Theoretical and Experimental Study of Bubble Dynamics and Thermal Performance in Two-phase Immersion Cooling

다국어 초록 (Multilingual Abstract)

In this study, a theoretical model describing bubble dynamics and thermal characteristics in a two-phase immersion cooling system was developed and validated experimentally. A lumped capacitance model was employed to theoretically predict the transient battery temperature, and the theoretical framework was established by distinguishing between the natural convection regime and the boiling regime. The boiling regime, in which stable bubble generation occurs, was identified based on the onset of nucleate boiling. Within the boiling regime, microlayer evaporation, transient heat transfer, and natural convection were taken into account. The theoretical heat generation of the battery was calculated using the Bernardi equation, based on which a simulated heat source was fabricated using copper. To validate the theoretical model, experiments were conducted using a dielectric fluid with a saturation temperature of 49 °C. Under a 5C-rate operating condition, the battery-to-battery spacing was varied as 0.5, 1, and 4 mm, and the filling ratio was adjusted to 25, 50, 75, and 100 %, while the temperatures of both the battery and the working fluid were measured. The experimental results indicated that the effect of battery spacing was negligible, whereas a decrease in the filling ratio led to an increase in battery superheat. Compared with the theoretically predicted temperature obtained without considering boiling, the battery temperature was reduced by approximately 11.69 °C when boiling was taken into account. Based on the established theoretical model, the effects of latent heat and contact angle on wall superheat were further analyzed. The results showed that a smaller latent heat and a smaller contact angle delay the onset of nucleate boiling, thereby resulting in an increase in the required wall superheat.

목차 (Table of Contents)

• CHAPTER 1 INTRODUCTION 1
• 1.1 Literature review and motivation 1
• CHAPTER 2 THEORETICAL APPROACH 3
• 2.1 Theoretical model 3
• 2.1.1 Departure bubble diameter 3
• 2.1.2 Bubble growth diameter 10
• 2.1.3 Onset of nucleate boiling 11
• CHAPTER 3 17
• 3.1 Heat generation characteristics 17
• 3.2 Experimental apparatus 17
• 3.3 Measurement points 18
• CHAPTER 4 RESULTS AND DISCUSSION 26
• 4.1 Experimental results 26
• 4.1.1 Effect of spacing 26
• 4.1.2 Effect of filling ratio 27
• 4.1.3 Analysis of performance of two-phase immersion cooling 28
• CHAPTER 5 CONCLUSIONS 43
• REFERENCES 44