Laminar Natural Convection in Isosceles Triangular Enclosures Heated From Below and Symmetrically Cooled From Above

2000 ◽  
Vol 122 (3) ◽  
pp. 485-491 ◽  
Author(s):  
G. A. Holtzman ◽  
R. W. Hill ◽  
K. S. Ball
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Pitchfork Bifurcation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Aspect Ratios ◽  
Triangular Enclosure ◽  
Laminar Natural Convection ◽  
Flow Symmetry

A numerical study of natural convection in an isosceles triangular enclosure with a heated horizontal base and cooled upper walls is presented. Nearly every previous study conducted on this subject to date has assumed that the geometric plane of symmetry is also a plane of symmetry for the flow. This problem is re-examined over aspect ratios ranging from 0.2 to 1.0 and Grashof numbers from 103 to 105. It is found that a pitchfork bifurcation occurs at a critical Grashof number for each of the aspect ratios considered, above which the symmetric solutions are unstable to finite perturbations and asymmetric solutions are instead obtained. Results are presented detailing the occurrence of the pitchfork bifurcation in each of the aspect ratios considered, and the resulting flow patterns are described. A flow visualization study is used to validate the numerical observations. Computed local and mean heat transfer coefficients are also presented and compared with results obtained when flow symmetry is assumed. Differences in local values of the Nusselt number between asymmetric and symmetric solutions are found to be more than 500 percent due to the shifting of the buoyancy-driven cells. [S0022-1481(00)02503-2]

The Correlation of Heat Transfer Coefficients for the Laminar Natural Convection in a Circular Finned-Tube Heat Exchanger

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Hie Chan Kang ◽  
Se-Myong Chang
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Nusselt Number ◽  
Natural Convection ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Finned Tube ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Laminar Natural Convection

This study proposes an empirical correlation for laminar natural convection applicable to external circular finned-tube heat exchangers with wide range of configuration parameters. The transient temperature response of the heat exchangers was used to obtain the heat transfer coefficient, and the experimental data with their characteristic lengths are discussed. The data lie in the range from 1 to 1000 for Rayleigh numbers based on the fin spacing: the ratio of fin height to tube diameter ranges from 0.1 to 0.9, and the ratio of fin pitch to height ranges from 0.13 to 2.6. Sixteen sets of finned-tube electroplated with nickel–chrome were tested. The convective heat transfer coefficients on the heat exchangers were measured by elimination of the thermal radiation effect from the heat exchanger surfaces. The Nusselt number was correlated with a newly suggested composite curve formula, which converges to the quarter power of the Rayleigh number for a single cylinder case. The proposed characteristic length for the Rayleigh number is the fin pitch while that for the Nusselt number is mean flow length, defined as half the perimeter of the mean radial position inside the flow region bounded by the tube surface and two adjacent fins. The flow is regarded as laminar, which covers heat exchangers from a single horizontal cylinder to infinite parallel disks. Consequently, the result of curve fitting for the experimental data shows the reasonable physical interpretation as well as the good quantitative agreement with the correction factors.

Natural Convection Heat Transfer From Horizontal Rectangular Ducts

2006 ◽  
Vol 129 (9) ◽  
pp. 1195-1202 ◽  
Author(s):  
Mohamed E. Ali
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Aspect Ratios ◽  
Rayleigh Numbers

Experimental investigations have been reported on steady state natural convection from the outer surface of horizontal ducts in air. Five ducts have been used with aspect ratios (Γ=duct height/duct width) of 2, 1, and 0.5. The ducts are heated using internal constant heat flux heating elements. The temperatures along the surface and peripheral directions of the duct wall are measured. Longitudinal (circumference averaged) heat transfer coefficients along the side of each duct are obtained for laminar and transition regimes of natural convection heat transfer. Total overall averaged heat transfer coefficients are also obtained. Longitudinal (circumference averaged) Nusselt numbers are evaluated and correlated using the modified Rayleigh numbers for transition regime using the axial distance as a characteristic length. Furthermore, total overall averaged Nusselt numbers are correlated with the modified Rayleigh numbers, the aspect ratio, and area ratio for the laminar and transition regimes. The longitudinal or total averaged heat transfer coefficients are observed to decrease in the laminar region and to increase in the transition region. Laminar regimes are obtained only at very small heat fluxes, otherwise, transitions are observed.

Natural convection in an inclined square cavity in regions of density inversion of water

1984 ◽  
Vol 142 ◽  
pp. 363-381 ◽  
Author(s):  
Hideo Inaba ◽  
Takeyuki Fukuda
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Water Layer ◽  
Density Inversion ◽  
Transfer Coefficients ◽  
Square Cavity ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
Inclination Angles ◽  
Laminar Natural Convection

The steady laminar natural convection of water in an inclined square cavity is investigated experimentally and analytically at temperatures in the neighbourhood of maximum density near 4°C. One hot wall of the square cavity is maintained at various uniform temperatures from 2 to 20°C and the opposing cold wall is kept at a uniform temperature of 0°C, while the other walls are thermally insulated. Photographs and analytical descriptions of the flow patterns, temperature profiles in the water layer and average heat-transfer coefficients are presented in this paper for various surface temperatures Th of the hot wall and inclination angles of the square cavity θ from 0° (heated from below) to 180° (heated from above) by 30° intervals. From this study it should be noted that the density inversion of water has a strong effect on the natural convection occurring in the inclined square cavity, and the average heat-transfer coefficient is a peculiar function of the surface temperature of the hot wall, unlike previous results for Boussinesq fluids without density inversion. Solutions of the governing equations for steady two-dimensional laminar natural convection are obtained numerically, and the results obtained agree reasonably well with the experimental ones in the ranges of 30° < θ ≤ 180° for Th > 8°C, 0° ≤ θ ≤ 120° for Th < 8°C, and 0° ≤ θ ≤ 180° for Th = 8°C.

A Numerical and Experimental Investigation of Turbulent Heat Transport Downstream From an Abrupt Pipe Expansion

1983 ◽  
Vol 105 (4) ◽  
pp. 862-869 ◽  
Author(s):  
R. S. Amano ◽  
M. K. Jensen ◽  
P. Goel
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Separated Flow ◽  
Flow Region ◽  
Reynolds Numbers ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Pipe Expansion

An experimental and numerical study is reported on heat transfer in the separated flow region created by an abrupt circular pipe expansion. Heat transfer coefficients were measured along the pipe wall downstream from an expansion for three different expansion ratios of d/D = 0.195, 0.391, and 0.586 for Reynolds numbers ranging from 104 to 1.5 × 105. The results are compared with the numerical solutions obtained with the k ∼ ε turbulence model. In this computation a new finite difference scheme is developed which shows several advantages over the ordinary hybrid scheme. The study also covers the derivation of a new wall function model. Generally good agreement between the measured and the computed results is shown.

Experimental and Numerical Study on the Effects of the Relative Position of Film Hole and Orientation Ribs on the Film Cooling With Ribbed Cross-Flow Coolant Channel

2020 ◽  
Author(s):  
Bingran Li ◽  
Cunliang Liu ◽  
Lin Ye ◽  
Huiren Zhu ◽  
Fan Zhang
Keyword(s):  
Heat Transfer ◽  
Relative Position ◽  
Film Cooling ◽  
Numerical Study ◽  
Cross Flow ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Cooling Performance ◽  
Heat Transfer Coefficients ◽  
Numerical Studies

Abstract To investigate the application of ribbed cross-flow coolant channels with film hole effusion and the effects of the internal cooling configuration on film cooling, experimental and numerical studies are conducted on the effect of the relative position of the film holes and different orientation ribs on the film cooling performance. Three cases of the relative position of the film holes and different orientation ribs (post-rib, centered, and pre-rib) in two ribbed cross-flow channels (135° and 45° orientation ribs) are investigated. The film cooling performances are measured under three blowing ratios by the transient liquid crystal measurement technique. A RANS simulation with the realizable k-ε turbulence model and enhanced wall treatment is performed. The results show that the cooling effectiveness and the downstream heat transfer coefficient for the 135° rib are basically the same in the three position cases, and the differences between the local effectiveness average values for the three are no more than 0.04. The differences between the heat transfer coefficients are no more than 0.1. The “pre-rib” and “centered” cases are studied for the 45° rib, and the position of the structures has little effect on the film cooling performance. In the different position cases, the outlet velocity distribution of the film holes, the jet pattern and the discharge coefficient are consistent with the variation in the cross flow. The related research previously published by the authors showed that the inclination of the ribs with respect to the holes affects the film cooling performance. This study reveals that the relative positions of the ribs and holes have little effect on the film cooling performance. This paper expands and improves the study of the effect of the internal cooling configuration on film cooling and makes a significant contribution to the design and industrial application of the internal cooling channel of a turbine blade.

Numerical Study of Boiling Heat Transfer Around Horizontal and Inclined Cylinders

2021 ◽  
Author(s):  
Avik Saha ◽  
Arup Kumar Das
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Horizontal Cylinder ◽  
Uniform Heat Flux ◽  
Cylinder Surface ◽  
Transfer Coefficients ◽  
Heated Cylinder ◽  
Heat Transfer Coefficients ◽  
Stages Of Growth ◽  
Saturated Water

Abstract Pool boiling around a heated cylinder having a diameter larger than the departure diameter of bubbles has been simulated numerically. Thermally uniform heat flux condition has been maintained at the outer surface of the cylinder, submerged at saturated water at atmospheric pressure. Using the Volume of Fluid type framework of liquid phase fraction in the domain, bubble life cycle around the horizontal cylinder has been analyzed to understand different stages of growth, sliding, merging prior to departure. An effort has also been made to characterize the bubble population, emerging from different sites over the cylindrical surface. The influence of cylinder inclination along its axis on these interfacial features has also been discussed using representative numerical simulation. Temperature profiles of the cylinder surface have been portrayed for both horizontal and inclined situations before presenting respective heat transfer coefficients.

Single-Phase and Boiling Cooling of Small Pin Fin Arrays by Multiple Nozzle Jet Impingement

1996 ◽  
Vol 118 (1) ◽  
pp. 21-26 ◽  
Author(s):  
David Copeland
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Single Phase ◽  
Jet Impingement ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Aspect Ratios ◽  
Pin Fin Arrays

Experimental measurements of multiple nozzle submerged jet array impingement single-phase and boiling heat transfer were made using FC-72 and 1 cm square copper pin fin arrays, having equal width and spacing of 0.1 and 0.2 mm, with aspect ratios from 1 to 5. Arrays of 25 and 100 nozzles were used, with diameters of 0.25 to 1.0 mm providing nozzle area from 5 to 20 mm2 (5 to 20% of the heat source base area). Flow rates of 2.5 to 10 cm3/s (0.15 to 0.6 l/min) were studied, with nozzle velocities from 0.125 to 2 m/s. Single nozzles and smooth surfaces were also evaluated for comparison. Single-phase heat transfer coefficients (based on planform area) from 2.4 to 49.3 kW/m2 K were measured, while critical heat flux varied from 45 to 395 W/cm2. Correlations of the single-phase heat transfer coefficient and critical heat flux as functions of pin fin dimensions, number of nozzles, nozzle area and liquid flow rate are provided.

Experimental Analysis of the Pool Boiling Phenomenon of Sugarcane Juice

2015 ◽  
Vol 789-790 ◽  
pp. 489-495 ◽  
Author(s):  
Daniel Marcelo ◽  
Paul Villar Yacila ◽  
Raúl La Madrid Olivares
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Experimental Analysis ◽  
Electrical Power ◽  
Power Input ◽  
Sugarcane Juice ◽  
Middle Level ◽  
Transfer Coefficients ◽  
Combustion Gases ◽  
Heat Transfer Coefficients

In Peru, jaggery making process has low energy efficiency and it is due to low heat transfer coefficients for natural convection linked to the sugar cane movement generated by the heat exchange between the sugarcane juice and the combustion gases. This low heat transfer coefficients are caused by improper heat exchangers designs. In this work, is performed an experimental analysis that consist in supplie heat to a pot containing sugarcane juice using a hot plate of constant electrical power. This study consist in identify boiling regimes and estimate the heat transfer coefficients linked to natural convection boiling, measuring: (i) the temperature at the bottom of the pot (ii) the temperature at the bottom level of sugarcane juice (iii) the temperature at middle level of sugarcane juice (iv) the temperature at free surface of sugarcane juice (v) rate of water evaporated. The method of linear regression and the correlation of Rohsenow were used for obtaining the values of the heat transfer coefficients ranging from 4088.6 W/m2°C to 12592.8 W/m2°C with power input ranging from 700W to 1300W.

Experimental Investigation of Natural Convection Heat Transfer in Volumetrically Heated Spherical Segments

1996 ◽  
Vol 118 (1) ◽  
pp. 31-37 ◽  
Author(s):  
F. J. Asfia ◽  
B. Frantz ◽  
V. K. Dhir
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Reactor Vessel ◽  
Core Material ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
External Cooling

External cooling of a light water reactor vessel by flooding of the concrete cavity with subcooled water is one of several management strategies currently being considered for accidents in which significant relocation of core material is predicted to occur. At present, uncertainty exists with respect to natural convection heat transfer coefficients between the pool of molten core material and the reactor vessel wall. In the present work, experiments were conducted to examine natural convection heat transfer in internally heated partially filled spherical pools with external cooling. In the experiments, Freon-113 was contained in a Pyrex bell jar, which was cooled externally with subcooled water. The pool was heated using a 750 W magnetron taken from a conventional microwave. The pool had a nearly adiabatic free surface. The vessel wall temperature was not uniform and varied from the stagnation point to the free surface. A series of chromel–alumel thermocouples was used to measure temperatures in both steady-state and transient conditions. Each thermocouple was placed in a specific vertical and radial location in order to determine the temperature distribution throughout the pool and along the inner and outer walls of the vessel. In the experiments, pool depth and radius were varied parametrically. Both local and averages heat transfer coefficients based on pool maximum temperature were obtained. Rayleigh numbers based on pool height were varied from 2 × 1010 to 1.1 × 1014. Correlations for the local heat transfer coefficient dependence on pool angle and for the dependence of average Nusselt number on Rayleigh number and pool depth have been developed.

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