Date of Award

6-2024

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical and Aerospace Engineering

First Advisor

Prof. Salah Al Omari

Second Advisor

Emad Elnajjar

Abstract

Electronics are integral to modern life, present in everything from household appliances to advanced computers. The performance and reliability of these devices are closely tied to their operating temperatures. High-power operations can lead to significant heating, necessitating effective thermal management to enhance functionality and prevent failure. This requirement drives the demand for efficient heat sinks, which dissipate the heat generated by these devices. Phase change material (PCM)-based heat sinks have become a popular passive cooling solution, increasingly replacing traditional heat sinks.

This research investigates finned PCM-based heat sinks using numerical simulations validated by existing literature and experimental data. Gallium is chosen as the PCM due to its favorable properties: low melting point, high thermal conductivity, compatibility with heat sink materials, and non-toxicity. The study focuses on heat sinks with fins to boost heat dissipation, targeting intermediate to high heat flux levels around 10 W/cm². Innovative heat sink designs with fins detached from the hot sink base are explored, differing from conventional attached fin designs. The study examines the benefits and drawbacks of both approaches, proposing new designs that combine the advantages of each. These novel designs enhance latent heat storage and internal buoyancy-driven circulations within the molten PCM, improving natural convection cooling beyond traditional designs' capabilities.

The research begins with 2D simulations, assuming an infinite sink cavity to negate end-wall effects. An optimal design is identified, combining beneficial features of both detached and attached fin approaches, including an increased outer fin surface area for heat dissipation and enhanced latent heat storage through a horizontally expanded sink cavity accommodating more gallium. The optimized design maintains cooler peak temperatures, averaging 12°C lower than baseline cases. The additional gallium prolongs the time required for complete melting by about 14%. This design, with increased outer fin height and surface area exposed to the environment, shows a complete melting time approximately 25 seconds longer than other designs, indicating superior performance.

To provide a comprehensive understanding, the study extends to 3D simulations to consider end-wall effects, offering a more realistic view of heat sink operation. The study compares 2D and 3D simulation results, evaluating the effectiveness of 2D simulations in assessing sink performance under the studied conditions. Initially, both 2D and 3D simulations show similar temperature levels. However, after 120 seconds, differences emerge as molten gallium in the 3D case moves towards the Z-direction, highlighting the end-wall's role and enhancing mixing in the liquid PCM. This results in more significant temperature fluctuations in the 3D case, with its average temperature being about 5°C lower than the 2D case between 120 and 200 seconds due to increased mixing. Despite the computational demands of 3D simulations, the 2D analysis still provides valuable insights into the heat sink's performance and its ability to cool high-power electronics. It effectively demonstrates the impact of various design modifications explored in this research.

Arabic Abstract


ﻣﺸﺘﺖ ﺣﺮاري ﻣﻊ زﻋﺎﻧﻒ وﻣﺎدة ﻣﺘﻐﯿﺮة اﻟﺤﺎﻟﺔ ﻟﺘﺒﺮﯾﺪ اﻷﺟﮭﺰة اﻹﻟﻜﺘﺮوﻧﯿﺔ ذات اﻟﻘﺪرة اﻟﻌﺎﻟﯿﺔ

اﻹﻟﻜﺘﺮوﻧﯿﺎت ﺟﺰء ﻻ ﯾﺘﺠﺰأ ﻣﻦ اﻟﺤﯿﺎة اﻟﺤﺪﯾﺜﺔ، ﺣﯿﺚ ﺗﺘﻮاﺟﺪ ﻓﻲ ﻛﻞ ﺷﻲء ﻣﻦ اﻷﺟﮭﺰة اﻟﻤﻨﺰﻟﯿﺔ إﻟﻰ اﻟﺤﻮاﺳﯿﺐ اﻟﻤﺘﻘﺪﻣﺔ. أداء وﻣﻮﺛﻮﻗﯿﺔ ھﺬه اﻷﺟﮭﺰة ﻣﺮﺗﺒﻄﺎن ﺑﺸﻜﻞ وﺛﯿﻖ ﺑﺪرﺟﺎت ﺣﺮارﺗﮭﺎ اﻟﺘﺸﻐﯿﻠﯿﺔ. اﻟﻌﻤﻠﯿﺎت ذات اﻟﻘﺪرة اﻟﻌﺎﻟﯿﺔ ﯾﻤﻜﻦ أن ﺗﺆدي إﻟﻰ ﺗﺴﺨﯿﻦ ﻛﺒﯿﺮ، ﻣﻤﺎ ﯾﺘﻄﻠﺐ إدارة ﺣﺮار ﯾﺔ ﻓﻌﺎﻟﺔ ﻟﺘﻌﺰﯾﺰ اﻷداء وﻣﻨﻊ اﻟﻔﺸﻞ. ھﺬا اﻻﺣﺘﯿﺎج ﯾﺰﯾﺪ ﻣﻦ اﻟﻄﻠﺐ ﻋﻠﻰ اﻟﻤﺒﺮدات اﻟﺤﺮارﯾﺔ اﻟﻔﻌﺎﻟﺔ، اﻟﺘﻲ ﺗﺸﺘﺖ اﻟﺤﺮارة اﻟﻤﺘﻮﻟﺪة ﻋﻦ ھﺬه اﻷﺟﮭﺰة. وﻗﺪ أﺻﺒﺤﺖ اﻟﻤﺒﺮدات اﻟﺤﺮارﯾﺔ اﻟﻤﻌﺘﻤﺪة ﻋﻠﻰ ﻣﻮاد ﻣﺘﻐﯿﺮ ة اﻟﺤﺎﻟﺔ (PCM) ﺣﻼً ﺷﺎﺋﻌًﺎ ﻟﻠﺘﺒﺮﯾﺪ اﻟﺴﻠﺒﻲ، ﺣﯿﺚ ﺗﺤﻞ ﺗﺪرﯾﺠﯿًﺎ ﻣﺤﻞ اﻟﻤﺒﺮ دات اﻟﺘﻘﻠﯿﺪﯾﺔ.

ﺗﺒﺤﺚ ھﺬه اﻟﺪراﺳﺔ ﻓﻲ اﻟﻤﺒﺮدات اﻟﺤﺮارﯾﺔ اﻟﻤﻌﺘﻤﺪة ﻋﻠﻰ ﻣﻮاد ﻣﺘﻐﯿﺮ ة اﻟﺤﺎﻟﺔ اﻟﻤﺰودة ﺑﺰﻋﻨﻔﺔ ﺑﺎﺳﺘﺨﺪام اﻟﻤﺤﺎﻛﺎة اﻟﻌﺪدﯾﺔ اﻟﺘﻲ ﺗﻢ اﻟﺘﺤﻘﻖ ﻣﻨﮭﺎ ﺑﻮاﺳﻄﺔ اﻷدﺑﯿﺎت اﻟﺤﺎﻟﯿﺔ واﻟﺒﯿﺎﻧﺎت اﻟﺘﺠﺮﯾﺒﯿﺔ. ﺗﻢ اﺧﺘﯿﺎر اﻟﻐﺎﻟﯿﻮم ﻛﻤﺎدة ﻣﺘﻐﯿﺮ ة اﻟﺤﺎﻟﺔ ﺑﺴﺒﺐ ﺧﺼﺎﺋﺼﮫ اﻟﻤﻮاﺗﯿﺔ: ﻧﻘﻄﺔ اﻧﺼﮭﺎر ﻣﻨﺨﻔﻀﺔ، ﻣﻮﺻﻠﯿﺔ ﺣﺮارﯾﺔ ﻋﺎﻟﯿﺔ، ﺗﻮاﻓﻖ ﻣﻊ ﻣﻮاد اﻟﻤﺒﺮد اﻟﺤﺮاري، وﻏﯿﺮ ﺳﺎم. ﺗﺮﻛﺰ اﻟﺪراﺳﺔ ﻋﻠﻰ اﻟﻤﺒﺮدات اﻟﺤﺮارﯾﺔ اﻟﻤﺰودة ﺑﺰﻋﻨﻔﺔ ﻟﺘﻌﺰﯾﺰ اﻟﺘﺒﺪﯾﺪ اﻟﺤﺮاري، ﻣﺴﺘﮭﺪﻓﺔ ﻣﺴﺘﻮﯾﺎت ﺗﺪﻓﻖ ﺣﺮاري ﻣﺘﻮﺳﻄﺔ إﻟﻰ ﻋﺎﻟﯿﺔ ﺣﻮاﻟﻲ 10واط/ﺳﻢ². ﯾﺘﻢ اﺳﺘﻜﺸﺎف ﺗﺼﺎﻣﯿﻢ ﻣﺒﺘﻜﺮة ﻟﻠﻤﺒﺮدات اﻟﺤﺮارﯾﺔ ذات اﻟﺰﻋﺎﻧﻒ اﻟﻤﻨﻔﺼﻠﺔ ﻋﻦ ﻗﺎﻋﺪة اﻟﻤﺒﺮد اﻟﺴﺎﺧﻦ، وﺗﺨﺘﻠﻒ ﻋﻦ اﻟﺘﺼﺎﻣﯿﻢ اﻟﺘﻘﻠﯿﺪﯾﺔ ذات اﻟﺰﻋﺎﻧﻒ اﻟﻤﻠﺘﺼﻘﺔ. ﺗﻔﺤﺺ اﻟﺪراﺳﺔ ﻓﻮاﺋﺪ وﻣﺴﺎوئ ﻛﻼ اﻟﻨﮭﺠﯿﻦ، وﺗﻘﺘﺮح ﺗﺼﺎﻣﯿﻢ ﺟﺪﯾﺪة ﺗﺠﻤﻊ ﺑﯿﻦ ﻣﺰاﯾﺎ ﻛﻞ ﻣﻨﮭﻤﺎ. ﺗﻌﺰز ھﺬه اﻟﺘﺼﺎﻣﯿﻢ اﻟﺠﺪﯾﺪة ﺗﺨﺰﯾﻦ اﻟﺤﺮارة اﻟﻜﺎﻣﻨﺔ واﻟﺪوران اﻟﺪاﺧﻠﻲ اﻟﻤﺪﻓﻮع ﺑﺎﻟﻄﻔﻮ داﺧﻞ اﻟﻤﻮاد ﻣﺘﻐﯿﺮة ا ﻟﺤﺎﻟﺔ اﻟﻤﻨﺼﮭﺮة ، ﻣﻤﺎ ﯾﺤﺴﻦ اﻟﺘﺒﺮﯾﺪ ﺑﺎﻟﺤﻤﻞ اﻟﻄﺒﯿﻌﻲ ﺑﻤﺎ ﯾﺘﺠﺎوز ﻗﺪرات اﻟﺘﺼﺎﻣﯿﻢ اﻟﺘﻘﻠﯿﺪﯾﺔ.

ﺗﺒﺪأ اﻟﺪراﺳﺔ ﺑﻤﺤﺎﻛﺎة ﺛﻨﺎﺋﯿﺔ اﻷﺑﻌﺎد، ﺑﺎﻓﺘﺮاض ﺣﺠﺮة ﻣﺒﺮد ﻻﻧﮭﺎﺋﯿﺔ ﻹﻟﻐﺎء ﺗﺄﺛﯿﺮات اﻟﺠﺪران اﻟﻨﮭﺎﺋﯿﺔ. ﯾﺘﻢ ﺗﺤﺪﯾﺪ ﺗﺼﻤﯿﻢ ﻣﺜﺎﻟﻲ ﯾﺠﻤﻊ ﺑﯿﻦ اﻟﻤﯿﺰات اﻟﻤﻔﯿﺪة ﻟﻜﻞ ﻣﻦ ﻧﮭﺠﻲ اﻟﺰﻋﺎﻧﻒ اﻟﻤﻨﻔﺼﻠﺔ واﻟﻤﻠﺘﺼﻘﺔ، ﺑﻤﺎ ﻓﻲ ذﻟﻚ زﯾﺎدة ﻣﺴﺎﺣﺔ ﺳﻄﺢ اﻟﺰﻋﻨﻔﺔ اﻟﺨﺎرﺟﯿﺔ ﻟﺘﺒﺪﯾﺪ اﻟﺤﺮارة وﺗﻌﺰﯾﺰ ﺗﺨﺰﯾﻦ اﻟﺤﺮارة اﻟﻜﺎﻣﻨﺔ ﻣﻦ ﺧﻼل ﺗﻮﺳﯿﻊ ﺣﺠﺮة اﻟﻤﺒﺮد أﻓﻘﯿﺎً ﻻﺳﺘﯿﻌﺎب اﻟﻤﺰﯾﺪ ﻣﻦ اﻟﻐﺎﻟﯿﻮم. ﯾﺤﺎﻓﻆ اﻟﺘﺼﻤﯿﻢ اﻷﻣﺜﻞ ﻋﻠﻰ درﺟﺎت ﺣﺮارة ذروة أﻛﺜﺮ ﺑﺮودة، ﺑﻤﺘﻮﺳﻂ 12درﺟﺔ ﻣﺌﻮﯾﺔ أﻗﻞ ﻣﻦ اﻟﺤﺎﻻت اﻷﺳﺎﺳﯿﺔ. ﯾﺰﯾﺪ اﻟﻐﺎﻟﯿﻮم اﻹﺿﺎﻓﻲ ﻣﻦ اﻟﻮﻗﺖ اﻟﻤﻄﻠﻮب ﻟﻠﺬوﺑﺎن اﻟﻜﺎﻣﻞ ﺑﺤﻮاﻟﻲ 14%. ﯾﻈﮭﺮ ھﺬا اﻟﺘﺼﻤﯿﻢ، ﺑﺎرﺗﻔﺎع ﺳﻄﺢ اﻟﺰﻋﻨﻔﺔ اﻟﺨﺎرﺟﯿﺔ وزﯾﺎدة اﻟﻤﺴﺎﺣﺔ اﻟﻤﻌﺮﺿﺔ ﻟﻠﺒﯿﺌﺔ، وﻗﺖ ذوﺑﺎن ﻛﺎﻣﻞ أطﻮل ﺑﺤﻮاﻟﻲ 25 ﺛﺎﻧﯿﺔ ﻣﻘﺎرﻧﺔً ﺑﺎﻟﺘﺼﺎﻣﯿﻢ اﻷﺧﺮى، ﻣﻤﺎ ﯾﺸﯿﺮ إﻟﻰ أداء ﻣﺘﻔﻮق.

ﻟﺘﻮﻓﯿﺮ ﻓﮭﻢ ﺷﺎﻣﻞ، ﺗﻤﺘﺪ اﻟﺪراﺳﺔ إﻟﻰ ﻣﺤﺎﻛﺎة ﺛﻼﺛﯿﺔ اﻷﺑﻌﺎد ﻟﻠﻨﻈﺮ ﻓﻲ ﺗﺄﺛﯿﺮات اﻟﺠﺪران اﻟﻨﮭﺎﺋﯿﺔ، ﻣﻤﺎ ﯾﻮﻓﺮ ﻧﻈﺮة أﻛﺜﺮ واﻗﻌﯿﺔ ﻋﻠﻰ ﺗﺸﻐﯿﻞ اﻟﻤﺒﺮد اﻟﺤﺮاري. ﺗﻘﺎرن اﻟﺪراﺳﺔ ﺑﯿﻦ ﻧﺘﺎﺋﺞ اﻟﻤﺤﺎﻛﺎة اﻟﺜﻨﺎﺋﯿﺔ واﻟﺜﻼﺛﯿﺔ اﻷﺑﻌﺎد، وﺗﻘﯿﻢ ﻓﻌﺎﻟﯿﺔ اﻟﻤﺤﺎﻛﺎة اﻟﺜﻨﺎﺋﯿﺔ اﻷﺑﻌﺎد ﻓﻲ ﺗﻘﯿﯿﻢ أداء اﻟﻤﺒﺮد ﺗﺤﺖ اﻟﻈﺮوف اﻟﻤﺪروﺳﺔ. ﻓﻲ اﻟﺒﺪاﯾﺔ، ﺗﻈﮭﺮ اﻟﻤﺤﺎﻛﺎة اﻟﺜﻨﺎﺋﯿﺔ واﻟﺜﻼﺛﯿﺔ اﻷﺑﻌﺎد ﻣﺴﺘﻮﯾﺎت درﺟﺔ ﺣﺮارة ﻣﺘﺸﺎﺑﮭﺔ. وﻣﻊ ذﻟﻚ، ﺑﻌﺪ 120 ﺛﺎﻧﯿﺔ، ﺗﻈﮭﺮ اﺧﺘﻼﻓﺎت ﺣﯿﺚ ﯾﺘﺤﺮك اﻟﻐﺎﻟﯿﻮم اﻟﻤﻨﺼﮭﺮ ﻓﻲ اﻟﺤﺎﻟﺔ اﻟﺜﻼﺛﯿﺔ اﻷﺑﻌﺎد ﻧﺤﻮ اﻻﺗﺠﺎه Z ، ﻣﻤﺎ ﯾﺒﺮز دور اﻟﺠﺪار اﻟﻨﮭﺎﺋﻲ وﯾﻌﺰز اﻟﺨﻠﻂ ﻓﻲ اﻟﻤﻮاد ﻣﺘﻐﯿﺮ ة اﻟﺤﺎﻟﺔ اﻟﺴﺎﺋﻠﺔ. ﯾﺆدي ھﺬا إﻟﻰ ﺗﻘﻠﺒﺎت ﺣﺮارﯾﺔ أﻛﺜﺮ وﺿﻮﺣًﺎ ﻓﻲ اﻟﺤﺎﻟﺔ اﻟﺜﻼﺛﯿﺔ اﻷﺑﻌﺎد، ﺣﯿﺚ ﺗﻜﻮن درﺟﺔ ﺣﺮارﺗﮭﺎ اﻟﻤﺘﻮﺳﻄﺔ ﺣﻮاﻟﻲ 5درﺟﺎت ﻣﺌﻮﯾﺔ أﻗﻞ ﻣﻦ اﻟﺤﺎﻟﺔ اﻟﺜﻨﺎﺋﯿﺔ اﻷﺑﻌﺎد ﺑﯿﻦ 120و 200 ﺛﺎﻧﯿﺔ ﺑﺴﺒﺐ زﯾﺎدة اﻟﺨﻠﻂ. ﻋﻠﻰ اﻟﺮﻏﻢ ﻣﻦ اﻟﻤﻄﺎﻟﺐ اﻟﺤﺴﺎﺑﯿﺔ ﻟﻠﻤﺤﺎﻛﺎة اﻟﺜﻼﺛﯿﺔ اﻷﺑﻌﺎد، إﻻ أن اﻟﺘﺤ ﻠﯿﻞ اﻟﺜﻨﺎﺋﻲ اﻷﺑﻌﺎد ﯾﻮﻓﺮ رؤى ﻗﯿﻤﺔ ﺣﻮل أداء اﻟﻤﺒﺮد اﻟﺤﺮاري وﻗﺪرﺗﮫ ﻋﻠﻰ ﺗﺒﺮﯾﺪ اﻹﻟﻜﺘﺮوﻧﯿﺎت ذات اﻟﻘﺪرة اﻟﻌﺎﻟﯿﺔ. ﯾﻮﺿﺢ ﺑﺸﻜﻞ ﻓﻌﺎل ﺗﺄﺛﯿﺮ اﻟﺘﻌﺪﯾﻼت اﻟﺘﺼﻤﯿﻤﯿﺔ اﻟﻤﺨﺘﻠﻔﺔ اﻟﻤﺴﺘﻜﺸﻔﺔ ﻓﻲ ھﺬه اﻟﺪراﺳﺔ.

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