1KMN S. Iqbal and 2M. A. R.
Akhanda
1 Dept. of Mechanical Engineering, IUBAT, Dhaka,
Bangladesh
kiqbal@iubat.edu
2Dept. of Mechanical and Chemical Engineering,
Islamic University of Technology, OIC, Dhaka, Bangladesh.
akhanda@iut-dhaka.edu
Abstract: Electronic machines are rapidly being developed with
the increasing benefits but, getting smaller in sizes resulting in more
thermal stress. To manage this stress, a comparative study was conducted
between a two-metal (Cu-Ag) micro heat pipe (TMMHP) and the presently
utilized single-metal (Cu) micro heat pipe (SMMHP). Thermal effects of
TMMHP of circular cross section at steady state were experimentally
investigated. Water and three low boiling point liquids – ethanol,
methanol and iso-propanol – are used as working liquids. In
consideration of the usage of the actual equipment, tests are conducted
by placing the heat pipe at three different orientations – horizontal,
vertical and at 45o inclination. To provide heat flux,
SGW36 (Ni-Cr) electric heater-coil is coiled around the evaporator
simulating the heat-generation of an actual device, and simultaneously
the condenser section is directly cooled by water in an annular space.
Internal fluid-flow is considered one dimensional. Ten calibrated K-type
thermocouples are installed at different locations – five of them are
to measure the temperatures of internal fluid and five are used to
measure the surface temperatures of the tube at different axial
locations. Temperatures are recorded by digital electronic thermometers.
Unlike in the SMMHP, it is found that the boiling and super heat effects
in the evaporator of TMMHP transform the two-phase flow into a single
phase superheated vapor flow, which increases TMMHP’s heat transfer
capability to three and half times the capacity of SMMHP. Such an
enhanced heat transfer coefficient may be possible from the improved
convection which is developed from the different heat conductivity of
metals that enables the TMMHP to reject heat at a higher rate through
its condenser than the rate it can take heat in SMMHP through its
evaporator.
Keywords: Micro heat pipe, two-metal micro heat pipe, TMMHP,
circular cross section, hydraulic diameter, inclination.