ABSTRACT
A two-phase closed thermosyphon (TPCT) is a device for heat transmission consisting
of an evacuated tube filled with a certain amount of working fluid. Fluids with
nanoparticles (particles smaller than 100 nm) suspended in them are called nanofluids
that they have a great potential in heat transfer enhancement. In the present study the
thermal performance of conventional two phase closed thermosyphon (CT) and
modified thermosyphon (MT) containing a separator in the evaporator section was
investigated in case of using distilled water and Al2O3/Water nanofluid as working
fluids. The effect of heat input (500 W
Q
1000 W), working fluid filling ratio (40%

FR
90%), inclination angle (40°

90°), separator diameter (ds = 25mm, 32mm
and 40mm) and nanoparticles volume concentration (0.5%
Ø
2%) on thermosyphon
thermal performance was experimentally investigated. The variation in Nusselt number
was taken as an indication to the thermosyphon performance.
The results showed that an average increase of 8 % up to 19.5 % in Nusselt number can
be achieved when using a separator in the evaporator section with distilled water as a
working fluid. Also an average increase of 24.5 % up to 164.5 % in Nusselt number was
achieved when using Al2O3/Water nanofluid instead of distilled water for CT. In case of
using Al2O3/Water nanofluid in the presence of a separator in the evaporator, an
average increase of 75 % up to 197 % in Nusselt number can be achieved. The
experimental data are compared to the available data from previous studies and the
agreement is found to be fairly good. A correlation was developed for prediction of the
Nusselt number taking into consideration the effect of the varying separator diameter.
The correlation agrees with the experimental data within ± 19.5% accuracy.