ORCID Identifier(s)

0000-0002-8453-328X

Graduation Semester and Year

2020

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Dereje Agonafer

Abstract

The increase on demand of communication and networking has resulted to increase for more powerful servers and bigger data centers. With increase the power of electronics, thermal management and cooling of the equipment become a gigantic challenge due to lower surface, they have higher power density and traditional methods of cooling become ineffective. Generally, air cooling method is the first option for cooling of the electronics due to cheaper price. To increase the efficiency and capacity of cooling liquid immersion cooling is used due to higher thermal properties like heat capacity and thermal conductivity compare to air. Two methods of immersion cooling can be used. The first one is the closed cycle cooling which uses flow boiling which still needs extra power for cooling to circulate the liquid inside the rack. The problem of using this method is that it is not easy to get out of a server for checking or maintenance. Furthermore, to move one server, we need to shut down all servers and wait till the system is cool down. Due to high pressure inside pipes, the leakage can happen in the system and the liquid which is very expensive must be substituted in the system. Also, the vapor can be trapped in the tank and removing vapor is not easy and during the operation, it can influence the thermal management of the system. The second method is the open bath method which simply, the servers can be submerged in the tank and the maintenance can be done from the opening of the tank. To increase the performance of cooling in this method, enhanced surface should be used on the surface of the processors. This study explores the cooling performance of 1cm by 1cm dyes which are placed in the different configurations. To make the dyes, a resistance was used and a copper plate is put on top of the heater. A thermocouple is designed in the center of the copper plate to measure the temperature of the surface. An open-bath test cell is designed with two condensers. The temperature of the bath is controlled with a hot plate at the bottom of the cell. To control the temperature inside the bath, a thermocouple is designed inside the bath. To make sure that the temperature is steady state, the results were taken after being sure that the temperature did not change any more. Pool boiling tests were performed on test boards which is able to make different configurations. The proposed work includes 3 different steps. In the first step, the effect of thermal shadowing will be checked to study the effect of bubble columns earlier dyes on the top dyes. For the 2nd steps, the effect of the front space on the surface temperature of the dyes will be checked by adding a glass wall in front of heater. In the last stage, the effect of surface enhancement will be studied. The surface enhancement is studied by adding micro particles on top of the copper plates, adding lattice structure on top of the heaters. The results will be presented in the form of characteristics curve of boiling which is the heat flux versus surface temperature. The critical heat flux of each configurations and surface will be found. Also, the heat convection coefficient of each configuration will be presented as a curve. To check the boiling phenomena, the photos of bubbles at the surface will be taken and it will be tried to find the bubble departure diameter of the surface.

Keywords

Two-phase, immersion cooling

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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