The HTD Laboratory has developed and
successfully tested noiseless (fanless) cooling systems for the central
processors of desktop personal computers. The systems were created on
the basis of Loop Heat Pipes. Processors Intel P4with a
clock rate of 2.8 GHz and Athlon XP 2500+with a clock
rate of 1.83 GHz were cooled. The capacity dissipated by the processors
mentioned above at the maximum load was about 70 W. The total
mass of the cooling systems, including the LHP and the radiator,
depending on the modification, was from 0.85 to 3.2 kg. The total
thermal resistance of the system was in the range from 0.5-0.8 Ê/W.
Copper-water miniature loop heat pipes
About 20 different variants of copper-water
miniature loop heat pipes (MLHPs) with a cylindrical and a flat
evaporator intended for cooling promising CPUs of portable computers
were developed and tested since 2001.
The table gives the main design characteristics of MLHPs:
Fig.3 and Fig.4 present the external view of copper-water miniature loop heat pipes with a flat and cylindrical evaporator.
A cooling system for CPU of a desktop PC was
developed and tested successfully in the laboratory conditions. The
system was created on the base of a copper-water loop heat pipe (LHP)
equipped with a flat-oval evaporator 7 mm in thickness and with lines
for vapor and liquid 4 mm in diameter.
In the passive state at an ambient temperature
of 22ºC the cooling system held a temperature of 70ºC on the
thermocontact surface of the CPU thermal simulator at a heat load of
about 90 W.
At present in the Laboratory of Heat-Transfer
Devices a new compact cooler AC-1 for desktop PCs created on the base
of a copper-water LHP is being tested. An axial-flow fan (92x92x25 mm),
which has an flow rate of 40 CFM and creates a noise at the level of 25
dBA at 2200 RPM, is used in the cooler. The cooler sizes are 100x100x75
mm, its weight is 585 gram.
The system total thermal resistance
“thermocontact surface of the CPU simulator - ambient air” decreases
from 0.3 up to 0.18ºÑ/W at a heat load increase from 50 up to 250
W. No signs of a heat-exchange crisis were observed at a maximum value
of 250 W reached during the testing.
Comparative testing of a new cooler and a
production run aluminum body cooler Intel/Sunyo Denki supplied with a
fan with a number of rotations of 2700 RPM was conducted at the Ural
computer engineering plant (Ekaterinburg).
Tcore1 is temperature of the 1st processor sensor
Tcore1 is temperature of the 2nd processor sensor
Tmb is temperature of the sensor on the motherboard
Tev is temperature on the thermal interface of the LHP evaporator.
It follows from the comparison of the indicated temperature values with the results, which were obtained earlier during the testing of a new cooler with a CPU thermal simulator, that the maximum power dissipated by a real processor makes up a value of about 130 W. Testing with a real processor demonstrated that the new cooler reduced the temperature of the first CPU core by 5,7ºÑ and the temperature of the motherboard – by 3,9ºÑ in comparison with a run production cooler. The temperature of the second processor core remained approximately at the same level at this.
The comparative testing of the cooler AC – 1a
and a cooler “Cooler Master” (Taiwan) supplied with aluminum finning
with the area of 3000 cm2, three heat pipes 6 mm in diameter
each and 92 mm fan PL92S12M-5 was conducted. The sizes of “Cooler
Master” with a casing are 145x125x100 mm, its weight is 804 g. The
coolers’ testing was being conducted with a CPU heat simulator and with
a fan “Cooler Master” at 1800 and 3200 RPM at an ambient temperature of
Within the range of heat load from 100 to 250 W
at 3200 RPM the total thermal resistance of “Cooler Master” was
changing from 0, 20 K/W to 0,19 K/W. For AC – 1a these values were
making up 0,19 K/W and 0,15 K/W accordingly.
External view of the cooler AC-1a
A new cooler AC-3/2 has been developed equipped with an aluminum heat sink with finning area of 0.24 m2. The cooler sizes are 150x120x85 mm, its weight is 766 gram. As coolers AC-1 and AC-2 it is created on the base of a copper-water LHP with flat-oval evaporator 7mm in thick.
The comparative tests have been conducted of the AC-3/2 with the cooler «Ice Hammer 4400A» that has four 8mm copper-water heat pipes. The sizes of IÍ 4400À are 150x126x75 mm, its weight is 835 gram, aluminum finning area is about 0.9 m2. The coolers were tested with a CPU thermal simulator at an ambient temperature of 22ºÑ with the sizes of 35x35 mm and 120 mm fan “Ice Hammer” at 1900 RPM. The ambient temperature was 20ºC.
Tests results are presented below on graph of
the heat load dependence on the thermocontact surface temperature the
CPU thermal simulator.
A flexible loop heat pipe with an effective length of 2 m, supplied with a cylindrical evaporator with an active zone 60 mm in length, vapor and liquid lines 2 mm in diameter was developed. This LHP can change its length and bend at an angle of 180. The maximum capacity of the device is 100 W at a thermal resistance of 0.19 C/W.
Miniature loop heat pipes with a complicated configuration of a heat-transfer zone were developed to remove heat from low-sized high-heat objects. The devices can operate at different orientation in the range of heat loads from 5 to 120 W. The minimum thermal resistance equal to 0.18 °C/W is achieved at heat loads from 60 to 120 W.