Study of Dynamics Behavior and Start-up Transient Characteristics of Loop Heat Pipes
Date Issued
2009
Date
2009
Author(s)
Huang, Huan-Hsiang
Abstract
The present study is to understand the dynamic behavior of a loop heat pipe (LHP) and deriving the dynamic model of a LHP. In addition, the stability analysis of the designed parameter and the analysis of start-up transient characteristics of a LHP are studied. he dynamic model of a LHP can be derived by the energy balance equation of a LHP. As a result, it is found that the system dynamics of a LHP is a multivariable system changing with operating conditions. The material properties are used in the model, which can be reduced a second-order system. Moreover, the model can be re-vised by the identified experiment. The dynamic model is used to develop a PI con-troller that the temperature of evaporator can be controlled within a deviation of 0.5 degree by changing the mass flow of a fan in the condenser. ccording to the results of stable analysis, porosity and latent heat of working fluid make unstable for the operation of a LHP except the thermal conductivity of wick, the thermal conductivity of liquid working fluid, the effectively thermal con-ductivity of wick, the length of wick, and charged volumes of working fluid.inal part of the present study has been carried out to test the start-up characte-ristics and behavior of a LHP with the different parameters, which are heat loads, orientation, working fluid, capillary forces, tube length, and charging volume. It is also found that the start-up phenomena of a LHP can be classified into four modes according to the heat loads: (1) failure mode,(2) oscillating mode, (3) overshoot mode, and (4) normal mode. System identification is used to identify those parameters of the start-up characteristics of a LHP and also to determine the relation-ship among those different factors affected the characteristics of a LHP in this study. The results show the major factor is the capillary forces and the secondary factors are working fluid, tube length, and charging volume.
Subjects
Loop heat pipes
Loop Heat Pipes
Dynamic Behavior
Transient Behavior
System Identifycation
Startup of Loop Heat Pipe
Type
thesis
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