Search Results

The main objective of this study is to develop a mathematical model for the simulation of the thermal characteristics of two-phase capillary pumped devices. The mathematical model presented in this paper is an extension of the earlier mathematical model developed for a conventional heat pipe. The three-dimensional incompressible energy, momentum and mass conservation equations are solved by using the finite element method. Except in the wick region, the viscous terms in the governing equations are neglected. However, the pressure drops due to frictional losses are introduced. The interface between vapor and liquid phases is assumed static and only converged steady-state solutions are retained. The reservoir dynamic is not modeled. The energy, momentum and mass jump conditions are written across the interface. The resulting set of equations is solved iteratively until the overall mass conservation is satisfied between the evaporator and condenser.

This study focuses on the mathematical modeling of the evaporator section of the two-phase heat transfer devices: heat pipes, loop heat pipes and capillary pumped loops. Although the heat pipe technology made its first public appearance in the early forties, some operational aspects of two-phase systems are still not well understood, and research in this area continues. The evaporation and condensation process, taking place in these systems is among the most complex phenomena encountered in engineering applications. In this study, full three-dimensional incompressible energy, momentum and mass conservation equations are solved by using the finite element method to predict thermal operational characteristics of the two-phase heat transfer devices. The main focus of the study is the modeling of the phase transition region in the evaporator section.

Loop Heat Pipes (LHPs) are two phase heat transport devices where the fluid circulation is achieved by capillary forces. Because of their high heat transport capability, robustness, reliability and compactness, they are becoming standard thermal control devices in several applications in space, aeronautics and electronics industry. Several mathematical models have been developed to predict the behavior of these devices. However, due to the complexity of the two-phase phenomena involved in LHPs, current models cannot simulate several performance characteristics. This paper presents an LHP mathematical model developed using the software simulation tool EcosimPro. The results of the mathematical model have been compared with the hardware test data for code validation. Results in both, steady and transient conditions, are presented and discussed.

Two-Phase Loops with Capillary Pump (Loop Heat Pipes (LHP) and Capillary Pumped Loops (CPL)) are currently among advanced thermal control technologies for aerospace applications. Large numbers of experimental and operational two-phase loops were successfully tested and used in several spacecraft in the past two decades. Novel technologies such as Advanced CPL-LHP, High Performance CPL, miniature LHPs, inversion (reversible, “Push-Pull") LHPs, ramified, multiple evaporator and condenser LHPs and CPLs, for complex thermal control systems are being proposed. This paper presents a state-of-the-art survey and analysis of these technologies. A classification of Two-Phase Loop with Capillary Pump designs is recommended. Basic principles, operational conditions and characteristics, temperature control and start-up initiation are discussed. The use of thermal control systems based on Two-Phase Loops with Capillary Pump for space applications is reviewed and summarized.

In this paper, we present an image registration approach to cope with inter-image illumination changes of arbitrary shape in order to monitor the development of micro-pitting in transmission gears. Traditional image registration approaches do not typically account for inter-image illumination variations that negatively affect the geometric registration precision. Given a set of captured images of gear surface degradation with different exposure times and geometric deformations, the correlation between the resulting aligned images is compared to a reference one. The presented image registration approach is used with an online health monitoring system involving the analysis of vibration, acoustic emission and oil debris to follow the development of micro-pitting in transmission gears. The proposed monitoring system achieves more registration precision compared to competing systems.