Tarik Kaya

Mathematical Modeling of Loop Heat Pipes and Experimental Validation

A mathematical model to calculate the steady-state performance of a loop heat pipe (LHP) is presented. The mathematical model is based on the steady-state energy conservation equations and the pressure drop calculations along the fluid path in the LHP. The LHP operating temperature is calculated as a function of the applied power at a given LHP condition. The beat exchange between each component of the LHP and the surroundings is taken into account. Both convection and radiation environments are modeled. Experimental validation of the model is attempted by using two different LHP designs. The validity of the mathematical model is investigated for different sink temperatures and elevations. The comparison of the calculations and experimental results showed good agreement (within 5% ). The proposed method proved to be a useful tool for reliable prediction of the steady-state performance characteristics of the LHP.

Mathematical Modeling of Loop Heat Pipes

The primary focus of this study is to model steady-state performance of a Loop Heat Pipe (LHP). The mathematical model is based on the steady-state energy balance equations at each component of the LHP. The heat exchange between each LHP component and the surrounding is taken into account. Both convection and radiation environments are modeled. The loop operating temperature is calculated as a function of the applied power at a given loop condition. Experimental validation of the model is attempted by using two different LHP designs. The mathematical model is tested at different sink temperatures and at different elevations of the loop. Tbc comparison of the calculations and experimental results showed very good agreement (within 3%). This method proved to be a useful tool in studying steady-state LHP performance characteristics.

Thermal Operational Characteristics of a Small-Loop Heat Pipe

This study investigates the distinctive thermal operational characteristics of a small-loop heat pipe (LHP). Tests are conducted under varying heat load and condenser sink temperatures at different orientations of the LHP. Successful startups at heat loads as low as 5 W are demonstrated. To investigate the effect of accelerating forces, the small LHP is tested on a spin table. Accelerating forces impose an additional pressure drop and change the fluid distribution inside the LHP, thereby affecting the startup characteristics and the LHP operating temperature. Spin tests have demonstrated successful operation of the LHP under accelerating forces. The steady-state mathematical model proves to be useful for assessment of the main factors influencing the operating temperature when the LHP is subjected to accelerating forces. The mathematical modeling of the LHP performance characteristics becomes more difficult as the size of the LHP decreases. For a better prediction of the small LHP characteristics, more detailed modeling of the evaporator core is essential.

Transient Thermo-Fluid Modeling of Loop Heat Pipes and Experimental Validation

A transient mathematical model is developed to study the transient response and analyze the distribution of heat load in a loop heat pipe. The model is based on the one-dimensional and time-dependent conservation equations for heat and fluid flow. The momentum and energy conservation equations for each of the loop heat pipe components are solved. The model results are compared against the data obtained from two miniature loop heat pipes using polytetrafluoroethylene wicks, ethanol, and acetone as working fluids. The mathematical model satisfactorily predicts the dynamic behavior of the loop heat pipe unit. It is shown that the percentage of heat leak across the wick decreases and the ratio of latent heat increases with increasing heat load. Some temperature overshoots observed in the calculation results are not observed in the experimental data. When a new power is applied, no time lag is observed in the loop heat pipe response between the simulation and experimental results.

Testing of A Loop Heat Pipe Subjected to Variable Accelerating Forces, Part 2: Temperature Stability

Testing of A Loop Heat Pipe Subjected to Variable AccelerationsPart 2: Temperature StabilityJentung KuLaura OttensteinGoddard Space Flight CenterGreenbelt, Maryland(301) 286-3130jentung.ku@gs fc.nasa.govTaril KayaInternational Space UniversityFrancePaul RogersUS Army TARDECWarren, MichiganCraig HoffKettering UniversityFlint, Michigan30 th International Conference on Environmental systemsJuly 10- 13, 2000, Toulouse, Francehttps://ntrs.nasa.gov/search.jsp?R=20000101592 2020-07-13T13:22:19+00:00Z

Mathematical Modeling of the Evaporator of Two-phase Heat Transfer Devices

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. Copyright

Start‐Up Performance of A Loop Heat Pipe With Variable Heating Patterns and Periodic Cycles

Despite recent intensive investigations on performances of Loop Heat Pipes (LHP), there are still many unexplained behaviors in the start‐up and transient operation of LHPs. The start‐up of a LHP has been the most critical and important part of an LHP operation specifically for space applications. It is highly desirable to ensure reliable and reproducible start‐ups and minimize temperature overshoots. The Canadian Space Agency has conducted a series of original tests in atmosphere and vacuum, in order to characterize the LHP operation as a thermal regulation device for spacecraft applications. Special attention has been paid to start‐up conditions including environments (vacuum versus atmosphere), thermal pre‐conditions (heating/cooling history), variable heating rates (from variable conductance to constant conductance regime), and variable heating patterns (space‐characterized heating). Different start‐up results have been observed under variety of conditions. Attempts have been made to characterize the ...