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Title: Mixed convection heat transfer to and from a horizontal cylinder in cross-flow with heating from below.

Abstract

Heat transfer to and from a circular cylinder in a cross-flow of water at low Reynolds number was studied both experimentally and numerically. The experiments were carried out in a high aspect ratio water channel. The test section inflow temperature and velocity, channel lower surface temperature and cylinder surface temperature were controlled to yield either laminar or turbulent flow for a desired Richardson number. When the lower surface was unheated, the temperatures of the lower surface and water upstream of the cylinder were maintained approximately equal and the flow was laminar. When the lower surface was heated, turbulence intensities as high as 20% were measured several cylinder diameters upstream of the cylinder due to turbulent thermal plumes produced by heating the lower surface. Variable property, two-dimensional simulations were undertaken using a variant of the u{sup 2}-f turbulence model with buoyancy production of turbulence accounted for by a simple gradient diffusion model. Predicted and measured heat flux distributions around the cylinder are compared for values of the Richardson number, Gr{sub d}/Re{sub d}{sup 2} from 0.3 to 9.3. For laminar flow, the predicted and measured heat flux results agreed to within the experimental uncertainty. When the lower surface was heated, and themore » flow was turbulent, there was qualitative agreement between predicted and measured heat flux distributions around the cylinder. However the predicted spatially averaged Nusselt number was from 37% to 53% larger than the measured spatially averaged Nusselt number. Additionally, spatially averaged Nusselt numbers are compared to correlations in the literature for mixed convection heat transfer to/from cylinders in cross-flow. The results presented here are larger than the correlation values. This is believed to be due to the effects of buoyancy-induced turbulence resulting from heating the lower surface and the proximity of the cylinder to that surface.« less

Authors:
 [1]; ;  [2];
  1. (University of California, Berkeley, CA)
  2. (Sandia National Laboratories, Albuquerque, NM)
Publication Date:
Research Org.:
Sandia National Laboratories
Sponsoring Org.:
USDOE
OSTI Identifier:
952100
Report Number(s):
SAND2006-0969J
TRN: US200913%%296
DOE Contract Number:
AC04-94AL85000
Resource Type:
Journal Article
Resource Relation:
Journal Name: Proposed for publication in the International Journal of Heat and Fluid Flow.
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; CONVECTION; HEAT TRANSFER; CYLINDERS; LAMINAR FLOW; TURBULENT FLOW; NUSSELT NUMBER; REYNOLDS NUMBER; RICHARDSON NUMBER; FLOW MODELS; TEMPERATURE MEASUREMENT

Citation Formats

Greif, Ralph, Evans, Gregory Herbert, Kearney, Sean Patrick, and Laskowski, Gregory Michael. Mixed convection heat transfer to and from a horizontal cylinder in cross-flow with heating from below.. United States: N. p., 2006. Web.
Greif, Ralph, Evans, Gregory Herbert, Kearney, Sean Patrick, & Laskowski, Gregory Michael. Mixed convection heat transfer to and from a horizontal cylinder in cross-flow with heating from below.. United States.
Greif, Ralph, Evans, Gregory Herbert, Kearney, Sean Patrick, and Laskowski, Gregory Michael. Wed . "Mixed convection heat transfer to and from a horizontal cylinder in cross-flow with heating from below.". United States. doi:.
@article{osti_952100,
title = {Mixed convection heat transfer to and from a horizontal cylinder in cross-flow with heating from below.},
author = {Greif, Ralph and Evans, Gregory Herbert and Kearney, Sean Patrick and Laskowski, Gregory Michael},
abstractNote = {Heat transfer to and from a circular cylinder in a cross-flow of water at low Reynolds number was studied both experimentally and numerically. The experiments were carried out in a high aspect ratio water channel. The test section inflow temperature and velocity, channel lower surface temperature and cylinder surface temperature were controlled to yield either laminar or turbulent flow for a desired Richardson number. When the lower surface was unheated, the temperatures of the lower surface and water upstream of the cylinder were maintained approximately equal and the flow was laminar. When the lower surface was heated, turbulence intensities as high as 20% were measured several cylinder diameters upstream of the cylinder due to turbulent thermal plumes produced by heating the lower surface. Variable property, two-dimensional simulations were undertaken using a variant of the u{sup 2}-f turbulence model with buoyancy production of turbulence accounted for by a simple gradient diffusion model. Predicted and measured heat flux distributions around the cylinder are compared for values of the Richardson number, Gr{sub d}/Re{sub d}{sup 2} from 0.3 to 9.3. For laminar flow, the predicted and measured heat flux results agreed to within the experimental uncertainty. When the lower surface was heated, and the flow was turbulent, there was qualitative agreement between predicted and measured heat flux distributions around the cylinder. However the predicted spatially averaged Nusselt number was from 37% to 53% larger than the measured spatially averaged Nusselt number. Additionally, spatially averaged Nusselt numbers are compared to correlations in the literature for mixed convection heat transfer to/from cylinders in cross-flow. The results presented here are larger than the correlation values. This is believed to be due to the effects of buoyancy-induced turbulence resulting from heating the lower surface and the proximity of the cylinder to that surface.},
doi = {},
journal = {Proposed for publication in the International Journal of Heat and Fluid Flow.},
number = ,
volume = ,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2006},
month = {Wed Feb 01 00:00:00 EST 2006}
}
  • The first two sections as listed in the title contain 7 papers. The third section on thermal analysis contains 18 papers arranged into the following topical areas: Thermal treatment and municipal wastes; Thermal hydraulics in hazardous and nuclear waste processing and disposal; and Waste processing. Heat transfer in fire and combustion systems contains 17 papers arranged into the following topical sections: Soot/radiation; Combustion systems; Multiphase combustion; and Flames and fires. Most papers have been processed separately for inclusion on the data base.
  • Results are reported for an experimental and numerical study of forced and mixed convective heat transfer in a liquid-saturated horizontal porous duct. The cross section of the duct has a sudden expansion with a heated region on the lower surface downstream and adjacent to the expansion. Within the framework of Darcy`s formulation, the calculated and measured Nusselt numbers for 0.1 < Pe < 100 and 50 < Ra < 500 are in excellent agreement. Further, the calculated Nusselt numbers are very close to those for the bottom-heated flat duct. This finding has important implications for convective heat and mass transfermore » in geophysical systems and porous matrix heat exchangers. The calculations were also carried out for glass bead-packed beds saturated with water using non-Darcy`s formula. The streamlines in the forced convection indicate that, even with non-Darcy effects included, recirculation is not observed downstream of an expansion and the heat transfer rate is decreased but only marginally.« less
  • Heat-transfer and pressure-drop measurements were performed in forced convection of air flow through a rectangular duct packed with spherical particles, which had upper cooled and lower heated surfaces. Four kinds of spherical particles with different diameters and thermal conductivities were used as the packing materials. The spherical particle boundary effects on fluid motion and heat transfer were examined. The heat-transfer rate from the heat-transfer surfaces was promoted by a thermal dispersion effect caused by a fluid mixing motion. However, it decreased in the vicinity of the near-wall region due to low effective thermal conductivity and weak fluid mixing motion. Itmore » was clarified that the ratio of the thermal boundary-layer thickness developed from the heat-transfer surface to the thickness of the near-wall region was the important factor for dealing with the heat-transfer data. Nondimensional heat-transfer correlation equations were derived, using various parameters expressing the average characteristics of a porous bed packed with spherical particles.« less
  • Because of its importance in industrial processes, overall natural convective heat transfer from horizontal cylinders has been the subject of many experimental and analytical studies. However, because of the dispersions in these results, there is still uncertainty about the value of the Nusselt number Nu at a particular Rayleigh number Ra, especially for Ra > 10{sup 3}. The values of Nu obtained from the most commonly used correlations do not reduce this uncertainty because of their own dispersion. To avoid the effect of higher Prandtl numbers Pr on the heat transfer, a review is made of the results from 34more » experimental studies in air (Pr = 0.7) in the range 10 {le} Ra {le} 10{sup 7}. A review is also made of 23 analytical and numerical studies. It is concluded that the mean values of Nu within each of the two groups agree to within 4% in the range 10 {le} Ra {le} 10{sup 4}. At higher Ra, the mean of the experimental values of Nu is higher than the mean of the analytical and numerical values, the difference increasing from 7.86% at Ra = 10{sup 5} to 11.3% at Ra = 10{sup 7}. Possible reasons for this discrepancy are discussed.« less
  • The objective of the present study is to clarify the heat transfer characteristic of natural convection around a horizontal circular cylinder immersed in liquid metals. Experimental work concerning liquid metals sometimes involves such a degree of error that is impossible to understand the observed characteristics in measurement. Numerical analysis is a powerful means to overcome this experimental disadvantage. In the present paper the authors first show that the Boussinesq approximation is more applicable heat transfer rates, even for a cylinder with a relatively large temperature difference (>100K) between the heat transfer surface and fluid. It is found from a comparisonmore » of the present results with previous work that the correlation equations that have already been proposed predict values lower than the present ones.« less