الفهرس 
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Abstract
Cooling temperature-sensitive devices, such as electronic components, has recently become
necessary to reduce the negative impact of excessive temperature rise on performance. Since
passive cooling methods have advantages over other active methods, such as less cost and
maintenance, and do not require an electrical source for operation, the current study focuses on
passive cooling of electronic devices by using a vapor chamber with a cylindrical cross-section
integrated with straight fin heat sink. Steam rooms have many advantages, including that they
can be installed in narrow areas without the need to use a pump or an electric fan, and they also
work to dissipate excess heat in more than one direction. It can be used in areas with high
temperatures. An insulated electric heater with a thick layer of rubber padding was used to
simulate heat dissipation from electronic devices without heat loss. The effect of two working
fluids (ethyl alcohol and water) inside the vapor chamber was investigated because of the high
amount of latent heat for each of them. The vapor chamber was charged with different charging
ratios (20%, 25%, 30%, 35%, 45%, 55%, and 65%) for each of the two working fluids and under
different heat loads (5, 8, 13, 19.2, 26, 34, and 45 watts), then it was compared to the performance
of a straight-fin heat sink without a vapor chamber and also a heat sink that is a solid copper
plate with 10mm thickness without fins under the same heat loads. The vapor chamber
performance was investigated at different inclination angles ranging from zero to 180 with a rise
of 45 degrees and under different heat loads. The results revealed that the use of the integrated
vapor chamber straight fins heat sink significantly reduces the average front wall temperature
associated with the electronic component when compared to other heat sinks. At heat flux values
of 1.4 W/cm2, the temperature of the heat source at steady state in the case of the straight-fin
heat sink and the combined heat sink with the vapor chamber filled with 23% pure water are 140
°C and 110 °C, respectively, which are Lower than the temperature with the solid copper plate
by about 27% and 43% after 46 minutes and 40 minutes, respectively. Moreover, the results
revealed that using pure water has better performance than ethyl alcohol. Whereas, the steadystate temperature of the heat source in the case of the combined heat sink with the vapor chamber
filled with 23% pure water and ethyl alcohol at the same charging ratio was 110 °C and 120 °C,
respectively. As for the effect of different charge ratios, the working fluid charge ratio has a
significant impact on the performance of the vapor chamber, and this enhancement appears more
clearly with the increase in heat load. At 34 W convection, the temperature of the heat source
using water was 108, 100, 102, 102, 117, 105, and 109 °C at charge ratios of 20%, 25%, 30%,
35%, 45%, and 55% and 65%, respectively. The results also indicate that the inclination angle
of the vapor chamber has a significant effect on the cooling performance, as indicated by the variation of heat source temperature and the system’s thermal resistance. At zero inclination
angle, the temperature of the heat source is the lowest, which indicates the best performance, and
in contrast, the highest temperature of the heat source is reached at an inclination angle of 180°,
regardless of the applied heat load or the charging ratio. other additional experiments focused on
the passive cooling of electronic devices in a vacuum space environment utilizing a vapor
chamber with a cylindrical cross-section that is integrated with a straight fin heat sink. Several
experiments were conducted to investigate the effect of two vacuum levels and compared them
to the condition of work in the atmospheric pressure. The experiments were performed with pure
water as a working fluid at a charge ratio of 25%, one system orientation 0◦, and one distinct
heat load value of 1.2 W/cm2 on overall system performance. The results reveal that using the
vapor chamber integrated with the straight fin heat sink significantly works better in the
atmospheric pressure as is obvious from the evaporator surface temperature. It presented a
notable good effect on its cooling performance as indicated by the variation of heat source
temperature at two vacuum levels. It reached to the steady state temperatures at atmospheric
pressure faster than at low vacuum level, and high vacuum level.