Experimental research on heat transfer of natural convection in vertical rectangular channels with large aspect ratio
Abstract
This work presents the experimental research on the steady laminar natural convection heat transfer of air in three vertical thin rectangular channels with different gap clearance. The much higher ratio of width to gap clearance (6024) and the ratio of length to gap clearance (800320) make the rectangular channels similar with the coolant flow passage in plate type fuel reactors. The vertical rectangular channels were composed of two stainless steal plates and were heated by electrical heating rods. The wall temperatures were detected with the Ktype thermocouples which were inserted into the blind holes drilled in the steal plates. Also the air temperatures at the inlet and outlet of the channel were detected. The wall heat fluxes added to the air flow were calculated by the Fourier heat conduction law. The heat transfer characteristics were analyzed, and the average Nusselt numbers in all the three channels could be well correlated with the Rayleigh number or the modified Rayleigh number in a uniform correlation. Furthermore, the maximum wall temperatures were investigated, which is a key parameter for the fuel's integrity during some accidents. It was found that even the wall heat flux was up to 1500 W/m{sup 2}, the maximum wallmore »
 Authors:
 State Key Laboratory of Multi Phase Flow in Power Engineering, Xi'an JIaotong University, Xi'an, Shaanxi 710049 (China)
 (China)
 School of Nuclear Science and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 (China)
 Publication Date:
 OSTI Identifier:
 21248834
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Experimental Thermal and Fluid Science; Journal Volume: 34; Journal Issue: 1; Other Information: Elsevier Ltd. All rights reserved
 Country of Publication:
 United States
 Language:
 English
 Subject:
 42 ENGINEERING; 22 GENERAL STUDIES OF NUCLEAR REACTORS; NATURAL CONVECTION; THERMAL CONDUCTION; ASPECT RATIO; RAYLEIGH NUMBER; WALLS; PLATES; AIR FLOW; HEAT FLUX; REACTORS; NUSSELT NUMBER; FUEL INTEGRITY; SAFETY ANALYSIS; COOLANTS; CORRELATIONS; DESIGN; HEATING; LAMINAR FLOW; STEADY FLOW; Rectangular channels
Citation Formats
Lu, Qing, Qiu, Suizheng, Su, Guanghui, School of Nuclear Science and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, Tian, Wenxi, and Ye, Zhonghao. Experimental research on heat transfer of natural convection in vertical rectangular channels with large aspect ratio. United States: N. p., 2010.
Web. doi:10.1016/J.EXPTHERMFLUSCI.2009.09.004.
Lu, Qing, Qiu, Suizheng, Su, Guanghui, School of Nuclear Science and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, Tian, Wenxi, & Ye, Zhonghao. Experimental research on heat transfer of natural convection in vertical rectangular channels with large aspect ratio. United States. doi:10.1016/J.EXPTHERMFLUSCI.2009.09.004.
Lu, Qing, Qiu, Suizheng, Su, Guanghui, School of Nuclear Science and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, Tian, Wenxi, and Ye, Zhonghao. Fri .
"Experimental research on heat transfer of natural convection in vertical rectangular channels with large aspect ratio". United States.
doi:10.1016/J.EXPTHERMFLUSCI.2009.09.004.
@article{osti_21248834,
title = {Experimental research on heat transfer of natural convection in vertical rectangular channels with large aspect ratio},
author = {Lu, Qing and Qiu, Suizheng and Su, Guanghui and School of Nuclear Science and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 and Tian, Wenxi and Ye, Zhonghao},
abstractNote = {This work presents the experimental research on the steady laminar natural convection heat transfer of air in three vertical thin rectangular channels with different gap clearance. The much higher ratio of width to gap clearance (6024) and the ratio of length to gap clearance (800320) make the rectangular channels similar with the coolant flow passage in plate type fuel reactors. The vertical rectangular channels were composed of two stainless steal plates and were heated by electrical heating rods. The wall temperatures were detected with the Ktype thermocouples which were inserted into the blind holes drilled in the steal plates. Also the air temperatures at the inlet and outlet of the channel were detected. The wall heat fluxes added to the air flow were calculated by the Fourier heat conduction law. The heat transfer characteristics were analyzed, and the average Nusselt numbers in all the three channels could be well correlated with the Rayleigh number or the modified Rayleigh number in a uniform correlation. Furthermore, the maximum wall temperatures were investigated, which is a key parameter for the fuel's integrity during some accidents. It was found that even the wall heat flux was up to 1500 W/m{sup 2}, the maximum wall temperature was lower than 350 C. All this work is valuable for the plate type reactor's design and safety analysis. (author)},
doi = {10.1016/J.EXPTHERMFLUSCI.2009.09.004},
journal = {Experimental Thermal and Fluid Science},
number = 1,
volume = 34,
place = {United States},
year = {Fri Jan 15 00:00:00 EST 2010},
month = {Fri Jan 15 00:00:00 EST 2010}
}

The effect of localized heating in rectangular channels was studied by solving the partial differential equations for the conservation of mass, momentum, and energy numerically using an unsteady state formulation and the alternatingdirectionimplicit method. The heating element was a long, horizontal, isothermal strip located in one, otherwiseinsulated vertical wall. The opposing wall was maintained at a lower uniform temperature and the upper and lower surfaces were insulated or maintained at the lower temperature. Computations were carried out for Pr = 0.7, 0 less than or equal to Ra less than or equal to 10/sup 5/, a complete range of heatermore »

Optimum aspect ratio for heat transfer enhancement in curved rectangular channels
Enhanced heat transfer in curved rectangular channels depends on at least two geometric factors, the radius of curvature of the duct and the aspect ratio, which is the width/depth ratio of the duct. In this work, an expression for optimum aspect ratio is derived mathematically from a correlation that includes both aspect ratio and bend curvature parameters. Enhancement factors are developed that show optimal, nearoptimal, and nonoptimal aspect ratios for curved rectangular ducts. Predicted enhancements are within 25% of published literature results for individual designs, two of which show heat transfer enhancement of 200% over that of a straight ductmore » 
The effect of aspect ratio and rounded corners on the laminar forced convection heat transfer of a non newtonian fluid in the entrance region of a rectangular duct
A numerical simulation was carried out to solve the full three dimensional governing equations for steady simultaneously developing laminar flow and heat transfer. The fluid was considered to be a purely viscous one which followed the power law behavior. Results are presented and discussed for constant wall heat flux (both axially and peripherally) and constant wall temperature boundary conditions over a range of power law indices. 
Natural convection heat transfer in moderate aspect ratio enclosures
Local and average heat transfer coefficients for natural convection between parallel plates separated by slats to create enclosures of moderate aspect ratio have been experimentally determined using an interferometric technique. The effects of Rayleigh number, tilt and slat angle, and aspect ratio on the Nusselt number have been determined. The Rayleigh number range tested was up to 7 x 10/sup 4/, and the aspect ratio (ratio of enclosure length to plate spacing) varied between 0.25 and 4. The angles of tilt of the enclosure with respect to the horizontal were 45, 60 and 90 deg. Slat angles of 45, 60more »