Study on Thermal Performance and Dynamic Behavior of Two-Phase Flow in Miniature Heat Pipes
Date Issued
2006
Date
2006
Author(s)
Lee, Ya-Wei
DOI
en-US
Abstract
無
Among the novel electronic cooling devices, miniature heat pipes (MHP) have been received attention in recent years. For understanding the thermal mechanism of MHPs completely, two types of MHPs have been investigated in this dissertation. One is a disk-shaped miniature heat pipe (DMHP) and the other is a multi-loop pulsating heat pipe (MLPHP).
A mounting base integrated with DMHP is designed for laser diode TO can package. For understanding the temperature distribution and physical phenomenon of DMHP, a CFD model is made using the commercial code, Fluent 6.1.18. Combining the applications of this package and user defined C++ program, two-phase heat/mass transfer mechanism is built. The modeling results and the experimental data are reported and are in good agreement with each other.
Mathematical modeling of the MLPHP is a contemporary problem that remains quite elusive. Simplifications and assumptions made in all the modeling approaches developed so far render them unsuitable for engineering design. In this dissertation, a more realistic modeling scheme is presented which proves considerable information for thought toward the next progressive step. At different operational conditions, the MLPHP experience bulk internal flow circulations. A time average model based on design parameters for predicting thermal performance has been developed, and from which the optimal suggestions could be provided. In addition, the non-linear auto-regressive moving average model with exogenous inputs (NARMAX) approach is employed to analyze the dynamics of the MLPHP. The nonlinearity would be represented in both time and frequency domains.
High speed flow visualization for the MLPHP is provided. It is identified that there exists the bulk circulation flow that lasts longer and the local flow direction switch flow. Dispersed bubbles, vapor plugs and the transition flow patterns from the dispersed bubbles to the vapor plugs are the major flow patterns in the MLPHP. By increasing the heating power, vapor plugs observed became shorter and more uniformly dispersed due to the vapor plug deformation and breakup mechanism. Bubble sizes have unsymmetrical distributions among various tubes. The complex combined effects of bubble nucleation, coalescence and condensation are responsible for the oscillation flow in the MLPHP.
From analyzing the effect of operational parameters on thermal performance of MLPHP, the vertical bottom heating mode is regarded as the optimal operational condition. In addition, a comprehensive description of the effect for each combination of conditions (charge ratio, heating power, heating mode, orientation) is provided by experiment.
Subjects
多迴路脈衝熱管
兩相流
能量頻譜密度
非線性系統識別
multi-loop pulsating heat pipe
two-phase flow oscillation
NARMAX
power spectral density
Type
thesis
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