Thermal Performances of Two Different Conductivity Metal (Cu-Ag) Micro
Heat Pipe of Circular Cross Section Using Different Liquids of Low
Boiling Point
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. αβγρ