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Heat transfer and friction factors in the ribbed square convergent and divergent channels

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Abstract

Heat transfer and friction factors are reported for the measurements of turbulent flows in the convergent and divergent square channels with one-sided ribbed wall as well as two opposite in-line ribbed walls. The study covers three different hydraulic diameter ratios between inlet and exit at the test section such as Dho/Dhi = 0.75, 1.0, and 1.33 and Reynolds numbers in the range of 25,000–79,000. The channels, composing of ten isolated copper sections in the length of test section of 1 m, have the hydraulic diameter of 87.5 mm for the straight channel (Dho/Dhi = 1.0); the rib height-to-hydraulic diameter is 0.114; the rib pitch-to-height ratio equals 10. On the contrary to public opinion that the friction factor depends on the portion of the ribbed area, the total friction factor in the two opposite ribbed walls are lower than in the one-sided ribbed wall in the divergent channel of Dho/Dhi = 1.33 because the total pressure, summing positive dynamic and negative static pressures, is acted. The results show that the two opposite ribbed divergent channel of Dho/Dhi = 1.33 provides the best heat transfer enhancement and the two opposite ribbed convergent channel of Dho/Dhi = 0.75 provides the worst friction factor enhancement, and the ribbed divergent channels are generally recommended.

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Abbreviations

A:

Heat transfer area

Dh :

Hydraulic diameter

e:

Rib height

fT :

Total friction factor

h:

Channel average convective heat transfer coefficient

Nu:

Channel average Nusselt number

k:

Conductivity

p:

Rib pitch

Pi − Po :

Static pressure drop

ΔPe:

Total pressure drop

Q − Qloss :

Total net heat transfer rate

Tb,x :

Local bulk air temperature

ubm :

(ubi + ubo)/2

av:

Channel average

i:

Inlet

o:

Outlet

ss:

Smooth tube

w:

Wall

x:

Local or distance from inlet to the thermocouple junction position

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Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (Grant Number 2012001401).

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Authors and Affiliations

  1. Department of Mechanical and System Engineering, Graduate School, Gyeongsang National University, Tongyeong, 650-160, Republic of Korea

    M. S. Lee

  2. Department of Mechanical and System Engineering, Institute of Marine Industry, Gyeongsang National University, Tongyeong, 650-160, Republic of Korea

    S. W. Ahn

Authors
  1. M. S. Lee
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  2. S. W. Ahn
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Correspondence to S. W. Ahn.

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Lee, M.S., Ahn, S.W. Heat transfer and friction factors in the ribbed square convergent and divergent channels. Heat Mass Transfer 52, 1109–1116 (2016). https://doi.org/10.1007/s00231-015-1630-3

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  • DOI: https://doi.org/10.1007/s00231-015-1630-3

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