Convective heat transfer in helical coils for constant-property and variable-property flows with high Reynolds numbers

Abstract

Forced convection heat transfer of single-phase water in helical coils was experimentally studied. The testing section was constructed from a stainless steel round tube with an inner diameter of 10 mm, coil diameter of 300 mm, and pitch of 50 mm. The experiments were conducted over a wide Reynolds number range of 40000 to 500000. Both constant-property flows at normal pressure and variable-property flows at supercritical pressure were investigated. The contribution of secondary flow in the helical coil to heat transfer was gradually suppressed with increasing Reynolds number. Hence, heat transfer coefficients of the helical tube were close to those of the straight tube under the same flow conditions when the Reynolds number is large enough. Based on the experimental data, heat transfer correlations for both incompressible flows and supercritical fluid flows through helical coils were proposed.

Key words： convective heat transfer; helical coils; high Reynolds number; supercritical pressure; variable property

Acknowledgements

This work was supported by the National Natural Science Foundation of China for Creative Research Groups (Grant No. 50821064).

Notation

cp	isobaric specific heat capacity/(J·kg-1·K-1)
D	coil diameter of the test section/m
d	inner diameter of the test section/m
G	mass velocity/(kg·m-2·s-1)
H	specific enthalpy/(J·kg-1)
h	heat transfer coefficient/(W·m-2·K-1)
Nu	Nusselt number
p	pressure/Pa
Pr	Prandtl number
q	heat flux/(W·m-2)
Re	Reynolds number
T	temperature/K
Greek symbols
λ	thermal conductivity/(W·m-1·K-1)
μ	dynamic viscosity/(N·s·m-2)
ρ	density/(kg·m-3)
Subscripts
B	bulk condition
cal	calculation
exp	experiment
pc	pseudo critical point
W	wall condition

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