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Numerical investigation of turbulent flow and heat transfer in flat tube

Effect of dimples with operational goals
  • Hadi Pourdel
  • Hamid Hassanzadeh Afrouzi
  • Omid Ali Akbari
  • Mehdi Miansari
  • Davood Toghraie
  • Ali Marzban
  • Ali Koveiti
Article
  • 17 Downloads

Abstract

In the present study, the fluid flow and heat transfer were numerically investigated in a flat tube under the constant heat flux using finite volume method and SIMPLEC algorithm. Also in this study, the range of Reynolds number is 5000–20,000, the range of dimensionless pitch (PN = PD/DL) is 1–2.33, and the range of dimensionless depth (DN = DD/DL) is 0.233–0.433. The use of second-order discretization for solving the governing equations on flow has made acceptable agreement between result between empirical and numerical results. The presence of dimples inside the channel, due to the creation of significant changes in flow physics and temperature field, considerably affects the flow and heat transfer parameters. The results indicate that by increasing Reynolds number, the convection heat transfer (Nusselt number) and the friction factor rise. Also, by decreasing the dimensionless pitch and increasing the dimensionless depth of dimple, Nusselt number and friction factor increase. The changes of Nusselt number are approximately related to the changes of dimensionless pitch and dimensionless depth of dimple, while the changes of friction factor are greatly related to the changes of dimensionless depth than the changes of dimensionless pitch. Based on the figures of average Nusselt number, using dimple in higher Reynolds numbers and constant DN ratio has a positive effect on Nusselt number increase. The main reason is the creation of stronger vortexes and better mixture of flow in higher Reynolds numbers. Hence, in average Nusselt number curves and in each constant DN ratio, the difference between graphs in Reynolds numbers of 2000 and 15,000 is higher than Reynolds numbers of 5000 and 10,000.

Keywords

Turbulent flow Flat tube Dimple Numerical simulation 

List of symbols

A

Area (m2)

C

Distance between the twisted tape to the tube diameter (m)

Cp

Heat capacity (J kg−1 K−1)

D

Tube diameter (m)

DD

Dimple spherical diameter (m)

DH = 9 mm

Large diameter flat tube (m)

DL = 3 mm

Small diameter of the flat tube (m)

DN = DD/DL

Dimensionless dimple depth

f

Friction factor

h

Convective heat transfer coefficient (W m−2 K−1)

k

Thermal conductivity (W m−1 K−1)

L

Tube length (m)

Nu

Nusselt number

P

Pressure (Pa)

PN = PD/DL

Dimensionless pitch (m)

PD

Dimple pitch (m)

Pr

Prandtl number

q

Heat flux (W m−2)

Re

Reynolds number

T

Temperature (K)

u

Inlet velocity in x directions (m s−1)

x, y, z

Cartesian coordinates

Greek symbols

µ

Dynamic viscosity (Pa s)

ρ

Density (kg m−3)

υ

Kinematics viscosity (m2 s−1)

Super- and subscripts

Ave

Average

C

Cold

F

Fluid

H

Hot

In

Inlet

W

Wall

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Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2018

Authors and Affiliations

  1. 1.Department of Mechanical Engineering, Qaemshahr BranchIslamic Azad UniversityQaemshahrIran
  2. 2.Department of Mechanical EngineeringBabol Noshirvani University of TechnologyBabolIran
  3. 3.Young Researchers and Elite Club, Khomeinishahr BranchIslamic Azad UniversityKhomeinishahrIran
  4. 4.Department of Mechanical Engineering, Khomeinishahr BranchIslamic Azad UniversityKhomeinishahrIran
  5. 5.Department of Mechanical Engineering, Aligoudarz BranchIslamic Azad UniversityAligoudarzIran

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