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Heat and Mass Transfer

, Volume 50, Issue 6, pp 877–885 | Cite as

Experimental and numerical study on unsteady natural convection heat transfer in helically coiled tube heat exchangers

  • E. NeshatEmail author
  • S. Hossainpour
  • F. Bahiraee
Original

Abstract

Both of experimental and numerical investigations were performed to understand unsteady natural convection from outer surface of helical coils. Four helical coils with two different curvature ratios were used. Each coil was mounted in the shell both vertically and horizontally. The cold water was entered the coil and the hot water in the shell was cooling by unsteady natural convection. A CFD code was developed to simulate natural convection heat transfer. Equations of tube and shell are solved simultaneously. Statistical analyses have been done on data points of temperature and natural convection Nusselt number. It was revealed that shell-side fluid temperature and the Nusselt number of the outer surface of coils are functions of in-tube fluid mass flow rate, specific heat of fluids and geometrical parameters including length, inner diameter of the tube and the volume of the shell, and time.

Keywords

Heat Transfer Coefficient Heat Exchanger Nusselt Number Natural Convection Rayleigh Number 
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

Surface area of helical coil (m2)

Cp

Specific heat (kJ kg−1 K−1)

D

Helix coil diameter (m)

d

Tube diameter (m)

De

Dean number (Re d i 0.5 D−0.5)

h

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

k

Thermal conductivity (W m−1 K−1)

L

Axial length of the pipe (m)

\( {\dot{\text{m}}} \)

Mass flow rate (kg s−1)

N

Number of helical coil turns

NDN

A non dimensional number

Nu

Nusselt number (hL k−1)

P

Coil pitch (m)

Pr

Prandtl number (να−1)

q

Heat transfer rate per area unit (W m−2)

Re

Reynolds number \( (4{\dot{\text{m}\text{d}}}^{ - 1} \upmu ) \)

Ra

Rayleigh number [gβL3 ν−1α−1(T − Tav)]

t

Time (s)

T

Temperature (K)

T0

Initial temperature of shell fluid (K)

Tav

Average temperature of in-tube fluid (0.5[(Tt)in + (Tt)out])

\( {\text{T}}^{ *} \)

Non dimensional temperature (T − T0)/(Tin − Tout)

U

Overall heat transfer coefficient

V

Volume of shell (m3)

Greek symbols

α

Thermal diffusivity (m2 s−1)

β

Coefficient for thermal expansion (K−1)

μ

Viscosity (kg m−1 s−1)

υ

Kinematic viscosity (m2 s−1)

ρ

Density (kg m−3)

Subscripts

av

Average

c

Coil

exp

Experimental value

cr

Critical

H

Horizontal

in

Inlet

i

Inside of helical coil

L

Characteristic length

num

Numerical value

o

Outside of helical coil

out

Outlet

s

Shell

T

Tube

V

Vertical

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Department of Mechanical EngineeringSahand University of TechnologyTabrizIran

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