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.

Numerical Study of Turbulent Flow Through Rib-Roughened Channels With Mist Injection

2014 ◽  
Author(s):  
Fifi N. M. Elwekeel ◽  
Qun Zheng ◽  
Antar M. M. Abdala
Keyword(s):  
Heat Transfer ◽  
Turbulence Model ◽  
Cross Sections ◽  
Numerical Study ◽  
Turbulence Models ◽  
Uniform Heat Flux ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Sst Turbulence Model ◽  
Volume Method

This study investigated heat transfer characteristics on various shaped ribs on the lower channel wall using steam and steam/mist as cooling fluid. The lower wall is subjected to a uniform heat flux condition while others walls are insulated. Calculations are carried out for ribs with square ribs (case A), triangular ribs (case B), trapezoidal ribs (case C) and (case D) cross sections over a range of Reynolds numbers (14000–35000), constant mist mass fraction (6%) and fixed rib height and pitch. To investigate turbulence model effects, computations based on a finite volume method, are carried out by utilizing three turbulence models: the standard k-ω, Omega Reynolds Stress (ωRS) and Shear Stress Transport (SST) turbulence models. The predicted results from using several turbulence models reveal that the SST turbulence model provide better agreement with available measurements than others. It is found that the heat transfer coefficients are enhanced in ribbed channels with injection of a small amount of mist. The steam/mist provides the higher heat transfer enhancement over steam when trapezoidal shaped ribs (38°, case 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.

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]

An experimental investigation of natural convection in the melted region around a heated horizontal cylinder

1979 ◽  
Vol 90 (2) ◽  
pp. 227-239 ◽  
Author(s):  
A. G. Bathelt ◽  
R. Viskanta ◽  
W. Leidenfrost
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Phase Change ◽  
Local Heat Transfer ◽  
Horizontal Cylinder ◽  
Conclusive Evidence ◽  
Transfer Coefficients ◽  
Quantitative Evidence ◽  
Analysis And Design ◽  
Heat Transfer Coefficients

Melting from an electrically heated horizontal cylinder embedded in a paraffin (n-octadecane, fusion temperature 301·3 °K) has been studied experimentally. The shape of the solid-liquid interface has been determined photographically, and the local heat transfer coefficients have been measured using a shadowgraph technique. The experiments provide conclusive evidence of the important role played by natural convection in melting a solid due to an embedded cylindrical heat source. The four distinct pieces of quantitative evidence which contribute to this conclusion are the melt shape, surface temperature, local and average heat transfer coefficients and their variation with time.The experimental findings prove the importance of natural convection in phase change problems involving melting and indicate that continued practice of neglecting the effects in the analysis of such problems does not appear reasonable. Natural convection should be considered in analysis and design of systems involving phase change.

Heat Transfer to Mercury Flowing In Line Through an Unbaffled Rod Bundle: Experimental Study of the Effect of Rod Displacement on Rod-Average Heat Transfer Coefficients

1969 ◽  
Vol 91 (4) ◽  
pp. 568-580 ◽  
Author(s):  
P. J. Hlavac ◽  
O. E. Dwyer ◽  
M. A. Helfant
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Uniform Heat Flux ◽  
Average Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
Rod Bundle

An experimental study of heat transfer to mercury flowing in line through an unbaffled rod bundle was carried out. The “rods” were special electrical heaters whose claddings had different thicknesses and thermal conductivities. The experiments were carried out under a thermal boundary condition approaching that of uniform heat flux in all directions at the inner wall of the rod cladding. It was found that displacement of a rod from its symmetrical position can result in a large reduction in its average heat transfer coefficient. This reduction increases exponentially with the amount of displacement. For a given direction and amount of displacement, the reduction is little affected by variations in cladding thickness and conductivity but is affected considerably by flow rate. Not only does the displaced rod suffer a reduction in its own average heat transfer coefficient, but so do those toward which it is displaced. At the same time, the average coefficients of the rods from which it is displaced remain about the same. Thus the overall average coefficient of the group of affected rods goes down when a single rod is displaced.

Multi-Jet Impingement Heat Transfer With a Dimple-Pimple Patterned Jet Plate

2020 ◽  
Author(s):  
Husam Zawati ◽  
Gaurav Gupta ◽  
Yakym Khlyapov ◽  
Erik Fernandez ◽  
Jayanta Kapat ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Underlying Mechanism ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Air Jets ◽  
Impingement Heat Transfer ◽  
Definition Of

Abstract The objective of the present study is the evaluation of the heat transfer difference between a novel jet plate configuration and a conventional flat jet orifice plate. Physical mechanisms that lead to a change in Nusselt number when comparing both configurations are discussed in two regions: impingement and crossflow. In the presented work, both plates with identical inline arrays of (20 × 26) circular air jets impinging orthogonally on a flat target comprised of 20 segments parallel to the jet orifice plates, are studied. The first is a staggered configuration of a pimple-dimple (convex-concave) plate. This plate features two jet diameters: (a) 4.63 mm emanating from negative sphere of 14.63 mm in radius inward imprint; (b) 2.19 mm emanating from a positive sphere of 17.07 mm in radius, protruding from the base of the plate. The second jet plate is flat, which serves as a baseline for the heat transfer study. This plate has a constant jet orifice diameters of 3.49 mm, found based on the definition of total average open area of the first plate (NPR configuration). Heat transfer characteristics and turbulent flow structures are investigated over jet-averaged Reynolds numbers (Reav,j) of 5,000, 7,000, and 9,000. Jet-to-plate distance (Z/Dj) is varied between (2.4 – 6.0) jet diameters. A numerical study is carried out to compare various turbulence models (κε-EB, κε-Lag EB, κε-v2f, κω-SST, RST). Numerical simulations are analyzed in detail to explain the underlying mechanism of heat transfer enhancement, related to such geometries. The convex-concaved plate yields lower globally-averaged heat transfer coefficients when compared to a flat jet plate in the impingement region. However, enhancement up to 23% is seen in the crossflow region, where the crossflow effects are dominant in a maximum-crossflow configuration.

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