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Heat and Mass Transfer

, Volume 49, Issue 11, pp 1577–1586 | Cite as

Heat transfer performance comparison of steam and air in gas turbine cooling channels with different rib angles

  • Xiaojun ShiEmail author
  • Jianmin Gao
  • Liang Xu
  • Fajin Li
Original

Abstract

Using steam as working fluid to replace compressed air is a promising cooling technology for internal cooling passages of blades and vanes. The local heat transfer characteristics and the thermal performance of steam flow in wide aspect ratio channels (W/H = 2) with different angled ribs on two opposite walls have been experimentally investigated in this paper. The averaged Nusselt number ratios and the friction factor ratios of steam and air in four ribbed channels were also measured under the same test conditions for comparison. The Reynolds number range is 6,000–70,000. The rib angles are 90°, 60°, 45°, and 30°, respectively. The rib height to hydraulic diameter ratio is 0.047. The pitch-to-rib height ratio is 10. The results show that the Nusselt number ratios of steam are 1.19–1.32 times greater than those of air over the range of Reynolds numbers studied. For wide aspect ratio channels using steam as the coolant, the 60° angled ribs has the best heat transfer performance and is recommended for cooling design.

Keywords

Heat Transfer Steam Nusselt Number Friction Factor Heat Transfer Enhancement 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of symbols

A

Heat transfer surface area (not include the rib surface area) (m2)

cp

Specific heat at constant pressure (kJ kg−1 K−1)

D

Hydraulic diameter of test channel (m)

e

Rib height (m)

F

Heat transfer performance factor

f

Friction factor

f0

Friction factor for fully developed turbulent flow in smooth circular tubes

G

Coolant mean mass velocity in the channel (kg m−2 s−1)

H

Flow channel height (mm)

hx

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

L

Channel length (m)

\( \dot{m} \)

Coolant mass flow rate (kg s−1)

Nu

Average Nusselt number along centerline of the ribbed wall

Nux

Local Nusselt numbers

Nu0

Nusselt number for fully developed turbulent flow in smooth tubes

P

Pressure (Pa)

p

Rib pitch (mm)

ΔP

Pressure drop across the test section (Pa)

Pr

Prandtl number

Q

Heat transfer rate (W)

Qel

Input electric power to the test channel (W)

Qnc

Natural convective heat transfer rate to the surroundings (W)

Qrad

Radiation heat transfer rate to the surroundings (W)

Qdis

Heat transfer rate dissipated through two flanges of the test channel (W)

Qloss

Heat loss to the environment (W)

qconv

Convective heat flux (W m−1)

qc

Coolant side heat flux (W m−1)

qm

Mean heat transfer flux (W m−1)

Re

Reynolds number

Tb

Bulk mean temperature (K)

Tw

Local wall temperature (K)

Tin,c

Coolant temperature at the entrance of the test channel (K)

Tout,c

Coolant temperature at the outlet of the test channel (K)

Tw,x

Local ribbed wall surface temperature (K)

Tb,x

Local bulk coolant temperature at distance x (K)

V

Velocity (m s−1)

W

Flow channel width (mm)

x

Axial distance from channel entrance (mm)

Greek letters

α

Rib angle of attack (°C)

λ

Thermal conductivity (W m−1 K−1)

μ

Dynamic viscosity of coolant (Pa s)

ρ

Density (kg m−3)

Notes

Acknowledgments

The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China [51276136].

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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.State Key Laboratory for Manufacturing Systems Engineering, School of Mechanical EngineeringXi’an Jiaotong UniversityXi’anChina

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