Mahmoud A. El-Kady* , Hesham M. Mostafa **
and Alaa-Eldin. M. Ibrahim ***
* Faculty of Engineering, Al Azhar University, Cairo, Egypt.
** Higher Technological Institute, Tenth of Ramadan City, Egypt.
*** Research student
An experimental study of the performance of a thermosyphon heat pipe was conducted. An
apparatus equipped with the required measuring instruments was designed and constructed to
investigate the effects of applied heat flux, wall temperature in the evaporator section, filling
ratio and the geometry for the outer surface of the condenser section on the performance of
thermosyphon. Pure water was used as working fluid inside thermosyphon throughout this
work. Three samples having different geometries for the outer surface of the condenser
section was studied. These samples are knurled sample, longitudinal grooved sample and
plain sample. The evaporator section was heated by using dry saturated steam to adjust and
control the evaporator wall temperature. The condenser section enclosed a double pipe heat
exchanger. The experimental measurements of temperature, pressure and volume flow rate are
collected and manipulated to calculate the convection heat transfer coefficient for water flow
in the annulus of the double pipe heat exchanger. Also, boiling, condensation and overall heat
transfer coefficient for thermosyphon heat pip are determined.
The obtained experimental results show that, the average values for the wall temperatures of
evaporator section and condenser section were reduced for the knurled sample and
longitudinal grooved sample than the plain sample, It is noticed that, decreasing filling ratio
from 1 to 0.5 cause a decrease in the wall temperature for the evaporator section and an
increases in the wall temperature for the condenser section, It is found that the condenser wall
temperature was reduced for both knurled and longitudinal grooved samples than plain
sample. Also, the temperature difference between the evaporator and condenser walls was
reduced for the same heat flux. This leads to an increase in the thermal performance of
thermosyphon when using knurled and longitudinal grooved samples than plain sample.
Boiling curves for knurled sample and longitudinal grooved sample gave higher heat flux than
plain sample. There is a certain decrease in the overall thermal resistance of thermosyphon
when using knurled sample and longitudinal grooved sample compared with plain sample.
The overall thermal resistance decreases with increasing heat flux, and take lower values for
knurled sample and longitudinal grooved sample compared with plain sample.
For water flow in the annulus of the double pipe heat exchanger which enclose the condenser
section Nusselt number increases with increasing Reynolds number. Also, Nusselt number
takes higher values for knurled sample than longitudinal grooved sample and plain sample
Also , The heat transfer coefficient by boiling and condensation increased in case off grooved
samed than smooth sample.