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Design of a two-phase loop thermosyphon for telecommunications system (II)

Analysis and simulation


A computer simulation is performed for a two-phase loop thermosyphon for the B-ISDN telecommunications. The aim of this code development is to provide capabilities to predict the affects of many variables on the performance of the proposed TLT system using different empirical correlations obtained from the literature for the evaporation and condensation, and the shape factors available. In the present study, the simulation code is based on the sectorial thermal resistance network built on the flow regimes of the two-phase flows involved. The nodal resistances are solved by the typical Gauss-Seidal iteration method. The code can predict whether the proposed design is possible based on the flooding limit calculation of the system and its results are compared with the experimental results.

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A :

Area (m2)

A f :

Flow area occupied by liquid phase (m2)

A g :

Flow area occupied by vapour phase (m2)

a :

Evaporator thickness (m)

A x :

Cross sectional area (m2)

b :

Evaporator width (m)

C :


C pt :

Specific heat of saturated liquid (J/kgK)

C SF :

A constant on Rohsenow’s pool boiling correlation

D :

Outer diameter of tube (m), parameter

d :

linner diameter (m)

D h :

Hydraulic diameter (m)

F :

Frictional parameter

f :

Friction factor

G :

Mass flux (kg/m2s)

g :

Acceleration due to gravity (m2/s)

H :

Specific enthalpy (J/kg)

h :

Heat transfer coefficient (W/m2 K), evaporator depth (m)

H fluid :

Specific enthalpy of fluid (J/kg)

H f :

Specific enthalpy of saturated liquid (J/kg)

H fg :

Latent heat of evaporation (J/kg)

k :

Thermal conductivity (W/m K)

L :

Length (m)

Nu :

Nusselt number

ΔP a :

Acceleration pressure drop

ΔP f :

Frictional pressure drop

ΔP h :

Hydraulic pressure drop

P :

Pressure (Pa)

(dP/dy) p :

Pressure gradient

Pr :

Prandtl number

Q :

Heat transfer rate (W)

q :

Heat flux (W/cm2)

R :

Resistance (K/W)

r :

Radius (m)

Ra :

Rayleigh number

Re :

Reynolds number

S :

Shape factor, defined as eqn. (2)

T, t :

Temperature (°C)

Δt :

Temperature difference between the heater and air (°C)


Two-phase closed thermosyphon


Two-phase loop thermosyphon

U T :

Overall heat transfer coefficient (W/m2 K)


Liquid or vapor flow velocity

W :

Mass rate of flow (kg/s)

WF :

Working fluid

W f :

Mass rate of flow of liquid phase (kg/s)

W g :

Mass rate of flow of gas phase (kg/s)

We :

Weber number

X :

Lockhart-Martinelli parameter

x :

Vapor quality

y :


a :

Acceleration in pressure gradient and pressure drop

air :

Surrounding air

b :

Bulk, boiling, bottom, bended section in Appendix E

cold :

Cold section

c, cond :

Condensation, condenser section

conv :


cr :


ct :

Condenser tube

e :


ev :

Evaporation, evaporator

e 3 :

Effective in dry-out region

ea :

Average evaporator

eb :

Average bulk

esb :

Effective subcooling boiling

ew :

Average evaporator wall

f :

Fluid, f is frictional for pressure drop term

f, tp :

Two-phase frictional pressure drop

do :

Dry-out region

fil :


g :

Gas, vapor state

h :

Heater, hot for Rescb, hydraulic for pressure drop

hol :

Heating section

i :


l :

Liquid, unit length

loop :

Thermosyphon loop

lp :


max :


mis :


o :


pl :

Evaporator plate

s, sat :


scb :

Subcooled boiling

T :


t :


tp :


tr :

Transporting section

v :


w :



Void fraction (α=A g/AT)


Inclination angle (degree)


Thickness (m)




Bended angle


Viscosity (kg/ms)


Density (kg/m3)


Suface tension (N/m)




Defined in Appendix E


Loss coefficient


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Kim, W.T., Kim, K.S. & Lee, Y. Design of a two-phase loop thermosyphon for telecommunications system (II). KSME International Journal 12, 942–955 (1998).

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Key Words

  • Thermosyphon
  • Sectorial Thermal Resistance
  • Simulation
  • Two-Phase Flow
  • Shape Factor