat Transfer with Extended Surface

2012 ◽  
Vol 501 ◽  
pp. 376-381
Author(s):  
Yan Zhou ◽  
Wen Juan Zheng ◽  
Xi Yan Fan ◽  
Jun Chao ◽  
Qing Ling Li
Keyword(s):  
Heat Transfer ◽  
Heat Storage ◽  
Numerical Study ◽  
Solar Chimney ◽  
Release Capacity ◽  
Vertical Heat ◽  
Heat Collector ◽  
Extended Surface ◽  
Solar Chimney Power Plant ◽  
Air Flow Velocity

The extended surface is used to enhance paraffin/air heat transfer because of the paraffin’s poor thermal conductivity, and the heat storing and releasing capacity of paraffin heat storage layer with variety of extended surface are compared by numerical simulation. The results show that: the heat storage layer with vertical rectangular fin extended surface has stronger ability on the heat storage and release, and can more effectively improve the air flow velocity in the solar chimney power plant system with vertical heat collector. Due to the restrictions of manufacturing, the heat storage and release capacity is stronger when the heat storage layer surface area with vertical rectangular fin is from 3.4 times to 5.8 times compare to the flat-plate heat storage layer.

Numerical Study on Conjugate Conduction–Convection in a Cubic Enclosure Submitted to Time-Periodic Sidewall Temperature

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Wei Zhang ◽  
Zhu Huang ◽  
Chuhua Zhang ◽  
Guang Xi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Wall Thickness ◽  
Numerical Study ◽  
Finite Thickness ◽  
Pseudospectral Method ◽  
Thermal Conductivity Ratio ◽  
Conjugate Conduction ◽  
Time Periodic ◽  
Diffusivity Ratio

The laminar conjugate conduction-natural convection heat transfer in a cubic enclosure of finite thickness conductive walls and central cavity filled with fluid is comprehensively studied by using recently developed high accuracy temporal-spatial multidomain pseudospectral method. The enclosure is assumed to have one sidewall submitted to time-periodic pulsating temperature and the opposing sidewall constant temperature, and the top, bottom and two lateral sidewalls are adiabatic. The present study is devoted to explore the fluid mechanics and heat transfer mechanisms of the time-periodic conjugate conduction-natural convection in the enclosure, with particular highlights on the heat transfer resonance and back heat transfer phenomena, the perturbation propagation patterns and the three-dimensional characteristics. The computations are performed for wide ranges of controlling parameters of engineering significance, i.e., the dimensionless wall thickness 0 ≤ s ≤ 0.10, the solid–fluid thermal conductivity ratio 10 ≤ k ≤ 50 and diffusivity ratio 0.001 ≤ a ≤ 0.1, and the sidewall temperature pulsating period 1 ≤ P ≤ 103. Numerical results reveal that the time-periodic fluid flow and conjugate heat transfer performances of the enclosure system are greatly affected by the conductive walls and complexly dependent on the controlling parameters. The thickness and thermophysical properties of the conductive walls, together with the pulsating period of the sidewall temperature, govern the sidewall temperature disturbance propagation patterns (amplitude, phase position and speed) within the enclosure. The heat transfer resonance only appears in cases of large diffusivity ratio, but the variation of period-averaged heat transfer rate with respect to the pulsating period is quite different from that of the zero wall thickness enclosure. The back heat transfer exists in region close to the corners formed by either the top or bottom walls and the enclosure hot sidewall, and the former is more remarkable in both scale and duration and is gradually disappearing as the pulsating period increases.

Numerical Study of Corrugation Amplitude Influence of a Wavy Fin in Overall Performance of a Compact Heat Exchanger

2014 ◽  
Vol 659 ◽  
pp. 405-410 ◽  
Author(s):  
Vlad Martian ◽  
Septimiu Albetel ◽  
Mihai Nagi
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Numerical Study ◽  
Special Kind ◽  
Cfd Simulations ◽  
Entire Study ◽  
Extended Surface ◽  
Extended Surfaces ◽  
Active Research ◽  
Goodness Factor

In the past few decades heat exchangers, especially air cooled ones, have become very important equipment in different fields of industry. This led to an active research in finding ways to reduce their overall size and costs. A very important role played in reducing the size of the heat exchanger is the convection capability of air, by being the lowest one, dictates the overall size of the heat exchanger. For this reason we are forced to use extended heat transfer surfaces on the air size. The geometry of such extended surfaces has a high impact on heat and pressure drop performances. The present paper focuses on a study, conducted at RAAL S.A. with the support of University “Politehnica” of Timișoara, to find the influence of the corrugation amplitude of a special kind of extended surface named wavy fin, in the overall performances of a heat exchangers by means of area goodness factor (j/f). Designing and building the different geometries needed in the study will be overkill for the company so we have decided to conduct this study with the help of CFD simulations. In order for this to work we will validate the numerical model with the help of a single experimental test, reducing the time and cost of the entire study. These results are afterwards used to modify the fin’s design to obtain an optimum one.

The effects of surface absorbed monolayer microdiffraction patterns

1988 ◽  
Vol 46 ◽  
pp. 680-681
Author(s):  
M. Pan ◽  
J.M. Cowley
Keyword(s):  
Surface Potential ◽  
Electron Probe ◽  
Potential Distribution ◽  
Crystal Surface ◽  
Normal Direction ◽  
Surface Image ◽  
Extended Surface ◽  
Gas Molecules ◽  
Surface Nature ◽  
Electron Microdiffraction

Electron microdiffraction patterns, obtained when a small electron probe with diameter of 10-15 Å is directed to run parallel to and outside a flat crystal surface, are sensitive to the surface nature of the crystals. Dynamical diffraction calculations have shown that most of the experimental observations for a flat (100) face of a MgO crystal, such as the streaking of the central spot in the surface normal direction and (100)-type forbidden reflections etc., could be explained satisfactorily by assuming a modified image potential field outside the crystal surface. However the origin of this extended surface potential remains uncertain. A theoretical analysis by Howie et al suggests that the surface image potential should have a form different from above-mentioned image potential and also be smaller by several orders of magnitude. Nevertheless the surface potential distribution may in practice be modified in various ways, such as by the adsorption of a monolayer of gas molecules.

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