Heat transfer analysis in a finned heat sink embedded with two-phase heat pipes

Thesis supervisor: Dr. Hongbin Ma.[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] The semiconductor technology development, as fast as consumer demands, led to advancements in miniaturization and power of computer chips. The low efficiency that transfers a significant amount of energy into waste heat and miniaturization which increases the heat density is challenging the thermal management solutions. A forced convection on single-phase heat sink cannot accommodate the high-density heat flux in the confined computer enclosure. The two-phase heat pipe is introduced as an innovative technology to take the waste heat away from the chip to the fined heat sink. In this study, a theoretical model for predicting the heat transfer performance of a finned heat sink embedded with two-phase heat pipes is presented. The theoretical model includes boiling mechanism in the evaporator, vapor flow influence, condensation mechanism in the condenser, wick structure and capillary effect, pressure drop, number and shape of fins, and air flow effect. The analysis demonstrates thermal resistance of heat sink can meet the requirements of thermal management solutions, so that the performance of heat sink can be applied to maintain the desktop CPU chip with power up to 300 W at 85 and less. The experiment setup consists of a wind tunnel, thermocouples, temperature data acquisition system (DAQ), computer, blower, variable autotransformer, heat sink and heat source assembly, power supply and measuring unit. The experimental results verify the theoretical analysis of the performance and indicate that the primary factor of the heat transfer performance is the contact resistance, and the second factor is the fins on condenser for convectional heat dissipation. The two-phase heat pipes can improve the heat transfer performance. In order to prove the analysis, an experiment was conducted to measure the temperature difference and calculate the thermal resistance based on the collected data. The results will determine the limitation of the heat sink and improve the design for a highly efficient heat sink.Includes bibliographical references (pages 56-59)