Free Convection Heat Transfer across Rectangular-Celled Diathermanous Honeycombs

1980 ◽  
Vol 102 (1) ◽  
pp. 75-80 ◽  
Author(s):  
D. R. Smart ◽  
K. G. T. Hollands ◽  
G. D. Raithby
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Critical Rayleigh Number ◽  
Convection Heat Transfer ◽  
Aspect Ratios ◽  
Cell Dimensions ◽  
Free Convection Heat ◽  
Rayleigh Numbers ◽  
Honeycomb Material

Experimentally obtained Nusselt number-Rayleigh number plots are presented for free convective heat transfer across inclined honeycomb panels filled with air. The honeycomb cells were rectangular in shape with very long cell dimensions across the slope and comparatively short dimensions up the slope. Elevation aspect ratios, AE, investigated were 3, 5 and 10; angles of inclination, θ, measured from the horizontal, were 0, 30, 60, 75 and 90 deg. The effect on the Nusselt number, of the emissivities of the plates bounding the honeycomb, and of the emissivity of honeycomb material, was also investigated. The measurements confirmed that the critical Rayleigh number and the post-critical heat transfer depend on the radiant properties of the honeycomb cells. The critical Rayleigh numbers at θ = 0 were well predicted by the methods of Sun and Edwards. For 0 < θ ≤ 75 deg, the critical Rayleigh numbers and the Nusselt-Rayleigh relations were both found to be essentially the same as their horizontal counterparts provided the Rayleigh number was first scaled by cos θ. For θ = 90 deg, the form of the Nusselt-Rayleigh relation was found to be very different from that for θ ≤ 75 deg and similar to that observed for square-celled honeycombs for θ ≥ 30 deg. The θ = 90 deg data were found to be closely correlated by an equation of the form recently proposed by Bejan and Tien.

An Experimental Study on the Effect of Partition Angle on Free Convection Heat Transfer in a Partition Cavity by Laser Interferometry Method

2010 ◽  
Author(s):  
Tooraj Yousefi ◽  
Sajjad Mahmoodi Nezhad ◽  
Masood Bigharaz ◽  
Saeed Ebrahimi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Free Convection ◽  
Average Nusselt Number ◽  
Convection Heat Transfer ◽  
Laser Interferometry ◽  
Heated Wall ◽  
Convection Heat ◽  
Free Convection Heat

Steady state two-dimensional free convection heat transfer in a partitioned cavity with adiabatic horizontal and isothermally vertical walls and an adiabatic partition has been investigated experimentally. The experiments have been carried out using a Mach-Zehnder interferometer. The effects of the angel of the adiabatic partition and Rayleigh number on the heat transfer from the heated wall are investigated. Experiments are performed for the values of Rayleigh number based on the cavity side length in the range between 1.5×105 to 4.5×105 and various angle of the partition with respect to horizon from 0° to 90°. The results indicate that at each angle of the adiabatic partition, by increasing the Rayleigh number, the average Nusselt number and heat transfer increase and at each Rayleigh number, the maximum and the minimum heat transfer occur at θ=45° and θ=90°, respectively. A correlation based on the experimental data for the average Nusselt number of the heated wall as a function of Rayleigh number and the angel of the adiabatic partition is presented in the aforementioned ranges.

Free Convection Heat Transfer Across Inclined Honeycomb Panels

1977 ◽  
Vol 99 (1) ◽  
pp. 86-91 ◽  
Author(s):  
R. L. D. Cane ◽  
K. G. T. Hollands ◽  
G. D. Raithby ◽  
T. E. Unny
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Free Convection ◽  
Convection Heat Transfer ◽  
Correlation Equation ◽  
Base Flow ◽  
Convection Heat ◽  
Radiative Coupling ◽  
Aspect Ratios ◽  
Free Convection Heat

Experimentally obtained Nusselt number-Rayleigh number plots are presented for free convective heat transfer across honeycomb panels, heated from below, and inclined with respect to the horizontal at angles of 0, 30, 45, 60, and 90 deg. Aspect ratios of honeycomb cells of 2, 3, 4, and 5 are included; the fluid contained in the cells is air. Substantial suppression of free convection is observed when compared with an air layer of the same depth but not containing a honeycomb. Heat transfer associated with the base flow is found to be of only moderate importance at angles near horizontal, but of considerable consequence for angles near the vertical. The honeycomb walls used were partly transparent to thermal radiation, and a strong radiative coupling is indicated. A correlation equation for the Nusselt number, valid over part of the experimental range, is presented.

scholarly journals Free Convection Heat Transfer from Horizontal Cylinders

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 559
Author(s):  
Janusz T. Cieśliński ◽  
Slawomir Smolen ◽  
Dorota Sawicka
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Free Convection ◽  
Convection Heat Transfer ◽  
Horizontal Tube ◽  
Correlation Equations ◽  
Convection Heat ◽  
Number Range ◽  
Heated Cylinder ◽  
Free Convection Heat

The results of experimental investigation of free convection heat transfer in a rectangular container are presented. The ability of the commonly accepted correlation equations to reproduce present experimental data was tested as well. It was assumed that the examined geometry fulfils the requirement of no-interaction between heated cylinder and bounded surfaces. In order to check this assumption recently published correlation equations that jointly describe the dependence of the average Nusselt number on Rayleigh number and confinement ratios were examined. As a heat source served electrically heated horizontal tube immersed in an ambient fluid. Experiments were performed with pure ethylene glycol (EG), distilled water (W), and a mixture of EG and water at 50%/50% by volume. A set of empirical correlation equations for the prediction of Nu numbers for Rayleigh number range 3.6 × 104 < Ra < 9.2 × 105 or 3.6 × 105 < Raq < 14.8 × 106 and Pr number range 4.5 ≤ Pr ≤ 160 has been developed. The proposed correlation equations are based on two characteristic lengths, i.e., cylinder diameter and boundary layer length.

On the Nusselt Number for H2 Heat Transfer in Rectangular Ducts of Large Aspect Ratios

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
C. Y. Wang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Forced Convection ◽  
Parallel Plate ◽  
Convection Heat Transfer ◽  
Analytic Method ◽  
Convection Heat ◽  
Forced Convection Heat Transfer ◽  
Aspect Ratios

The H1 and H2 forced convection heat transfer in rectangular ducts are studied using an accurate, analytic method. It is confirmed that, as the aspect ratio tends to infinity, the Nusselt number for the H2 case approaches 2.9162, much lower than the parallel plate value of 8.2353 attained by the H1 case. The controversy about the H2 limit is thus settled. An explanation of the behavior is suggested.

Buoyancy estimation of a Montgolfière in the atmosphere of Titan

2013 ◽  
Vol 117 (1195) ◽  
pp. 943-957 ◽  
Author(s):  
G. E. Dorrington
Keyword(s):  
Heat Transfer ◽  
Transfer Rate ◽  
Convection Heat Transfer ◽  
Lower Troposphere ◽  
Convection Heat ◽  
Free Convection Heat ◽  
Parameter Values ◽  
Rayleigh Numbers ◽  
Cryogenic Conditions ◽  
Thermal Balloon

AbstractPrediction of the buoyancy of a thermal balloon, or Montgolfière, intended to float in the atmosphere of Titan is discussed. A laboratory based experiment designed to measure the buoyant lift of an electrically-heated, single-wall, natural-shape balloon is described. The experimental results presented closely match an analytical model employing established heat transfer correlations with selected parameter values. When the model is extrapolated to the cryogenic conditions representative of Titan’s lower troposphere, using the same correlations and parameters, the estimated buoyancy is found to be substantially higher than has been previously predicted. To account for the buoyancy difference, it is suggested that the internal free convection heat transfer rate is significantly lower than has been assumed in previous studies. To substantiate this result, it is recommended that further experiments should be performed at higher Rayleigh numbers.

A Comparison Between the Local Free Convection Heat Transfer Coefficients of Horizontal Cylinders in Vertical and Inclined Arrays

2006 ◽  
Author(s):  
Mehdi Ashjaee ◽  
Tooraj Yousefi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Rayleigh Number ◽  
Free Convection ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Horizontal Cylinder ◽  
Convection Heat ◽  
Free Convection Heat

Laminar free convection heat transfer from vertical and inclined arrays of horizontal isothermal cylinders in air was investigated experimentally and numerically. Experiments were carried out using Mach-Zehnder interferometer and the FLUENT code was used for numerical study. Investigation was performed for vertical and horizontal cylinder spacing from 2 to 5 and to 2 cylinder diameter respectively. The Rayleigh number based on the cylinder diameter varied between 103 and 3×103. The effect of vertical and horizontal cylinder spacing and Rayleigh number on the local heat transfer from each individual cylinder was investigated. It was seen that the local heat transfer coefficient of each cylinder strongly depends on its position relative to the others. This variation of the local heat transfer coefficient was explained by the interaction of plume’s temperature and velocity profiles.

A Numerical Study of Natural Convection in a Cavity With Two Fins Attached to Its Vertical Walls

2007 ◽  
Author(s):  
G. A. Sheikhzadeh ◽  
M. Pirmohammadi ◽  
M. Ghassemi
Keyword(s):  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Square Cavity ◽  
Vertical Walls ◽  
The Mean ◽  
Energy Equations ◽  
Rayleigh Numbers

Numerical study natural convection heat transfer inside a differentially heated square cavity with adiabatic horizontal walls and vertical isothermal walls is investigated. Two perfectly conductive thin fins are attached to the isothermal walls. To solve the governing differential mass, momentum and energy equations a finite volume code based on Pantenkar’s simpler method is developed and utilized. The results are presented in form of streamlines, isotherms as well as Nusselt number for Rayleigh number ranging from 104 up to 107. It is shown that the mean Nusselt number is affected by the position of the fins and length of the fins as well as the Rayleigh number. It is also observed that maximum Nusselt number occurs about the middle of the enclosure where Lf is grater the 0.5. In addition the Nusselt number stays constant and does not varies with width of the cavity (lf) when Lf is equal to 0.5 and Rayleigh number is equal to 104 and 107 as well as when Lf is equal to 0.6 and low Rayleigh numbers.

scholarly journals Heat Transfer Performance of Different Fluids During Natural Convection in Enclosures with Varying Aspect Ratios

2021 ◽  
Vol 287 ◽  
pp. 03010
Author(s):  
Rajashekhar Pendyala ◽  
Suhaib Umer Ilyas ◽  
Yean Sang Wong
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Heat Transfer Performance ◽  
Convection Heat Transfer ◽  
Heat Transfer Process ◽  
Natural Convection Heat Transfer ◽  
Transfer Performance ◽  
Convection Heat ◽  
Aspect Ratios

The heat transfer process takes place in numerous applications through the natural convection of fluids. Investigations of the natural convection heat transfer in enclosures have gained vital importance in the last decade for the improvement in thermal performance and design of the heating/cooling systems. Aspect ratios (AR=height/length) of the enclosures are one of the crucial factors during the natural convection heat transfer process. The investigated fluids consisting of air, water, engine oil, mercury, and glycerine have numerous engineering applications. Heat transfer and fluid flow characteristics are studied in 3-dimensional rectangular enclosures with varying aspect ratios (0.125 to 150) using computational fluid dynamics (CFD) simulations. Studies are carried out using the five different fluids having Prandtl number range 0.01 to 4500 in rectangular enclosures with the hot and cold surface with varying temperature difference 20K to 100K. The Nusselt number and heat transfer coefficients are estimated at all conditions to understand the dependency of ARs on the heat transfer performance of selected fluids. Temperature and velocity profiles are compared to study the flow pattern of different fluids during natural convection. The Nusselt number correlations are developed in terms of aspect ratio and Rayleigh number to signify the natural convection heat transfer performance.

scholarly journals Prediction of Natural Convection Heat Transfer Phenomena of Nanofluids in Corrugated Annulus

2020 ◽  
Author(s):  
Sattar Aljobair ◽  
Akeel Abdullah Mohammed ◽  
Israa Alesbe
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Average Nusselt Number ◽  
Volume Fraction ◽  
Outer Cylinder ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat

Abstract The natural convection heat transfer and fluid flow characteristic of water based Al2O3 nano-fluids in a symmetrical and unsymmetrical corrugated annulus enclosure has been studied numerically using CFD. The inner cylinder is heated isothermally while the outer cylinder is kept constant cold temperature. The study includes eight models of corrugated annulus enclosure with constant aspect ratio of 1.5. The governing equations of fluid motion and heat transfer are solved using stream-vorticity formulation in curvilinear coordinates. The range of solid volume fractions of nanoparticles extends from PHI=0 to 0.25, and Rayleigh number varies from 104 to 107. Streamlines, isotherms, local and average Nusselt number of inner and outer cylinder has been investigated in this study. Sixty-four correlations have been deduced for the average Nusselt number for the inner and outer cylinders as a function of Rayleigh number have been deduced for eight models and five values of volume fraction of nano particles with an accuracy range 6-12 %. The results show that, the average heat transfer rate increases significantly as particle volume fraction and Rayleigh number increase. Also, increase the number of undulations in unsymmetrical annuli reduces the heat transfer rates which remain higher than that in symmetrical annuli. There is no remarkable change in isotherms contour with increase of volume fraction of nanofluid.

scholarly journals Effect of Various Tilted Positions of a Thin Fin on Natural Convection of Laminar Viscous Flow in a Square Cavity

2021 ◽  
Vol 39 (5) ◽  
pp. 1634-1642
Author(s):  
Syed Fazuruddin ◽  
Seelam Sreekanth ◽  
G Sankara Sekhar Raju
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Finite Difference ◽  
Average Nusselt Number ◽  
Vertical Position ◽  
Inclination Angles ◽  
Rayleigh Numbers

An exhaustive numerical investigation is carried out to analyze the role of an isothermal heated thin fin on fluid flow and temperature distribution visualization in an enclosure. Natural convection within square enclosures finds remarkable pragmatic applications. In the present study, a finite difference approach is performed on two-dimensional laminar flow inside an enclosure with cold side walls and adiabatic horizontal walls. The fluid flow equations are reconstructed into vorticity - stream function formulation and these equations are employed utilizing the finite-difference strategy with incremental time steps. The parametric study includes a wide scope of Rayleigh number, Ra, and inclination angle ϴ of the thin fin. The effect of different Rayleigh numbers ranging Ra = 104-106 with Pr=0.71 for all the inclination angles from 0°-360° with uniform rotational length of angle 450 of an inclined heated fin on fluid flow and heat transfer have been investigated. The heat transfer rate within the enclosure is measured by means of local and average Nusselt numbers. Regardless of inclination angles of the thin fin, a slight enhancement in the average Nusselt number is observed when Rayleigh number increased for both the cases of the horizontal and vertical position of the thin fin. When the fin has inclined no change in average Nusselt number is noticed for distinct Rayleigh numbers.

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