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Title: Mixed convection through vertical porous annuli locally heated from the inner cylinder

The purpose of the present study is to examine the influence of both aiding and opposing external flows on the buoyancy-induced natural convection in vertical porous annuli. The effects of radius ratio are taken into account in a numerical study. Measurements of heat transfer coefficients in aiding and opposing flows cover the free to forced convective heat transfer regimes. Mixed convection in a vertical annulus filled with a saturated porous medium is numerically and experimentally investigated. Calculations are carried out under the traditional Darcy assumptions and cover the ranges 10 {le} Ra {le} 200 and 0.01 {le} Pe {le} 200. Both numerical and experimental results show that the Nusselt number increases with either Ra or Pe when the imposed flow is in the same direction as the buoyancy-induced flow. When the imposed flow opposes buoyancy-induced flow, the Nusselt number first decreases with an increase of the Peclet number and reaches a minimum before increasing again. Under certain circumstances, the Nusselt number for a lower Rayleigh number may exceed that for larger value. Nusselt numbers are correlated by the parameter groups Nu/Pe{sup 1/2} and Ra/Pe{sup 3/2}. Good agreement exists between measured and predicted Nusselt numbers, and the occurrence of a minimummore » Nusselt number in mean flow that opposes buoyancy is verified experimentally.« less
Authors:
 [1] ;  [2]
  1. (Univ. of Arizona, Tucson (United States))
  2. (Colorado State Univ., Fort Collins (United States))
Publication Date:
OSTI Identifier:
5020244
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Heat Transfer (Transactions of the ASME (American Society of Mechanical Engineers), Series C); (United States); Journal Volume: 114:1
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; ANNULAR SPACE; CONVECTION; POROUS MATERIALS; BENCH-SCALE EXPERIMENTS; CALCULATION METHODS; CYLINDERS; DARCY LAW; NUMERICAL ANALYSIS; NUSSELT NUMBER; CONFIGURATION; ENERGY TRANSFER; HEAT TRANSFER; MASS TRANSFER; MATERIALS; MATHEMATICS; SPACE 420400* -- Engineering-- Heat Transfer & Fluid Flow