Investigation of Vapor-liquid Interface Characteristics in a Loop Heat Pipe Evaporator Under High Heat Flux Condition Using Pore Network Simulation

다국어 초록 (Multilingual Abstract)

This study numerically investigated the maximum heat flux of the loop heat pipe considering the vapor-liquid interface within the evaporator using pore network simulation. Numerical model was modified from previous researchers’ boundary conditions and pressure distribution. Also, for high heat flux condition, the screen mesh wick and multiscale wick, fabricated by the SAC305 particles on the conventional screen mesh wick to enhance the capillary performance were used and compare their thermal performance. To apply the mesh wicks to pore network simulation, porous medium approach was used, and the wick characteristics were experimentally measured using the rate-of-rise method. Based on the numerical model, the maximum heat flux of the LHP evaporator was investigated by predicting the vapor-liquid interface according to the working fluids, characteristics of porous materials, such as mesh number, multiscale wick, and double-layer wick. As a result, the working fluid with higher latent heat has a higher maximum heat flux, and an improvement in the capillary performance of the porous medium leads to an increase in the maximum heat flux. This is because a higher latent heat and stronger capillary forces restrain the growth and invasion of the vapor–liquid interface, thereby delaying the dry-out. In addition, by using the double-layer wick, extending the vapor-liquid interface toward the vapor groove increases the evaporation and it leads to an improvement of the maximum heat flux.

목차 (Table of Contents)

• CHAPTER 1 INTRODUCTION 1
• 1.1 Literature review and Motivation 1
• 1.2 Objectives 4
• CHAPTER 2 NUMERICAL APPROACH 5
• 2.1 Modeling of pore network simulation 5
• 2.2 Numerical modeling 7
• 2.2.1 Temperature distribution 9
• 2.2.2 Pressure distribution 10
• 2.2.3 Boundary conditions 11
• 2.3 Porous medium approach 13
• 2.4 Pressure and temperature of the vapor groove 15
• 2.5 Numerical algorithm 21
• 2.6 Limitation of numerical model 23
• CHAPTER 3 EXPERIMENTAL APPROACH 24
• 3.1 Multiscale wick 24
• 3.2 Rate-of-rise method 27
• 3.3 Uncertainty analysis 29
• CHAPTER 4 RESULTS AND DISCUSSION 31
• 4.1 Validation of numerical model 31
• 4.2. Dry-out criterion 35
• 4.3 Effects of the working fluid 38
• 4.4 Effects of the mesh number 41
• 4.5 Measured effective pore radius and permeability of multiscale wick 44
• 4.6 Effects of the multiscale wick 49
• 4.7 Effects of the bi-porous wick 52
• CHAPTER 5 CONCLUSIONS 55
• REFERENCES 56