Spelling suggestions: "subject:"heat spreading"" "subject:"meat spreading""
1 |
THERMAL HYDRAULIC PERFORMANCE OF AN OSCILLATING HEAT PIPE FOR AXIAL HEAT TRANSFER AND AS A HEAT SPREADERAbdelnabi, Mohamed January 2022 (has links)
In this thesis, a stacked double-layer flat plate oscillating heat pipe charged with degassed DI water was designed, fabricated and characterized under different operating conditions (orientation, system or cooling water temperature and heat load). The oscillating heat pipe was designed to dissipate 500 W within a footprint of 170 x 100 mm2. The oscillating heat pipe had a total of 46 channels (23 channels per layer) with a nominal diameter of 2 mm. Tests were performed to characterize the performance of the oscillating heat pipe for (i) axial heat transfer and (ii) as a heat spreader. The stacked oscillating heat pipe showed a distinctive feature in that it overcame the absence of the gravity effect when operated in a horizontal orientation. The thermal performance was found to be greatly dependent on the operational parameters. The oscillating heat pipe was able to dissipate a heat load greater than 500 W without any indication of dry-out. An increase in the cooling water temperature enhanced the performance and was accompanied with an increase in the on/off oscillation ratio. The lowest thermal resistance of 0.06 K/W was achieved at 500 W with a 50℃ cooling water temperature, with a corresponding evaporator heat transfer coefficient of 0.78 W/cm2K. The oscillating heat pipe improved the heat spreading capability when locally heated at the middle and end locations. The thermal performance was enhanced by 27 percent and 21 percent, respectively, when compared to a plain heat spreader. / Thesis / Master of Applied Science (MASc)
|
2 |
Thermal analysis of high power led arraysHa, Min Seok 17 November 2009 (has links)
LEDs are being developed as the next generation lighting source due to their high
efficiency and long life time, with a potential to save $15 billion per year in energy cost
by 2020. State of the art LEDs are capable of emitting light at ~115 lm/W and have
lifetime over 50,000 hours. It has already surpassed the efficiency of incandescent light
sources, and is even comparable to that of fluorescent lamps. Since the total luminous
flux generated by a single LED is considerably lower than other light sources, to be
competitive the total light output must be increased with higher forward currents and
packages of multiple LEDs. However, both of these solutions would increase the
junction temperature, which degrades the performance of the LED--as the operating
temperature goes up, the light intensity decreases, the lifetime is reduced, and the light
color changes. The word "junction" refers to the p-n junction within the LED-chips.
Critical to the temperature rise in high powered LED sources is the very large heat flux at
the die level (100-500 W/cm2) which must be addressed in order to lower the operating
temperature in the die. It is possible to address the spreading requirements of high
powered LED die through the use of power electronic substrates for efficient heat
dissipation, especially when the die are directly mounted to the power substrate in a chipon-
board (COB) architecture. COB is a very attractive technology for packaging power
LEDs which can lead improved price competiveness, package integration and thermal
performance.
In our work high power LED-chips (>1W/die) implementing COB architectures
were designed and studied. Substrates for these packaging configurations include two
types of power electronic substrates; insulated-metal-substrates (IMS) and direct-bonded-copper (DBC). To lower the operating temperature both the thermal impedance of the
dielectric layer and the heat spreading in the copper circuit layers must be studied. In the
analysis of our architectures, several lead free solders and thermal interface materials
were considered. We start with the analysis of single-chip LED package and extend the
result to the multi-chip arrays. The thermal resistance of the system is only a function of
geometry and thermal conductivity if temperature-independent properties are used. Thus
through finite element analysis (ANSYS) the effect of geometry and thermal conductivity
on the thermal resistance was investigated. The drawback of finite element analysis is
that many simulations must be conducted whenever the geometry or the thermal
conductivity is changed. To bypass same of the computational load, a thermal resistance
network was developed. We developed analytical expressions of the thermal resistance,
especially focusing on the heat spreading effect at the substrate level. Finally, multi-chip
LED arrays were analyzed through finite element analysis and an analytical analysis;
where die-spacing is another important factor to determine the junction temperature.
With this thermal analysis, critical design considerations were investigated in order to
minimize device temperatures and thereby maximizing light output while also
maximizing device reliability.
|
Page generated in 0.0936 seconds