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Title: Turbulent heat transfer with combined forced and natural convection along a vertical flat plate. Effect of Prandtl number

Abstract

The turbulent heat transfer of combined forced and natural convection along a vertical flat plate was investigated experimentally both with aiding and opposing flows of air. Local heat-transfer coefficients were measured in the vertical direction. The results show that the local Nusselt numbers for aiding flow become smaller than those for the forced and the natural convection, while the Nusselt numbers for the opposing flow are increased significantly. These results are compared with the previous results for water. It has been found that the nondimensional parameter Z(= Gr{sub x}*/Nu{sub x}Re{sub x}){sup 2.7}Pr{sup 0.6} can predict the behavior of heat transfer both for air and water. Furthermore, the natural, forced, and combined convection regions can be classified in terms of the above parameter.

Authors:
 [1];  [2]
  1. (Toyota College of Technology (JP))
  2. (Toyohashi Univ. of Technology (JP))
Publication Date:
OSTI Identifier:
6427618
Resource Type:
Journal Article
Resource Relation:
Journal Name: Heat Transfer - Japanese Research; (USA); Journal Volume: 19:2
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; 14 SOLAR ENERGY; AIR; HEAT TRANSFER; FLAT PLATE COLLECTORS; TURBULENT FLOW; WATER; AIR FLOW; EXPERIMENTAL DATA; FORCED CONVECTION; MEASURING METHODS; NATURAL CONVECTION; NUSSELT NUMBER; PRANDTL NUMBER; CONVECTION; DATA; ENERGY TRANSFER; EQUIPMENT; FLUID FLOW; FLUIDS; GAS FLOW; GASES; HYDROGEN COMPOUNDS; INFORMATION; MASS TRANSFER; NUMERICAL DATA; OXYGEN COMPOUNDS; SOLAR COLLECTORS; SOLAR EQUIPMENT 420400* -- Engineering-- Heat Transfer & Fluid Flow; 142000 -- Solar Energy-- Heat Storage-- (1980-); 141000 -- Solar Collectors & Concentrators

Citation Formats

Inagaki, T., and Kitamura, K. Turbulent heat transfer with combined forced and natural convection along a vertical flat plate. Effect of Prandtl number. United States: N. p., 1990. Web.
Inagaki, T., & Kitamura, K. Turbulent heat transfer with combined forced and natural convection along a vertical flat plate. Effect of Prandtl number. United States.
Inagaki, T., and Kitamura, K. 1990. "Turbulent heat transfer with combined forced and natural convection along a vertical flat plate. Effect of Prandtl number". United States. doi:.
@article{osti_6427618,
title = {Turbulent heat transfer with combined forced and natural convection along a vertical flat plate. Effect of Prandtl number},
author = {Inagaki, T. and Kitamura, K.},
abstractNote = {The turbulent heat transfer of combined forced and natural convection along a vertical flat plate was investigated experimentally both with aiding and opposing flows of air. Local heat-transfer coefficients were measured in the vertical direction. The results show that the local Nusselt numbers for aiding flow become smaller than those for the forced and the natural convection, while the Nusselt numbers for the opposing flow are increased significantly. These results are compared with the previous results for water. It has been found that the nondimensional parameter Z(= Gr{sub x}*/Nu{sub x}Re{sub x}){sup 2.7}Pr{sup 0.6} can predict the behavior of heat transfer both for air and water. Furthermore, the natural, forced, and combined convection regions can be classified in terms of the above parameter.},
doi = {},
journal = {Heat Transfer - Japanese Research; (USA)},
number = ,
volume = 19:2,
place = {United States},
year = 1990,
month = 1
}
  • The mechanisms of the retardation and enhancement of heat transfer in the combined convection region of aiding and opposing flows were investigated both experimentally and analytically. The surface temperature distributions were visualized by a liquid crystal sheet. The results show that low-temperature streaks or spots of large sizes appear in the whole regions of forced, natural, and combined convections, and they exert a significant role a on the heat transfer. Such low-temperature streaks or spots are generated as a result of the penetration of low-temperature fluid lumps into the near wall regions. The surface renewal model is proposed to simulatemore » the heat transport by the above fluid motion. It is found that the model predicted the heat transfer of the combined convection quite satisfactorily.« less
  • To attain a high enhancement rate in convective heat transfer, deformation or destruction of the boundary layer by some methods, including active and passive enhancement methods, is a necessary condition. For instance, the application of fluid injection or suction to the temperature field is one of the most fundamental active methods. Although several attempts of heat-transfer enhancement have been investigated in laminar and turbulent forced convection, any effective enhancement techniques for heat transfer of turbulent natural convection have not yet been discussed. In particular, it is important to analyze its enhancement mechanism when only natural convection is applicable to cooling.more » In this paper, therefore, fluid injection and suction were added to turbulent natural convection along a vertical flat plate, and then the possibility of its heat-transfer enhancement was investigated. It was found that the local Nusselt numbers affected by fluid injection and suction were 1.5 [approximately] 1.6 times as much as those for pure turbulent natural convection.« less
  • Heat transfer by natural convection along a vertical flat plate was investigated semi-analytically. In natural convection, measurements of turbulent quantities near the wall are usually difficult as a result of strong temperature fluctuations. On the other hand, a number of attempts to describe turbulent heat transfer have been made and reliable data were presented. Therefore, in this study, a penetration model was introduced and natural-convection heat transfer was considered in relation to its turbulent structure.
  • In this study, two-equation models for velocity and temperature fields are applied to an aiding flow of combined forced and natural convection in a uniformly heated vertical pipe and the predicted results are then compared with experimental results. The numerical calculations are in generally satisfactory agreement with the experimental data. The reduction of heat transfer in the combined convection regime is also found numerically. This reduction in heat transfer is thought to be caused mainly by turbulence suppression.
  • This paper reports on an opposing flow of turbulent combined forced and natural convection along a vertical flat plate heated with a uniform heat flux that was investigated experimentally. The local heat-transfer coefficients along the vertical direction were measured at high Rayleigh and Reynolds numbers. It was found that the heat-transfer rates in the combined convection region became much larger than those for both the pure forced and pure natural convection. The natural, forced, and their combined convection regions are classified in terms of the nondimensional parameter, {zeta} = (Gr{sub x}*/Nu{sub x}Re{sub x}{sup 2.7}). These results are then compared withmore » those for aiding flow.« less